Improved processes for the enzymatic saccharification

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improved processes for the enzymatic saccharification of corn fibers into sugars, and various methods of improving corn ethanol process efficiencies. The mature corn-to-ethanol industry has many similarities to the emerging lignocellulose- to-ethanol industry. It is certainly possible that some of the early practitioners of this new technology will be the current corn ethanol producers. 1,2,3 In order to begin to explore synergies between the two industries, a joint project between two agencies responsible for aiding these technologies in the Federal government was established. This joint project of the USDA-ARS and DOE with NREL looked at the two processes on a similar process design and engineering basis, and will eventually explore ways to combine them. This report describes the comparison of the processes, each producing 25 million annual gallons of fuel ethanol. This paper attempts to compare the two processes as mature technologies, which requires assuming that the technology improvements needed to make the lignocellulosic process commercializable are achieved, and enough plants have been built to make the design well-understood. Assumptions about yield are based on the assumed successful demonstration of the integration of technologies we feel exist for the lignocellulose process. In order to compare the lignocellulose-to-ethanol process costs with the commercial corn-to-ethanol costs, it was assumed that the lignocellulose plant was an N th generation plant, assuming no first-of-a-kind costs. This places the lignocellulose plant costs on a similar level with the current, established corn ethanol industry, whose costs are well known. The feedstock used for each process is different but related. There were 9.76 billion bushels of corn, a commodity crop, produced in the 1998-1999 crop year. Of this, 526 million bushels (14.7 million tons at 15% moisture) were used in the corn ethanol
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2 industry to produce fuel ethanol. 4 Corn stover, the residue left in the fields after harvesting corn, has been identified as a near- to mid-term agriculture residue feedstock for the lignocellulose-to-ethanol process. Corn stover has a high carbohydrate content, can be collected in a sustainable fashion, and will provide economic benefits to the farm community. Corn kernels have starch, which is an alpha-linked glucose polymer that can be easily broken down to glucose monomers and fermented to ethanol. It has fiber, which encases the starch, and about 15% moisture. An approximate composition of corn is shown in Table 1. In this analysis of the dry mill corn-to±ethanol process, a slightly different and simpler composition for corn (on a dry weight basis, 70% starch, and for non- fermentables, 18% suspended and 12% dissolved) was used. The market price of corn varies, ranging from $1.94 to $3.24 per bushel during the last 3 years.
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