9-32: Production of Green Fuels and Chemicals from Black Liquor

Implementation of the sustainability concept and the goal of CO₂ emission reduction have created an increased interest in the development of biorefineries, i.e. processing facilities that convert biomass components into green fuels and chemicals. Chemical pulp mills such as Kraft, soda, or sulfite mills are current examples of biorefineries that can convert lignocellulosic biomass into energy, pulp or cellulose derivatives, and tall oil.

Today lignin and part of hemicellulose end up in the black liquor and are burned in a recovery boiler with the energy is recovered as steam, supplying a large fraction of the mills process steam requirements. Most of the energy is provided by lignin, since hemicellulose has a very low heating value. The hemicellulose fraction is therefore an underutilized renewable resource in many mills and a more attractive alternative would be to extract the hemicellulose from the black liquor and use it for biochemical conversion into fuels and chemicals. Fractionation of black liquor represents, therefore, a very interesting opportunity for many pulp mills. Depending on microorganism used, a number of organic acids can be produced from five-carbon sugar.

This study presents the fractionation of birch black liquor into xylose, acid soluble lignin and acid insoluble lignin and thereafter the conversion of the sugar fractions into succinic acid.