Process engineering could provide the means to develop economically viable and environmentally friendly technologies for the production of fuel ethanol. Process synthesis will play a very important role in the evaluation of different technologi­cal proposals, especially those related to the integration of reaction-separation processes, which could have major effects on the economy globally. Similarly, the integration of different chemical and biological processes for the complete

Research Trends and Priorities for improving Fuel Ethanol Production from Different Feedstocks

TABLE 13.1 (Continued) Research Trends and Priorities for improving Fuel Ethanol Production from Different Feedstocks
Issue An feedstocks a sucrose-Containing Materials starchy Materials Hydrolysis Low temperature digestion of starch	lignocellulosic Biomass Increase in specific activity, thermal stability and cellulose-specific binding of cellulases (e. g., by protein engineering) Reduction of costs of cellulases production (10-fold reduction) Cellulases production by solid-state fermentation Recycling of cellulases Improvement of acid hydrolysis of MSW Increase in conversion of glucose and pentoses to ethanol Recombinant strains with increased stability and efficiency for assimilating hexoses and pentoses, and for working at higher temperatures Development of strains more tolerant to the inhibitors Increase of ethanol tolerance in pentose-fermenting microorganisms
Fermentation Continuous fermentation with high cell density and increased yields and productivity
Reduction of inhibition by ethanol Microorganisms with increased osmotolerance or flocculating properties	Recombinant strains of yeasts with increased productivity and ethanol tolerance High cell-density fermentation (e. g., immobilized cells, flocculating yeasts, membrane reactors) Very high gravity fermentations
Refers to the three analyzed groups of feedstock: sucrose-containing materials, starchy materials, and lignocellulosic biomass.

utilization of the feedstocks should lead to the development of large biorefineries that allow the production of large amounts of fuel ethanol and many other valu­able co-products at smaller volumes, improving the overall economical effective­ness of the conversion of a given raw material. Integration opportunities may provide the way for qualitative and quantitative improvement of the process so that not only technoeconomical, but also environmental criteria can be met.

The increasing energy requirements of the world’s population will augment the pressure on R&D centers, both public and private, for finding new renew­able sources of energy and for optimizing their production and utilization. The use of bioethanol as an energy source requires that the technology for its pro­duction from lignocellulosic biomass be fully developed by the middle of this century. This need is much more urgent for those countries that do not have the agroecological conditions for the cultivation of energy-rich crops like sugarcane, as is true with North American and European countries. Even from governmen­tal biofuel programs in the United States, the retrofitting of the ethanol industry from corn starch to lignocellulosic residues (corn stover, woody materials, and municipal solid waste) has been recommended. Some countries, such as Brazil and Colombia, are in an excellent situation in this field considering the great availability of the three types of analyzed feedstocks. Although the more logical option is sugarcane, social benefits for rural communities when other alternative feedstocks, such as cassava or typical agricultural and tropical residues, are taken into account. Here, the process engineering strategy for assessing the real possi­bilities of tropical countries to develop fuel ethanol production is a real and rapid approach to be used by governments, investors, and decision makers.

Current development of the ethanol industry shows that complex technical problems affecting the indicators of global process have not been properly solved. The growing cost of energy, the design of more intensive and compact processes, and the concern of the populace about the environment have forced the necessity of employing totally new and integrated approaches for the design and opera­tion of bioethanol production processes, quite different from those utilized for the operation of the old refineries. The spectrum of objectives and constraints that should be taken into account for the development of technologies for bio­fuels production grows wider and more diverse. The socioeconomic component involved during the production of biofuels in the global context should be noted. Practically every country can produce its own biofuel. In this way, the feedstock supply for ethanol production is “decentralized” and does not coincide with the supply centers of fossil fuels. This would make it possible for countries that are now dependent on oil to use biofuels at a high scale and, thus decrease their dependency on fossil fuels. In addition, human development indexes could be improved in two ways: the creation of new rural jobs and the reduction of gas emissions that produce a greenhouse effect. However, ethanol production costs are higher than those of the fossil fuels, especially in the case of biomass ethanol. Nevertheless, during the past two years, oil prices have persistently increased. There is no doubt that the price of gasoline and other oil-derived fuels have a sub­sidy paid by all taxpayers of the world and that is not necessarily made effective in gas stations. This “subsidy” is intended to compensate the inversions made for maintaining the status quo of international relationships. Logically, we also pay the consequences of the measures taken to “offset” this state of affairs: social instability and, unfortunately, to a certain degree, terrorism.

Therefore, the relatively higher production cost of ethanol is the main obstacle to be overcome. To undertake this, process engineering plays a central role for the generation, design, analysis, and implementation of technologies improving the indexes of the global process, or for the retrofitting of employed bioprocesses. Undoubtedly, process intensification through integration of different phenomena and unit operations, as well as the implementation of consolidated bioprocess­ing of different feedstocks into ethanol (that requires the development of tailored recombinant microorganisms), will offer the most significant outcomes during the search for efficiency in fuel ethanol production. Great efforts should be focused on the development of consolidated bioprocessing (CBP) of biomass, as ligno — cellulosics is the most promising feedstock for ethanol production. Additionally, the intensification of biological processes indicates a better utilization of the feedstocks and the reduction of process effluents improving the environmental performance of the proposed configurations. Attaining this set of goals is a colos­sal challenge to be faced through the fruitful interaction between biotechnology and chemical engineering. The most important and promising research priorities linked to process engineering for improving the global process are briefly sum­marized in Table 13.2.

Finally, regarding process engineering, this approach has more importance today when oil prices can change drastically depending on not-easy-to-predict factors. Then bioethanol “fashion” should be supported by numbers and projec­tions based on serious studies.