Production of first and second generation biofuels: A comprehensive review

https://doi.org/10.1016/j.rser.2009.10.003Get rights and content

Abstract

Sustainable economic and industrial growth requires safe, sustainable resources of energy. For the future re-arrangement of a sustainable economy to biological raw materials, completely new approaches in research and development, production, and economy are necessary. The ‘first-generation’ biofuels appear unsustainable because of the potential stress that their production places on food commodities. For organic chemicals and materials these needs to follow a biorefinery model under environmentally sustainable conditions. Where these operate at present, their product range is largely limited to simple materials (i.e. cellulose, ethanol, and biofuels). Second generation biorefineries need to build on the need for sustainable chemical products through modern and proven green chemical technologies such as bioprocessing including pyrolysis, Fisher Tropsch, and other catalytic processes in order to make more complex molecules and materials on which a future sustainable society will be based. This review focus on cost effective technologies and the processes to convert biomass into useful liquid biofuels and bioproducts, with particular focus on some biorefinery concepts based on different feedstocks aiming at the integral utilization of these feedstocks for the production of value added chemicals.

Introduction

In the twentieth century major research emphasis was given for the development of petroleum, coal, and natural gas based refinery to exploit the cheaply available fossil feed stock. These feedstocks are used in industry to produce multiple products such as fuel, fine chemicals, pharmaceuticals, detergents, synthetic fiber, plastics, pesticides, fertilizers, lubricants, solvent, waxes, coke, asphalt, etc. to meet the growing demand of the population [1], [2]. Currently, the fossil resources are not regarded as sustainable and questionable from the economic, ecology and environmental point of views [3]. The burning of fossil fuels is a big contributor to increasing the level of CO2 in the atmosphere which is directly associated with global warming observed in recent decades [4]. The adverse effects of greenhouse gas (GHG) emissions on the environment, together with declining petroleum reserves, have been realized. Therefore, the quest for sustainable and environmentally benign sources of energy for our industrial economies and consumer societies has become urgent in recent years [5]. Consequently, there is renewed interest in the production and use of fuels from plants or organic waste.

The biofuels produced from the renewable resources could help to minimize the fossil fuel burning and CO2 production. Biofuels produced from biomass such as plants or organic waste could help to reduce both the world's dependence on oil and CO2 production. These biofuels have the potential to cut CO2 emission because the plants they are made from use CO2 as they grow [6]. Biofuels and bioproducts produced from plant biomass would mitigate global warming. This may due to the CO2 released in burning equals the CO2 tied up by the plant during photosynthesis and thus does not increase the net CO2 in the atmosphere. Additionally, biofuel production along with bioproducts can provide new income and employment opportunities in rural areas. 21st Century is looking for a shift to alternate industrial feedstock and green processes to produce these chemicals from renewable biomass resources [7].

‘First generation’ biofuels can offer some CO2 benefits and can help to improve domestic energy security. But concerns exist about the sourcing of feedstocks, including the impact it may have on biodiversity and land use and competition with food crops. A ‘first generation’ biofuel (i.e. biodiesel (bio-esters), bio-ethanol, and biogas) is characterized either by its ability to be blended with petroleum-based fuels, combusted in existing internal combustion engines, and distributed through existing infrastructure, or by the use in existing alternative vehicle technology like FFVs (“Flexible Fuel Vehicle”) or natural gas vehicles. The production of 1st generation biofuels is commercial today, with almost 50 billion liters produced annually. There are also other niche biofuels, such as biogas which have been derived by anaerobic treatment of manure and other biomass materials. However, the volumes of biogas used for transportation are relatively small today [4].

However, the first generation biofuels seems to create some skepticism to scientists. There are concerns about environmental impacts and carbon balances, which sets limits in the increasing production of biofuels of first generation. The main disadvantage of first generation biofuels is the food-versus-fuel debate, one of the reasons for rising food prices is due to the increase in the production of these fuels [8]. Additionally it is claimed that biodiesel is not a cost efficient emission abatement technology. Therefore, for the abatement of GHG, it is recommended to have more efficient alternatives based on both renewable and conventional technologies [9].

Therefore, lignocellulosic feedstock can offer the potential to provide novel biofuels, the biofuels of the ‘second generation’ [10]. Second-generation biofuels produced from ‘plant biomass’ refers largely to lignocellulosic materials, as this makes up the majority of the cheap and abundant nonfood materials available from plants. But, at present, the production of such fuels is not cost effective because there are a number of technical barriers that need to be overcome before their potential can be realized [9]. Plant biomass represents one of the most abundant and underutilized biological resources on the planet, and is seen as a promising source of material for fuels and raw materials. At its most basic, plant biomass can simply be burned in order to produce heat and electricity. However, there is great potential in the use of plant biomass to produce liquid biofuels. However, biofuel production from agricultural by-products could only satisfy a proportion of the increasing demand for liquid fuels. This has generated great interest in making use of dedicated biomass crops as feedstock for biofuel production [11]. The examples of 2nd generation biofuels are cellulosic ethanol and Fischer–Tropsch fuels. The production of 2nd generation biofuels is non-commercial at this time, although pilot and demonstration facilities are being developed. Therefore it is anticipated that, these 2nd generation biofuels could significantly reduce CO2 production, do not compete with food crops and some types can offer better engine performance. When commercialized, the cost of second generation biofuels has the potential to be more comparable with standard petrol, diesel, and would be most cost effective route to renewable, low carbon energy for road transport [4].

Therefore due to many advantages and disadvantages of the 1st generation biofuels and obvious advantages of 2nd generation biofuels as shown in Fig. 1, the approaches to integral utilization of biomass for sustainable development are more reasonable, where all parts of the plant such as leaves, bark, fruits, and seeds can be utilized to useful products. The term ‘Biorefinery’ was initially established by NREL during 1990, for the utilization of biomass for production of fuels and other bioproducts. This term refers to a facility (or group of facilities) which combines the production of materials, chemicals, or fuel products with energy production [12]. The biorefinery system includes biomass production, biomass transformation/processing, and end use. The total biomass production on earth is approximately 100 billion tones organic dry matter of land biomass per annum and 50 billion tones of aquatic biomass. The part of it is used as food, feed, energy and industrial raw materials, where food use is only 1.25% of the entire land biomass. The rest of the biomass is unused or recycled in to the earth system, which can be used as raw material for chemical production. Currently, starches, sugar, oils and fats, cellulose, rubbers have been used industrially as well [6].

So far many research papers on the biorefinery concept have been published: wheat straw biorefinery [13], corn biorefinery [14] and forest residue based biorefinery [5], etc. Also, many review papers are available in the literature i.e. bioethanol from biomass, green diesel, chemicals from glycerol, etc. but the information on the first, second generation biofuel and related chemicals from non-food crops are scanty. In this paper an attempt has been made to review the literature on first and second generation biofuels and anticipated biochemicals from the non-food crop biomass. In this respect, the present paper is a part of research program aiming at the integrated utilization of Jatropha in India and cereal crop residues in Canada, attempting to contribute to the first generation biofuels production (i.e. biodiesel) and parallel use of the residues for energy and 2nd generation biofuels production. In addition some biorefinery concepts based on different biomass feedstocks for 2nd generation biofuels and their bioproducts with example have been discussed.

Section snippets

Biomass as multiple feedstocks for biorefinery

Biomass derived from trees, agro-forest residues, grasses, plants, aquatic plants and crops are versatile and important renewable feed stock for chemical industry as shown in Fig. 2. Through photosynthesis process, plants convert carbon dioxide and water in to primary and secondary metabolite biochemicals. Both of these are industrially important chemicals. Primary metabolites are carbohydrate (simple sugar, cellulose, hemicellulose, starch, etc.) and lignin called lignocellulose present in

First generation biofuels

The dramatic rise in oil prices seen in the last decade has also enabled liquid biofuels to become cost-competitive with petroleum-based transportation fuels, and this has led to a surge in research and production around the world. The three main types of first generation biofuels used commercially are biodiesel (bio-esters), ethanol, and biogas of which world wide large quantities have been produced so far and for which the production process is considered ‘established technology’. Biodiesel

Second generation biofuels

Second generation biofuels are produced from biomass in a more sustainable fashion, which is truly carbon neutral or even carbon negative in terms of its impact on CO2 concentrations. In the context of biofuel production, the term ‘plant biomass’ refers largely to lignocellulosic material as this makes up the majority of the cheap and abundant nonfood materials available from plants [11], [31]. At present, the production of such fuels is not cost-effective because there are a number of

Green biorefinery

A green biorefinery is a multiproduct system which handles its refinery cuts, products, and fractions in accordance with the physiology of the corresponding plant material as described by Kamm and Kamm [21], Fernando et al. [12] and illustrated in Fig. 15. A green biorefinery uses natural wet feedstocks derived from untreated products, such as grass, green plants, or green crops as inputs, which are produced in large quantities in green plants. The first step of the refinery is to treat the

Conclusions

The paper has discussed first and second generation biofuel, concept of biorefineries, different types of biorefineries, and associated technical challenges. However, growing concerns over first generation biofuels in terms of their impact on food prices and the environment have led to an increasingly bad press in the last year. The unfortunate effect is that biofuel is starting to generate resistance particularly in poor countries with environmental agendas. As the replacement of fossil fuels

Acknowledgements

Financial support from Natural Sciences and Engineering Research Council of Canada (NSERC), and Canada Research Chair (CRC) funding to Dr. A.K. Dalai, is gratefully acknowledged.

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