The main Cellulosic Ethanol Production Processes, Technologies and Companies are summarized below.
Cellulosic ethanol derived from lignocellulosic biomass and biodiesel derived from non food oil crops such as Jatropha which are capable of growing in land not suitable for most food crops make the second generation biofuels.
The feedstocks of first generation of biofuels are starch crops such as corn (biofuel from corn in US), sugar crops such as sugarcane (Brazil) and oil crops such as rapeseed (European countries) and soybean (US). The one characteristic of these crops that connects them all is their requirement of suitable arable fertile land to grow. Their cultivation invariably results in cutting down the area under cultivation with food crops. This restricted the acceptance of first generation biofuel crops and resulted in the development of biofuel production from lignocellulosic biomass and algae.
Feedstock for Cellulosic Ethanol
Crop residues that include stalk sand leaves, wood residues, dedicated energy crops such as Poplar, Switchgrass and Miscanthus and industrial and other wastes such as municipal solid waste and black liquor from paper and pulp industry all come under the lignocellulosic biomass feedstock. These are suitable for second generation bioethanol or cellulosic ethanol production.
The main Cellulosic Ethanol Production Processes, Technologies and Companies are listed below.
Lignocellulose to Cellulosic Ethanol Production Processes and Conversion Technologies
Lignocellulosic biomass is composed of cellulose, hemicellulose, and lignin. The release of these three components from the biomass to get sugars is the major challenge and various technologies are being developed to overcome the hurdle. Article describes briefly the technologies applied for conversion of lignocellulosic biomass into ethanol.
(A) Via thermo-chemical conversion
This route involves gasification, scrubing of syngas and catalytic conversion of syngas into alcohol. In the gasification step the dried and chopped biomass is fed into a gasifier. At a high temperature and oxygen-limited steam environment it gets converted into synthesis gas which is a mixture of carbon monoxide (CO) and hydrogen (H2).
In the next step syngas is scrubbed to remove the trace elements. The clean syngas is passed over a catalyst which converts it into an alcohol or mixture of alcohols. The alcohol mixture is dehydrated and separated to specification purity.
Enerkem utilizes this approach to produce cellulosic ethanol from lignocellulosic biomass.
(B) via thermo-biochemical pathway
(i) Conversion of lignocellulosic biomass into sugar followed by its microbial fermentation
In this route the first step is pre-treatment which is done by dilute acid or steam explosion. This results in separation of cellulose from lignin and hemicelluloses. In the next step the cellulose is subjected to hydrolysis by concentrated acid, dilute acid or enzyme which breaks down the cellulose into small sugar units. The sugars released in the previous step are fermented into ethanol with the help of microorganisms such as the common brewer’s yeast in the last step.
(ii) Conversation of biomass into syngas followed by syngas fermentation:
The first step in this route is gasification of dried and chopped lignocellulosic biomass at high temperature and oxygen limiting environment. It results into the production of syngas (CO+H2) and some CO2. In the next step syngas is fermented in a special fermenter by microbes that consume carbon monoxide, carbon dioxide and hydrogen and produce ethanol and water. This process generally uses bacteria rather than yeasts.
INEOS Bio utilizes this approach to produce bioethanol from lignocellulosic biomass.
3. Consolidated Bioprocessing
Consolidated bioporcessing aims to combine the various steps of bioethanol production from lignocelluloses, such as hydrolysis of the pretreated biomass and the fermentation of released sugars as much as possible into one step. The microbes utilized in this route are specially engineered to express the enzymes needed to degrade cellulose into sugars and sugars into alcohols.
Although very promising fourth generation biofuel production technologies have come, the developments in the cellulosic waste to bioethanol conversion technologies are happening at a fast speed.