Synergy in food, energy and advanced materials production from biomass

Towards a sustainable bioeconomy

Growing demands of the ever increasing human population coupled to non-renewable resource depletion led many researchers and policy-makers to issue warnings like those expressed in the well-known book “Limits of Growth”, and its more recent update [1].

Specific answers to these concerns call for a shift towards renewable resources that can be used without the risk of depletion, and great successes were achieved in recent years thanks to new technologies in solar and wind energy production, to the growing use of biomass for energy and raw materials production and to other promising but less-developed technologies.

However, neither solar- or wind-to-electricity technologies contribute directly to raw materials production. For this reason, they can only partially replace the current fossil carbon products, especially the fuels that have lower unit value than petrochemicals. Current production of petrochemicals is based on naphtha (from oil) or natural gas. This means that petrochemical industry is based on a small fraction of the overall fossil carbon used, but its annual output is ca. 40% of the global oil and gas industry revenue. Petrochemical industry has been highly successful for many decades and this is due to a number of factors, including the intensive efforts to improve its economics. For instance, recent publications describe decision support systems to minimize purchase costs and to maximize profits by production planning [2], as well as the optimization of the use of resources [3].

The high value of petrochemical products suggests that oil and other fossil fuels should be saved for chemical production, largely extending the duration of existing reserves. This looks logical but we should recall that petroleum extraction, refining and petrochemical production are process industries whose viability is strongly dependent on the production scale. This means that saving oil for the chemical production will necessarily make it much more expensive.

The viability of the petrochemical industry is critically dependent on the prices and availability of its current inputs, oil or gas. This is demonstrated by the rapid growth of this industry in the Middle East, since the 1980s and even more spectacularly by the upturn of the American industry since shale gas availability increased steeply, for the past 10 years.

On the other hand, food production is necessarily accompanied by the production of a huge amount of crop residues. In some cases, residues largely exceed the amounts of edible material and they are especially significant in large food producers. In Brazil, the amount of agricultural residues is now in excess of 1 billion metric tons every year, whose energy content is roughly equivalent to 200 million metric tons of oil.

Agricultural residues are thus an interesting possibility to increase the use of renewable resources as energy and industrial feedstocks. There are many examples of their use in the past and an outstanding case is sugarcane [4] that underwent a large change in its role, during the past four centuries. It was introduced in South and Central Americas by the Portuguese (in the 16^th century), Spanish and French, becoming the major global source of food sucrose.

Until the 1970s, ethanol was just a sugar byproduct. Mother liquor resulting from sugar crystallization was fermented and distilled to produce beverages like the lower grades of cachaça. In the 1920s, a fuel factory named Usga operated in the Brazilian northeast, delivering a mixture of ethanol, ethyl ether and castor oil that was used to fuel cars. However, the production of fuel ethanol was not significant and it remained insufficient to benefit from the opportunity created by the scarcity of oil, during the Second World War. Indeed, cars that could not be fueled with the hardly imported gasoline in Brazil used water gas (gasogênio) as a fuel, a very ineffective solution.

Later in 1942, a large plantation of sugarcane was established in the Campinas region in São Paulo, by the Rhodia company that previously used to import ethanol from Germany, for its chemicals production in Brazil. This was not feasible during war time and new, extensive cane plantations supplied ethanol that went into the production of acetic acid, ethyl acetate, diethyl ether, ethyl chloride and other derivatives. Beyond, the fermentation process also yielded significant amounts of other lower alcohols that were also fed to the chemical industry.

In the 1970s oil prices grew in two big steps and this led many countries to create stimuli and subsidies for fuel ethanol production. This was then critical in Brazil, because the country was not a significant oil producer, and its dependence on fuel imports was unbearable. Indeed, the country was then buying foreign oil with borrowed money, which led to financial default in the early 1980s, creating one of the biggest crises in the country, ever.

Fuel ethanol production was initially strongly subsidized at an estimated overall cost of 10–12 US$ billions but this was worthwhile [5]. In the 1990s, subsidies were eliminated in the southeast that contributed 90% of the total Brazilian production and later in the whole country. In 2002, ethanol was fully competitive with gasoline and it took a large share within the fuel market [6], becoming also an attractive oil replacement for the chemical industry.

Ethanol production spread to other states adjacent to São Paulo: Mato Grosso, Goiás, Minas Gerais and Paraná, without subsidies. Sugarcane soon became the input for a highly diversified industrial production, including butanol, polyethylene, wax, green solvents and surfactants, nanosilica, cellulose, paper and pulp, microcrystalline cellulose, poly(hydroxibutirate) and other thermoplastics, lysine (>600 000 tons/year), electricity and cattle fodder. Today, some companies obtain as much as 20% of their income from selling electricity to the grid. CO₂ collected from the fermentation tanks and sold to industrial users is another source of additional income, in some plants. The main output currents (sugar or ethanol) are adjusted according to their respective market prices. An extensive account of the chemicals and materials that can be obtained from sugarcane was published recently [7].

Sugarcane main products perform well, considering greenhouse gas emissions. For sugar production, GHG emissions were estimated at 234 g CO₂eq/kg, considerably less than beet sugar produced in Europe. As for anhydrous ethanol, life cycle emissions were evaluated as 21.3 g CO₂eq/MJ, corresponding to an emission mitigation of 80% as compared to gasoline [8].

New products derived from sugarcane and ethanol are appearing, in different places. Two examples are the Miralene^® solvent from the Amyris company, in the US. It is presented as a new high-performance, sustainably sourced and cost-competitive product based on β-farnesene. It is produced in Brazil on a commercial scale by fermentation of sugarcane juice using special strains of baker’s yeast [9]. The SIP Ltd. company (UK) presented a product containing farnesene and farnesane, Sipdrill RS^®, as the first renewable, hydrocarbon drilling base fluid for high performance drilling mud systems.

Thus, sugarcane that was initially planted for sugar only is thus currently the main input of a large economic activity, as the source of food, energy and industrial raw materials. Its potential for growth and diversification is very large, considering its success in the regeneration of formerly low-yield pasture land, since the 1980s.

Moreover, “second-generation” ethanol production from wood and lignocellulosic residues is now becoming a reality, from tropical areas to Scandinavia. It can also spread to other areas with temperate climate, allowing many countries to become significant biofuel producers, based on agricultural and forestry residues.

Different from oil and gas that are produced in relatively few areas across the world, agricultural residues are widespread, although highly variable. This requires attention to logistic requirements for their economic use and it also opens opportunities for process intensification, so as to achieve higher outputs from smaller, distributed units.

An important path to oil replacement in the petrochemical industry is the development or modification of chemical processes to use increasing amounts of biomass together with oil, in existing petrochemical plants. There are now outstanding research results in this direction, from many groups [10] and this topic has already received extensively coverage in the literature.

The prices of natural resources, financial speculation and the food crisis

Market and political forces play an important role in determining prices for natural resources. In the long run, scarcity should necessarily lead to higher prices but this does not show clearly in the prices for commodities as a function of time. The case of oil is remarkable: inflation-adjusted prices show abrupt changes up and down, largely related to strategic decisions taken by the producers, to the level of economic activity and the incidence of recessions as well as sheer speculation, rather than the amounts of existing reserves. Sharp peak oil prices were recorded in April 1980 (US$119), Nov 1990 (US$53) and Jun 2008 (US$156), while deep depressions took place in Feb 1986 (US$29), Dec 1998 (US$18), Jan 2009 (US$48) and Jan 2016 (US$29). The current price (June 2017) is lower than figures recorded in 1974 and 1985 or during most of the time, since 2004.

Looking at data for other commodities, it is clear that financial speculation and other factors played a dominating role in determining prices for critical non-renewable resources. Since 2005, prices for phosphate rock and potash (that are essential for agricultural production) parallel each other closely, with a large peak in 2008–2010. The historical prices of soybeans parallel those of fertilizers and it is tempting to associate these trends to the “food crisis” of 2007–2008. At this time and still currently, the crisis was assigned by many persons to the increased use of land to produce energy crops, in the first years of this century. However, the industry reports show the same trends in the prices of the ores used to make tin, nickel, lead, zinc and other metals that have nothing to do with food. This correlation is easily explained considering another factor: the downfall of the American real-estate market that led investors to look for protection in other markets, like commodities that were then attractive and seemingly safe targets. Thus, speculation played a major role in creating the “food crisis” but this is often forgotten: this crisis is frequently presented as a direct consequence of land use for energy production, by many authors.

The association between the use of agricultural products as fuels or raw materials and the food crisis gained strong footing in the public opinion and it has been a major roadblock on the way to increasing the use of biomass as a major renewable industrial feed.

Synergy instead of competition

Criticism to land use for energy and raw materials production can be read in many places, as for instance in the earlier reports of the International Food Policy Research Institute (IFPRI). The argument is based on simple arithmetic: using land to produce non-food crops competes with food production, thus contributing to global hunger.

However, the 2016 report from IFPRI states: “...biofuels may offer an opportunity to improve food security. Yet, for many poorer countries in Africa and elsewhere, biofuels may be better viewed as a potential export or as a means for reducing fossil fuel imports. ...producing conventional biofuels in low-income countries could raise rural incomes beyond what is required to offset rising food prices”. Moreover, studies in Ethiopia led to the following conclusion: “...farmers’ participation in biofuel programs encouraged greater use of fertilizers and improved farming technologies, leading to higher food-crop productivity and better food security during the year. One precondition for success, however, was farmers’ access to high-quality, productive biofuel crops” [11].

The IFPRI 2016 report is extremely important because it demonstrates the synergy between food and fuels production from biomass, as opposed to the often-touted food vs. fuel arguments. It verifies the conclusions drawn from the Brazilian experience from the past 40 years, showing how food and non-food crops may both increase steeply thanks to new technologies, on essentially constant planting area. Moreover, many crops are simultaneously sources of food, energy and raw materials for the industry, like sugarcane that was previously discussed, in this paper.

Competition for land use

Beyond the availability of land, the consequences of land-use change (LUC) are strongly debated. How is the available land distributed and is there more land available for biomass production, worldwide? Crops, fruits and the planted forests currently occupy 5.7% of the Brazilian territory, while 18.8% (160 million ha) are occupied by pasture land, out of which 60 million hectares are suitable for agriculture. Shortly, the area used for agriculture in Brazil can be doubled, at least, without introducing any change in the forest and other pristine biomes [12]. This is being done by transforming low-yield, often pre-desert pasture land subjected to heavy erosion into high-yield pasture land and intensively cultivated land. Moreover, the protection of water fountains and rivers is now done by replanting many areas with native species, thus recovering environments that were heavily disturbed during the two previous centuries. Land use change can be highly beneficial: increased C stocks were found in pasture areas converted to sugarcane cultivation [13] contributing to CO₂ sequestering from the atmosphere.

An attractive possibility is provided by the agroforestry systems that have been introduced since the early 1970s and are now growing fast. There are many configurations, associating annual and perennial crops, or associating crops, trees and cattle in the same area, with positive synergies. They are making an impressive contribution to improve land outputs [14] and they are also playing multiple desirable roles: increasing biodiversity, sequestering carbon and improving food security [15].

A current ambitious program in Africa targets the restoration of 100 million hectares, in 22 participating countries. Adoption of the FMNR (farmer-managed regeneration approach) contributed the following benefits to a community in northern Ghana: increased crop yields and incomes, increased assets in the form of tree stocks and improved livestock, increased wild resources for household consumption and sale with associated dietary health benefits, improved psycho-social wellbeing, a more positive outlook and improved soil fertility, added to carbon sequestering [16].

Existing land area is thus limited but its output can be multiplied many-fold by using new (and some old) approaches to its use. In Brazil, the sugar cane planted area underwent a 92% expansion between 2002 and 2012 but this did not constrain the expansion of the area used for annual crops and commercial forests, while cattle production also increased. In the case of soybeans, the planted area grew by 25% between 1976 and 2012, while the production grew more than three-fold, from <50 million tons to nearly 170 million tons. This was achieved by bringing new technologies to the field, from soil management to seeds and pest control. Productivity through the new sustainable technologies is thus much more important than the available area. Thanks to productivity growth, the output of agriculture can increase many-fold without harming the forest or other biomes.

Summing up, there is no reason against the use of biomass for energy and raw materials production, based on land availability or environmental protection. Quite the opposite, different experiences from Brazil and Ethiopia show that the dissemination of well-established technologies as well as the introduction of new sound practices overcome the limitations of available land. Thus, the overall amount of biomass produced in the world may increase many times, providing all the needed food and spreading wealth, allowing people to pay for food and contributing large amounts of energy and industrial raw materials to build new patterns of sustainable industrial activity.

Advanced materials from biomass

Biomass has been providing important materials for human use, since pre-historical times. During part of the past century, there was the feeling that synthetic polymers would replace natural materials due to oil availability and low cost, associated to the supposedly superior properties of synthetic polymers. However, wood, paper, pulp and cellulosic fibers as well as natural rubber continue to exhibit a remarkable vitality.

Natural rubber and cellulose are often seen as well-known, mature materials that do not offer significant research opportunities. However, recent results show previously unsuspected features that attracted a lot of attention and are being explored in new products and industrial processes.

Natural rubber

Natural rubber from Hevea brasiliensis is usually referred to plainly as a “cis-poly(isoprene)”. However, this designation cannot explain why the natural rubber was never fully replaced by the synthetic products and why is it still required by companies making tires and adhesives. Reasons given by industry experts are found as in the following unpublished statement from Velson, relative to choosing natural or synthetic rubber to make tires: “In general, as the tire size increases and the level of punishment the tire will take goes up, the amount of natural rubber increases due to natural rubber’s good shear resistance, load bearing capability, and high level of resistance to cuts”.

Beyond cis-poly(isoprene), natural rubber contains many non-rubber constituents, notably inorganic compounds, proteins and phospholipids. Their distribution in the rubber was observed by electron spectroscopy imaging (ESI-TEM) in the analytical transmission microscope, which produces elemental maps as shown in Fig. 1 [17]. These micrographs were obtained using inelastically scattered electrons, selected with the help of an electron spectrometer mounted within the column of the microscope. The bright spots are the areas that accumulate each element, showing the rubber filled with small particles containing sulfur, aluminum, phosphorus, nitrogen and other elements [17].

Fig. 1:

Bright-field and elemental distribution images of a thin film cast from dialysed natural rubber latex. Scale bar is 150 nm. (From Ref. [17], by permission of Elsevier.)

Most remarkable, thicker rubber domains surround the particles, showing a surprising adhesion to the rubber matrix. This is evidenced by the contrast around the dark spots in the brightfield image and by the increased brightness in the same area, in the C map. Natural rubber is thus a natural nanocomposite, filled with reinforcing mineral nanoparticles. It contains also calcium ions that diffuse in the freshly cast films, crystallizing latter as calcium sulfates [18].

Proteins and phospholipids found in the rubber also contribute to adhesion among its various constituent phases, thanks to their amphiphilic character and to electrostatic adhesion: the apolar domains fit within the rubber matrix while the polar ends bind to the inorganic particles and to calcium ions.

Finding that natural rubber is a nanocomposite was done at about the same time when the “latex route” [19] was emerging, as an attractive approach for making polymer nanocomposites. The is done just by mixing aqueous Na-montmorillonite or other clay dispersion and the latex, followed by drying the mixture [20]. The resulting solids show remarkable mechanical properties that may be tuned within a broad range, by changing the clay content. Clay-polymer nanocomposites are current an important new class of polymer materials.

Since hydrophilic clays and common polymers are usually incompatible, this raised the following question: why are strong materials obtained by mixing the aqueous dispersions but not the dry powders? The adhesion between clay lamellae and a rubber particle is evidenced by their mutual insertion seen in the micrographs in Fig. 2. Detailed investigation of the factors in the spontaneous intimate mixing of the two phases showed that it arises due to capillary adhesion during water evaporation followed by electrostatic adhesion between rubber and clay particles in the dry solid, mediated by the counter-ions [20, 21], as in the scheme shown in Fig. 3.

Fig. 2:

ESI-TEM micrographs of a rubber–clay particles cluster formed when a dilute dispersion of latex and montmorillonite is allowed to dry over a microscope grid: (a) bright field image, (b) carbon map and (c) silicon map. (From Ref. [20], by permission of ACS.)

Fig. 3:

Schematic description of the events involved in the adhesion of silica to latex particles. (From Ref. [21], by permission of ACS.)

These findings have been exploited in the development of new fabrication processes with desirable features: they use only water-based raw materials, process temperatures are usually lower than 120°C under ambient pressure, producing minimal waste. This is now a general approach for the development of biomass-based functional complex materials, since it overcomes well-known problems in the miscibility and compatibility of the different constituent phases. For instance, blends of usually incompatible polymers like natural rubber, PVC, starch and cellulose are easily prepared in aqueous media, displaying unprecedented compatibility and properties. Addition of clays, other inorganic solids and carbon particles is done without difficulty, as required to achieve the desired structural and functional properties.

Conclusions

Food, energy and industrial raw materials production may increase manifold globally with little or no expansion of the used area, as shown by large-scale results in Brazil and very recent data from Ethiopia. This has been largely due to improvements in all aspects of agricultural practice at any scale, from huge plantations to small properties. Higher biomass output creates wealth and it contributes to improved food security for all, including low-income populations. It is now likely that similar results will appear shortly, in other parts of Africa and elsewhere. Moreover, agriculture expansion on regenerated land is taking place simultaneously with the preservation of existing natural biomes.

As for the industrial raw materials, biomass contributes a number of “petrochemical-like” building blocks. Beyond, cellulose, natural rubber and other biopolymers offer still untapped possibilities for creating new nanostructured materials that can in turn bring new possibilities for large-scale manufacture, throughout the world. It is thus possible to decrease our dependence on oil, gas and coal as inputs for the chemical industry and for making materials required for human activities, by increasing biomass production and use and by progressing in the discovery and exploitation of its ever surprising properties.