In catalysis, molecules undergo a reaction made possible by the presence of catalysts. Catalysts are compounds that lower the activation energy required for a chemical reaction to take place, jumpstarting these reactions and making them occur at an increased rate. Unlike a reactant, a catalyst does not undergo any chemical transformation over the course of the reaction. In addition to increased productivity due to faster chemical reactions and reduced energy requirements, catalysts provide proven process reliability and demonstrated scalability to large production volumes. Catalysts are capable of utilizing variable feedstocks and producing a range of molecules.
Production of biofuels from lignocellulose has the advantage of abundant and diverse raw material but requires a greater amount of processing to make the sugar monomers available to the microorganisms that are typically used to produce ethanol by fermentation.
There are two ways of producing ethanol from cellulose, both which use distillation to isolate pure ethanol, gasification and cellulosic processes.
Utilizing a gasification process transforms the lignocellulosic raw material into gaseous carbon monoxide and hydrogen. These gases can be converted to biofuels by fermentation or chemical catalysis. The gasification process does not rely on chemical decomposition of the cellulosis but rather than of breaking the cellulose into sugar molecules. The carbon is converted into synthesis gas, using what amounts to partial combustion. The carbon monoxide, carbon dioxide and hydrogen may then be fed into a special kind of fermenter. This process uses a microorganism rather than yeast which consumes carbon monoxide, carbon dioxide and hydrogen and produces ethanol and water.
The cellulose molecules are composed of long chains of sugar molecules. In the hydrolysis process, these chains are broken down to free the sugar, before it is fermented for alcohol production. There are two major cellulose hydrolysis processes: a chemical reaction using acids, or an enzymatic reaction. With the rapid development of enzyme technologies in the last 2 decades, the acid hydrolysis process has gradually been replaced by enzymatic hydrolysis.
The main source of alcohol fermentation is sugar, for which feed stocks include sugar canes, sugar beets and others. Fermentation of cellulosic biomass happens only after other pre-treatment processes break down the cellulose, hemicelluloses, lignin and pectin. Once the sugars are freed from the matrix, they are available to be fermented into biofuels. A number of advanced cellulosic companies plan to turn syngas into ethanol by fermentation.
Alcohol is a short chain fermentation product produced by microbial metabolism, so making recovery of the alcohol is energy intensive and expensive with the requirement of complex distillation.
Gasification is the process by which solid biomass is deconstructed through the use of a high temperature, high pressure process and converted in to smaller molecules. The resulting gas mixture, synthesis gas, or syngas, is a combustible fuel with a number of useful applications including the production of renewable biofuels.
Recently developed gasification processes remove harmful impurities like carbon dioxide, and regulated pollutants are removed and/or captured. The result is a cleaner, more efficient syngas than in traditional production methods.
Other gasification processes gain efficiencies using concentrated solar energy to achieve the high temperatures necessary for gasification. Therefore, these technologies are able to produce syngas without burning another material to create the heat necessary for the process to work, lowering the overall greenhouse gas footprint of the produced fuels.
Hydrolysis literally means reaction with water and is the chemical reaction that converts the complex polysaccharides in the raw feedstock to simple sugars. In the biomass-to-biofuels process, acids and enzymes are used to catalyze this reaction. In the chemical process a molecule is cleaved into two parts by the addition of a molecule of water. One fragment of the parent molecule gains a hydrogen ion (H + ) from the additional water molecule. The other group collects the remaining hydroxyl group (OH − ).
Hydroprocessing is not a single process, but rather a general term for any chemical engineering process that breaks heavy hydrocarbons (fat, oil, etc.) into lighter fractions by the addition of hydrogen. Hydroprocessing is common in the traditional crude oil refining industry.
In the biofuels arena, hydroprocessing has applications as a method for transforming waste animal fats (beef tallow, chicken fat, greases and vegetable oils) to produce a wide variety of fuels, including bio-diesel, renewable diesel or jet fuels.
Synthetic Biology is a new area of biological research that is at the intersection of science and engineering advances. Synthetic biology refers to both the design and fabrication of biological components and systems that do not already exist in the natural world, and the redesign and fabrication of existing biological systems.