Some potential biofuel plants for production of biodiesel in semi-arid and arid conditions: A review

In India the demand of petroleum products has significantly increased during the last two decades due to rapid expansion in transport, industrial and agricultural sector. Plants provide source of renewable energy. A number of plants belonging to families Euphorbiaceae, Asclepiadaceae, Apocynaceae, Convolvulaceae etc. posses hydrocarbons. These triterpenoids are hexane extractable and can be converted into biofuel using hydro in their saps and latex. They contain hydrocarbons, which have over 30% of tri-terpenoids cracking. Screening of various biofuel plants was carried out.


Increasing
industrialization and unsustainable consumption patterns of natural resources are enhancing the environmental problems due to depletion of resources and energy.The unsustainable use of renewable resources is creating problems to biodiversity environment and human health.Industrial production of hydrocarbon yielding plants as sources of fuel is considered to be one of the best strategies to provide the paradigm to put our society on the path of sustainability.
Solar energy, accumulated under earth in the form of fossil fuels since the inception of life, accounts for more than 97% of the world consumption of energy of which the share of oil is about 39%.The biomass accounts for 43% of the total energy supply in the developing countries as compared to only 1% in the development countries (Hall, 1982).With the present rate of consumption of 65 million barrels of crude oil per day and projected estimates, the present crude reserves may be badly depleted within the next 40 years.The energy costs for extracting the residual crude oil shall far exceed the energy gain after that period (Calvin, 1977).
Also in India, the demand of petroleum products has  (Vimal, 1986).
In the third world, biomass is used mainly as fuel wood by over 90% of the population.The world's total yearly supply of fuel wood, which is more than double in the last 40 years up to 1950, is estimated to have leveled off at about 1070 million m 3 per cent thereafter (Lewis, 1981).Tropical forests in the world are estimated to be vanishing at an annual rate of about 7 million hectares while the corresponding rate for woodlands in the semi-arid zones is 4 million hectares (Tebicke, 1985).On steeply sloping terrain receiving substantial rainfall, as well as in arid and semi-arid zones, clear cutting of forests and woodlands is followed by severe water and wind erosion and land degradation.
In India, 68.5% of the energy used in households is from the firewood and 64.2% of it is collected from natural sources.The shortfall in fuel production is likely to rise to 137 million tonnes in 2000 A.D. from the present 84 million tonnes (Vimal, 1986).The indiscriminate felling of trees has reduced the forest cover to 23% against 33% during the last decade.The annual production of dry dung is of the order of 350 million tonnes from about 240 million cattle, which is capable of generating 70 billion cubic meters of gas annually in biogas processing plants.However, most of the dry dung is used for burning (Murty, 1985).
Energy sources can be broadly divided into three distinct groups: fossil fuels, fissionable nuclear fuels and non-fossil, non-nuclear energy sources.Inspite of their outstanding virtues, fossil fuels have two insurmountable drawbacks.Firstly, these are non-renewable and thus supply of such fuels is either approaching exhaustion or getting more difficult to procure due to transport bottlenecks and steep hike in their price level.Secondly, their continued and increasing use creates environmental problems.Like fossil fuels, fissionable nuclear fuels also suffer from two serious drawbacks.Their supply from relatively cheap sources is drying up even for the most advanced countries.Moreover, the production and use of this source cause a plethora of hazards both to man and his balanced environment.
The non-fossil, non-nuclear energy possibilities fall in three groups: namely, non-solar such as geothermal and tides; indirectly solar such as winds and ocean thermal gradients and directly solar, which among other options includes photosynthesis.All other alternative sources under this category have one or the other practical hurdles in the way of their harnessing energy.Viewed from economic, technological, social, and material factors, they lack the capacity of meeting our future energy needs.Photosynthesis or the photobiological process is a continuous activity, creating organic carbon that burns with less air pollution than fossil fuels.Photosynthesis helps to remove carbon dioxide from the atmosphere and generates oxygen, the life sustaining gas.It thus helps to minimize environmental pollution.During the last hundred years, the concentration of carbon dioxide has significantly increased due to an ever increasing use of fossil fuels.In the last decade alone, it has increased by about 100 ppm.This is likely to warm Garg and Kumar 125 up the upper layers of the oceans and cause a rise in the sea level (Vimal and Tyagi, 1984).
The only appropriate alternative to the socio-economic conditions prevailing in this country is the photosynthetic model of development.It has been the source of an old, reliable and renewable form of energy, now referred to under a new name, biomass.This is relevant even for all developing countries, although its extent and nature may vary from one country to another (Khoshoo, 1984).Out of the total solar energy on earth (3 × 10 24 J), the plant life utilize about 0.1% annually, leading to an annual net production of 2 × 10 11 tonnes of organic matter, which has an energy content of 3 × 10 12 J the total annual energy use, however, is of the order of 3 × 10 20 J (Hall, 1982).One of the natural assets of our country is the abundant sunshine.The total solar radiation received in India is about 60 × 10 13 MWH, with 250 to 300 days of useful sunshine per year in most parts of the country.The daily average direct radiation at places in the central part of the country is 5 to 7 Kwh/m 2 .There is thus, a vast scope for harvesting solar energy and improvement in photosynthetic efficiency (Dayal, 1984).
Biomass energy is thus, environmentally a very acceptable resource.The wide use of biomass for development offers minimal ecological imbalance and provide means of recycle nutrients and carbon dioxide from the atmosphere (Dayal, 1986;Vimal, 1986).
In India until recently, the energy from biomass came almost entirely from fuel wood, crop and livestock residues.However, in the last few years, attention has been given to the question of energy plantation and energy cropping, specifically for the purpose of providing fuel.Technologies are being developed to convert these sources into traditional forms of commercial energy that is, liquid, solid and gaseous fuels.If the new technologies find wider index acceptance and percolate in the rural areas, energy from biomass can meet 77% of the total energy needs of the country (Vimal and Tyagi, 1984).

MODERN BIOENERGY TECHNOLOGIES AND BIOFUELS
Modern bioenergy technologies and biofuels are relatively benign from environmental view point and produce very little pollution if burned correctly and completely.The creation of new employment opportunities within the community and particularly in rural areas is one of the major social benefits from the exploitation of biomass for energy, industry and environment.Use of biomass for energy and industry allows a significant quantity of hydrocarbons to be consumed without increasing the CO 2 content of the atmosphere and thus makes a positive contribution to the Greenhouse effect and to the problems of "global change" as it occurs in both industrialized and developing countries.Further advantages from utilization of biomass include: liquid fuels produced from biomass contain no sulfur, thus avoiding SO 2 emissions and also reducing emission of N0x.Improved agronomic practices and well managed biomass plantations will also provide a basis for environmental improvement by helping to stabilize certain soils, avoiding desertification which is already occurring rapidly in tropical countries.

CALOTROPIS PROCERA
Calotropis procera carried in arid and semi arid lands which occupy one third of the earth's surface.Indian arid zone occupies an area of about 0.3 million sq.km.90% of which about 270,000 sq.km. is confined to north west Indian covering most of Western Rajasthan, part of Gujarat and small portions of Punjab and Haryana.India with its vast expanse of wasteland unsuitable for agricultural production (nearly 180 million ha) could be considered for economically viable production of biofuels.

PRODUCTIVITY
If 10,000 plants are grown in one ha at 1×1 m distance and average plant weight is 20kg then the fresh biomass produced will be 200,000 kg/ha/annum and the dry biomass will be 40,000 kg or 40 tonnes/ha/annum (20% of fresh wt.).This will yield 4 to 4.8 tonnes / ha/annum maximum biocrude (10-12%).If the cost of biocrude is Rs.30/-per kg then the total value will be Rs.120,000.The remaining biomass (90%) will be 36 tonnes/ha/annum and if it is Rs.1/-per kg then its value will be Rs.36,000 thus the total amount will be 120,000+36,000 = Rs.156,000.00.
If 5,000 plants are grown in one ha at 2 × 2 m distance and average plant weight is 100kg then the fresh biomass produced will be 500,000 kg/ha/annum and the dry biomass will be 100,000 kg or 100 tonnes/ha/ annum (20% of fresh wt.).This will yield 10 tonnes/ha/annum maximum biocrude (10%).If the cost of biocrude is Rs.30/ kg -1 then the total value will be Rs.300,000.The remaining biomass (90%) will be 90 tonnes/ha/annum and if it is Rs.1/ kg -1 then its value will be Rs.90,000 thus the total amount will be 300,000+90,000=Rs, 390,000.00

BIODIESEL PRODUCTION
A recent World Bank report concluded that "Energy policies will need to be concerned about the supply and use of biofuels as they are about modern fuels (and) they must support ways to use biofuels more efficiently and in sustainable manner.
Although, there is significant volume of biodiesel already produced in Europe there are remaining risks slowing down the further expansion to the target set by the European Commission to reach 5% market share in transportation fuels by the year 2000".These risks are insecurity in raw material supply and prices, doubts about adequate quality assurance and hesitance for a wider acceptance by the Diesel engine manufacturers, mission marketing strategies for targeting biodiesel differential advantages into specific market niches and last not least missing legal frame conditions similar to clean air act in the USA.

BIOMASS AS POTENTIAL RESOURCES
Biomass resources are potentially the world's largest and sustainable energy source a renewable resource comprising 220 billion oven dry tones (about 4500 EJ) of annual primary production.
The annual bioenergy potential is about 2900 EJ though only 270 EJ could be considered available on sustainable basis and at competitive prices.Most major energy scenarios recognize bioenergy as an important component in the future world's energy.Projections indicate the biomass energy use to the range of 85 EJ to 215 EJ in 2025 compared to current global energy use of about 400 EJ of which 55 EJ are derived from biomass (Hall and Calle 1998).

SOME IMPORTANT AGRONOMIC ASPECTS FOR CALOTROPIS PROCERA CULTIVATION
Although Calotropis procera can be germinated throughout the year however the suitable time for sowing of Calotropis procera is May-June.Suitable sowing depth for Calotropis procera is 3 to 4 cm.Calotropis does not require deep tillage.One irrigation should be applied immediately after sowing if there is no rainfall.The intensify of weeds badly affects the plant growth therefore it is prudent to eradicate them.Suitable time for weed erradication is 45 days after sowing.First harvest may be done after three to four months after sowing.Plants may be thinned to have suitable number of plant for per unit area for better plant growth.The suitable time for thinning is after about 45 days after germination.An experiment is in progress to determine the suitable density of plants in per unit area.
However for developing countries it is important to develop crop plants that grow on wastelands and are able to produce sufficient biocrude at economic costs.The present papers presented the details for strategy for wastland colonization using hydrocarbon yielding plants which could be employed for several developing countries (Kumar 1998).