Biofuels, Biochemicals and Bio Plastics
Sugar and Starch-based Biomass
Today nearly all biofuels and biochemicals are derived from starch- and sugar-based feedstocks. The sugars in these feedstocks are easy to extract and convert, making large-scale production economical. Corn is the leading U.S. crop and serves as the feedstock for most U.S. ethanol production. Globally sugarcane and cassava are also used. There is much criticism, and many countries have restricted or banned the use of food crops for fuel.
Cellulosic feedstocks are non-food based feedstocks that include crop residues, wood residues, yard waste, and dedicated energy crops such as Giant King Grass. These feedstocks are composed of cellulose, hemicellulose, and lignin. It's more challenging to release the sugars in these feedstocks for conversion to biofuels and chemicals. Many companies are building their first commercial plants to implement processes for large scale production of second-generation biofuels, biochemicals and bio plastics. Cellulosic feedstocks offer several advantages over starch- and sugar-based feedstocks. They are cheaper and more abundant so they provide a solution for producing more substantial amounts of biofuels and biochemicals to replace fossil fuels.
Biofuels and biochemicals are produced in factories called biorefineries which integrate biomass conversion processes and equipment to produce fuels, power, chemicals and bio materials from biomass. According to the National Renewable Energy Laboratory (NREL), the biorefinery concept is analogous to today's petroleum refineries, which produce multiple fuels and products from petroleum. Industrial biorefineries have been identified as the most promising route to the creation of a new biobased industry.
By producing multiple products, a biorefinery can take advantage of the differences in biomass components and intermediates and maximize the value derived from the biomass feedstock. A biorefinery might, for example, produce one or several low-volume, but high-value, chemical products and a low-value, but high-volume liquid transportation fuel, while generating electricity and process heat for its own use and perhaps enough for sale of electricity. The high-value products enhance profitability, the high-volume fuel helps meet national energy needs, and the power production reduces costs and avoids greenhouse-gas emissions. NREL's biorefinery concept is built on two different "platforms" to promote different product slates. The "sugar platform" is based on biochemical conversion processes and focuses on the fermentation of sugars extracted from biomass feedstocks. The "syngas platform" is based on thermochemical conversion processes and focuses on the gasification of biomass feedstocks and by-products from conversion processes. High-value chemicals produced in a biorefinery can be used to make plastics, replace nylon, make detergents, antibiotics, cosmetics, sweeteners, flavors and fragrances. Protein can be recovered and used for food and feed ingredients.
Giant King Grass as a Cellulosic Feedstock
In the US, ethanol producers that use corn as a feedstock are building cellulosic ethanol plants adjacent to their corn ethanol plants. The cellulosic feedstock they plan to use is corn straw (corn Stover)-- the leaves and stalk of the corn plant. All of their processes are developed and optimized for corn straw.
Three companies have independently tested Giant King Grass as a feedstock for cellulosic ethanol production. These include well-known companies in the ethanol business. The average results are shown below and compared to Corn Stover which is their baseline feedstock. The first measurement is the sugar, lignin and ash composition of a completely dried sample. Glucan, xylan and arabinan are polymer sugars which are desirable, and lignin and ash are undesirable.
The data clearly shows that one dry ton of Giant King Grass has somewhat higher glucan and essentially the same amounts of the other quantities. Or roughly speaking, a ton of Giant King Grass is just as good as a ton of Corn Stover in terms of its sugar content-- perhaps even a little better than Corn Stover.
Now the question is yield. How many tons of Giant King Grass can you harvest per acre compared to tons of Corn Stover? Extremely high yield is the major advantage of Giant King Grass.
Giant King Grass has 10 times the yield per acre compared to Corn Stover. The comparison isn't entirely apples to apples because corn will grow in cold areas and Giant King Grass is a tropical and subtropical crops that does not grow in freezing areas. Nevertheless the advantage of Giant King Grass is clear.
The companies also conducted pretreatment and enzymatic hydrolysis and projected the ethanol production to be 78.5 – 80 gallons per dry ton. Simply multiplying the ethanol yield times the grass yield gives you the land use efficiency in terms of gallons of ethanol per acre of land. This is shown in the figure below. For reference the data on sugarcane ethanol production in Brazil is also included.
Feedstock is the largest complement in the cost of cellulosic ethanol. The high yield of Giant King Grass can lower feedstock costs substantially and co-location of the bio refinery and the Giant King Grass plantation can reduce costs additionally. Together, feedstock costs could be reduced by 40 to 50% which could make cellulosic ethanol from Giant King Grass profitable today.
Green Chemicals from Renewable Biomass
The National Renewable Energy Laboratory has identified 12 important chemical building blocks that can be made from the sugars in cellulosic biomass like Giant King Grass. The high yield of Giant King Grass means that it will be a low-cost feedstock for these processes as well.
The 12 building-blocking chemicals were converted either biologically or chemically from sugar. All building-block chemicals were further converted to a wide spectrum of derivatives through chemical processes, such as reduction, oxidation, dehydration, hydrogenolysis and direct polymerization. Those chemicals can be used widely as solvents, fiber, antifreeze, and new plastic polymers (such as polyesters, polyamides, and polyurethane) with better polymeric properties, than those currently derived from petroleum.
The subject of green chemicals was reviewed by Xu, Hanna and Isom, The Open AgricultureJournal, 2008, 2, 54-61, and much of the information below is taken from that source.
Utilization of biomass resources to replace petroleum as a primary feedstock for liquid fuels, chemicals and materials has become a topic of interest around the world, due to rising oil prices, the negative effects of petroleum on the environment and the advantages of renewable resources, such as their abundance and sustainability. The most popular feedstocks for commodity and specialty chemicals are carbohydrates as they account for approximately 95% of the biomass produced annually.
Organic chemicals play important roles in our everyday lives. Since the middle of the 20 th century, fossil oil and natural gas have served as the main raw material resources for chemicals production. Currently, almost all organic compounds can be derived from seven basic building blocks, including syngas from methane, ethylene, propylene, butanes, butylenes, butadiene, and BTX (which is a mixture of benzene, toluene, and xylene). These building blocks are obtained from natural gas, petroleum and coal. Currently, in the United States, ~13% of the crude oil is used to produce nonfuel chemicals. There is a growing interest in the replacement of fossil-based chemicals with biochemicals. Biochemicals refer to the chemicals produced from biomass. Renewable resources, generally known as biomass, refer to any material having recent biological origin, including plant materials, agricultural crops, and even animal manure. As a naturally abundant resource, biomass is a desirable alternative to petroleum for production of chemicals because of its sustainability and often low cost. Further, biomass, comprised of C, H, O, and N, has a chemical composition similar to fossil feedstocks which contain C and H. As a consequence, products produced from petroleum can be produced from biomass. Presently, only 5% of chemicals are derived from renewable resources. Therefore, there is huge potential for biobased chemicals to share markets with their fossil based counterparts.
The most popular biomass feedstock for commodity and specialty chemicals production are carbohydrates. Carbohydrates are, by far, the largest bulk of organic compounds on earth and account for approximately 95% of the biomass produced annually. Carbohydrates exist primarily in the form of polysaccharides, including starch and cellulose. Traditionally, starch has been used as a basic organic raw material by chemical industries. Many bulk chemicals and polymers can be produced by chemical modification or fermentation of starch and its monosaccharide derivative (D-glucose). However, there is a concern about the competition between industrial and food applications of starch. Therefore, in the medium to long term, conversion of lignocellulosics biomass into glucose and xylose using microbes and other biological systems for fuel and biochemical production is more attractive. Cellulosic biomass, or lignocellulosics, refers to woody and herbaceous plants and major crop residues such as sugar cane bagasse, wheat straw, rice straw and corn stover or dedicated energy crops such as Giant King Grass. Lignocellulosic materials are composed mainly of cellulose, hemicellulose and lignin. Most of the biomass on earth is in the form of lignocellulose. Theoretically, lignocellulosic material is an ideal source of raw sugars for industrial processes since it does not affect food supplies and price. Many efforts have been made to utilize biological, thermal, and chemical conversion technologies to convert lignocellulosic biomass to ethanol and chemicals. In addition, lignocellulosic materials could be liquefied into chemical intermediates rich in hydroxyl groups. However, different from its starch counterpart, the highly ordered crystalline structure of cellulose itself, together with the protective sheath (lignin and hemicellulose layers) around it, requires some form of pretreatment to open up the structure to effectively convert it to glucose.