Applications of ionizing irradiation in oil industry: a review

2.1 Gamma ray irradiation

GI is a process that involves the use of gamma rays, which are high-energy electromagnetic radiation, to treat materials or substances. It is commonly used for sterilization, food preservation, and radiation therapy. Gamma rays are emitted from a radioactive source, such as ⁶⁰Co or ¹³⁷Cs, and can penetrate deeply into materials, causing chemical and biological changes. This method is effective in killing microorganisms, insects, and pests, as well as in modifying the properties of materials.

GI offers advantages such as a wide penetration range, uniform dose distribution, and no residual radioactivity in treated materials. GI technology also provides numerous benefits, including:

1. Efficient sterilization of medical equipment and packaging materials.

2. Improved shelf life and safety of food products by eliminating pathogens.

3. Enhanced polymer properties through controlled crosslinking and degradation processes.

4. Increased product quality in industries such as pharmaceuticals, cosmetics, and agriculture.

It is important to note that the specific effects of GI on hydrocarbon molecules can vary depending on factors such as the dose of radiation, the chemical composition of the hydrocarbon, and the presence of other additives or impurities.

2.2 Electron beam irradiation

Electron Beam Irradiation (EBI) is a technique that utilizes a high-energy electron beam (EB) to treat materials or substances. It is commonly used in various fields, including sterilization, polymer modification, and wastewater treatment. EB interacts with the target material, causing chemical and physical changes that can be beneficial for a range of applications. EB is generated by electron accelerators such as linear electron accelerators (LINAC) and can penetrate into the material, interacting with its atoms and molecules. This interaction leads to the breaking of chemical bonds, ionization, and the generation of free radicals. These changes can result in various effects such as the sterilization of pathogens, cracking of hydrocarbon molecules, crosslinking or degradation of polymers, and treatment of wastewater contaminants. EBI is a versatile and efficient method with applications in industries such as healthcare, manufacturing, and environmental remediation.

EBI technology offers several advantages:

1. Provides versatile applications: EBI has a wide range of applications across various industries. It can be used for the sterilization of medical devices, pharmaceuticals, and food products. It can also modify polymers, improve material properties, and treat wastewater contaminants.

2. Offers a chemical-free process: Unlike other treatment methods, EBI does not require the use of chemicals or additives like catalysts. It relies solely on the energy of EB, making it an environmentally friendly technology.

3. Increases productivity: EBI is a rapid process that can be easily integrated into existing production lines. It offers high throughput and shorter processing times compared to traditional methods, leading to increased productivity and cost-effectiveness.

4. Enhances safety: EBI technology does not leave any residual radiation in the treated materials, ensuring their safety for subsequent use. It also minimizes the risk of contamination or the introduction of harmful by-products.

5. Ensures efficient and precise Treatment: In contrast to the gamma-rays, EB allows for more controlled delivery of high-energy electrons, enabling targeted surface treatments and modifications due to more controllable penetration depth. Regard this, EBI offers better precision and localized effects, making it suitable for applications requiring focused energy delivery. However, we should keep it in mind that the effects of ionizing radiation depend on material composition and exposure conditions, and nearby regions may be affected unless mitigated by appropriate techniques, such as antioxidants (Głuszewski 2021).

6. Preserves product quality: EBI facilitates sterilization or modification while maintaining the quality and functionality of treated products. Its limited penetration, compared to gamma rays, reduces the likelihood of extensive material alterations, making it particularly suitable for surface-level treatments. However, like all ionizing radiation, EBI can cause changes in material properties, necessitating stabilization strategies to ensure product integrity. For instance, EBI can enhance the physical properties of certain polymers through cross-linking, but it may also degrade others by breaking chemical bonds.

Overall, EBI technology provides efficient, versatile, and environmentally friendly solutions for various industries, making it a preferred choice for many applications.

3.1 Direct (transformer) accelerators

In direct type accelerators, electrons are accelerated within a constant electric field generated by a high-voltage DC source. These accelerators dominate industrial applications due to their higher efficiency and lower cost compared to other systems (Chmielewski 2023; Hamm and Hamm 2012). However, their primary limitation is their medium energy output range, as achieving higher energy levels significantly increases costs. As a result, DC accelerators are ideal for applications such as polymer processing, wire production, and surface treatment.

The main types of DC accelerator structures for high beam powers at medium energy include (Hamm and Hamm 2012): 1) Insulating core transformer (ICT): Uses series-coupled transformer cores with rectifiers and capacitors to generate DC voltages ranging from 300 kV to 3 MV with power outputs up to 100 kW. It is commonly employed in thin-film processing, 2) Electron transformer-rectifier (ELV): Employs parallel coupling with a primary winding along the high-voltage assembly, producing outputs from 400 kV to 2.5 MV and up to 400 kW at 1 MV, 3) Transformer-driven DC Accelerators: Similar to ELVs but with conical primary windings extending through the accelerator, achieving voltages up to 750 kV, 4) Cockcroft–Walton system: Utilizes a series-coupled cascade rectifier system energized at 3 kHz, capable of generating voltages up to 5 MV at 150 kW, making it suitable for X-ray generation, 5) Dynamitron: Operates with high-frequency (100 kHz) AC power and parallel rectifiers, producing up to 300 kW at 5 MV, used for high-power applications like X-ray generation.

Additionally, research studies in oil cracking have employed lower-energy and power accelerators, such as the Van de Graaff (VDG) generator, demonstrating their utility in specific scientific and industrial contexts.

3.2 Radio frequency (RF) electron accelerators

In the high-energy range (5–10 MeV), most industrial EB accelerators utilize RF power to create electric fields for electron acceleration, as high-voltage DC generators at these energy levels are significantly larger and more costly. LINACs are predominant in this range, employing resonant cavities powered by microwave generators, such as magnetrons and klystrons, and categorized into frequency bands (L-, S-, and C-band). L-band LINACs can deliver up to 100 kW beam power, while the more compact S-band LINACs typically produce up to 30 kW. Rhodotrons, which utilize coaxial resonant cavities for electron recirculation, achieve even higher powers (up to 700 kW) and support multiple beamlines for diverse applications, including X-ray generation. These advancements have facilitated applications in medical sterilization, and food irradiation (Hamm and Hamm 2012). However, the high cost and low efficiency of these accelerators remain key limitations to their broader industrial adoption (Chmielewski 2023).

4.1 Radiation-thermal cracking

RTC is a process that combines high-energy radiation and heat to break down hydrocarbon molecules. This results in the production of smaller and more valuable products, such as light hydrocarbons. By adjusting the irradiation parameters, the selectivity towards specific products can be controlled, offering opportunities for tailored outcomes in different applications. Figure 1 shows a scheme for the cracking of an instant hydrocarbon molecule using high-energy electrons.

Figure 1:

Schematic view of the cracking of hydrocarbon molecules using high-energy electrons (Wang et al. 2020); reproduced with permission from Elsevier.

The studies presented in this subsection are listed in Table 1.

The RTC was discovered and studied in the 1960s. It was revealed the mechanisms of chemical reactions induced by radiation in hydrocarbons, focusing on chain reactions in RTC. These early studies provided the first evidence of the rapid chemical conversion of hydrocarbons under the combined influence of radiation and heat. The discovery of RTC was highly significant, as it demonstrated that chain reactions were essential for achieving efficient oil refining processes at an industrial scale (Zaikin 2016).

As part of the initial attempts, an experiment was conducted using an EB machine and a gamma ray generator to study the effects of irradiation on n-hexadecane (n-C₁₆). It was observed that the effects of irradiation on n-C₁₆ appeared to be independent of the radiation source and dose rate (Salovey and Falconer 1965). In another study, RTC experiments were performed on n-C₁₆ using gamma rays and it was found that radiation actually enhanced the cracking process (Yang 2009).

After that, the significant and positive effect of EBI was discovered in the RTC process (Zaykina et al. 2001, 2002b).

High-density, high-viscosity oil with sulfur and resin content was irradiated with 4 MeV electrons and a dose rate of 1 kGy/s. The results showed that processing heavy oil using RTC is more efficient than thermal methods like TCC, yielding higher amounts of gasoline and kerosene-gas-oil fractions, and lower concentrations of vanadium compounds (Zaykina et al. 2002a).

Energy consumption for chain cracking reactions in hydrocarbons was examined for various processing techniques. EB technology for hydrocarbon enhancement was compared to thermal and thermocatalytic methods (Zaykin et al. 2003).

The use of EBI to convert heavy and/or viscous hydrocarbons into lighter and more fluid substances, as well as to improve the composition of hydrocarbon mixtures was briefly reviewed (Mirkin et al. 2003).

Also, the impact of absorbed dose on the viscosities of heavy oil in the presence of various solvents was assessed. Additionally, the influence of EBI on the yields of light fractions was investigated. The results indicated that EBI of hydrocarbons increases molecular weight, leading to viscosity changes (Zhussupov 2006).

The chemical effects of irradiation on high-pressure methane and noble gas mixtures using gamma ray, EB, and neutron irradiation were investigated. It was shown that neutron irradiation resulted in measurable increases in ethane and hydrogen concentrations, while gamma and EB irradiations did not show significant changes (Clemens 2014).

A mathematical model was proposed to study the behavior of a low-conductive multicomponent hydrocarbon mixture under electron irradiation. The model utilizes the Navier–Stokes equation, the Adams-Bashforth scheme, the Crank-Nicolson method, and the matrix sweep method to solve the various equations involved (Kizbayev et al. 2018).

Asphaltenes from oil were exposed to low-energy EB irradiation. The results indicated that after EB treatment in a propane-butane atmosphere, the asphaltenes experienced a more significant loss of mass. The degradation of the asphaltenes themselves was minimally affected by EB exposure. However, various compounds, including resins, aromatic compounds, and hydrocarbons, were formed (Neyfel’d et al. 2023).

The radiolysis of a hydrocarbon mixture, specifically the hexane/hexene system, was investigated using GI. Different physical and chemical parameters were analyzed immediately after irradiation and after 30 days. The irradiation led to changes in the iodine number, and for doses exceeding 48 kGy, polymerization became the dominant process in systems containing more than 20 % olefin (Jabbarova et al. 2022a).

The use of EBI for the RTC of hydrocarbons, such as heavy oils and lignin, was reviewed. The experiments demonstrated high conversion rates and yields of light fractions. The authors also highlighted the advantage of EB in enabling the direct processing of natural gas into commercial products (Pavlov et al. 2022).

A Monte Carlo modeling study was performed on different hydrocarbons in hexane and hexane-water mixtures, revealing the kinetics of radical accumulation and radiolysis product formation involving reactive species such as hydrated electrons, hydrogen atoms, and hydroxyl radicals (Ali et al. 2024).

4.2 Low-temperature radiation cracking (cold cracking)

At high temperatures and high dose rates of ionizing irradiation, hydrocarbons undergo radiation-induced cracking, which is a self-sustaining chain reaction of hydrocarbon decomposition. This phenomenon can be categorized into two types: RTC, which occurs at temperatures between 350 °C and 420 °C, and low-temperature radiation cracking, which occurs at temperatures below 350 °C. Both types of cracking follow a radical mechanism, similar to classic TC (Kharisov et al. 2013).

For years, the phenomenon of low-temperature radiation cracking was not extensively discussed or observed for two main reasons. Firstly, observing ‘cold’ radiation cracking requires high dose rates; however, most experiments on oil radiation processing have been conducted at relatively low dose rates. Additionally, the dose rate was not considered a crucial process parameter. Secondly, it was believed that ionizing irradiation cannot generate sufficient concentrations of long-lived excited molecular states that are necessary for the propagation of the chain reaction (Kharisov et al. 2013).

Extensive research has focused on the concept of low-temperature RTC to improve the characteristics of hydrocarbons. Below, we have outlined some of the reviewed studies in Table 2.

One study was directed at the application of cold cracking to refine petroleum products, with goals including increasing the value of the oil supply, reducing capital investment and operating energy costs, and decreasing sulfur content. The study found that there are challenges related to energy efficiency, cost-effectiveness, and environmental responsibility. It was also proposed that further research and testing are needed to determine the viability of radiation refining (National Energy Technology Laoratory 2006).

In another study, the combined effects of ionized ozone air and ionizing radiation (2 MeV electrons and Bremsstrahlung radiation) on oil yields and hydrocarbon content were investigated. Pre-treatment with ozone air resulted in a reduction of cracking temperature and improved the characteristics of light fractions (Zaykin and Zaykina 2004a).

Finally, a mechanism of the process was proposed that considers the interaction between chain carriers and radiation-excited molecules, as well as radiation-induced reactive molecular groups, such as isolated pairs of ‘hydrogen atom–unstable hydrocarbon radical.’ The study examined the effects of ionizing radiation on liquid hydrocarbons at low temperatures. It was found that high doses of radiation can trigger chain reactions leading to the degradation of hydrocarbons, even without the need for thermal activation (Zaikin 2008, 2013, 2016; Zaikin and Zaikina 2008a,b, 2016).

They introduced the principles of low-temperature (cold) radiation-induced cracking of hydrocarbon compounds. It has been suggested that at temperatures between 150 °C and 350 °C, the rate of cracking shows a weaker dependence on temperature compared to higher temperatures, due to diffusion-controlled decomposition within the oil cluster system. Higher dose rates activate thermally induced diffusion of free radicals, which increases the rate of chain cracking reactions. At around 250 °C and average dose rates of 3–5 kGy/s, the contributions from electronically and thermally excited molecules are comparable. With further increases in dose rate, there is a higher probability of thermal electron excitation, which enables chain propagation. At low temperatures, where thermal molecular excitation and radical diffusion are negligible, a transition occurs from radiation-thermal to “cold” radiation-induced cracking, where initiation and propagation result solely from radiation exposure. The rate of radiation-induced cold cracking has been defined as Eq. (1) (Zaikin 2008):

where, K ₃ is reaction rate Constant, K _r is the radical recombination rate constant, G _r the radiation-chemical yield of light radicals capable of initiating cracking and c* is the concentration of radiation-excited molecules:

where, K* is the rate of energy losses by the excited molecular states and G* is the radiation-chemical yield of the excited molecules and P is the dose rate. However, no experimental results were provided, and the required dose rate for such a process was found to be excessively high.

The influence of high-energy electron particles was investigated on the rheological properties of heavy deasphalted petroleum fluids. Researchers found that the impact of radiation-induced chain reactions was strongly influenced by temperature, with lower temperatures favoring polymerization reactions and higher temperatures triggering chain reactions that resulted in reduced viscosity (Alfi 2012; Alfi et al. 2012b, 2013).

A kinetic model was developed to study the effects of chemical structure and radiation-based processes on the radiation-thermal and low-temperature radiation cracking of heavy hydrocarbon feedstock (Zaikin and Zaikina 2013).

Another study theorized that long-lived excited states of hydrocarbon molecules, produced through ionizing radiation, are important in low-temperature chain cracking reactions in heavy oil and bitumen. The research focused on investigating the kinetics of the generation of these radiation-excited unstable molecular states, which are involved in both chain cracking and isomerization processes (Zaikin 2013).

In an experimental-theoretical study, the low-temperature radiation cracking of heavy oils was analyzed under continuous and pulsed electron irradiation. The study employed kinetic equations with modified initial conditions to describe the behavior of the yields of light products resulting from radiation cracking (Zaikin 2016).

The use of EBI to improve the low-temperature cracking of heavy crude oil and reduce its viscosity was studied, focusing on the analysis of fluid properties and the characterization of heavy crude oils before and after treatment. Initial experiments have shown a reduction in viscosity and conversion of heavy residue (Damarla 2016).

High dose rate EBI was studied as a method for low-temperature cracking of heavy oil, with experimentation on various parameters, including dose, gas donors, and the chemical composition of the petroleum. Based on the results, saturated hydrocarbons showed a higher product yield compared to unsaturated hydrocarbons. Additionally, the presence of rings in saturated hydrocarbons increased their tendency to produce polymerized products (Wang 2019).

The EBI of mineral oils was investigated in a continuous flow system. The addition of bubbling gases (helium and methane) and low temperatures modified the chemical pathways. Analysis showed a conversion rate of 7–12 % and a selectivity of 60–70 % to light hydrocarbons post-irradiation. Methane processing demonstrated higher performance compared to helium (Wang et al. 2020). In another study, heavy oil was irradiated using EBI in the presence of methane at low temperatures, and the conversion and yields of gasoline and diesel fuels were measured. This process offers an approach to convert heavy fractions into stable intermediate products within the diesel range, without the formation of coke. The economic analysis indicated that the processing cost is less than $1.50 per barrel to convert heavy fractions into diesel range products (Wang et al. 2023).

4.3 Radiation cracking of extra-heavy oil and bitumen

Upgrading heavy oil and bitumen poses challenges due to the need for significant thermal energy and costly catalysts. The high viscosity of heavy oils also presents transportation difficulties. Existing methods for transporting heavy oil, such as dilution, partial upgrading, and pipeline insulation or warming, have been explored but are considered costly. Upgrading refers to the conversion of heavy crude oil into lighter, more valuable crude or transportation fuels. Various technologies are available for this process. TC-based technologies, such as visbreaking, delayed coking, and fluid coking, are the most commonly used methods. During cracking, larger molecules undergo C–C bond cleavage, breaking down into smaller molecules through free-radical chain reactions (Yang 2009). The studies reviewed in this subsection are presented in Table 3.

Radiation processing could potentially be a solution for enhancing the efficiency of heavy oil processing. By utilizing irradiation processing, it becomes possible to effectively control various radiation-induced reactions in hydrocarbons. These technologies have been successfully applied to process heavy and highly paraffinic oils, bitumen, oil extraction waste, and heavy oil residua. RTC has several advantages over conventional TC in heavy crude oil, including higher yields of gasoline and light oil fractions, elimination of catalysts, and the potential for lower temperature cracking (Zhussupov 2006).

In the early 2000s, systematic experiments on the radiation processing of heavy oil were initiated. These studies revealed significant differences in the radiation-chemical conversion of complex hydrocarbon systems compared to TC and RTC processes in light oils. Notably, strong synergetic effects resulting from the redistribution of radiation energy between the original components of the hydrocarbon system and intermediate products play a crucial role in heavy hydrocarbon feedstock. These phenomena promote non-destructive side reactions and greatly influence the rate of feedstock conversion and the composition of the final products (Zaikin 2016; Zaikin and Zaikina 2014; Zaykin and Zaykina 2004b; Zaykin et al. 2004; Zaykina et al. 2001, 2003).

Some experiments were conducted on the radiation processing of complex crude oil from the Karazhanbas field. The purpose of the study was to refine heavy oil, process oil residues, and purify the crude oil by removing harmful sulfur compounds. The resulting RTC products included feedstock, gas oil fractions, and semicoke, with a reduced presence of heavy oil residues (Zaykina et al. 2001).

The stability of a petroleum fraction known as distillate aromatic extract (DAE) was evaluated after exposure to gamma irradiation using ⁶⁰Co. The results indicated that while radiation caused an increase in the hexane-insoluble fraction and the release of H₂ and CH₄ gases, the chemical structure of DAE remained largely unaffected. The researchers proposed that DAE could potentially be used as a carrier for the emission spectra of certain astronomical objects (Cataldo and Baccaro 2003).

In another study, the RTC of high-paraffinic oil was investigated, and it was found that this process led to a high rate of polymerization and low levels of olefins in the resulting products. Additionally, the authors concluded that lower irradiation dose rates resulted in lower yields of light fractions, while higher dose rates had the opposite effect (Zaykin et al. 2004).

Throughout the research, it was demonstrated that RTC is a highly effective method for producing light fractions and gasoline with high concentrations of isoparaffins. The authors derived an empirical equation to estimate maximum isomer yields in the gasoline fraction. Their study revealed that RTC outperforms other methods, such as thermocatalytic cracking and ozonolysis combined with thermal processing (Zaykin et al. 2004).

A study was conducted on the thermoradiation conversion of oil-bituminous rock (OBR) samples. The samples were exposed to gamma radiation from a ⁶⁰Co source. The research focused on the kinetic studies of OBR and OBR + H₂O systems, specifically examining the conversion of hydrogen, carbon monoxide, and methane (Mustafaev et al. 2004).

Exposure of oil bitumen samples to ⁶⁰Co gamma radiation led to an increase in asphaltene content. The results suggested that radiation, combined with heat from the earth, plays a role in the formation of coal, oils, etc. (Cataldo et al. 2004).

The use of EBI on n-C₁₆, naphtha, and asphaltene was explored, and it was found that in naphtha distillation, EBI led to exothermic reactions. The asphaltene showed enhanced C–C bond decomposition and isomerization, with reduced aromatic content. Additionally, the results of this work demonstrated simultaneous C–C bond cleavage and polymerization, which can be mitigated with radical trapping (Yang 2009).

The effect of RTC on heavy oil viscosity and the yields of light fractions were evaluated in comparison to conventional thermal conversion (CTC). The results showed that irradiation of pure oil increased the molecular weight, and the storage of irradiated samples increased their viscosity, especially when organic solvents and distilled water were used. The authors also provided an economic feasibility study in their article (Zhussupov 2006).

EBI was employed to initiate the thermal conversion of natural bitumen with bubbling by various gases. The researchers observed that when utilizing the RTC technique, the resulting products had diminished levels of sulfur and unsaturated compounds. In contrast, they noticed a heightened concentration of branched hydrocarbons in the products post-RTC with EBI (Bludenko et al. 2007).

In a series of studies, research projects were conducted on RTC processing of heavy oil. In these studies, naphtha and asphaltene were irradiated with EB. The results showed that radiation minimizes the required energy for upgrading and refining heavy oil by lowering the distillation temperature while increasing the yield of light fractions. Additionally, in the case of asphaltene, RTC showed fewer aromatics and higher isoparaffins compared to thermal conversion (Yang et al. 2009, 2010).

The formation of H₂, CO, and C₁–C₄ hydrocarbons from lignites was studied utilizing RTC. The samples were processed with both EBI and GI. Gas yield was reported during the RTC, and it was found that EBI results in higher radiation-chemical yields compared to GI (Mustafayev et al. 2011).

The use of EBI was studied to reduce the viscosity of heavy petroleum samples, offering potential advantages over conventional methods. The research found that irradiated fluids exhibited lower viscosities compared to thermally cracked samples, with reaction temperature playing a significant role. Additionally, some additives such as ethanol, butanol, glycerol, and tetralin were found to completely suppress radiolytic reactions in hydrocarbon molecules (Alfi et al. 2012a,b).

In another study, a kinetic model of RTC in heavy hydrocarbon feedstock was developed at low temperatures. Factors such as radiation-induced polymerization and chemical adsorption were considered important in limiting heavy oil conversion. The results showed that the absorption coefficient and viscosity reduction play significant roles in the cracking kinetics of this process (Zaikin and Zaikina 2013).

Moreover, it was theoretically shown that long-lived excited states of hydrocarbon molecules generated by ionizing radiation play a crucial role in low-temperature chain cracking reactions in heavy oil and bitumen. The researchers concluded that alkanes disintegrate into radicals upon irradiation, and chain propagation occurs through the interaction of these radicals with excited states of alkane molecules (Zaikin 2013).

The effect of GI on heavy oil was studied and found that different gases have different radiation-chemical yields, and that paraffinic and polycyclic aromatic hydrocarbons are resistant to radiation, while functional groups and olefins show low radiation resistance. The stability of organic compounds towards radiation is influenced by specific chemical groups and their electronic characteristics (Mustafaev et al. 2013).

In another work, the lube oil fractions derived from heavy bituminous oil were studied. The radiation-chemical conversion of these lube oil fractions due to GI was investigated. The study concluded that lube oils have lower radiation resistance compared to bituminous crude oil resins (Mustafaev et al. 2014).

The cracking product yield of heavy oil after EBI was investigated at different dose rates, using paraffin as a simplified model compound. The findings indicated that the paraffin cracking process can be extremely effective (Mikhailenko et al. 2015).

The impact of EBI on the hydro-conversion of vacuum tower residues was assessed in the presence of hydrogen flow and aqueous ammonium paramolybdate nanoparticles. The research revealed that higher doses of EBI led to decreased unconverted residue and increased yields of distillate fractions and gaseous products (Kadiev et al. 2015).

The cracking behavior of heavy asphaltic oil (HAO) and de-asphalted oil (DAO) was studied under EBI, which exhibited different cracking behaviors at different temperatures due to radiation-induced degradation of aromatics in asphaltene aggregates (Alfi et al. 2015).

The use of EBI in the processing of heavy crude oil and reducing its viscosity was studied by analyzing the fluid properties and characterization of heavy crude oils before and after treatment. Initial experiments showed a reduction in viscosity and conversion of heavy residue (Damarla 2016).

The low-temperature radiation cracking of heavy oils using continuous and pulsed EBI was studied utilizing kinetic equations to describe the yields of light products resulting from RTC in comparison with experimental data. It was concluded that continuous irradiation demonstrates higher efficiency (Zaikin 2016).

High dose rate EBI was also utilized to irradiate mineral oils in a continuous flow system employing bubbling gas (helium and methane) at low temperatures. Processing with helium at higher temperatures enhanced stability, selectivity, and yield of light products. Methane gas yielded even more stable light products, higher selectivity, and overall greater yield. Aging of three years negatively affected conversion and selectivity, particularly with helium (Table 4). The viscosity of treated oils remained similar to the control with methane but significantly increased with helium. A reduced presence of olefins and distillation curves shifted towards the raw sample due to reduced product stability from irradiation. Economic challenges arise from product instability and require attention (Wang et al. 2020).

In another study, the effects of EBI were investigated on the resin-asphalt components in oil. It was found that the low-intensity EB did not cause significant cleavage of chemical bonds in the resin-asphalt components. However, it led to the dissociation of complex structural units (CSU) in the presence of propane-butane and air, or the association of aromatic hydrocarbons, resins, and asphaltenes in a hydrogen atmosphere (Savinykh et al. 2022).

Later, the radiation resistance of oil samples obtained from natural bitumen was evaluated under GI. The research found that higher concentrations of tar and asphaltenes in the bituminous rocks increased their resistance to radiation. The oil from these rocks exhibited relatively high radiation resistance, which was attributed to the presence of paraffinic, polycyclic, and aromatic hydrocarbons, as well as resinous asphaltene substances (Jabbarova et al. 2022b).

Furthermore, the irradiation of heavy oil utilizing EBI was studied in the presence of methane at low temperatures, measuring the conversion and yields of gasoline and diesel fuels. This process offers a low energy input and a cost-effective approach to converting heavy fractions into stable intermediate products within the diesel range, without the formation of coke (Wang et al. 2023).

4.4 Radiation-enhanced isomerization

Isomerization in oil radiation cracking refers to the process of converting straight-chain hydrocarbon molecules into their corresponding branched or isomeric forms through irradiation. It involves breaking and rearranging the chemical bonds within the hydrocarbon molecules to create a different structural arrangement. This isomerization process can alter the properties of the oil, such as its viscosity, volatility, and reactivity, potentially leading to changes in its overall behavior and suitability for various applications (Zaikin and Zaikina 2014). For instance, Figure 2 presents examples of octane isomerization. Comprehensive details about the isomerization process of octane have been previously studied (Angeira 2008).

Figure 2:

Scheme examples of isomerization of octane.

The isomerization of hydrocarbons can have various applications in the petroleum industry. Some of these applications include:

1. Fuel production: Isomerization can enhance the octane rating of gasoline by converting straight-chain hydrocarbons into branched isomers, which have better anti-knocking properties. This improves the efficiency and performance of gasoline as a fuel.

2. Lubricant production: Isomerization can be used to produce lubricants with improved viscosity and stability. By converting straight-chain hydrocarbons into branched isomers, the resulting lubricants exhibit better flow properties and resistance to thermal and oxidative degradation.

3. Chemical synthesis: Isomerization can be employed in the production of various chemicals, such as solvents, polymers, and specialty chemicals. By selectively isomerizing specific hydrocarbon molecules, desired chemical properties can be achieved for specific applications.

4. Petrochemical industry: Isomerization plays a crucial role in the production of petrochemicals, such as olefins and aromatics. By converting straight-chain hydrocarbons into branched isomers, the desired chemical structure and reactivity can be obtained for the synthesis of specific petrochemical compounds.

These are just a few examples of the applications of isomerization in oil irradiation cracking. The specific applications may vary depending on the desired end products and the requirements of different industries.

The primary reason for isomerization in the RTC of oil is indeed the radical mechanism. During the cracking process, high-energy radiation, such as EBs, generates free radicals within the hydrocarbon molecules. These free radicals can initiate various chemical reactions, including isomerization.

The free radicals can abstract hydrogen atoms from the hydrocarbon molecules, leading to the formation of new carbon-carbon bonds and rearrangement of the molecular structure. This rearrangement can result in the conversion of straight-chain hydrocarbons into branched isomers.

Additionally, the high temperatures involved in RTC can also contribute to isomerization. The thermal energy can promote the breaking and rearranging of chemical bonds, facilitating the isomerization process.

While the radical mechanism is the primary driver of isomerization in RTC, other factors such as temperature, reaction time, and the presence of catalysts or reactive species can also influence the extent and selectivity of the isomerization reactions (Zaikin and Zaikina 2014).

Radiation-induced isomerization is a significant process in high-viscosity oils that contain high levels of heavy aromatic compounds. Isomerization reactions are more favorable at lower dose rates and temperatures. The experiments conducted on high-paraffin and heavy oils have highlighted the importance of radiation-enhanced isomerization and radiation-induced polymerization in conditions like those in refining, treating, and cracking. Understanding the conditions and intensity of these effects is crucial for achieving high yields of light products during oil radiation processing and ensuring their quality (Zaikin and Zaikina 2013, 2016). Some of the recent works related to RTC based isomerization of hydrocarbon molecules are listed in Table 5.

Initial studies were conducted to assess the isomerization of 2-butene induced by GI in benzene. Based on the results of this work, iodine, ferric chloride, dose rate, anthracene, naphthalene, and oxygen exhibited varying effects on the rates and yields of isomerization in different solvents. Various mechanisms have been discussed, with positive ion and energy transfer being applicable in different hydrocarbon solutions (Cundall and Griffiths 1963).

A strong effect of radiation-induced isomerization of alkanes during the RTC of heavy oil was observed by studying two different irradiation modes, with mode 1 showing intense molecular destruction and mode 2 being more favorable for isomerization. Based on the results, the presence of heavy aromatics promotes isomerization at lower temperatures (Zaykina et al. 2001).

A study was conducted on the radiolysis of natural gas and associated petroleum gas under EBI, with the aim of assessing the isomeric composition. The study found that the molar mass of natural gas increased while the molar mass of associated petroleum gas decreased. The composition of the liquid products and the ratio between isomers in the fractions depended on the dose rate and flow rate of the circulating gas mixture (Ponomarev and Makarov 2006).

Further studies have shown that RTC is consistently accompanied by intense isomerization, which is especially pronounced in heavy oils and bitumen with high contents of heavy aromatic compounds. The analysis of data on the radiation cracking of hydrocarbons indicates a significant role of isomerization processes in the mechanism of chain reaction propagation at lowered temperatures (Zaikin and Zaikina 2014).

Additional research has demonstrated the successful utilization of radiation-enhanced isomerization to increase gasoline octane numbers. This was achieved by employing heavy oil residua as catalysts for low-temperature isomerization. The process of isomerization is primarily driven by radiation-excited unstable states. These findings highlight the potential of radiation-enhanced isomerization as a valuable technique for improving fuel quality (Zaikin 2013; Zaikin and Zaikina 2014).

A review discussed radiation-enhanced isomerization for upgrading and refining heavy paraffinic oil (Zaikin and Zaikina 2016).

The impact of GI on crude oil transformation and the isomerization of n-alkanes was investigated. The researchers utilized nanostructured bentonite clay as a cost-effective additive catalyst. The findings suggest that radiation induces distortion, transformation, and weakening of the molecular structure of crude oil, resulting in the conversion of n-alkanes into branched hydrocarbons (Ismayilova et al. 2020).

Other research suggested a combined isomerization-polymerization method activated by EB irradiation of small hydrocarbons under ambient conditions. As a result, the study demonstrated the conversion of small molecules into liquid fuels and valuable chemicals within the C₆–C₁₅ range. Figure 3 illustrates the mechanism schematically (Wang and Staack 2020, 2022).

Figure 3:

Isomerization-polymerization combined reaction of hydrocarbons induced by EBI (Wang and Staack 2020); reproduced with permission from ACS publications.

4.5 Radiation induced polymerization

Radiation-induced polymerization is a versatile process that offers unique advantages in the synthesis of polymers. One of its key benefits is the ability to initiate polymerization without the need for heat or chemical initiators, making it a more energy-efficient and environmentally friendly approach. The use of radiation as a trigger allows for precise control over the polymerization process, enabling the production of polymers with tailored properties and molecular weights.

Additionally, radiation-induced polymerization can be conducted at ambient temperatures, which is particularly advantageous for heat-sensitive monomers or for applications where elevated temperatures are not feasible. The process also offers a high degree of versatility, as it can be applied to a wide range of monomers, including organic and inorganic compounds.

Furthermore, radiation-induced polymerization allows for the creation of polymers with unique structures and functionalities that are difficult to achieve through conventional polymerization methods. The ability to control the reaction conditions, such as the dose and rate of irradiation, enables fine-tuning of the polymer properties, such as molecular weight, cross-linking density, and chain branching.

Overall, radiation-induced polymerization is a valuable tool in polymer science and engineering, offering enhanced control, efficiency, and the potential for novel polymer materials with tailored properties for various industrial and technological applications.

Hydrocarbon polymerization induced by irradiation refers to the process in which hydrocarbon molecules undergo the formation of larger, chain-like structures when exposed to radiation, such as Gamma rays or EBs. Irradiation causes the molecular bonds in hydrocarbons to break, leading to the formation of new bonds and the joining of smaller hydrocarbons into larger polymer chains. This process can result in the production of higher molecular weight compounds and can be utilized in various applications, including the upgrading of heavy oils and the synthesis of polymers (Kharisov et al. 2013; Zaikin and Zaikina 2014).

The principles and kinetics of low-temperature (cold) radiation-induced cracking of hydrocarbon compounds were introduced, with polymerization identified as a limiting factor in oil conversion. The researchers concluded that the maximum yield of stable light products in radiation-induced cracking is limited by the critical irradiation dose, as higher doses result in unstable products due to continued polymerization and adsorption of light fractions (Zaikin 2008; Zaikin and Zaikina 2013, 2016).

In contrast, as mentioned in subsection 4.4, a novel approach was later introduced that involves the combined isomerization-polymerization method, utilizing EBI to convert small molecules into valuable chemicals and liquid fuels within the C₆–C₁₅ range (Wang and Staack 2020, 2022).

4.6 Radiation methods for oil demercaptanization and desulfurization

Radiation methods for oil demercaptanization and desulfurization involve the use of radiation, such as gamma rays or EBs, to facilitate the removal of mercaptans and sulfur compounds from crude oil or petroleum products. These methods offer advantages over traditional chemical-based processes by providing a more efficient and environmentally friendly approach.

In the demercaptanization process, radiation interacts with the mercaptan molecules present in the oil, causing the breaking of sulfur-hydrogen bonds. This interaction results in the formation of free radicals, which can then react with other molecules to form larger, less volatile compounds that can be easily separated from the oil. For desulfurization, radiation-induced reactions can break the sulfur-carbon bonds in sulfur compounds, leading to the generation of radicals that can be further reacted or removed from the oil. This process reduces the sulfur content of the oil, which is desirable for environmental and regulatory compliance.

Radiation methods offer several advantages, including higher selectivity for sulfur removal, lower energy consumption, and reduced production of waste compared to conventional methods. They can be applied to various types of crude oil or petroleum products, making them versatile and adaptable to different refining processes. The high sulfur content of heavy oil causes pipeline corrosion, which is a major cause of pipeline failures. The easiest way to remove sulfur is through field upgrading using cracking methods (Yang 2009). The research on oil demercaptanization and desulfurization discussed in this subsection is summarized in Table 6.

The effect of EBI was studied on the conversion of mercaptans and other light sulfur species to sulfones, sulfur oxides, and acids in hydrocarbon mixtures. The results showed that the irradiation of the feedstock resulted in high yields of motor fuels, with an 80 % conversion of mercaptans, as well as a reduction of disulfides and sulfides (Zaykina et al. 2002a).

In another study, the focus was on employing EBI for the reduction of sulfur in crude oil and oil products. It was demonstrated that a combination of preliminary treatment with ozone-containing air at room temperature and subsequent high-temperature radiation processing effectively reduces sulfur content in light fractions and decreases the overall amount of sulfur, which is mainly found in high-molecular compounds (Zaykina et al. 2004).

Furthermore, it was found that using GI led to the degradation of mercaptans in petroleum. It was proposed that low-dose irradiation with oxygen greatly improved the degradation process, thereby reducing the required irradiation dose. Other chemicals, such as acetone and carbon tetrachloride, were found to enhance the degradation efficiency by over 25 %. The main degradation product was identified as didodecyl disulfide (Naiqiang et al. 2004).

Utilizing irradiation-induced radiochemical reactions was investigated for the removal of sulfur compounds in petroleum. A simulated petroleum sample containing dibenzothiophene (DBT) dissolved in dodecane was analyzed, resulting in a 33 % removal of DBT. Additional experiments explored the kinetics and improved removal methods, including the synergistic effects of hydrogen peroxide (H₂O₂) and acetic acid (HAC), as well as the use of co-oxide impregnated on γ-Al₂O₃ as a catalyst, which resulted in a significant increase in DBT removal efficiency of over 40 % (Qu et al. 2006).

The synergistic effect of irradiation and the catalyst was assessed on the decomposition of DBT in simulated petroleum. It was found that GI, along with zirconium oxide impregnated on alumina (Zr/Al₂O₃), exhibited the highest activity. Using the Zr/Al₂O₃ catalyst at a radiation dose of 179 kGy, the DBT removal efficiency was found to be 98.9 %, representing an increase of over 80 % compared to the absence of a catalyst. The results indicated that lower dose rates also improved removal efficiency. Additionally, the catalyst remained stable under GI, except for surface coverage by oxidized organic compounds (Qu et al. 2007).

In another study, a comprehensive review was conducted on various methods for the desulfurization of hydrocarbon fuels, including radiation-based techniques (Srivastava 2012).

The desulfurization of light distillation fractions from Arabian crude oils was investigated using GI. Based on the results, sulfur transfer decreased in extra light oil and increased in medium crude oil due to radiation exposure. Additionally, it was shown that extra light crude oils exhibited a higher desulfurization efficacy than heavy and light crude oils (Basfar and Mohamed 2011).

Additionally, the effects of GI on sulfur, hydrocarbons, and nitrogen compounds were assessed in oil and diesel. In this context, benzothiophene, diesel, and crude oil samples were irradiated with gamma rays. It was observed that the sulfur compounds in diesel and petroleum were effectively reduced (Andrade 2014).

Another study was conducted on the use of GI to degrade sulfur compounds in crude oil and diesel fuel samples, demonstrating efficient degradation of benzothiophene and benzenethiol, which formed fragments such as 1,2-dimethylbenzene and toluene. Some diesel samples initially showed an increase in sulfur compounds at lower doses; however, this trend reversed at higher doses. In contrast, petroleum samples exhibited a decrease in sulfur compound concentration after irradiation. A comparison of sulfur compound removal percentages in petroleum and diesel samples is presented in Table 7 (Andrade et al. 2015).

The decomposition efficiency of sulfur compounds using EBI showed that higher initial concentrations and lower adsorbed doses increased the efficiency. The researchers reported that the presence of N and O radicals resulted in the highest removal efficiencies for certain compounds, while reactions with the O radical were most effective for others (Son and Kim 2015; Son et al. 2015a,b).

Other researchers have suggested that ionizing radiation positively affects the reduction of sulfur components in crude oil and aids in catalyst regeneration (see also subsection 4.7) (Kondo et al. 2016).

The desulfurization of light distillation fractions from Arabian crude oils was examined using GI. The efficiency of sulfur removal was found to be significantly higher for extra light crude oil compared to both heavy and light crude oils (Basfar et al. 2017).

It is important to note that radiation methods for oil demercaptanization and desulfurization are still being researched and developed, and their commercial-scale implementation may require further optimization and cost-effectiveness analysis.

4.7 Irradiation of catalysts

Hydrocracking catalysts are commonly used in the petroleum refining industry to convert heavy hydrocarbon feedstocks into lighter, more valuable products. Over time, these catalysts can become deactivated due to the deposition of coke and other contaminants on their surfaces, leading to a decline in performance.

Gamma ray or electron beam irradiation has been explored as a potential method for regenerating and rejuvenating hydrocracking catalysts. When catalysts are exposed to high-energy radiation, several effects can occur. Firstly, the radiation can break down the carbonaceous deposits (coke) that accumulate on the catalyst surface, effectively removing the deactivating species. This process is known as coke removal or decoking. Additionally, high-energy radiation can activate catalytic sites that may have been blocked or deactivated by coke deposition. Initial studies have shown promising results in the regeneration of hydrocracking catalysts using gamma ray or electron beam irradiation. For example, gamma irradiation was shown to significantly boost the H₂-D₂ exchange activity of the γ-Al₂O₃ catalyst (Kohn and Taylor 1959).

In another study, an analysis of published data on catalytic reactions under ionizing radiation was conducted, emphasizing the intersection of heterogeneous catalysis and the effects of radiation (Zhabrova and Vladimirova 1969).

Later, cumene hydrocracking was performed on gamma ray irradiated Ni/Al₂O₃ solids. The results indicated that gamma irradiation enhanced the catalytic activity of the samples (El-Shobaky et al. 2004).

Furthermore, it was shown that using high-energy EBs or gamma rays did not aid in lanthanum extraction or nickel removal in FCC catalysts, which is crucial for preventing irreversible catalyst deactivation. Irradiating depleted HCC catalysts in the lower bed with EBs effectively extracted molybdenum, resulting in double the yield compared to non-irradiated catalysts. Similarly, the irradiation of spent HCC catalysts in the upper bed showed efficient molybdenum extraction, though less prominently, with irradiated catalysts at 1,050 °C exhibiting extraction levels similar to those of non-irradiated ones (Kondo 2014).

In another study, it was observed that ionizing irradiation positively impacts catalyst regeneration by eliminating sulfur compounds from catalyst surfaces. Both virgin and exhausted catalysts were irradiated with GI and EBI at room temperature. However, they found that under these experimental conditions, irradiation does not induce changes in the catalyst structure and does not efficiently eliminate nickel contaminants (Kondo et al. 2016).

Again, EBI (1.5 MeV, 37.5 kW) was employed to extract high-value metals, specifically molybdenum, from spent hydrocracking catalysts (Figure 4). EBI demonstrated a positive contribution compared to traditional thermal and chemical methods (Kondo et al. 2022).

Figure 4:

Radiation thermal processing on spent catalyst: (a) virgin catalyst, (b) spent catalyst, (c) alumina crucible and (d) MoO₃ crystal formed after EBI (Kondo et al. 2022); reproduced with permission from Elsevier.

4.8 Cleaning and refining of used oil products

The environmental impacts of used oil products have prompted researchers to find a way to reprocess them efficiently to produce base lubricants and motor fuels. The method should involve high-capacity production and yields of commodity products while contributing to environmental protection. By utilizing radiation-induced reactions, the technology enables effective cleaning and regeneration of used oil mixtures, producing regenerated lubricants, motor fuels, and basic lubricants through fractionation. The process involves irradiation with high-energy electrons or gamma rays to stimulate reactions such as decomposition, oxidation, polymerization, and chemical adsorption for the successful regeneration of the oil products (Zaikin and Zaikina 2014). Based on their work, Figure 5 presents a schematic of the apparatus designed for treating used and residual oil products with EBI or GI.

Figure 5:

Device layout for treating used and residual oil products with EBI and GI.

The improvement of the two lubricant samples following irradiation, which satisfies the standard requirements for basic lubricants is reported in (Zaikin and Zaikina 2014).

It was found that ionizing radiation treatment effectively removes metals from used automotive lubricant oil, achieving satisfactory removal of elements P, S, Ca, Cl, Zn, and V. Additionally, different irradiation doses and the use of H₂O₂ did not cause changes in the organic compound profile of the oil (Scapin et al. 2007).

In another study, the degradation of hydrocarbons in waste automotive lubricating oil was investigated through GI (100–500 kGy) at varying doses, identifying the degraded organic compounds (Scapin et al. 2009).

The use of EBI was studied to create modified pitch from pyrolyzed fuel oil, showing potential for diverse applications. EBI (1.14 MeV, 270 °C) at doses of 20–50 kGy on AlCl₃-containing samples led to decreased nitrogen, hydrogen, and sulfur contents, while the carbon content increased. Heat treatment alone was insufficient for pitch formation, but EBI enhanced the carbon content (Jung et al. 2014).

4.9 Fuel and diesel production

Radiation processing can be used in the production of fuel and diesel through a process called radiation-induced polymerization. In this process, high-energy radiation, such as gamma rays or EBs, is used to initiate polymerization reactions in hydrocarbon feedstocks. This can lead to the formation of polymers or oligomers that can be blended with conventional fuels to improve their properties, such as cetane number, lubricity, and stability.

Additionally, radiation processing can also be used to reduce the sulfur content in diesel fuel through the radiation-induced desulfurization.

Overall, radiation processing offers a promising approach to enhance the quality of fuels and diesel by modifying their chemical composition and properties through targeted reactions initiated by ionizing radiation. Table 8 presents the reviewed works in this subsection.

Researchers discovered that irradiating gaseous propane with EBI in the presence of water resulted in the production of condensable alkanes, alcohols, and ethers. Their studies revealed that the quantity of these compounds was impacted by cooling conditions, radiation dose, and gas flow rate. Additionally, the research delved into the mechanisms behind the formation of these compounds. (Gafiatullin et al. 1997; Ponomarev et al. 2000, 2002).

Additionally, the researchers investigated the impact of radiolysis using EBI on gaseous alkanes. They focused on analyzing changes in gas-phase composition and the generation of liquid products during irradiation. The results indicated that treating volatile alkanes with EBs leads to the production of low molar mass mixtures containing highly branched liquid products (Ponomarev and Tsivadze 2006). Subsequently, it was proposed to use EBI to create highly branched liquid hydrocarbons from gaseous alkane mixtures with high-octane values suitable for motor gasoline (Ponomarev 2009a).

Additionally, the application of EBI was investigated for the chain destruction and distillation of lignocellulose materials, showing its efficiency in transforming plant materials into valuable products such as polymerization retarders, monomers, and alternative fuel (Ponomarev 2009b). Furthermore, researchers discussed utilizing EBI to synthesize liquid fuel from gaseous alkanes through a two-stage process that converts macromolecules into stable fuel, demonstrating the potential of these methods for traditional or alternative engine fuels production and enhancing light alkanes in fuel manufacturing (Ponomarev et al. 2012). Additionally, the use of EB technology was studied in the chain cracking of heavy crude oil, synthesis of premium gasoline from oil gases, and processes such as hydrogenation, alkylation, and isomerization of unsaturated oil products (Ponomarev et al. 2015).

High temperature EBI and simultaneous distillation (RDC) were introduced to crack C₁₇–C₁₂₀ paraffins, yielding a distillate with 61.5 % alkanes, 38.5 % alkenes, and 32.3 % gasoline fraction (Metreveli and Ponomarev 2016a). In other studies, EB processing methods were compared for paraffins and methane (Metreveli and Ponomarev 2016b; Metreveli et al. 2016).

Furthermore, radiation-induced methods were investigated for the synthesis of gasoline and diesel fuel, demonstrating higher yields in methane-based processes and the potential for waste-free treatment conditions to enhance gas fixation and transformation processes (Metreveli and Ponomarev 2016c).

The impact of irradiation on hydrocarbons was studied, focusing on fuel conversion mechanisms. Using GI, tests on gasoline and diesel fuels revealed insights into their radiation stability, composition changes, and quality variations. Results indicated that higher absorbed doses and longer irradiation times led to increased viscosity and density in the fuels, with those high in unsaturated hydrocarbons showing a greater tendency to form coke and degrade in color during storage (Cabbarova and Mustafayev 2017; Jabbarova 2019, 2020; Jabbarova and Mustafayev 2018, 2021a,b; Jabbarova et al. 2017). The gamma radiation resistance of a hexane–hexene mixture was assessed under static conditions using GI. The findings showed increased viscosity and density post-irradiation, along with altered absorption bands, including reduced valence oscillations of СН₃. The irradiation caused significant changes in alkane and alkene bonds, resulting in increased coking and color deterioration during storage due to higher levels of unsaturated hydrocarbons (Akberov et al. 2020).

The impact of GI on the properties of petro-diesel fuel was explored using GI. Researchers studied the density, distillation, kinematic viscosity, flash point, and cetane number as functions of absorbed doses (Osman et al. 2021).

A chemical kinetic model was created to analyze EBI. The simulation tracked stable product concentrations, radicals, and ions over time, demonstrating variations in product yield with dose rate. The predominant stable products were H₂ and C₂H₆, with H₂ production linked to cation-CH₄ reactions and ethane destruction associated with CH₅₊ cation reactions, primarily driven by a few key reactions (Gu and Dibble 2022).

The use of EBI was showcased to induce chemical transformations in hydrocarbons at low temperatures with helium purging. Hydrocarbons with different saturation levels were tested; pentane and cyclohexane exhibited significant fragmentation, while tetralin and toluene showed less fragmentation due to their higher bond energy. The color and GC-MS spectra for the selected hydrocarbon compounds before and after irradiation have been reported in their work (Wang and Staack 2022).

A cyclone-type reactor paired with an EB was studied for converting methane into heavier compounds, such as C₂–C₅ alkanes, thereby decreasing methane content and predominantly yielding high-ethane content alkanes (Ponomarev 2023).

4.10 Gas purification

Gas purification after heavy oil combustion using EB involves the application of high-energy electrons to treat the exhaust gases, leading to the breakdown of harmful pollutants into less harmful compounds. This process can effectively reduce the levels of sulfur dioxide (SO₂) and nitrogen oxides (NO_x), which are common pollutants emitted during the combustion of heavy oils. By utilizing EB technology for gas purification, industries can mitigate environmental impact, comply with emission regulations, and enhance overall air quality in the vicinity of heavy oil combustion facilities.

A comprehensive explanation of the chemical kinetics involved in the removal of NO_x and SO₂ from flue gas was provided using EBI. They stated that the removal of NO_x and SO₂ from flue gas via EBI involves three steps: conditioning, irradiation, and filtration. During conditioning, the gas is cooled (60–100 °C), humidified, and ammonia is added in stoichiometric amounts ([NH₃] = [NO_x] + 2 [SO₂]). Electron beam irradiation oxidizes NOx and SO₂ to nitric and sulfuric acids, which react with ammonia to form ammonium nitrate and sulfate particulates, later filtered from the gas (Mätzing 1991; Mätzing et al. 1996).

The works reviewed in this subsection are summarized in Table 9.

The breakdown of aromatic volatile organic compounds (VOCs) was explored using EBI with specific parameters. Researchers discovered that adding chlorinated compounds enhanced the decomposition of aromatic VOCs under EBI. A dose of 10 kGy resulted in decomposition rates of 55–65 % for non-chlorinated VOCs and 85 % for chlorobenzene, suggesting a degradation mechanism to increase degradation rates and decrease dioxin formation in industrial off-gases (Han et al. 2003).

The breakdown of fluorene was examined through a dual approach involving GI and ozone treatment in an alkaline, aqueous environment. The findings revealed that while ozonation effectively decomposed fluorene, the combined method led to even more efficient substrate degradation (Popov and Getoff 2004).

Technical innovations were suggested to enhance electron accelerator efficiency for increased total power output. The research focused on utilizing these accelerators in coal and oil power plants to eliminate pollutants from flue gases. Proposed solutions included a basic electron accelerator, a plasma reactor for desulfurization and selective catalytic reduction, and the blueprint for a pilot plant tailored for the oil sector (Korenev and Johnson 2008).

The elimination of butane using EB irradiation was investigated in various background gases, including nitrogen, air, and helium. Removal efficiencies were 40 % at 2.5 kGy and 66 % at 10 kGy for an initial concentration of 60 ppm, producing by-products such as CO₂, CO, acetaldehyde, and acetone. The study noted a higher decomposition efficiency of butane in nitrogen and oxygen backgrounds compared to helium (Son et al. 2010).

In another study, a pilot-scale EB flue gas treatment plant was established to treat 2,000 Nm³/h of flue gas from a heavy fuel oil-fired boiler. The pilot plant demonstrated effective simultaneous control of sulfur dioxide (SO₂) and nitrogen oxides (NO_x), achieving high removal efficiencies. The byproducts collected were high-quality fertilizer, primarily ammonium sulfate (98 %–99 %) with low heavy metal content (Pawelec et al. 2016).

A review was conducted on the utilization of EBI for environmental pollution control. This review explored the application of EBI in diverse sectors, such as flue gas treatment, sludge management, and sewage treatment, while also analyzing industrial projects worldwide that have implemented this method (Chmielewski and Han 2016).

Modeling advances in EB flue gas treatment have provided critical insights into pollutant removal processes. A study developed a detailed kinetic model addressing the complex interactions in both gas and liquid phases. Sensitivity analysis revealed that removal efficiency for SO₂ and NOₓ is strongly influenced by hydroxyl radicals (HO·), with the competition for these radicals between SO₂ and NOₓ being a significant factor limiting efficiency. The study also showed that the irradiation dose and humidity content were key parameters, while temperature had minimal impact on the reactions (Zwolińska et al. 2017).

In another review, the limitations of conventional removal methods and the development of EBI over the past decades were discussed, showcasing its ability to simultaneously remove SO₂ and NO_x while generating valuable by-products, such as fertilizer. The review outlined the progression of EB technology from laboratory to industrial-scale plants globally, including the exploration of new EB hybrid approaches to address existing challenges and future prospects (Park et al. 2019).

Again, the application of EBI in the removal of NO_x and SO₂ from the flue gas of diesel power plants was reviewed (Zwolinska et al. 2019).

Recent studies have demonstrated the efficacy of hybrid EBI and wet scrubbing systems for removing NO_x and SO₂ from diesel engine flue gases. The addition of oxidants like NaClO₂ significantly enhances NO_x removal efficiency, achieving up to 95.03 % at 10.9 kGy dose when combined with phosphate buffer–simulated seawater. This approach proposes the rapid oxidation of NO to NO₂ and NO₃⁻ induced by EBI, coupled with efficient absorption in wet scrubbers (Zhao et al. 2020).

A simulation study demonstrated that EBI alone achieves limited NO_x removal efficiency (∼4.9 % at 10.9 kGy dose) due to the reverse formation of NO_x. However, coupling EBI with a water scrubber significantly improved removal efficiency to 22.4 % under the same dose, by leveraging the absorption of NO₂ into water to form HNO₃ (Sun et al. 2020).

The use of additives to improve the removal efficiency of NO_x and SO₂ in flue gas was studied using EBI. The researchers found that adding NaOH to the process resulted in the highest removal efficiencies for both target gases. They also assessed the utilization of mixed additives such as NaOH + NaCl or NaOH + NaClO₂, which increased the removal efficiency of NO and NO₂ (Seo et al. 2020).

Advancements in hybrid EB technologies have demonstrated their potential for removing high concentrations of NO_x and SO₂ from diesel engine off-gases. A study has achieved 100 % SO₂ removal efficiency across all tested wet scrubbing solutions and up to 89.6 % NO_x removal efficiency using a buffered NaCl solution with NaClO₂. The hybrid system leverages the synergistic effects of electron beam irradiation for oxidation and wet scrubbing for absorption, with oxidants like NaClO₂ playing a crucial role in enhancing performance (Zwolińska et al. 2020).

A work has studied the development of a hybrid electron accelerator system designed to treat marine diesel exhaust gases, addressing emissions of NO_x, SO_x, and particulate matter. The system combines EBI with wet scrubbing technology to efficiently remove pollutants in a single process. The proof-of-concept trials demonstrated its feasibility in a maritime environment, achieving significant reductions in NO_x and SO_x emissions (Sun et al. 2021; Torims et al. 2020).

The use of EBI was explored to treat air pollutants such as NO_x and SO₂ from stationary sources, with NH₃ commonly added to enhance removal efficiency. The study identified the need for more effective additives to improve NO_x removal. By evaluating parameters such as additives, absorbed doses, and initial concentrations, it was found that using NH₄OH alone achieved a removal rate of 46.7 %. However, when NaOH was added, the removal efficiency increased to 80.6 %. The type of additives had the most significant impact on removal efficiency, particularly for NO_x (Jo et al. 2021).

A combination of additives was employed to enhance the removal of NO_x and SO₂ using EBI. Factors such as the presence of additives, the oxidant stoichiometric ratio, and the absorbed dose were studied to evaluate removal efficiency. The results showed higher efficiency with NaOH as a base additive compared to NH₄OH, with NaOH alone achieving 87.90 % efficiency for NO removal. Increasing the absorbed dose generally improved removal efficiency, except when NaClO₂ was used as the oxidant. However, a mixture of NaOH and NaClO₂ at a low dose demonstrated high removal efficiencies of 89.28 % for NO and 88.16 % for NO₂ (Seo et al. 2022).

The removal of NO_x pollutants using EB-assisted flue gas treatment was studied. When using EBI with NaOH and NH₄OH additives, NO and NO₂ were removed by 100 % and over 94 %, respectively. Higher removal efficiency was observed with lower initial NO_x concentrations and increased EB doses (Shin et al. 2022).

4.11 Polluted soil and ground water remediation

Soil and groundwater remediation using irradiation involves employing high-energy EBs or gamma rays to treat polluted soils or water contaminated with total petroleum hydrocarbons (TPH). Irradiation breaks down TPH molecules, reducing their concentration. This method is effective in decontaminating by destroying organic pollutants, making it a promising approach for remediation projects aimed at efficiently and environmentally friendly reducing TPH levels in polluted soils and groundwater. Initial studies explored the combined effect of ozonization and EBI for pollutant decomposition in contaminated groundwater. This combined approach improves economic efficiency compared to irradiation alone, especially for cleaning up water layers thicker than the electron penetration depth, with ozone further enhancing the effectiveness of the process (Gehringer and Eschweiler 1996; Gehringer et al. 1995).

In another study, the radiolytic degradation of chlorinated hydrocarbons in water was investigated using gamma rays. The results showed that degradation increased with higher radiation doses, accompanied by rising concentrations of methane, ethane, CO₂, and C_l−, while the O₂ concentration decreased. The addition of H₂O₂ enhanced decomposition, and the method proved effective in transforming chlorine into chloride ions and producing clean energy in the form of methane and ethane (Wu et al. 2002).

A proof of concept for EB remediation of hydrocarbon-polluted soils was demonstrated using EBI (LINAC: 10 MeV, 15 kW). The experiments showed a reduction in TPH. TPH reduction was observed to increase with dosage and treatment temperature, while it decreased with moisture content. The reduction was reported to be up to 10 % for a total delivered dose of approximately 2000 kGy (Briggs 2015).

A review highlighted the use of ionizing radiation for the treatment of groundwater and soil, focusing on the degradation of various types of contaminants, including hydrocarbon compositions (Bao et al. 2022).

The effect of EBI (LINAC: 10 MeV, 15 kW) on the reduction of TPH in crude oil impacted soils was investigated. It was found that TPH can be reduced from approximately 9 % to below 1 % with irradiation doses ranging from 700 kGy to 1,100 kGy and treatment times of less than 200 s at a temperature of 450 °C (Lassalle et al. 2023).

4.12 Wastewater treatment

Oilfield produced wastewater treatment using high-energy radiation irradiation follows a procedure similar to that mentioned in subsection 4.11. Ionizing radiation, a modern advanced oxidation method for treating wastewater, utilizes gamma rays or EB radiation. This approach involves the direct impact of radiation and the oxidation–reduction reactions facilitated by active species such as ⋅OH, eaq, and ⋅H, which are produced during water radiolysis (Chu and Wang 2022; Spinks and Woods 1990). The studies reviewed in this subsection are listed in Table 10.

In a related study, the rate constants for the reaction of ethyl tert-butyl, diisopropyl, and methyl tert-amyl ethers with the hydroxyl radical, hydrated electron, and hydrogen atom in water were determined using both EBI and GI. The findings suggest that the hydroxyl radical is the dominant reaction pathway for treating ether-contaminated water (Mezyk et al. 2001).

In another study, the use of free radicals generated by EBI and GI was investigated for the removal of naphthalene contamination, a common aromatic compound found in most petroleum products, from water. The research found that low doses of GI and EB treatments effectively removed naphthalene from water, with the EB process showing potential for treating other polynuclear aromatic hydrocarbons due to its high degradation efficiency (Coopera et al. 2002).

EBI was also investigated for its ability to decompose pollutants in industrial effluent. The effluent samples from eight industrial units were treated, demonstrating efficient destruction of organic compounds such as chloroform and toluene. Furthermore, an EB pilot plant was proposed for wastewater treatment, as shown in Figure 6 (Duarte et al. 2002).

Figure 6:

A schematic view of a pilot plant designed for the treatment of wastewater (Duarte et al. 2002); reproduced with permission from Elsevier.

In another study, an evaluation was conducted on the efficiency of EBI for treating oilfield produced water. The study demonstrated that irradiation processing, particularly at high doses, effectively removes organic compounds such as benzene, toluene, xylene, and phenol from oilfield produced water (Duarte et al. 2004).

Various studies on the treatment of industrial wastewater using EBI, including applications for oilfield-produced wastewater, have been reviewed by (Hossain et al. 2018).

Different studies on treatment of industrial wastewater by EBI have been reviewed in (Hossain et al. 2018) including those related to oilfield produced wastewater.

The removal of petroleum pollutants (benzene, toluene, xylene) from seawater was studied using the GI, which found higher decomposition yields in purified water. Removal efficiency varied among the compounds, with benzene requiring higher doses for effective removal. It was revealed that the presence of salts in seawater impacted the distribution of reactive species during the removal process, suggesting that irradiation effectiveness can be influenced by water composition (Almeida et al. 2006).

A review article discussed the advantages of using ionizing radiation, including GI and electron EBI, for the decomposition of environmental pollutants, specifically persistent organic pollutants in water and wastewater (Trojanowicz 2020).

The use of EBI was evaluated for the pretreatment of polymer-containing oilfield wastewater, demonstrating an enhanced oil removal efficiency through coagulation. The improvement in oil removal was reported to be between 47 % and 85 % at a low dose of 1 kGy when combined with conventional treatment processes. A cost analysis was also conducted for the proposed method. Figure 7 schematically illustrates their setup (Chu and Wang 2022).

Figure 7:

A schematic view of an EBI plant to treat oil-field produced wastewater (Chu and Wang 2022); reproduced with permission from Elsevier.

A research work investigated the treatment of polyacrylamide-containing wastewater using GI. The study showed that absorbed doses of up to 10 kGy effectively degraded polyacrylamide, reducing its molecular weight and achieving a 62–78 % removal rate. The radiation process also significantly decreased the wastewater’s viscosity and destabilized colloidal particles, facilitating oil-water separation (Fang et al. 2023).

Another study evaluated the effect of EBI as a pretreatment for alkali/surfactant/polymer flooding-produced wastewater to enhance oil–water separation. By applying absorbed doses of 0.1–5.0 kGy, significant improvements in oil separation were achieved, with oil content reduced from 69.5 % in untreated wastewater to 20–29 % after irradiation. Radiation-induced changes in rheological properties, including a transition from pseudoplastic to Newtonian behavior, and the degradation of organic components such as polyacrylamide contributed to the enhanced separation process (Chu and Wang 2024).

The use of GI was investigated to control microbial communities in oil-field produced water from conventional and unconventional oil processes. The results showed a significant reduction in microbial loads, with higher radiation doses leading to greater decreases in bacterial concentration. Molecular analysis revealed that specific bacteria, such as Halanaerobium sp. and Pseudomonas sp., decreased with increased irradiation (Soler-Arango et al. 2024).

A recent review article explored the environmental applications of electron beam irradiation (EBI), including its effectiveness in treating wastewater contaminated with various pollutants, such as aromatic hydrocarbons (Chmielewski et al. 2024).

4.13 Sludge treatment

EBI is utilized for treating petroleum sludge by breaking down the complex hydrocarbons present in the sludge into simpler, more manageable compounds. This process helps reduce the volume of petroleum sludge, minimizes environmental impact, and facilitates easier disposal. EB treatment offers an efficient and environmentally friendly method for addressing petroleum sludge, making it a promising technology for sustainable waste management practices in the petroleum industry. The impact of high-temperature EBI (LINAC, 8 MeV, 4 kW) was studied on petroleum sludge. The findings showed that at high doses (∼280 kGy), thermal radiolysis transforms high-molecular-weight paraffins in the sludge into fuel hydrocarbons. Additionally, based on their results, introducing lignin to the sludge increased the condensate yield and transparency of the resulting lightweight fuel mixtures (Metreveli et al. 2018).

In another study, Brazilian oil sludge was characterized to explore the effects of EBI (1.5 MeV, 37 kW) combined with H₂O₂ on the degradation of organic compounds in petroleum wastes. The research showed that EBI, especially at high doses around 200 kGy, significantly decreased the solid phase organic carbon content. Meanwhile, H₂O₂ had a minimal impact (Tessaroa et al. 2021).

4.14 Aging of petroleum fluids

A new approach has been proposed to estimate the residence time of petroleum fluids in subsurface reservoirs by analyzing the chemical changes in crude oil composition due to GI. This method allows for monitoring the destruction of identifiable species or assessing the production of new chemical moieties, which can provide insights into the residence age of reservoir fluids (Larter et al. 2019).

4.15 Naturally occurring irradiation

Naturally occurring irradiation of hydrocarbons refers to the exposure of hydrocarbon deposits to radioactive elements present in the surrounding rock formations. This exposure leads to radiolysis, which breaks down the hydrocarbon molecules and alters their chemical composition. The process can impact the quality and quantity of hydrocarbons present, influencing properties such as viscosity, American Petroleum Institute (API) gravity, and sulfur content. Understanding the effects of natural irradiation is crucial for evaluating the characteristics and behavior of hydrocarbon reservoirs. As preliminary research, the impact of high uranium concentrations in Alum Shale, Sweden, on organic matter over 500 million years was evaluated. Radiation-induced polymerization of alkanes altered the shale, leading to changes in oil yields and composition, atomic ratios, and steroid hydrocarbons. Despite stable carbon isotopes remaining unaffected, the estimated radiation dosage for the observed alterations exceeds 105 Mrads, indicating varying radiation damage potential across geological periods (Lewan and Buchardt 1989).

An interdisciplinary study was conducted on the effects of uranium radiogenic decay on immature organic-rich Alum Shale, finding that irradiation influenced the composition of organic matter, gas-oil ratios, and aromaticities. The analysis indicated structural changes in the shale samples due to natural irradiation, which affected their petroleum potential (Yang et al. 2018).

Another study examined the impact of natural radioactivity on the generation of hydrocarbon gases from sedimentary organic matter. These radiolytic transformations occurred at doses similar to those found in natural geological settings over long periods. The isotopic signatures of these gases may be misinterpreted as “biogenic” based solely on the carbon isotope ratio of methane, highlighting their importance in certain scenarios (Renzo et al. 2019).

The effects of uranium (U) irradiation, occurring naturally, were investigated on organic matter (OM) in U-rich shales. It was found that radiation caused structural alterations in the OM, leading to the generation of various gases and oxidized compounds. The dominant reactions during OM radiolysis were identified as cracking, cross-linking, and oxidation (Wenqing et al. 2022).

Researchers studied a source of natural gas through the radiolysis of organic matter in U-rich and organic-rich shales. Their results showed that the radiolytic gas containing methane, ethane, and propane can account for more than 25 % of natural gas mixtures in shale gas (Naumenko-Dezes et al. 2022).

Another study reviewed the natural irradiation of OM and its impact on the elemental, isotopic, bulk, and molecular compositions of OM over geological time scales. The review covers various topics, including the radiation of kerogen in radioactive shales, radiolytic alteration of crude oil for tracing oil residence time, characteristics of radiolytic natural gases, and radiolytic synthesis of larger OM molecules. The study highlights the potential use of radiolytic changes in OM as geochronometers for oil residence time dating and the interpretation of natural gas formations based on geochemical templates (Yin et al. 2023).