Separation and Purification Technologies in Biorefineries E-Book
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- Herausgeber: John Wiley & Sons
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- Sprache: Englisch
Separation and purification processes play a critical role in biorefineries and their optimal selection, design and operation to maximise product yields and improve overall process efficiency. Separations and purifications are necessary for upstream processes as well as in maximising and improving product recovery in downstream processes. These processes account for a significant fraction of the total capital and operating costs and also are highly energy intensive. Consequently, a better understanding of separation and purification processes, current and possible alternative and novel advanced methods is essential for achieving the overall techno-economic feasibility and commercial success of sustainable biorefineries.
This book presents a comprehensive overview focused specifically on the present state, future challenges and opportunities for separation and purification methods and technologies in biorefineries.
Topics covered include:
Equilibrium Separations: Distillation, liquid-liquid extraction and supercritical fluid extraction.
Affinity-Based Separations: Adsorption, ion exchange, and simulated moving bed technologies.
Membrane Based Separations: Microfiltration, ultrafiltration and diafiltration, nanofiltration, membrane pervaporation, and membrane distillation.
Solid-liquid Separations: Conventional filtration and solid-liquid extraction.
Hybrid/Integrated Reaction-Separation Systems: Membrane bioreactors, extractive fermentation, reactive distillation and reactive absorption.
For each of these processes, the fundamental principles and design aspects are presented, followed by a detailed discussion and specific examples of applications in biorefineries. Each chapter also considers the market needs, industrial challenges, future opportunities, and economic importance of the separation and purification methods. The book concludes with a series of detailed case studies including cellulosic bioethanol production, extraction of algae oil from microalgae, and production of biopolymers.
Separation and Purification Technologies in Biorefineries is an essential resource for scientists and engineers, as well as researchers and academics working in the broader conventional and emerging bio-based products industry, including biomaterials, biochemicals, biofuels and bioenergy.
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Table of Contents
Title Page
Copyright
List of Contributors
Preface
Part I: Introduction
Chapter 1: Overview of Biomass Conversion Processes and Separation and Purification Technologies in Biorefineries
1.1 Introduction
1.2 Biochemical conversion biorefineries
1.3 Thermo-chemical and other chemical conversion biorefineries
1.4 Integrated lignocellulose biorefineries
1.5 Separation and purification processes
1.6 Summary
References
Part II: Equilibrium-Based Separation Technologies
Chapter 2: Distillation
2.1 Introduction
2.2 Ordinary distillation
2.3 Azeotropic distillation
2.4 Extractive distillation
2.5 Molecular distillation
2.6 Comparisons of different distillation processes
2.7 Conclusions and future trends
Acknowledgement
References
Chapter 3: Liquid-Liquid Extraction (LLE)
3.1 Introduction to LLE: Literature review and recent developments
3.2 Fundamental principles of LLE
3.3 Categories of LLE design
3.4 Equipment for the LLE process
3.5 Applications in biorefineries
3.6 The future development of LLE for the biorefinery setting
References
Chapter 4: Supercritical Fluid Extraction
4.1 Introduction
4.2 Principles of supercritical fluids
4.3 Market and industrial needs
4.4 Design and modeling of the process
4.5 Specific examples in biorefineries
4.6 Economic importance and industrial challenges
4.7 Conclusions and future trends
References
Part III: Affinity-Based Separation Technologies
Chapter 5: Adsorption
5.1 Introduction
5.2 Essential principles of adsorption
5.3 Adsorbent selection criteria
5.4 Commercial and new adsorbents and their properties
5.5 Adsorption separation processes
5.6 Adsorber modeling
5.7 Application of adsorption in biorefineries
5.8 A case study: Recovery of 1-butanol from ABE fermentation broth using TSA
5.9 Research needs and prospects
5.10 Conclusions
Acknowledgement
References
Chapter 6: Ion Exchange
6.1 Introduction
6.2 Essential principles
6.3 Ion-exchange market and industrial needs
6.4 Commercial ion-exchange resins
6.5 Specific examples in biorefineries
6.6 Conclusions and future trends
References
Chapter 7: Simulated Moving-Bed Technology for Biorefinery Applications
7.1 Introduction
7.2 Essential SMB design principles and tools
7.3 Simulated moving-bed technology in biorefineries
7.4 Conclusions and future trends
References
Part IV: Membrane Separation
Chapter 8: Microfiltration, Ultrafiltration and Diafiltration
8.1 Introduction
8.2 Membrane plant design
8.3 Economic considerations
8.4 Process design
8.5 Operating parameters
8.6 Diafiltration
8.7 Fouling and cleaning
8.8 Conclusions and future trends
References
Chapter 9: Nanofiltration
9.1 Introduction
9.2 Nanofiltration market and industrial needs
9.3 Fundamental principles
9.4 Design and simulation
9.5 Membrane materials and properties
9.6 Commercial nanofiltration membranes
9.7 Nanofiltration examples in biorefineries
9.8 Conclusions and challenges
References
Chapter 10: Membrane Pervaporation
10.1 Introduction
10.2 Membrane pervaporation market and industrial needs
10.3 Fundamental principles
10.4 Design principles of the pervaporation membrane
10.5 Pervaporation in the current integrated biorefinery system
10.6 Conclusions and future trends
Acknowledgements
References
Chapter 11: Membrane Distillation
11.1 Introduction
11.2 Membrane distillation market and industrial needs
11.3 Basic principles of membrane distillation
11.4 Design and simulation
11.5 Examples in biorefineries
11.6 Economic importance and industrial challenges
11.7 Comparisons with other membrane-separation technologies
11.8 Conclusions and future trends
References
Part V: Solid-Liquid Separations
Chapter 12: Filtration-Based Separations in the Biorefinery
12.1 Introduction
12.2 Biorefinery
12.3 Solid–liquid separations in the biorefinery
12.4 Introduction to cake filtration
12.5 Basics of cake filtration
12.6 Designing a dead-end filtration
12.7 Model development
12.8 Conclusions
References
Chapter 13: Solid–Liquid Extraction in Biorefinery
13.1 Introduction
13.2 Principles of solid–liquid extraction
13.3 State of the art technology
13.4 Design and modeling of SLE process
13.5 Industrial extractors
13.6 Economic importance and industrial challenges
13.7 Conclusions
References
Part VI: Hybrid/Integrated Reaction-Separation Systems—Process Intensification
Chapter 14: Membrane Bioreactors for Biofuel Production
14.1 Introduction
14.2 Basic principles
14.3 Examples of membrane bioreactors for biofuel production
14.4 Conclusions and future trends
References
Chapter 15: Extraction-Fermentation Hybrid (Extractive Fermentation)
15.1 Introduction
15.2 The market and industrial needs
15.3 Basic principles of extractive fermentation
15.4 Separation technologies for integrated fermentation product recovery
15.5 Examples in biorefineries
15.6 Economic importance and industrial challenges
15.7 Conclusions and future trends
References
Chapter 16: Reactive Distillation for the Biorefinery
16.1 Introduction
16.2 Column internals for reactive distillation
16.3 Simulation of reactive distillation systems
16.4 Reactive distillation for the biorefinery
16.5 Recently commercialized reactive distillation processes for the biorefinery
16.6 Conclusions
References
Chapter 17: Reactive Absorption
17.1 Introduction
17.2 Market and industrial needs
17.3 Basic principles of reactive absorption
17.4 Modelling, design and simulation
17.5 Case study: Biodiesel production by catalytic reactive absorption
17.6 Economic importance and industrial challenges
17.7 Conclusions and future trends
References
Part VII: Case Studies of Separation and Purification Technologies in Biorefineries
Chapter 18: Cellulosic Bioethanol Production
18.1 Introduction: The market and industrial needs
18.2 Separation procedures and their integration within a bioethanol plant
18.3 Importance and challenges of separation processes
18.4 Pilot and demonstration scale
18.5 Conclusions and future trends
References
Chapter 19: Dehydration of Ethanol using Pressure Swing Adsorption
19.1 Introduction
19.2 Ethanol dehydration process using pressure swing adsorption
19.3 Future trends and industrial challenges
19.4 Conclusions
References
Chapter 20: Separation and Purification of Lignocellulose Hydrolyzates
20.1 Introduction
20.2 The market and industrial needs
20.3 Operation variables and conditions
20.4 The hydrolyzates detoxification and separation processes
20.5 Separation performances and results
20.6 Economic importance and industrial challenges
20.7 Conclusions
References
Chapter 21: Case Studies of Separation in Biorefineries—Extraction of Algae Oil from Microalgae
21.1 Introduction
21.2 The market and industrial needs
21.3 The algae oil extraction process
21.4 Extraction
21.5 Separation performance and results
21.6 Economic importance and industrial challenges
21.7 Conclusions and future trends
References
Chapter 22: Separation Processes in Biopolymer Production
22.1 Introduction
22.2 The market and industrial needs
22.3 Lactic acid recovery processes
22.4 Separation performance and results of autocatalytic counter current reactive distillation of lactic acid with methanol and hydrolysis of methyl lactate into highly pure lactic acid using 3-CSTRs in series
22.5 Economic importance and industrial challenges
22.6 Conclusions and future trends
Acknowledgements
References
Index
This edition first published 2013
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Cover Acknowledgement
Cover photos and design advice courtesy of David Hansen, Minnesota Agricultural Experiment Station; Sara Specht, Graphic Designer, College of Food, Agricultural, and Natural Resource Sciences, University of Minnesota, USA
Library of Congress Cataloguing-in-Publication Data
Ramaswamy, Shri, 1957-
Separation and purification technologies in biorefineries / Shri Ramaswamy, Hua-Jiang Huang, Bandaru V. Ramarao.
pages cm
Includes index.
ISBN 978-0-470-97796-5 (cloth)
1. Biomass conversion. 2. Biomass energy. I. Title.
TP248.B55R36 2013
333.95'39–dc23
2012035282
A catalogue record for this book is available from the British Library.
ISBN: 9780470977965
List of Contributors
Preface
The depletion of fossil resources, global climate change, and a growing world population all make it imperative that we find alternative, renewable sources of materials, chemicals, transportation fuels, and energy to address increasing global demand. Biorefineries will be an integral part of the future sustainable bioeconomy. In addition to sustainable biomass resources and effective biomass conversion technologies, separation and purification technologies will play a very important role in the successful development and commercial implementation of biorefineries. Due to the widely varying characteristics and composition of biomass, and the varying associated potential conversion technologies, biorefineries offer very interesting challenges and opportunities associated with the separation and purification of complex biomass components and the manufacture of valuable products and co-products. Generally, separation and purification processes can account for a large fraction (about 20–50%) of the total capital and operating costs of biorefineries. Significant improvement in separation and purification technologies can greatly reduce overall production costs and improve economic viability and environmental sustainability.
Examples of separation and purification needs in biorefineries include pre-extraction of value-added phytochemicals from lignocellulosic biomass, separation of biomass components (including cellulose, hemicellulose, lignin and extractives), extraction and purification of hemicellulose prior to pulping, separation of valuable chemicals from biomass hydrolyzate, removal of fermentation inhibitors enabling improved conversion efficiency and yield, concentrating process streams for varying end products and applications, integration of separation and purification technologies with bioprocessing, as well as downstream product separation and purification, syngas clean-up, purification of reactants, purification of glycerol from biodiesel production for production of intermediates such as succinic acid, and separation and purification of products such as ethanol, butanol, and lactic acid (there are many more examples).
In this book, technical experts from around the world offer their perspectives on the different separation and purification technologies that pertain to biorefineries. They provide basic principles, engineering design and specific applications in biorefineries, and also highlight the immense challenges and opportunities. There are significant opportunities for developing totally new approaches to separation and purification especially suitable for biorefineries and their full integration in the overall biorefineries. For example, adsorption with a molecular sieve is efficient in breaking the ethanol–water or butanol-water azeotrope for biofuel dehydration. Membrane separation, especially ultrafiltration and nanofiltration, represents a promising procedure for recovery of hemicelluloses from hydrolyzates and lignin from spent liquor. Hybrid separation systems such as extractive-fermentation and fermentation-membrane pervaporation are promising approaches to the removal of product inhibition, and hence to the improvement of process performance. Fermentation, bipolar membrane electrodialysis, reactive distillation, and reactive absorption are suitable for separation of products obtained by esterification, as in biodiesel production. Integrated bioprocessing—consolidated bioprocessing integrating pre-treatment, bioprocessing, separation, and purification—offers tremendously exciting new opportunities in future biorefineries.
The editors are grateful to all the contributors for making this very timely book possible. We hope that it will serve as a good resource for industrial and academic researchers, scientists, and engineers as we all work together to address the challenges, develop innovative solutions, and contribute to the development of sustainable biorefineries.
Shri RamaswamyHua-Jiang HuangBandaru V. Ramarao
Part I
Introduction
Chapter 1
Overview of Biomass Conversion Processes and Separation and Purification Technologies in Biorefineries
Hua-Jiang Huang and Shri Ramaswamy
Department of Bioproducts and Biosystems Engineering, University of Minnesota, USA
1.1 Introduction
There has been an increasing interest in conversion of biomass to biofuels, energy and chemicals due to increase in global demand, price and decrease in potential availability of crude oil, the need for energy independence and energy security, and the need for reduction in greenhouse gases emission from fossil fuel contributing to global climate change, and so forth.
Biomass feedstock suitable for producing biofuels, energy and co-products can be starchy biomass (e.g., corn/wheat kernel, cassava), sugarcane and sugar beet, ligocellulosic biomass including agricultural residues (e.g., corn stover, crop residues such as wheat straw and barley straw, and sugar cane bagasse), forest wastes, fast-growing trees such as hybrid poplar and willow, fast-growing herbaceous crops such as switchgrass and alfalfa, oily plants such as soybean and rapeseed, microalgae, waste cooking oil, animal manure, as well as municipal solid waste. The total amount of biomass feedstock available is huge. In the United States, based on the estimation by U.S. Department of Energy (U.S. Department of Energy 2011), total potential biomass resource is about 258 (baseline)–340 (high-yield scenario) million dry tons in 2012. Potential supplies at a forest roadside or farmgate price of $60 per dry ton range from 602 to 1009 million dry tons by 2022 and from about 767 to 1305 million dry tons by 2030, depending on the assumptions for energy crop productivity (1% to 4% annual increase over current yields). This estimate excludes resources that are currently being used, such as corn grain and woody biomass used in the forest products industry. Worldwide, the biomass availability is also significantly high of the order of 5.0 billion tons per year (Bauen et al. 2009; U.S. Department of Energy 2011).
Biofuels made from starchy crops, sugar plants as well as vegetable oils are usually called first-generation biofuels; for example, bioethanol produced from maize, starch, or sugar via fermentation, biodiesel from soybean oil, rapeseed oil, palm oil, or other plant oil by transesterification. Biogas from anaerobic digestion of waste streams also belongs to the first-generation biofuels. As the first-generation biofuels produced from food crops competes with food production and supply, and biogas can only be produced in small quantities, the first-generation biofuels alone generally cannot meet our energy requirements. Biofuels such as cellulosic ethanol made from lignocellulosic biomass such as woody crops, fast-growing trees and herbaceous crops, agricultural residues and forestry waste are referred to as the second-generation biofuels. The focus for second-generation biofuels was primarily ethanol. Unlike the first-generation biofuels, the second-generation biofuels are based on non-food crops and other lignocellulosic biomass; it can also bring about significant reduction in greenhouse gas emissions as well as reduction in fossil fuel use. The third-generation biofuels are made from genetically modified energy crops that may be carbon-neutral, biofuels from algae, or biofuels directly produced from microorganisms or using advances in biochemistry. Fourth-generation biofuels have also been suggested, which are carbon negative—they consume more carbon than they generate during their entire life cycle. Examples of this could be carbon-fixing plants such as low input high-diversity perennial grasses (Tilman, Hill, and Lehman 2006).
A biorefinery is a facility to convert biomass to bioproducts including bioenergy (fuels, heat and power) and diverse array of co-products (including materials and chemicals) (Huang et al. 2008; Huang and Ramaswamy 2012). The biorefinery concept is similar to today's petroleum refinery, which produces multiple fuels and products from petroleum (http://www.nrel.gov/biomass/biorefinery.html). Biorefinery can be divided into two basic conversion platforms: biochemical conversions, and thermo-chemical conversions. A biorefinery can also be a combination of both biochemical and thermo-chemical conversion approaches. Biochemical conversions of biomass using enzymes and microorganisms (yeast and bacteria) are often referred to as “sugar-platform” conversions, where biomass is firstly pretreated and hydrolyzed to mono-sugars: glucose, xylose, arabinose, galactose, and mannose, and so forth. The mono-sugars are then fermented or digested to biofuels such as bioethanol and biobutanol, or chemicals such as lactic acid and succinic acid, depending on the biocatalysts used. Thermo-chemical conversion of biomass includes biomass combustion for heat and power, pyrolysis for bio-oil and biochar, hydrothermal liquefaction to bio-oils as major product, and biomass gasification to syngas. Syngas (mainly CO and H2) from biomass gasification can be further synthesized into a wide range of different fuels and chemicals under different catalysts and operating conditions; biomass gasification or “syngas platform” represents the major thermo-chemical platform. In addition to these basic thermo-chemical conversions, there are a variety of other chemical conversion processes such as conversion of oil-containing biomass such as soybean and microalgae for biodiesel, and the conversion of building block chemicals such as lactic acid to its corresponding commodities, chemicals, polymers and materials.
This chapter provides an overview of the separation and purification technologies in biorefineries for producing bioproducts including biofuels, bioenergy, biochemicals and materials, with more emphasis on lignocelluose biorefineries.
1.2 Biochemical conversion biorefineries
In the biochemical conversion biorefineries or “sugar platforms,” biomass is subjected to hydrolysis and saccharification and then the resulting sugars, including hexoses (glucose, mannose, and galactose) and pentoses (xylose, arabinose) are converted to biofuels such as ethanol and butanol, chemicals, and materials.
As an example, the basic process for conversion of cellulosic biomass to fuel ethanol is shown in Figure 1.1, which mainly consists of the following eight major process areas (Aden et al. 2002):
Figure 1.1Simplified process block diagram of basic lignocellulose to ethanol biorefinery (Aden et al. 2002; Huang et al. 2008)
This process involves a number of separation tasks as follows:
removal of inhibitors from hydrolyzate prior to fermentation;
liquid–solid separation such as separation of prehydrolyzate slurry and postdistillation slurry;
ethanol recovery from beer by distillation and its dehydration using molecular sieve adsorption;
water scrubbing of fermentation vents for recovering of the ethanol;
water recovery by multiple effect evaporation;
gas-solid (particles) separation from combustion flue gas.
The capital and operating costs of all the above separation processes account for a large fraction of the total capital and operation costs of the whole process.
The lignocellulose bioethanol process described above is only one case of “sugar-platform” biorefineries. Other bioconversion processes have similar steps in preparation of fermentable mono-sugars from biomass feedstock. In other words, in addition to bioethanol the biomass-derived mono-sugars including pentose and hexose can be fermented to other biofuels such as butanol, and biochemicals such as carboxylic acids (including succinic, fumaric, malic, itaconic, glutamic, lactic, 3-hydroxypropionic, citric, and butyric acids) (Yang et al. 2006), other chemicals (e.g., 1,3-propanediol), and materials, depending on the microorganism used. Among the carboxylic acids, succinic, fumaric, malic, itaconic, glutamic acids, and 3-hydroxypropionic acids are the major building block chemicals that can subsequently be converted to a number of high-value bio-based chemicals and materials. Building-block chemicals are molecules with multiple functional groups that have the potential to be transformed into new families of useful molecules. Biological transformations account for the majority of routes from plant feedstocks to building blocks, but chemical transformations predominate in the conversion of building blocks to molecular derivatives and intermediates (U.S. Department of Energy 2004). In addition, xylitol, and arabinitol are also important building-block chemicals. They can be employed to produce commodity and specialty chemicals such as xylaric acid, glycerol, propylene glycol, ethylene glycol, and lactic acid. Xylitol and arabinitol can be produced by hydrogenation of sugars or extraction from biomass pretreatment (U.S. Department of Energy 2004). In the following section, some important biofuel and building block chemicals including biobutanol, succinic acid, itaconic acid, 3-Hydroxypropionic acid, 1,3-propanediol, and lactic acid will be briefly introduced.
Succinic acid (HOOCCH2CH2COOH), also called amber acid or butanedioic acid, is primarily used as a sweetener in the food industry. In addition, it is a key building block for deriving both commodity and specialty chemicals such as 1,4-butanediol (BDO), tetrahydrofuran (THF), γ-butyrolactone (GBL), pyrrolidinones, and N-Methylpyrrolidone (NMP) (U.S. Department of Energy 2004; Cukalovic and Stevens 2008). Succinic acid is produced by fermentation of glucose using an engineered form of the organism A. succiniciproducens and, most recently, via an engineered Eschericia coli strain. Currently, highly efficient microorganism for production of succinic acid are A. succinogenes, A. succiniciproducens, and M. succiniciproducens (Cheng et al. 2012). The process also has the benefit of carbon dioxide fixation, as seen in its reaction formula (Zeikus, Jain and Elankovan 1999):
In addition to glucose, glycerol can also be the carbon source for succinic acid fermentation. This provides a good opportunity to produce a value-added chemical from glycerol, the relatively cheap co-product of biodiesel production.
Itaconic acid, or methylsuccinic acid (HO2CCH2CH(CH3)CO2H), is used in polymers, paints, coatings, medicines, and cosmetics (Bressler and Braun 1999). As a value-added building block chemical, itaconic acid has the potential to be used for deriving both commodity and specialty chemicals such as 2-methyl-1,4-BDO, 3-methyl THF, 3-&4-methyl-GBL, 2-methyl-1,4-butanediamine, and other value-added chemicals (U.S. Department of Energy 2004). It is produced commercially by the fungal fermentation of carbohydrates. The most commonly used organism for itaconic acid production is Aspergillus terreus, grown under phosphate-limited conditions (Willke and Vorlop 2001).
3-Hydroxypropionic acid (3-HPA), as an important C3 building block, has the potential to derive several commodity and specialty chemicals such as 1,3-propanediol (1,3-PDO), acrylic acid, methyl acrylate, acrylamide, and other valuable chemicals (U.S. Department of Energy 2004). 3-HPA can be produced from glycerol using a recombinant strain E. coli (Raj et al. 2008), Klebsiella pneumoniae (Luo et al. 2010a; Huang et al. 2012), or from glucose using a recombinant strain E. coli (Rathnasingh et al. 2010). When cultivated aerobically on a glycerol medium containing yeast extract, the recombinant E. coli SH254 produced 3-HPA at a maximum of 6.5 mmol l−1 (0.58 g l−1). The highest specific rate and yield of 3-HPA production were estimated as 6.6 mmol g−1 cdw h−1 and 0.48 mol mol−1 glycerol, respectively (Raj et al. 2008). The engineered K. pneumoniae can effectively produce 3-HPA and 1,3-PDO from glycerol under anaerobic conditions (Huang et al. 2012).
1,3-propanediol (1,3-PDO) is used in manufacturing polymers, medicines, cosmetics, food, and lubricants (Drodyska, Leja and Czaczyk 2011). It can be produced from glycerol using pathogenic microorganisms such as Klebsiella pneumoniae and non-pathogenic microorganisms such as Clostridium butyricum, Clostridium acetobutylicum, and Lactobacillus diolivorans. C. butyricum has been reported to produce 1,3-PDO with a titer of 94 g/l when using glycerol as the carbon source (Wilkens et al. 2012). A recombinant strain of C. acetobutylicum produces up to 84 g/l in fed-batch cultivation (González-Pajuelo et al. 2005). The 1,3-PDO concentration obtained was 73.7 g/l in a fed-batch co-feeding glucose and glycerol with a molar ratio of 0.1. L. diolivorans proves to be a top candidate microorganism for industrial production of 1,3-PDO from glycerol. The wild-type strain produces up to 0.85 g 1,3-PDO/l h and product concentrations up to 85.4 g/l (Pflügl et al. 2012). 1,3-PDO can also be produced from glucose and molasses in a two-step process using two recombinant microorganisms. The first step is the conversion of glucose or other sugar into glycerol by the metabolic engineered S. cerevisiae strain HC42 adapted to high (>200 g l−1) glucose concentrations. The second step is to convert glycerol to 1,3-PDO in the same bioreactor using the engineered strain C. acetobutylicum DG1 (pSPD5). The best results were obtained with an initial glucose concentration of 103 g l−1, leading to a final 1,3-PDO concentration of 25.5 g l−1, a productivity of 0.16 g l−1 h−1 and 1,3-PDO yields of 0.56 g g−1 glycerol and 0.24 g g−1 sugar (Mendes et al. 2011). Recently, 1,3-PDO production by microorganisms were reviewed (Saxena et al. 2009; Drodyska, Leja, and Czaczyk 2011).
Lactic acid is widely used in the food industry (Zhang, Jin, and Kelly 2007), and as a building-block chemical (Lee et al. 2011). It can be used for the production of biodegradable and biocompatible polymers such as polylactic acid (PLA), lactate esters, propylene glycol, acrylic acid and esters (Adsul et al. 2011). The current status of the production of potentially valuable chemicals from lactic acid via biotechnological routes has been reviewed recently (Gao, Ma and Xu 2011). Lactic acid can be produced from lignocellulose-derived sugars using microorganisms such as recombinant Escherichia coli (Dien, Nichols and Bothast 2001), Bacillus coagulans (Maas et al. 2008), Lactobacillus sp. (Wee and Ryu 2009), and Lactococcus lactis (Laopaiboon et al. 2010). There has been a recent overview of the lactic acid production (Vijayakumar, Aravindan, and Viruthagiri 2008; Abdel-Rahman, Tashiro, and Sonomoto 2011).
Biofuels (ethanol and butanol) and valued-added building-block chemicals (e.g., succinic acid, 3-HPA, and 1,3-PDO) derived from lignocellulosic carbohydates by biochemical conversion as described earlier, are often very dilute in their fermentation broths. This usually causes high production costs. In addition to improving microbial biocatalysts to increase substrate and hence product concentrations, yields, and productivities, development of efficient separation and purification processes with low costs are much needed.
1.3 Thermo-chemical and other chemical conversion biorefineries
1.3.1 Thermo-chemical conversion biorefineries
The major thermo-chemical conversion biorefineries involve combustion, hydrothermal liquefaction, pyrolysis, and gasification of biomass into heat (steam) and power, biofuels and chemicals.
Biomass combustion, the complete oxidation process, is a simple way to recover energy from biomass. As the steam turbine used in the process for generating power is not efficient, combustion of biomass, especially the whole biomass, is not the best option. Owing to the simplicity and the maturity of the combustion technology, combustion of the whole biomass, including non-fermentable residues, is commercially common. Combustion of biomass solid residues from distillation for steam and power for process use, as part of Figure 1.1, is a typical example. The carbon dioxide produced from biomass combustion was originally absorbed by the biomass plant during growth from environment via photosynthesis; so it is assumed to be carbon-neutral. In terms of separation, postcombustion capturing and sequestration of CO2 from flue gases produced by the biomass combustion is very important and interesting.
Biomass pyrolysis is a thermal conversion process converting biomass to liquid (bio-oil), solid (char) and gas in the absence of oxygen. Based on different reaction rates and product distributions, pyrolysis can be classified as four categories: torrefaction, carbonization, intermediate pyrolysis, and fast pyrolysis. Table 1.1 shows the typical product yields for pyrolysis of wood using different modes and conditions.
Table 1.1Typical product weight yields (dry wood basis) for different pyrolysis of wood. Adapted from Bridgwater, A. V., © 2012 with permission from Elsevier
The pyrolysis bio-oil can be used as feedstock of gasification for producing syngas, which can then be synthesized into fuels and chemicals. In addition, bio-oil can be used to produce transportation fuels. Fast pyrolysis liquid has a higher heating value of about 17 MJ/kg as produced with about 25 wt.% water that cannot easily be separated. Besides, pyrolysis bio-oil has a high oxygen content of around 35–40 wt% (Bridgwater 2012), leading to instability and relatively low heating value. Thus, pyrolysis bio-oil needs to be catalytically upgraded to transportation fuels and fuel additives by hydrotreating, cracking and decarboxylation, or esterification of bio-oil with alcohols followed by water separation to reduce their oxygen content and improve their thermal stability (Bulushev and Ross 2011). Bio-oil upgrading technologies have been recently reviewed (Huber and Corma 2007; Bulushev and Ross 2011; Bridgwater 2012). Furthermore, the separation of some chemicals such as acids and phenolics from bio-oil is another alternative option. Bio-oil is a complex mixture of several hundreds of organic compounds including hydroxyaldehydes, hydroxyketones, sugars, carboxylic acids, phenolics (phenols, guaiacols, catechols, syringols, isoeugenol) and other oligomeric lignin derivatives, along with around 25% water. About 35–50% of the bio-oil constituents are non-volatile (Czernik and Bridgewater 2004). Separation of value-added compounds from bio-oil becomes significantly important.
Hydrothermal liquefaction (HTL) is the process where the reaction of biomass is carried out in water media at high temperature and pressure with or without added catalyst. Its products include a bio-oil fraction, a water fraction containing some polar organic compounds, a gaseous fraction and a solid residue fraction (Biller and Ross 2011). Generally, HTL operates at 280–370 °C and 10–25 MPa (Behrendt et al. 2008). As HTL operates in water media, it can process directly the wet biomass feedstock such as wet microalgae (Wu, DeLuca and Payne 2010; Zou et al. 2010; Anastasakis and Ross 2011; Vardon et al. 2011; Vardon et al. 2012), animal manure (Yin et al. 2010; Vardon et al. 2011; Theegala and Midgett 2012), and digested anaerobic sludge (Vardon et al. 2011) without the need for predrying the biomass. Thus, the HTL process has energy-saving potential and it is a promising conversion process. There has been a recent overview of HTL of biomass for bio-oil (Akhtar and Amin 2011; Toor, Rosendahl and Rudolf 2011). The Hydro Thermal Upgrading (HTU®) process is one example of HTL. The HTU process, carried out at 300–350 °C, 100–180 bar and a residence time of 5–20 min, produces bio-oil (or biocrude) having a heating value of 30–35 MJ/kg (Goudriaan and Naber 2008; Toor et al. 2011). Due to the low oxygen content (10–18%wt), this bio-oil can be upgraded by hydrodeoxygenation (HDO) to premium quality diesel fuel. The thermal efficiency of the HTU process is 70–90% (Goudriaan and Naber 2008).
Biomass gasification is a partial oxidation process operating at a temperature in the range of 700–850 °C and a pressure of 0.1–3 MPa using steam, air or oxygen as oxidant. For gasification of black liquor from pulp mills can be conducted at conditions of 900–1200 °C and 2–3 MPa. It is one of the prominent thermochemical conversion methods to produce renewable fuels, energy, chemicals and materials. In addition to producing heat and power, synthesis gas from biomass gasification can be subsequently converted into liquid transportation fuels such as diesel and gasoline, alternative fuels such as methanol, dimethyl ether (DME) and ethanol, and other chemicals under different catalysts and operating conditions (Huang and Ramaswamy 2009). Synthetic diesel can be produced by the Fischer–Tropsch (FT) synthesis of syngas over iron or cobalt-based or hybrid (composite) catalysts (Khodakov, Chu, and Fongarland 2007). Methanol, which is also a material for fuel cell in addition to being an alternative fuel, can be synthesized from syngas over the Cu/ZnO catalyst (Zhang et al. 2009). Dimethyl ether can be produced by dehydration of methanol. It can also be manufactured directly from syngas by a single-step process using the hybrid catalyst composed of CuO, ZnO, Al2O3, and/or Cr2O3) for methanol synthesis and an acid function catalyst (such as γ-Al2O3, H-ZSM-5 or HY zeolites) for conversion of methanol into DME (Bae et al. 2008). In addition, mixed alcohols can be synthesized from syngas. Mixed alcohols synthesis from syngas is an important process for the production of oxygenated fuels, fuel additives, and other intermediates for value-added chemical feedstock for applications in medicine, cosmetics, as lubricants, as detergents, and for polyester (Fang et al. 2009). The potential catalysts for mixed alcohols synthesis from syngas include Cu-based catalysts and Mo-based catalysts. The synthesis of mixed alcohols from syngas over Cu-Fe based catalyst consists of alcohol formation (major reaction), hydrocarbon formation, and water–gas shift reaction are the side reactions (Fang et al. 2009). Methanol can also be synthesized to gasoline over zeolites. Hydrogen can be produced from syngas for fuel cell or power generation, or synthesis of ammonia for fertilizer. Table 1.2 shows the reactions of these important biofuels.
Table 1.2Reactions of common syngas-based fuel synthesis
1.3.1.1 Example: Biomass to gasoline process
Biomass can be converted to gasoline via methanol synthesis and methanol-to-gasoline (MTG) technologies, as illustrated in Figure 1.2. In this process, biomass feedstock, after shredding and drying, is sent to the gasifier for producing syngas. The raw syngas is sent to a tar reformer, a particulate scrubber, and finally a sulfur removal unit. Then the syngas enters a steam reformer where CH4 is converted to H2 and CO and the H2/CO ratio is adjusted to that required by methanol synthesis. Excess CO2 is removed by amine absorption. The clean syngas is then compressed and sent to the methanol synthesis. Part of the purge gas from methanol synthesis is used to produce hydrogen by a pressure swing adsorption (PSA) unit; the remaining purge gas is used as fuel for drying the feedstock. Raw methanol is converted to hydrocarbons and water in the MTG reactors. The raw gasoline isolated from water by phase separation, is distilled to produce fuel gas, liquefied petroleum gas (LPG), light gasoline, and heavy gasoline. The heavy gasoline is hydrotreated with hydrogen from the PSA to meet the final gasoline specifications. Steam generated in the process is collected and sent to the steam cycle for power generation. Some steam is used in steam reforming and other processes (Jones and Zhu 2009).
Figure 1.2Block diagram of biomass-to-gasoline process (Jones and Zhu 2009)
1.3.2 Other chemical conversion biorefineries
In addition to the major thermo-chemical conversion approaches mentioned above, biorefineries may also involve various other chemical conversion processes. For instance, production of value-added building block chemicals such as levulinic acid and sorbitol, the conversion of oil-containing biomass for biodiesel, and conversion of those building block chemicals described above to commodity, chemicals and materials. Next, some important value-added building block chemicals including levulinic acid, glycerol, sorbitol, and xylitol/arabinitol are briefly introduced, followed by an example of chemical conversion process.
1.3.2.1 Levulinic acid
Levulinic acid is an important platform molecule that can be used to produce a wide range of compounds such as γ–valerolactone (GVL), 2-methyltetrahydrofuran, δ-aminolevulinic acid, β-acetylacrylic acid, diphenolic acid, and 1,4-pentanediol (U.S. Department of Energy 2004). Levulinic acid can be catalytically converted to fuel additives through intermediates such as γ-valerolactone and valeric acid, and this has been recently highlighted (Lange et al. 2010; Bond et al. 2010; Bozell 2010). Also, 2-methyltetrahydrofuran and various levulinate esters derived from levulinic acid can be used as gasoline and biodiesel additives, respectively (U.S. Department of Energy 2004). Different from biofuels production via fermentation of biomass-derived sugars, levulinic acid is produced by acid catalyzed hydrolysis of biomass-derived sugars, a conventional chemical processing approach. This presents another promising route for biofuels.
1.3.2.2 Glycerol
Glycerol can be used as raw material for the cosmetics, pharmaceutical, and food industries (Leoneti, Aragão-Leoneti, and de Oliveira 2012). It is the major co-product of biodiesel production by transesterification of oils, with a weight ratio of 1/10 (glycerol/biodiesel). Glycerol can be considered a renewable building block for producing value-added products obtained by chemical (syn-gas, acrolein, and 1,2-propanediol) or bio-chemical (ethanol, 1,3-propanediol, D-lactic acid, succinic acid, propionic acid, and poly-3-hydroxybutyrate) routes (Posada et al. 2012). The wide use of glycerol in producing so many chemical building blocks plus its low price due to the fast growth of biodiesel industry and the surplus of glycerol makes it an excellent renewable feedstock and important building block for producing multiple products in biorefineries. Moreover, glycerol can be utilized to produce triacetin (or 1,2,3-triacetoxypropane), a biofuel additive, by esterification of glycerol with acetic acid. However, the glycerol from biodiesel production as a by-product must be purified before it is used in these industries (Leoneti, Aragão-Leoneti and de Oliveira 2012). Distillation, solvent extraction, ionic exchange, electrodialysis, and simulated moving bed (SMB) can be used for separation and purification of glycerol.
1.3.2.3 Sorbitol
Sorbitol is a potential key chemical intermediate from biomass resources for deriving a number of intermediates and chemicals such as propylene glycol, ethylene glycol, glycerol, lactic acid, and isosorbide (U.S. Department of Energy 2004). Sorbitol is commercially produced by the hydrogenation of glucose.
1.3.2.4 Xylitol/Arabinitol
Xylitol and arabinitol, the sugar alcohols, can be produced by hydrogenation of 5-carbon sugars xylose and arabinose from biomass. There is no major technical barrier associated with the production of xylitol and arabinitol (U.S. Department of Energy 2004). Separation and purification of the pentoses, xylose and arabinose, is important for production of xylitol and arabinitol. In addition, xylitol, and arabinitol can be produced by direct extraction from biomass pretreatment processes. Efficient separation and purification approaches such as ion exchange and nanofiltration are also necessary for this route.
1.3.2.5 Example: Conversion of oil-containing biomass for biodiesel
As an example, the conventional process of the plant oil to biodiesel conversion is shown in Figure 1.3. In this process, fatty acid methyl ester (FAME, biodiesel) is synthesized by esterification of oil with methanol over an alkali catalyst (NaOH). The resultant liquid mixture enters the methanol distillation column where methanol is removed and recycled for use as the reactant. The bottom liquid out of the distillation column is then washed and separated into the oil phase (raw FAME) and the aqueous phase (mainly glycerol). The raw FAME is purified by distillation, while the aqueous solution is neutralized with H3PO4, followed by filtering out the solid Na3PO4, and the distillation for glycerol concentration.
Figure 1.3Simplified block diagram of conventional biodiesel production process (Zhang, Dube and McLean 2003)
This homogeneous process using liquid catalyst (NaOH) has many disadvantages: requirement of alkali and acid chemicals and their handling, large separation burden and hence high separation capital and operation costs. In addition, dehydrated vegetable oil with less than 0.5 wt.% free fatty acids, an anhydrous alkali catalyst and anhydrous alcohol are necessary for commercially viable alkali-catalyzed systems, and thus the low-cost waste cooking oil is not suitable as feedstock for this process; otherwise, soap occurs during the biodiesel production and this requires additional soap related separation, making the system more costly (Zhang, Dube, and McLean 2003). To overcome these disadvantages of the conventional biodiesel process, heterogeneous biodiesel process using solid catalyst can be applied. Figure 1.4 shows the simplified block diagram of the Esterfip–H biodiesel process (Axens-IFP Group Technologies).
Figure 1.4Simplified block diagram of Esterfip–H biodiesel process (Bacovsky et al. 2007)
In this continuous system, oil reacts with methanol in two fixed-bed reactors packed with a non-noble metal solid catalyst supplied by Axens. Excess methanol is removed after each of the two reactors by a partial flash vaporization. Esters and glycerol are then separated in a settler. Glycerol phases from each reactor, after being separated from settlers, are combined and the last traces of methanol are removed by vaporization. Biodiesel is produced after final recovery of methanol by full vaporization under vacuum (Bacovsky et al. 2007). This process has many advantages: high biodiesel yield (close to theoretical); high purity glyderol without the need for further purification; no soap formation and no low-value fatty acids; no handling of hazardous acid and base chemicals; much lower catalytic cost as compared to other processes (Bacovsky et al. 2007).
1.4 Integrated lignocellulose biorefineries
Integrated lignocellulose biorefineries (ILCB) or integrated forest biorefineries (IFBR) are comprehensive approaches that make full use of all the components of biomass feedstock to produce heat (steam) and power, biofuels, cellulose fibers for pulp and paper, and multiple products (chemicals, polymers or materials). Figure 1.5 below is the general ILCB, modified from the diagram of the advanced pulp mill-based integrated forest biorefinery (IFBR) (Huang et al. 2010). The ILCB include not only the pulping process for pulp and paper, but also the following processes that could make value-added coproducts:
separation of phytochemicals from woody biomass at mild conditions (optional);
extraction of hemicellulose prior to pulping for biofuels and chemicals;
extraction of lignin and chemicals (e.g., acetic acid) from spent pulping liquors;
gasification of biomass including spent pulping liquor and forest residues and agricultural residues, for heat and power, syngas production, and syngas synthesis into fuels an chemicals such as methanol, DME, diesel, gasoline, and mixed alcohols;
the extracted hemicellulose, combined with isolated short fiber, is hydrolyzed to monosugars, which are then fermented to sugar-based biofuels (e.g., ethanol, butanol), building blocks (e.g., lactic acid, succinic), and chemicals, depending on the microorganism used.
Figure 1.5Block diagram of the general ILCB
For changing a current pulp mill to an ILCB, the additional incremental costs for realizing a commercial biorefinery can be minimized by fully utilizing the existing infrastructure. Modification of the modern day pulp mills into ILCB presents an excellent opportunity to produce, in addition to valuable cellulose fiber, co-products include fuel grade ethanol/butanol and additional energy, thus resulting in increased revenue streams and profitability and potentially lower the greenhouse gas emissions (Huang et al. 2010).
Separation and purification technologies also play a significant role in the ILCB. Pre-extraction of value-added chemicals such as phytochemicals and extraction of hemicellulose prior to pulping, separation of valuable chemicals from biomass prehydrolysis liquor, syngas cleanup, purification of reactants, for example purification of glycerol from biodiesel production for production of intermediates such as succinic acid, and separation and purification of products (ethanol, butanol, lactic acids etc.) are only some of the examples. Generally, the capital and operating costs of separation and purification processes usually account for a large fraction (about 20–50%) of the total capital and operating costs of biorefineries. Significant improvement in of separation and purification technologies can significantly reduce the overall production costs.
1.5 Separation and purification processes
As discussed earlier, in each of the multitude of lignocellulose based biorefinery applications, in addition to the biomass conversion processes, separation and purification of the biomass components and the products streams and their full integration with the overall process is of utmost importance. In many instances this can be the single biggest factor influencing the overall success and commercialization of biorefineries. Given the significance and importance of this area, separation and purifications technologies and their applications in biorefineries is the focus of this book.
The following section presents a brief introduction and outlines the challenges and opportunities in many of the plausible separation and purification technologies in biorefineries. Each of the separation and purification technologies is then the focus of the remainder of the book and they are dealt in greater detail in each of the following chapters.
1.5.1 Equilibrium-based separation processes
1.5.1.1 Absorption
Absorption is often used for separation of particles or desired gas components from a gas mixture into a liquid solvent phase. In biorefineries, absorption is commonly used for removal of acid gases such as H2S and CO2 from syngas prior to synthesis of syngas into methanol and diesel, and so forth. There are two major type of absorption: physical and chemical absorption. Physical absorption is commercially used to remove acid gas such as CO2 and H2S from syngas in the production of hydrogen, ammonia and methanol. The most well-known physical absorption processes are the Selexol process using the dimethyl ethers of polyethylene glycol at relatively high pressure (2.07–13.8 MPa) and the Rectisol process using cold methanol at −40 °C and 2.76–6.89 MPa for separating H2S and CO2 (Kohl and Nielsen 1997). Other major absorption processes include the Purisol process using N-methyl-2-pyrollidone, and the FLUOR process using propylene carbonate (Olajire 2010).
Currently, both the chemical absorption based on aqueous methyldiethanolamine (MDEA) and the Selexol process are selected in commercial IGCC (Integrated Gasification Combined Cycle) facilities for removal of acid gases. While physical absorption processes can meet the stringent sulfur cleanup required by catalytic synthesis of syngas, they are more expensive than the MDEA-based chemical absorption. On the other hand, although the Selexol process by itself is more expensive than an MDEA process, the total acid gas removal (AGR), sulfur recovery process, and tailgas treating process system, based on Selexol, could be more cost effective than the system based on MDEA, especially if the syngas pressure is high and deep sulfur removal (e.g., to 10–20 ppmv) is required. The Rectisol process is capable of deep sulfur removal, but it is the most expensive AGR process. Hence, Rectisol is generally used for chemical synthesis of syngas where very pure syngas is required (Korens, Simbeck and Wilhelm 2002). An overview of CO2 separation has recently been presented elsewhere (Olajire 2010).
1.5.1.2 Distillation
Distillation is a commonly used separation method in chemical and biochemical industries. There are different distillation processes for liquid mixture separation: ordinary distillation, azeotropic distillation, extractive distillation. For separation and dehydration of ethanol from fermentation broth, it is impossible to separate ethanol–water in a single distillation column because ethanol forms an azeotropic mixture or azeotrope, at 95.6% by weight with water at a temperature of 78.15 °C. The separation and dehydration of ethanol usually consists of two steps: the ordinary distillation is firstly used to obtain approximately 92.4 wt% ethanol from the dilute broth, azeotropic distillation, extractive distillation, liquid–liquid extraction, and adsorption and so forth are then applied for further dehydration. The major distillation processes including ordinary distillation, azeotropic distillation, and extractive distillation potentially used in biorefineries has been reviewed taking ethanol separation and dehydration as example (Huang et al. 2008).
Molecular distillation (MD) is a special distillation process that is carried out under high-vacuum conditions and is suitable for the fractionation and separation of chemicals from pyrolysis bio-oils (Wang et al. 2009; Guo et al. 2009, 2010). Under these conditions the mean free path length of the molecules to be separated is generally longer than the distance between the evaporation surface and the condenser surface. It can also be used for purification of biodiesel obtained by esterification of cooking oil with methanol (Wang et al. 2010), and isolating heat sensitive phytochemicals from biomass or biomass extract (Huang and Ramaswamy 2012). As described before, the properties of pyrolysis liquid can be improved by hydrogenation and/or HDO. On the other hand, pyrolysis bio-oil is a valuable source for the production of chemicals, such as alcohols, aldehydes, ketones, acids, phenolics and sugars. Separation of these chemicals, for example the acid compounds for refining pyrolysis oil (Guo et al. 2009) and phenolic fraction for production of pharmaceuticals, adhesives, and specialty polymers (Žilnik and Jazbinšek 2011) from bio-oil, is an alternative option. Wang et al. (2010) explored the purification of crude biodiesel with molecular distillation and showed that it resulted in the high yield of FAME (up to 98.32%). In order to enhance the condensation efficiency of molecular distillation, traditional vacuum distillation was firstly used to remove most of the water in the crude bio-oil. The resulting bio-oil was then fractionated by molecular distillation. Results indicated that the distilled fractions were rich in low molecular weight carboxylic acids and ketones; the residual fraction hardly contains water and it has improved heating values of 21.29 MJ/kg and 22.34 MJ/kg for two operating conditions (80 °C, 1600 Pa and 80 °C, 340 Pa), respectively.
Steam distillation is a conventional commercially utilized process for isolating volatile organic compounds such as essential oils that are sensitive to high heat from plant material. Different from the earlier separation methods, steam distillation is used for direct separation of the desirable components from solid biomass feedstock, not liquid mixture. In this method, steam is introduced by heating water, and passed through the oil-containing plant material. With the addition of steam, the oil–water mixture boils at a lower temperature (<100 °C at 1 atm) allowing heat-sensitive compounds to be separated with less decomposition. Steam distillation is suitable for extracting light components whose vapour pressures are relatively high (≥1.33 kPa at 100 °C). For components whose vapour pressures at 100 °C are between 0.67 kPa and 1.33 kPa, superheated steam is used for the distillation. Steam distillation can be used to separate light components of essential oils and bioactive compounds from biomass (Huang and Ramaswamy 2012), and this could bring value-added co-products for biorefineries.
Chapter 2 by Lei et al. provides additional details on distillation and its applications in biorefineries.
1.5.1.3 Liquid-liquid extraction
Liquid-liquid extraction (LLE), or solvent extraction, is a conventional separation process where one or more mixed solvents are used to extract desirable component from the feed liquid phase to the solvent phase. Liquid-liquid extraction can be used for separating biofuels and chemicals from dilute liquid mixtures—for example, extracting bioalcohols (Simoni et al. 2010) and carboxylic acids (Bressler and Braun 1999; Açi and nci 2012; Oliveira et al. 2012) from their fermentation broths, extracting inhibitors (compounds toxic to microorganisms used for fermentation) from biomass hydrolyzates (Grzenia, Schell, and Wickramasinghe 2011), and removing impurities (soap, methanol, and glycerol) in biodiesel from used cooking oils (Berrios et al. 2011). For example, Chapeaux et al. (2008) and Simoni et al. (2010) studied the LLE of 1-butanol from water using ionic liquids (ILs) as solvents. Experimental results show that some ILs have high distribution coefficients and selectivities of 30 to 300. 1-hexyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate shows especially good extraction capability with the distribution coefficient of 5 and the selectivity of 300 for 5 wt% 1-butanol aqueous mixture.
Organic acids such as succinic, maleic, lactic, and itaconic acids can be extracted from their fermentation broths by amine extractants, which is based on reactive extraction. For instance, extraction of itaconic acid from aqueous solutions has been studied by six different solutions of trioctylamine (TOA)–tridodecylamine (TDA) mixtures and one of the following diluents: dimethyl phthalate (DMP), methyl isobutyl ketone (MIBK), 2-octanone, 1-octanol, cyclohexyleacetate (CHA), and 1-decanol. The maximum itaconic acid recovery was 98.39% with DMP and 3.14 mol L−1 initial concentration of the TOA–TDA mixture (Açi and nci 2012). In addition, organic acids, particularly acetic acid, are reported from the aqueous fraction of the pyrolysis liquid using a long chain aliphatic tertiary amine. The best results were obtained with TOA in 2-ethyl-hexanol (40 wt%, as diluent) with 84% acetic acid recovery at equilibrium conditions (room temperature). Formic acid and glycolic acid present in the feed were also co-extracted with 92% and 69% extraction efficiencies respectively, as well as relatively non-polar compounds such as substituted phenolics and ketones (Rasrendra et al. 2011). Furthermore, the extraction of succinic acids, l-lactic, and l-malic from fermentation broths and dilute waste water using ionic liquid as extractant was investigated, and the results show that phosphonium-based ILs can be better extractants than the organic solvents traditionally used (Oliveira et al. 2012).
Extraction of acetic acid from biomass hydrolysates using mixed solvent consisting of 85% octanol and 15% Alamine 336 (w/w) for the purpose of inhibitor removal or detoxification, extraction of 5-hydroxymethylfurfural (HMF) from an aqueous reaction solution obtained by acid dehydration of six carbon sugars for production of HMF, using MIBK as extractant, and the extraction of glycerol from 2-butanol into an aqueous phase during the manufacture of biodiesel have also been studied (Grzenia et al. 2011).
Liquid-liquid extraction of the key chemicals from bio-oils have been investigated (Vitasari, Meindersma, and de Haan 2011; Žilnik and Jazbinšek 2011). For instance, different aqueous extractions and extraction with combined use of a hydrophobic-polar solvent and antisolvent for extraction of fast pyrolysis bio-oils were studied. Results show that alkali solution was more efficient than water or aqueous NaHSO3 solution; MIBK was shown to be the most efficient solvent for extraction of phenolics from bio-oil in combination with 0.1 M or 0.5 M aqueous NaOH solution, followed by butyl acetate (Žilnik and Jazbinšek 2011).
Chapter 3 by Hu et al. provides additional details on liquid-liquid extraction and its applications in biorefineries.
1.5.1.4 Supercritical fluid extraction
In the supercritical fluid extraction (SFE) process, a supercritical fluid is used to extract the valuable solutes from a solid matrix or a liquid mixture at its supercritical condition. ScCO2 is the most commonly used supercritical fluid in the food, pharmaceutical, and chemical industries. Being non-polar, or hydrophobic, ScCO2 is very suitable for extracting hydrophobic constituents from biomass (Huang and Ramaswamy 2012). For example, some value-added phytochemicals such as pigments, phenolics, and carotenoids can be recovered from microalgae with ScCO2 extraction. Phytochemicals from plants including other plants such as switchgrass and alfalfa have the potential to be used in pharmaceuticals, cosmetics, nutritional, and consumer products. Extraction of phytochemicals at mild conditions prior to biomass pretreatment could bring value-added co-products in addition to using biomass for producing biofuels, chemicals, and materials. This could help lower the overall production cost of the major products of biorefineries. In addition, lipid in microalgae can be extracted via ScCO2 extraction for biodiesel production (Halim et al. 2011; Soh and Zimmerman 2011). The extracted lipid in this case had a suitable fatty acid composition for biodiesel (Halim et al. 2011). Besides, the ScCO2
