Global potential bioethanol production from wasted crops and crop residues

Abstract

The global annual potential bioethanol production from the major crops, corn, barley, oat, rice, wheat, sorghum, and sugar cane, is estimated. To avoid conflicts between human food use and industrial use of crops, only the wasted crop, which is defined as crop lost in distribution, is considered as feedstock. Lignocellulosic biomass such as crop residues and sugar cane bagasse are included in feedstock for producing bioethanol as well. There are about $\text{73.9}\text{Tg}$ of dry wasted crops in the world that could potentially produce $\text{49.1}\text{GL}\text{year}{}^{\mathrm{-1}}$ of bioethanol. About $\text{1.5}\text{Pg}\text{year}{}^{\mathrm{-1}}$ of dry lignocellulosic biomass from these seven crops is also available for conversion to bioethanol. Lignocellulosic biomass could produce up to $\text{442}\text{GL}\text{year}{}^{\mathrm{-1}}$ of bioethanol. Thus, the total potential bioethanol production from crop residues and wasted crops is $\text{491}\text{GL}\text{year}{}^{\mathrm{-1}}$, about 16 times higher than the current world ethanol production. The potential bioethanol production could replace $\text{353}\text{GL}$ of gasoline (32% of the global gasoline consumption) when bioethanol is used in E85 fuel for a midsize passenger vehicle. Furthermore, lignin-rich fermentation residue, which is the coproduct of bioethanol made from crop residues and sugar cane bagasse, can potentially generate both $\text{458}\text{TWh}$ of electricity (about 3.6% of world electricity production) and $\text{2.6}\text{EJ}$ of steam. Asia is the largest potential producer of bioethanol from crop residues and wasted crops, and could produce up to $\text{291}\text{GL}\text{year}{}^{\mathrm{-1}}$ of bioethanol. Rice straw, wheat straw, and corn stover are the most favorable bioethanol feedstocks in Asia. The next highest potential region is Europe ($\text{69.2}\text{GL}$ of bioethanol), in which most bioethanol comes from wheat straw. Corn stover is the main feedstock in North America, from which about $\text{38.4}\text{GL}\text{year}{}^{\mathrm{-1}}$ of bioethanol can potentially be produced. Globally rice straw can produce $\text{205}\text{GL}$ of bioethanol, which is the largest amount from single biomass feedstock. The next highest potential feedstock is wheat straw, which can produce $\text{104}\text{GL}$ of bioethanol. This paper is intended to give some perspective on the size of the bioethanol feedstock resource, globally and by region, and to summarize relevant data that we believe others will find useful, for example, those who are interested in producing biobased products such as lactic acid, rather than ethanol, from crops and wastes. The paper does not attempt to indicate how much, if any, of this waste material could actually be converted to bioethanol.

Introduction

Biomass energy currently contributes 9–13% of the global energy supply—accounting for $\text{45±10}\text{EJ}$ per year [1]. Biomass energy includes both traditional uses (e.g., firing for cooking and heating) and modern uses (e.g., producing electricity and steam, and liquid biofuels). Use of biomass energy in modern ways is estimated at $\text{7}\text{EJ}$ a year, while the remainder is in traditional uses. Biomass energy is derived from renewable resources. With proper management and technologies, biomass feedstocks can be produced sustainably.

Ethanol derived from biomass, one of the modern forms of biomass energy, has the potential to be a sustainable transportation fuel, as well as a fuel oxygenate that can replace gasoline [2]. Shapouri et al. [3], [4] concluded that the energy content of ethanol was higher than the energy required to produce ethanol. Kim and Dale [5] also estimated the total energy requirement for producing ethanol from corn grain at $\text{560}\text{kJ}\text{MJ}{}^{\mathrm{-1}}$ of ethanol, indicating that ethanol used as a liquid transportation fuel could reduce domestic consumption of fossil fuels, particularly petroleum.

The world ethanol production in 2001 was $\text{31}\text{GL}$ [6]. The major producers of ethanol are Brazil and the US, which account for about 62% of world production. The major feedstock for ethanol in Brazil is sugar cane, while corn grain is the main feedstock for ethanol in the US. Ethanol can be produced from any sugar or starch crop. Another potential resource for ethanol is lignocellulosic biomass, which includes materials such as agricultural residues (e.g., corn stover, crop straw, sugar cane bagasse), herbaceous crops (e.g., alfalfa, switchgrass), forestry wastes, wastepaper, and other wastes [7]. The utilization of lignocellulosic biomass for fuel ethanol is still under development.

This study estimated how much bioethanol can potentially be produced from starch, sugar crops, and agricultural residues. These crops include corn, barley, oat, rice, wheat, sorghum, and sugar cane. To avoid conflicts between food use and industrial uses of crops, only wasted crops are assumed to be available for producing ethanol. Wasted crops are defined as crops lost during the year at all stages between the farm and the household level during handling, storage, and transport. Waste of the edible and inedible parts of the commodity that occurs after the commodity has entered the household and the quantities lost during processing are not considered here. The agricultural residues include corn stover, crop straws, and sugar cane bagasse, generated during sugar cane processing.