Ethanol Production Process Information
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Ethanol from Corn
** The following describes the dry milling process
1. Milling - corn is first ground into flour (meal) and then water, enzymes, and ammonia are added to form a mash. Enzymes are required to convert the starch to a simple sugar (dextrose) and ammonia is added for pH control and as a nutrient for the yeast
2. Cooking - this step is performed to reduce bacteria levels prior to fermentation
3. Fermentation - Here, sugars are converted to alcohol and water. Yeast is added to facilitate this process.
4. Distillation - The water and alcohol are separated at this step
5. Byproduct and Residue Processing - This final step involves processing the leftovers from the process - typically called distillers grain.
Even though in the following section I have stated why and listed sites to reference that show how & why Cellulosic Ethanol is more advantageous than corn ethanol, a few years ago at home, I made about 20oz of ethanol from corn - this since the process to pretreat Switchgrass had not yet made itself available to the small scale, individual brewer. To see the results of this test, click here to view these results, and to view information on the process to follow for 'Home Brewing" ethanol, see the bottom of this page. Also further down this page, see how I intend to attempt producing ethanol from Switchgrass at home.
Consider what Energy Farming would do for small communities and jobs - it goes without saying that in upstate NY, dairy farming is weak and jobs are scarce, so what would it mean to pursue farming crops for a purpose other than dairy or vegetable farming - certainly something like this would revive communities & family farms, and produce jobs in the US that can't be shipped off shore. Some claim energy crops, specifically ethanol from corn, will cut into our food supply, however, ethanol made from other biomass such as Switchgrass, Corn Stover, or Reed Canary Grass, according to the USDA in a 2005 study, would not cut into the production of food supplies (https://php.radford.edu/~wkovarik/drupal/?q=node/46 ). Often in the summer from the North Country to Central New York I see hay left standing and fields unattended to. Since these fields are idle and none the less not feeding people, why not grow crops on them that could be used as fuel sources and heat sources, where we could press the hay from them into densified heating fuel sources and plant high cellulose grasses to make ethanol from. In cases where only the cobs are used for food or grain, (or even corn ethanol) and the stalks are left behind to rot, we can take the wasted stalks such as is done in the mid west, extract the cellulose, break it down into its C5 and C6 sugars, and then ferment and distill it into ethanol - all from the same single plant that provides food.
A detailed example of how a farm could produce multiple products from a single crop is:
Ethanol from Corn | Cellulosic Ethanol Summary | Sample Processes | Cellulosic Ethanol Production Process | Cellulosic Ethanol Challenges
Information sources, unless specifically noted after a statement for the remainder of this page are 1)http://www.wikipedia.org/ or 2) Biofuels, Biotechnology, Chemistry, and Sustainable Development by David M. Mousdale CRC Press Taylor & Francis Group, 2008, ISBN 13: 978-1-4200-5124-7
7) The following is a simple diagram I put together that shows the Cellulosic Ethanol production process:
Cellulosic Ethanol Production Process
This step separates the biomass and its components by disrupting the sheath found around the biomass material. The reason for this is to expose the plants Cellulose for Hydrolysis and to make the most surface area possible available to enzymes or chemicals in the Hydrolysis step.
Pretreatment is accomplished via one of or a combination of the following means:
▪ Physical milling (milling)
▪ Thermo physical (steam)
▪ Chemical (acids, ect)
▪ Biological (microbes)
Specific methods of Cellulolysis Pretreatment are listed as follows:
1) Dilute Acid - Steam Explosion
▪ feedstock is impregnated with acid (H2S04 - sulfuric acid) H2SO4 is used because of its low cost
▪ feedstock is then processed in a steam explosion reactor
▪ time in the reactor (residence time) and temperature levels of the reactor seem to determine the ethanol yield down the line
▪ A good sample experiment of this using corn stover is at http://www.nrel.gov/docs/gen/fy03/32119.pdf
2) Ammonia Fiber Expansion
▪ Liquid ammonia is used to pretreat and explode biomass
▪ Ammonia is recycled
▪ Process is run at 60-100C, 20-80% moisture, and biomass ration is .5 to 1.3-1.0
- For more details, see http://www1.eere.energy.gov/biomass/pdfs/34861.pdf
▪ Ammonia Fiber Expansion (AFEX) is a promising pretreatment with no inhibitory effect in resulting hydrolysate (meaning it leaves no impurities that
3) Lime Pretreatment
▪ For more details, see http://www1.eere.energy.gov/biomass/pdfs/34861.pdf
▪ Takes 1 to 2 months - looks to be done in a pile or bunk silo
4) Flow through Pretreatment
▪ For more details, see http://www1.eere.energy.gov/biomass/pdfs/34861.pdf
5) Controlled PH Pretreatment
▪ For more details, see http://www1.eere.energy.gov/biomass/pdfs/34861.pdf
6) Ozone Pretreatment
7) Alkaline Wet Oxidation
David M Mousdale in his book states that biological pretreatment methods (instead of chemical methods) have the following advantages:
▪ Less energy is required
▪ Hardware demands are less
▪ No environmental damaging waste products result
▪ Dangerous chemical situations are avoided
Scientists call the next step cellulose hydrolysis. Here acid from pretreatment (if used) is washed off, and the mixture goes to tanks with enzymes (if going the Enzymatic hydrolysis route) called cellulases, where the role of cellulases is to turn cellulose into glucose.
Hydrolysis converts the complex carbohydrates of the biomass to fermentable sugars - specifically, it breaks down the plants Hemicellulose to its C5 sugars (xylose, mannose, arabinose and galactose) and Cellulose to its C6 sugars. This conversion is accomplished via several of methods, where the choice of method is dependant on several variables that include, type of feedstock, available sugars, operating conditions, economics, and conversion typically is biological or chemical in nature.
Some specific methods of hydrolysis are listed as follows:
Chemical (Acid) Hydrolysis
1) Dilute Acid
▪ process uses more heat and pressure
▪ sugar degradation is a problem and can lower sugar yield and toxins can be left over that hamper fermentation
▪ uses 1% sulfuric acid solution in a continuous flow reactor at 215�C
▪ Sugar conversion efficiency is 50%
▪ Two step process, since hemicellulose (5 carbon sugar) degrades faster than 6 carbon sugars (Cellulose)
a) mild conditions to recover 5 carbon sugars
b) harsher process to recover 6 carbon sugars
- both resulting hydrolyzed solutions are then fermented to alcohol. Lime is used to neutralize acids prior to fermentation, and leftover lignin is used
to as boiler fuel or to make steam to produce electricity
2) Concentrated Acid
▪ process uses lower heat and pressure
▪ uses concentrated sulfuric acid and then dilution with water to dissolve and hydrolyze material into sugar
▪ process converts cellulose to glucose, and hemicellulose to 5 carbon sugars
▪ acid is recycled in the process
▪ Two step process:
a) Hemicellulose hydrolyzation uses a 70% sulfuric acid solution and is hydrolyzed at 100F for 2-6 hours in a hemicellulose hydrolysis reactor.
Material is then soaked with water and drained many times to recover the sugars
b) Cellulose hydrolyzation - from step a, the solids are taken and soaked in a 30-40% sulfuric acid solution for 1-4 hours. Material is then drained
and dried, and the acid rate is increased to 70% and placed in another container for 1-4 hours at low temperatures. The sugar and acid are then
recovered. This acid is then used in step A.
▪ This process has about 90% sugar conversion efficiency.
In this process, enzymes are used to hydrolyze the cellulose (C6 Sugar) and hemicellulose (C5 sugars). The list of enzymes that have been tried and can be used is extensive. Examples of this list are contained in a list of patents & applications for cellulase and hemicellulase enzymes & technologies that are listed on pages 77-79 in David M. Mousdale's book. In this list, over 30 patents and patent applications are listed for Cellulase Enzymology, a dozen for Hemicellulases, and several patents and patent applications are listed for Hemicellulase Enzymology. Many of these are found on forest floors and some are classified are used for degrading lignin (David M. Mousdale's book, pages 78 & 81) .
Some examples of Cellulase and Hemicellulase are (these are needed to convert cellulose and hemicellulose to sugars (glucose molecules):
Cellulase Sources and Examples:
▪ Trichoderma reesei - produces cellulase enzymes
Hemicellulase Sources and Examples:
▪ Yeasts and Fungi
▪ Marine Algae
▪ Wood-digesting insects
▪ Higher Plants (in germinating seeds)
Companies who currently produce Enzymes for this process are:
▪ Iogen - http://www.iogen.ca/
▪ Genecor - http://www.genencor.com/wps/wcm/connect/genencor/genencor
▪ Novozymes - http://www.novozymes.com/
▪ Dyadic International Inc - http://www.dyadic.com/wt/home
▪ Verenium - http://www.verenium.com/
Online resources that list details for scientists and researchers to reference when working to find the right combinations of microbes and enzymes to use with the various feedstocks are:
Here, sugars are converted to alcohol and water by the same means that consumable alcohol is produced. This process starts with a combination of the Hydrolized substrate and an appropriate microbe that will digest the sugars and secrete alcohol. For this, many yeasts and microbes have been tested & used (where one of the best for producing ethanol is Saccharomyec Cerevisiae), while other genetic research has led to more cost effective & efficient strains to be developed.
Some common yeasts used for fermentation are defined as follows:
Zymomonas mobilis (Z. mobilis) - bacterium that converts sugars to pyruvate, which is then fermented to ethanol and carbon dioxide. NREL has
developed a version that leads to more efficient fermentation of both C5 and C6 sugars. Arkenol will be using the NREL
Saccharomyces cerevisiae - bakers yeast used in brewery industry to produce ethanol from C6 sugars
Escherichia coli - (E. coli) uses mixed-acid fermentation in anaerobic conditions, producing lactate, succinate, ethanol, acetate and carbon dioxide
Consolidating process steps in any situation generally improves efficiency, produces economical gain, and simplifies an operation. In Cellulosic Ethanol production, recent developments have come about where ethanol and required enzymes for the process are produced from the same microorganism, or to state it another way, options to allow for the consolidation of steps that break down biomass and also produce ethanol are beginning to present themselves (Ethanol Producer Magazine, April 2012). Any of the following terms are used to reference this consolidation, where each has the same general meaning:
▪ Direct Microbial Conversion
▪ Consolidated Bioprocessing
▪ Simultaneous scarification and fermentation (SSF)
Some examples and instances of how this is being achieved are:
1) Some bacteria have been found to convert cellulose directly to ethanol. Examples of these bacteria are:Clostridium thermocellum (C. thermocellum) - this
bacterium will convert cellulose directly to ethanol, but has some other byproducts that can reduce efficiency during fermentation
2) Recently (article posted 02/23/2012) Novozymes "unveiled a new high-efficient enzyme - called Cellic CTec3 - it says CTec3 will break down corn
husks, Switchgrass and other feedstocks into sugars to make cellulosic ethanol but at a lower cost". This article found at
http://www.governorsbiofuelscoalition.org/?p=1668 also states that CTec3 is "one-and-a-half times better and you will only need one fifth the amount
compared to competing enzymes" and then goes on further to state that "50 kilograms of Cellic CTec3 will produce one ton of ethanol made from
biomass compared to the 250 kilograms of competing enzymes"
3) Recently, researchers from the US DOE and Oak Ridge National Laboratory identified Caldicellulosiruptor obsidiansis in a hot spring at Yellowstone
National Park. Given its characteristics of functioning well in a hot environment, researchers believe that it can be used in consolidated bioprocessing
(Ethanol Producer Magazine, April 2012).
4) http://en.wikipedia.org/wiki/Cellulosic_ethanol - In 2010, a genetically engineered yeast strain was developed that produces its own cellulose-digesting
enzymes. Assuming this technology can be scaled to industrial levels, it would eliminate one or more steps of cellulolysis, reducing both the time
required and costs of production
5) Anaerobic bacteria (David M. Mousdale's book, page 67)
6) With SSF, cellulose and hemicelluloses are converted to soluble sugars simultaneously (David M. Mousdale's book , page 189). Tables on page 193
also list enzymes & microbe used in SSF, including one for Reed Canary Grass, two for Switchgrass, and several for corn stalks & cobs (corn stover)
The water and alcohol are separated at this step. This process of separating alcohol from water is the same as is used in making corn ethanol. In the traditional process, the 'beer' is be heated to the point where the alcohol (which boils at a lower temperature than water) evaporates up leaving water behind. The alcohol vapor is contained and cooled, which turns it back to a liquid, with this liquid being mainly alcohol (some water will/may remain, so to purify the alcohol it may be run thru the distillation system repeatedly until the desired % of alcohol content is achieved.
Since a production facility would need to choose the right distillation method for the situation in order to keep costs down, the following are some other distillation options & methods available to use (David M. Mousdale's book , pages 194-196)
▪ Continuous Ethanol recovery from fermentors - this removes ethanol during Fermentation
▪ Molecular Sieving - these are synthetic zeolite resins and crystalline lattices that allow the penetration of water molecules, but exclude ethanol. Per
David M. Mousdale's, page 194, this process has been used on an industrial scale and new plants are being built using molecular sieve dehydrators
▪ Vacuum dehydration
▪ Liquid extraction
▪ Super critical fluid extraction
As an example of what a commercial Cellulosic Plants output/year might look like, David M Mousdale calls a large production plant one that produces greater than 40 million gallons of ethanol/year.
5. Byproduct and Residue Processing
Once the alcohol has been separated, this final step involves processing and making use of the leftovers from the process. Some examples of this use of leftovers are listed below.
Iogen in Ottawa Ontario is a leader in developing Cellolosic Ethanol technologies, and currently is following a process where lignin, at the end of their process, is burned in CHP (Combined Heat and Power) (David M. Mousdale's book , pages 157-168). Process followed by other companies are using production process leftovers by producing thermal energy and electricity from these leftovers that is then used in the cellulosic ethanol production process. A diagram showing this can be found at http://zfacts.com/p/85.html
Other process leftovers that have value are:
▪ CO2 from the fermentation process
▪ DDS (Dry Distillers Grain)
▪ Water that is recycled (David M. Mousdale's book, page 183)
Using the right microbes and yeasts:
Pretreatment: separation of 4 components of biomass - hemicellulose, cellulose, lignin, and extractives so that they can then be broken down into their sugar
Cellulolysis: the hydrolysis of cellulose
Lignin: A complex polymer, the chief noncarbohydrate constituent of wood, that binds to cellulose fibers and hardens and strengthens the cell walls of plants (1)
Cellulosic Ethanol News Links
Governors Biofuels Coalition: http://www.governorsbiofuelscoalition.org/?cat=1
Sweetwater Energy: http://sweetwater.us/news
Oak Ridge National Laboratory: http://www.ornl.gov/info/press_releases/newsroom.cfm
Avro Technologies: http://www.avrotechnologies.com/info/
I'm now successfully converting Switchgrass and Corn Stalks (cellulose) that we grow on the farm in Calaboga to sugar, and then am completing fermentation and final distillation to alcohol/ethanol. The goal of this work is to understand the process and identify feasibility for establishing this process on a residential and community basis, where centralized processing could be set up to utilize both dedicated energy crops and agricultural left overs to produce ethanol and other products that could serve as income and energy sources for local farms and a local community.
Here the pretreated substrate was mixed with distilled water, pH and temperature stabilized and then a Cellulase enzyme was added using the hydrolysis set up shown below. For both Switchgrass and corn stalks, I run a 27 hour agitation at 50 - 55 degrees Celcius. During and after the 27 hour agitation, using a diabetes BG meter I was able to measure the presence of sugar (middle picture) in the slurry (far right picture below) as also shown below: