GB2075053A

GB2075053A - A Process for the continuous production of fermentation alcohol

Info

Publication number: GB2075053A
Application number: GB8014922A
Authority: GB
Original assignee: Sim Chem Ltd
Current assignee: Sim Chem Ltd
Priority date: 1980-05-03
Filing date: 1980-05-03
Publication date: 1981-11-11

Abstract

A process for the continuous production of fermentation alcohol, comprising the steps of effecting fermentation of a continuous supply of a liquid substrate by anaerobic bacteria of a kind capable of producing a high rate of ethyl alcohol per unit of cell mass and sugar substrate, and a high tolerance to the inhibitory effects of alcohol and high sugar concentration, includes the step of causing agglomeration of the bacterial cells, for example by the addition of a flocculating agent or an organic acid, or by adding an inert particulate support medium or a magnetic support medium, to render them capable of being separated from the fermentation liquor and thus retained within the process or returned thereto after separation from liquor discharged from the process. The preferred species of bacteria is Zymomonas Mobilis.

Description

SPECIFICATION A process for the continuous production of fermentation alcohol This invention relates to a process for the continuous production of fermentation alcohol.

The process is particularly, though by no means exclusively, concerned with the fermentation of glucose solutions by anaerobic bacteria of the kind capable of producing ethyl alcohol substantially in the absence of air.

It is recognised that in the production of alcohol by the fermentation of sugars using yeasts, considerable advantages result from the natural floccuience of certain yeast strains, in that strongly flocculent yeasts can be separated from the fermentation liquor, and thus can be retained within the process or returned thereto after extraction from liquor discharged from the process. By maintaining the population of the micro-organism within the process considerable productivity advantages are experienced.

As an alternative to using yeast for the fermentation, there are available a variety of bacteria of a kind which are capable of producing ethyl alcohol in this process. One example of such a bacteria is Zymomonas, and in particular, various strains of the species Zymomonas mobilis which possess such desirable properties as a high rate of alcohol production per unit of cell mass, a high yield of alcohol based on utilisation of the sugar substrate, and a high tolerance to the inhibitory effects of alcohol and high sugar concentration.

Indeed, it is known to use such micro-organisms in the batch production of alcohol from sugars.

Established continuous culture methods have also been used to effect a continuous anaerobic fermentation of sugars using Zymomonas mobilis, but the productivity of such processes is limited by the fact that in the anaerobic condition the yield of bacterial cells is low; therefore the expected higher rate of alcohol production per unit of cell mass is not achieved since there is not a correspondingly high rate of production of cells.

With yeasts, an initially high cell yield can be attained by using the capability of the yeast to grow profusely under aerobic conditions, and under subsequent anaerobic conditions the retention of a cell population sufficient to sustain a high rate of alcohol production per unit volume, is facilitated by the natural tendency of many yeast cells to flocculate, making them more readily capable of being retained within the process or returned thereto after removal. In contrast, Zymomonas normally exists as a dispersed suspension of relatively small cells or cell aggregates. In general, even with selection of particularly flocculent strains of Zymomonas bacteria, such strains do not form a stable dense, rapidly-settling flocculent growth of the type which has shown to be of advantage in the case of yeast.The same characteristics are applicable with many other alcohol-producing fermentative bacteria.

An object of the present invention is to provide a process for the continuous production of fermentation alcohol, wherein bacteria of a suitable kind are used in a manner which enhances the productivity of the process as a whole.

According to the present invention there is provided a process for the continuous production of fermentation alcohol, comprising the steps of effecting fermentation of a continuous supply of a liquid substrate by anaerobic bacteria of a kind capable of producing ethyl alcohol, while effecting agglomeration of the bacterial cells to render them capable of being separated from the fermentation liquor and thus retained within the process of returned thereto after separation from liquor discharged from the princess.

The concept of this invention is generated as a result of the recognition that it is preferable to use a micro-organism which in other respects demonstrates very desirable characteristics, such as a suitable species of the genus Zymomonas, or as an example a suitable strain of the species Zymomonas mobilis, and to confer upon it the desired separation characteristics, similar to those which can be exploited in the use of yeasts.

Therefore, in the process, the bacteria effects anaerobic fermentation of a continuous supply of a liquid substrate such as an aqueous solution of glucose, in a fermentation vessel, and the bacterial cells are caused to aggregate.

The required aggregation may be attained by the addition of a suitable flocculating agent to the liquor in the vessel, such as a dispersed polyelectrolyte, or particles of an insoluble polyelectrolyte, or an inorganic flocculating agent such as basic ferric sulphate, or an organic agent such as a suitable grade of lignosulphonic acid.

Alternatively, or in addition, it may be desirable to add to the liquor in the fermentation vessel, a relatively dense inert particulate support medium such as sand or polymer particles or ceramic particles or a magnetic support medium such as one containing ferrite. Alternatively, or in addition, the cells of the anaerobic bacteria may be immobilized upon or within any of a variety of commonly known particulate support media, by any of the methods known for immobilizing bacterial cells.

With such means the aggregated bacteria may be simply retained either within the fermentation vessel proper or within a separation vessel communicating therewith, either because of the size of the particles, or of their density, or of their magnetic properties, or of a combination of such factors. Such bacteria may then be used in several kinds of process design which have been devised to take particular advantage of the settling characteristics of strongly flocculent yeasts, or alternatively in packed bed or fluidised bed reactors such as have been described for the utilisation of immobilised yeast cells on inert support particles. In these cases the advantages of unit productivity which such systems make possible may be combined with the high specific productivities per unit cell mass that are characteristic of anaerobic bacteria such as Zymomonas mobilis, with consequent very high overall productivity per unit reactor volume.

Claims

1. A process for the continuous production of fermentation alcohol, comprising the steps of effecting fermentation of a continuous supply of a liquid substrate by anaerobic bacteria of a kind capable of producing ethyl alcohol, and causing agglomeration of the bacterial cells to render them capable of being separated from the fermentation liquor and thus retained within the process or returned thereto after separation from liquor discharged from the process.

2. A process according to Claim 1 , wherein the agglomeration of the bacterial cells is caused by the addition to the fermentation liquor of a flocculating agent.

3. A process according to Claim 1, wherein the agglomeration of bacterial cells is caused by the addition to the fermentation liquor of an organic acid.

4. A process according to Claim 1, wherein the agglomeration of the bacterial cells is caused by the addition to the fermentation liquor of an inert particulate support medium.

5. A process according to Claim 1 , wherein the agglomeration of the bacterial cells is caused by the addition to the fermentation liquor of a magnetic support medium.

6. A process according to any one of the preceding claims, wherein as the anaerobic bacteria, there is used a species of the genus Zymomonas.

7. A process according to Claim 6, wherein said species is Zymomonas Mobilis.