PRODUCTION OF MOTOR FUEL FROM MOLASSES
Economic development of any society is crucially dependent on energy
By ENGR. ABDUL WAHEED BHUTTO
Sep 20 - 26, 2004
Sugarcane is an important cash crop of Pakistan and serves as major raw material for the production of white sugar and gur. A small quantity of sugar is also produced from beet-sugar. It is an important source of income and employment. It share in value-added of agriculture and GDP 4.2 percent and 1 percent respectively. Sugarcane was cultivated on an area of 1,074 thousand hectares during 2003-2004 and the size of sugarcane crop is estimated at 53419 thousand tones. To produce sugar from cane 72 sugar mills have already been installed with a crushing capacity of 62 million tons of cane and a sugar production capacity of 5.30 million tonnes. Apart from that, four mills located in the North West Frontier Province, are based on sugar beet. During the 2003-04 season, national sugar industry rolled out a record sugar output at 3.997 million tonnes, processing 43.468 million tonnes of sugarcane.
Process of sugar manufacture from cane or beet, releases the molasses, which is typically 4 percent by weight on the quantity of cane or beet processed, or 40 percent on the sugar produced. The actual quantity of molasses produced cannot be directly and accurately correlated to the annual sugar or crop production, because quantity of molasses may vary depending on the type of sugar produced.
Molasses is a syrup containing mixture of uncrystallizable sugar, non-sugar solids originating from cane or beet, chemicals from the sugar manufacturing process and some water. It contain approximately 50 percent sucrose and 50 percent other components that include water, various organic components (other than sucrose) and inorganic salts. Because of its high sucrose content, a substantial portion of the molasses is used worldwide for the production of ethyl alcohol through fermentation. It has been estimated that around 80 percent of the world's molasses is used for alcohol production whereas rest is used for animal feeds and other products.
A good quality molasses having higher sugar contents is used for producing wide range of edible goods and industrial materials. The lower quality molasses is mostly used in preparation of animal feeds as well as chicken feeds.
Molasses is converted into ethanol (ethyl alcohol) through biochemical processes based on fermentation. After preparation of a mash with the appropriate concentration of sugar and solid, the pulp is transferred into fermentator (Biochemical reactor), where sugar is transformed into alcohol using yeasts as the catalyst. Fermentation takes four to 12 hours during which, significant amount of CO2 and heat is liberated. The CO2 liberated during fermentation can be converted into valuable products, such as dry ice, liquid CO2 for soft drinks, fire-fighting foams, filtration products, and various industrial uses. The fermentation is carried out in batch or continuously process, using open or closed fermentation tanks. Continuous processing increases the productivity of fermentation, i.e. the amount of ethanol fermented per unit volume per hour. High productivity reduces the volume capacity required for fermentation tanks, thereby reducing costs. After fermentation, the ethanol is separated from other by-products by distillation, to produce hydrous ethanol that contains 5 percent water. Hydrous ethanol is used commercially, but it cannot be blended with gasoline. It is not technically possible to separate the azeotropic mixture of 94 percent ethanol and 6 percent water by simple distillation process. Normally cyclo-hexane is added as solvent to form a tertiary azeotropic mixture with water and alcohol, to produce 100 percent pure ethanol that can be blended with gasoline.
In distilleries low steam utilization technologies have been introduced through heat integration using waste heat to increase the temperature and pressure of other processes. Due to high scaling and corrosive nature of molasses, continuous operations of distillation or evaporation are normally subjected to frequent shutdowns. Installation distillation systems with appropriate combination of vacuum/pressure and temperatures not only helps in preventing the downtime but also is useful in improving alcohol quality considerably.
In a cane or beet sugar factory, sugar production process comprises of juice extraction, clarification, evaporation, crystallization and centrifugal separation. During these operations, juice-holding time, exposure temperature and addition of chemical affect the composition of molasses. High temperature along with high or low pH increases sugar caramelization. Use of lime, sulfur and CO2, increase the content of calcium and carbonates in molasses. Prolonged holding of juice at low temperature and inadequate mill sanitation, increases the microbial contamination and acids in molasses. Many mills operator add biocides in sugar syrup to control microbe's growth. These biocides are extracted in molasses as residuals, and affect the yeast in distillery fermentation. Molasses as it is produced from the centrifugal stage is in a hot condition (52 to 55oC). Similarly due to the chemical treatments, it contains large amount of sulfurous gases. On line cooling and mixing of molasses it is important to avoid the caramelization of sugars and release of self generated gases. Molasses if not cooled properly helps growth of heat stable microbes that affects fermentation.
Processing of fresh molasses is usually result high microbial count in distillery fermentation. Sulfurous gases can inhibit yeast. Similarly fresh molasses has high foaming tendency as well as high buffering capacity. It also contains high level of suspended sludge. Due to above reasons fresh molasses is stored for at least a month before using in distillery. Cooling and frequent mixing by re-circulation is carried out during storage to avoid internal combustion and caramelization that deteriorate quality. Over storage of molasses above six month on the other hand can reduce the fermentable sugar content slowly. Molasses is stored in steel tank to prevent contamination. In order to control the effects of age of molasses, recording the production span, life and operating with first in first out principles are normally necessary.
Proper sanitation during storage of molasses is necessary to avoid the microbial contamination. Contact with water and pockets of dilution in bulk stock, can give rise to high microbial flora. Contact of soil with molasses also should be avoided. It is necessary to handle and store in protective environment, taking above-mentioned account into consideration.
Molasses quality plays influential role in the outputs and efficiencies of alcohol production. Experience, understanding of the effects of composition on various process operations, and adapting to innovative technological advancements to effectively and positively control the effects, can help in maintaining consistently high alcohol yields and high spirit quality with minimum needs of process/energy inputs as well as treatment of wastewaters.
The conversion of molasses to ethane is the first step to enhance value addition for sugar industry. Industrial alcohol, acetic acid, oxalic acid, citric acid, acetone, pharmaceuticals, ether and ethyl acetate can be produced from molasses and then a chain of other organic chemicals can be manufactured.
Alcohols have been used as fuels since the inception of the automobile. With the oil crises of the 1970s, ethanol became established as an alternative fuel in many countries including Brazil and the United States. In addition to the energy rationale, ethanol/gasoline blends in the United States has been promoted as an environmentally driven practice initially as an octane enhancer to replace lead. Ethanol also has value as oxygenate in clean-burning gasoline to reduce vehicle exhaust emissions.
In the Brazil programme to promote ethanol production was established in 1975 to reduce the country's dependence on imported oil, and to help stabilize sugar production. Now most of the cars and light vehicles use either neat-ethanol (94 per cent ethanol, 6 per cent water) or gasohol (78 per cent gasoline, 22 per cent ethanol) as fuel. Additionally, the programme was almost entirely based on locally manufactured equipment that helped in establishing a strong agro-industrial system, with a significant number of indirect jobs. The country has demonstrated technological developments, in both agriculture and cane processing, leading to lower ethanol costs and the possibility of a large surplus in biomass-based (bagasse and trash) electricity. It has helped to reduce oil imports, to stabilize and promote the growth of the sugar industry, to create quality jobs, and to reduce automobile pollution in urban areas. It is a model for biomass-to-energy programmes elsewhere.
In the United States, ethanol supplies at present account for about one percent of the highway motor vehicle fuel market, in the form of a gasoline-blending component. Most of this ethanol is used in a 10 percent blend with gasoline traditionally referred to as gasohol, a term which is being replaced with ethanol/gasoline blends or E10. Lower percentage blends, containing 5.7 percent or 7.7 percent ethanol are also being used in some areas to conform to air quality regulations affecting the oxygen content of reformulated gasoline.
No special engine modification or handling precautions are needed when using a 10 percent ethanol blend. Such widespread international experience indicates that the viability and functionality of petrohol will be much the same as of the corresponding petrol with which the ethanol is blended. Ethanol can loosen contaminants and residues that have been deposited by previous gasoline fills. These can collect in the fuel filter. This problem has happened occasionally in older cars, and can easily be corrected by changing fuel filters.
SCENARIO IN PAKISTAN
During the crushing season 2002-2003, the country's has produced around 2 million tonnes of molasses out of that 1.45 million tonnes were exported at a nominal rate of $35 per tonne. According to official figures around 134,000 tonnes of fresh molasses has already been exported during the current season 2003-2004. The average export price of ethanol in the world market is around $360 per tonne.
In the country, sugar mills generally do not have proper storage system of molasses and normally most of the mills store the produce in open and in kutcha pits, which are exposed to atmospheric changes as well as dirt. Very few mills had steel tank storage facilities. The poor sanitation condition deteriorate the quality of molasses, at the same time the molasses is contamination by microbial. The contaminated molasses when processed in distillery give lower yield. Once the quality and sugar content in molasses improves, exporters could fetch better price in the world market.
According to industry sources, average ethanol recovery from one tonne of molasses is estimated at 240 to 270 liters depending on the quality of molasses. If the country manages to process the entire two million tons of molasses in the distilleries, ethanol production will be over 0.408 million tonnes, and on exporting the same at an average price of $360 per tonne, around $147 million could be earned on its export. On the other hand, if the entire quantity of two million tonnes of molasses were exported it would only fetch $70 million at an average price of $35 per tonne. Thus, there is a glaring difference in earning foreign exchange between two products. But at present the country is only producing around 0.183 million tonnes of ethanol (This include the production from four distilleries, which are not attached, with any sugar mill and they produce around 17.70 million liters of ethanol). By export of 0.183 million tonnes of ethyl alcohol, the country will earn $66 million as against $70 on the export of entire quantity of two million tonnes of molasses. The country should reap addition benefit from local production of ethanol by promoting the use of ethanol as gasoline blending component
The present consumption of petrol stands at 1.27 million tons per year. At this consumption, complete replacement of petrol with gasohol, containing 10 percent ethanol, will require around 0.127 million tonnes of ethanol. Local production/import of automobiles based on ethanol fuel and implementation of gasohol program can result in substantial reduction in import bill and country's dependence on imported crude oil.
Economic development of any society is crucially dependent on energy. The way this energy is produced supplied and consumed strongly affects the local and global environment. It is, therefore, a key issue in sustainable development. Pakistan is the world's fifth largest sugar producing country after Brazil, India, China and Mexico. The country can successfully implement alcohol fuel programmes by promoting impart/local production of ethanol-based automobiles and providing incentives of investment in local distillery industry. Brazil can be the role model in this project where almost 10 per cent automobiles are based on ethanol fuel that is far more environment-friendly than diesel or petrol. Several other developing countries are producing fuel ethanol from cane molasses, and in some of the countries national alcohol fuel programmes have started to pay the dividend.
NO. OF DISTILLERIES OPERATING IN PAKISTAN