Further development of chemical and biological processes for the production of bio-ethanol
Production of ethanol from both the cellulose and hemicellulose fraction of wet oxidized wheat straw was investigated.
Lignocellulose, whether from primary (forestry or non-food energy crops) or secondary sources (agricultural or forestry waste) represents an non-utilized energy source which can be converted into a CO2 neutral fuel, bio-ethanol. For an agricultural country like Denmark, waste products such as rape-straw which, in the future could be extended to include energy crops like willow, represent forms of biomass which are rich in carbohydrates. However, the chemical and physical barriers, such as lignin and crystalline cellulose, that protect the living crops from microbial degradation, are the same barriers that give technical and microbiological problems when converting these lignocellulosic biomasses into ethanol. At the research center Risø National Laboratory a new pretreatment method, wet oxidation, will be examined for an optimal release of fermentable sugars, from three different kinds of lignocellulosic biomass (wheatstraw, rape-straw and willow). The chosen cellulose and hemicellulose before and after pre-treatment, the release fermentable carbohydrates, and the amount of inhibitors produced are studied. Data from these experiments will be compared with the widely used steam explosion method. At the Technical University of Denmark, two ethanol fermentation concepts will be examined for the conversion of pretreated lignocelluosic materials into ethanol. One, with two separate process streams, where the cellulose is hydrolysed to glucose and converted into ethanol by mesophilic yeast, and the other where hemicellulose is converted into ethanol by a thermophilic ethanol producer. The second concept is one process stream where the pretreated lignocellulose is pumped into a fermenter, and the hydrolysed cellulose is fermented into ethanol by yeast. The ethanol is then stripped off, followed by a thermophilic convertion of the hemicellulose into ethanol. Furthermore, experiments on increasing the ethanol productivity of thermophilic anaerobic bacteria by cell recirculation in the fermenter will be conducted. The project is an extension of a research collaboration between The Technical University of Denmark and Risø National Laboratory, which will give Danish knowhow in pretreatment and fermentation of lignocellulose into ethanol
Saccharomyces cerevisiae was used for the cellulose fraction and Thermoanaerobacter mathranii A3M4 was used for the hemicellulose fraction. Utilization of the hemicellulose fraction was tested both after separation of the cellulose and hemicellulose fraction, and as one single process stream containing both fractions. Conditions for wet oxidation best suitable for fermentation, was obtained with oxygen at 3 atm. The ethanol yield was 9.9 mM with T. mathranii A3M4. For increased availabillity of xylose, the wet oxidized wheat straw was treated with different enzymes. From those tested, only CelluClast increased the ethanol yield from T. mathranii. Addition of glucose to the medium increased the ethanol yield from xylose significantly, fermenting with T. mathranii. Acid hydrolysis of hydrolysate had no positiv effect on the ethanol with T. mathranii. Using one process stream the ethanol yield from Saccharomyces cerevisiae was 142 mM, 27 mM from T. mathranii and 63,6 m3 methane/ton wheat straw from cleaning at the process water for acetate and remaining sugars, using a consortia of methane producing bacteria from household waste. Omission/addition of yeast extract to the fermentation substrate had no effect on the ethanol yield from Saccharomyces cerevisiae. The yield from T. mathranii decreased 5-6 times, if yeast extract was omitted. Wet oxidized wheat straw had no inhibitiry effect on organism. 50% of the process water can be recirculated for fermentation with saccharomyces cerevisiae. For increased ethanol yield from T. mathranii A3M4, a plasmid capable of replicating in this organism has been found. This can be used for introduction of new genes important for the ethanol yield in T. mathranii. The plasmid is stable also under non selective conditions
Key figures
Category
Participants
| Partner | Subsidy | Auto financing |
|---|---|---|
| Danmarks Tekniske Universitet (DTU) |
Contact
Øvr. Partnere:
