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Unlocking the value potential of lignin in wheat straw

Lignin is a natural substance in biomass, but it is unwanted in processes like in the production of paper or cellulosic ethanol. In those processes, lignin is considered as waste and is used as fuel in heat and power plants. At the University of Borås in Sweden, a team of researchers is investigating methods to extract and refine lignin to a high-value bio-oil intermediary that can be used for refining into biofuels or biochemicals.

Swarnima Agnihotri is looking to extract lignin from wheat straw (photo courtesy Solveig Klug / University of Borås).

While the commercial lignocellulose to ethanol plants use the lignin after pretreatment as biomass feedstock to heat and power plants, in the EU Horizon 2020 project AGROinLOG, lignin will instead be transformed into bio-oil based products.

If biofuels are to become a reality, we need to realize the industrial potential of lignin and get more value from it. Seeing the complexity and richness of its functional groups, there are various potential applications of lignin by converting it in variety of value added products like high performance carbon fibre, bio-oil and vanillin, to name a few, said Swarnima Agnihotri, a researcher at the University of Borås, Sweden who has been refining methods to extract lignin from the lignin rich wheat straw.

The project aims at utilizing an agricultural residue, wheat straw, a lignin rich feedstock that is available in surplus in Sweden, and in other European countries. The Swedish team, comprising of Swedish Institute of Agricultural and Environmental Engineering and SP Processum, both subsidiaries of Research Institutes of Sweden (RISE), Lantmännen and University of Borås, is the part of the AGROinLOG’s Integrated Biomass Logistic Centre (IBLC) demonstration for wheat straw

Wheat straw lignin valorization will add value to the whole process, and in turn provide benefit to industry, as well as further insight in creating value from lignin, which has been considered a waste until now, she said.

Addressing costs by adding additional value

The integration of lignocellulose based feedstock in ethanol plants is not new. There are a number of techniques already producing ethanol from lignocelluloses at commercial scale.

It is the high investment costs and the low profitability of the process which needs to be addressed. The goal with this AGROinLOG project will be to see the possibilities of adding a high valuable byproduct, for example, bio-oil, to the whole production chain, and therefore increase the profitability of the process. Finding a cost effective biomass fractionation process was a challenge. There is a lot of ongoing research on pretreatment for a better lignin extraction from lignocelluloses, but still, the main challenge is to bring the cost down. We have tried cheaper processes like hot water/alkaline extraction along with the very effective, but expensive, ethanol organosolv process used in paper production, and compared them. The results are interesting and motivating, Agnihotri reveals.

Process scale-up next

The next step in the project is to scale-up the pretreatment process and convert the lignin into a bio-oil.

Now, when we have optimized an efficient pretreatment process for effective lignin extraction from wheat straw, we will scale up the process, and the pure lignin obtained will be transformed into bio-oil through a hydrothermal liquefaction process done, that is, extracting liquid and get a concentrated oil. The bio-oil product obtained will be a high value byproduct since it can be further upgraded in refineries to obtain green chemicals and biofuels, ended Agnihotri.

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