Ethanol economic considerations

Effect of Operating Variables. The direct hydration of ethylene is an equilibrium i eaction (see Sec. V) which is favored by low temperatures, high pressures, and high steam. ethylene ratios. He catalytic activity of the phosphoric acid catalyst increases with increasing temperature, decreases with increasing pressure because of lower concentration, and decreases with high steam ethylene ratios at hi pressures because of moisture absorption. Thus, the process conditions that favor ethanol production adversely affect the catalyst activity. For this reason, operating conditions must necessarily be chosen on the basis of economic considerations. 

Silica gel, per se, is not so frequently used in LC as the reversed phases or the bonded phases, because silica separates substances largely by polar interactions with the silanol groups on the silica surface. In contrast, the reversed and bonded phases separate material largely by interactions with the dispersive components of the solute. As the dispersive character of substances, in general, vary more subtly than does their polar character, the reversed and bonded phases are usually preferred. In addition, silica has a significant solubility in many solvents, particularly aqueous solvents and, thus, silica columns can be less stable than those packed with bonded phases. The analytical procedure can be a little more complex and costly with silica gel columns as, in general, a wider variety of more expensive solvents are required. Reversed and bonded phases utilize blended solvents such as hexane/ethanol, methanol/water or acetonitrile/water mixtures as the mobile phase and, consequently, are considerably more economical. Nevertheless, silica gel has certain areas of application for which it is particularly useful and is very effective for separating polarizable substances such as the polynuclear aromatic hydrocarbons and substances... 

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. 

Biodiesel was prepared in various supercritical alcohol treatments with methanol, ethanol, 1-propanol, 1-butanol, or 1-octanol to study transesterification of rapeseed oil and alkyl esterification of fatty acid at temperatures of 300 and 350°C. The results showed that in transesterification, the reactivity was greatly correlated to the alcohol the longer the alkyl chain of alcohol, the longer the reaction treatment. In alkyl esterification of fatty acids, the conversion did not depend on the alcohol type because they had a similar reactivity. Therefore, the selection of alcohol in biodiesel production should be based on consideration of its performance of properties and economics. 

The cost of enzyme preparations has been decreasing in recent years however, it continues to affect considerably the price of ethanol obtained from cellulosic raw materials. Increased enzymatic hydrolysis efficiency is one way to reduce the enz)me cost in bioethanol production. Another method is enzyme recycle and reuse. Immobilization of biocatalysts allows for their economic reuse and development of continuous bioprocess. Although immobilization poses problems of substrate accessibility and binding for most endo- and exocellulases, P-glucosidase exhibits characteristics amenable to immobilization, such as activity on soluble substrates and the lack of a carbohydrate-binding module. Among the possible approaches, immobilization of (J-glucosidase is one prospective solution to the problem. 

Although the production of biofuels is of considerable economic relevance, it is also characterized by heated political, ecological, and social debates. Recombinant technologies and second-generation fuels are expected to contribute to a reduction in the dependence on fossil resources and to significantly reduce greenhouse gas emissions ([73], section 12.2). A calculation of emissions yielded 94 for gasoline, 77 for currently available bioethanol, and 11 for cellulosic-based ethanol... 

A different approach is provided by the utilization of carbon sources that have a considerable market value and do not constitute waste materials, but are produced in a process integrating the fabrication of the carbon substrate and PHA. This has been implemented on a pilot scale by the company PHB Industrial in the state of Sao Paulo, Brazil. Starting from sugar cane, the company produces saccharose and ethanol. The waste streams from the sugar production (bagasse) and the bioethanol production (fusel alcohols) are used for running the PHA production and making it economically competitive. 

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