Birgitte K. Ahring (И) • Peter Westermann

Bioscience and Technology, BioCentrum-DTU, Technical University of Denmark,

Building 227, 2800 Lyngby, Denmark

bka@biocentrum. dtu. dk

1 Introduction……………………………………………………………………………………………… 290

2 Hydrogen Production………………………………………………………………………………… 291

3 Methane Production…………………………………………………………………………………. 291

4 Production of Biofuels Using the Maxifuel Concept……………………………………… 292

4.1 Pretreatment…………………………………………………………………………………………….. 295

4.2 Hydrolysis………………………………………………………………………………………………… 296

4.3 Separation………………………………………………………………………………………………… 296

4.4 Fermentation…………………………………………………………………………………………….. 296

4.5 Waste Water Treatment…………………………………………………………………………….. 297

4.6 Bio/Catalytic Refineries……………………………………………………………………………… 299

4.7 Integrating Conventional and Bio/Catalytic Refineries………………………………….. 299

5 Conclusion……………………………………………………………………………………………….. 301

References……………………………………………………………………………………………………. 301

Abstract Large scale transformation of biomass to more versatile energy carriers has most commonly been focused on one product such as ethanol or methane. Due to the nature of the biomass and thermodynamic and biological constraints, this approach is not optimal if the energy content of the biomass is supposed to be exploited maximally. In natural ecosystems, biomass is degraded to numerous intermediary compounds, and we suggest that this principle is utilized in biorefinery concepts, which could provide dif­ferent fuels with different end use possibilities. In this chapter we describe one of the first pilot-scale biorefineries for multiple fuel production and also discuss perspectives for further enhancement of biofuel yields from biomass. The major fuels produced in this refinery are ethanol, hydrogen, and methane.

We also discuss the applicability of our biorefinery concept as a bolt-on plant on conventional corn — or grain-based bioethanol plants, and suggest that petroleum-base re­fineries and biorefineries appropriately can be coupled during the transition period from a fossil fuel to a renewable fuel economy.

Keywords Biorefinery • Fuel cells • Hydrogen • Methane • Reforming

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Introduction

Traditionally, the development of biological processes to transform biomass to more versatile energy carriers has focused on the production of one en­ergy carrier, either hydrogen, methane, or ethanol. Among these products, only methane is released from the conversion of organic matter in nature; both hydrogen and ethanol are intermediates during anaerobic degradation and are further metabolized to methane in nature [1]. The production of these two energy carriers, therefore, demands a physical separation of indi­vidual processes in the anaerobic degradation chain, or the use of defined microbial cultures under controlled conditions. This can be carried out in a biorefinery, which is a facility that integrates biomass conversion processes and equipment to produce fuels, power, and chemicals from biomass [2,3]. The biorefinery concept is analogous to today’s petroleum refineries, which produce multiple fuels and products from petroleum.

Instead of concentrating on the biological production of only one en­ergy carrier, the simultaneous production of hydrogen, methane, and ethanol leaves the possibility to optimize the exploitation of the specific energy car­riers to suit specific needs, corresponding to the current use of specific fossil fuels for specific purposes. Hydrogen can for instance be used in fuel cells for urban transportation. Ethanol can be used in fuel cells in rural areas, and me­thane can be used in fuel cells for local electricity and heat production in fuel cells or micro-turbines [4]. Although the fuel cell technology was developed initially for molecular hydrogen, this technology is in rapid progression, and fuel cell systems dealing with more complex compounds such as ethanol are currently being developed [5,6].

Despite the obvious advantages of combining the production of different energy carriers, only a few concepts have been published. Common to the known concepts is a much better exploitation of the biomass by suiting spe­cific microbiological processes to the conversion of different fractions of the substrates to different fuels. The different processes are thereby exploited in an additive sequential fermentation, transforming most of the energy avail­able in the substrate to usable energy carriers. Furthermore, biorefineries might be considered as more environmentally friendly processes since pro­cess water and nutrients from the different processes can be recirculated, and waste production can be kept minimal [4].

By producing multiple products, a biorefinery can also take advantage of the differences in biomass components and intermediates and maximize the value derived from the biomass feedstock. A biorefinery might, for ex­ample, produce one or several low-volume, but high-value, chemical products and a low-value, but high-volume liquid transportation fuel, while generat­ing electricity and process heat for its own use and perhaps enough for sale of electricity. The high-value products enhance profitability, the high-volume fuel helps meet national energy needs, and the power production reduces costs and avoids greenhouse-gas emissions.

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