Course: Chemical Technology (Organic) Module V

Lecture 1

Introduction to Sugar, Fermentation Industry and

Manufacture of Alcohol

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LECTURE 1 SUGAR AND FERMENTATION INDUSTRY

INTRODUCTION

Sugar industry is one of the most important agro-based industries in India and has an important

impact on rural economy. India is the first two largest sugar producing countries in the world

sugar production during 2007-08 wasRs.263 lakh. There are 624 sugar factories in the country as

on 31-03-2009. Sector wise breakup is as follows in Table M-V 1.1.

Table M-V 1.1: Profile of sugar industry

Sector No. of sugar factories Private 245 Public 62 Cooperatives 317 Total 624

As per 2010-11 Area 4.98 million hectares Cane production 346.00 Million tonnes Sugar production 24.20-24.50 Million tonnes Source: Business standard April 24, 2012

In 2010-11, sugarcane was planted in 4.98 million hectares across the country, of which 1

million hectares was in Maharashtra and over 2 million hectares in Uttar Pradesh, official

estimates show. Uttar Pradesh and Maharashtra are the two largest sugarcane producing states in

the country, accounting for more than 80percent of the annual crop production. India is one of

the largest producers of alcohol in the world and there has been a steady increase in its

production over the last 15 years, according to fresh statistics.

India is a dominant producer of alcohol in the South-East Asian region with 65percent of the

total shares and contributes to around seven percent of the total alcohol beverage imports into the

region. More than two-thirds of the total beverage alcohol consumption within the region is in

India, according to figures in the newly compiled Alcohol Atlas of India. There has been a steady

increase in the production of alcohol in the country, with the production doubling from 887.2

million liters in 1992-93 to 1,654 million liters in 1999-2000 and was expected to treble to 2300

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million liters by 2007-08. Sugar industry is highly seasonal industry, with season lengths of

about 6-18 weeks for beets and 20-32 weeks for cane [Pollution Prevention hand book, World

Bank group July, 1998]

PROCESS STEPS IN SUGAR MANUFACTURE Sugar contains 70percent water, 14percent fibre, 13.3percent saccharose (about 10-15percent

sucrose) and 2.7percent impurities. The yield of sugar depends mostly on the quality of cane and

the efficiency of the extraction of juice crushing, milling and squeezing of juice through a series

of pressure mills containing grooved walls Weak juice and make up water is added as extractant

before squeezing to maximize juice yield. After crushing and extraction of juice, baggase is left

as residue which is about 33.3percent of the total cane crushed. Bagasse is used as fuel for

boilers. However about 10percent of bagasse is available surplus which is used for paper making

it can be also used for manufacture of alcohol.

Purification of juice for removal of impurities by addition of calcium phosphate followed by

addition of lime to precipitate the impurities in the form of colloid. This followed by bubbling of

SO2 for maximum flocculation of impurities. SO2 also acts as a bleaching agent. Further the

flocculation of the impurities is achieved in the continuous settler. Double carbonation using CO2

and double sulphitation using SO2 is used. The Clarified solution goes to evaporator and the

underflow of clarifier goes to rotary filter for removal of the impurities as cake. The filtrate

containing sugar from the rotary filter is recycled. Clarified juice is concentrated in the in

multiple effect evaporator to about 40 percent. The concentrated syrup is again bleached by

passing SO2 through it. Concentrated sugar solution is then sent to vacuum pan where thickened

syrup is boiled three to four times and then sent to crystallizer where separation of sugar crystal

takes place. It is sent to high speed basket centrifuges for separation of sugar crystal. The syrup

is re-concentrated and cooled successively to obtain one or two crops of crystal. The final mother

liquor called molasses is sent to distilleries for production of alcohol by fermentation process.

Schematics diagram of sugar production process is shown in Figure M-V 1.1.

PROCESSING SUGAR BEAT: Sugar beat contains 75 percent water and about 17

percent sugar. In processing of beet first it is washed and sliced the slices are then go to rotary

diffuser where a counter current flow of water is used to remove sugar from beet slices. Various

stages in manufacture of sugar from sugar beets are:

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Figure M-V 1.1: Schematics of Sugar Production Process

Source: Kaul et al.,1998

 

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EXTRACTION OF JUICE: This involves washing, shredding and extraction of juice

JUICE PURIFICATION: The extracted juice is purified using lime and CO2 for removing non-

sugar substance from the Juice.

EVAPORATION OF JUICE: Evaporation of the purified juice from 15percent sugar content

to 65-70percent sugar content

CRYSTALLISATION: Crystallization of concentrated sugar solution to sugar crystal.

Molasses are left behind after crystallization which is use for production of alcohol.

REFINING OF THE RAW SUGAR: The raw sugar is dissolved, filters and crystallized again

to get high grade refined sugar.

ETHANOL India is amongst two largest sugar producing countries in the world and converts the molasses

from sugar plant to alcohol. India is fourth largest producer of ethanol in the world and second

largest in Asia. India produces about 2.75 billion liters alcohol annually. The demand for potable

alcohol has been ever increasing [Chauhan et al., 2012]. Today 95 percent of ethanol is produced

by fermentation and only 5percent is produced from petroleum feed stock by ethylene route

[Data, 2011]

Ethanol has become one of the important products as alternative feedstock for large number of

organic chemicals and fuel. Ethanol is an oxygenated fuel that contains 35percent oxygen, which

reduces particulate and NOx emissions from combustion [Badger, 2002]. Alcohol is now being

used for potable liquor, as chemical feed stock, as solvent and as oxygenates. Process

manufacturing of alcohol is shown in Figure M-V 1.2.

Various routes for manufacture of ethanol are:

Alcohol from Fermentation of molasses

Alcohol from Lignocelluloses biomass

Alcohol from starchy feed stocks

Petrochemical route via Catalytic hydration of ethylene and Ethylene esterification and

hydrolysis

Fermentation of Molasses

 

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Molasses is the residue left after extraction of crystallised sugar and is one of the major

byproducts of the sugar industry. Ethyl alcohol is made from molasses by fermentation process

utilising yeast enzymes.

A typical distillery consist of

Molasses handling

Fermentation feeding system

Preparation of yeast inculam, propagation of yeast

Fermentation

Distillation of dilute alcohol for removal of impurities

Concentration of the dilute alcohol to rectified spirit and absolute alcohol

Molasses handling involves weighing of the molasses and pumping of molasses to the molasses

tank from which the measured quantity of molasses is transferred to the fermenter.

Preparation of yeast inculam, propagation of yeast: Yeast material is prepared in water cooled

yeast vessels by inoculating molasses with yeast and then transferred to aerated yeast activation

vessel to allow time for yeast cell multiplication

Fermentation involves fermentation of fermentable sugars by microorganism and formation of

alcohol and other by-products. Yeast (Saccharomyces cerevisiae) is commonly used for the

fermentation of glucose to ethanol. After the fermentation alcohol of 7-8percent strength is

obtained. Fermentation is exothermic process and heat is generated. Removal of heat is

necessary to maintain the temperature in fermenter. High temperature lowers the alcohol

productivity. Nutrients are added to the fermenter intermittently depending upon the

requirement. Sulphuric acid is added to adjust the pH of fermenter liquid. Excess foaming in the

fermenter is controlled by antifoam solution. During the normal operation treated yeast cells

recovered from the fermented wash are recycled from the yeast treatment system to activation

vessel and after that transfer to the fermenter.

After fermentation is completed, the dil. liquor (8-10percent alcohol) is preheated and pumped to

the beer still where the alcohol 50-60percent) and other volatiles like aldehydes are distilled off

from the top and send to the aldehyde column for separation of aldehydes and other low boiling

impurities. The residue from the bottom of the beer column is known as slops or tillage are

discharged and treated for recovery of energy or concentrated and used. Alcohol drawn from side

 

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stream of the aldehyde column is sent to rectifying column. The azeotrop alcohol containing

alcohol about 95-96percent alcohol is taken as top side stream from the rectifying column.

Figure M-V 1.2: Process of Manufacturing of Alcohol Alcohol recovery: this section involves the recovery of alcohol from the fermentation section to

minimize the possible losses of alcohol along with generated CO2 and sludge from fermented.

Typical reactions involved are C12H22OH + H2O C6H12 O6 + C6H12 O6

 

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Molasses Glucose + Fructose C6H12 O6 C2H5OH + 2CO2

ALCOHOL FROM BIOMASS In India alcohol is mainly produced by the sugar and distilleries industries as a byproduct of

molasses fermentation Technologies for producing ethanol from cellulosic biomass through

fermentation and chemical hydrolysis have been developed from lab to commercial scale.

Globally, if even 10 percent of biomass is used for fuel production there may be substantial

reduction in oil consumption.

Ethanol thus produced can be a promising chemical feedstock. US based Primus green Energy

has developed a high conversion efficiency biomass to gasoline process based on innovative

thermal chemical conversion and the process can generate 416 litres of gasoline per tonne of

biomass [Chemical Industry digest March 2012, p.56].

Lignocellulosic biomass is available abundantly and can be used as the alternative feedstock for

bioethanol production. Lignocellulosic biomass includes forest residues such as wood;

agricultural residues such as sugarcane bagasse, corn cob, corn stover, wheat and rice straw;

industrial residues such as pulp and paper processing waste, lignin from pulp and paper mills and

municipal solid wastes, and energy corps such as switch grass. These have the potential for use

as feedstock for the production of fuel ethanol [Reshamwala et al., 1995; Mielenz, 2001; Kim et

al., 2002; Kadam et al., 2003; Kumar et al., 2010]. The nature and availability of lignocellulosic

feed stocks in different parts of the world depend on climate and other environmental factors,

agricultural practices, technological developments, and current usage/consumption [Claassen et

al., 1999; Van Maris et al., 2006]. Composition of common agricultural residues and wastes is

given in Table M-V 1.2.

Table M-V 1.2: Composition of Common Agricultural Residues and Wastes Agricultural residue Cellulose

(percent) Hemicellulose (percent)

Lignin (percent)

Hardwood stem 40−50 24−40 18−25 Softwood stem 45−50 25−35 25−35 Nut shells 25−30 25−30 30−40 Corn cobs 45 35 15 Grasses 25−40 35−50 10−30 Wheat straw 33−40 20−25 15−20

 

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Rice straw 40 18 5.5 Leaves 15−20 80−85 0 Sorted refuse 60 20 20 Cotton seed hairs 80−90 5−20 0 Coastal Bermuda grass 25 35.7 6.4 Switch grass 30−50 10−40 5−20 Solid cattle manure 1.6−4.7 1.4−3.3 2.7−5.7 Swine waste 6.0 28 Primary waste water solids 8−15 NA 24−29 Paper 85−99 0 0−15 Newspaper 40−55 25−40 18−30 Waste paper from chemical pulp

60−70 10−20 5−10

Source: Bhoopathy, 1998; Cheung and Anderson, 1997

PROCESS TECHNOLOGY

All conversion schemes involves following basic steps:

Feedstock harvest, transport and storage

Pretreatment of lignocellulosic biomass

Enzyme hydrolysis of cellulose in the lignocellulosic materials to fermentable reducing sugars

Fermentation of sugar into ethanol

Downstream processing of ethanol Pretreatment of biomass is a prerequisite to the biological conversion of lignocellosic biomass to

ethanol. Pretreatment is done either physically, chemically or biologically to make pretreated

biomass more amenable to subsequent cellulose hydrolysis. Pretreatment alter the size and

structure of the biomass as well as chemical composition [Thakur et al., 2011]. Figure M-V 1.3

shows process diagram of Biochemical Conversion Route of Biomass to Biofuels

Ethanol from cellulosic material is produced either by acid hydrolysis using sulphuric acid or

enzymatic hydrolysis. Both dilute and concentrated sulphuric acid are used in acid hydrolysis.

Dilute sulphuric acid involves milder condition than concentrated sulphuric acid hydrolysis. In

acidic hydrolysis first converts cellulosic materials to sugar followed by conversion of sugar to

other chemicals.

Enzymatic hydrolysis of cellulose another route for alcohol. Enzymatic processes required

pretreatment of lignocellulosic to break the crystalline structure of lignocellulosic and remove

the lignin to expose the cellulose and hemicelluloses. Depending on the biomass material

physical or chemical pretreatment methods may be used. Physical method may use high

 

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temperature and pressure, milling, radiation or freezing. The chemical method uses a solvent to

break apart and dissolve the crystalline structure [Badger, 2002].

Figure M-V 1.3: Biochemical Conversion Route of Biomass to Biofuels

Technological Barriers: Some of the technological barrier which needs to be addressed in

efficient conversion of biomass to ethanol are: [Thakur et al., 2011]

Pretreatment, saccharification of cellulose and hemicelluloses matrix Simultaneous fermentation

of hexose and pentose sugars.

Pre-treatment: The most commonly method used are steam explosion and dilute acid pre hydrolysis, which are followed by enzymatic hydrolysis. Acid hydrolysis are only applied in the two stage acid processes, following acid pre-treatment both dilute and concentrated versions occur. The enzymatic hydrolysis are accomplished by cellulose enzyme. Advantage of lignocelluloses for ethanol production:

To a larger extent, locally/domestically and provide security of supply

Generate low net greenhouse gas emission, reducing environmental impacts, particularly climate change

Also provide employment in rural areas

Greater avoidance of conflict with land used for food and the feed production

A much greater displacement of fossil energy per litre of fuel, due to nearly completely biomass powered system

Much lower net well to wheel greenhouse gas emissions than with grain to ethanol processes powered primarily by fossil energy

The process steps involved are:

Gasification of biomass to hydrogen rich synthesis gas. The gasifier uses superheated steam at elevated pressure.

Carbon dioxide separation and scrubbing of the syn gas

Liquid fuel synthesis using four stage catalytic system

 

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decolouristion of spent wash”, 2012 International conference on future environment and

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4. Chemical Industry digest March 2012, p.56

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