Ethanol is the most appropriate fuel for India to replace petrol, and the utmost of efforts have been made to increase alcohol production in the country. India is in an extremely happy position in this regard as it is the world’s largest producer of sugarcane, a major source of alcohol. India topped the world in sugar production with 181 Mton (in 1978), followed by Brazil (130 Mton) and Cuba (67 Mton).

Alcohol is derived not directly from sugarcane but molasses-sugar­cane by-products. All starch-rich plants like maize, tapioca, and potato can be used to produce alcohol; cellulosic waste materials can also be used. Production of ethanol from biomass involves fermentation and distillation of crops. India has a vast potential to produce ethanol, and only 2.5% of the country’s irrigated land is used to produce sugarcane. This can be raised to a much higher level without adversely affecting the production of food-bearing crops.

At present, Brazil is the only country that produces fuel alcohol on a large scale from agricultural products (mainly sugarcane). Other coun­tries, especially those with an substantial agricultural surpluses, such as the United States and Canada, are also bound to enter into this field of so-called energy forming. The area of land required is substantial. A medium-sized car with an annual run of 15,000 km needs 2000 L of ethanol. To produce this amount, the crop areas required are given in Table 7.2. To provide enough sugar beet alcohol to fuel 20 million cars in Germany requires half the area of the entire country.

Sugarcane. The present method adopted to obtain alcohol for energy purposes requires three stages: (1) extracting the juice from sugarcane, (2) fermentation of the juice, and (3) distillation into 90-95% alcohol.

Molasses. The black residue remaining after the sugar is extracted from sugarcane is called molasses. It contains mostly invert sugars and some sucrose. This sucrose also undergoes hydrolysis to produce invert sugar by a catalytic action of acids in molasses.

C12H22O11 + H2O ^ C6H12O11 (D-Glucose) + C6H12O6 (D-Fructose)

This mixture product is not crystallizable. Yeast organisms in the pres­ence of oxygen oxidize sugars into CO2 and H2O and convert sucrose mostly into ethyl alcohol.

C6H12O6 ^ 2C2H5OH + 2CO2

Process adopted. Molasses is mixed with water so that the concentra­tion of sugar in it is 10-18% (optimum is 12%). If the concentration is high, more alcohol may be produced and may kill the yeast. Then, a selected strain of yeast is added (it should not contain any wild yeast). For some nutrient substances like ammonium and phosphates, the pH value is kept between 4 and 5, which favors the growth of yeast organ­isms. H2SO4 is used for lowering pH. The temperature of the mixture is kept at 15-25°C. The fermentation takes place as follows:

1. First, the yeast cells multiply at an optimum temperature (30°C).

2. Rapid fermentation takes place at the boiling temperature, and oxygen is given off. The optimum temperature (50°C) is maintained, and the process is continued for 20-30 h.

3. The fermentation rate is reduced, and alcohol is produced slowly. Total time for fermentation is 36-48 h, depending upon the temper­ature and sugar content. Last, the formed ethanol is distilled.

Starch. In this process, starchy materials are first converted into fer­mentable sugars. This is done by enzymatic conversion (by means of malt process) or by acid hydrolysis.

Starch ^ C12H22O11 (Maltose) + C6H12O6 (Dextrose)

Malt process. Malt is prepared by germination of barley grains to pro­duce required enzymes. The grain is ground and steam cooked at 100-150oC to break the cell wall of starch. For every 25 kg of grain, 100 L of water is added. Then the formed mass is cooled to 60-700C and taken to large vessels where malt is added within 2 h and 60-70% of the stock is converted into maltose. Converted mash is cooled to a fermenting temperature of 20-250C. pH is adjusted and fermentation is affected, producing ethanol.

Acid hydrolysis. This process involves treatment with concentrated sulfuric or hydrochloric acid at pH 2-3 and 10-20 kg pressure in an auto­clave to make sugar and then conversion of sugar to alcohol by yeast.

Cellulose material.

Wood. Cellulose from wood is hydrolyzed into simple sugars by using diluted acid at a high temperature or concentrated acid at a low tem­perature. Similarly, cellulosic agricultural waste and straws can be used in place of wood.

Sulfite waste liquor from paper manufacture. Waste liquor contains 2-3.5% of sugar, out of which 65% is fermentable into alcohol. Before fermen­tation, all acids in the liquor are removed by adding calcium. Then fer­mentation is carried out by special yeasts. Generally, 1% of liquor is converted into alcohol.

Hydrocarbon gases.

Hydration of ethylene. Conversion of ethylene to ethyl alcohol can be carried out with high yield by first treating ethylene with H2SO4, forming ethyl hydrogen sulphate and diethyl sulfate, as given by the following reactions:

C2H5HSO4 — (C2H5)2SO4 2C2H4 + H2SO4 — (C2H5)2SO4

These products, ethyl sulfuric acid and diethyl sulfate, when treated with water give ethanol as per the following reactions:

C2H5HSO4 + H2O — C2H5OH + H2SO4
(C2H5)2SO4 + 2H2O — 2C2H5OH + H2SO4

Direct hydration. Ethanol is also formed as per the following chemical reaction:

C2H4 + H2O — C2H5OH

This type of conversion is very small as the reaction is exothermic; it is not a suitable method for mass production. The corn is first ground, then mixed with water and enzymes, and cooked at 150oC to convert starch to sugar. The mixture is then cooled and sent to fermentation tanks, where yeast is added and the sugar is allowed to ferment into ethanol. After 60 h in the tanks, the mixture is sent to distillation columns, where ethanol is evaporated out, condensed, and mixed with unleaded gaso­line to form gasohol, which contains 90% gasoline and 10% ethanol.

Tapioca materials. Tapioca is available in plenty in Asia, the United States, central Europe, and Africa. Its production can be increased through modern cultivation techniques. The process consists of con­verting the tapioca flour into fermentation sugars with enzymes prior to fermentation with yeast. Modern technology uses a-amyl glycosidase, one of two enzymes required in the process, and then saccharification of the material into alcohol by using yeast.

Anhydrous alcohol from vegetable wastes. The Philippines has embarked on an “alcogas program” to produce its own anhydrous alcohol from local vegetable wastes for blending with petrol. The program is cur­rently based on sugarcane juice and molasses, but it plans to diversify by using other raw materials. In the basic process, cellulose conversion begins with the pretreatment of the raw materials, which may include coffee hulls, rice straw, grass—even sawmill wastes. Enzymes then take over by converting the feedstock into a sugary liquid that is fermented and finally distilled into anhydrous alcohol. After distillation, waste residues can be evaporated into syrup to feed animals, while uncon­verted cellulose is used as the primary fuel for the plant. If the Philippines could engineer a breakthrough in this area, its agricultural and forestry wastes could supply energy equivalent to 9720 mL of oil annually. In the years to come, this new energy source could make a sig­nificant economic impact on a country that depends on imports of crude oil for 95% of its energy.

Manioc. As oil prices continue to rise, more and more work is being done on alternatives. Manioc is one such staple crop in many tropical lands. Brazil has planned to use manioc in its ethanol production plants, aiming to make 35,000 bbl a day from 400 X 103 ha of manioc plantation. Conversion of manioc to ethanol is somewhat more complex than is the case with sugarcane. The raw material has to be turned into sugar by fer­mentation. This first step requires the use of enzymes. Danish Co. has developed the necessary heat-resistant enzymes in a pilot plant in Brazil.

Manioc does not grow in higher temperature zones; so scientists have turned to other plants, and there is work being done in Sweden that is in an advanced stage. They have developed fast-growing poplars and wil­lows. Their yield is 30 ton/ha, which is equal to 12 tons of fuel oil.

It is estimated that 1000 X 103 ha planted with such trees can pro­vide 10% of Sweden’s electricity. Also in Sweden, work has been carried out on the common reed, and the estimated yield is 10 ton/(yr • ha), which is equal to 4.5 tons of oil. Sweden has plans to have 100 X 103 ha of reeds. Brazil’s program of ethanol from sugarcane and manioc may employ 200 X 103 people and save $1600 million each year in foreign exchange.