Ethanol enzymatic production

Mono- and diglycerides are important food emulsifiers. They can be made enzymatically by the glycerolysis of fats and oils.191 The reaction can be run continuously in a membrane reactor with an enzyme half-life of 3 weeks at 40°C. Higher concentrations of glycerol can be used if silica is present to prevent blockage of the enzyme by glycerol.192 Depending on the conditions and lipase chosen for transesterifications with ethanol, the product can be the 2-mono-... 

Biochemistry resulted from the early elucidation of the pathway of enzymatic conversion of glucose to ethanol by yeasts and its relation to carbohydrate metaboHsm in animals. The word enzyme means "in yeast," and the earfler word ferment has an obvious connection. Partly because of the importance of wine and related products and partly because yeasts are relatively easily studied, yeasts and fermentation were important in early scientific development and stiU figure widely in studies of biochemical mechanisms, genetic control, cell characteristics, etc. Fermentation yeast was the first eukaryote to have its genome elucidated. 

Biological—Biochemical Processes. Fermentation is a biological process in which a water slurry or solution of raw material interacts with microorganisms and is enzymatically converted to other products. Biomass can be subjected to fermentation conditions to form a variety of products. Two of the most common fermentation processes yield methane and ethanol. Biochemical processes include those that occur naturally within the biomass. 

Starch is converted enzymatically toglucose either by diastase present in sprouting grain or by fungal amylase. The resulting dextrose is fermented to ethanol with the aid of yeast, producing CO2 as a coproduct. Other by-products depend on the type of process. 

The reduction of a-hydroxynitriles to yield vicinal amino alcohols is conveniently accomplished with complex metal hydrides for example, lithium aluminum hydride or sodium borohydride [69]. However, it is still worth noting that a two-step chemo-enzymatic synthesis of (R)-2-amino-l-(2-furyl)ethanol for laboratory production was developed followed by successful up-scaling to kilogram scale using NaBH4/CF3COOH as reductant [70],... 

Recent studies suggest that many factors may affect hydroxyl radical generation by microsomes. Reinke et al. [34] demonstrated that the hydroxyl radical-mediated oxidation of ethanol in rat liver microsomes depended on phosphate or Tris buffer. Cytochrome bs can also participate in the microsomal production of hydroxyl radicals catalyzed by NADH-cytochrome bs reductase [35,36]. Considering the numerous demonstrations of hydroxyl radical formation in microsomes, it becomes obvious that this is not a genuine enzymatic process because it depends on the presence or absence of free iron. Consequently, in vitro experiments in buffers containing iron ions can significantly differ from real biological systems. 

Bioethanol is the largest biofuel today and is used in low 5%—10% blends with gasoline (E5, E10), but also as E85 in flexible-fuel vehicles. Conventional production is a well known process, based on the enzymatic conversion of starchy biomass (cereals) into sugars, and fermentation of 6-carbon sugars with final distillation of ethanol to fuel grade. 

Bioconversion platforms for lignocellulosics-to-ethanol are beginning to become commercially viable, but the effectiveness of the pretreatment stage should still be improved, the cost of the enzymatic hydrolysis stage decreased, and overall process efficiencies improved by better synergies between various process stages. There is also a need to improve process economics by creating co-products that can add revenue to the process. 

Enzymatic hydrolysis in the digestive tract breaks down foodstuffs into their resorbable components. Resorption of the cleavage products takes place primarily in the small intestine. Only ethanol and short-chain fatty acids are already resorbed to some extent in the stomach. 

The advances made in enzymatic hydrolysis of cellulosic materials (14) are also of interest. This technology involves only moderate temperature processes in simple equipment which promises to be of significantly lower capital cost than the pressure equipment associated with conventional acid wood hydrolysis processes. All of these considerations combined to lead us to study processes for ethanol production from wood, especially in an effort to obtain data for material and energy balances, and possibly for the economics. 

The data above enable us to make some rough estimates of costs associated with two processes (i) ACID, that is aspen wood-autohydrolysis-caustic extraction-acid hydrolysis-fermentation-distillation and (ii) ENZYME, that is aspen wood-autohydrolysis-caustic extraction-enzymatic hydrolysis-fermentation-distillation. For purposes of comparison, the product in both cases will be assumed to be 10 million gallons of 95% ethanol per year, a minimum economic size. 

The above rough economics suggest a significant advantage for the enzymatic process, about 10% in capital costs and 6% in product "cost", or, since it includes an allowance for adequate return on investment, price. The price per gallon would make this ethanol competitive with industrial alcohol today, but it is too expensive to be considered for motor fuel at present gasoline prices. 

---