Biswarup Sen

Abstract In the past decades, the ‘food versus fuel’ debate has caused a transition of first-generation biofuels to advanced biofuels. Although the later seems quite promising, due to its sustainability and low GHG emissions qualities, it is still far from deployment. The major hurdles to the deployment of advanced biofuels include technical and economic challenges, which must be overcome in the near future. Extensive R&D is in progress to bridge the gap between the current techno­logical status and commercial venture. To overcome the significant challenges that make the commercialization of advanced liquid biofuels unrealistic, at this moment, is of prime importance. One of the most significant challenges is the technological barriers, which will probably require some more years of extensive R&D efforts to minimize the issues and concerns. This chapter deals with the technological challenges that the liquid biofuels industry is currently facing in the biochemical conversion of second- and third-generation feedstocks to advanced liquid biofuels. A general introduction to the topic includes the types of liquid biofuels categorized under ‘advanced biofuels’ and their common routes of production namely biochem­ical and thermochemical. A detailed description of the current technological issues in the biochemical conversion process is presented mainly under the subcategories: improving feedstocks, pretreatment methods, hydrolytic enzymes efficacy and cost, and process integration. The chapter ends with a review of the current status of R&D in biochemical conversion route for advanced liquid biofuels.

B. Sen (*)

Department of Environment Engineering and Science, Feng Chia University,

Taichung 40724, Taiwan

e-mail: bsen@fcu. edu. tw; bisens@yahoo. com

B. Sen

Master Program of Green Energy Science and Technology, Feng Chia University, Taichung 40724, Taiwan

B. Sen

Green Energy Development Center, Feng Chia University, Taichung 40724, Taiwan

A. Domingos Padula et al. (eds.), Liquid Biofuels: Emergence, Development and Prospects, Lecture Notes in Energy 27, DOI: 10.1007/978-1-4471-6482-1_10, © Springer-Verlag London 2014

1 Introduction

Biofuels can be produced from agricultural or industrial wastes and are renewable with a potential to decrease our society’s dependence on petroleum. Focus on bio­fuels has gained global attention both amidst the general mass and scientific com­munity, due to various compelling factors such as increasing oil prices, low carbon emission of biofuels, and less impact on the environment. Among all biofuels, liq­uid biofuels have attracted attention of the scientific community, as it is the most convenient form of fuel for the automobile industry. Liquid biofuels usually include bioethanol, biodiesel, butanol, and oil from algae (Demirbas 2009). Bioethanol is produced by fermentation of sugars (carbohydrates) usually derived from sugar — rich crops like sugarcane or sugar beet and/or from starch-rich crops like corn (first-generation biofuel). Bioethanol is also produced from cellulosic biomass (non-food sources) and from grasses and trees (second generation). Bioethanol is widely used in Brazil and also in the USA.

Biodiesel, on the other hand, is produced by trans-esterification of oils, and its chemical composition consists of fatty acid methyl esters (FAMEs). Feedstocks from which biodiesel is produced usually include animal fats, vegetable oils, palm oil, soy, jatropha, mustard, flax, sunflower, pongamia, and algae. Biodiesel can be used in blends with petrodiesel, the purest form of which is B100; however, B20 and lower blends are suitable for diesel engines. Recently, biobutanol production is being researched extensively owing to its better properties as a fuel than bioethanol and is usually produced under anaerobic fermentation called ABE (acetone, butanol, and ethanol) fermentation. Starch can be fermented by microorganisms like Clostridium to produce ABE in the ratio of 3:6:1. Ralstonia sp. can be used to produce biobu­tanol in electro-bioreactor using carbon dioxide and electricity. Metabolically engi­neered E. coli have also been shown to produce butanol. DuPont and BP have jointly ventured into the large-scale production of butanol (Anton and Dobson 2008).

Worldwide biofuel production has reached 105 billion liters in 2010, up by 17 % from 2009; still biofuels just fulfill 2.7 % of the world’s fuel need for transporta­tion. Brazil and USA are currently top producers, accounting for 90 % of total global production of biofuels, while biodiesel production by the EU accounts for 53 % of total biodiesel production as of 2010. The International Energy Agency (IEA) has a mission for biofuels in meeting the demand for global fuel production at least by a quarter by 2050. Global ethanol production for use as bioethanol tripled between the period 2000 and 2007, which amounts to 52 billion liters. In recent years (2011), its production reached 84.6 billion liters; the USA topped with 52.6 billion lit­ers ethanol production, contributing 62.2 % in global production, whereas Brazil with 21.1 billion liters ranked second. Ethanol-based fuel is largely used in Brazil and in the USA, responsible for 87.1 % global ethanol-based fuel production as of 2011. Most cars in the USA run on blends of up to 10 % ethanol. Brazilian gov­ernment has made it mandatory since 1976 to blend ethanol with gasoline; from 2007 onwards, the legal blend is E25. As of December 2011, Brazil had 14.8 mil­lion automobiles and 1.5 million motorcycles that use only pure ethanol fuel (E100).

The USA uses com as a major source to produce bioethanol. Com in general is an energy-intensive crop, consuming a unit of fossil-based fuel energy to create just 0.9-1.3 energy units of bioethanol. General Motors has initiated production of E85 fuel from cellulose ethanol for a possible projected cost of $1 a gallon.

A directive issued in 2010 by the EU has a targeted goal where all members are required to achieve a 5-10 % biofuel usage by 2020. India and China are vastly exploring the usage of both bioethanol and biodiesel. Currently, India is expanding Jatropha plantations to be used in biodiesel production. India is also setting a target of incorporating at least 5 % bioethanol into its transportation fuel. China that is a major bioethanol producer in Asia has a task plan for 15 % bioethanol incorporation into transport fuels. In the developing countries, biomass like cattle dung, wood, and other agricultural wastes are used extensively as fuel for cooking and heating. IEA claims that biomass energy provides for 30 % of energy supply in developing coun­tries for over 2 billion people. In spite of the many advantages of using biofuels for transportation and energy supply, there exits several technical issues that need to be resolved before biofuels can enter into the market with a cost equivalent to gasoline.

There are some common issues related to the use of liquid biofuels. Higher amount of alcohols in petrodiesel fuel blends is reported to cause corrosion of components in aluminum-based designs; this corrosion can be minimized with the addition of water to the blends; tests based on this concept showed that when water content was up to 1 %, there was no evidence of corrosion; only material discolouration was visualized. Biodiesel under low-temperature conditions showed molecular aggregation and formed crystals. Biodiesel usually contains small quan­tities of water, which arise during trans-esterification attributing to the occurrence of mono — and diglycerides because of incomplete reactions. These molecules act as an emulsifying agent making very small quantity of water miscible. Presence of water reduces fuel efficiency causing more smoke, leads to corrosion of fuel system components. Water presence can also interfere with the production process and may also impact the additives used.

On the other hand, butanol is toxic and its production and usage needs to undergo Tier 1 and Tier 2 health effects testing as per the EPA guidelines. As of 2010 food grade algae cost $5,000/tonne, this is attributed to high capital and operating costs, which may impact its contribution as a second-generation biofuel crop. The US Department of Energy estimates that 15,000 square miles of land will be required for algal cultivation if it has to augment replacement of conventional fuel in the USA. The USA alone consumes nearly 1 million barrels/day of conventional biofuels, and the world consumes about 2 million barrels/day. This number will certainly increase twofold to threefold in the next 20-30 years. However, most conventional biofuels (use first-generation feedstock) are highly government subsidized, which mean they are not economically sustainable, except ethanol from Brazil. Therefore, significant technical challenges must be overcome to ensure that biofuels can become economi­cal and affordable at large scale worldwide. The future of biofuels largely depends on the price of biomass and oil-based fuels, which in turn will increase as the demand for biofuels rises. Therefore, technological breakthroughs in the non-food feedstocks development are the most important challenge that needs to be resolved.