Production of lignin with a low molecular weight from kraft black liquor

The origin of biomass available in a country largely depends on where it is located, the properties of the soil and to which extent the country is exploited. Sweden, which is a small country in northern Europe, has 50% of its land area covered in forests. This makes the forest not only a base for one of the largest industry sectors but also a potential source for different products derived from biomass.

One such product is lignin, which is a biopolymer with a structural resemblance to the polyaromatics found in oil. Therefore, lignin could be used as a raw material for the production of different kinds of fuels as well as for the production of carbon fibers, vanillin and dispersants. The potential of producing a green fuel from wood derived materials is an intriguing path forward for countries with a large forest industry in order to reduce the emissions based on the use of fossil fuels.

Production of pulp by the kraft process provides an interesting waste stream, the black liquor, which could be used for the production of lignin. There are processes available on the market for this purpose today. However, by introducing a first step of membrane filtration followed by a heat-treatment of the concentrated liquid, a slurry containing a lignin fraction with a lower molecular weight could be obtained. This is preferable in many applications. Furthermore, the heat-treatment improved the process performance downstream.