Biofuels and Biomaterials From An Arid Lands Plant, Grindelia Squarrosa
AuthorNeupane, Bishnu P.
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Grindelia squarrosa, commonly called curlytop gumweed, can potentially be cultivated for biofuel production in the semiarid and arid lands of western USA. It can be grown on marginal land with less than 25 cm of water and has low nutrient requirements. The average amount of dry biomass that was produced by growing gumweed in plots in the agricultural experimental field stations of University of Nevada Reno was approximately ten tons per hectare 9950 kilogram per hectare (kg/ha). The germination success was approximately 87% in the greenhouse and 61% in the field, where germination requires damp conditions. The biennial plant blooms for 1.5 months with an initial milky stage of the pre-bloom, followed by yellow flowers in August of the second year of planting. The buds produce a diterpene carboxylic acid, grindelic acid, as the primary component and additional carboxylic acids and various terpenes. Constraints on production of the crop include various weeds and occasional fungal infections.The biofuel potential is greatest when the plant contains 50% flowers, and can be harvested, field dried and then ground/milled with a hammer mill. The acetone extraction of the ground gumweed biomass produced an average of 12.5% biocrude using a pilot scale bioreactor, while a more complete soxhlet extraction produced 15.5% biocrude. The carboxylic acid fraction was 68% of the weight of the biocrude. The average amount of biocrude production was 1,260 kg/ha while the average amount of carboxylic acid fraction production was 816 kg/ha.Acid catalyzed methylation of biocrude produced about 72.5% hexane extractable materials, consisting primarily of methyl esters of the carboxylic acids and various terpenes. When the carboxylic acid fraction of the biocrude was isolated and methylated, the hexane extract contained 85% of the weight. Those hexane extracted materials are the materials examined for biofuel values. Although the methylated components produced a viscous liquid, this fraction could be mixed with petroleum diesel fuel up to 20%, the blend met the biofuel standards despite its slightly higher viscosity. A single peak of grindelic acid methyl ester (GAME) was observed by gas-chromatography mass spectrometry (gc-ms) using diazomethane as the methylation agent, while the acid catalyzed methylation produced an additional peak, also identified by gs-ms as GAME. The differences in structure of the two compounds were not determined. While the average amount of useful biofuel production from gumweed was about 865 liter per hectare (L/ha) (92 gallons per acre (gal/ac)), the best plots suggested that it could be produced up to 1290 L/ha on a biennial basis which is equivalent to 138 gal/ac.Grindelic acid, a C20 diterpene carboxylic acid is the major component of gumweed which is present as about 80% of carboxylic acid fraction, 52% of biocrude, and 6.5% of biomass in average. The total potential of producing grindelic acid from the gumweed grown in Nevada lands is 629 kg/ha. The biocrude contains about 4.7% terpenes, including like pinene, limonene, germacrene, elemene and camphene, which is about 0.73% of the starting biomass.Pyrolysis of biocrude and the carboxylic acid fraction produced a promising biofuel, which has characteristics close to biojet fuel in properties. When the biocrude was heated up to 450 oC, about 47% of the biocrude was obtained in the form of a pyrolyzed oil mixture. When the pyrolyzed oil was subjected to redistillation, three distinct cuts were obtained. The first cut, which is about 6% of the biocrude, had a higher acid number and contains water and a variety of alcohols and other lower molecular weight compounds. The second and third cuts, which contained higher molecular weight hydrocarbons, contained approximately 29% and 11% of the weight of the pyrolyzed biocrude. The second cut consisting primarily of two tetralin compounds of C13H18 and C14H20. The third cut also consisted primarily of the C14H20 tetralin and other higher molecular weight compounds that are similar to biojet fuel. Based on data obtained from the pyrolysis experiments, an average of 570 L/ha (61 gal/ac) of this fuel was obtained when the second and third cuts were combined. Grindelic acid also has structural, compositional, and functional group similarities with abietic acid and suggests that it can be used as a substitute to abietic acid which has declined in domestic production in the USA. These uses include agrochemical, medicinal, and the naval stores industry.