Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing oxygen-containing organic compound
Reexamination Certificate
2001-05-01
2003-04-29
Weber, Jon P. (Department: 1651)
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Preparing oxygen-containing organic compound
C435S161000, C435S132000
Reexamination Certificate
active
06555350
ABSTRACT:
FIELD OF THE INVENTION
In its broadest aspect, the present invention relates to the conversion of lignocellulosic biomass materials into combustible fuel products. In particular, there is provided a continuous process for fermentatively converting such biomass materials into ethanol using a process design that permits all or part of the process water from the ethanol fermentation process to be recycled so as to significantly reduce the consumption of process water.
TECHNICAL BACKGROUND AND PRIOR ART
Increasing global energy requirements and heightened environmental awareness have resulted in increasing focus on alternatives to fossil fuels as energy sources. Human activity with respect to combustion of fossil fuels contributes significantly to the total amount of carbon dioxide (CO
2
) released into the atmosphere. Carbon dioxide is purported to be a so called “greenhouse gas” and thus to contribute to global warming.
In contrast to energy production by combustion of fossil fuels, energy production by combustion of contemporary biomass (predominantly in the form of harvested plant material) or fuels derived from such biomass is regarded as being “CO
2
-neutral”, since the amount of CO
2
released by combustion of a given amount of such biomass corresponds to the amount of CO
2
which was originally taken up from the atmosphere during the build-up of that amount of biomass.
Among fuels derived from plant biomass, ethanol has received particular attention as a potential replacement for or supplement to petroleum-derived liquid hydrocarbon products. To minimise the production cost of ethanol produced from biomass (also referred to in the following as “bioethanol”) It is important to use biomass in the form of low-cost by-products from gardening, agriculture, forestry, the timber industry and the like; thus, for example, materials such as straw, maize stems, forestry waste (log slash, bark, small branches, twigs and the like), sawdust and wood-chips are all materials which can be employed to produce bioethanol.
In general, however, the price of bioethanol has not been competitive with that of traditional fossil fuels and it is therefore highly needed to reduce production costs as far as possible by optimising or improving upon bioethanol production technologies.
One important factor in relation to bioethanol production on a commercial scale is the cost of the process water employed. In general, the aqueous effluent from conventional bioethanol production based on the above biomass materials contains substances at a level which, if such process water is recycled, will be rate limiting for the pre-treatment of the lignocellulosic material and/or inhibitory for subsequent hydrolysis of the pre-treated material and fermentation of sugars therein. Accordingly, it is a current practice in bioethanol production to dispose of this water effluent and replace it in the process with fresh process water.
There is thus an industrial need to design bioethanol production processes wherein all or part of the process water can be recycled.
In U.S. Pat. No. 5,221,357 there is described a process for treating a polysaccharide material such as cellulose, hemicellulose and lignocellulose by a two stage acidic hydrolysis to produce monosaccharides and a wet oxidation of the solids such as lignin to produce soluble products e.g. organic acids. The monosaccharides produced are subsequently subjected to fermentation to produce ethanol. Residues from wet oxidation and fermentation are subjected to a methanation step. However, in order to be capable of recycling the remaining liquid and solids into the system a secondary wet oxidation step after methanation is needed which is an additional cost in the production of ethanol.
Thus, the industry is not in the possession of any commercially attractive processes for continuously producing combustible fuel products which permit the process water to be recycled.
It is therefore one significant objective of the present invention to provide a process for continuously processing lignocellulosic material into valuable fuel products wherein the wastewater effluent from the ethanol fermentation effluent is subjected to a treatment, such as an anaerobic fermentation step generating a further combustible fuel product and a wastewater effluent in which the amount of potential inhibitory substances is at a sub-inhibitory level, which in turn permits all or part of the effluent water from the anaerobic fermentation step to be recycled into the process.
The process of the invention thus has the advantages of being capable of 1) giving a very high degree of conversion of carbon in the starting lignocellulosic biomass to useful products, 2) reducing the consumption of water used in the process, and 3) minimising the mounts of residual waste material emerging from the process.
Thus, the process of the invention not only provides improved process economy, e.g. with respect to production of a further combustible fuel product, but is also more environmentally friendly than traditional processes for obtaining such products.
SUMMARY OF THE INVENTION
Accordingly, the present invention pertains to a process for continuously converting solid lignocellulosic biomass material into ethanol, the method comprising the steps of:
(i) providing an aqueous slurry of the biomass material,
(ii) subjecting, in a reaction vessel, said aqueous slurry to elevated temperature conditions and/or an oxygen enriched atmosphere to obtain a slurry in which at least partial separation of the biomass material into cellulose, hemicellulose and lignin has occurred,
(iii) subjecting the slurry resulting from step (ii) and/or the aqueous phase hereof to a a treatment resulting in at least partial hydrolysis of the cellulose and hemicelulose to obtain a slurry and/or aqueous phase containing an amount of microbially fermentable sugars that permits the slurry or aqueous phase to be used as an ethanol fermentation medium,
(iv) subjecting the slurry and/or aqueous phase of step (iii) to at least one ethanol fermentation step,
(v) separating the ethanol from the fermentation medium resulting from step (iv) resulting in a fermentation wastewater effluent containing a level of inhibitory substances that, if present in any of the preceding steps (ii) to (iv) would be rate limiting or inhibitory;
(vi) subjecting said wastewater effluent to a treatment whereby the level of the inhibitory substances is reduced to a level that, if the wastewater effluent is introduced into any of the preceding steps (ii) to (iv) is not rate limiting or inhibitory;
(vii) introducing all or part of the thus treated wastewater effluent into any of the preceding steps (i) to (v), and
(viii) continuously repeating steps (i) to (vii).
As shown herein, it was possible to provide a fully operational process for continuously converting solid lignocellulosic biomass material, which process comprises wet oxidation or treatment at an elevated temperature such as steam explosion, enzymatic hydrolysis, ethanol fermentation and finally wastewater treatment. An interesting feature of the process according to the invention is that it is not necessary to incorporate any detoxification steps in the process as all substances produced during each single step of the process served as a substrate for the organisms used in a subsequent step.
As described above, the lignocellulosic biomass material is subjected to a pre-treatment in step (ii), which is wet oxidation or a treatment at an elevated temperature such as e.g. steam explosion. If used, the amount of oxidising agent employed in this step will in general be an amount which is effective to substantially prevent or minimise formation of undesirable reduction products, e.g. furfural and/or furfural derivatives. A well suited oxidising agent is oxygen per se, and presently preferred processes of the invention are performed in the presence of oxygen introduced into the reactor at an initial partial pressure of oxygen equal to or exceeding ambient partial pressure of oxygen.
It appears that cellulose and any hemic
Ahring Birgitte Kiær
Thomsen Anne Belinda
Forskningscenter Riso
Hunton & Williams
Weber Jon P.
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