Y. T. Shah

Abstract This chapter briefly reviews the state of art on the conversion of biomass to biofuels by gasification followed by the gas to liquid conversion of biosyngas via Fischer-Tropsch and related syntheses. An integrated process to produce heat, elec­tricity, or fuel by gasification and Fischer-Tropsch synthesis is analyzed. The present state of gasification reactor technology is outlined. The strategies for syn-gas cleanup are delineated. The catalysis and processes for methanol, Fischer-Tropsch, and isosynthesis are briefly evaluated. Finally, various approaches to an integrated process design depending on the desired end results (heat, electricity, or fuel) and the associated economics for each approach are outlined and briefly discussed.

1 Introduction

The world energy demand is increasing at a faster rate than its supply. This is particu­larly true for the transportation fuel. The sources for total world energy supply at the present time are graphically illustrated in Fig. 1. It is clear from this graph that coal and renewable sources combine to provide as much energy as oil. Heat, electricity, and transportation fuel are the major forms of energy use. While heat and electricity are derived from all sources of energy, transportation fuel has been largely obtained from the oil and natural gas. Although the major world reserve of crudes, heavy oils, and natural gas reside in regions like Middle East, Canada, Venezuela, Russia, etc., the United States is the largest consumer of these forms of energy. In fact, because of the supply and demand discrepancies for the United States, more than 60% of oil con­sumed by the United States is imported from the foreign countries. Furthermore, the global supply of oil is decreasing, while the demand is increasing. One of the reasons

Y. T. Shah (*)

Department of Engineering, Norfolk State University, Norfolk, VA 23504, USA e-mail: ytshah@nsu. edu

J. W. Lee (ed.), Advanced Biofuels and Bioproducts, DOI 10.1007/978-1-4614-3348-4_12, 185

© Springer Science+Business Media New York 2013

for this is the aggressive economic development and the resulting energy need by the countries such as China, India, Latin America, and Russia among others [1, 2].

It is imperative for the United States to be less dependent on foreign oil and develop alternate domestic sources to produce power for heat and electricity and synthetic oils. Besides crude oil and natural gas, the United States also uses considerable amount of coal, particularly for the power industries. The United States has the largest reserve of coal (which can last up to 200 years) [1, 2], which can also be a very good oil substi­tute for the production of transportation fuels. This can decrease the U. S. dependence on the foreign crude and heavy oil significantly. The technologies that have the most promise to convert coal to heat and electricity and/or liquid fuel include coal pyroly­sis, combustion, and gasification. Gasification converts coal into producer gas with different amounts of methane, depending upon the gasification technology. The pro­ducer gas can either be used for heat and electricity or it can be converted into syngas (which largely contains CO and H2) by reforming technology. The syngas can then be converted to a liquid fuel by means of Fischer-Tropsch (FT) synthesis. Both coal — based power production and CTL (coal-to-liquid) technology are commercially avail­able. Unfortunately, they suffer from unacceptable production of green house gases (GHG) such as carbon dioxide and other harmful volatile organic compounds. While other toxic compounds can be removed from power generation and CTL plants, the sequestration of carbon dioxide still remains a major issue.

While for the past several decades the use of biomass for the source of heat, electricity, and transportation fuel has been extensively examined in Europe, Brazil, and several other countries, in recent years the use of biomass as a raw material for heat and electricity and transportation fuels is also becoming increasingly important in the United States. The energy available from renewable biomass sources in the United States has been estimated to be about 20% of the U. S. energy consumption [1, 2]. There are basically three classes of feedstocks derived from biomass that are appropriate for the production of renewable fuels for heat, electricity, and transportation

fuel: (1) starchy and edible feedstocks such as corn, beets, sugar cane, (2) triglyceride feedstocks such as soybeans, algae, jatropha, and about 350 other types of crop oils, and (3) lignocellulosic feedstocks. While, bioethanol and biodiesel derived from first two sources are commercialized and continue to be examined, it is the lignocel­lulosic biomass that is the most abundant class of biomass. While starch and triglyc­erides are only present in some crops, lignocellulose contributes structural integrity to plants and thus always present. In general, most energy crops and waste biomass, such as switch grass, miscanthus, agricultural residues, municipal wastes, animal wastes, waste from wood processing, waste from paper and pulp industries, etc., are lignocellulose that can be used for the generation of heat, electricity, and transportation fuel. The analysis carried out by EPA [4] shows that the use of biomass fuel sources results in the generation of significantly lower quantities of anthropogenic CO2 emissions during power or fuel productions.

Biomass can be converted to biofuels in a number of different ways. For lignocel — lulosic biomass, thermochemical methods for the productions of biosyngas and bioliquids are very popular. These methods utilize gasification, reforming, pyrolysis, extraction, and liquefaction technologies to convert biomass into a variety of biogas and bioliquids. One method widely used is the gasification of biomass followed by reforming and gas cleaning to produce clean syngas. This syngas can be converted to a variety of bioliquids via well-known FT and related syntheses. This method is very versatile in that it can generate biofuels for heat, electricity, or transportation as well as for chemical feed stock. This brief chapter addresses three aspects of this method of biomass conversion: (a) basic chemistry and catalysis of FT and related processes for the conversion of biosyngas to bioliquids, (b) brief descriptions of various processes that currently exist for biomass to biosyngas and biosyngas to methanol and transportation fuels via FT and related syntheses, and (c) a brief assessment of an integrated process for the conversion of biomass to synthetic biodiesel fuel.