Bioethanol production technologies: Where are we? Where should we be?

W.D.S.S. PemasingheBS/2004/233

Contents Why we need alternative fuels? What are the main candidates for biofuels? What is bioethanol? What are the production schemes for bioethanol? How does bioethanol become a good solution?

economic issues environmental issues

Problems and suggested solutions

Why we need alternative fuels? Continuous depletion of limited fossil fuel

stock (Global issue).

Ensure protection and betterment of the environment (Global issue).

National security- to be dependent on foreign nations for energy (USA and the European Union)

Who are the main candidates for biofuels?

Bioethanol

Biodiesel

What is bioethanol?

Ethanol derived from agricultural sources, as distinct from petrochemical sources, is referred to as bioethanol.

Esvc000085.wic012u.server-web.com/pubs/biofuels.doc

Production schemes for bioethanol Bioethanol is mainly produced in three ways.

sugar ethanol

starch sugar ethanol

cellulose and hemicellulose ethanol

Direct conversion of sugar to ethanol This is usually done using molasses.

Molasses is a thick dark syrup produced by boiling down juice from sugarcane; specially during sugar refining.

As molasses is a by product, ethanol production from molasses is not done in a large scale around the world.

The main reaction involved is fermentation

C6H12O6

sugar (e.g.:-glucose)

yeast2 C2H5OH

ethanol

+ 2 CO2

carbon dioxide

Wet milling

The process of separating the corn kernel into starch, protein, germ and fiber in an aqueous medium prior to fermentation

The primary products starch and starch-derived products (e.g. high fructose corn syrup and

ethanol) corn oil, corn gluten, and corn gluten .

Dry milling

The entire corn kernel is first ground into flour and the starch in the flour is converted to ethanol via fermentation.

Other than ethanol carbon dioxide - carbonated beverage industry distillers dried grain with solubles (DDGS) - animal feed

Malting

Steep the corn in water, start germination, stop germination at a particular by drying to stop further growth.

Conversion of starch to sugar and then sugar to ethanolEg:-1) wheat

Fermentation conditions

Temperature - 32˚C and 35˚C pH - 5.2.

Ethanol is produced at 10-15% concentration and the solution is distilled to produce ethanol at higher concentrations

Eg:- 2) sugar cane

Simplest of all the processes

• Fermentation conditions are similar to the above process

Eg:- 3) CornThe main producer - United States

http://www.dft.gov.uk/pgr/roads/environment/research.htm

Economics of non-cellulosic ethanol Ethanol production using sugarcane, sugarbeet,

corn are well established.

Rise of the Food vs. Fuel crisis and the shift towards cellulosic ethanol "...large increases in biofuels production in

the United States and Europe are the main reason behind the steep rise in global food prices" -World Bank policy research working paper July 2008

Using crops that can be used for food, to produce bio-fuels

Government support of biofuels with tax breaks, mandated use, and subsidies.

land that was also formerly used to grow crops for food is now used to grow crops for biofuels

placing energy markets in competition with food markets

unintended consequence of diverting resources from food production and leading to surging food prices and the potential destruction of natural habitats.

Food vs. Fuel crisis

Challenge for the future…

Improvement of the cellulosic ethanol production process.

Since it is produced from non-edible parts of plants, cellulosic ethanol does not compete with the production of food, resulting in no contribution for the price surge of food.

Cellulosic ethanol

www.agwest.sk.ca/publications/documents/BPfeb05.pdf

Overview of the cellulosic ethanol production technology

Conversion of cellulose and hemicellulose to ethanol 4 steps1. Pretreatment2. Hydrolysis3. Fermentation4. Distillation of the product mixture to

separate ethanol

1) Pretreatment

The solubilization and separation of one or more of the four major components of biomass – hemicellulose, cellulose, lignin, and extractives – to make the remaining solid biomass more accessible to further chemical or biological treatment.

2) Hydrolysis

The breaking down of the glycosidic bonds in cellulose and hemicellulose

acid hydrolysis Sugars made after acid hydrolysis get converted into

furfural in the acidic medium which can act as fermentation inhibitors.

Reaction should be rapid Sugars should be rapidly removed

enzymatic hydrolysis

Dilute acid hydrolysis

Done using dilute acid (1% sulfuric acid) Two reaction chambers.

Chamber1- hydrolysis of hemicellulose (mild conditions) Chamber2- hydrolysis of cellulose (harsh conditions)

High temperatures and pressures Disadvantages

Costs are high Yields are quite low

Therefore concentrated acid hydrolysis is used

Concentrated acid hydrolysis

Done using concentrated acid (70% sulfuric acid)

Done in one reaction chamber

Provides a complete and rapid conversion of cellulose and hemicellulose to C6 and C5 sugars

Advantages Optimize sugar recovery Cost effectively recover the acid for recycling

Acid hydrolysis of cellulose

http://www.turon.com/papers/ethanol.htm

Enzyme hydrolysis

Bacteria and fungi are used as sources of cellulases, hemicellulases that could be used for the hydrolysis of pretreated lignocelulosics.

There are two technological developments. Enzymatic conversion Direct microbial conversion (DMC)

Direct microbial conversion (DMC)

A single microorganism does both hydrolysis and fermentation.

Advantage Cellulose enzyme production or purchase is a significant

cost in enzymatic hydrolysis under development. With DMC, a dedicated step for production of cellulase enzyme is not necessary.

Disadvantage Currently available microbes cannot do both processes

at the required efficiencies

Enzymatic conversion

The enzymes are extracted from microorganisms and are modified genetically to increase efficiencies.

For enzymes to work efficiently, they must obtain access to the molecules to be hydrolyzed.

This further asserts the necessity of pretreatment process to remove crystalline structure of cellulose to expose the molecules to the microorganisms.

Applications of enzymatic hydrolysis(a) Simultaneous sacchrification and fermentation

(SSF)

Cellulase enzymes and fermenting microbes are added to one vessel - hydrolysis and fermentation happen in one reaction vessel.

Advantage Reduces cost

Disadvantage

Cellulase enzymes and the fermentation enzymes have to operate under the same conditions - decreases the sugar and ethanol yields.

(b) Sequential hydrolysis and fermentation (SHF)

Hydrolysis and fermentation are done in separate reaction chambers.

Advantage Enables optimization of conditions for the enzymes.

Disadvantage Operational and maintenance costs are high.

3) Fermentation Fermentation of both C5 and C6 sugars

Problem The ability to ferment pentoses along with hexoses is not widespread among microorganisms.

SolutionDevelop genetically modified microorganisms using recombinant DNA technology which can ferment both forms of sugars.

Zymomonas mobilis - The National Renewable Energy Laboratory (NREL)

4) Distillation This is done to separate ethanol from other products.

Ethanol & economy (e.g.-American economy)

Creating new high-paying jobs Increasing market opportunities for farmers Generating additional household income tax and revenues Stimulating capital investment

In 2007, the ethanol industry provided employment for 238,000 workers in all sectors of the U.S. economy, added $47.6 billion to the nation’s GDP, and put an additional $12.3 billion into the pockets of American consumers. (Source: Contribution of the Ethanol Industry to the Economy of the United States)

The increase in good paying jobs as a result of the facility boosted local household incomes by more than $100 million. (Source: "Contribution of the Ethanol Industry to the Economy of the United States," LECG, LLC, Feb 2008.)

Environmental impact of bioethanol technologies Positives Uses energy from renewable energy sources; no net CO2 is added to

the atmosphere, making ethanol an environmentally beneficial energy source

Toxicity of exhaust emissions is lower than that of petroleum sources

Energy crops grown for the production of ethanol absorbs huge amounts of green house gases (GHG) released by the burning of fossil fuels.

Ethanol contains 35% oxygen that helps complete combustion of fuel and thus reduces particulate emission that pose health hazard to living beings.

Negatives

Deriving ethanol from crops (eg:- corn) consumes copious amounts of nitrogen fertilizer and extensive top-soil erosion associated with cultivation of this particular crop. contamination of the Mississippi River -‘dead zone’

Recent researches Manipulate nitrogen metabolism and fixation pathways to

reduce the dependence on environmentally damaging fertilizers.

To enhance performance of enzymes, encapsulate enzymes in silicon or carbon nanostructures, providing enzymes with protection from pH and thermal denaturation.

Genetically manipulate Saccharomyces cerevisiae (yeast) so that it can ferment both C5 sugars and C6 sugars

FermentationGlycolysis

Alcoholic fermentation

Inhibition by furfural