a review of integrated processes to get value-added chemicals and fuels from petrocrops

B~source Technology49(1994) l-6 1994 E~e~erSeienceLimited

Printedm GreatBritain 0960-8524/94/$7.00

ELSEVIER

A REVIEW OF INTEGRATED PROCESSES TO GET VALUE- ADDED CI-W MICALS AND FUELS FROM PETROCROPS

D. K. Sharma

Fuels & Biofuels Engineering Laboratory, Centre for Energy Studies, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi- 110 016, India

M. Tiwari & B. K. Behera

Department of Biosciences, M. D. University, Rohtak-124001, India

(Received 20 October 1993; revised version received 23 January 1994; accepted 31 January 1994 )

Abstract Twenty-one species of laticiferous, resinous, medicinal, wild-growing, oil-seed-bearing and essential-oil-yielding plants have been selected and studied for their potential to yield biocrude, which can be processed into oil. The spent residues obtained after the recovery of biocrude can be processed to obtain fermentable sugars, ethanol aromatic chemicals and other value-added chemicals and fuels. An integrated process to produce oil and other value-added chemicals and fuels from potential petrocrops has been suggested after assessing the potential for ethanol and aromatic chemicals production. Potential candidates for petrofarming have been recommended. The paper aims to invite the attention of technologists to petrocrops, as this renewable resource has a great potential to yieM chemicals and fuels, and desert land can be utilised to grow these plants. Research in this area should be extended.

Key words: Petrocrops, biocrude, spent residue, integrated process, ethanol, chemicals, fuels, oil, fermentable sugars.

INTRODUCTION

Oil reserves of the world are being depleted. In the long term, there is a need to find a substitute for oil which may afford an infinite supply of energy. Petrocrops are such a source, being a renewable resource of petroleum. These plants can be grown in semiarid and arid zones without much agricultural input and manage- ment and do not compete with fuel wood, food and fibre crops. Therefore, research in the area of petrocrops was started in the mid-1970s and 1980s (McLaughlin & Hoffman, 1982; Adams & McChes- ney, 1983; Calvin, 1983; McLaughlin et aL, 1983; Sharma & Babu, 1984; Hoffman, 1986; Sharma & Prasad, 1986; Carr & Bagby, 1987; Adams et al., 1986; Sharma et al., 1990), however interest in this field has faded recently. This has been due partly to the fact that plenty of oil is now available and partly

because of the fact that production of oil from petrocrops is not economically attractive. Growing petrocrops merely to get oil by tapping, extraction and by hydrocracking of biocrude cannot be cost-effective. However, if the spent residue obtained after the extraction of biocrude from petrocrops (which could be 90-95% of the whole plant) could be effectively utilised to get value-added fuels and chemicals then petrofarming could become an interesting option for getting a wide range of products for a variety of uses. As a part of a large programme on exploring several interesting ways to utilise this major portion of petrocrops, the authors have for the first time suggested that the spent residue obtained after extraction of biocrude can be processed to get solid char and oil tar (Sharma & Prasad, 1986), or utilised through anaerobic fermentation to get biomethane and manure (Sharma & Babu, 1984; Sharma & Mbise, 1988; Sharma et al., 1990) or through solvolytic liquefaction (Sharma et al., 1994b), wherein the biomass can be extracted in organic solvents, such as anthracene oil, liquid paraffin, or quinoline after its depolymerisation. The extracted biomass can be easily hydrocracked to obtain oil. It is easier to hydrocrack extract than to hydrocrack the solid biomass. Recently, Arora et al. (1993) have also reported several techniques to coagulate the Calotropis procera latex. The coagulated material (coagulate), containing mostly triterpenes, hydrocarbons, etc., can be easily hydrocracked to obtain oil (Sharma et al., 1994a). The present review deals with the studies of the potential of a wide variety of plants for fielding biocrude and further studying the potential of the spent residues to get ethanol and aromatic hydrocarbons. It was reported earlier that lignocellulosic residues (agro- wastes) can be hydrolysed using either acid (Goldstein, 1981; Singh et al., 1984a,b) or enzyme catalysts (Gold- stein, 1981; Sharma & Das, 1992) to get fermentable sugars and lignin. The sugars can be fermented to ethanol and the lignin can be hydrocracked to produce aromatic hydrocarbons (Wise, 1983; Sharma & Goldstein, 1990; Costa et al., 1992). This was commercially prac-

2 D.K. Sharma, M. Tiwari, B. K. Behera

tised during the world wars and until recently it was in commercial practice in Russia.

Twenty-one species of laticiferous, resinous, oil- seed-bearing, essential-oil-yielding, medicinal and wild-growing plants have been evaluated for their biocrude production potential. The spent residues obtained were analysed for their potential to yield ethanol and aromatic hydrocarbons and phenols, on the basis of their summative analysis. These studies could lead to the development of processes for the future petrocrop industries, which are inevitable as petroleum reserves are limited.

METHODS

The plant materials were dried in solar driers initially and then dried in an oven at 60°C, and crushed to 40-60 BSS mesh (417-495/zm particle size).

Extraction of biocrude Biomass (50 g) was taken in the Soxhlet extractor and the extraction was carded out with hexane for 8 h. The spent residue obtained was dried and weighed to deter- mine the loss in weight which represented hexane extraction.

The spent residue obtained from the hexane extraction was then Soxhlet extracted with methanol for 8 h. The loss in weight of the dried spent residue (SR) represented the methanol extraction.

The sum of hexane and methanol extractions showed the total biocrude yield. The experiments were performed in triplicate and the average results are reported. An error of + 1% may be involved.

Chemical composition of the SR The procedures for the determination of the hemicellulose, cellulose and lignin contents of the SR have been reported earlier (Singh et aL, 1984a). Analyses were performed in triplicate and the average results are reported. An error of + 2% may be involved.

RESULTS AND DISCUSSION

Most of the laticiferous, resinous, oil-seed-bearing, essential-oil-yielding, medicinal and wild-growing plants have been reported (Wealth of India, 1959) to possess some ancient medicinal and commercial values. Careful studies of the literature on properties of the plants in these categories and on petrocrops studied (Wealth of India, 1959; McLaughlin & Hoffman, 1982; Sharma & Babu, 1984; Adams et al., 1986; Hoffman, 1986; Sharma & Prasad, 1986; Carr & Bagby, 1987; Sharma et aL, 1990) helped the authors to initially narrow down the numbers and focus attention only on the following plants for the present study. These were: Ipomoea purpurea (Convolvulaceae), Croton bonplandianum (Euphorbiaceae), Lantana camara (Ver- benaceae), Argemone maxicana and Parthenium hysterophorus (Compositae) from wild-growing plants;

Calotropis procera (Ascelpiadaceae), Tabernaemon- tana divaricata (Apocynaceae), Asclepias currassavica (Asclepiadaceae), Carisa carandus (Apocynaceae), Plumeria rubra (Apocynaceae), Ficus benghalensis and Ficus religiosa (Urticaceae); Nerium indicum (Apocyn- aceae) and Atrocarpus integrifolia (Urticaceae) from laticiferous plants; Helianthus annus (Compositae) from resinous plants; Jatropha curcas (Euphorbiaceae) Eucalyptus lanceoltus, Plumeria acutifolia, Ricinus communis (Euphorbiaceae), and Alumeria acertifolia (Apocynaceae) from oil-seed and essential-oil-bearing plants; and Adhatoda vasicca (Acanthaceae), and Vinca rosea (Apocynaceae)from medicinal plants.

Leaves and stems of these plants were taken separ- ately for studies of their biocrude contents. Nonpolar components such as hydrocarbons, waxes, resins, terpenoids, steroids, fats, chlorophylls, etc., can be extracted from these plants using hexane as extractant (Sharma & Prasad, 1986). Polar components such as polyphenols, alkaloids, tannins, etc., can be extracted using methanol as the extracting solvent (Sharma & Prasad, 1986). Hexane extract can be more useful for hydrocracking to yield oil. However, total biocrude, i.e. hexane extract plus methanol extract, can also be hydrotreated to obtain oil under somewhat more severe conditions with relatively more hydrogen con- sumption.

Wild-growing plants Table 1 shows the biocrude yields from wild plants. Leaves showed higher biocrude yields than the corre- sponding stems. Croton bonplandianum leaves showed maximum yield of nonpolar biocrude, whereas Arge- mone maxicana leaves showed the maximum total biocrude yields. The stems of Lantana camara showed good yields of nonpolar biocrude.

Table 2 shows the analysis of the spent residues obtained after the extraction of biocrude. These contained mainly the cellulose, hemicellulose and lignin. Cellulose and hemicellulose can be hydrolysed to fermentable sugars which can be fermented to ethanol. The technology for this process has been well deve- loped (Goldstein, 1981; Singh et al., 1984a,b; Sharma & Das, 1992). The lignin can be hydrocracked to aromatic hydrocarbons and phenols (Sharma & Gold- stein, 1990). The technology of hydrocracking lignins is also well known (Goldstein, 1981; Singh et al., 1984a, 1992). Earlier, it was demonstrated (Sharma et al., 1990) that the spent residue from the stems of Croton bonplandianum (petrocrop) could be hydrolysed to yield sugars which were fermented to ethanol, and lignin could be utilised to obtain aromatic chemicals. Therefore, in the present work total hemicellu- losic and cellulosic contents were taken as the ethanol production potential (EPP) of the spent residues and the lignin contents showed the aromatic hydrocarbons and phenolic compounds production potential (AHP). EPP and AHP then represented the estimate of ethanol and aromatic hydrocarbons production. It is known that the natural biopolymers present in the spent resi-

Chemicals and fuels from petrocrops

Table 1. Biocrude yield from wild plants

Plant Plant part % Hexane % Methanol % Total extracted extractables extractables extractables

Ipomoea purpurea Leaves 4.3 18-7 23.0 Ipomoea purpurea Stems 0.7 17-6 18.3 Croton bonplandianum Leaves 10.1 2-6 12.7 Croton bonplandianum Stems 3"3 15-0 18"3 Argemone maxicana Leaves 7.3 24.6 31.9 Argemone maxicana Stems 2"2 18"9 21.1 Lantana camara Stems 7.9 6"7 14.6 Parthenium hysterophorus Stems 1.6 18.8 20-4

dues may not give 100% yields. However, EPP and AHP may be considered as the potential yields within the limits of conversion. The utilisation of these conversion processes will be dictated more by (near) future needs than by the present economy, but it is essential to know the lignocellulosic composition of the residues before future industries can be planned to use these. The conversion efficiencies and yields of these biopolymers to ethanol and aromatic chemicals have been studied earlier (Sharma et al., 1990), therefore, further work in this direction was not undertaken. Table 2 shows that the SR of Lantana camara stems had the maximum EPP and Croton bonplandianum stems had reasonably good EPP and maximum AHP.

Laticiferous and resinous plants Table 3 shows the biocrude yield from latex-beating plants. Stems of Ficus religiosa were found to contain the maximum nonpolar biocrude. The maximum total biocrude yield was found in the leaves of Tabernae- montana divaricata. The stems of C. procera showed good total biocrude yields. The spent residues obtained from C. procera also showed considerable EPP and AHP (Table 4). These results showed that C. procera was the potential candidate for petrofarming amongst the latex-bearing plants screened. Helianthus annus, a resinous plant, showed poor biocrude yields (Table 3), but Lantana camara, which is also a resinous plant, could be a promising candidate for petrofarming (Tables 1 and 2).

Oil-seed-bearing and essential-oil-yielding plants Earlier studies (Sharma & Babu, 1984; Sharma & Prasad, 1986; Sharma & Mbise, 1988) from this laboratory were concentrated mainly on obtaining non- edible oil from the oil seeds and essential oil from essential-oil-yielding plants. The object of the present study was to screen the stems and leaves of these plants for the yield of nonpolar biocrude and total extractives. Ricinum communis stems, Eucalyptus lanceolatus leaves and Plumeria acutifolia leaves contained about 7-8% nonpolar biocrude (Table 5). Plumeria acutifolia showed 26% total biocrude yield (Table 3). The oil from the seeds of these plants can be used as a diesel

oil substitute and the biocrude from the stems of leaves can be processed to get petroleum.

Medicinal plants Recently, interest in herbal plants to find effective medicines for diseases such as cancer, AIDS, etc., has increased. Medicinal plants from the flora of India are a store-house of several pharmacodynamic compounds (Chopra et al., 1956; Wealth of India, 1959) and the drug potential of such compounds in the allopathic system of medicines has been lately realised (Taylor & Farnsworth, 1973; Harborne, 1988; Sharma & Hall, 1991). The spent residue obtained after recovery of medicinal compounds can be processed to obtain biocrude. Present studies have shown that Vinca rosea leaves and stems can yield 8.2 and 7.2% nonpolar biocrude, respectively, and 33.2 and 18.1% total biocrude, respectively (Table 6). Vinca rosea stems contained considerable EPP and AHP (Table 7). Vinca rosea (also a resinous plant) is being exploited commercially for anti-tumour and anti-cancer alkaloids (Taylor & Farnsworth, 1973). This drug industry could be easily linked with a petrofarming industry to obtain drugs as well as petroleum from Vinca rosea plants.

CONCLUSIONS

The present study has shown that leaves of the plants give better biocrude yields than stems, but the EPP and AHP of the leaves is poor. The stems of Lantana camara (a resinous wild plant), Calotropis procera (a laticiferous plant) and Vinca rosea (a medicinal and resinous plant) give good yields of nonpolar biocrude, which can be easily processed to produce oil. The spent residue obtained after the recovery of biocrude can be processed to obtain fermentable sugars such as xylose, mannose, galactose and glucose. Xylose and glucose can be used as feedstocks for the production of a large number of chemicals including ethanol, butanol, isopropanol and acetone (Goldstein, 1981; Wise, 1983). Ethanol can be processed to ethylene and buta- diene (Goldstein, 1981; Wise, 1983). The spent residue can also be processed to produce aromatic chemicals. A multiple use of Lantana camara and C.

4 D. K. Sharma, M. Tiwari, B. K. Behera

Table 2. Chemical composition (% lignin, cellulose and hemicellulose) of residues of wild plants

Plant Source of % % % % % spent Lignin Cellulose Hemicellulose AHP ~ Epp b

residue

lpomoea purpurea Leaves 11.3 17.0 7.0 11.3 24-0 lpomoeapurpurea Stems 33.0 42.0 17.9 33-0 59-9 Croton bonplandianum Leaves 9.8 10-8 4.7 9.8 15-5 Croton bonplandianum Stems 34.9 51.8 12.5 34.9 64.3 A rgemone maxicana Leaves 11.5 34.3 22.8 11.5 57.1 A rgemone maxicana Stems 12.2 34-8 25-6 12-2 60"4 Lantana camara Stems 15"9 53.8 30.1 15.9 83.9

"AHP, aromatic hydrocarbon and phenolic compounds production potential. hEPP, ethanol production potential.

Table 3. Percentage ofbiocrude yield from laticiferous and resinous plants


Calotropis procera Leaves 6-1 6"7 12"8 Calotropis procera Stems 10-4 13"4 23-8 Tabernaemontana divaricata Leaves 13-2 27.1 40.3 Tabernaemontana divaricata Stems 2"7 13"7 16"4 Asclepias currassavica Leaves 8.4 12.0 20.4 Carisa carandus Leaves 4.5 26.7 31.2 Carisa carandus Stems 2.0 6.4 8"4 Plumeria rubra Leaves 6.3 20.6 26.9 Plumeria rubra Stems 4.6 12.8 16.9 Ficus benghalensis Leaves 1.6 30.0 31.6 Ficus religiosa Leaves 0-9 15.6 16.5 Ficus religiosa Stems 17.2 8.0 25.2 Nerium indicum Leaves 3.8 24.0 27.8 Nerium indicum Stems 2"8 17.8 20"6 Atrocarpus integrifolia Leaves 3.1 9.3 12.4 Atrocarpus integrifolia Stems 3-3 11.3 14.6 Helianthus annus Leaves 1-3 10.6 11.9 Helianthus annus Stems 0.8 12-0 12"8

Table 4. Chemical composition (% lignin, cellulose and hemicellulose) of residues of latieiferous and resinous plants

Plant Source of % % % % spent Lignin Cellulose Hemicellulose AHP a

residue

% EpP b

Calotropis procera Leaves 14-5 19.0 13'7 14.5 32-7 Calotropis procera Stems 13"6 52.5 9'7 13"6 62.2 Carisa carandus Leaves 33-0 32-5 11.5 33.0 44-0 Carisa carandus Stems 13.12 71-7 8.8 13.2 80-1 Plumeria rubra Leaves 14.0 31.4 8.9 14.0 40.3 Plumeria rubra Stems 33-8 44-3 11"4 33.8 55"7 Nerium indicum Leaves 16.8 23.1 13.7 16.8 36.8 Nerium indicum Stems 22.0 35-5 12.4 22.0 47-9 Atrocarpus integrifolia Stems 25"8 35"3 15"2 25.8 50"5 Atrocarpus integrifolia Leaves 15-8 57.5 20.0 15-8 77.5 Helianthus annus Leaves 12-3 24-1 5.4 12.3 29-5 Helianthus annus Stems 20.8 57.5 16.4 20.8 73.9

aAHP, aromatic hydrocarbon and phenolics production potential. bEPP, ethanol production potential.

Chemicals and fuels from petrocrops 5

procera could be interesting, as these plants also have some medicinal properties and have been reported to yield some extracellular enzymes (Wealth of India, 1959; Vasudevan et al., 1981). Figure 1 shows the flow scheme of an integrated process to obtain value-added chemicals and fuels from petrocrops.

The oil-seed- and essential-oil-bearing plants can yield a diesel-oil substitute as well as biocrude (for processing to petroleum). The integrated process to obtain biocrude and fermentable sugars, ethanol,

aromatic and other value-added chemicals and fuels from petrocrops can be an alternative process for effective utilisation of petrocrops. The petrofarming industries would help in the utilisation of arid, semiarid and waste lands and this would also help in generating employment in these areas. Research in the area of petrocrops should be further extended.

The utilisation of spent residues may depend on social, local and political factors at a particular loca- tion. In future, once oil reserves are totally depleted or

Table 5. Percentage of biocrude yield from oil-seed-bearing and essential-oil-yielding plants


Jatropha curcas Leaves 4.8 8"3 13-0 Jatropha curcas Stems 1'7 5-8 7.5 Ricinus communis Leaves 2-9 6.7 9.6 Ricinus communis Stems 6"9 7.4 14.3 Eucalyptus lanceolatus Leaves 6-8 13.7 20.5 Eucalyptus lanceolatus Stems 4-3 7.8 12" 1 Plumeria acutifolia Leaves 7-7 20-0 27.7 Plumeria acutifolia Stems 4.7 9-8 14.5

Table 6. Percentage of biocrude yield from medicinal plants


Ocimum sanctum Stems 0" 1 6.4 6"5 Adhatoda vasica Leaves 4.9 13.7 18-6 Adhatoda vasica Stems 1"3 18"3 19-6 Vinca rosea Leaves 8.2 25.0 33.2 Vinca rosea Stems 7'2 10-9 18" 1

Petrocrops

Fig. 1.

Prehydrolysis

' It MedicineSEnzymeSsteroids I <no,He: ~ Furfural a~Xyfitol 0..* HL Hydroaracking

Essential Aromatic and Fermentation etc. I Fermentation phenolic chemicals \ Eth~o I E ~ o I aad f~uels

I[ Hydrocmcking Hydtocracking ! V - Vitamin C

~ _ ~ S - Single-call pcoteins H - Hyd~xyn~hyl fuffural L - Lacvulini¢ acid 0 - Several other chemicals

Water

Flow scheme of the integrated process to get oil, fermentable sugars, ethanol and aromatic chemicals from petrocrops.

6 D.K. Sharma, M. Tiwari, B. K. Behera

become scarce, the petrocrop industry might be deve- loped to produce oil, but alcohols are definitely cleaner fuels. These are presently being used after blending with gasoline as a lead-free gasohol fuel to prevent environmental pollution caused by the use of tetraethyl lead. Production of ethanol and aromatic chemicals from spent residues may then become a suitable alternative to oil. In the future, interest in the development of processes to get value-added fuels and chemicals from petrocrops, the renewable energy sources from arid zones, will increase. Present studies can make the use of petrocrops more effective so that these sources of oil and chemicals can be fully exploited in the future.

REFERENCES

Adams, R. E & McChesney, J. D. (1983). Phytochemicals for liquid fuels and petrochemical substitution; extraction procedures and screening results. Econ. Bot., 37,207-15.

Adams, R. E, Balandrin, M. E, Brown, K. J., Stone, G. A., Gruel, S. M. & Bagby, M. O. (1986). Extraction of liquid fuels from terrestrial higher plants. Part I. Yields from a survey of 614 Western United States plants Texa. Bio- mass, 9, 255-92.

Arora, M., Behera, B. K. & Sharma, D. K. (1993). Efect of various preservatives and coagulants on latex of Calotro- pis procera (Ait.) R.Br. and an alternate light scattering technique to screen the coagulants. Int. J. Energy Res., 17, 349.

Calvin, M. (1983). New sources for fuel and materials. Science, 219, 24-6.

Carr, M. E. & Bagby, M. O. (1987). Tennessee plant species screened for renewable energy sources. Econ. Bot., 41, 78-85.

Chopra, R. N., Nayar, S. L. & Chopra, I. C. (1956). Glossary of Indian Medicinal Plants, Publication and Information Directorate. CSIR, New Delhi, India, Suppl. 1969.

Costa, E., Aguado, J., Ovejero, G. & Canizares, E (1992). Conversion of guayule resin to CI-CI0 hydrocarbons on zeolite based catalysts. Fuel, 71,109-13.

Goidstein, I. S. (1981). Organic Chemicals from Biomass. CRC Press, Boca Raton, FL, USA.

Gruel, S. M. & Bagby, M. O. (1986). Extraction of liquid fuels and chemicals from terrestrial higher plants. Part I. Yields from a survey of 614 Western United States Plants Texa. Biomass, 9, 255-92.

Harborne, J. B. (1988). The Flavonoids, Advances in Research Since 1980. Chapman and Hall, London, UK.

Hoffman, J. J. (1986). Amsonia species: Potential new crops for arid lands. Biomass, 9, 93-100.

McLaughlin, S. P. & Hoffman, J. J. (1982). Survey of biocrude producing plants from the southwest. Econ. Bot., 36, 323-39.

McLaughlin, S. P., Kingsolver, B. E. & Hoffman, J. J. (1983). Biocrude production in add lands. Econ. Bot., 37, 150-8.

Sharma, D. K. & Babu, C. R. (1984). Production of hydrocarbons (liquid fuels and chemical feedstocks from biomass) -- A renewable source. Ind. J. Technol., 20, 454-6.

Sharma, D. K. & Das, K. (1992). Enzymatic hydrolysis of chemically pretreated bagasse. Ind. Chem. Engng, 34, 63-9.

Sharma, D. K. & Goldstein, I. S. (1990). Reactivity towards phenolation of sulphuric acid lignins. J. Wood Chem. Technol., 10, 379-86.

Sharma, D. K. & Hall, I. H. (1991). Hypolipidemic, anti- inflammatory and antineoplastic and cytotoxicity of flavonolignans isolated from Hydnocarpus Weightiana. J. Natural Products, 54, 1298-302.

Sharma, D. K. & Mbise, H. A. (1988). Biocrude and biomethane from Croton bonplandianum. Resources Cons. & Recycl., 3, 49-53.

Sharma, D. K. & Prasad, R. (1986). Oil and nonpolluting fuel from latex bearing plants. Biomass, 11, 75-9.

Sharma, D. K., Mbise, H. A. & Singh, S. K. (1990). Produc- tion of biocrude and fermentable sugars from Croton bonplandianum and fermentation of hydrolysate. Cellulose Chem. Technol., 24, 193-200.

Sharma, D. K., Dastidar, M. G., Gadgil, K. & Choudhury, R. (1992). Overview of research activities of fuel technology group (coal). J. Energy Opportunities, 7, 81-8.

Sharma, D. K., Behera, B. K. & Arora, M. (1994a). Hydro- gen transfer hydrocracking of C. Procera latex under ambient pressure conditions to get value-added chemicals and fuels. FueI Sci. and Technol. Int. (in press).

Sharma, D. K., Tiwari, M., Pradeep, A. K. & Behera, B. K. (1994b). Bioresource Technol. (accepted for publication).

Singh, A., Das, K. & Sharma, D. K. (1984a). Integrated process for production of furfural, xylose, glucose and ethanol by two step acid hydrolysis. Ind. Engng Chem. Prod. Res. Dev., 23,257-62.

Singh, A., Das, K. & Sharma, D. K. (1984b). Production of furfural, xylose, fermentable sugars and ethanol from agricultural wastes. J. Chem. Technol. Biotechnol., 34, 51-61.

Taylor, W. I. & Farnsworth, N. R. (eds) (1973). The Vinca Alkaloids -- Botany, Chemistry and Pharmacology. Marcel Dekker Inc., New York, USA.

Vasudevan, P., Durga Kumari & Patwardhan, S. V. (1981). An integrated approach in weed utilization: Calotropis procera (Ait.) R. Br. and C gigantea (Linn.) R. Br. ex. Air. J. Sci. Ind. Res., 40, 778-82.

Wealth of India (1959). Raw Materials. CSIR, New Delhi, India.

Wise, D. L. (1983). Organic Chemicals from Biomass. The Benjamin Cumming Pub. Co., Inc., Menlo Park, CA, USA.

a review of integrated processes to get value-added chemicals and fuels from petrocrops

Documents