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ERA-IB: Production and processing of 2,3-butanediol from biomass (PUBB), sub-projects 5: Fermentation raw materials
Project
Project code: TI-HF-08-PID1630
Contract period: 01.03.2009
- 31.08.2012
Budget: 173,581 Euro
Purpose of research: Applied research
Steam treatment with subsequent enzymatic hydrolysis is one of the most promising processes for the production of fermentable sugars from lignocelluloses. The process was optimized and the different process modifications were intensively discussed and evaluated. The objective of the overall project was the development of an efficient fermentation process to produce the platform chemical 2,3-butanediol (2,3-BD) from low-cost renewable feedstock. 2,3-butanediol is a valuable chemical useful as anti-freeze and as raw materials for pesticides, pharmaceuticals, plasticizers, fragrances, moistening agents etc. Further on 2,3-BD can be used for the production of 2-butanone, a fuel additive and for conversion to 1,3-butadiene (1,3-BD), a multi million ton bulk chemical mainly used for the production of synthetic rubber, polyamides and other plastic materials. In the subproject “raw materials for fermentation” wood from short rotation plantation was used as a raw material (poplar and willow). In order to utilize the wood a separation of lignin, hexose sugars and pentose sugars is required. This can be achieved by the combination of steam refining and enzymatic hydrolysis. Steaming refining was optimized with regard to humidity of starting material, temperature (170°C – 220°C), time (5 – 30 min) and addition of catalysts (with and without SO2). After this process cellulose and lignin were obtained in the fibre fraction while the pentoses are enriched in the process liquor. After a subsequent enzymatic hydrolysis of the fibre fraction a glucose solution is obtained. The lignin remains in the hydrolysis residue and can be utilized for materials or for energy production. The impact of steam refining conditions on enzymatic hydrolysis was monitored by factorial design and hydrolysates were be provided for the project partners in order to develop the fermentation process to 2,3-BD. By-product utilisation was a further challenge of the project, since a complete utilisation of raw materials is a prerequisite of a sustainable bio-refinery. The process was optimised with various statistical designs. Under optimal reaction conditions the process modifications steam explosion and steam refining were compared using also reaction devises of external labs. Together with process partners it was evaluated, which process liquors were suitable for fermentation. In this context inhibitive compounds were identified and concepts for their discharge were developed.
Poplar and willow wood from fast rotation plantation were used without debarking. The steam treatment was optimized with and without SO2 as catalyst and complete process balances were established including lignin and by-products as well as inhibitive compounds. After steaming with addition of SO2 higher xylose yields were obtained in the aqueous process streams. In addition, the enzymatic hydrolysis of the fiber fraction was superior and the amount of degradation products reduced compared to the process without SO2. Steam refining was compared to the steam explosion process both followed by enzymatic hydrolysis of the fiber fraction. No significant difference existed between these two processes regarding the product yields. For the utilization of lignin the alkaline extraction of lignin from the fiber fraction prior to enzymatic hydrolysis was investigated. Alternatively the lignin was obtained directly as a residue from enzymatic hydrolysis of the fibers. The later approach is simpler but resulted in higher carbohydrate impurities in the lignin. For both variants a thermal or material utilization of lignin is possible. First tests showed that even the hydrolysis lignin is suitable for lignin-phenol resin synthesis. Accordingly, the alkaline extraction can be omitted. The fermentation of fiber hydrolysates to 2,3-butandiole was successfully established by the project partner TU Braunschweig. The addition of pentose rich extracts to the fermentation induced a significant inhibition of the microorganism. Therefore the utilisation of extracts for biogas production was evaluated. This process could tolerate all the compounds which were inhibitive for the fermentation to 2,3-butandiole. Accordingly, it is recommended to use the two process streams separately. Fiber hydrolsates should be fermented to2,3-butanediol, while the aqueous extracts containing pentoses and degradation products can be used for the production of methane.
Section overview
Subjects
- Renewable Resources
- Climate Change
