Biomass conversion processes, carbohydrates

Compositional variability can have a significant impact on biomass conversion process economics. The large effect (i.e., at least 0.30/gal ethanol) of observed compositional diversity on process economics is shown in Fig. 33.19 and is primarily due to the fact that the maximum theoretical product yield is proportional to feedstock carbohydrate content (Fig. 33.20).131 Yield is the major economic driver for the technoeconomic model used to assess the economic impact of composition on minimum product selling price,130 as can be seen from the data in Fig. 33.21. 

The conversion of biomass to automotive fuels has perhaps received the most attention of any chemical biomass conversion process. One of the most visible technologies under this classification is the aqueous phase reforming (APR) process [35], in which the oxygen content of carbohydrate feedstocks is reduced with in-situ... 

This chapter surveys different process options to convert terpenes, plant oils, carbohydrates and lignocellulosic materials into valuable chemicals and polymers. Three different strategies of conversion processes integrated in a biorefinery scheme are proposed from biomass to bioproducts via degraded molecules , from platform molecules to bioproducts , and from biomass to bioproducts via new synthesis routes . Selected examples representative of the three options are given. Attention is focused on conversions based on one-pot reactions involving one or several catalytic steps that could be used to replace conventional synthetic routes developed for hydrocarbons. 

Effective utilization of biomass for value-added chemical product synthesis will require development of new applications of important unit operations. Carbohydrate recovery from the biomass is the key near-term application for production of commodity chemicals. Protein recovery will continue to have an important niche market in tlie purified form as food and a larger low-value market in the crude form as animal feed. Important processing information for carbohydrate depolymerization can be found in the literature from biochemical conversion of biomass. New process applications of separation technologies are just now being developed and refined for use with biomass-derived carbohydrate and protein streams. The use of an aqueous processing environment for carbohydrates will require careful consideration of the differences that type of environment entails, such as the effect on catalyst formulations. 

Biochemical conversion processes Enz)unes and micro-organisms are frequently used as biocatalysts to convert biomass or biomass-derived compounds into desirable products. Cellulase and hemicellulase enzymes break down the carbohydrate fractions of biomass into five-and six-carbon sugars, a process known as hydrolysis. Yeast and bacteria ferment the sugars into products such as ethanol. Biotechnology advances are expected to lead to dramatic biochemical conversion improvements. 

Hydrothermal carbonization is a thermochemical process involving the conversion of carbohydrate components (i. e., cellulose and hemicellulose) of biomass into carbon-rich solids in water at elevated temperature and pressure (Titirici et al., 2007b). Under acidic conditions with catalysis by iron salts, the reaction temperature during carbonation may be as low as 200°C (Titirici et al., 2007a). Iron oxide nanoparticles and iron ions were found to be effective in catalyzing hydrothermal carbonization of starch and rice grains under mild temperatures of < 200°C and gave attractive nanostructures (Cui et al., 2006). 

Process Design Strategies for Biomass Conversion Systems Table 6.5 Carbohydrate composition of selected microalgae... 

Biomass can be converted into biofuels via two main types of processes thermochemical and biochemical/biological conversion (Huang and Yuan, 2015). The typical products of the thermochemical conversion process include syngas, bio-oil, and biochar and the products of the biochemical conversion process are bioalcohols, carbohydrates, and lignin. Our concern in this chapter is biochemical production of bioalcohols, or biorefinery process through the well-known sugar platform. ... 

Pyrolysis has a long history in the upgrading of biomass. The dry distillation of hardwood was applied in the early 1990s to produce organic intermediates (methanol and acetic acid), charcoal and fuel gas [3]. Today s processes can be tuned to form char, oil and/or gas, all depending on the temperature and reaction time, from 300 °C and hours, to 400-500 °C and seconds-minutes, to >700 °C and a fraction of a second [3, 19, 23, 24], The process is typically carried out under inert atmosphere. We illustrate the basic chemistry of pyrolysis by focusing on the conversion of the carbohydrate components (Fig. 2.4). The reaction of the lignin will not be covered here but should obviously be considered in a real process. Interested readers could consult the literature, e.g., [25]. Pyrolysis is discussed in more details elsewhere in this book [26],... 

Over the past two decades, considerable interest has been directed toward the conversion of cellulosic biomass (such materials as wood wastes, bagasse, and straw) into useful products, notably fuels. Several procedures, including fermentation, gasification, liquefaction, and pyrolysis, have been commercially applied to carbohydrates with various degrees of success. In order to use the polysaccharides present in lignocel-lulosic materials as a substrate in fermentation processes, pretreatments are necessary, such as with steam (under slightly acid conditions) or... 

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