Producing stable pyrolysis liquids from the oil-seed presscakes of mustard family plants: pennycress (Thlaspi arvense L.) and camelina (Camelina sativa)

Authors: BOATENG, AKWASI; Mullen, Charles; Goldberg, Neil

Submitted to: Energy and Fuels
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/25/2010
Publication Date: 11/15/2010
Citation: Boateng, A.A., Mullen, C.A., Goldberg, N.M. 2010. Producing stable pyrolysis liquids from the oil-seed presscakes of mustard family plants: pennycress (Thlaspi arvense L.) and camelina (Camelina sativa). Energy and Fuels. 24:6624-6632.

Interpretive Summary: The bio-diesel industry in the United States currently produces 500 million gallons of renewable fuels per year. Much of this is produced from edible oils such as soybean oils, but in order to sustainably produce the food and fuel needs of this country, non-edible sources of feedstock need to be found. Pennycress is a plant that produces seeds that are 36% oil that can be converted to bio-diesel and can be grown on the fallow lands of the winter in the Midwest so it does not interfere with food production. However, unlike soybean, the remaining seed material after oil extraction (often called meal or presscake) cannot be use as an animal feed source because it contains toxic proteins. Therefore, another use for this material should be found. In this study we carried out fast pyrolysis, (the rapid heating in the absence of air) on the presscakes of pennycress and its mustard seed family relative camelina. Fast pyrolysis produces a liquid product called pyrolysis oil or bio-oil. Many are considering bio-oil from many sources as a feedstock to produce additional bio-fuel by refining it to renewable gasoline, diesel or jet-fuel. Usually bio-oil made from wood or crop material is acidic and unstable, meaning it is difficult to handle, process, and refine. However, we found that when bio-oil is made by pyrolysis of the presscakes of pennycress or camelina it is reduced in acidity and is storage stable, and therefore can be more easily refined into additional sources of renewable fuels. This information will be useful to those considering producing bio-diesel or pyrolysis oils, refiners looking to produce renewable fuels, or those who advise farmers who are looking to produce an extra crop on winter fallow lands.

Technical Abstract: Natural oil from non-food oil-seeds such as camelina, jatropha, and pennycress are increasingly becoming the feedstock of choice for biodiesel production through transesterification to fatty acid methyl esters (FAME) and green diesel production via catalytic hydrotreating. Unlike the presscakes from food-based feedstocks such as soy and palm fruits, the residual oil-extracted presscakes from non-food feedstocks such as camelina and jatropha are often not suitable for consumption as animal feed. However their abundance and the fact that these feedstocks are already collected give them a logistical advantage as a bioenergy resource over conventional lignocellulosic biomass which is yet to be harvested. Vegetable oil-seed presscakes make an ideal thermochemical conversion feedstock due to their inherently high initial calorific value. We carried out fast pyrolysis of the entire value chain of two of the mustard family oil seeds i.e., pennycress and camelina and found that at the optimum fast pyrolysis conditions not only high carbon, high energy liquid fuel intermediates can be produced but that these liquids are low-oxygen, stable intermediates that do not oligomerize over time to higher molecular weight or increase in viscosity over time according to the accelerated ageing test. Liquid fuel quality was high with gross calorific value ranging between 29.0 MJ/kg for defatted oil to 34.7 MJ/kg for the whole seed on dry basis. The corresponding carbon conversion efficiency, defined as feed carbon converted to the pyrolysate, ranged between 60% and 80%. It is envisioned that co-location of a commercial fast pyrolysis facility with a commercial green diesel plant that utilizes mustard family seed oil could provide additional gallons of renewable biofuels and a reliable source of aromatic hydrocarbon compounds needed for the formulation of renewable jet fuels.