Ahmad Hafiidz Mohammad Fauzi and Nor Aishah Saidina Amin

Abstract The necessity to search for fossil fuel alternative is getting more critical with the increasing fossil fuel price and also its limited supply. The use of mineral diesel for transport sector is unfeasible as it is nonrenewable and emits greenhouse gases to the atmosphere during combustion, particularly carbon dioxide which can lead to global warming phenomena. Biodiesel is a type of biofuel that can be pro­duced using renewable resources such as biomass. It can be produced from oils and fats through transesterification process. The presence of catalyst is important to ensure that the reaction can progress at shorter time and produce high biodiesel yield. Numerous catalysts have been used to assist the transesterification process. They include homogeneous and heterogeneous catalysts and can be further divided into acid and base nature. The catalysis in biodiesel production is progressing at faster rate in order to find a catalyst that is more practical for larger production scale. Ionic liquids and ionic solids are among new catalysts introduced with aim to improve the efficiency of the process. This chapter focused on the benefits and draw­backs of different catalysts for biodiesel synthesis. The applications of novel pro­cesses for more sustainable and enhanced biodiesel production are also discussed.

Keywords Biodiesel • Catalyst • Homogeneous • Heterogeneous • Novel process

9.1 Introduction

Competition among countries for energy supplies is likely to become more intense in the coming years. This is contributed by the growth and development in different sectors that consumes a great amount of energy, such as light and heavy industries,

A. H.M. Fauzi • N. A.S. Amin (*)

Chemical Reaction Engineering Group (CREG), Faculty of Chemical Engineering, Universiti Teknologi Malaysia, 81310 UTM Skudai, Johor, Malaysia e-mail: noraishah@cheme. utm. my

R. Pogaku and R. Hj. Sarbatly (eds.), Advances in Biofuels,

DOI 10.1007/978-1-4614-6249-1_9, © Springer Science+Business Media New York 2013

agriculture, commercial, public services, and transportation. Primary energy sources such as crude oil, natural gas, and coal are all nonrenewable and originated from the same source, which are fossil fuels.

Formed by decomposition of organic materials million years ago, fossil fuels are considered nonrenewable because they cannot be replaced when they are used up and they will run out one day. Relying on them for energy generation is unsustain­able. Hence, the need to find more renewable and sustainable alternatives for energy generation is becoming priority today.

Natural gas and coal are widely used for generating electricity, providing heat and power to industry and also to residential. Crude oil products including gaso­line, kerosene, diesel oil, and fuel oil are mainly intended for the transportation sector. The main end user of energy is the road transport sector, followed by the aviation sector as the second-largest transport user of energy. According to IEA (2010), the global transport energy increased steadily between 2 and 2.5% a year, from 1971 to 2007. This situation is impractical because using crude oil derivatives as the fuel source emits carbon dioxide (CO2) gas into the atmosphere during the combustion process. CO2 is undesirable as it contributes to the increase of green­house gas in the atmosphere and resulted in the increase of the earth surface’s temperature.

Substantial efforts are done to find suitable alternatives for these crude oil prod­ucts, as fossil fuel supply is finite. Biofuel has started to gain attention as substitute to fossil fuel derivatives, where it can be produced from different biomass sources. Common types of biofuels available nowadays are bioethanol and biodiesel. The former is usually used as an additive to gasoline, while the latter as a substitute for diesel fuel. Global biofuel production increased from 16 billion L in 2000 to more than 100 billion L in 2010, as a result from countries implementing use of biofuels and introduction of support policies on biofuel usage (IEA 2011) . The trend of increasing biofuel production is depicted in Fig. 9.1. Today, biofuels contributed to about 3% of total road transport fuel globally. It is expected that by 2050, biofuels

could provide 27% of total transport fuel and contribute for the replacement of die­sel, kerosene, and jet fuel, particularly.

Biodiesel is a diesel fuel consists of long-chain alkyl esters derived from vegeta­ble oil and animal fat, and it is produced from renewable resources. Biodiesel holds several advantages over diesel from fossil fuel, such as being biodegradable, close to sulfur-free, and emits less carbon dioxide. Biodiesel can be used in standard diesel engines with minimal modification or blended with diesel fuel in certain proportion. Transesterification is the common method utilized to produce biodiesel. Feedstock such as oil or fat is converted into fatty acid alkyl ester (FAAE) accom­panied by an alcohol and a catalyst. The process produces biodiesel as the main product and glycerol as the by-product. The resultant product is later refined to meet the international standards of biodiesel. Other methods available to produce bio­diesel are direct use and blending, microemulsions, and pyrolysis.

Transesterification can proceed without the presence of catalyst but requires severe operating conditions, such as higher reaction temperature and high pressure. Conventional catalysts for transesterification are sodium hydroxide (NaOH) and potassium hydroxide (KOH). They enable the reaction to be accomplished in shorter time and high product yield. Acidic catalyst such as sulfuric acid (H2SO4) is more suitable for feedstock containing high free fatty acid (FFA) content. In recent years, more researchers are focused on using heterogeneous catalysts as they are more practical in terms of separating the reactants and recyclable. Nonetheless, each cata­lyst has its own advantages and disadvantages. This chapter is intended to discuss more on this subject, together with the challenges and future perspectives on cata­lysts used for biodiesel production.