What Is 2G Ethanol Plant ? Technology, Production Process

ASN Fuels Pvt Ltd has filed a patent for loop reactor technology. It is a long, serpentine tubular reactor, in which fermentable sugars are converted to ethanol with the help of brewer’s yeast. Ethanol plant experts pointed out a need  of few kilometres of pipeline when the pipeline reactor technology scaling up calculations were done to suit the industrial standards for an average rated capacity of 50 kilo litres per day (KLPD).

This ignited an idea to come up with reactive pipeline technology, wherein the pipeline relates the sugar factories where the ethanol is produced to the blending depot at the closest oil manufacturing companies.

Reactive pipeline technology is poised to be a game-changer for sugar factories and grain-based distilleries since uninterrupted raw material supply is a major challenge. Our dependency on oil / fuel will greatly be reduced and we will become Atmanirbhar Bharat as more and more ethanol is made available.

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There are number of advantages of using bioethanol as fuel. Some of the benefits are the following:

• Reduced dependency on crude oil imports: For oil importing countries like India, The major driving
  force is to reduce their dependency on fossil fuels. It benefits energy security as it can reduce
  crude oil by using domestically produced energy sources. Countries like India, having a limited
  access to crude oil resources, can grow crops for energy use and gain some economic freedom.
• Cleaner environment: Due to the fact that the exhausts from the automobile engines using
  bioethanol blended gasoline is more cleaner in nature, the second major benefit of using
  bioethanol is its ability to reduce the overall carbon footprint and their use help in reduction of
  greenhouse gas (GHG) emissions. It will also reduce the GHG emissions by reducing the of
  agriculture residues burning.
• Renewable energy source: Bioethanol is produced using plant materials such as corn, sugarcane,
  crop residues, etc. Since, all these are crops can be grown; bioethanol fuel is a renewable energy
  source.
• Financial benefit for farmers: Agricultural residues and wastes which otherwise are burnt by
  farmers can be utilized for producing bioethanol.

Raw material components:

As stated earlier, the 2G bioethanol technology uses ligno-cellulosic biomass as a feedstock.
Lignocellulosic biomass is mainly composed of plant cell walls. It essentially contains three major
components viz. Lignin, Cellulose, and Hemicelluloses. Cellulose and Hemicelluloses are the structural
carbohydrates while lignin is heterogeneous phenolic polymer.
Cellulose is a polysaccharide made up of linear glucan chains held together by intra molecular hydrogen
bonds and by intermolecular Van-der Waals forces. In order to obtain glucose, the crystalline cellulose
must be subjected to some preliminary chemical or mechanical degradation.
Hemicellulose consists of short, highly branched chains of sugars. Hemicelluloses are highly amorphous
and branched structures. It contains pentoses, hemicelluloses chains. Compared to cellulose, the
hemicelluloses can easily be broken down to form their simple monomeric sugars. The exact sugar
composition of hemicelluloses can vary depending on the type of plant.
Lignin is a non-sugar-based polymer. Lignin is not a suitable component for microbial fermentation process.
It inhibits microbial growth and fermentation. However, lignin can be used as energy source as it yields more energy when burned, and thus can be utilized for combined heat and power production in the
bioethanol process.

Process Description:

The bioethanol process is carried out in following four major steps.
1. Pre treatment: Physical or chemical pre-treatment of the fibers to expose the cellulose so as to
reduce its crystallinity.
2. Hydrolysis : Cellulose polymer is hydrolysed with enzymes or acids, to convert it into simple
(glucose) sugars
3. Fermentation: Microbial fermentation of simple sugars to form ethanol.
4. Distillation and dehydration to produce 99.5% vol. fuel grade ethanol.

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Pretreatment:

Due to the presence of lignin in ‘Lignocellulosic “materials, and compared to the accessibility of sucrose in
sugar cane and starch in grains, cellulose and hemicelluloses are not easily and readily available for
saccharification and fermentation. A “pre-treatment” step is hence required to facilitate conversion of
cellulose and hemicelluloses to fermentable sugars.
The pre-treatment process converts hemicellulose carbohydrates into soluble sugars (like glucose, xylose,
etc.) by hydrolysis reactions in which acetyl groups in the hemicellulose are liberated in the form of acetic
acid. Biomass feedstock is chemically treated by disrupting cell wall structures in the pre-treatment step
which facilitates downstream enzymatic hydrolysis. This section is also termed as ‘Delignification’ section
as the pre-treatment drives some lignin into solution. This step reduces cellulose crystallinity and chain
length. Process parameters such as residence time, temperature, and catalyst loading affects the pre
treatment process. The pre treated biomass is sent to the hydrolysis reactor.

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Hydrolysis:

Hydrolysis process is used to convert hemicellulose and cellulose content of lignocellulosic biomass into
fermentable monomeric sugars. This process can be carried out by two different routes. These routes are
Acid hydrolysis and Enzymatic hydrolysis.
In acid hydrolysis process, mineral acids such as HCl, H2SO4, HNO3, or HF are widely used for hydrolysing
lignocellulosic biomass. In enzymatic hydrolysis, Cellulose is converted to glucose using cellulase
enzymes. Enzymatic hydrolysis process is also termed as ‘Enzymatic Saccharification’ process. A
cellulase enzyme is prepared from mixture of enzymes (catalytic proteins) which work together to break
down cellulose fibers into glucose monomers.
For higher conversion and it’s suitability to the lower grade of metallurgy, enzymatic hydrolysis route is
preferred over the acid hydrolysis route.
The glucose and other sugars obtained from hydrolysis of hemicelluloses are co-fermented to form ethanol in the next step.

Fermentation:

Fermentation process step is similar to the 1G ethanol technology. In this step, the hexoses and pentoses
are converted into ethanol by employing variety of micro organisms, such as yeast, bacteria, fungi, etc.
Depending on how the enzymatic hydrolysis and fermentation steps are integrated, the technology can
follow either of following route.
 Separate Hydrolysis and Fermentation
 Separate Hydrolysis and Co-fermentation
 Simultaneous Saccharification and Co-fermentationDistillation and Purification:
Distillation and purification steps are also similar to the technology used in 1G bioethanol process. From
fermented mash, fuel grade ethanol is produced through distillation and adsorption via molecular sieve.
Etanol and water forms an azeotropic mixture. Hence, the distillation can be used to obtain ethanol purity
only upto 95.5 vol.% (corresponding to azeotropic composition) Desired fuel grade ethanol specification (of 99.5% vol.) is achieved by passing the 95.5 vol.% ethanol obtained from distillation through a molecular sieve.

Technology Selection Criteria:

There are various technologies presently available for manufacturing 2G bioethanol. The main parameters
that influence the technology selection are discussed in brief.
(1) Feedstock: Ability to process variety of feedstocks like rice straw, wheat straw, bagasse, corn cob,
cotton stalk etc. Technology suitable to use mixed feedstock can be preferred.
(2) Conversion Efficiency: This decides the quantity of feedstock required for the given ethanol
throughput. Technology with higher conversion efficiency is preferred. Typical conversion
efficiencies are 20%.
(3) Conversion time: This varies from each technology. The hydrolysis, fermentation are batch
processes and depending upon the technology used, the net conversion time will vary. Apart from
start up time, this impacts capital costs and inventory costs.
(4) Enzyme/Yeast Requirement: Quantity and cost of enzymes/yeast may affect overall economics of
the technology selected.
(5) Utility requirement: In general, the 2G ethanol technologies require significant amount of steam for
removing water from the raw ethanol stream. The concentration of ethanol leaving the fermenter
hence thus dominates the steam requirements; this is usually `5%.
(6) Water recycle: Technology to be optimized and preferred when fresh water intake is minimized.
(7) Turn down requirements: Ability of the technology to run on low turndown, say 25% is preferred.

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Technological Challenges:

Since the 2G technology is not fully commercialized in India, few technological challenges still needs to be addressed. These issues need a detailed assessment and are briefed as below.
1. Commercial scale operation of 2G Ethanol Process: The commercial scale plant experience is
available for one technology licensor. And others have demo or pilot scale experience.
2. Higher cost of production compared to first generation ethanol: The cost of ethanol production from
lignocellulosic biomass is higher than first generation ethanol and there may be requirement of
subsidy for economic viability and competitive ethanol pricing.
3. Commercial availability of lignin boiler: Lignin is recommended to be used as fuel in boiler and
therefore the commercial availability of such applications needs to be ascertained.
4. Pretreatment forms a critical section and is the main process step that separates the 1G and 2G
technologies. Commercial experience for pretreatment section is not available.
5. The availability of biomass round the year depends on proper pre planning and it is essential to
build the ecosystem for ensuring biomass supply. Supply of secondary fuel for use in boiler is also
to be addressed.
6. Biogas and Co2 utilization: Finding the consumer and/or disposal of Biogas and Co2 produced
from 2G technology remains an open issue.

Indian Scenario:

The practice of blending ethanol in gasoline was begun in India in 2001. Government of India, in 2003,
mandated blending of 5% ethanol with gasoline in 9 States and 4 Union Territories. This was subsequently
continued on an all-India basis in November 2006 (in 20 States and 8 Union Territories except a few North
East states and Jammu & Kashmir). Indian Oil companies were asked to increase the ethanol blending
target to 15% by Ministry of Petroleum and Natural Gas, on 1 September, 2015 and achieve this blend in
as many states as possible.
At 10% blending, the projected ethanol demand is ~5500 million liters per anum by year 2021-2022. It
would certainly require significant investments in near future. Presently, First few plants to produce
bioethanol using 2G technologies are under consideration and are at various stages of planning and
design.

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Future Technology:

Third generation (3G) bioethanol technology is based on ethanol production from Microalgae. At present,
Microalgae is gaining more attention as it is an alternative renewable source of biomass which can be
used for 3G bioethanol production. The increased interest to use microalgae is also attributed to the fact
that it can be generated all year along and does not need any pesticides or herbicides. It can be produced in sea water or brackish water and thus do not compete with agricultural land. Comparatively, microalgae have ability to reduce freshwater consumption as it needs less water than terrestrial crops. Another technology to generate bioethanol from the CO2 emission sources (Iron and steel producers) is also recently commercialized.

Conclusion

Bio-ethanol is regarded as an important renewable fuel. The Indian economy is growing at a rate of
approximately 7% to 7.5% resulting in the increased demand for energy. Bioethanol presents a sustainable source of energy. 2G Bioethanol technologies are being used in India. TCE is connected with one of the first 2G bioethanol plants being installed in India and have first hand experience of commercializing such technology.