Introduction

Solar energy, accumulated under earth in the form of fossil fuels since the inception of life, accounts for more than 97 per cent of the world consumption of energy of which the share of oil is about 39 per cent. The biomass accounts for 43 per cent of the total energy supply in the developing countries as compared to only 1 per cent in the developed 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).

          In India also, the demand of petroleum products has significantly increased during the last two decades due to rapid expansion in transport, industrial and agricultural sector. Despite the fact that indigenous production of crude oil increased from 6.82 million tonnes during 1971-72 to 28.99 million tonnes during 1984-85,imports also increased from 12.77 million tonnes to 19.73 million tonnes during the corresponding period, thus implying a huge drain of foreign exchange. The demand of petroleum products increased from 19.1 million tonnes in 1970-71 to40.50 million tonnes in 1984-85. This is estimated to touch 57.0 million tonnes in 1990-91 and 92.0 million tonnes by 2000 A.D. This indicates considerable shortage in energy supply during the coming years (Vimal, 1986).

          In the third world, biomass is used mainly as fuel wood by over 90 per cent of the population. The world's total yearly supply of fuel wood, which more than doubled in the 40 years up to 1950, is estimated to have lavelled off at about 1070 million m³ per cent thereafter (Lewis, 1981). Tropical forestsin 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 percent of the energy used in households is form the firewood and 64.2 per cent of it is collected from natural sources. The shortfall in fuel production islikely to raise to 137 million tonnes in 2000 A.D. from the present 84 million tonnes (Vimel, 1986). The indiscriminate falling of trees has reduced theforest cover to 23 per cent against 33 per cent during the last decade (Murty,1985). 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 cubicmeters of gas annually in biogas processing plants. However, most of the dry dung is used for burning (Murty, 1985).

          Sourcewise, energy consumption in the household sector in the rural areas is as follows: non-commercial sources like fuel wood (68.5 pe cent), animal dung (8.3per cent); commercial energy sources like oil (16.9 per cent), coal (2.3 percent), electricity (0.6 per cent) and others (3.4 per cent) (Vimal and Tyagi,1984).

          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 unsurmountable drawbacks. Firstly,these are non-renewable and thus supply of many 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 on earth.

          Then non-fossil, non-nuclear energy possibilities fall in three groups: namely,non-solar such as geothermal and tides; indirectly solar such as winds andocean thermal gradients and directly solar which among other options includes photosynthesis. All other alternative sources under this category have one orthe other practical hurdles in the way of their harnessing energy. Viewed fromeconomic, technological, social, and material factors, they lack the capacityof meeting our future energy needs. Photosynthesis or the photobiological process is a continuous activity, creating organic carbon that burns with lessair pollution than fossil fuels. Photosynthesis helps to remove carbon dioxide from the atmosphere and generates oxygen, the life sustaining gas. It thus helps to minimise 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 up the upper layers of the oceans andcause a rise in the sea level (Vimal and Tyagi, 1984).

          The only appropriate alternative to the socio-economic conditions prevailling inthis country is the photosynthetic model of development. It has been the sourceof an old, reliable and renewable form of energy, now referred to under a newname, biomass. This is relevant even for all developing countries, although its extent and nature may vary from one country to another (Khoshoo, 1984).

          Out ofthe total solar energy on earth (3 × 10²⁴J), the plant life utilizeabout 0.1 per cent annually, leading to an annual net production of 2 × 10¹¹tonnes of organic matter which has an energy content of 3 × 10¹²J.the total annual energy use, however, is of the order of 3 × 10²⁰J(Hall, 1982). One of the natural assets of our country is the abundantsunshine. The total solar radiation received in India is about 60 × 10¹³MWH, with 250 to 300 days of useful sunshine per year in most parts of thecountry. The daily average direct radiation at places in the central part ofthe country is 5 to 7 Kwh/m². There is thus, a vast scope forharvesting solar energy and improvement in photosynthetic efficiency (Dayal,1984).

          Thebest solar converting machine available today is the green plant which canproduced fuel and material on renewable basis (Szego and Kemp, 1973; Calvin,1976, 1977, 1978a, 1978b, 1979bm, 1980, 1983a, 1983a, 1983b, 1984, 1985; Calvinet al., 1981, 1982; Buchanan andOtey, 1979; Buchanan et al., 1978a, 1978b; Vergara and Pimental, 1978; Weiszand Marshall, 1979; Bagby et al., 1980;Hall, 1980; Johnson and Hinman, 1980; Coffey and Halloran, 1981; Lipinsky,1981; Lipinsky et al., 1980; Tidemanand Hawaker, 1981; Wang and Huffman, 1981; Khoshoo, 1982; McLaughiin andHoffman, 1982; McLaughiin et al.,1983; Stewart et al., 1982; Adams andMcChesney, 1983; Bhatia and Srivastava, 1983; Hoffman, 1983; Nemethy, 1984 andVimal, 1986).

          Biomassenergy is thus, environmentally a very acceptable resources. The wide use ofbiomass for development offers minimal ecological imbalance and provide meansof recycle nutrients and carbon dioxide from the atmosphere (Dayal, 1986 andVimal, 1986).

          In India untilrecently, the energy from biomass came almost entirely from fuel wood, crop andlivestock residues. However, in the last few years, attention has been given tothe question of energy plantation and energy cropping, specifically for thepurpose of providing fuel. Technologies are being developed to convert thesesources into traditional forms of commercial energy i.e. liquid, solid andgaseous fuels. If the new technologies find wider index acceptance andpercolate in the rural areas, energy from biomass can meet 77 per cent of thetotal energy needs of the country (Vimaland Tyagi, 1984).

          The urgencyof solving the energy problem has prompted growth by giving priority to theimplementation of programmes to accelerate the development of alternativeenergy sources. In Indiaalso, the Department of non-conventional energy sources has been establishedduring 1982.

          Photosyntheticefficiency depends greatly on geographical location and climatic conditions.Input of solar energy, water, carbon dioxide, nitrogen phosphorus and variousminerals, all contribute to plant growth and productivity (Hall, 1982).

          Photosyntheticis far and away the best quantum converting, light converting that we knowtoday for the production of organic matter and all of our living things aredependent on  the sun and ultimately onthe green plant. Today we are dependent on plants for food and fiber and may betomorrow we will depend on plants for our currents energy requirements also(Calvin, 1977).

          India has arich flora with nearly 45,000 species of flowering and nonflowering plants ofwhich there are about 15,000 flowering plants. There are atleast 85 familiesthat represent members which yield hydrocarbons (Srivastava, 1985). Plant latexis a milky or frequently pale, cloudy yellow or red fluid in specialized cellsor tube like structures known as laticifers in many species of plants ofdiverse families (Metcalfe, 1967). It is a liquid matrix or serum containingminute organic particles in dispersion or suspension. Water and hydrocarbonshave been found to be the principal components of latex in many plants (Schery,1972). Normally the hydrocarbons found in the plant latex are polymers ofisoprene (C₅H₈)_n ranging from relatively largemolecules such as natural rubber (MW 5,00,000 to 20,000,000) to relativelysmall molecules (MW 50,000) or less. The best examples of the plant having arich latex exudate is the rubber tree "Heveabrasiliensis". Almost all the 2000 species of genus Euphorbia belonging to familyEuphorbiaceae yield latex, similar to Hevea latex containing one thirdhydrocarbon, one fifth protein and the balance water. Various species of Euphorbia grow throughout the world inareas which are not very productivity – south west United States, Africa, Morocco,Indiaand Western Costs of Chile. Several plant sources have been reported to produceliquid fuels resembling diesel.

          Thefollowing are the main plant sources which have been recognized to produceenergy fuels of the diesel type :

(a)             Seed oils – Cocos nucifera L. (Coconut), Elaeis quinensis Jacq. (palm oil), Jatropha curcas L. (Jatropha), Ricinus communis L., (Castor), Simmondsie chinensis (Link) Schneider(Jojoba), Pittosporum resiniferum Hems.(Petroleum nut).

(b)            Essential oils –Eucalyptus oil, and

(c)             Exudates andextracts – Euphorbia antisyphilitica Zucc.,E. lactea Haw., E. lathyris Linn., E.tirucalli Linn., Asclepias spp., Calotropis procera (Ait.) R. Br., C. giantea (Linn.) R. Br., Crvotostegia orandiflora (Roxb.) R. Br.

These plants belong to thefamilies Palmae, Asclepiadaceae, Buxaceae, Euphorbiaceae, Myrtaceae, andPittosporaceae.

Besides this, there are about10 denroid (tree type) Euphorbia spp.,occurring in India,out of these 6 have widespread distribution and these could be considered asnatural renewable reservoir of hydrocarbons. The species are Euphorbia antiquorum Linn., E. caducifolia Haines, E. neriifolia Linn., E. nivulia Buch-Ham., E. rovleana Linn. and E. trioona Haw.

386 Indigenous laticiferousplants belonging to the families Euphorbiaceae, Asclepiadaceae, Apocynaceae,Urticaceae (Moraceae), Convolvulaceae and Sapotaceae were selected on the basisof distribution, sufficient latex content, and possibility of easy cultivation(Bhatia et al., 1984). Screening ofthese species has resulted in the selection of 16 potential crops which havebeen further narrowed down to four only for hydrocracking of hydrocarbons.

Conversion of jojoba oil,castor oil, corn oil, Hevea brasiliensis (overHZSM catalyst in the presence of hydrogen) (Weisz et al., 1979) and of bio-crude from Euphorbia tirucalli (Fernandez, 1984), Asclepias soeciosa, Euphorbia lathyris, Grindelia suarrosa (Mobil'sZSM – 5 Zeolite catalyst ) Haag et al., 1980and Adams et al., 1984), Euphorbia lathyris and Synadenium orantii (Co Mo Catalystin  the presence of hydrogen) Held et al., 1985), into hydrocarbon fuels,particularly in gasoline range, has already been demonstrated.

Calvin (1977) conducteddetailed investigations on the E.lathyris and E. tirucalli. Largescale cultivation of E. lathyris hasbeen carried out in different parts of the world (Hinman et al., 1980; Johnson and Hinman, 1980; Sachs and Nock, 1980;Peoples et al., 1981; Kingsolver,1982; McLaughlin and Hoffman, 1982; Ayerbe etal., 1983a, 1983b, 1984a; Calvin, 1984 and Nemethy, 1984).

Euphorbia lathyris can yield upto 20,000 kg dry matter per ha (Ayerbe et al., 1983a, 1983b, 1984a, 1984b of which between 5 to 8 per centare hydrocarbons and  20 per cent arefermentable sugars (Nemethy et al., 1981a,1981b).

The process to recoverterpenoids and sugars from E. lathyris hasbeen calculated on a 1000 tons of dry matter/day basis (Calvin, 1983a). Theproduct from 1000 tons is 80 tons of oil extract in the same way as soybeanoil. In addition to oil the residue on extraction with methanol/water to removefermentables, gives 200 tones of sugars. The 200 tons of sugars is equivalentto 100 tons of alcohol. Therefore, there are two liquid products obtainablefrom 1000 tons of dry matter, 80 tons of oil and 100 tons of alcohol. Besidesthis, 200 tons of bagasse is also obtained. Thus the combination of theseproducts makes cultivation of hydrocarbon yielding plants as attractiveproposition (Calvin, 1977).

There are currentlyplantations of E. lathyris inmediterranean countries, Africa, the Canary islands and Australia(Coffey and Halloran, 1981). Its water requirement ranges from 30-37.5 cmannually and can grow in land which has poor soils not suitable for foodproduction. The plant attains the harvest size in 5 to 7 months and theextraction process is standard for chemical industry. Besides oil, the plantcontains a substantial quantity of sugars, fermentable to alcohol. It may giveyield of 6 to 10 barrels of oil acre^–1 year^–1 using seedsof wild plants (Calvin, 1979a).

In India, attempts to growpetro-crops namely Euphorbiaantisyphilitica, E. tirucalli, E. lathyris, different verities of Pedilanthus tithvmaloides, etc. havebeen made at National Botanical Research Institute, Lucknow (Bhatia andSrivastava, 1983; Bhatia et al., 1984,1986; Srivastava, 1985, 1986; Srivastava and Bhatia, 1986 and Srivastava etal., 1981, 1985).

The systematic work onpetro-crops was first started by the experimental plantings of E. lathyris and E. tirucalli in U.S.A.(Calvin, 1978a, 1978b). His preliminary studies on the chemical analysis ofboth whole plantextracts and late proved that plantings produced oil at therate of 8 to12 per cent of the total dry weight, which Calvin (1983) calculated15-25 barrels of oil per hectare per year for E. lathyris. Results of a preliminary economic study of aconceptual process including biomass operation and processing plant, theextracts the oil material, indicate a cost of 30-40 US $ per barrel for the oilextracted (Calvin, 1979a). If plants can produce30 barrels of oil per acre peryear, the price of the recovered oil from hydrocarbon producing plants can be anywhere from US $ 10 to 30 per barrel including capital costs. However, startingwith 25 barrels of oil per hectare per year, it should be possible through theuse of improved agronomic practices, to raise this figure to not less than 125barrels per hectare per year. This improvement in yield modification in the oilcomposition to more desirable compound are feasible expectations (Calvin,1979a). Euphorbia lathryis has beenconsidered a potential petro-crop by several workers (Calvin, 1978a, 1978b;Nemethy et al., 1978, 1981a, 1981b;Johnson and Hinman, 1980; Sachs et al., 1981;Kingsolver, 1982; Ward, 1982 and Ayerbe etal., 1984a, 1984b).

Vast areas (42 per cent) ofland in Indiarepresent arid and semi-arid regions (Fig. 1), (Raychaudhuri, 1978). Most of thisland is not suitable for raising normal crops but a large number of Euphorbia specie are found growing wildin these region (Kumar, 1984; Kumar and Kumar, 1985). Gujarathas about 1800 km of coastline with saline patches. The Saurashtra climate istypically semi-arid with annual rainfall of 150 mm spread over June toSeptember. It has high temperature during summer and moderate in winter. In theeastern coast of Orissa, snd deposits occurover 1 million hectare along 960 km coastal belt and in Tamil Nadu, large anddeposits are scattered, particularly in Kanya-Kumari and Ramanathapuramdistricts. The eastern coast presents varied climatic conditions from semi-aridto sub-humid (Iyengar et al., 1984).

Rajasthan, the secondlargest state of the country in terms of area and ninth on population basis, islocated between 23°4' 10''N latitude to 30°15'5''N latitude and 69°30'5'' Elongitude to 78°16'50'' E longitude. It is situated in the western most part ofIndiawith an area of 3,42,239 sq. kms. Considerable variations in soil types arerecorded in Rajasthan (Fig. 2). The only important mountains of the state arelow rugged highly dissected Aravallis, stretching into one or more parallelranges to a length of 690 km from south west to north east, with an averageelevation ranging from 304 to 914 meters above mean seal level. The state ofRajasthan is divided into two main natural divisions namely the North-West andSouth-East. The North-West region covers 58 per cent area which is mostly lyingcovered with sand dunes and interspersed with inselbergs. The subsoil water isoften brackish and lies at varying depths from 20 to 100 metes. The regionbeyond Jodhpure is called the Thar desert,having extreme aridity while area east to this is semi-arid.

The climate of the state ischaracterised by extremely high range of temperature and aridity alongwithvicissitudes of rainfall. Temperature ranges from 2.8°C (Bikaner) in winters to up to 50°C recorded inShri Ganganagar and Dohlpur in Summer. Rainfall is very low, highly erratic andvariable. The average rainfall of North-West Rajasthan is 5 to 40 cm while thatof South-East part is between 40 to 100 cm. The rainfall is mainly during Juneto September which accounts for nearly 90 per cent of the total rainfall (Parmanik,1952). The relief and climate of the state has greatly affected its drainagepattern. Most of the rivers and the streams flow in the North-East andSouth-West direction while a vast area in the west and North is free from anydrainage system and has thus got an inland drainage pattern. The Aravallis formthe most important water parting line. East Rajasthancomes under the chambal catchment. Thenotablerivers of the area ae chambal,Banas, Morel, Banganga and Sota-Sabi. Except for the Chambal, whch is parennial,all others are ephemeral and flow only in the monsoon season. In the west,Luniis the only river of importance but its water is brackish. Most of the areahas internal drainage and no water is lost in the desert sands. The mostimportant tributaries of Luni are Bandi, Sukri, Mitri, Jawai and Sagi. Thisriver system covers the area of Pali, Jodhpur,Jalore and Sirohi districts.

Euphorbia lathyris is a biennial, growing from 0.5 to 2 meters high with decussate, linearto lanceolate leaves. The plant does not form basal rosette, but typically overwinters before producing flowers and fruits. E. lathyris is the sole representative of the section Lathyris in the sub-genus Esula. Likeall Euphorbia species, E. lathyris produces a three seededcapsule. Unlike most species in the genus, the capsule is relatively large,with a spongy pericarp that is tardily dehiscent (Anonymous, 1982).

The place of origin of E. lathyris is uncertain. Smith andTutin (1968) suggested that the plant is native only to the central and easternMediterranean region. However, Prokhanove (1949) reported that the plant occurswild in the western portion of mountainous Chinaand that it might have been introduced into Europeduring the middle ages.

The plant has a long historyof utilization and commercial use of by-products and could affect hydrocarbonproduction economy. The seeds have been used as a substitute productioneconomy. The seeds have been used as a substitute for coffee (Tanaka, 1976), asan emetic (Scharsnberg and Paris, 1977) and in the treatment of dropsy (Chopra et al., 1956). The plant occasionallyhas been cultivated as an oilseed crop in parts of Soviet Union, China andJapan(Prokhanove, 1949).

In California two ecotypes have beenidentified. The northern ecotype as used by Sachs et al. (1981) has a vernalisation or crop chiling requirement ofsix to eight weeks before it becomes reproductive in the spring and earlysummer. A similar feature was shown by E.lathvris grown at Melbourne University (Coffey andHallorn, 1981). A Souther-Californian ecotype being grown experimentally inArizone grows to maturity in about 180 days regardless of time of sowing and itis more productive than the northern ecotype in Arizona (Stewart et al., 1981).

Euphorbia lathyris yields a total of 35 per cent of its dry weight as simple organicextractables. Chemical analysis of the extracts has shown that 5 per cent ofthe dry weight is a mixture of reduced terpenoids in the form of triterpenoids,and 20 per cent of the dry weight is simple sugars in the form of hexoses.these terpenoids can be converted to gasoline like substances and the sugarscan be fermented to alcohol. Based on a biomass yield of 10 dry tons acre^–1year^–1, the total energy that can be obtained from this plant in theform of liquid fuels is 45 × 10⁴ Btu acre^–1 year^–1,25 × 10⁴ Btu in the form of hydrocarbons add 20 × 10⁴ Btuin the form of ethanol (Calvin et al.,1981).

The possibility of obtainingliquid fuels from plants by direct extraction has led to a shift in researchfrom maximising the biomass production to the interest in improving the qualityand quantity of certain plant constituents. The presence of whole plant oils(or "bio-crude") is an important criterion in the selection ofpotential energy crops (Buchanan and Otey, 1979 and Buchanan et al., 1978a, 1978b).

The recent researches haveindicated that there is inverse relationship between biomass yields and amountof bio-crude produced by the desert plants (Mc Laughlin and Hoffman, 1982).Economic considerations also dictate an approach in which plant quality, ratherthan quantity is emphasised. Because of the greater economic value of reactivechemical intermediates which can be obtained from these plants, the productionof chemical feedstocks is now considered to be an attractive short term goal inthe development of bio-energy crops for arid lands (Lipinsky et al., 1980 and Palsson et al., 1981).

During recent yearsagricultural output per unit land area under cultivation has increased verygreatly through the use of new improve varieties, fertilizers application ofgrowth regulators and disease and pest management. 

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