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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
PRODUCTION of BIOBUTANOL from BIOMASS The book covers all current technologies of lignocellulosic biobutanol production as well as the environmental and socioeconomic impact assessment. N-butanol is a bulk chemical that is used as an industrial solvent and as a component in paint, coatings, and adhesives, among other things. When compared to other biofuels, biobutanol has the advantages of being immiscible in water, having a higher energy content, and having a lower vapor pressure. There are various benefits to producing biobutanol from lignocellulosic biomass. However, there are challenges in producing butanol from lignocellulosic biomass, such as biomass's complex structure, low butanol yield, and high cost of production, etc. The 13 chapters comprising this book discuss the current technology and prospects of biobutanol production. The first four chapters provide an overview of the current technological status, while the next six chapters discuss different strategies for enhanced biobutanol production from lignocellulosic biomass. The last three chapters present the industrial status and techno-economic analysis of lignocellulosic biobutanol production. Audience The book will be useful for researchers in the areas of various branches of life sciences such as environmental biotechnology, bioprocess engineering, renewable energy, chemical engineering, nanotechnology, biotechnology, microbiology.
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Veröffentlichungsjahr: 2023
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Table of Contents
Cover
Table of Contents
Series Page
Title Page
Copyright Page
Preface
1 Biobutanol: An Overview
1.1 Introduction
1.2 General Aspects of Butanol Fermentation
1.3
Clostridium
Species That Produce ABE and Their Respective Metabolic Characteristics
1.4 Traits of the Molecularly Developed Strain and the ABE-Producing Clostridia
1.5 Substrate for ABE Fermentation in Research
1.6 Problem and Limitation of ABE Fermentation
1.7 The Development of Butanol from Designed and Modifying Biomass
1.8 Butanol Production Enhancement Using Advanced Technology
1.9 Utilizing Pre-Treatment and Saccharification to Produce Butanol from Lignocellulosic Biomass
1.10 Eliminating CCR to Produce Butanol
1.11 Butanol Production from Alternative Substrate to Sugar
1.12 Economics of Biobutanol
1.13 Future Prospects
1.14 Conclusion
References
2 Recent Trends in the Pre-Treatment Process of Lignocellulosic Biomass for Enhanced Biofuel Production
2.1 Introduction
2.2 Composition of Lignocellulosic Biomass
2.3 Insight on the Pre-Treatment of LCB
2.4 Physical Pre-Treatment Method
2.5 Chemical Pre-Treatment Methods
2.6 Biological Pre-Treatment Methods
2.7 Future Prospects
2.8 Conclusion
References
3 Current Status of Enzymatic Hydrolysis of Cellulosic Biomass
3.1 Introduction
3.2 Overview on Biofuels and Its Classification
3.3 Pre-Treatment Methodologies for Hydrolysis of Lignocellulosic Biomass
3.4 Conclusion
References
4 Present Status and Future Prospect of Butanol Fermentation
4.1 Introduction
4.2 Biobutanol Production
4.3 Perspectives
4.4 Conclusion
References
5 Strategies of Strain Improvement for Butanol Fermentation
5.1 Introduction
5.2 Background
5.3 Microorganism
5.4 ABE Fermentation
5.5 Selection of Biomass for the Production of Butanol
5.6 Processes Improvement
5.7 Strain Improvement
5.8 Production of Butanol From Bioethanol Through Chemical Processes
5.9 Advances in Genetically Engineered Microbes can Produce Biobutanol
5.10 Economics of Biobutanol Fermentation
5.11 Applications of Butanol
5.12 Butanol Advantages
5.13 Conclusion
References
6 Process Integration and Intensification of Biobutanol Production
6.1 Introduction
6.2 Biobutanol
6.3 Biobutanol Production and Recovery
6.4 Process Intensification
6.5 Process Integration
6.6 Conclusion
References
7 Bioprocess Development and Bioreactor Designs for Biobutanol Production
7.1 Introduction
7.2 Steps in Biobutanol Production
7.3 Feedstock Selection
7.4 Microbial Strain Selection
7.5 Solvent Toxicity
7.6 Fermentation Technologies
7.7 Butanol Separation Techniques
7.8 Current Status and Economics
7.9 Concluding Remarks
References
8 Advances in Microbial Metabolic Engineering for Increased Biobutanol Production
8.1 Introduction
8.2 Metabolic Engineering
8.3 Microorganisms for Butanol Production
8.4 Metabolic Engineering of Clostridia
8.5 Metabolic Engineering of
Escherichia coli
8.6 Microbial Strain
8.7 Butanol Tolerance Improvement Through Genetic Engineering
8.8 Economic Viability
8.9 Problems and Limitations of ABE Fermentation
8.10 Future Outlook
8.11 Conclusion
Acknowledgment
References
9 Advanced CRISPR/Cas-Based Genome Editing Tools for Biobutanol Production
9.1 Introduction
9.2 Microorganisms as the Primary Producer of Biobutanol
9.3 Acetone–Butanol–Ethanol Producing
Clostridia
and Its Limitations
9.4 CRISPR–Cas System for Genome Editing
9.5 Conclusion
References
10 Role of Nanotechnology in Biomass-Based Biobutanol Production
10.1 Introduction
10.2 Nanoparticles for Producing of Biofuel
10.3 Factors Affecting the Performance of Nanoparticles in Biofuel’s Manufacturing
10.4 Role of Nanomaterials in the Synthesis of Biofuels
10.5 Utilization of Nanomaterials in Biofuel Production
10.6 Nanotechnology in Bioethanol/Biobutanol Production
10.7 Future Perspective
10.8 Conclusion
Acknowledgment
References
11 Commercial Status and Future Scope of Biobutanol Production from Biomass
11.1 Introduction
11.2 Biobutanol—Its Brief Background Story
11.3 Commercial Aspect of Biobutanol Production from Biomass: Strength Analysis
11.4 Commercial Aspect of Biobutanol Production from Biomass: Weakness Analysis
11.5 Commercial Aspect of Biobutanol Production from Biomass: Opportunities and Challenges
11.6 Discussion: Evaluating the Future Prospects of Biobutanol
Acknowledgment
References
12 Current Status and Challenges of Biobutanol Production from Biomass
12.1 Introduction
12.2 Overview of Biofuel
12.3 Classification of Bioethanol
12.4 Production of Biobutanol
12.5 Conclusion
References
13 Biobutanol: A Promising Liquid Biofuel
13.1 Introduction
13.2 Biobutanol
13.3 Biorefinery and Biobutanol Production
13.4 Commercial Importance of Biobutanol
13.5 Conclusion
Abbreviations
References
Index
End User License Agreement
List of Tables
Chapter 1
Table 1.1 Genetically modified butanol-producing strains.
Table 1.2 Research on butanol fermentation using designed and modified substra...
Table 1.3 Examining the impact of temperature, pH, and other environmental fac...
Table 1.4 Investigating the effects of temperature, pH, and other environmenta...
Table 1.5 Using immobilised cells during continuous, high-density fermentation...
Table 1.6 ABE fermentation refers to the process of producing acetone, butanol...
Table 1.7 ABE fermentation with butanol elimination.
Chapter 2
Table 2.1 LCB composition from varying sources.
Table 2.2 Impact of LCB constitution and structure on recalcitrance.
Table 2.3 List of ILs used for LCB delignification.
Table 2.4 Lignin and cellulose solubility in various DESs..
Chapter 3
Table 3.1 Effect of different types of pre-treatment methodologies on hydrolys...
Chapter 4
Table 4.1 Comparison of fuel characteristics of different biofuel.
Table 4.2 List of commercial applications of biobutanol.
Table 4.3 Advantages and drawbacks of some butanol recovery methods.
Chapter 5
Table 5.1 Various raw materials used in acetone–butanol–ethanol fermentation [...
Table 5.2 Different mutagenesis experiments in organisms producing butanol.
Table 5.3 Various genes are concerned in the genetic engineering of clostridia...
Table 5.4 Butanol production from recombinant strains [64, 78, 80, 100].
Chapter 8
Table 8.1 Microbial species and substrate used for the production of butanol....
Chapter 9
Table 9.1 List of microorganisms that produce biobutanol in nature.
Table 9.2 CRISPR Cas9 systems for butanol production.
Table 9.3 List of different substrates for butanol production using geneticall...
Chapter 10
Table 10.1 Comparison of fuel properties for gasoline and alcohol-based fuel....
Chapter 12
Table 12.1 Historical events for production of acetone through ABE fermentatio...
Chapter 13
Table 13.1 Comparison between different generations of biofuels.
Table 13.2 Specifications of isomers of butanol with other fuels.
Table 13.3 Some companies involved in butanol production [13–16].
Table 13.4 Major feedstock, their composition and hydrolyzing bacteria.
Table 13.5 Characteristics of products obtained from ABE fermentation [95].
List of Illustrations
Chapter 1
Figure 1.1 The metabolic process of ABE-producing clostridia is depicted below...
Figure 1.2 Balance of mass and energy during the fermentation of wheat straw t...
Figure 1.3 During the fermentation process of making ABE from wheat straw, the...
Figure 1.4 Volume-based market shares of n-various butanol’s applications in 2...
Chapter 2
Figure 2.1 A schematic diagram of steps in biofuel production.
Figure 2.2 Overview of different LCB pre-treatment processes.
Chapter 3
Figure 3.1 Different techniques for physical, chemical and biological pre-trea...
Figure 3.2 Biomass based on Lignocellulosic materials are being classified as ...
Figure 3.3 Different pre-treatment methodologies opted for hydrolysis of cellu...
Figure 3.4 Downstream processing techniques for biosepration of ethanol and bu...
Chapter 4
Figure 4.1 A schematic illustration of the production of biofuel from biomass....
Figure 4.2 Metabolic pathways in ABE fermentation by
Clostridia
. In the yellow...
Figure 4.3 Challenges in biobutanol production.
Chapter 5
Figure 5.1 Improvement strategies for biobutanol production.
Figure 5.2 Overview of different strain improvement strategies.
Figure 5.3 Metabolic pathway of acetone–butanol–ethanol fermentation of
Clostr
...
Chapter 6
Figure 6.1 Route for the production of biobutanol.
Chapter 8
Figure 8.1 The schematic diagram represents the various processes for butanol ...
Figure 8.2 The schematic diagram represents the keto-acid route for the produc...
Figure 8.3 The schematic diagram represents the keto-acid route for the produc...
Figure 8.4 The schematic diagram represents the cell cycle of solvent forming ...
Figure 8.5 The schematic diagram represents the metabolic route in
Clostridium
...
Chapter 9
Figure 9.1 Schematic representation of the strategies used for improvement of ...
Figure 9.2 Outline of the pathways found in bacteria that are being utilized f...
Figure 9.3 Strategies for reducing off target effects by modifying Cas9. (a) I...
Chapter 10
Figure 10.1 Different nanocatalysts for biomass conversion.
Chapter 11
Figure 11.1 Different examples of biomass for bio-fuel production.
Figure 11.2 Simplified schematic of ABE fermentation pathway.
Figure 11.3 Transformation of different biomass to appropriate sugars that can...
Figure 11.4 Upstream processing of lignocellulose includes pre-treatment and d...
Figure 11.5 Advantages of biobutanol that adds to its future prospect.
Chapter 12
Figure 12.1 Production path of biobutanol from various generations of feedstoc...
Figure 12.2 Different steps for processing of biobutanol in industrial sectors...
Figure 12.3 Limitations and suggestions on the various stages involved in the ...
Chapter 13
Figure 13.1 Schematic representation of upstream and downstream processes invo...
Figure 13.2 Three types of polymers and their structures constituting lignocel...
Figure 13.3 Schematic representation for processes involved in the production ...
Figure 13.4 Applications of biobutanol.
Guide
Cover
Table of Contents
Series Page
Title Page
Copyright Page
Preface
Begin Reading
Index
End User License Agreement
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Scrivener Publishing100 Cummings Center, Suite 541JBeverly, MA 01915-6106
Publishers at ScrivenerMartin Scrivener ([email protected])Phillip Carmical ([email protected])
Production of Biobutanol from Biomass
Edited by
Arindam Kuila
Department of Bioscience & Biotechnology, Banasthali Vidyapith, India
and
Mainak Mukhopadhyay
Department of Biotechnology, Swami Vivekananda University, Kolkata, West Bengal, India
This edition first published 2024 by John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, USA and Scrivener Publishing LLC, 100 Cummings Center, Suite 541J, Beverly, MA 01915, USA© 2024 Scrivener Publishing LLCFor more information about Scrivener publications please visit www.scrivenerpublishing.com.
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Library of Congress Cataloging-in-Publication Data
ISBN 978-1-394-17239-9
Cover image: Pixabay.ComCover design by Russell Richardson
Preface
N-butanol is a bulk chemical that is used as an industrial solvent and as a component in paint, coating, and adhesives, among other things. When compared to other biofuels, biobutanol has the advantages of being immiscible in water, having a higher energy content, and having a lower vapor pressure. There are various benefits to producing biobutanol from lignocellulosic biomass. However, there are challenges in producing butanol from lignocellulosic biomass, such as biomass’s complex structure, low butanol yield, and high cost of production, etc. This book discusses all of these issues, as well as the current state and future prospects of lignocellulosic biobutanol production.
The 13 chapters herein discuss the current technology and future prospects of biobutanol production. The first four chapters provide an overview of the current technological status, while the next six chapters discuss different strategies for enhanced biobutanol production from lignocellulosic biomass. The last three chapters present the industrial status and techno-economic analysis of lignocellulosic biobutanol production.
This book is useful for students and researchers in the various branches of life sciences, including environmental biotechnology, bioprocess engineering, renewable energy, chemical engineering, nanotechnology, biotechnology, microbiology, etc.
We are grateful to Wiley and Scrivener Publishing, especially Linda Mohr and Martin Scrivener, for their cooperation and assistance in the timely publication of this book. We would like to express our gratitude to the writers and contributors for their efforts as well.
Dr. Arindam Kuila
Dr. Mainak Mukhopadhyay
1Biobutanol: An Overview
Bidisha Saha1, Debalina Bhattacharya2 and Mainak Mukhopadhyay3*
1Department of Biotechnology, JIS University, Kolkata, West Bengal, India
2Department of Microbiology, Maulana Azad College, Kolkata, West Bengal, India
3Department of Bioscience, JIS University Kolkata, West Bengal, India
Abstract
There is hope that butanol can help offset the decline in supplies of fossil fuelbased liquid fuels. When combined with liquid fuels, butanol can be utilized as a biofuel at any concentration. The majority of the fermentative organisms employed in biobutanol synthesis are clostridia. Acetone–butanol–ethanol (ABE) fermentation is a potential niche market for these organisms, as they can convert various forms of renewable biomass into butanol. When compared with other biofuels like ethanol, butanol has various advantages. Inefficient product inhibition and heterofermentation contribute to low productivity and yield, increasing production costs for ABE fermentation. High-yield butanol synthesis has thus far relied on the application of molecular biological approaches and fermentation engineering strategies. In order to convert agricultural waste into a usable feedstock for butanol manufacturing, scientists have recently been studying methods of pre-treatment and enzymatic saccharification. This article summarizes previous studies on the topic, covering topics such as metabolic profiles and traits of clostridia that produce ABE. The study also discusses the evolution of ABE fermentation in terms of the development of extremely effective butanol production processes, including batch, continuous cultures, fed-batch with the addition of butanol removal, and the development of butanol production from biomass resources or substitute substrates to sugars.
Keywords: ABE fermentation, biobutanol production, Clostridia sp., fermentation process, biofuel
1.1 Introduction
Increased demand for energy sources due to industrialization and motorization has been caused by the overconsumption of fuels in the form of petroleum based products as the energy source for operating a variety of engines. Fossil fuels currently account for 80% of all major energy sources used worldwide, with the transportation sector alone using about 58% of them. Although fossil fuels provide a reliable supply of energy for most of the world, they also play a significant role in the production of greenhouse gases (GHG), biodiversity loss, sea level rise, glacier retreat, and other problems. Alternative energy sources have drawn more and more attention globally as a result of anticipating the problems brought on by energy security, climatic changes, and rising raw material prices.
The shift to sustainable and environment renewable resources is essential to addressing the fuel scarcity, environmental considerations, and global warming. The usage of sustainable and renewable energy will become more prevalent in the future to meet the world’s energy needs and protect the environment for coming generations. Butanol is particularly intriguing among the renewable energy sources that could be used.
Butanol has some characteristics that render it suitable for use as a conventional diesel biofuel and as a biofuel for existing automobiles, including a high energy content and low pollution output. Additionally, Butanol is nonflammable and has a low vapour pressure, which makes it safe to handle and store [1]. In the chemical and cosmetics sectors, butanol is used as a solvent [2]. By fermenting sugars from biomass, such as algal biomass [3], cane molasses [4], cassava starch [5], cheese whey [6], corn stover [7], inulin [8], palm oil mill effluent [9], sugarcane bagasse (SCB) [10], and food waste, an alcohol known as biobutanol (or butyl alcohol) can be synthesized. Acetone–butanol– ethanol (ABE) fermentation is the common name for this process [11].
Traditional fermentation processes employed on an industrial scale in the 20th century include the employment of a clostridia strain to produce butanol from biomass via ABE fermentation. This procedure can be carried out using a variety of bacteria strains, with clostridia being the most popular option. The two unique steps of acidogenesis and solventogenesis define the metabolism of clostridia, stringent anaerobe bacteria. In the initial stage, known as acidogenesis, carbon dioxide, hydrogen, organic acids are the primary end products. The subsequent process, called “solventogenesis,” involves the reabsorption of the acids that were used in the formation of acetone, butanol, and ethanol (or isopropanol, which is produced by some strains of Clostridium beijerinckii in replacement of acetone). A drastic alteration in the gene expression profile is what drives the transition from the acidogenic to the solventogenesis phase [12, 13]. The fundamental issue with ABE fermentation is the solvent’s toxicity, which prevents clostridia from metabolizing ABE at concentrations of 20 g/L or higher. This inhibition restricts how effectively clostridia utilize the carbon sources throughout fermentation [14]. In addition, when created at a specific quantity during fermentation, butanol is poisonous for clostridia cells. Substrate cost, butanol output and productivity, and separation and purification expenses are the three key elements that define how economically viable ABE fermentation is in producing butanol.
1.2 General Aspects of Butanol Fermentation
1.2.1 Microbes That Produce Butanol, Both in Their Wild Type and After Genetic Modification
Wild type microorganisms; The main microbe utilized to produce butanol is clostridium. Among these, C. beijerinckii, Clostridium acetobutylicum are often and effectively employed in laboratory applications. A gram-positive, strictly anaerobic rod-shaped bacterium called clostridia produces butanol [12, 15, 16]. Clostridium spp. that produce ABE are capable of fermenting a wide variety of carbon sources, including fructose, galactose, glucose, glycerol, inulin, mannose, sucrose, xylose etc. [10, 17]. Feedstocks for fermentation production employing butanol-producing clostridia frequently consist of a combination of natural carbohydrates and sugars such as sweet sorghum [18], and a variety of agricultural [19, 20] and residential wastes [21, 22]. These cheap and inedible feedstocks could make butanol fermentation more profitable.
Genetically Modified microorganisms; Improving a microbe’s output is achieved mostly through adjusting metabolic activity in order to more efficiently collect the target products and generate fewer unwanted byproducts [22]. Improving butanol synthesis through genetic alteration of ABE-producing clostridia often involves the insertion of heterogeneous genes, the amplification of genetic alterations, or gene deletion and reduction. Overexpression of the expression cassette and thiolase genes led to a considerable increase in butanol synthesis (17.4 g/L) when Wang et al. (2017) [23] altered a critical gene in Clostridium saccharoperbutylacetonicum N1–4. Recently, improved butanol synthesis and protection against the “acid crash” were seen after overexpressing adhE2 and ctfAB in C. beijerinckiiCC101-SV6. Inhibitor product resistance and butanol concentration are both expressed in C. beijerinckii CC101-SV6 [10]. In addition, a number of metabolic pathways have been screwed with by the application of integrational plasmid technology [24]. Due of the intricacy of clostridia genes, researchers are now studying other species (such Escherichia) as suitable hosts for butanol-producing genes [25]. In order to prevent byproducts like pyruvate and butanoate while enhancing AdhE2 activity, highest butanol percentage (18.3 g/L) was achieved using metabolic engineering of Escherichia coli[26]. It was investigated whether metabolic engineering of C. acetobutylicum might transform acetone into isopropanol during ABE fermentation since isopropanol, as opposed to the acetone formed by C. acetobutylicum during ABE fermentation, and could be utilized as fuel [27]. That is why researchers endeavored to optimize the C. acetobutylicum DSM 792 strain [28]. Using genetically modified microorganisms to improve butanol fermentation is difficult, despite numerous experiments in the field [25]. These findings offer crucial guidelines for further investigation into strains that produce genetically engineered hyper butanol (Table 1.1).
1.3 Clostridium Species That Produce ABE and Their Respective Metabolic Characteristics
The clostridia that make ABE need both carbon and electrons to function biologically. The Emden–Meyerhof–Parnas (EMP) pathway transforms glucose into pyruvate. Two molecules of ATP are produced during glycolysis [29]. Carboxylic acid first forms, followed by the formation of pyruvate. The two distinct metabolic processes in clostridia that primarily result in the production of ABE are acidogenesis, in which a variety of organic acids are produced, and solventogenesis, in which solvents are polymerized while also recycling the derived organic acids. Both of these processes are accompanied by an increase in the pH of the surrounding environment that is fueled by acid consumption [30]. A rapid alteration in the patterns of gene expression causes the two phases to switch (Figure 1.1). Using energy produced during the acidogenesis phase by the synthesis of organic acids, primarily butyrate and acetate, which are formed from butyryl-CoA and acetyl-CoA, respectively, by CoA transferase or the inverse processes of each organic acid’s biosynthesis, the cells quickly enlarge while focusing on the flow of carbon. The pH of the culture broth is lowered by these organic acids. Something occurs as the cell growth nears a standstill phase. The decrease in organic acids causes the pH of the culture broth to increase. Finally, certain dehydrogenases would change acetyl-CoA to ethanol and butyryl-CoA to butanol. Ferredoxin, a protein that functions as an electron transporter, is crucial for measuring the electron flux. During the process of acidogenesis, which results in the production of hydrogen molecules, extra electrons are transferred from reduced ferredoxin to hydrogen atoms [31]. Solventogenesis, which results in an excess of nicotinamide adenine dinucleotide being generated and employed as a reduction in absorbance in the formation of ethanol and butanol, considerably slows down this process. In conclusion, both carbon and electron transport regulate the metabolism of clostridia that produce ABE.
Table 1.1 Genetically modified butanol-producing strains.
Strains
Substrate
Remark
The temperature and time parameters are as follows
Butanol concentration (g/l)
Total solvent concentration (g/l)
References
C. acetobutylicum
ATCC 824
Glucose
Expression of
adh
from
C. beijerinckii
NRRL B593
Fed-batch fermentation mode for 48 hours at 37°C with gas stripping
25.10
35.60
[27]
C. acetobutylicum
DSM 792
Batch fermentation mode for 210 hours at 37°C
10.80
18.00
[28]
C. beijerinckii
CC101
Glucose
Overexpressing
adhE2
and
ctfAB
Batch fermentation mode for 72 hours at 37°C with CaCO3.
12.00
No Data
[10]
C. pasteurianum
Glucose
hydA
,
rex
, and
dhaCBE
were removed out
Batch fermentation mode for 210 hours at 37°C
9.80
No Data
[90]
C. saccharoperbutylacetonicum
N1-4
Glucose
Increased levels of EC expression (
thl-hbd-crt-bcd
)
Batch fermentation mode for 72 hours at 30°C
17.40
30.60
[23]
Glucose
The
butR smr
gene was introduced to control
adhE and bdhA
expression.
Batch fermentation mode for 72 hours at 30°C
16.50
No Data
[91]
Sucrose
The impact of CCR was reduced after
scrR
was deleted.
Batch fermentation mode for 96 hours at 35°C
17.00
26.50
[92]
C. tyrobutyricum
Glucose
The
cat1
gene was switched out for the
adhE1/ adhE2
genes.
Batch fermentation mode for 72 hours at 20°C
26.20
35.10
[93]
Sucrose, sugarcane
ScrB, ScrA
, and
ScrK
Overexpression together along with adhesion to
adhE2
Batch fermentation mode for 6 days at 30°C
16.00
21.80
[94]
Figure 1.1 The metabolic process of ABE-producing clostridia is depicted below; the violet region explains the production of organic acids during acidogenesis, and the green region depicts the production of solvents during solventogenesis.
1.4 Traits of the Molecularly Developed Strain and the ABE-Producing Clostridia
Clostridium saccharoperbutylacetonicum N1-4 (ATCC 13564), C. acetobutylicum ATCC 824T, and C. beijerinckii NCIMB 8052 are the three main wild-type strains of the clostridia that produce the chemical and are frequently employed in studies on ABE fermentation [32–34]. These wildtype strains, among other characteristics, have a poor tolerance to butanol, a low yield, and a weak butanol titer. Mutagenesis and genetic engineering are two methods being researched to increase butanol output. The C. acetobutylicum strain’s genome was described by Nolling et al. in 2001 [35], which sparked interest in using genetic engineering methods on the strain. To boost butanol synthesis by 32% over the strain, Tomas et al.[36] induced the expression of the groESL operon beneath the thiolase promoter of clostridium to produce C. acetobutylicum ATCC 824 (pGROE1). N-methyl-N-nitro-N-nitrosoguanidine and specific enrichment on the glucose analogue 2-deoxyglucose were used by Annous et al.[37] to transform C. beijerinckii NCIMB 8052 into a C. beijerinckii BA101 strain that produces hyper butanol. The highest concentration of butanol (20.9 g/L) has been discovered to be produced by the BA101 strain [38]. To combat issues like butanol tolerance and inadequate butanol output, genetic engineering is now used.
1.5 Substrate for ABE Fermentation in Research
Due to glucose’s highly effective use by clostridia that produce ABE, it has been used frequently as a feedstock for ABE fermentation. Recent research has shown that even while amylases saccharify starch to glucose, starch can still be employed directly as a substrate for ABE fermentation [39, 40]. A favorable substrate, on the other hand, has been suggested for lignocellulosic biomass, which includes agricultural wastes like wheat and rice straw because of its abundance and inedibility [41]. Nevertheless, biomass that also contains cellulose and hemicellulose is where lignocellulose is found. Because of this, the ultimate product of saccharified lignocellulose would be a mixture of hexoses (such as glucose and fructose) and pentoses (such as xylose and arabinose), both of which are fermentable sugars. In order to establish a highly effective butanol synthesis method using heterogeneous sugars as substrates, current research into ABE fermentation is described in Sections 1.8 and 1.10.
1.6 Problem and Limitation of ABE Fermentation
The following issues arise in typical batch ABE fermentation and limit the industrial use of butanol as a fuel substitute for fossil fuels [41, 42]:
Reduced butanol concentration levels (nearby 20 g/L) due to butanol feedback inhibition;
Minimal butanol yields (nearby 0.35 g/g) due to hetero fermentation;
Low volumetric butanol efficiency (nearby 0.5 g/L/h) due to cell reduced titre;
Massive price of butanol recovery (traditional distillation is energy required);
The few occurrences of ABE fermentation using lignocellulosic biomass as the fermentative substrate come through after-enzymatic saccharification, even though the majority of clostridia that produce ABE are unable to use lignocellulose directly [33, 43, 44]. Despite being a practical method for turning lignocellulosic biomass into fermentable sugars, enzymatic saccharification still faces challenges due to the high cost of the various enzymes, such as cellulases and hemicellulases, used in the process. The efficient utilization of lignocelluloses as a feedstock for ABE fermentation requires the development of fermentative techniques and less expensive substrate conversion. To overcome these difficulties, the researchers focused on creating fermentation technology for butanol production as well as genetically engineered metabolic butanol production from planned and modified biomass.
1.7 The Development of Butanol from Designed and Modifying Biomass
Biomass with cosubstrates like acid compounds and other low-cost products generated during hydrolysis is called “designed biomass.” With this modified biomass, butanol production increases while fermentation expenses decrease. Hence, during the process of being developed, utilizing acetic acid as the cosubstrate with glucose promotes metabolic efficiency and enhances solvents generation [24]. The addition of acetic acid greatly increases butanol and ABE synthesis, as discovered by Gao et al. (2016) [45]. When lactic acid was included in the specified biomass, C. saccharoperbutylacetonicum N1-4 was capable of producing butanol [46, 47]. Table 1.2 compiles the results of several research projects into butanol synthesis from engineered biomass.
Table 1.2 Research on butanol fermentation using designed and modified substrates.
Strains
Substrates
The temperature and time parameters are as follows
Butanol concentration (g/l)
Total solvent concentration (g/l)
Ref
Clostridium saccharoperbutylacetonicum
N1-4
Glucose & acetic acid
pH stat batch fermentation mode for 48 hours at 30°C
15.13
24.37
[45]
Fed-batch fermentation mode for 72 hours at 30°C
13.90
No Data
[11]
Glucose & butyric acid
Batch fermentation mode for 120 hours at 30°C
17.76
23.51
[
95
,
96
]
Batch fermentation mode at 30°C
13.00
15.40
[97]
Glucose & lactic acid
pH stat batch fermentation mode for 48 hours at 30°C
15.50
19.90
[46]
Pentose & lactic acid
Fed-batch fermentation mode for 72 hours at 30°C
15.60
19.33
[47]
1.8 Butanol Production Enhancement Using Advanced Technology
Many studies have concentrated on increasing concentration, productivity, and yield while using various culture methods and environmental conditions, including batch fermentation, continuous fermentation, fed-batch fermentation and butanol production processes combined with butanol recovery. The production of butanol in batch, continuous culture, fed-batch modes while utilizing integrated butanol recovery processes has been the main emphasis of this section.
1.8.1 Batch Fermentation
Since batch culture is the most straightforward of the three culture types, it has undergone extensive research for a number of factors, including pH regulation, the ratio of carbon to nitrogen sources (C/N ratio), partial pressures of hydrogen or carbon monoxide in the fermenter headspace, and the addition of electron carriers (Table 1.3). At comparatively more and less pH, C. acetobutylicum and C. beijerinckii played a crucial role in acidogenesis and solventogenesis, respectively. The C. acetobutylicum ATCC 824T strain produced just 1 g/L of ABE while producing nearly 20 g/L of total organic acids at a pH of 6.0. The organism produced around 17 g/L of ABE while only 3 g/L of total organic acids were synthesized at a pH of 4.5.
On the other hand, it has been thought that the partial pressure of CO and H2 in the fermentor headspace, along with the introduction of electron carriers, might significantly alter the electron flow. In batch cultures of C. acetobutylicum ATCC 824T [48], C. acetobutylicum ATCC 4295 [49], and C. saccharoperbutylacetonicum ATCC 27021 [50] increasing the pressure of CO or H2 in the fermentor headspace enhanced the butanol yield, sometimes with lower yields of acetone or acids. This is because carbon monoxide (CO) and hydrogen (H2) have been implicated as hydrogenase inhibitors that produce excess electron evolution. Besides, it has been demonstrated that a number of electron carriers, including methylene blue and methyl viologen (MV), work as reducing agents for clostridia that make ABE and boost ABE production and yields. Previous research indicated that MV shifted metabolic flow away from acetone production and towards butanol production, indicating that the extra reducing power supplied may be used to produce butanol. Transcriptome explanation of batch fermentation by C. acetobutylicum ATCC 824T with 1 mM MV showed that MV might decrease the expression of the sol operon, which includes ctfAB (encoding CoA transferase), adhE1 (encoding aldehyde/alcohol dehydrogenase), adc (encoding acetoacetate decarboxylase), whereas The expression of adhE2 (encoding aldehyde/alcohol dehydrogenase) was increased by more than a factor of 100 during MV-supplemented batch fermentation [51, 52].
Table 1.3 Examining the impact of temperature, pH, and other environmental factors on solventogenic and acidogenic acetone-butanol-ethanol (ABE) fermentation in batch cultures.
Strains
Factors
Substrate
pH
Conditions
Trait
Ref
Clostridium acetobutylicum
ATCC 824T
Addition of methyl viologen (MV)
Glucose
5.0
When MV is not supplied
Minimal butanol yield (0.41mol/mol)
[98]
When 1mM MV is added
Maximum butanol production (0.58mol/mol)
When MV is not supplied
The presence of a significant amount of acetic acid (73mM)Minimal butanol concentration (<110mM)
[51]
When 1mM MV is added after 7.5h
Concentrations of acetic acid that are not too high (<16mM)Maximum butanol concentration (150mM)
Addition of methylene blue (MB)
-
When MB is not added
Minimal concentrations of ABE (13.4g/l)
[99]
When 4g/l MB is added
Maximum concentrations of ABE (23.1g/l)
Carbon : Nitrogen (C/N Ratio)
-
With a molar ratio of ammonium to glucose of 0.16, the C/N ratio is 6.25.
Maximum yield of ABE (0.545 mol/mol)Minimal acid yield (0.550mol/mol)
[100]
With a molar ratio of ammonium to glucose of 1.52, the C/N ratio is 0.658.
Minimal yield of ABE (0.211 mol/mol)Maximum acid yield (0.884 mol/mol)
Hydrogen challenge
-
With Hydrogen challenge at 274–1479 kPa
Maximum yield of acetic acid (0.168 C-mol/C-mol)Minimal yield of butanol (0.298 C-mol/C-mol)
[48]
Without Hydrogen challenge
Maximum yield of butanol (0.345-0.361 C-mol/C-mol)Minimal yield of acetic acid (0.091-0.130 C-mol/C-mol)
Clostridium acetobutylicum
ATCC 824T
pH
Glucose
4.5
-
High concentration of ABE (17 g/L)Low concentration of acid (<3g/l)
[101]
6.0
-
High concentration of acid(17 g/L)Low concentration of ABE (<3g/l)
Clostridium beijerinckii
NCIMB 8052
Lactose
5.0
-
High concentration of ABE (5.1 g/L)Low concentration of acid (3.4g/l)
[102]
7.0
High concentration of acid (6.3g/L)Low concentration of ABE (0.075g/l)
Batch cultures have been demonstrated to benefit from a variety of crucial properties, such as low pH, a reasonable C/N ratio, an increase in CO and H2 partial pressures, and the presence of electron carriers, as indicated in the opening sentence of article. Three problems continue to limit the amount of butanol that can be produced and how productively it can be produced in batch cultures: substrate inhibition [53, 54], carbon catabolite repression (CCR) of consumption of less preferred sugars caused by a more preferred sugar, and product inhibition by acquired butanol at preliminary good level [55].
1.8.2 Fed-Batch Fermentation
Benefits of fed-batch cultures over batch cultures include the removal of substrate inhibition due to factors like large initial intensity, nutrient supplementation during fermentation, the use of elevated substrates (such as starch), and the avoidance of CCR due to the use of further preferable sugars (such as glucose).To take advantage of these benefits, a number of fed-batch cultures have been developed for ABE fermentation.
Sugars like glucose and xylose usually present in higher concentrations to cause substrate inhibition, result in a prolonged lag phase and decreased butanol production [53, 54]. The ideal sugar concentration is normally between 50g/L and 60g/L, even though a butanol concentration of more than 10g/L generated may stop cell proliferation, sugar ingestion, and further butanol production. This prompted in-depth study of fed-batch cultures for the generation of butanol, which led to the invention of fresh methods for butanol recovery to prevent substrate inhibition and for sugars and other nutrients to release butanol inhibition, as mentioned in Section 1.8.4. However, a number of organic acids, including acetic acid [56], butyric acid [57], and lactic acid [58, 59], as well as cosubstrates like glucose or arabinose, are feasible substrates for butanol synthesis when taking into account the reutilization pathways used by ABE-producing clostridia. However, it has been shown that high concentrations of these organic acids at pH values of 4.76, 4.82, and 3.79, respectively, result in substrate inhibition. The pH-stat is helpful because it enables continuous management of the levels of organic acids in the broth by only measuring the pH. The C. saccharoperbutylacetonicum N1-4 (ATCC 13564) strain was able to produce approximately 16 g/L of butanol by converting butyric acid [57] or lactic acid [58] to butanol in a fed-batch growth method.
Batch ABE fermentation of the C. acetobutylicum ATCC 824T strain is reported to exhibit CCR of xylose intake (a less preferred sugar) when more than 15 g/L glucose (a higher preferred sugar) is present [55]. For their study, Fond et al. used a fed-batch culture in which the C. acetobutylicum ATCC 824T strain was provided 15 g of glucose and xylose per day at a consistent rate. While simultaneously producing 12 g/L butanol, this fed-batch culture was able to consume carbohydrates at concentrations of less than 0.1 g/L glucose and 0.7 g/L xylose [60]. Many fed-batch cultures, as detailed in the preceding and following paragraph, can increase butanol synthesis by utilizing organic acids and emitting CCR to prevent substrate inhibition. Moreover, fed-batch culture using butanol recovery techniques has been found to be more effective than fed-batch culture without them for butanol production.
1.8.3 Continuous Fermentation
The disadvantage of butanol inhibition can be mitigated by diluted butanol in the broth with fresh medium in a continuous culture system, making the process more conducive to high butanol production. Continuous culture is preferable than batch and fed-batch cultures in terms of operational stability, even if the butanol concentration in continuous culture should be lower than those in those two types of cultures. As a result, much effort is put into researching continuous cultures in order to build a highly productive butanol manufacturing process.
It is not uncommon for a continuous-chemostat culture to reach a steady state after three or more medium changes, with respect to cell, substrate, and product concentrations in the broth. Some of the variables that have been studied in relation to ABE fermentation in continuous-chemostat cultures include: CO challenge, dilution rate, electron carriers, nutrients, pH, substrate concentration (Table 1.4). High butanol productivity highly depends on pH regulation. Continuous cultures of C. acetobutylicum using glucose as the feedstock showed metabolic flows towards butanol formation and acid generation at pH ranging from as 4.3 to 6.0 [61, 62]. However, C. beijerinckii and C. saccharoperbutylacetonicum from glucose and xylose respectively [63, 64], generated 0.34 g/L/h and 0.529 g/L/h of butanol at moderate pH values of 5.5 and 5.6, and 0.14 g/L/h and 0.199 g/L/h of butanol at low pH values of 5.0 and 4.6. Additionally, it has been observed that employing C. acetobutylicum and C. beijerinckii, CO challenge, yeast extract, ρ-aminobenzoic acid, NH4Cl, and greater glucose concentrations can boost butanol or ABE productivity from glucose [62, 63, 65, 66].
Table 1.4 Investigating the effects of temperature, pH, and other environmental factors on solventogenic and acidogenic continuous cultures of acetone-butanol-ethanol (ABE) fermentation.
Strains
Factors
Substrates
D/h
pH control
Other conditions
Traits
Ref.
C. acetobutylicum
ATCC 824T
Dilution rate
Glucose (40g/L)
0.06
4.8
-
Productivity of ABE is high (0.75 g/L/h)Productivity of acid is low (0.15 g/L/h)
[118]
0.1
Productivity of ABE is low (0.194 g/L/h)Productivity of acid is high (0.29 g/L/h)
Addition of yeast extract, CO challenge, Glucose concentration, Dilution rate, pH
Glucose (44 mM)
0.25
4.5
Without CO challenge
Productivity of Butyric acid and acetic acid are high (0.626g/L/h), (0.290g/L/h).Productivity of butanol and acetone are low (0.0853g/L/h), (0.0231g/L/h).
[119]
With CO challenge
Productivity of butanol is high (0.211g/L/h)Productivity of Butyric acid, acetic acid, acetone are low (0.147 g/L/h), (0.138g/L/h), (0.146g/L/h).
Glucose (139 mM)
0.125
Without CO challenge
Productivity of butanol and acetic acid are high (0.341 g/L/h), (0.0529g/L/h).Productivity of Butyric acid and acetic acid are low (0.229g/L/h), (0.202g/L/h).
Glucose (139 mM)
0.25
4.5
Without CO challenge, With 5 g/L yeast extract
Productivity of butanol, butyric acid, acetic acid and acetone are high (0.514g/L/h), (0.667g/L/h).(0.537g/L/h), (0.143g/L/h).
6.0
Without CO challenge
Productivity of Butyric acid and acetic acid are high (1.54g/L/h), (0.738g/L/h).Productivity of butanol, acetic acid, acetone are low (0.09 g/L/h), (0g/L/h)
Glucose (44 mM
Productivity of butanol, butyric acid, acetic acid and acetone are low (0g/L/h), (0.601g/L/h).(0.201g/L/h), (0g/L/h).
C. acetobutylicum
ATCC 824T
Addition of ρ-aminobenzoic acid in synthetic medium
Glucose (51.7 g/L)
0.28
4.4
No ρ-aminobenzoic acid
Productivity of ABE and cell concentration is low (0.09g/L/h), (0.32g/L/h)
[65]
8.0 g/L ρ-aminobenzoic acid
Productivity of ABE and cell concentration is high (1.89 g/L/h), (2.07g/L/h)
Clostridium beijerinckii
NCIMB 8052
pH,Dilution rate
Glucose (50 g/L)
0.0610
5.0
-
Productivity of Butyric acid and acetic acid are high (0.091/L/h), (0.12 g/L/h).Productivity of butanol, and acetone are low (0.14 g/L/h), (0.058g/L/h)
[120]
0.0610
5.5
Productivity of butanol, and acetone are high (0.34 g/L/h), (0.16g/L/h)Productivity of Butyric acid and acetic acid are low (0.059/L/h), (0.082 g/L/h).
0.158
5.5
Productivity of butanol, butyric acid, acetic acid and acetone are high (0.35 g/L/h), (0.10 g/L/h).(0.249g/L/h), (0.14g/L/h).
Xylose (50 g/L)
0.20
Productivity of butanol is low (0.272g/L/h)
Clostridium beijerinckii
NCIMB 8052
NH4Cl concentration
Glucose (20 g/L)
0.06
5.5
0.24 g/L NH4Cl
Productivity of Butyric acid is high (0.352g/L/h)Productivity of butanol and acetic acid are low (0.031/L/h), (0.0013 g/L/h).
[120]
0.72 g/L NH4Cl
Productivity of butanol and acetic acid are high (0.085/L/h), (0.0097 g/L/h).Productivity of Butyric acid is low (0.158g/L/h)
Continuous cultures with high concentrations of cells have been produced as a means of overcoming the major problem of low cell concentration in chemostat cultures. The enhanced butanol productivity, reduced reactor sizes, and accessibility of medium made for production rather than growth are some advantages of this approach. Cell immobilization on a variety of carriers (Table 1.5) and membrane-based cell recycling (Table 1.6) are two techniques claimed to increase cell density for butanol synthesis and cell recycling using membranes. Several carriers, including brick, calcium alginate, and κcarrageenan, have been explored for their potential to immobilize cells. C. beijerinckii BA101 has the highest ABE production at 16.2 g/L/h and can work at a high dilution rate of up to 2/h when utilizing brick as the carrier. Nevertheless, ultrafiltration and microfiltration membranes can execute cell recycling at dilution rates greater than 0.3/h (Table 1.4). Tashiro et al. concentrated 4 L of the broth to 0.4 L, and therefore reached a high cell concentration of 20 g/L in only 12 h, despite the fact that this is typically a time-consuming process [67]. It has also been demonstrated that cell-bleeding technique at dilution rates of 0.11 to 0.16/h maintains a consistent cell concentration in the fermentor, providing greater operating stability (207 h) than typical (48 h) without any cell bleeding. With a total dilution rate of 0.85/h, including 0.11 to 0.16/h for cell bleeding, C. saccharoperbutylacetonicum N1-4 (ATCC 13564) obtained the highest ABE productivity to date, 7.55 g/L/h [67]. However, in batch, fed-batch, and continuous cultures, a high butanol concentration should impede cell growth and butanol synthesis. To successfully produce higher quantities of butanol, as detailed in Section 1.8.4, it is therefore important to research both fermentation technology and butanol removal methods.
Table 1.5 Using immobilised cells during continuous, high-density fermentation of acetone, butanol, and ethanol (ABE).
Carrier
Strain
Dilution rate/h
ABE productivity (g/L/h)
Ref.
Brick
Clostridium beijerinckii
BA101
2
15.8
[103]
Clostridium acetobutylicum
BCRC10639
0.054
0.48
[104]
Bonechar
Clostridium saccharobutylicum
NCP 262T
1
4.1
[105]
Ca-alginate
Clostridium saccharobutylicum
spoA2
0.196
3.02
[106]
Clostridium acetobutylicum
DSM 792
1.02
4.02
[107]
Coke
Clostridium acetobutylicum
ATCC 824T
0.1
1.12
[108]
Fibrous bed
Clostridium acetobutylicum
ATCC 55025
0.6
4.6
[109]
Sponge segments
Clostridium acetobutylicum
ATCC 824T
0.272
4.2
[110]
Table 1.6 ABE fermentation refers to the process of producing acetone, butanol, and ethanol in a continuous, high-density culture by recycling the cells.
Membrane
Strain
Dilution rate of cell (recycling)
Dilution rate of cell (bleeding)
ABE productivity (g/L/h)
Ref.
Microfiltration membrane
Clostridium acetobutylicum
ATCC 824T
0.64
-
5.4
[111]
Clostridium saccharobutylicum
NCP 262T
0.39
0.02
4.06
[112]
Clostridium saccharoperbutylacetonicum
N1–4 (ATCC 13564)
0.71
0.11, 0.14, 0.16
7.55
[67]
Ultrafiltration membrane
Clostridium acetobutylicum
ATCC 824T
0.44
0.065
6.5
[113]
Clostridium saccharobutylicum
NCP 262T
0.4
-
4.1
[114]
1.8.4 ABE Fermentation with Butanol Elimination
Pervaporation, gas stripping, liquid–liquid extraction, and liquid–membrane extraction are a few techniques for separating butanol (Table 1.7). Also, it has been shown that fed-batch fermentation, when compared to batch cultures, is substantially more successful at increasing butanol synthesis. Pervaporation is the act of regaining and gathering a volatile substance that has been selectively separated across a membrane under less pressure. By using fed-batch culture along with pervaporation as opposed to conventional batch culture (12.8 g/L), Qureshi et al. were able to produce higher butanol percentages (105 g/L) [68]. However, the cells and culture broth had to be separated because pervaporation demands a higher temperature than fermentation. Liu, however, was able to do fed-batch cultivation with in situ pervaporation at 37 degrees Celsius using a polydimethyl polyxan-ceramic membrane [69]. Moreover, the process of “gas stripping” uses aeration to transform components from the liquid phase into the gas phase. When fed-batch culture was employed in conjunction with gas stripping as opposed to batch culture (18.6 g/L), butanol production was increased by Ezeji et al. (81.3 g/L) [70]. Moreover, Grobben reported a butanol concentration of 27 g/L and a yield of 0.32 g/g in his fed-batch culture studies employing liquid–membrane extraction with methyl fatty acid [71]. Researchers also developed methods for avoiding butanol feedback inhibition through the use of different extraction techniques for high titer and pure butanol production.
Table 1.7 ABE fermentation with butanol elimination.
Strains
Elimination method
ABE
Butanol
Ref.
Concentration g/L
Productivity g/L/h
Yields g/g
Concentration g/L
Productivity g/L/h
Yields g/g
Clostridium acetobutylicum
ATCC 824T
Pervaporation
155
0.18
0.348
105
0.121
0.237
[68]
Clostridium acetobutylicum
JB200
Gas stripping
109
0.41
0.32
76.4
0.29
0.23
[44]
Clostridium beijerinckii
BA101
Pervaporation
51.5
0.69
0.42
No Data
No Data
No Data
[115]
Gas stripping
81.3
0.593
0.360
56.2
0.410
0.249
[70]
Clostridium saccharoperbutylacetonicum
N1–4 (ATCC 13564)
Liquid–liquid extraction
29. 8
0.784
0.400
20.9
0.55
0.281
[116]
Liquid membrane
No Data
No Data
No Data
20.1
0.394
0.234
[117]
1.9 Utilizing Pre-Treatment and Saccharification to Produce Butanol from Lignocellulosic Biomass
Global environmental problems and unexpected increases in fuel price are direct results of widespread usage of fossil fuels in both developing and industrialized nations [72]. The America and Brasil have increased their use of biodiesel made from food biomasses like sugarcane, corn as a response to this [73]. But this has contributed to a scarcity of agricultural supplies, driving up the cost of food. Thus, there is a lot of interest in developing methods to create biofuels from nonfood sources such lignocellulosic materials. The higher order crystal structure of the cellulose and hemicellulose that make up lignocellulosic biomass makes it challenging for the most common strains employed in biofuel production to directly consume it [74]. To get fermentable sugars out of lignocellulosic biomass, various preprocessing and saccharification processes have been devised. Physical, chemical, and biological methods are the primary categories of lignocellulosic biomass utilization processes. Steam explosion [75] is one example of a physical method, while concentrated sulphuric acid and alkaline treatment [76, 77] are the most common chemical methods. However, cellulase and hemicellulase are just two of the enzymes used in the biological perspective. Despite its imperfections (such as fuel consumption, hazardous wastes, and expensive demand), these methods are necessary for the effective exploitation of lignocellulosic biomasses and will be further developed.
1.10 Eliminating CCR to Produce Butanol
The processing and saccharification of lignocellulosic materials release various amounts of fermentable sugars, such as arabinose, glucose, and xylose. Yet, when bacteria are cultured in a solution containing glucose and other carbs, glucose inhibits the catabolism of the bacteria. Glucose causes the Carbon Catabolite Repression (CCR) phenomenon, which limits the microorganism’s utilization of other sugars and results in inefficient ABE fermentation. This behavior has been linked to ABE-producing clostridia as well as other bacteria and yeast [78]. Metabolic engineering, mixed culture, using an ABE-producing strain in a mixed sugar fermentation system with the addition of exogenous trace elements, and using a semihydrolysis method for lignocellulosic biomass have all been investigated and shown to be efficient ways to get around this restriction [79]. Recently, single and dual strains were metabolically engineered to consume glucose and glycerol simultaneously, and both cultures thrived when using this sugar combination. To create up to 6 g/L of butanol, the single strain in particular used all of the glycerol and glucose available [80]. Bruder et al. (2015) [81] recommended employing both glucose and xylose at the same time to get around CCR’s inhibitory effects; a modified C. acetobutylicum utilized 30% of the xylose. Following 48 hours of fermentation, glucose enabled the production of C. aacetobutylicum, which had a 7.5-fold higher yield than the strain’s wild counterpart. With moderate zinc treatment, it may be possible to increase ABE fermentation from xylose/glucose sugar combinations. Wu et al.’s use of xylose and glucose resulted in 11.5 g/L of butanol at a specific xylose consumption rate of 0.3 g g-DCW/h [82]. Noguchi et al. (2013) [83] fermented mixed sugars (xylose/cellobiose) without CCR and produced significant amounts of butanol (16 g/L) and ABE (23 g/L) using C. saccharoperbutylacetonicum N1-4. After 72 hours of fermentation, the productivity of xylose and cellobiose increased by 1.9 and 1.8 g/L/h, respectively. As was previously mentioned, semihydrolysis of lignocellulosic biomass can stop CCR. Zhao et al. (2018) [79] created a semihydrolysate with minimum enzyme loading using pre-treatment rice straw and H2SO4 to minimize CCR and increase butanol fermentation efficiency. In addition, the output of butanol increased from 0.0628 to 0.265 g/L/h.
1.11 Butanol Production from Alternative Substrate to Sugar
Using ABE-producing clostridia, no one has yet impact on daily ABE fermentation from lignocellulosic biomass before even treating it to processing and saccharification methods. We are currently looking at various substrates for ABE fermentation that can be derived from lignocellulosic biomass through other fermentation methods including lactate fermentation [58, 59]. While dl-lactic acid cannot be used as feedstock for poly-lactic acid, Oshiro et al.[58] used pH stat fed-batch culture to efficiently utilize lactate with sugar as the cosubstrate, resulting in high butanol synthesis (15.5 g/L). Besides that, Yoshida et al. studied at arabinose as such cosubstrate in replacement of glucose and gained immense butanol synthesis (15.6 g/L) without using a pH controller [59]. Utilizing various substrates will become a major aspect of any approach for optimizing lignocellulosic biomass and establishing biorefinery-based civilizations.
1.12 Economics of Biobutanol
Manufacturing on a broad scale of biobutanol is hindered by factors such as the low butanol fermentation yield and the common citizenry’s lack of knowledge about the benefits of biobutanol [84]. Since the productivity level of biobutanol via ABE fermentation from biomass is still questionable in comparison to the petrochemical route, its branding and contribution to the biofuel industry are constrained. This ambiguity is caused by the multiple sugar types present in the biomass, the poor performance of infomercial microbes in regards to the biobutanol, and the ineffectiveness of current separation techniques. Research on wheat straw, hydrolysate distiller’s dried grains with solubles (DDGS), C. beijerinki BA101, and C. acetobutylicum P260 indicates that industrial synthesis of biobutanol from agricultural residues is conceivable [85].
On the other hand, the economy of the ABE fermentation process is closely related to the mass and energy balance [86]. The mass and energy balance of ABE fermentation using wheat straw is shown in Figure 1.2[87]. The investigation on ABE fermentation was carried out using Life Cycle Inventory (LCI) data sets that were located in Ecoinvent. To produce biobutanol efficiently and economically on a large scale, significant advancements in microbial culture, fermentation, and waste feedstock are needed. As a result, a large number of research institutions linked to global corporations are continuously looking for solutions to these issues. Extensive research and development activities in England, France, China, Switzerland, and the United States have led to technological advances in the production pathways of biobutanol from residual crops, such as cereal straws. China (45%) and North America (23%), which are shown to have the highest production and consumption rates of butanol, respectively, in Figure 1.3. There are currently reports of some technoeconomic study on the production of butanol from biomass. According to Okoli and Adams (2014) [88], the minimum butanol selling price (MBSP) of biobutanol production from lignocellulosic bio material across the thermochemical range is between $0.55 and $1.17/L, which puts it in the same price range as ABE butanol ($0.59 to $1.05/L) and petrol ($0.82 to Lbeq). From a financial perspective, fermenting cornflour to produce biobutanol only makes sense if the resulting n-biobutanol can be sold as a premium commodity. With a final MBSP of $1.58/L, ABE fermentation using 2-ethyl-hexanol as an extractant may be the most cost-effective alternative [89].
Figure 1.2 Balance of mass and energy during the fermentation of wheat straw to produce ABE.
Figure 1.3 During the fermentation process of making ABE from wheat straw, the mass and energy balance are monitored.
Requirement for n-butanol as a, chemical intermediary, coating, solvent, for butyl acetate, ethers, and other compounds is increasing rapidly because of its widespread application in the construction sector. The manufacturing and construction industries are the largest consumers of n-butanol due to its use in a variety of products such paints and coatings, lubricants, varnishes. Increased demand for paints and coatings is expected to drive growth in the n-butanol market over the next few years, as building and infrastructure projects continue to mushroom around the world. By 2032, analysts predict that the worldwide n-butanol market will have expanded to 82,000 metric tons (Figure 1.4).
When broken down by geography, it’s clear that Asia Pacific is where n-butanol really shines. This area accounted for over 35% of worldwide n-butanol consumption in 2021. Construction activity in fast developing nations like India, China, and Japan will increase, generating a slew of new industrial projects that in turn will drive up demand for paints and coatings for use in the region’s buildings and other infrastructure, driving up prices for n-butanol.
Figure 1.4 Volume-based market shares of n-various butanol’s applications in 2021 and 2032.
The global n-butanol market is divided into several submarkets based on application: solvent, plasticizer, coating, and others. In 2021, the Solvent sector alone will account for almost 40% of the global n-butanol market. N-butyl acetate, made from n-butanol, is a clear solvent that works well with a wide variety of materials, including cellulose nitrate, hydrocarbons, plastics, polymers. The chemical, ink, leather, paint industries all use it. N-butyl acrylate, another derivative of n-butanol, is utilized in a broad variety of industries, including the coatings industry, to increase low-temperature and chemical resistance. It is also found in adhesives, fiber, inks paints, paper, rubber, textiles.
OQ Chemicals, Formosa Plastics Corporation, Sasol Limited, INEOS Group Limited, The Dow Chemical Company, BASF SE, Yancon Cathay Coal Chemicals Co. Ltd., Lihuayi Weiyuan Chemical Co. Ltd., Eastman Chemical Company etc are among the world’s largest manufacturers of n-butanol.
1.13 Future Prospects
Biobutanol is a second-generation alcoholic fuel used in the biofuel industry that has reduced volatility and a higher energy density than ethanol. The commercial development of biobutanol is the primary objective of numerous businesses. The food supply is unaffected by biobutanol, a new form of biofuel that can compete with oil. Advanced technologies are being made to improve the glucose extraction, energy outputs, and sugar mixture fermentation of lignocellulosic biomass on a widespread scale. Although there has been a lot of research on fermenting lignocellulosic biomass to produce butanol, this process is still hindered by the necessity of a pre-treatment step. Biorefineries, unlike oil refineries, will need to process a wider variety of raw materials, necessitating the use of numerous pre-treatment processes. However, lignocellulosic biomass hinders biodegradation due to its stiff and complicated structure and variable chemical composition, while agricultural biomass as substrate (e.g., cornflour) has proven technology to manufacture these large value byproducts. Nonlignocellulosic biomass, such food waste, should be the subject of research since it contains a lot of starch, which clostridia can readily devour to make butanol. Furthermore, because starchy food waste was already gelatinized during cooking, it does not require pre-treatment with gelatinization to dissolve the intermolecular bonds of starch molecules. Another strategy is to use “designed biomass” as the butanol synthesis substrate. This sort of modified biomass increases butanol production while decreasing the cost of the fermentation process since it uses cosubstituents that are less expensive, including acid compounds.
The need for fuel is growing, which has stoked researchers’ interest in discovering alternative, sustainable, and renewable energy sources. By utilizing renewable feedstock, petrol that is both commercially feasible and environmentally responsible can be distributed throughout the world. The promising renewable biofuel biobutanol could replace nonrenewable fossil fuels for both present and future generations.
