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Researchers Propose Method for Co-processing of Carbohydrates and Lipids in Oil Crops To Produce a Hybrid Biodiesel

Mark Mascal and Edward Nikitin from the University of California Davis are proposing a method that can use both the carbohydrates as well as the oils in oil seed plants—such as soybean, sunflower, jatropha, camelina, safflower, and canola—to produce a hybrid lipidic/cellulosic biodiesel with greater product yield than conventional transesterification. A paper on their method was published online 12 February in the ACS journal Energy & Fuels.

Mascal and Nikitin have previously reported on a biphasic acid/solvent process that converts carbohydrates in biomass feedstocks into the biofuel precursor CMF. (Earlier post.) In the new work, they applied that method to the processing of oil seed feedstocks, resulting in a substantial increase in fuel production from this type of biomass.

At present, biodiesel is produced by the transesterification of mainly plant-derived oils. Oil seeds of course also contain significant carbohydrate profiles, in the form of starch, cellulose (“fiber”), hemicellulose, and free sugars. We have previously shown that hexoses in any form, whether mono-, di-, or polysaccharides, can be converted into a mixture of 5-(chloromethyl)furfural (CMF) and levulinic acid in combined yields up to 95%. The major product of the reaction is CMF, which accounts for between 70 and 90% of the organic material isolated, depending upon the reactor loading, while compound 2 comprises less than 10% of the product mixture. To our knowledge, this level of conversion of carbohydrate feedstocks into simple organic molecules is unrivaled in the literature.

—Mascal and Nikitin

They introduced soybean, sunflower, jatropha, camelina, safflower and canola feedstocks into a biphasic reactor containing aqueous hydrochloric acid and 1,2-dichloroethane and heated the mixture at 80 °C for 3 hours. When the experiment is conducted at 80 °C, the triglyceride structure remained fully intact. Raising the temperature to 100 °C led to the appearance of a minor side product. Because working at higher temperatures afforded no real advantages in terms of carbohydrate to CMF conversion, reactions were generally run below 100 °C to avoid this hydrolysis reaction.

They found that useful quantities of carbohydrate-derived CMF were produced from each feedstock investigated. Their study used only the seeds of the crops; the CMF fraction could in principle be increased if the entire plant, including stalks and leaves, were likewise processed, they said.

Yields of Lipid and CMF (g) per Dry Kilogram Biomass Feedstocks
 LipidCMFTotal organic
extract
CMF % of total
organic extract
soybean (Glycine max) 257.0 67.9 324.9 20.9%
sunflower (Helianthus annuus) 358.7 110.2 470.7 23.5%
jatropha (Jatropha curcas) 392.1 78.6 470.7 16.7%
camelina (Camelina sativa) 374.5 102.5 477.0 21.5%
safflower (Carthamus tinctorius) 371.3 113.0 484.3 23.3%
canola (Brassica napus) 448.3 120.0 568.3 21.2%

Mixtures of the seed oil and CMF can be submitted to ethanolysis to give ethyl levulinate and biodiesel ethyl ester. Alternatively, heating seed oil-CMF mixtures in water results in the hydrolysis of [CMF] to levulinic acid while leaving the oil intact. Levulinate esters are short-chain oxygenates, which can be blended with diesel fuel and may improve its cold-performance properties.

The methodology described here has the potential to revolutionize biodiesel production by merging lipid- and cellulose-based biomass conversion technologies and thereby substantially increasing the overall yield of fuel produced from oil crops.

—Mascal and Nikitin

Resources

  • Mark Mascal and Edward B. Nikitin (2010) Co-processing of Carbohydrates and Lipids in Oil Crops To Produce a Hybrid Biodiesel. Energy Fuels, Article ASAP doi: 10.1021/ef9013373

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