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Acetone–butanol–ethanol (ABE) fermentation, also known as the Weizmann process, is a process that uses bacterial
fermentation Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic molecules, such as glucose or other sugars, are catabolized and reduce ...
to produce
acetone Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...
,
n-butanol 1-Butanol, also known as butan-1-ol or ''n''-butanol, is a Alcohol (chemistry), primary alcohol with the chemical formula C4H9OH and a linear structure. Isomers of 1-butanol are isobutanol, butan-2-ol and tert-butanol, ''tert''-butanol. The unmodi ...
, and
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...
from carbohydrates such as starch and
glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...
. It was developed by
chemist A chemist (from Greek ''chēm(ía)'' alchemy; replacing ''chymist'' from Medieval Latin ''alchemist'') is a graduated scientist trained in the study of chemistry, or an officially enrolled student in the field. Chemists study the composition of ...
Chaim Weizmann Chaim Azriel Weizmann ( ; 27 November 1874 – 9 November 1952) was a Russian-born Israeli statesman, biochemist, and Zionist leader who served as president of the World Zionist Organization, Zionist Organization and later as the first pre ...
and was the primary process used to produce acetone, which was needed to make cordite, a substance essential for the British war industry during
World War I World War I or the First World War (28 July 1914 – 11 November 1918), also known as the Great War, was a World war, global conflict between two coalitions: the Allies of World War I, Allies (or Entente) and the Central Powers. Fighting to ...
.


Process

The process may be likened to how
yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are est ...
ferments sugars to produce ethanol for wine, beer, or fuel, but the organisms that carry out the ABE fermentation are strictly anaerobic (obligate anaerobes). The ABE fermentation produces solvents in a ratio of 3 parts acetone, 6 parts butanol to 1 part ethanol. It usually uses a strain of bacteria from class
Clostridia The Clostridia are a highly polyphyletic class of Bacillota, including '' Clostridium'' and other similar genera. They are distinguished from the Bacilli by lacking aerobic respiration. They are obligate anaerobes and oxygen is toxic to them ...
(family
Clostridiaceae The Clostridiaceae are a family of the bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryo ...
). '' Clostridium acetobutylicum'' is the most well-studied and widely used. Although less effective, '' Clostridium beijerinckii'' and '' Clostridium saccharobutylicum'' bacterial strains have shown good results as well. The ABE fermentation pathway generally proceeds in two phases. In the initial acidogenesis phase, the cells grow exponentially and accumulate
acetate An acetate is a salt formed by the combination of acetic acid with a base (e.g. alkaline, earthy, metallic, nonmetallic, or radical base). "Acetate" also describes the conjugate base or ion (specifically, the negatively charged ion called ...
and butyrate. The low pH along with other factors then trigger a metabolic shift to the solventogenesis phase, in which acetate and butyrate are used to produce the solvents. For gas stripping, the most common gases used are the off-gases from the fermentation itself, a mixture of
carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
and
hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
gas.


History

The production of butanol by biological means was first performed by
Louis Pasteur Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist, pharmacist, and microbiologist renowned for his discoveries of the principles of vaccination, Fermentation, microbial fermentation, and pasteurization, the la ...
in 1861. In 1905, Austrian biochemist Franz Schardinger found that acetone could similarly be produced. In 1910 Auguste Fernbach (1860–1939) developed a bacterial fermentation process using potato starch as a feedstock in the production of butanol. Industrial exploitation of ABE fermentation started in 1916, during World War I, with Chaim Weizmann's isolation of Clostridium acetobutylicum, as described in U.S. patent 1315585. The Weizmann process was operated by Commercial Solvents Corporation from about 1920 to 1964 with plants in the US ( Terre Haute, IN, and Peoria, IL), and
Liverpool, England Liverpool is a port city and metropolitan borough in Merseyside, England. It is situated on the eastern side of the Mersey Estuary, near the Irish Sea, north-west of London. With a population of (in ), Liverpool is the administrative, c ...
. The Peoria plant was the largest of the three. It used molasses as feedstock and had 96 fermenters with a volume of 96,000 gallons each. After
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
, ABE fermentation became generally non-profitable, compared to the production of the same three solvents (
acetone Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...
, butanol,
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...
) from
petroleum Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...
. During the 1950s and 1960s, ABE fermentation was replaced by petroleum chemical plants. Due to different raw material costs, ABE fermentation was viable in
South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...
until the early 1980s, with the last plant closing in 1983. Green Biologics Ltd operated the last attempt to resurrect the process at scale but the plant closed in Minnesota in June 2019. A new ABE biorefinery has been developed in Scotland by Celtic Renewables Ltd and will begin production in early 2022. The key difference in the process is the use of low value spent materials or residues from other processes removing the variable costs of raw feedstock crops and materials.


Improvement attempts

The most critical aspect in biomass fermentation processes is related to its productivity. The ABE fermentation via '' Clostridium beijerinckii'' or '' Clostridium acetobutylicum'' for instance is characterized by product inhibition. This means that there is a product concentration threshold that cannot be overcome, resulting in a product stream highly diluted in water. For this reason, in order to have a comparable productivity and profitability with respect to the petrochemical processes, cost and energy effective solutions for the product purification sections are required to provide a significant product recovery at the desired purity. The main solutions adopted during the last decades have been as follows: * The employment of less expensive raw materials, and in particular lignocellulosic waste or
algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...
; * The microorganisms modifications or the research of new strains less sensitive to the butanol concentration poisoning to increase productivity and selectivity towards the butanol species; * The
fermentation Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic molecules, such as glucose or other sugars, are catabolized and reduce ...
reactor optimization aimed at increasing the productivity; * The reduction of the energy costs of the separation and purification downstream processing and, in particular, to carry out the separation in-situ in the reactor; * The use of side products such as
hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
and
carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...
, solid wastes and discharged microorganisms and carry out less expensive process
wastewater treatment Wastewater treatment is a process which removes and eliminates contaminants from wastewater. It thus converts it into an effluent that can be returned to the water cycle. Once back in the water cycle, the effluent creates an acceptable impact on ...
s. In the second half of the 20th century, these technologies allowed an increase in the final product concentration in the broth from 15 to 30 g/L, an increase in the final productivity from 0.46 to 4.6 g/(L*h) and an increase in the yield from 15 to 42%. From a compound purification perspective, the main criticalities in the ABE/W product recovery are due to the water–alcohol mixture's non-ideal interactions leading to homogeneous and heterogeneous azeotropic species, as shown by the ternary equilibrium diagram. This causes the separation by standard distillation to be particularly impractical but, on the other hand, allows the exploitation of the liquid–liquid demixing region both for analogous and alternative separation processes. Therefore, in order to enhance the ABE fermentation yield, mainly in situ product recovery systems have been developed. These include gas stripping,
pervaporation Pervaporation (or pervaporative separation) is a processing method for the separation of mixtures of liquids by partial vaporization through a non-porous or porous membrane. Theory The term ''pervaporation'' is a portmanteau of the two steps of ...
,
liquid–liquid extraction Liquid–liquid extraction, also known as solvent extraction and partitioning, is a method to separate compounds or metal complexes, based on their relative solubility, solubilities in two different Miscibility, immiscible liquids, usually wate ...
, distillation via Dividing Wall Column, membrane distillation, membrane separation, adsorption, and reverse osmosis. Green Biologics Ltd. implemented many of these technologies at an industrial scale. Moreover, differently from crude oil feedstocks,
biomass Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...
es nature fluctuates over the year's seasons and according to the geographical location. For this reasons, biorefinery operations need not only to be effective but also to be flexible and to be able to switch between two operating conditions rather quickly. citation needed''">wikipedia:Citation needed">citation needed''


Current perspectives

ABE fermentation is attracting renewed interest with a focus on butanol as a renewable biofuel.
Sustainability Sustainability is a social goal for people to co-exist on Earth over a long period of time. Definitions of this term are disputed and have varied with literature, context, and time. Sustainability usually has three dimensions (or pillars): env ...
is by far the topic of major concern over the last years. The energy challenge is the key point of the environmental friendly policies adopted by all the most developed and industrialized countries worldwide. For this purpose Horizon 2020, the biggest EU Research and Innovation programme, was funded by the
European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...
over the 2014–2020 period. The
International Energy Agency The International Energy Agency (IEA) is a Paris-based autonomous intergovernmental organization, established in 1974, that provides policy recommendations, analysis and data on the global energy sector. The 31 member countries and 13 associatio ...
defines renewables as the centre of the transition to a less carbon-intensive and more
sustainable energy Energy system, Energy is sustainability, sustainable if it "meets the needs of the present without compromising the ability of future generations to meet their own needs." Definitions of sustainable energy usually look at its effects on the e ...
system. Biofuels are believed to represent around 30% of energy consumption in transport by 2060. Their role is particularly important in sectors which are difficult to decarbonise, such as
aviation Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' include fixed-wing and rotary-wing types, morphable wings, wing-less lifting bodies, as well as lighter-than-air aircraft such as h ...
,
shipping Freight transport, also referred to as freight forwarding, is the physical process of transporting commodities and merchandise goods and cargo. The term shipping originally referred to transport by sea but in American English, it has been ...
and other long-haul transport. That is why several bioprocesses have seen a renewed interest in recent years, both from a research and an industrial perspective. For this reason, the ABE fermentation process has been reconsidered from a different perspective. Although it was originally conceived to produce
acetone Acetone (2-propanone or dimethyl ketone) is an organic compound with the chemical formula, formula . It is the simplest and smallest ketone (). It is a colorless, highly Volatile organic compound, volatile, and flammable liquid with a charact ...
, it is considered as a suitable production pathway for biobutanol that has become the product of major interest. Biogenic butanol is a possible substitute of bioethanol or even better and it is already employed both as fuel additive and as pure fuel instead of standard
gasoline Gasoline ( North American English) or petrol ( Commonwealth English) is a petrochemical product characterized as a transparent, yellowish, and flammable liquid normally used as a fuel for spark-ignited internal combustion engines. When for ...
because, differently from
ethanol Ethanol (also called ethyl alcohol, grain alcohol, drinking alcohol, or simply alcohol) is an organic compound with the chemical formula . It is an Alcohol (chemistry), alcohol, with its formula also written as , or EtOH, where Et is the ps ...
, it can be directly and efficiently used in gasoline engines. Moreover, it has the advantage that it can be shipped and distributed through existing pipelines and
filling station A filling station (also known as a gas station [] or petrol station []) is a facility that sells fuel and engine lubricants for motor vehicles. The most common fuels sold are gasoline (or petrol) and diesel fuel. Fuel dispensers are used to ...
s. Finally biobutanol is widely used as a direct
solvent A solvent (from the Latin language, Latin ''wikt:solvo#Latin, solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a Solution (chemistry), solution. A solvent is usually a liquid but can also be a solid, a gas ...
for paints,
coating A coating is a covering that is applied to the surface of an object, or substrate. The purpose of applying the coating may be decorative, functional, or both. Coatings may be applied as liquids, gases or solids e.g. powder coatings. Paints ...
s, varnishes,
resin A resin is a solid or highly viscous liquid that can be converted into a polymer. Resins may be biological or synthetic in origin, but are typically harvested from plants. Resins are mixtures of organic compounds, predominantly terpenes. Commo ...
s, dyes, camphor, vegetable oils, fats, waxes, shellac, rubbers and
alkaloid Alkaloids are a broad class of natural product, naturally occurring organic compounds that contain at least one nitrogen atom. Some synthetic compounds of similar structure may also be termed alkaloids. Alkaloids are produced by a large varie ...
s due to its higher energy density, lower volatility, and lower hygroscopicity. It can be produced from different kinds of cellulosic biomass and can be used for further processing of advanced biofuels such as butyl levulinate as well. The application of n-butanol in the production of butyl acrylate has a wide scope for its expansion, which in turn would help in increasing the consumption of n-butanol globally. Butyl acrylate was the biggest n-butanol application in 2014 and is projected to be worth US$3.9 billion by 2020.


References

{{DEFAULTSORT:Acetone-Butanol-Ethanol Fermentation Fermentation