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Bioconversion of mountain pine beetle-killed lodgepole pine to ethanol

University of British Columbia

Global warming is widely acknowledged as being caused by an increase in the production of greenhouse gases, largely CO₂, generated from the burning of fossil fuels such as gasoline. By offsetting a portion of gasoline usage with alternative fuels, such as ethanol, CO₂ emissions could be reduced. Bioethanol can be produced from many types of biomass, including softwoods. For maximal ethanol yield from softwoods, the most effective bioconversion process is considered by many to be SO₂-catalysed steam explosion followed by separate or simultaneous hydrolysis and fermentation. This method has been shown to be effective on both spruce and Radiata pine, although past research at UBC on Douglas-fir showed that additional delignification was necessary in order to obtain satisfactory sugar recovery and hydrolytic conversion. Another promising softwood species for bioconversion in British Columbia is lodgepole pine, which has been severely affected by the mountain pine beetle and its associated fungus and is consequently widely available and relatively inexpensive. Prior to investigating the bioconversion of lodgepole pine, the UBC steam explosion process was evaluated and was found to be comparable to that used at Lund University in Sweden. Following this, optimization of pretreatment conditions of beetle-killed lodgepole pine for maximal ethanol yield revealed that the highest ethanol yield after SSF, 77% of theoretical, was derived from substrates pretreated at 200°C, 5 min, 4% SO₂. When these and other conditions were applied to healthy, and mixed (50/50 healthy/beetle-killed) wood, the beetle-killed substrate provided higher sugar recovery after pretreatment, higher hydrolytic conversion, and higher overall ethanol yield after SSF. This was likely a result of two factors. The first, reduced uptake of SO₂ during the impregnation step effectively reduced the pretreatment severity and increased sugar recovery and fermentability. Secondly, increased fines may have improved the enzymatic digestibility of the substrate. The work in this thesis established the technical feasibility of producing ethanol from lodgepole pine in a two-step process consisting of SO₂-catalyzed steam explosion followed by SSF of the combined liquid and solid fractions. In addition, the short residence time required for SSF as well as the reduced cost of the raw material suggest that the process could be economically attractive as well.

Text

2010-01-09

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http://hdl.handle.net/2429/17981

Forestry

University of British Columbia

UBCV

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