• How is ethanol produced on an industrial scale? The major steps involved in the industrial production of ethanol are:
1. Formulation of Medium
The preparation of the medium is the first step of ethanol production. For this purpose, the sugar concentration of cane molasses and of other carbohydrates in the medium is diluted to 10 - 18%. This sugar concentration favours the growth of the microorganisms. Ammonium sulphate or ammonium phosphate is added to the diluted medium. The pH of the medium is adjusted to 4 – 5 by using dilute sulphuric acid. Sometimes lactic acid bacteria are inoculated into the medium when the medium has high pH value. The lactic acid bacteria grow well and, initiate the production of alcohol. Other microbial contaminants’ should be avoided during the
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industrial production of ethanol. The starchy media like corn, rye and barley are hydrolysed with dilute acids before they are pumped into the fermentor. The hydrolysis of starch yield simple sugars which are directly converted into ethanol. Sometimes starchy feed stock is treated with amylase enzyme, extracted from Aspergillus and Rhizopus. Amylase converts the starch into 80% maltose and 20% dextrine.
2. Structure of a Fermentation System:
The fermentation system consists of three molasses tanks, three seed tanks, a fermentor and a wash chamber on of the three molasses tanks, one is larger in volume and is loaded with ample molasses; it named molasses storage tank. The stored molasses enter another tank where the, molasses are diluted properly with-water. The diluted molasses then enter the sterilization tank where the diluted molasses are sterilized clearly for the production of ethanol. The sterilized medium then enters both the fermentor and the seed tanks through pipelines. The seed tanks, are rather smaller vessels which are
interconnected by pipeline through which the microbes and the medium flow from one tank to the others. These tanks participate in the production of enough amount of microbial inoculum for the production of ethanol.
A fermentor is a large vessel where sugar is converted into ethanol by the action of microorganisms. The fermentor is connected with 5 pipelines:
1. The first pipeline is concerned with the supply of enough amount of sterilized medium into the fermentor.-
2. The second pipeline is concerned with the supply of enough amount of inoculum into the fermentor. .
3. The third pipeline participates in the addition of certain chemicals into the fermentor
4. The fourth pipeline is concerned with the supply of cooling water to the fermentor for helping to maintain proper temperature inside the fermentor.
5. The fifth pipeline is used to harvest the spent medium from the fermentor. The spent medium is then transferred to a wash chamber where it is processed for extract ethanol from it.
The actual process of ethanol production can be briefly summerised as follows:
The ethanol-producing microbes are inoculated into the fermentor containing full of nutrient medium and chemicals. These microbes convert the carbohydrates present in the medium into ethanol and carbon dioxide which is release from the fermentor. They require 2 - 3 days to produce 80% ethanol in the medium.
After a sufficient period of incubation, the spent medium is transferred to a wash chamber where it is processed (distilled) to extract 96% of ethanol.
It must be borne in mind that that this is the conventional method of ethanol production. Modern production techniques are based on advanced continuous fermentation.
• ·hat are the drawbacks of ethanol production?
Ethanol is highly toxic to the microorganisms like bacteria; it sterilizes the bacteria and reduces their biomass. This is true,
but some organisms resisting ethanol are used for the extraction of ethanol.
Carbohydrates are very costly and so the produced ethanol must fetch a high price. This problem can be solved by using wastes as substrate for the production of ethanol.
The isolation and purification of ethanol is mainly effected by distillation which needs some amount of energy. So there is wastage of energy during the manufacture of ethanol.
• What are the various applications of ethanol?
Ethanol is an active solvent of dyes, lubricants, adhesives, a few detergents, some pesticides, paints, explosives and resins. It is also used as an organic solvent for the extraction of some organic compounds from living things.
Ethanol is used in the manufacture of synthetic rubber.It is used in the manufacture of synthetic fibres like rayon, polyester, etc.It is used in the extraction of certain pharmaceutical products.It is used in the manufacture of acetaldehyde.It is used in the manufacture of
perfumes.Ethanol is used as fuel in internal combustion engines either, in the form of anhydrous ethanol (98.S% of ethanol) or mixed with Petrol or in the form of hydrated ethanol. The yield of energy will be very high when it is used along with petrol. In most cases, 15% or 10-20% of ethanol is mixed with petrol for fuel purpose in engines and in chemical industries. The energy contents of ethanol are 19 MJ/t.
• In Brazil nearly one-third of cars are running by consuming ethanol as fuel. Brazil produces above 66 million hectoliter of ethanol per year for its need.
• Americans use ethanol along with petrol for running their cars. They are marketing petrol along with ethanol. This country produces 55 billion liters of ethanol per year.
• India produces nearly 10 million hectoliter’s of ethanol per year.
• Can we produce ethanol from carbohydrate based waste? We certainly can. Let us study the following case.In order to produce ethanol from biomass and waste, two stages are required:
1. Hydrolysis to break the material down into simple sugar molecules
2. Fermentation to produce ethanol
Feedstock Composition
Feedstock may include purpose-grown crops (including maize and corn), crop waste, paper mill sludge, forest residues and household waste (including sewage). These are mostly lignocellulosic materials containing cellulose, hemicellulose and lignin. Cellulose and hemicellulose are long chain polymers that make up the bulk of plant material, and lignin is the chemical “glue” that holds them together.
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Hydrolysis
This process breaks the long cellulose and hemicellulose chains into simple sugars. Cellulose yields primarily glucose (a six- carbon sugar) whereas hemicellulose, in the region of 20% of the material, gives a mixture including several five-carbon sugars. Methods of hydrolysis include using enzymes and using dilute or concentrated acids. Whereas in the past
hydrochloric or hydrofluoric acid may have been used, sulphuric acid is found in newer processes.
Sugar Separation
After hydrolysis, the sugar for fermentation must be separated from the acid. A new process developed by the company Arkenol in the United States, which is still at the pilot stage, makes use of ion exchange to improve the separation, allowing a greater proportion of the acid to be concentrated and re-used. Final traces of acid are precipitated as “gypsum” (calcium sulphate) by addition of lime.
Fermentation
Fermentation is a complex series of reactions, which convert carbohydrates, mainly sugars and starches, into ethanol and carbon dioxide. Several enzymes, such as zymase in yeasts, catalyse these reactions. Yeast is a living organism, and these are the products of anaerobic respiration.
Conditions
Fermentation with yeast works best at temperatures in the range 25 - 37°C, in the absence of oxygen (anaerobic) and will produce aqueous solutions of up to 14% ethanol.
Below 25°C the reaction rate is too slow, but at higher temperatures the enzymes start to denature and lose efficiency. If oxygen is present, aerobic respiration will occur producing carboxylic acids, in this case acetic acid (vinegar).
The toxicity of ethanol to the organisms used limits the ethanol concentration possible.
• What are the benefits of Arkenol process?
Conventional yeasts cannot make use of five-carbon sugars that arise from the hydrolysis of hemicellulose.
Conventional methods for ethanol fermentation do not utilize this resource, which may count as 20% of the feedstock.
The process developed by Arkenol uses specially bred yeast (not genetically engineered) that feeds preferentially on C5 sugars, as well as on C6 sugars. In this way, a greater proportion of the feed is utilized.
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• Interesting. Tell me more about this.
Yeast is very good at converting glucose, and other six- carbon sugars into ethanol. Unfortunately, a significant proportion of waste biomass consists of complex natural polymers made from sugars that are not “digested” readily by yeast enzymes.These include hemicellulose, which on hydrolysis produces a range of sugars including: mannose, xylose, arabinose and galactose, depending on the original source.
Genetically engineered Bacteria
A genetically modified bacterium, developed by the
microbiologist Lonnie Ingram in 1987, has enabled these sugars to be converted to ethanol. The bacterium, referred to as KO11, would normally produce acids, but the modification means ethanol is produced instead.
The advantage over yeast is that a wider range of sugars can be processed, enabling the utilization of biomass waste such as wood waste, corn stalks, rice hulls, and other organic waste, which would otherwise require disposal by some other method, or which could only be partially utilized by conventional fermentation methods, making them uneconomic.
• Can ethanol be produced from cellulose based feedstock ? How?
The production of ethanol from corn is a mature technology that is not likely to see significant reductions in production costs. Substantial cost reductions may be possible, however, if cellulose-based feedstocks are used instead of corn. Producers are experimenting with units equipped to convert cellulose-based feedstocks, using sulfuric acid to break down cellulose and hemicellulose into fermentable sugar. Although the process is expensive at present, advances in
biotechnology could decrease conversion costs substantially. The cost of producing ethanol could be reduced by as much as 60 cents per gallon by 2015.
The two most common methods to increase the oxygen level of gasoline are blending with MTBE and blending with ethanol. Because ethanol has higher oxygen content than MTBE, only about half the volume is required to produce the same oxygen level in gasoline.
• What is the process like?
Ethanol is produced from the fermentation of sugar by enzymes produced from specific varieties of yeast. The five major sugars are the five-carbon xylose and arabinose and the six-carbon glucose, galactose, and mannose. Traditional fermentation processes rely on yeasts that convert six-carbon sugars to ethanol. Glucose, the preferred form of sugar for fermentation, is contained in both carbohydrates and cellulose. Because carbohydrates are easier than cellulose to convert to glucose, the majority of ethanol currently produced in the United States is made from corn, which produces large quantities of carbohydrates. Also, the organisms and enzymes for carbohydrate conversion and glucose fermentation on a commercial scale are readily available.
The conversion of cellulosic biomass to ethanol parallels the corn conversion process. The cellulose must first be converted to sugars by hydrolysis and then fermented to produce ethanol. Cellulosic feedstocks (composed of cellulose and hemicellulose) are more difficult to convert to sugar than are carbohydrates. Two common methods for converting cellulose to sugar are: 1. Dilute acid hydrolysis and
2. Concentrated acid hydrolysis,
Both these processes include use sulfuric acid. Dilute acid hydrolysis occurs in two stages to take advantage of the differences between hemicellulose and cellulose:
The first stage is performed at low temperature to maximize the yield from the hemicellulose, and
The second, higher temperature stage is optimized for hydrolysis of the cellulose portion of the feedstock.
Concentrated acid hydrolysis uses a dilute acid pretreatment to separate the hemicellulose and cellulose. The biomass is then dried before the addition of the concentrated sulfuric acid. Water is added to dilute the acid and then heated to release the sugars, producing a gel that can be separated from residual solids. Column chromatographic is used to separate the acid from the sugars.
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• What are the drawbacks of this process?
Dilute acid hydrolysis of cellulose tends to yield a large amount of byproducts. Concentrated acid hydrolysis forms fewer byproducts, but for economic reasons the acid must be recycled.The separation and reconcentration of the sulfuric acid adds more complexity to the process. In addition, sulfuric acid is highly corrosive and difficult to handle. The concentrated and dilute sulfuric acid processes are performed at high temperatures (100 and 220oC) which can degrade the sugars, reducing the carbon source and ultimately lowering the ethanol yield.
Thus, the concentrated acid process has a smaller potential for cost reductions from process improvements.
• What is the alternative process then?
It is called countercurrent hydrolysis. This is a two stage process:
In the first stage, cellulose feedstock is introduced to a horizontal co-current reactor with a conveyor. Steam is added to raise the temperature to 180oC (no acid is added at this point). After a residence time of about 8 minutes, during which some 60 percent of the hemicellulose is hydrolyzed, the feed exits the reactor.
It then enters the second stage through a vertical reactor operated at 225oC. Very dilute sulfuric acid is added to the feed at this stage, where virtually all of the remaining hemicellulose and, depending on the residence time, anywhere from 60 percent to all of the cellulose is hydrolyzed.
The countercurrent hydrolysis process offers more potential for cost reductions than the dilute sulfuric acid process. Its is estimated that this process may allow an increase in glucose yields to 84 percent, an increase in fermentation temperature to 55oC, and an increase in fermentation yield of ethanol to 95 percent, with potential cumulative production cost savings of about 33 cents per gallon.
The use of cellulosic biomass in the production of ethanol also has environmental benefits. Converting cellulose to ethanol increases the net energy balance of ethanol compared to converting corn to ethanol. The net energy balance is calculated by subtracting the energy required to produce a gallon of ethanol from the energy contained in a gallon of ethanol (approximately 76,000 Btu). Corn-based ethanol has a net energy balance of 20,000 to 25,000 Btu per gallon, whereas cellulosic ethanol has a net energy balance of more than 60,000 Btu per gallon. In addition, cellulosic ethanol use can reduce greenhouse gas emissions. Argonne National Laboratory estimates that a 2-percent reduction in
greenhouse gas emissions per vehicle mile traveled is achieved when corn-based ethanol is used in gasohol (E10), and that a 24- to 26-percent reduction is achieved when it is used in E85. Cellulosic ethanol can produce an 8- to 10- percent reduction in greenhouse gas emissions when used in E10 and a 68- to 91-percent reduction when used in E85.
• So what do we conclude from all this?
In American context, ethanol has enjoyed some success as a renewable fuel, primarily as a gasoline volume extender and also as an oxygenate for high-oxygen fuels, an oxygenate in RFG in some markets, and potentially as a fuel in flexible- fuel vehicles. A large part of its success has been the Federal ethanol subsidy. The future of ethanol may depend on whether it can compete with crude oil on its own merits. Ethanol costs could be reduced dramatically if efforts to produce ethanol from biomass are successful. Biomass feedstocks, including forest residue, agricultural residue, and energy crops, are abundant and relatively inexpensive, and they are expected to lower the cost of producing ethanol and provide stability to supply and price. In addition, the use of corn stover would lend continued support to the U.S. corn industry. Analysis of NREL technological goals for cellulose ethanol conversion suggests that ethanol could compete favorably with other gasoline additives without the benefit of a Federal subsidy if the goals were achieved. Enzymatic hydrolysis of cellulose appears to have the most potential for achieving the goals, but substantial reductions in the cost of producing cellulase enzymes and improvements in the fermentation of nonglucose sugars to ethanol still are needed. Significant barriers to the success of cellulose-derived ethanol remain. For example, it may be difficult to create strains of genetically engineered yeast that are hardy enough to be used for ethanol production on a commercial scale. In addition, genetically modified organisms may have to be strictly contained. Other issues include the cost and mechanical difficulties associated with processing large amounts of wet solids. Proponents of biomass ethanol remain confident, however, that the process will succeed and low-cost ethanol will become a reality.
Ethanol production is a multifaceted operation. From the processing and storage of incoming raw materials through to the storage and shipment of the final products, many industrial processes come into play. Ethanol production combines aspects of both the grain handling and chemical production industries.
Despite the best available technology and strictest attention to safety procedures, human error and mechanical failure must be taken into account when considering potential hazards to employees and the surrounding community.
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Learning Objectives
In this lecture, you will learn• Antibiotics & alkaloid products
• Penicillin fermentation
Antibiotics are probably the most important group of
compounds synthesized by industrial microorganisms. They are not produced in the greatest quantity, nor are they the most economically valuable. Nevertheless, over the last 60 years their influence in improving human health has been immense. ‘The other major health-care products derived from microbial fermentations and/or biotransformation are alkaloids, steroids, toxins and vaccines; along with vitamins, certain enzymes, and viable microbial cell preparations used as probiotics. In addition, genetic engineering techniques have made it possible for microorganisms to produce a wide variety of mammalian proteins and peptides that have various therapeutic properties. Those of considerable medical importance and with established markets include insulin, interferons, human growth hormone and monoclonal antibodies. Apart from these therapeutic agents, which cure or reduce the incidence of disease, many diagnostic products are also derived from microorganisms. These are extensively used to test for the presence of various health and disease states.
Let us first see about the most well known product group, viz. antibiotics.
Before we start with the study of antibiotic fermentations as such, let us go back a little and start with the definition of an antibiotic. So, what is an antibiotic and how does it differ from other antimicrobial substances?
If antibiotic is a substance that kills microorganisms or inhibits their growth, can common disinfectants like phenyl, chlorine, iodine etc. can be called antibiotics? No? Why not?
If antibiotic is a substance that kills microorganisms or inhibits their growth at very very low concentrations, then can we call cyanide or peracetic acid an antibiotic? No? Why not? If antibiotic is a substance that is produced by one organism and kills or inhibits their growth of other organism, can we call snake venom an antibiotic?
No? Why not?
The answers of all the three above questions are obviously negative. This is because the definition of an antibiotic is actually a combination of all that is mentioned above. Thus, an antibiotic is an organic compound produced by one organism