Projected Process Economics for Ethanol Production from Corn

Report Introduction: In order to identify technology which can reduce the cost of producing ethanol by fermentation using com as the raw material, an engineering and economic analysis was completed on the design for the base case of a typical existing dry mill/ethanol plant and three alternatives. The criteria for choosing an alternative are that the essential concepts of the technology have been demonstrated at a pilot plant scale or larger and that it is likely to be implemented in the next 3 to 5 years. This focus avoids getting into many innovative ideas that are in the laboratory stage, where reliable mass and energy balances and capital and operating costs are unavailable or self-promoting. The first alternative is the Biostil Process which was initially developed be Alfa-Laval in Sweden. The process has been acquired by Chematur of Sweden and is available in the U.S. from Weatherly, Inc. of Atlanta, Georgia. The process uses a single continuous fermentor with several on-line loops involving screens and centrifugal separators and mash column. The net result is a process that produces a stillage at about 30 wt% total solids at the bottom of the mash column. With the high total solids, there is no need for an evaporator and the high pressure steam to run the turbine for the vapor recompressor. Thus a cheaper low-pressure packaged boiler can be used. The process is used world-wide in cane molasses fermentation to ethanol. Also, two plants using wheat starch fermentation are in operation. It is an ideal concept to be applied to com based fermentation. The second alternative is a technology for dehydrating ethanol using com grits as an adsorbent for the water. The process was developed by Professor Ladisch of Purdue University and is used by the ADM Corporation in their plants. It is the only known adsorption dehydration technology that is practiced above an ethanol plant capacity of 30 million gallons per year (a limit for the use of molecular sieves). The adsorption columns and regeneration loop equipment replace the conventional azeotropic solvent distillation and solvent recovery columns. Naturally, there is no need for have the solvent, such benzene, in the plant. The third alternative is not so much a process alternative but a commentary of the role of fuels, boilers, cogeneration options and energy costs. There are trade-offs between capital cost and energy cost that change as fuel and electricity costs change. A quick summary chart comparing the capital and operating costs of the process alternatives is given in Table 1

Fermentation of Cellulosic Substrates in Batch and Continuous Culture by Clostridium thermocellum

Fermentation of dilute-acid-pretreated mixed hardwood and Avicel by Clostridium thermocellum was compared in batch and continuous cultures. Maximum specific growth rates per hour obtained on cellulosic substrates were 0.1 in batch culture and >0.13 in continuous culture. Cell yields (grams of cells per gram of substrate) in batch culture were 0.17 for pretreated wood and 0.15 for Avicel. Ethanol and acetate were the main products observed under all conditions. Ethanol:acetate ratios (in grams) were approximately 1.8:1 in batch culture and generally slightly less than 1:1 in continuous culture. Utilization of cellulosic substrates was essentially complete in batch culture. A prolonged lag phase was initially observed in batch culture on pretreated wood; the length of the lag phase could be shortened by addition of cell-free spent medium. In continuous culture with ∼5 g of glucose equivalent per liter in the feed, substrate conversion relative to theoretical ranged from 0.86 at a dilution rate (D) of 0.05/h to 0.48 at a D of 0.167/h for Avicel and from 0.75 at a D of 0.05/h to 0.43 at a D of 0.11/h for pretreated wood. At feed concentrations of <4.5 g of glucose equivalent per liter, conversion of pretreated wood was 80 to 90% at D = 0.083/h. Lower conversion was obtained at higher feed substrate concentrations, consistent with a limiting factor other than cellulose. Free Avicelase activities of 12 to 84 mU/ml were observed, with activity increasing in this order: batch cellobiose, batch pretreated wood < batch Avicel, continuous pretreated wood < continuous Avicel. Free cellulase activity was higher at increasing extents of substrate utilization for both pretreated wood and Avicel under all conditions tested. The results indicate that fermentation parameters, with the exception of free cellulase activity, are essentially the same for pretreated mixed hardwood and Avicel under a variety of conditions. Hydrolysis yields obtained with C. thermocellum cellulase acting either in vitro or in vivo were comparable to those previously reported for Trichoderma reesei on the same substrates

Effect of Environmental Conditions on Extracellular Protease Activity in Lignolytic Cultures of Phanerochaete chrysosporium

Two different types of extracellular protease activity were identified in the culture fluid of Phanerochaete chrysosporium wild-type BKM-F grown in submerged batch culture on N-limited media. The first activity, which appears to be inherent to the active growth phase, displayed a maximum on day 2 and decreased to a very low level on day 4. The second activity, which appeared at day 8 following the peak of ligninase activity, seems to be characteristic of late secondary metabolism and is stimulated by carbon starvation. Cultures started with half the amount of glucose of other cultures showed a remarkably earlier development of secondary activity. In contrast, the fed-batch addition of glucose started when ligninase activity was at a maximum (day 6) completely repressed secondary protease activity and enhanced ligninase production. The addition of exogenous veratryl alcohol increased the level of secondary protease activity, whereas the oxygen supply pattern significantly affected both the time course and the level of overall proteolytic activity. The addition of phenylmethylsulfonyl fluoride to growing cultures (0, 1, or 6 days) diminished overall protease activity, while it significantly enhanced ligninase activity. In all cases, the time courses of protease and ligninase activities were negatively correlated, indicating that protease activity promotes the decline of ligninase activity in batch culture