Butanol Fermentation Process

In the traditional AB fermentation process for butanol production, the cell density in a batch reactor is limited to no more than 4gl−1 (DCW), which is an important reason for the low productivity.

From: Comprehensive Biotechnology (Second Edition) , 2011

Integrated industrial lignocellulose biorefinery chains

Hongzhang Chen , in Lignocellulose Biorefinery Engineering, 2015

7.2.1.3 An industrial production line for straw refining with a capacity of 300,000 tons/year

A 300,000 tons/year industrial production line for straw refining was established in September 2010 by Songyuan Laihe Chemical Co. Ltd in Jilin Province, China. Songyuan Laihe Chemical Co. Ltd is a private enterprise in China focused on the research and utilization of agricultural wastes. Since 2007, the company began technical cooperation with the Institute of Process Engineering, Chinese Academy of Sciences. They established a demonstration project for the fermentation of straw hemicellulose to produce butanol and its utilization technology. In this project, a pilot plant of 600 tons/year was approved following expert appraisal in October 2009, with the claim that the entire technology and equipment represented an international advance. The demonstration project, based on the structural properties of the materials, involved the multilevel conversion of cellulose, the fermentation of hemicelluloses for butanol production, and the high-value utilization of lignin. The process route is shown in Figure 7.2. The technical characteristic of the route is the maximum utilization of cellulose and hemicelluloses of corn stalks for butanol fermentation, in order to improve the utilization of straw as a fermentation substrate. After grading of fibers, short fibers can be used as fermentation substrate or can be liquefied to prepare polyether polyol and polyurethane, and long fibers can be used in the preparation of microcrystalline cellulose and dissolving pulp, increasing the added value of the straw fiber products. After alkaline extraction, the lignin obtained may be used as a raw material for carbon fiber, phenol resin, and other high-end products. The major types of products are shown in Figure 7.3.

Figure 7.2. Straw biorefining industrial production route.

Figure 7.3. Product of the straw biorefining.

The butanol fermentation process of hemicelluloses and the comprehensive utilization of cellulose and lignin is shown in Figure 7.4 and is described as follows:

Figure 7.4. Process flow diagram of butanol production by corn straw hemicellulose fermentation and comprehensive utilization of cellulose and lignin.
1.

Pretreatment process. After steam explosion, the corn stalks were put into the hydrolysis tank, and then 0.3–0.5% of the dilute sulfuric acid was added with the solid-to-liquid ratio controlled at 1:5 to 1:7. Then materials were hydrolyzed at 110–120   °C for 0.5–1   h. After the hydrolysis, a screw extruder was used to separate the liquid fraction and solid fraction of hydrolyzed materials to obtain the hydrolysis residues and hydrolysis liquid.

2.

Butanol fermentation of hydrolysis liquid. Hydrolysis liquid was first filtered to eliminate large particles, and then distilled in a vacuum tower for the removal of furfural. The acid ions in the condensed liquid obtained were removed via electrodialysis, and then the liquid was added to activated carbon to remove the fermentation inhibitors. The liquid was mixed with a certain amount of corn juice and sterilized at 120   °C for 40–60   min, then cooled and conveyed to the fermentation tank. In the fermentation tank, the substrate was inoculated with domesticated strains and fermented at 35–40   °C for 40   h. Finally, butanol, acetone, and ethanol were produced through the subsequent differential distillation and rectification.

3.

Separation of cellulose and lignin. Hydrolysis residues were put into an alkali extraction tank and 0.5–2% sodium hydroxide solution was added with five- to sevenfold mass of the hydrolysis residues. The mixture was kept at a temperature of 150–160   °C for 2–3   h. After cooling to the ambient temperature, the mixture was separated through a plate-and-frame filter press to obtain extracts and extracted solids. The extracts were filtered by ultrafiltration and then a nanofiltration membrane system to obtain two liquids. The liquid throughout the nanofiltration membrane was sodium hydroxide solution, which could be recycled into the extraction tank; the liquid that had not gone through the ultrafiltration membrane was conveyed into the neutralization tank. Sulfuric acid was added in the neutralization tank to adjust the pH to 4.5–5.0, followed by centrifugation. The clear liquid was sent to a sewage plant, and the solid was washed with a threefold volume of water and centrifuged again. The residual solid was dried to obtain high-purity lignin. The concentrated liquid after membrane separation was dried to obtain lignin. The extracted solids were conveyed to the sieving machine and separated into long and short fibers. Long fibers were used to prepare dissolving pulp, and short fibers were used for butanol fermentation or liquefied to prepare polyether polyol.

Mass balance was calculated using the following parameters. Corn stalk was calculated as absolute dry material, the ratio of butanol to acetone to ethanol in fermentation liquid was 7:2:1, the material loss after electrodialysis and active carbon treatment was 5%, the ratio of corn stalk to hydrolysis liquid was 1:10, the butanol yield from Clostridium acetobutylicum fermentation was 0.35   g/g, the material loss after alkali extraction was 5%, the lignin yield was 80%, and the cellulose yield was 70%. The mass balance of the whole process is shown in Figure 7.5.

Figure 7.5. Material balance of the butanol production process from corn straw hemicellulose fermentation and comprehensive utilization of cellulose and lignin.

In summary, the 300,000 tons/year straw refining industrial production line is a multiproduct, recycling, and high-value utilization route for corn stalks, in which butanol, acetone, and ethanol are produced by the fermentation of hemicelluloses, long fibers are used for paper making, and short fibers and lignin are used to prepare polyether, phenolic resins, and other products. A variety of bio-based products obtained by this route can be applied in the energy, plastics, materials, and chemical industries, and so on, providing a new pathway for the high-value utilization of corn stalk resources. In 2009, the 300,000 tons/year straw refining industrial production line was established in Jilin Province. The annual design capacity was 50,000 tons of butanol, acetone, and ethanol; 30,000 tons of high-purity lignin; and 120,000 tons of cellulose. Taking the lignin and cellulose obtained as raw materials, a production line for 50,000 tons of biopolyether polyols and 20,000 tons of phenolic resin will soon be put into operation. After commissioning, the project can generate an annual income of 1.2 billion yuan and a profit of about 100 million yuan. Currently, the operation of a 300,000 tons/year straw refining industrial production line marks the breakthrough in overcoming several technical problems in butanol fermentation and comprehensive utilization of straws, achieving validation of the industrial technology. Technologies in this route have completely independent intellectual property rights. It is the first low-cost, high-value, large-scale biorefinery production line for straw feedstock at an international level.

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Biofuels

Yaser Dahman , ... Banafsheh Mohtasebi , in Biomass, Biopolymer-Based Materials, and Bioenergy, 2019

14.10.3 Biobutanol

Biobutanol production through anaerobic bacteria fermentation has been observed since 1861, as witnessed by Pasteur. During anaerobic bacteria fermentation processes, butanol is a single product among many. By the beginning of the 20th century, interest in butanol had risen sharply. A shortage of natural rubber had a great impact and efforts were undertaken to make a synthetic rubber. It was found that butadiene or isoprene rubber could be synthesized from butanol or isoamyl alcohol. This discovery stimulated great interest in anaerobic fermentative processes for compound production.

Fermentation processes began to experience a decline after the end of World War 2. In 1960, petrochemical production of solvents became much easier and cheaper, whereas farmer interests in molasses caused molasses prices to increase dramatically. The combination of these events made fermentative production of acetone and butanol inefficient and uneconomical. In the middle of the 20th century, biobutanol was made from corn or molasses by fermentation involving C. acetobutylicum. The final products consisted of acetone, butanol, and ethanol and the process was referred to as ABE. Byproducts of ABE fermentation include hydrogen, isopropanol, acetic, lactic, propionic and butyric acids, carbon dioxide, and lipids. The need to separate the main fermentation products and to remove byproducts causes an increase in the production cost of each liter of butanol. ABE fermentation using bacteria C. acetobutylicum is one of the pioneering processes used for industrial butanol fermentation. Based on the application of the above anaerobic microorganisms, the microbiological production industry was established. However, prior to the introduction of a new strain, called C. beijerinckii, and the development of a novel technology by Environmental Energy Company, fermentation was a complicated and barely controllable process.

At the beginning of 21st century, Hans Blaschek, a Professor of the Food Microbiology Department of the University of Illinois in the United States, isolated a new Clostridium strain. In 2004, C. beijerinckii was selected by the US Department of Energy for gene mapping. Using a genetically modified microorganism, C. beijerinckii, patented Dr. Blaschek, it was possible to transformed corn into butanol. Professor Blaschek has developed fundamentals of butanol production technology through its extraction from gas. In this case, butanol will be inexpensive and contain no impurities, which could be found in the product if membrane-based technologies are used. In 2006, BP and DuPont announced their joint efforts in the production of advanced biofuel, putting an emphasis on biobutanol. The partnership objective was to develop a process of biobutanol production economically equal to the process of bioethanol production by 2010. In general, BP and DuPont invested about US$400   M in the construction of a new facility for biofuel process development.

Nasib Qureshi, a Professor at the Department of Food Science and Human Nutrition of the University of Illinois in the US developed a membrane process for more effective butanol production in the fermentation conditions. Though butanol-forming bacteria generate enzymes that convert simple sugars into alcohol, butanol itself is toxic for these microbes. As a result of this inhibition by butanol, there is a low alcohol concentration in the fermenting medium. Thus, the butanol yield is reduced, and production costs have grown. These challenges occur through the use of highly purified raw materials. When less expensive biological raw materials are used, the additional bacterial inhibitors are produced at the stage of preliminary treatment. Strategies are being developed to reduce butanol toxicity and increase its output, including several integrated levels in the process of control of microbiological cultures.

Biobutanol is another biofuel that is produced from the ABE fermentation of traditional feedstock. Biobutanol has an energy content that is close to that of gasoline and contains 25% greater energy density per liter than ethanol, meaning that it gets more mileage per liter than ethanol. Butanol is also less corrosive than ethanol and is thus safer to handle. In addition, it can be blended directly with gasoline and transported by gas lines, whereas ethanol must be transported separately and mixed at the fuel outlet, most commonly a gas station. Biobutanol does not need engine modifications and uses fuel-to-air ratios that are closer to those of gasoline and not ethanol. It is also considered to be environmentally friendly as it does not yield any toxic compounds upon combustion.

Significant research efforts have focused on developing or genetically improving butanol-producing cultures, which can tolerate elevated acetone–butanol concentration levels ranging from 20.0 to 30.0   g/L. In a recent report, microbial cultures, such as Escherichia coli have been developed for producing butanol with concentrations in the range of 14–16   g/L. The newly developed butanol-producing strain cannot tolerate butanol in excess of 15   g/L as butanol is more toxic than isobutanol [138]. Likewise, a butanol concentration above 25   g/L is toxic to C. beijerinckii BA101 [139]. The aim of the present study is to introduce a novel approach by using an improved microorganism strain, C. fusant, that is, formed through protoplast fusion to produce butanol by simultaneous SSF; nevertheless, because of the small-scale production, butanol did not show toxicity.

For enhanced butanol tolerance, an effective solution can be addressed in two ways: (1) use of genetic engineering techniques to develop strains that could tolerate a higher concentration of butanol and (2) use of engineering techniques to ferment and remove products simultaneously; thus, the toxic butanol concentration inside the reactor is never reached. Employing the first approach, cultures have been developed for the toleration and production of up to 30   g/L AB [140]. However, butanol when present at 13   g/L in the fermentation medium becomes toxic to the culture due to its hydrophobic nature [141].

The primary reason for producing low butanol concentration is its toxicity. In this concern, recovery technology can give a solution; simultaneous removal of ABE will not allow a high concentration of butanol in the fermentation broth. Usually, product-removal techniques include gas stripping, adsorption, liquid–liquid extraction, perstraction, pervaporation, and reverse osmosis. Simultaneous removal of ABE has been exercised in batch, fed-batch, and continuous immobilized cell reactors. It should be noted that removal of ABE from batch and fed-batch systems can be directly applied to existing fermentation industries that are not likely to make changes to their existing infrastructure [142].

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Conversion of biomass into biofuel: a cutting-edge technology

Md. Saiful Alam , Md. Sifat Tanveer , in Bioreactors, 2020

5.2.2.3 Biobutanol

5.2.2.3.1 Introduction

Recently, the biofuel market has been primarily dominated by bioethanol, biobutanol, and biogas, relying on substrates such as sugars, starch, oil crops, agricultural and animal residue, and lignocellulosic biomass. Fuel properties like energy density and hygroscopicity are higher in butanol (C4H9OH) than in traditional fuels. However, due to its low production cost and availability over the seasons, lignocellulosic biomass is the most suitable raw material for butanol production [24].

5.2.2.3.2 Biobutanol production

The conversion route for biobutanol is similar to the that used in the production of bioethanol, but requires the use of different enzymes. Traditionally, biobutanol is produced through an acetone–butanol–ethanol (ABE) fermentation process in which Clostridia species, namely Clostridium acetobutylicum, Clostridium beijerinckii, Clostridium saccharobutylicum, and Clostridium saccharoper butylacetonicum are used [25,26]. ABE fermentation is a process that uses bacterial fermentation to produce three solvents, namely acetone, n-butanol, and ethanol, from carbohydrates such as starch and glucose. ABE fermentation produces solvents in a ratio of three parts acetone (CH3–CO–CH3), six parts butanol (CH3–CH2–CH2–CH2OH), and one part ethanol (CH3–CH2–OH). However, traditional butanol fermentation processes have some major challenges, and these are listed here [24].

•

Increased operating costs due to high raw material cost.

•

High cost of recovery due to low production yield.

•

Increased capital and operating costs due to low volumetric productivity.

•

High cost for product recovery with conventional distillation processes.

•

Toxicity of the produced biobutanol to microorganisms at high concentration.

•

Some by-products such as acetone and ethanol hinder the purification processes.

•

Culture degeneration.

•

Phage contamination especially in large-scaled units.

To produce sustainable biobutanol and to overcome the challenges mentioned above, some possible recommended ways are:

•

Finding cheaper and sustainable lignocellulosic raw materials.

•

Development of butanol selective microorganisms with improved yield.

•

Development of novel reactive separation processes.

•

Development of continuous fermentation processes toward reducing reaction times.

•

Development of low-cost energy efficient methods for solvent purification and recovery.

•

Avoiding the excessive acidification of the culture.

•

Good culture practices, proper sterilization, and the use of phage resistant strains.

5.2.2.3.3 Properties of biobutanol

The chemical composition of biobutanol is identical to that of n-butanol and, therefore, it does not differ in other parameters. Having some intrinsic properties, biobutanol becomes an attractive source of biofuel. Comparisons of biobutanol to other fuels are shown in Table 5.1. The energy content of biobutanol is quite close to that of gasoline, and the energy density per liter of biobutanol is 25% greater than that of ethanol. Although the production costs of butanol are more than that of ethanol, it gives a better performance in engines. A further energy advantage is that about 18% more energy as hydrogen is produced in the production of biobutanol by fermentation from the same amount of fermentable substrate as ethanol [18]. In addition, the high flash point of biobutanol (36°C) over ethanol and gasoline makes it safer to use and handle.

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Utilization of agricultural biomass for bio-butanol production

Mohamad Faizal Ibrahim , ... Phang Lai Yee , in Value-Chain of Biofuels, 2022

10.5.3 Fermentation process

Clostridia capable of producing bio-butanol, such as C. acetobutylicum, Clostridium beijerinckii, and Clostridium pasteurianum have similar metabolic pathways. Several by-products such as acetate, acetone, and ethanol are also formed from these metabolic pathways, in addition to the main products of butyrate and bio-butanol [47]. The researcher is targeting to increase the bio-butanol concentration and ratio of butanol, acetone, and ethanol that has been roughly produced at molar ratio of 6:3:1 (butanol: acetone: ethanol), without changing the total solvent productivity [55]. In addition to the bio-butanol production, some biofuel-producing microbes may also produce other value-added products like riboflavin (vitamin B2), thus, will increase the value of the bio-butanol fermentation process [48]. The fermentation products and their ratios vary depending on the strains and substrates used in the fermentation, as well as the optimal fermentation conditions such as pH, temperature, and nutrients [56].

Clostridia produces the bio-butanol via a biphasic fermentation process. The first stage is the acidogenic stage, and followed by the solventogenesis stage. During the acidogenesis, sugar is metabolized into acetic and butyric acids, and then these acids are re-assimilated to produce bio-butanol along with acetone and ethanol during the solventogenesis [36,57], as shown in the metabolic pathway of Clostridia (Fig. 10.1) [58].

Figure 10.1. Solventogenic fermentation performed by Clostridium acetobutylicum [58].

The products of acidogenesis are then transferred to the solventogenic phase as shown in Fig. 10.2 during the spore formation, as the organism reduces acid production and absorbs excreted acetate and butyrate, by converting them to bio-butanol and acetone as solvents. Butyric acid is converted to butanol, whereas acetic acid can be converted to ethanol or acetone [58,59]. In other words, acids are converted into the solvents of acetone and bio-butanol, where butanol is produced two-times more than acetone. It is a response to deteriorating the environmental conditions [58]. These two-stage fermentation processes may also capable to produce bio-butanol without significant amounts of acetone or ethanol produced [47]. The direct forming path, known as the hot channel, can produce bio-butanol too, but its contribution to bio-butanol production is still understudied [60].

Figure 10.2. Acidogenic fermentation performed by Clostridium acetobutylicum.

Separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) are the two main processes for producing biofuels from lignocellulosic biomass. SHF is a distinct process involving two distinct saccharification and fermentation process, allowing cellulose hydrolysis and fermentation to occur at their different respective optimum conditions [61]. This process is mostly used in bio-butanol production from the lignocellulosic biomass. The SHF on the other hand, has a number of drawbacks including the accumulation of glucose during enzymatic hydrolysis, which may inhibit cellulases activity in the hydrolysis process, the high cost of equipment due to dual different processes, and the possibility of microbial contamination, which makes the process uneconomically feasible [62]. According to Cao et al. [62], to grow the microorganism during the bio-butanol fermentation, the SSF process for bio-butanol production is typically run at a lower temperature, usually between 35°C–37°C. However, there is a drawback of low sugar concentration, which is unfavorable from the the viewpoint of fermentation kinetics [63].

Besides, bio-butanol fermentation can be conducted in a batch, fed-batch, or continuous process depending on the production capacity. For small scale bio-butanol processing, batch or fed-batch fermentation is preferable. Batch fermentation is commonly used in the industry, while fed-batch fermentation is mainly performed in laboratories. With low productivity and high solvent inhibition, re-inoculation is required, and both batch and fed-batch processes take a long time for the sterilization of the bioreactor. Continuous fermentation, on the other hand, is a good choice for large-scale bio-butanol fuel production, due to its high productivity, economical, low labor, and maintenance costs. However, its contamination risk and capital cost are also high [38,64]. Thereby, the actual ABE fermentation is a relatively complex and difficult process to manage [47].

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Mixed Sugar Fermentation by Clostridia and Metabolic Engineering for Butanol Production

T.C. Ezeji , ... N. Qureshi , in Biorefineries, 2014

9.1 Introduction

Biofuels produced from biomass can be categorized as liquid (ethanol, butanol), gas (hydrogen, methane), and solid (wood, charcoal) fuels. Among these categories, liquid biofuels command the greatest attention because their transportation characteristics resemble the characteristics of gasoline and diesel. Liquid fuels and chemicals are essential components of the global energy and chemical infrastructure because cars, boats, and aircraft rely on the high energy density of liquid fuels to achieve their needed operational ranges. Given the increased demand for gasoline and diesel, along with the global depletion of petroleum deposits, the impact of liquid biofuels on the automotive fuel market is expected to increase markedly in the coming decades. For example, the Environmental Protection Agency Renewable Fuel Standard 2 (EPA-RFS2) mandates the production of 36 billion gallons (136 billion liters; in US, 1 billion   =   109) of renewable fuels in the US market by 2022. Similarly, the European Union has mandated the replacement of 10% of their transportation fuel with biofuel by 2020. In spite of these driving factors, the production of biofuels still faces some key challenges, including feedstock availability, fermentation of agricultural biomass into liquid biofuels, and cost-competitive product recovery, and these challenges must be addressed before biofuel production can be fully commercialized.

Substrate cost is a major factor influencing the economic viability of fermentative butanol production, accounting for up to 50% of the cost of the butanol fermentation process [ 1]. Traditionally, butanol is produced through the fermentation of starch (corn, wheat, cassava, potato) and cane molasses [2]. In an effort to use cheap and readily available raw materials for butanol production, researchers have isolated and improved strains of solventogenic Clostridium species. Interestingly, solventogenic Clostridium species have the ability to metabolize pentose and hexose sugars for growth and acetone-butanol-ethanol (ABE, or AB) production [3,4]. Lignocellulosic biomass represents the most abundant renewable energy resource on the planet. The "Billion Ton Study" published by the US Department of Energy (DOE) in 2005 showed that about 1.3 billion dry tons of biomass could be available each year, providing enough feedstock to produce biofuels to meet more than one-third of the current demand for transportation fuels in the United States.

The commercial production of butanol as a biofuel (beyond its role as a chemical feedstock) requires the development of lignocellulose as a feedstock, and the production of butanol from readily available lignocellulosic biomass avoids the direct fuel-versus-food competition caused by the use of corn and cane feedstocks in biofuel production. Lignocellulosic biomass hydrolyzates obtained from various sources have different hexose-to-pentose ratios (Table 9.1). The maximum amount of these sugars must be released from the lignocellulosic biomass prior to fermentation, and freeing the sugars involves pretreating the biomass with chemicals such as dilute sulfuric acid or dilute NaOH followed by enzymatic hydrolysis. These pretreatment processes often generate inhibitory compounds, including furfural, hydroxymethyl furfural (HMF), hydroxybenzaldehyde, and coumaric acid [4]. As their name suggests, these compounds inhibit cell growth and fermentation by disrupting cell membranes, damaging polynucleotides, repressing central metabolic enzymes, decreasing intracellular pH, increasing cell turgor pressure, and inducing oxidative stress [5,6]. Therefore, to enhance the utilization of mixed sugars from lignocellulosic biomass, researchers must develop inhibitor-tolerant strains of bacteria. Interestingly, pretreatment processes sometimes generate chemical by-products that, at optimal concentration, stimulate growth and butanol production in solventogenic Clostridium species [3,7].

Table 9.1. Production of Acetone Butanol Ethanol (ABE) from Lignocellulosic Biomass by Clostridium Species

Substrates Hexose/ Pentose ratio Pretreatment method Microorganisms ABE produced (g/L) Productivity (g/L.h) Reference
DDGS 1.5 Hot water C. beijerinckii 260 12.8 0.21 7
C. acetobutylicum 824 11.4 0.19
C. saccharobutylicum 262 10.5 0.18
C. butylicum 592 12.9 0.22
C. beijerinckii BA101 11.5 0.19
DDGS 2.0 AFEX C. beijerinckii 260 10.2 0.17 7
C. acetobutylicum 824 9.0 0.15
C. saccharobutylicum 262 7.9 0.13
C. butylicum 592 11.6 0.19
C. beijerinckii BA101 10.4 0.17
Wheat straw 1.40 DSA C. beijerinckii P260 25.0 0.63 53
Barley straw 0.95 DSA C. beijerinckii P260 26.6 0.39 54
Corn stover 0.98 DSA C. beijerinckii P260 26.3 0.31 55
Switchgrass 1.30 DSA C. beijerinckii P260 14.6 0.17 55
Corn fiber 0.82 DSA C. beijerinckii BA101 15.6 0.18 4
Wood ND SO2 plus heat C. acetobutylicum P262 17.6 0.73 56
Rice straw ND Alkali C. saccharoperbutylacetonicum ATCC 27022 13.0 0.15 18
Cane bagasse ND Alkali C. saccharoperbutylacetonicum ATCC 27022 18.1 0.30 18

ND – Not determined; DDGS – Dried distillers grains and solubles

AFEX – Ammonia fiber expansion; DSA – Dilute sulfuric acid

Solventogenic Clostridium species metabolize a wide range of pure carbohydrates, such as starch, sucrose, glucose, fructose, galactose, cellobiose, xylose, arabinose, glycerol, lactose, and inulin [3,4,8,9]. The microorganisms' efficiency at metabolizing these carbohydrates in mixed form tends to decrease their utilization due to a phenomenon called carbon catabolite repression. (CCR). CCR reduces or prevents the utilization of xylose and arabinose in the presence of a preferred carbon source such as glucose [10,11]. Thus, the sustainable production of butanol and biobased chemicals from lignocellulosic biomass will require new metabolic engineering approaches to override this intrinsic hierarchy in sugar utilization, along with the development of inhibitor-tolerant strains, ultimately enabling the efficient simultaneous fermentation of sugar mixtures into butanol.

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Industrial Biotechnology and Commodity Products

H. Dong , ... Y. Li , in Comprehensive Biotechnology (Second Edition), 2011

3.08.2 History

3.08.2.1 Discovery of Butanol-Producing Bacteria

The term 'AB fermentation' represents acetone and butanol fermentation, which is also called 'ABE fermentation' because of ethanol produced in the process. AB fermentation dates back to 1861, when the famous French scientist Louis Pasteur reported that butanol was a fermentation product of Vibrion butyrique, which was not a pure culture, and may have contained C. butyricum or C. acetobutylicum [1]. Albert Fitz, probably, was the first person who isolated the pure bacterium named Bacillus butylicus and did some seminal studies about this strain. Around the turn of the twentieth century, many scientists isolated some new butanol-producing bacteria with different designations due to a lack of consistent taxonomic standards.

3.08.2.2 AB Fermentation for Producing Butanol to Synthesize Rubber

At the dawn of the twentieth century, the shortage of natural rubber resulted in a high price. Strange and Graham Ltd. in England then planned to synthesize rubber artificially using isoprene, a product of butanol derivatives such as isoamyl alcohol or butadiene. The firm employed Perkins and Weizmann of Manchester University and subsequently employed Fernbach and Schoen of the Institut Pasteur to work on this project since 1910. In 1911, Fernbach isolated a culture that was able to ferment potatoes, but not maize starch, to produce butanol. After resigning from Strange and Graham Ltd. in 1912, Weizmann also isolated a butanol-producing strain BY, which was later named C. acetobutylicum with better fermentation performance than Fernbach's original culture. In the middle of 1913, Strange and Graham Ltd. began butanol production using Fernbach's strain at Rainham. The plant produced butanol and the byproduct acetone from potatoes [1].

3.08.2.3 AB Fermentation for Producing Acetone to Manufacture Cordite in World War I

With the advent of World War I in 1914, AB fermentation was developed dramatically. The British needed cordite (smokeless powder) in large quantities to produce ammunition. For preparation of cordite, acetone was used as the colloidal solvent for nitrocellulose. Due to the acute shortage of chemically produced acetone in England at the outbreak of the war, the until-then unnoticed acetone that was produced during butanol microbial production caught the attention of the British War Office. Strange and Graham Ltd. was then asked to provide acetone to the government. During this period, Weizmann developed another AB fermentation process (Weizmann process) and applied for a patent in March 1915. Because of the apparent advantages of the Weizmann process, acetone was produced from maize in several plants in England, including Strange and Graham Ltd., using this process. Due to the grain shortage caused by the German blockade, the fermentation process was transferred to Canada and the USA, in 1916 and 1917, respectively [1].

3.08.2.4 AB Fermentation for Producing Butanol to Manufacture Quick-Drying Lacquer

With armistice in 1918, it was no longer necessary to produce acetone. However, how to treat the large amount of butanol accumulated in the acetone-producing process became a problem. Fortunately, at that time, the automobile industry underwent rapid development because of Henry Ford and required a kind of quick-drying lacquer, which resulted in a demand for a suitable solvent. Hence, butanol was selected as a potential candidate. Therefore, many plants engaged in AB fermentation were set up to produce butanol for the automobile industry, and intensive research was also carried out rapidly. At its peak capacity in 1927, the Commercial Solvent Corporation Plant in Peoria, IL (USA), had 96 fermentors in operation with a total volume of 18   168   m3, representing the largest fermentation facility for AB fermentation at that time [1].

3.08.2.5 AB Fermentation for Producing Acetone to Manufacture Cordite in World War II

With the outbreak of Word War II, AB fermentation was once again used to produce acetone for the cordite manufacture. Moreover, given the high demand for acetone during the war, continuous distillation was carried out in AB fermentation. The production capacity for acetone and butanol from the AB fermentation continued to increase until its peak in 1945, when two-thirds of butanol and one-tenth of acetone in the United States were derived from AB fermentation [1].

3.08.2.6 AB Fermentation Decline since the 1950s

From the 1950s onward, AB fermentation declined rapidly and almost ceased in the 1960s due to multiple reasons. First, the formerly cheap substrate molasses began to be used as feeding additives for pig and cow breeding and showed decreasing quality by improved sugar-processing technology. Second, AB fermentation was apt to be infected by phage at that time. Third, there was no significant progress on both the industrial strain improvement and the fermentation process to reduce the production costs, although some efforts had been made, such as screening for new strains and developing a continuous fermentation process. Fourth, AB fermentation was strongly limited by the toxicity of its product butanol (10–13   g   l−1), which is still currently a bottleneck for improving AB fermentation. Most importantly, when acetone and butanol were also produced cheaply from petroleum oil by the developing petrochemical industry, AB fermentation lost the economic competition completely and was discontinued in the industrialized Western countries during the 1960s [1].

3.08.2.7 AB Fermentation for Producing Butanol as a Potential Biofuel Nowadays

Although the new economic base had been established on petroleum oil given the rapid development of the petrochemical industry, the oil crisis of the 1970s warned that human dependence on oil was not sustainable. So, scientists still had a keen interest in AB fermentation, in spite of industrial production coming to a halt. The current acute shortage of oil restimulates governments and scientists to find some substitutes from renewable biomass. Among them, liquid fuels are the most stringent, so biofuel has been placed on a strategic position. Considering its many excellent characteristics used as a fuel, such as higher energy content, lower water absorption, and better blending ability, the concept of butanol as a potential biofuel have become a hot topic for research since 2005. BP and DuPont announced their partnership to develop and commercialize biobutanol in 2006 and presented plans to produce 30   000 tons of butanol per year in a modified ethanol facility of British Sugar in the UK. Furthermore, China is reopening its fermentation plants, and a new one has been set up in Brazil [2]. Currently, AB fermentation has received much attention, resulting in many important developments, such as the release of genomic sequences of butanol-producing strains, omic-level analyses of the bacterial physiology, and metabolic engineering. Thus, biobutanol is predicted to be a feasible substitute biofuel for gasoline in future.

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Developments in biobutanol production: New insights

Manish Kumar , Kalyan Gayen , in Applied Energy, 2011

10 Economics of biobutanol fermentation

Fermentation processes are exothermic and hence, the products will have less energy than substrates. The theoretical mass and energy yield of ABE fermentation are 37% and 94% respectively, calculated on the basis of energy combustions and products ratio obtained in fermentation [68]. During a study, it was reported that economic feasibility of ABE fermentation might not be possible on meeting 100% yield. However, substrate costs, accounting to approximately 60% of the total production costs, play a major role in the economics of fermentation [8,114]. None of the starch and sugar containing crops can make fermentation economically feasible on the basis of the current market needs and scenario. Consequently, cheaper agriculture wastes (lignocellulosic materials) and other industrial wastes may be suitable for the economical ABE fermentation [67,115] . Ethanol distilleries have already proven to be more economically productive when utilizing low cost raw materials. However, the economy of ABE fermentation is more sensitive to substrate than yield; but it is estimated that butanol fermentation process will not be feasible while yield becomes less than 25% [68]. Strain improvement is effective technique in improving the yield; however it has lower influence in economics than other factors (mainly cost of substrate and product recovery). Interestingly, capital costs of butanol fermentation was higher and production costs were lesser than petrochemical production of butanol [116]. Batch fermentation processes have been found less economical than continuous processes comprising extra burden of sterilization equipment, piping and valves. However, the contamination problem in continuous fermentation is a key challenge. Product market is also a vital point in economics of butanol fermentation. Still, the market is good enough in absorbing the products of ABE fermentation. It is hoped that after adapting biobutanol as a liquid fuel, demands will be huge. Byproducts including acetone, ethanol, H2, and CO2 can also contribute substantially to economics of butanol production [63]. Another cost-intensive process in butanol production is recovery of products from diluted fermentation broth. It should be noted that butanol production itself is a cost-intensive process, and recovery technology of this fermentation is far away from feasibility. The following endeavors can materialize in economical feasibility of ABE fermentation. Firstly, improvement in butanol tolerance of strain can enhance the fermentation time, productivity and economic feasibility of the process. Estimated fermentation time of 40–60   h was significant in commercialization of biobutanol production. Secondly, reduction in product inhibition and recovery cost can be achieved by online selective removal of product [69]. Till date, the gas stripping process was found the most effective process for online recovery of butanol [92]. Combination of fluidized bed reactor using immobilized cells and removal of product by membrane was also suggested to ensure the economic sustainability of ABE fermentation [114]. Therefore, it is concluded that raw materials being used and product recovery are the most crucial factors for cost-effective butanol fermentation process. It is a considerable challenge in identifying cheaper substrates and developing suitable recovery processes for cost effective ABE fermentation.

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Food waste valorization: Energy production using novel integrated systems

Anita Talan , ... P. Drogui , in Bioresource Technology, 2021

2.5 Butanol production system

Butanol or butyl alcohol is used as a solvent, extractant in the pharmaceutical and cosmetics industry, supplements, eluent, and transporting fuel. Conventionally, butanol is produced by three chemical processes: crotonaldehyde hydrogenation, Reppe synthesis, and oxo synthesis (hydroformylation) (Abo et al., 2019). Biobutanol is produced from the fermentation of sugar and starchy biomass. Research investigation regraded butanol as next-generation biofuel over ethanol due to its high energy content and lower volatility (Abo et al., 2019; Ndaba et al., 2015). Moreover, the high boiling point and less corrosive characteristics facilitate its distribution through petrol pipelines. Despite the benefits of butanol, its production is limited due to the high raw material cost and low product yield. The most promising route of butanol production is via the fermentation of glycerol, lignocellulose waste, and food waste. The butanol production involves the extraction of sugar from feedstock vis various pre-treatment processes, followed by fermentation by micro-organisms belonging to the Clostridiaceae family (Dahiya et al., 2018 ). The butanol fermentation process yields acetone and ethanol along with butanol, thus known as acetone –butanol-ethanol (ABE) fermentation ( Abo et al., 2019). Apart from acetone and ethanol, the ABE fermentation generated other byproducts, including lactic acid, isopropanol, acetic acid, and dihydrogen (Abo et al., 2019).

Due to the abundance of carbohydrates, high carbon to nitrogen ratio, and high moisture content, FW is considered a better alternative for biobutanol production (Abo et al., 2019). The hydrolysis of FW facilitates the release of sugar from the carbohydrates. Since FW could contain a complex mixture of different sugars such as glucose, xylose, lactose, arabinose, and many more; Clostridiaceae did not consume all kinds of sugars, thus could limit butanol production and lead to carbon catabolite repression (Abo et al., 2019). For conversion of FW to butanol hydrolysis can be achieved enzymatically or via physicochemical treatments. Enzymatic hydrolysis is environmentally friendly while physicochemical pre-treatment methods are less selective due to formation of inhibitors that have detrimental effect on butanol production (Kiran et al., 2014). Research studies attempted to avoid carbon catabolite repression by genetic engineering strategies (Abo et al., 2019; Bruder et al., 2015). Bruder et al. (Bruder et al., 2015) reported the genetic modulation in Clostridiaceae, allowing simultaneous utilization of glucose and xylose and preventing carbohydrate loss during fermentation. The pretreatment of FW for butanol production includes steam explosion treatment, organosolv treatment, and enzymatic hydrolysis (Abo et al., 2019). Although FW could be a suitable substrate for butanol production, certain challenges such as effective pretreatment, utilization of different sugars by microbial strain required detailed investigation.

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