Volume 18, Issue 1 -

Research activities discuss about the global environmental impacts of carbon dioxide (CO 2 ) emissions. Government authorities and international conferences aim to reduce greenhouse gas emissions and encourage the development of sustainable processes using renewable sources. In order to reduce emissions from the industrial sector, CO 2 capture and reuse as a raw material in the production of marketable products have encouraged the development of technologies. Among many possible chemical products manufactured from CO 2 , sodium bicarbonate appears in this context as an important compound in the chemical, food, textile and pharmaceutical industries. Then, the main objective of this work was to carry out a bibliographical review of the main production processes available in the literature for synthesis of sodium bicarbonate and the main chemical reactions involved in the crystallization reactor. Regarding to the processes, soda ash carbonation from trona, the Solvay process and the sodium sulfate route were assessed and compared. Among the main raw materials used in the production process of sodium bicarbonate, sodium chloride is presented as most economically feasible while sodium carbonate and sodium sulfate are indicated as the most environmentally viable alternatives. Beyond, the global processes were presented for each route discussing advantages and disadvantages for the separation and purification steps required after the reaction. It is notable that the main raw material is sodium chloride due to its easy possibility of obtaining, from seawater, and large availability for applications at the food industry. Indeed, the production of sodium bicarbonate by means of the Solvay process was the route that presented the best results regarding to the technology development and economic cost. Use of sodium sulfate as raw material has proved to be a possible route, besides presenting numerous advantages such as production of valuable byproducts. However, this route may be not totally viable compared to conventional routes due to the complexity of products separation and purification. The review showed that there is a lack in the scientific literature regarding to the development of studies evaluating sodium bicarbonate crystallization and purification in a cost effective and technical detailed approach.

Direct evidence of the control of yield, thermal stability and photoluminescence property of the polyaniline (PANI) nanofibers have been reported by systematically varying the reaction time in the range of 2–6 hours (h) in the synthesis process. Both FTIR and UV–visible spectra revealed the formation of PANI fibers for all synthesis batches. The mass of the obtained PANI was increased with the increase of reaction time from 2 to 6 h. FESEM data confirmed the formation of PANI in nanofibers form for all the synthesis batches. TGA data showed that the highest thermal stability of PANI nanofibers could be obtained for the 4 h reaction time. PL data indeed showed the variation of luminescence intensity of PANI with the reaction time which indicate the formation of different quality fibers in terms of their π conjugation. Thus the three main results can be summarized: one is the increase of PANI fibers yield and another two are the thermal stability and luminescence property modification which shows that such properties of PANI can be controlled by varying the reaction time of the synthesis process.

Bubble size distribution (BSD) is important for gas-liquid jet loop reactor (JLR)’s mass transfer performance of inter-phases. A self-designed reversed JLR was investigated with air-water system on the BSD. The CCD camera of particle imaging velocimetry (PIV) system and image processing technique were used to obtain the reliable photo. The influences of four parameters, gas phase flow rate, liquid phase flow rate, draft tube diameter and ejector mounting position, on the BSD were studied in detail. The results showed that the local BSD is accordance with log-normal distribution under the experimental conditions and the average diameter and BSD range increase with the increase of the gas phase flow rate, and decrease with the increase of the liquid phase flow rate, the downward movement of the nozzle installation position and the increase of the diameter of the draft tube.

The work was aimed at evaluating the adsorptive properties of neem leave/chitosan aggregates for methylene blue removal. The adsorbent was screened to form coarse (CCANL, 600 µm), medium (MCANL, 300 µm) and fine (FCANL, 150 µm) neem leave/chitosan particles. The samples were characterized for pH, water binding capacity (WBC), surface chemistry by Fourier transform infrared spectroscopy, surface morphology by scanning electron microscope and textural properties by Brunauer-Emmett-Teller method. CCANL, MCANL and FCANL possessed specific surface area of 255, 258 and 242 m 2 /g, respectively. The effects of initial concentration, adsorbent dosage, contact time, pH and temperature were studied. CCANL, MCANL and FCANL demonstrated adsorption capacity of 102, 92.5 and 105 mg/g, respectively, in which ionic interaction and mesopore filling were the possible adsorption mechanisms. The equilibrium data were well fitted by Redlich-Peterson model, suggesting a monolayer adsorption onto a heterogeneous surface of adsorbent. The kinetics data were best described by pseudo-second-order and intraparticle diffusion models, for which the film diffusion, intraparticle diffusion and surface adsorption could co-exist as the controlling steps in adsorption. Adsorption of methylene blue onto chitosan composites was spontaneous, endothermic and demonstrated increased randomness at solid-solution interface.

Phenyllactic acid (PLA), an organic acid with extensive antimicrobial activity, is considered as a promising natural preservative to replace chemical preservatives. In order to study the inhibitory pattern of PLA, this paper established a novel mathematical model for the growth of Staphylococcus epidermidis under PLA inhibition. The simulated results showed that the relationship between the antimicrobial activity of PLA against S. epidermidis and its concentration was suitable to be represented by an exponential function. Based on the proposed model, the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of PLA against S. epidermidis were evaluated. The computed results were found to match experimental data. The MBC value was found to be independent of the initial biomass of S. epidermidis from both the simulated results and experimental data, revealing that PLA was not consumed while killing the bacteria. Another kinetic model was established to describe the production of PLA by the engineered Escherichia coli . This model was then used to calculate the minimum biomass of E. coli to produce the MBC of PLA. The proposed models help to understand the inhibitory pattern of PLA, serving as a theoretical guide for the selection an appropriate strain to improve the product shelf-life.

In this research, a simple procedure for synthesis of reactor network (RN) is presented. This method could find the best possible optimum solutions with high grantees for the synthesis of RN, which generally is kind of mixed integer nonlinear programming (MINLP) models. In this work, instead of solving the discrete and continuous variables simultaneously, (like MINLP problems), a combination of stochastic algorithm and mathematical methods (i. e. Non-dominated Sorting Genetic Algorithm II (NSGA II) + quasi LP (QLP)) has been used. The reason for using NSGA II is because of the possibility of considering several objective functions instead of a single function in obtaining RN synthesis solutions. This algorithm could provide several optimal structure of RNs as set of final optimal solutions by use of its operators. The isothermal RNs produced by NSGA II are sent to QLP model to compute the amount of objective functions. In the QLP model, whilst all continues variables of RN calculated with just using a linear and a non-linear equations set with outer search loop, their general objective functions are also calculated. Comparison the results with the references shows that the presented method is capable of producing better solutions, which, in some cases improvement of about one percent in concentration of the main material in the product and a decrease of 77 % of the residence time of the materials in the reactor system is observed.

Our previous pilot-scale studies (Bioresource Technology 2018, 267: 102–109) preliminarily demonstrated the feasibility of performing air gasification with a novel two-stage system, including a medium-temperature bubbling fluidized bed (BFB) reactor and a high-temperature swirl-flow furnace reactor, using rice husk as the fuel. As an extension of that work, this study aims to further investigate the reaction mechanism and application prospect of this technology in the use of a more representative biomass fuel, i. e. rice straw. The operation stability, flow behaviors and reaction characteristics in the first-stage medium-temperature gasification reactor are studied in a lab-scale BFB gasifier. The effects of important operating conditions on the syngas quality, tar yield, compositions of carbon residue, and risk of agglomeration are elucidated in depth. The results have shown that an increase in the gasification temperature can promote syngas quality, gasification efficiency, and carbon conversion, but also increases the risk of agglomeration. An increase in the gasification equivalent ratio leads to positive effects on the syngas yield, carbon conversion, and tar concentration, but also has negative effects on the syngas heating value, tar yield, and especially the restrain of agglomeration. An increase in the raw material moisture content has negative influence on the gasification performance of rice straw, in terms of the gasification efficiency, carbon conversion, tar yield, and so on. However, the increase of moisture content can reduce the cost of raw material drying, and avoid the fluctuation of bed temperature, and therefore, a practical gasification system is recommended to be designed and operated under a certain conditions with moderate moisture contents.

A pelletized ZSM-5/alumina catalyst was prepared by the extrusion technique. The catalyst was activated by ion-exchange with NH 4 NO 3 aqueous solution. The activated catalyst was trained in the methanol-to-hydrocarbons reaction which caused the catalyst deactivation due to coke deposition (6.5 % wt.). Coke deposition resulted in a two-time decrease in the micropore volume. The methane, benzene, and methanol transport through ZSM-5/alumina pellet were consequently studied prior to activation, after activation, and after catalyst deactivation. A slight decrease in the diffusion rate after catalyst activation is observed. After deactivation, the diffusion rate increases insignificantly. The diffusion regime remains unchanged with respect to either activation or deactivation procedure. Contrary, for the methanol, the diffusion rate through a deactivated catalyst pellet remarkably increases due to micropore blockage by coke deposition. The obtained results reveal that the micropores blockage during the catalyst deactivation enhances the methanol mass transfer.

The absorption of carbon dioxide by hydrates is considered as one of the potential methods for carbon capture and storage. In this work, a new impinging stream reactor was designed to investigate the characteristics of carbon dioxide hydrate formation process. The experiments were carried out at different pressure, temperature and impinging strength. It was shown that the carbon dioxide hydrate formation process could be enhanced by the impinging stream technique. With the increased of impinging strength, both gas consumption and hydration rate were increased. In addition, initial pressure and temperature also had an effect on the carbon dioxide hydrate formation process. Moreover, the kinetics of carbon dioxide hydrate formation was discussed. When the initial pressure was 3.5 MPa and impinging strength was 0.21, the activation energy was 24.74 kJ/mol, which was similar to the experimental data available in the literature.

Lubricant reactions in internal combustion engines follow complex reaction pathways, in which oil (hydrocarbons) and additives form protecting films (known as tribofilms) on the surfaces of the cylinder-piston couple. Up-to-date there is not a fundamental model useful to describe the chemistry involved in formation of these tribofilms, and degradation of oils and additives as result of working time of the engine. One of the main problems associated is the impossible measuring of the actual phenomena inside the engine, at working conditions. In order to model formation of tribofilms, starting by lumping two main groups of lubricating molecules, anti-shear and anti-wear, the lumped kinetics model for degradation products was solved, based on actual data collected in commercial engine workshops. Later these two-lump reaction schemes were delumped into two new systems, each one consisting of three lumps, in order to infer lubricant reaction pathways that form tribofilms and degrade lubricants. Distribution of anti-shear and anti-wear lubricants in tribofilms was predicted by simulation of these two delumped schemes.