Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing oxygen-containing organic compound
Patent
1988-06-20
1989-12-12
Lilling, Herbert J.
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Preparing oxygen-containing organic compound
435161, 435911, C12P 706
Patent
active
048867519
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the production of ethanol through fermentation of a carbohydrate containing substrate in a fermentor during continuous discharge of a stream of fermentation liquor from the fermentor, which stream is separated in a centrifugal separation step into a yeast enriched stream, which is recirculated to the fermentor, and an essentially yeast-free stream, which in a primary distillation step is separated into an ethanol enriched top stream and a residual liquid bottom stream, of which a part is recirculated to the fermentor and the residual part is supplied to a secondary distillation step for stripping off remaining ethanol to form a concentrated stillage impoverished in ethanol.
In known processes of the above mentioned kind with continuous stillage recirculation and yeast recirculation, as disclosed for example in applicant's American Pat. No. 4,358,536, one essential advantage of the process is the low water input and the low energy costs associated therewith for evaporation of the stillage obtained as by-product. At a typical fermentation process with for example cane sugar molasses as raw material a stillage with a maximum dry substance content (DS) of non-fermentable material of about 10% by weight can be achieved, while in said continuous recirculation process normally a DS-content in the range of 22-25% by weight is reached in the stillage from the secondary distillation step, the DS-content in the fermentor being in the order of 15% by weight.
Mathematically, a further increase of the DS-content of the final stillage and thereby a further reduction of the evaporation energy required could be achieved by simply further reducing the water input to the process and increasing the fraction of the intermediate stillage recirculated from the primary distillation step. For the above mentioned continuous recirculation process the minimal required water input is settled by two essentially different criteria. One criterium emanates from the fact that a certain part of the non-fermentable substance contained in the raw material, the concentration of which increases with reduced water input to the fermentor, consists of osmosis forming dissolved salts and molecularly dissolved substances. Increasing concentration of osmosis forming substances in the fermentation liquor leads to a condition, at which the yeast growth rate is less than the rate with which the living yeast cells are killed off. The total ethanol productivity decreases due to reduced number of active yeast cells and also due to decreasing ethanol productivity of still active yeast cells.
The second criterium, which can be dimensioning for the water input, is set by the flow condition of the system. For example in case of fermentation on a grain raw material, which contains moderate amounts of soluble osmosis forming substances, the minimum water input limit is generally not set by the content of soluble substances but by the maximum content of insoluble substances for achieving the required fluidity in the system. In fermentation of certain sugar raw material, such as beet and cane sugar molasses, however, the fluidity conditions allow such a low water input that the fermentation almost completely stops due to a too high concentration of osmosis forming substances in the fermentor.
The object of the present invention is to modify the process for ethanol fermentation of the introductively mentioned kind so that a further, in dry substance concentrated stillage is obtained from the secondary distillation step.
This object has been reached in the process for ethanol fermentation on beet or cane sugar molasses and is primarily characterized in that the process water input is controlled, for example by controlling the concentration of the supplied molasses substrate, so that during a first period of time, the concentration of non-fermentable substance in the fermentor, calculated as water-free substance (DS) increases from a start value in the range 5-15% by weight DS to a value in the range 20-30% by weight DS,
REFERENCES:
patent: 4358536 (1982-11-01), Thorsson et al.
patent: 4511437 (1985-04-01), Heck et al.
patent: 4522920 (1985-06-01), Thorsson et al.
patent: 4769112 (1988-09-01), Wheldon
Derwent Abs. 85-171994/29 DD-220045 (3-85) Khackmos et al.
Derwent Abs 88-119380/17 WO8802649 (4-88) Erickson.
Derwent Abs 86-157244/25 EP-185010 (6-86) Krenn.
Derwent Abs 83-49100k/20 WO8301627 (5-83) Wallner.
Lilling Herbert J.
Nobel Chematur AB
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