GB2029432A

GB2029432A - Improvements in Starch Conversion

Info

Publication number: GB2029432A
Application number: GB7831287A
Authority: GB
Original assignee: APV Corp Ltd
Current assignee: SPX Flow Technology Crawley Ltd
Priority date: 1978-07-27
Filing date: 1978-07-27
Publication date: 1980-03-19
Also published as: MY8400372A; BR7904813A; GB2029432B; DE2930614A1; AU4958579A; ZA793859B

Abstract

The continuous liquefaction of starch such as from Cassava, using an enzyme is carried out in a reaction column in which a starch slurry dosed with enzyme and heated to gelatinization temperature, is fed in at the bottom. The column has zones for holding for gelatinization, cooling to dextrinization temperature and long term holding for dextrinization. The liquefied starch is drawn off at the top of the column.

Description

SPECIFICATION Improvements in Starch Conversion This invention relates to starch conversion.

There is currently much commercial interest in the conversion of starch sources, such as Cassava, to sugar for subsequent fermentation to alcohol, particularly as a petroleum substitute.

The first stage in the conversion is liquefaction and it is to this step that the present invention is directed, in particular in connection with the use of high-temperature-resistant bacterial enzymes.

Conventionally, the starch is heated by steam injection as a slurry, e.g. of 30% total solids, with an appropriate dosage of an enzyme such as a bacterial amylase. After heating, the slurry is held at 1000 to 1 050C for 2 to 5 minutes, cooled to about 90"C and held at this temperature for up to 2 hours for dextrinization.

The usual method is to carry out the operations separately, using a steam injection and hold section under pressure, a flash coo!ing system, and a stirred holding vessel.

Such an arrangement of plant is not truly satisfactory for a continuous process on a large scale and is unduly expensive in cases where high quality sugar is not the final aim and very accurately controlled conversion is therefore not necessary. According to a first aspect of the invention, there is provided apparatus for the liquefaction of starch comprising a rising column reaction tube, means for feeding a starch slurry continuously to the lower end of the tube, means for dosing the slurry with enzyme, and steam injection means for heating the slurry to gelatinization temperature, the column including a holding stage for gelatinization at the bottom of the column, succeeded by a cooling stage equipped with means for cooling the slurry in the stage to dextrinization temperature, and the column also having, above the cooling stage, a holding zone through which the cooled feedstock rises quiescently for dextrinization over its residence time.

According to a second aspect of the invention, there is provided a method for the continuous liquefaction of starch comprising the steps of dosing a starch slurry with an enzyme, heating the slurry to gelatinization temperature and passing the heated slurrey continuously into a rising reaction column where it is successively held for gelatinization, cooled to dextrinization temperature and held for dextrinization while rising quiescently through the column.

The invention will be further described with reference to the accompanying diagrammatic drawing, in which: Figure 1 is a flow diagram of a preferred method of liquefaction according to the invention; and Figure 2 is a diagrammatic sectional view showing flow straightening in a reaction column.

Turning first to Figure 1, there is shown a slurrying tank 1 shown to be equipped with an agitator 2, and in this is formed a slurry of, for example 30% total solids, of a starch from a source such as Cassava, in water with or without the correct enzyme dosage. This slurry is fed by a pump 3 along a line 4 and in passage along that line it passes an alternative enzyme dosing point 5 at which an enzyme, such as a bacterial amylase, may be added in an appropriate dosage.

The slurry then passes along the line where steam is injected into it to raise it from a temperature of, for example, 200C, to the gelatinization temperature of about 1 050C. This is achieved by steam injection at a steam injection point 6. The slurry at this gelatinization temperature is fed into the bottom of a single reaction column 7 in which is rises without substantial back mixing. In the lower portion of the column indicated by reference numeral 8, there is a gelatinization zone in which the slurry is held at substantially its gelatinization temperature for a residence time of, for instance 2 to 5 minutes.After the gelatinization stage, the slurry moves into a cooling zone 9 of the column which is provided with cooling devices for reducing the temperature of the slurry from about 1 05 OC to about 900C, which is the dextrinization temperature. When cooled to this temperature, the slurry enters the uppermost and longest portion of the column, namely a dextrinization holding stage 10 in which it has a residence time of up to 2 hours to enable adequate dextrinization to about 8 to 1 2DE (Dextrose Equivalent) during its long residence time. Dextrose equivalent is a measure of the reducing sugar content calculated as dextrose and expressed as percentage of the total dry solids, That is, 8 DE means that the product contains 8% sugar in the dry solids expressed as dextrose and is a measure of the extent of conversion of starch to sugar.

At approximately the inlet to the dextrinization holding stage, there is provided a second enzyme dosage point 11 as it is known to be beneficial in some circumstances to apply the toatal enzyme dose in two stages, one before, one after gelatinization. The dextrinated starch is drawn off at the top of the column and is suitable at that stage for cooling directly to a saccharification temperature or further to a fermentation temperature if desired, without danger of retrogradation to starch.

The column 7 should be of sufficient height that it prevents boiling of the slurry at the genatinization temperature and for example it can be 7 metres high and 2 metres in diameter. Such a size should enable a sufficient residence time at the enzyme operating temperature of between 80 and 950C for dextrinization.

With a column of this size, it may be necessary to provide flow straightening devices, e.g. in the form of partitioning baffles 12 as shown in Figure 2 to recuce turbulence and avoid excess back mixing of the slurry as it rises within the column.

A small amount of mixing would not be objectionable as the object of the process is to get sufficient dextrinization to enable saccharification to begin and not to obtain sugars of a high quality which would necessitate stricter control of the liquefaction.

Where such partitioning baffles or flow straighteners are provided within the column, they may be used to house the cooling device within the cooling stage 9. For this, the baffle system would comprise a series of radially spaced baffles each consisting of two metal sheets sealed on all edges but spaced apart sufficiently to provide a flow channel for cooling fluid.

Various modifications may be made within the scope of the invention.

Claims

1. Apparatus for the liquefaction of starch comprising a rising column reaction tube, means for feeding a starch slurry continuously to the lower end of the tube, means for dosing the slurry with enzyme, and steam injection means for heating the slurry to gelatinization temperature,.

the column including a holding stage for gelatinization at the bottom of the column, succeeded by a cooling stage equipped with means for cooling the slurry in that stage to dextrinization temperature, and the column also having, above the cooling stage, a holding zone through which the cooled feed stock rises quiescently for dextrinization over its residence time.

2. Apparatus as claimed in claim 1, in which at least the holding zone is equipped with flow straighteners to reduce turbulence.

3. Apparatus as claimed in claim 2, in which the cooling zone is also equipped with flow straighteners and these flow straighteners are provided with the cooling means.

4. Apparatus as claimed in any of claims 1 to 3 in which means is provided for a second dosing with enzyme after cooling the feed stock.

5. A method for the continuous liquefaction of starch comprising the steps of dosing a starch slurry with an enzyme, heating the slurry to gelatinization temperature and passing the heated slurry continuously into a rising reaction column where it is successively held for gelatinization, cooled to dextrinization temperature, and held for dextrinization while rising quiescently through the column.

6. A method as claimed in claim 5, wherein a second dosage of enzyme is applied after cooling.

7. A method as claimed in claim 5 or 6, in which the slurry is heated by steam injection.

8. A method as claimed in claim 5, 6 or 7, in which the column contains flow straighteners to.

reduce turbulence and avoid excessive back mixing during the holding stage.

9. A method as claimed in any of claims 5 to 8, in which the enzyme is a bacterial amylase.