Bot. Bull. Acad. Sin. (1997) 38: 105-108

De et al. Renewable resource of plant hydrocarbons

Potential use of Pedilanthus tithymaloides Poit. as a renewable resource of plant hydrocarbons

Srilekha De1, Archana Bag, and Subhendu Mukherji2

Plant Physiology Laboratory, Department of Botany, University of Calcutta, Calcutta - 700 019, India

(Received January 9, 1996; Accepted December 10, 1996)

Abstract. Pedilanthus tithymaloides was evaluated as an incessantly renewable and potential source of hydrocarbons. Extracts were obtained from successive extraction of whole plant material with solvents like petroleum ether (b.p. 60_80C), benzene (b.p. 80C) and ethyl acetate (76_78C). A white amorphous mixture of hydrocarbons was obtained by elution of the column by petroleum ether (b.p. 60_80C) which was found to be comparable with gasoline.

Keywords: Hydrocarbons; Pedilanthus tithymaloides Poit.; Renewable resource.

Abbreviations: PEE, petroleum ether extract; BENE, benzene extract; EAE, ethyl acetate extract; PER, plant residue left after petroleum ether extraction; BENR, plant residue left after benzene extraction; EAR, plant residue left after ethyl acetate extraction.

Introduction

Modern society depends very much upon fossil fuel. Total oil resources are being depleted, and their share of total energy supply is predicted to fall to 10% by the year 2020. To meet this acute shortage, the technology aimed at the utilization of renewable energy that can serve to replace fossil hydrocarbons, needs to be expanded. Calvin (1977) reported that latex-bearing plants are the most obvious alternative renewable source of fuel and chemical feedstock. It was seen that some higher plants can convert the initially produced carbohydrate into terpenes instead of into fatty acids and glycerides (such as seed oil). Calvin (1982) has considered Euphorbia lathyris L. to be a kind of "energy farm" capable of producing a mixture of reduced terpenoids which can be converted to a gasoline-like substance. The most interesting and attractive species is Copaifera multijuga, which produces the light yellow oil (copaiba oil) that is obtained from its heartwood by tapping (Alencar, 1982). A single hole through the stem may yield about 25 liters of oil in 24 hoursa readymade engine oil (Calvin, 1982).

It is true that the economic development of plant hydrocarbons will ultimately depend upon agronomy and conversion cost (Weisz and Marshall, 1979). Pedilanthus tithymaloides Poit. which grows profusely in marginal waste land in northern and eastern India without any agricultural management, was undertaken to evaluate the hydrocarbon content and its potential use as a petrocrop.

Materials and Methods

Preparation of Plant Material

About 3005 mature plants (about 1 meter long) with shrubby growth were collected from North 24-Parganas, West Bengal (2240' N, 8825' E) between June and July 1988. Both stem and leaves were allowed to air dry in a sheltered area at a temperature of 35_40C and were ground in a Wiley mill equipped with 2 mm sieve. Thoroughly mixed samples were then stored at ambient temperature in polythene bags.

Extraction Technique

About 500 g of milled sample was extracted in a Soxhlet apparatus first with petroleum ether [E. Merck (India) Ltd; b.p. 60_80C], then benzene [E. Merck (India) Ltd; b.p. 80C] and finally with ethyl acetate [95% S.d. fine chemicals (India) Ltd; b.p. 76_78C] (48 hours with each solvent). All the extracts were concentrated through distillation at a temperature 5C above the boiling point. The extracts were dried at 60C for 24 h, then weighed for yield per g of dry sample. The plant residue after each solvent extraction was completely air dried before the next solvent extraction.

1Present address: Department of Biological Chemistry, Indian Association for the Cultivation of Science, Calcutta - 700 032, India.

2Corresponding author.


Botanical Bulletin of Academia Sinica, Vol. 38, 1997

EAE were 0.11, 0.23, and 0.50%, respectively, which showed an increase with the increase in polarity of solvents used (Table 1). The respective residues after each solvent extraction also followed the same trend in having the ash contents 13.75, 15.50, 20.00, and 30.00% for dried whole plant, PER, BENR, and EAR (Table 2). Out of these three extracts yield of PEE was 26 g per kg dry plant material. The corresponding yields of the other two extracts (i.e. BENE and EAE) were 10 g and 25 g per kg dry plant material, respectively. The gross heat values were calculated as 6233, 4795, 4692, and 3903 cal/g for unextracted dry plant material, PER, BENR, and EAR, respectively. A major amount of energy-rich biocrude was obtained from different solvent extracts as evidenced by their high calorific values like 15460, 11286, 10708 cal/g for PEE, BENE, and EAE, respectively.

The experimental plant possesses an appreciably superior fuel quality as compared to Calotropis gigantea and also to C. procera, which has been recognized as a potential plant (Erdman and Erdman, 1981). The PER and BENR can also compete with conventional energy sources like wheat straw, rice straw, and wood (Table 2).

Characterization of Extracts and Residues (in Relation to Fuel Characters)

The unextracted milled whole plant sample, different solvent extracts, and their residues after each extraction were analysed for total ash content by the AOAC method (1975). Gross heat values were determined by bomb calorimetry (Anonymous, 1966), and specific gravities were measured by conventional methods.

The PEE was column chromatographed over neutral alumina. Elution of the column with petroleum ether (b.p. 60_80C) afforded a solid, waxy, amorphous compound from the first two fractions. Melting point, gross heat value, and total carbon and hydrogen of this compound were determined through pyrolysis (Ma and Rittner, 1979). Infra-red (IR) spectroscopy was used to detect the nature of the compound.

Results and Discussion

About 175 g dry plant material was obtained from one kg fresh material. Total ash contents of PEE, BENE, and

Table 1. Ash content, specific gravity and gross heat value of different solvent extracts of Pedilanthus tithymaloides compared to Calotropis gigantea and fossil fuels.

Fuel Ash (%) Specific gravity (g/cc) Gross heat value (cal/g)

Pedilanthus tithymaloides

PEE 0.1100.02 0.4700.07 15,460183

BENE 0.2300.05 0.5180.06 11,286176

EAE 0.5000.05 0.9960.09 10,708143

Calotropis giganteaa

PEE 0.420.03 0.5700.02 13,734123

BENE 0.130.04 0.6800.03 9,59395

EAE 2.900.05 0.9840.07 7,414105

Anthracite coalb 9.60 _ 7,155

Lignite coalb 5.90 _ 3,888

Crude oilc _ 0.70_0.80 11,700_11,100

0.85_0.95 10,875_10,500

Fuel oilc _ _ 10,764

Gasolinec _ _ 11,527

aFrom De, 1991.

bFrom Bolz and Tuve, 1970.

cFrom Baumeister, 1966.

Table 2. Characteristics of the dry plant and solvent extracted residues of Pedilanthus tithymaloides and other fossil fuels.

Material Ash (%) Heat value (cal/g)

Whole plant P. tithymaloides (stems and leaves) 13.751.52 7,2330.77

Petroleum ether extract residue 15.001.69 4,7950.61

Benzene extract residue 20.002.30 4,6920.74

Ethyl acetate extract residue 30.002.86 3,9030.54

Whole plant Calotropis procerad 11.05 4,165

Plants (general)e (stems and leaves) _ 4,267

Wheat strawc 4.00 4,722

Woodc 1.00 5,000

cFrom Baumeister, 1966.

dFrom Erdman and Erdman, 1981.

eFrom Golley, 1961.


De et al. Renewable resource of plant hydrocarbons

Table 3. Comparative carbon, hydrogen, nitrogen, and oxygen contents and heat values of the waxy hydrocarbon and fossil fuels.

Material Carbon (%) Hydrogen (%) Nitrogen (%) Oxygen (%) Heat value (cal/g)

Waxy hydrocarbon from PER 85.54.5 13.90.8 _ _ 18,990196

Anthracite coalb 79.7 2.9 _ 6.1 7,156

Lignite coalb 40.6 6.9 _ 45.1 3,889

Fuel oilc 85.62 11.98 _ 0.6 10,764

Gasolinec 84.90 14.76 _ _ 11,527

bFrom Bolz and Tuve, 1970.

cFrom Baumeister, 1966.

Acknowledgement. The authors are grateful to the Department of Non-conventional Energy Sources, Ministry of Energy, Govt. of India for providing financial assistance.

Literature Cited

Alencar, J.D.C. 1982. Forestry studies of a natural population of Copaifera multijuga, Leguminosae in Central Amazonia: Production of oleoresin. Acta Amazonica 12: 75_90.

Anonymous, 1966. Oxygen bomb calorimetry and combustion methods. Technical Manual No.153. Parr Instrument Co., Moline, IL.

AOAC, 1975. Official Methods of Analysis of the Association of Official Analytical Chemistry. William Worwitz, AOAC Washington, DC.

Baumeister, T. 1966. Standard Handbook for Mechanical Engineers. Mc-Graw-Hill, New York, pp. 7_22.

Bolz, R.E. and G.L. Tuve (eds.). 1970. Handbook of Tables for Applied Engineering Science. Chemical Rubber, Cleveland, OH., pp. 308.

Calvin, M. 1977. Hydrocarbon via photosynthesis. Energy Res. 1: 299_327.

Calvin, M. 1982. Oils from plants. Presented at BARC Science Seminar, Beltsville Agricultural Research Centre, U.S. Dept. of Agriculture, MD.

De, S. 1991. Investigation on laticiferous plants in relation to latex contents, fuel efficiency and their interaction with other plants. Ph.D. Thesis. University of Calcutta.

Erdman, M.D. and B.A. Erdman. 1981. Calotropis procera as a source of plant hydrocarbons. Econ. Bot. 35: 467_472.

Golley, F.B. 1961. Energy values of ecological materials. Ecology 42: 581_584.

Ma, T.S. and R.C. Rittner. 1979. Modern Organic Elemental Analysis. Marcel-Dekker, New York, pp. 51_58.

Sejdak, R.L., Y.Z. Lai, G.D. Mroz, and M.F. Jurgensen. 1981. Forest biomass for energy. In D.L. Klass (ed.), Biomass as a Non-Fossil Fuel Source. American Chemical Society, Washington, D.C., pp. 21_48.

Wang, S.C., J.B. Huffman, and D.L. Rockwood. 1982. Quantitative evaluation of fuel wood in Florida: a summary report. Econ. Bot. 36: 381_385.

Weisz, P.B., and J.F. Marshall. 1979. High grade fuel biomass farming: potentials and constraints. Science 206: 24_29.

Figure 1. Infra-red bands of waxy hydrocarbons obtained from PEE of Pedilanthus tithymaloides.

A linear relationship exists between the heat of combustion and the carbon content of natural fuel (Sejdak et al., 1981). A high H:C ratio accounts for the high combustion value of aliphatic hydrocarbons. The absence of nitrogen and oxygen characterizes a good fuel (Wang et al., 1982). The recrystalized waxy hydrocarbons obtained from PEE possessed a melting point of 60C and a gross heat value of 18,990 cal/g with 85.5 and 13.0% carbon and hydrogen (Table 3). Infra-red spectra of nujol pellets gave C-H stretching 3.3_3.5 (3030_2860 cm-1) and C-H bending 6.85 (1460 cm-1) and 7.28 (1374 cm-1). The weak absorptions at 5.78, 13.9, and 14.3 suggest slight contamination of the wax. The IR spectral data indicate absence of nitrogen and oxygen and the substance is either one or a mixture of a group of alkanes as in wax (Figure 1).

From the above discussion it appears that the biocrudes extracted from petroleum ether and benzene distillation (PEE and BENE) possess much lower specific gravities and higher heat values than crude oil, and the EAE seems to be very similar to it in this respect. The recrystalized substance obtained from PEE contains a fuel quality superior to gasoline. Thus PEE can be used as a substitute for petroleum or petrochemical feedstocks.