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Kuzma Ustinov
Kuzma Ustinov

Second Generation Biofuels And Biomass: Essenti...

The recently identified limitations of 1st-generation biofuels produced from food crops (with perhaps the exception of sugarcane ethanol) have caused greater emphasis to be placed on 2nd-generation biofuels produced from ligno-cellulosic feedstocks. Although significant progress continues to be made to overcome the technical and economic challenges, 2nd-generation biofuels production will continue to face major constraints to full commercial deployment. The logistics of providing a competitive, all-year-round, supply of biomass feedstock to a commercial-scale plant is challenging, as is improving the performance of the conversion process to reduce costs. The biochemical route, being less mature, probably has a greater cost reduction potential than the thermo-chemical route, but here a wider range of synthetic fuels can be produced to better suit heavy truck, aviation and marine applications. Continued investment in research and demonstration by both public and private sectors, coupled with appropriate policy support mechanisms, are essential if full commercialisation is to be achieved within the next decade. After that, the biofuel industry will grow only at a steady rate and encompass both 1st- and 2nd-generation technologies that meet agreed environmental, sustainability and economic policy goals.

Second Generation Biofuels and Biomass: Essenti...

Traditionally, distillation is used to separate alcohol and water. Distillation can generate a maximum of 95% pure ethanol. Molecular sieves or additives are then needed to break the azeotrope to get pure ethanol. Although simple, distillation is an energy intensive process and requires initial ethanol concentrations greater than 4% to be economical [232]. Mostly grains or extracted sugar is used in the first generation biorefinery and therefore there are almost no degradation products in the substrate to inhibit enzymes or microbes. Hence, ethanol titer >10% are easily achievable allowing an economical distillation process. Researchers are looking at different biofuels that are insoluble in water that can be phase separated to avoid distillation process [233].

One of the potential coproducts in a biorefinery is microbial biomass [118]. In the batch fermentation mode, part of the microbe could be reused for the subsequent fermentation process [259]. The remaining biomass could be sold as an animal feed if using a native organism. Since most of the microbes used for fermentation in the second generation biorefineries are genetically modified organisms (that could efficiently consume both glucose and xylose) there may be some potential regulations for the use of microbial biomass as animal feed. In the semicontinuous rapid bioconversion with integrated recycle technology (RaBIT) process, the same concept may apply [169], where in the microbial cells are recycled every 24 hours for subsequent fermentation cycle. Excess cells are used for other applications. Furthermore, separated cells will contain several lignin degraded products and may lower the quality of feed [260]. Processing the proteins from these organisms followed by converting them to amino acids by acid hydrolysis is another option that could be used to produce chemicals, which can be used as precursors for making biomaterials.

Producing biofuels using the sugar platform is a water intensive process. Water is used in almost all the processing steps. In order to meet the water requirements, important decisions should be made regarding the location of the biorefineries. In many cases, water will be pumped from the ground, which may add considerable stress to the local water resources [267, 268]. Recycling water will help to reduce this stress, but will require additional investment. Given the process and processing conditions used in the biorefineries, it will be a prerequisite to do the following when recycling the water: remove salts generated during neutralization, remove organic content, and recycle the catalysts [267]. Clarification steps have been widely adopted in the pulp and paper industry to remove suspended solids and to reduce chemical oxygen demand/biochemical oxygen demand in water. Several novel technologies have been developed to treat the water, which include biological treatment (e.g., anaerobic digestion, algal treatment), coagulation, electrocoagulation, polymer resin filtration, and coagulation-flocculation techniques. Among these techniques, coagulation (using ferric sulphate, alum, water soluble polymers, chitosan, poly aluminum chloride, fly ash, etc.) is found to be an economical approach to remove organics [269]. It is important to use minimal water in each processing step in order to reduce water recycling cost. In some cases, the choice of pretreatment in a second generation biorefinery will be determined based on the water availability in the region. Colocating the second and the first generation biorefineries will minimize waste water and reduce the stress on the water table [152, 270].

The promise of the second-generation (2G) bioconversion industry is that it will transform cellulose-based, nonedible biomass and agricultural waste into clean and affordable high-value fuels or chemicals. (The first-generation, or 1G, technology converts edible biomass.) In this way, 2G could offer an alternative source both of energy and of chemical-industry inputs, which other renewable technologies cannot provide.

The use of biofuels in Europe has been rightly scrutinised due to first generation biofuels and their reliance on food crops, impacting food security, land use and the wider environment. Furthermore, the fuels produced are unable to be blended at higher ratios.

For example, traditional first-generation biofuels use crops as feedstock. This either requires large amounts of land to be dedicated to new biofuel crops or for food crops to be diverted to biofuel use.

This change in land use can have devastating impacts on ecosystems and deforestation when biofuels are produced at scale. As a result, we are seeing first-generation biofuels being phased out through policy change.

Second-generation biofuels were designed to address this issue. By using exclusively waste products to create liquid fuels, second-generation biofuels do not impact land use and do not represent the same sustainability challenge at scale.

Unlike other renewable energy sources, biomass can be converted directly into liquid fuels, called "biofuels," to help meet transportation fuel needs. The two most common types of biofuels in use today are ethanol and biodiesel, both of which represent the first generation of biofuel technology.

In 2012, researchers from MIT, ExxonMobil and Viridos (formerly Synthetic Genomics, Inc.) published an assessment of algal biofuels in the peer-reviewed journal Environmental Science and Technology, which concluded that if key research hurdles are overcome, algal biofuels will have about 50 percent lower life cycle greenhouse gas emissions than petroleum-derived fuel. In contrast, there is a robust debate in the academic research community regarding the carbon footprint of first generation biofuels, which the EPA defines as those generated from edible crops (such as corn). Many peer-reviewed papers in the scientific literature suggest that the direct life cycle GHG emissions are lower than fossil fuels but that indirect consequences of first generation biofuel development, including changes in forest and agricultural land use change, may result in higher total GHG emissions than petroleum-derived fuels.

For these reasons, ExxonMobil is pursuing research into second generation biofuels to determine how they may best fit into our energy future. Second generation biofuels are defined as those produced from non-edible crops, crop residues or biologically generated gas and therefore do not take away from the total food or fresh water supply. Examples include algae, corn stover, switchgrass or methane emitted from microbial activity in landfills.

We are funding a broad portfolio of biofuels research programs, including our ongoing efforts on algae as well as programs on converting alternative, non-food based biomass feedstocks, i.e. cellulosic biomass, to advanced biofuels. We believe our work with algae offers some of the greatest promise for next-generation biofuels, which is why ExxonMobil has committed hundreds of millions of dollars to algae research. We are working with leading researchers and have designed our portfolio to progress the science that we feel will be needed to deliver advanced biofuels with environmental benefits.

Algae can provide a diverse and highly desirable non-food source of the important renewable molecules that can be used to produce second generation biofuels. Some strains of algae can be optimized to produce bio-diesel precursors. Other algae strains can be optimized as a source of fermentable sugars, with compositions similar to those derived from corn kernels that are used to manufacture first generation biofuels like ethanol.

In light of the growing scarcity of oil resources, biofuels constitute an alternative solution, since they can serve as a complement to fossil fuels. As part of its policy aimed at reducing greenhouse gas emissions, the European Union is requiring that renewable energy sources be increased to 10% of global fuel volume by 2020. Unlike first generation biofuels, the production of second generation biofuels uses only the non-edible part of the plant.

The demonstration unit, which combines in a single facility all of the various second generation biofuel production elements, will be the first production unit of this kind in France.

Unlike first generation biofuels, which process the noble part of the plants, second generation biofuels do not compete with food chain needs, since they only use residues from agricultural or forestry production. These biofuels, which are very pure and sulfur free, offer not just excellent engine fueling characteristics; they also generate fewer CO2 emissions compared to conventional fuel, thereby contributing to the fight against climate change. 041b061a72


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