Critical analysis of techno-economic estimates for the production cost of lignocellulosic bio-ethanol

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Abstract

Bio-ethanol has been claimed to be a green and sustainable alternative to gasoline. The use of food crops on a large scale is ethically unacceptable, but lignocellulosic ethanol has potential to become an alternativfe transportation fuel. This relates to technical issues, and to the eventual cost of bio-ethanol, which requires determination of an absolute production cost. The minimum ethanol selling price (MESP) estimated in different studies varies between $234 and $1210 per m³ ethanol ($0.89 and $4.58 per gallon), although often the same processing methods are assumed. This entails uncertainties about the potential of bio-ethanol from lignocellulosic sources.

In this study, the main key factors determining these deviations are pinpointed. The assumed values in the different studies were critically investigated and more accurate, unambiguous values proposed. By doing this, a current production cost of $651 per m³ ethanol was calculated and a realistic projection towards the near future estimates an MESP of $511. Corn ethanol has already a higher price than the current price of lignocellulosic ethanol due to the high cost of corn. A comparison with gasoline yields a 10% lower price than the future MESP of lignocellulosic ethanol. Due to rising gasoline prices, lignocellulosic ethanol is likely to become in the future not only a more ecological but also a more economical attractive transportation fuel.

Introduction

Concerns about rapidly increasing oil prices, global warming, depletion of fossil fuels and security of energy supply have stimulated interest in more sustainable energy sources [1]. The combustion of fossil fuels is responsible for more than 70% of the carbon dioxide production [2], [3] The transport sector has a major contribution in greenhouse gas (GHG) emissions, of which the impact will continue to increase in the future [4], [5]. According to Goldemberg [6], motor vehicles account for 19% of global carbon dioxide (CO2) emissions [7]. Hence, reducing emissions in this sector would significantly help in reaching targets on climate change. Bio-ethanol, or ethanol derived from biomass, has been recognized as a potential alternative to petroleum based transportation fossil fuels [8]. Furthermore, it is by far the most widely used biofuel for transportation worldwide [9]. Worldwide, countries have become gradually more interested in developing and expanding their biofuel market. As a consequence, the annual world fuel bio-ethanol production has increased remarkably over the last few years from 49 billion (109) liters (~13 billion gallons) in 2007 to about 110 billion liters (~29 billion gallons) in 2011 [10].

Even though first generation ethanol has managed to offset some of the gasoline consumption, it has been increasingly criticized. The main reasons are the competition with the food industry and the limited GHG emission savings in comparison to fossil fuels [9], [11], [12], [13]. Lignocellulosic biomass has been found to be the most promising feedstock for fermentation processes, due to its availability, low cost and the absence of competition with food production [14].

It was found that wordwide, 1623 Tg (1012 g) of waste crops and lignocellulosic biomass are potentially available for bio-ethanol production. From these materials, about 491 billion liters of bio-ethanol might be produced, which is about 16 times higher than the current world ethanol production (31 billion liters) [14]. Kim and Dale (2004) studied the global potential bio-ethanol production from lignocellulosic biomass and found that bio-ethanol could replace 353 billion liters of gasoline, which is equivalent to 32% of the global gasoline worldwide consumption, when used in E85 fuel (85% ethanol and 15% gasoline) for a midsized passenger vehicle [2]. Moreover, GHG reductions are projected in the range of 70–85% [15].

Lignocellulosic biomass production is technologically feasible and being tested on a demonstration-scale in many countries including the United States, Spain, Italy, Denmark and Germany [16]. Despite the large amount of research that has been carried out in this field, the economic picture of commercial large-scale lignocellulosic bio-ethanol production still remains uncertain. Therefore many techno-economic models have been developed with the aim of (1) comparing process designs, (2) evaluating the potential of research developments to reduce the production cost, and (3) determining an absolute cost to of lignocellulosic ethanol [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34]. However, results of these techno-economic models vary significantly from one another, as presented in Fig. 1, where the minimum ethanol selling price (MESP) is plotted against the feedstock cost, expressed in dollars ($) per dry metric (DM) tonne, of the different studies. Even when the same process technology methods and feedstock are taken into account, the wide scatter in MESP remains.

The aim of this study is to compare the existing techno-economic models and to understand and clarify the causes of this large discrepancy in results. This must result in a better understanding of data obtained from previous studies and will allow making a more accurate estimate of the current ethanol cost and a more realistic projection to the future.

Comparing research studies should be easy and straightforward. This is only possible with a consistent use of units, and by preference SI-units, which are an internationally recognized standard [35]. Almost all the techno-economic research studies considered here use non SI-units, such as gallons, short tons or express results per heating value. Furthermore, SI and non-SI units are sometimes mixed. As an example, most research studies express their plant size in metric tonnes (=1000 kg) per day, while feedstock cost and ethanol yield are often expressed per short (U.S.) ton, which is equal to 2000 pounds or 907.2 kg. This of course can easily lead to misinterpreting of reported values. All the reported values in this study, were carefully examined, and are expressed in standard ‘base’ SI-units or powers of these base units, which will be emphasized through the text. A similar argument holds true for the use of currencies. Most studies express their values in dollar ($), but sometimes values are reported in euro (€) or even local currencies. Since currency conversions daily fluctuate, a simple comparison is difficult. In this work, all values will be expressed in dollar, since most data are provided in this currency.

Section snippets

Techno-economic models

In general process models are developed for a selected process scenario in ASPEN PlusTM and process flow diagrams (PFDs) are generated which represent a lignocellulosic refinery. From this, a techno-economic model is derived. A techno-economic model allows to process designs in order to assess the potential of research developments to reduce the production cost. Furthermore, it can also be used for making an estimate of the absolute production cost of lignocellulosic ethanol, based on defined

Pretreatment step

Although most techno-economic studies assume dilute sulfuric acid as a pretreatment step, other pretreatment methods can be utilized as well. Kazi et al. [25] and Eggeman and Elander [20] both made an economic comparison of the main pretreatment methods, which is presented in Table 1. Both studies assume corn stover as feedstock.

As briefly mentioned in Section 2.1, this analysis confirms that dilute sulfuric acid is the most viable pretreatment option to commercialize lignocellulosic ethanol in

Cost estimation of lignocellulosic ethanol

From the analysis above, it is clear that there are different factors responsible for the wide scatter in calculated MESP values from one techno-economic study to another. In this section, first, a more accurate estimate on the current MESP of an nth lignocellulosic refinery plant will be made, including a sensitivity analysis discussion. Subsequently, a realistic projection of the future MESP price will be discussed. To conclude, the current and future MESP of lignocellulosic ethanol will be

Conclusions

Lignocellulosic ethanol is a potential transportation biofuel, which does not have to cope with the criticism of traditional first generation biofuels. Many techno-economic research studies have been performed with the aim to minimize the production cost and to determine the final minimal ethanol selling price (MESP). Although often the same processing methods and feedstock are assumed, the forecasted production cost shows a very wide scatter. Mainly the estimated overall ethanol yield,

Acknowledgements

The work leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under Grant agreement no. NMP3-SL-2009-228631, project DoubleNanoMem.

References (70)

  • T. Eggeman et al.

    Process and economic analysis of pretreatment technologies

    Bioresource Technology

    (2005)
  • C.N. Hamelinck et al.

    Ethanol from lignocellulosic biomass: techno-economic performance in short-,middle- and long-term

    Biomass and Bioenergy

    (2005)
  • J. Iranmahboob et al.

    Optimizing acid-hydrolysis: a critical step for production of ethanol from mixed wood chips

    Biomass and Bioenergy

    (2002)
  • D. Klein-Marcuschamer et al.

    Technoeconomic analysis of biofuels: a wiki-based platform for lignocellulosic biorefineries

    Biomass and Bioenergy

    (2010)
  • E. Sendich et al.

    Recent process improvements for the ammonia fiber expansion (AFEX) process and resulting reductions in minimum ethanol selling price

    Bioresource Technology

    (2008)
  • Y. Sun et al.

    Hydrolysis of lignocellulosic materials for ethanol production: a review

    Bioresource Technology

    (2002)
  • X. Zhang et al.

    Ethanolic cofermentation with glucose and xylose by the recombinant industrial strain Saccharomyces cerevisiae NAN-127 and the effect of furfural on xylitol production

    Bioresource Technology

    (2010)
  • B. Hahn-Hagerdal et al.

    Bio-ethanol—the fuel of tomorrow from the residues of today

    Trends in Biotechnolgy

    (2006)
  • D.R. Petrolia

    The economics of harvesting and transporting corn stover for conversion to fuel ethanol: a case study for Minnesota

    Biomass and Bioenergy

    (2008)
  • W.G. Hettinga et al.

    Understanding the reductions in US corn ethanol production costs: an experience curve approach

    Energy Policy

    (2009)
  • F. Yuksel et al.

    The use of ethanol–gasoline blend as a fuel

    Renewable Energy

    (2004)
  • A. Lokhorst et al.

    Introduction on CO2 geological storage. Classification of storage options

    Oil and Gas Science and Technology Review IFP

    (2005)
  • Goldemberg J. Environmental and ecological dimensions of biofuels. Proceedings of the conference on the ecological...
  • Renewable Fuels Association. Ethanol industry statistics. Washington (DC); c2005–2012. Available from:...
  • J. Hill et al.

    Environmental, economic, and energetic costs and benefits of biodiesel and ethanol biofuels

    Proceedings of the National Academy of Sciences

    (2006)
  • S.I. Mussato et al.

    Technological trends, global market, and challenges of bio-ethanol production

    Biotechnology Advances

    (2010)
  • A.K. Chandel et al.

    Key drivers influencing the commercialization of ethanol-based biorefineries

    Journal of Commerce and Biotechnology

    (2010)
  • A. Aden et al.

    Technoeconomic analysis of the dilute sulfuric acid and enzymatic hydrolysis process for conversion of corn stover to ethanol

    Cellulose

    (2009)
  • Aden A, Ruth M, Ibsen K, Jechura J, Neeves K, Sheehan J, et al. Lignocellulosic biomass to ethanol process design and...
  • A. Dutta et al.

    An economic comparison of different fermentation configurations to convert corn stover to ethanol using Z. mobilis and Saccharomyces

    Biotechnology Progress

    (2010)
  • Humbird D, Aden A. Biochemical production of ethanol from corn stover: 2008 state of technology model. Golden (CO):...
  • Humbird D, Davis R, Tao L, Kinchin C, Hsu D, Aden A, et al. Process design and economics for biochemical conversion of...
  • Kazi FK, Fortman J, Anex RP, Kothandaraman G, Hsu D, Aden A. Techno-economic analysis of biochemical scenarios for...
  • L.R. Lynd

    Overview and evaluation of fuel ethanol from cellulosic biomass: technology, economics, the environment, and policy

    Annual Review of Energy and the Environment

    (1996)
  • K. Olofsson et al.

    A short review on SSF—an interesting process option for ethanol production from lignocellulosic feedstocks

    Biotechnology for Biofuels

    (2008)
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