WO1993025585A1

WO1993025585A1 - Process for purification of starch

Info

Publication number: WO1993025585A1
Application number: PCT/US1993/005339
Authority: WO
Inventors: Georg Osthaus
Original assignee: Dorr-Oliver Incorporated
Priority date: 1992-06-05
Filing date: 1993-06-04
Publication date: 1993-12-23
Also published as: CN1085966A; DE4218667A1

Abstract

The invention relates to a process for precipitating starch from a starch milk from which uniform fibers are formed. The reaction of the starch gel takes place in the shear area of a rotor-stator stage (6) of a short post-reaction. In an additional preliminary rotor-stator stage the starch milk can be transformed at low temperature to starch gel. In a filter plant (21) the thus produced uniform fibers can be simply and thoroughly scrubbed, dehydrated and withdrawn in dry condition.

Description

PROCESS FOR PURIFICATION OF STARCH

The invention relates to a process for precipitating starch from a starch milk from which - after a boiling step, a reaction step with the addition of a salt solution, and a post-reaction step with the addition of a salt solution the resulting fibers are withdrawn via a filtering step.

In such a process dissolved starch is precipitated with certain salts in fiber form; as salts ammonium sulfate aluminum sulfate, or magnesium sulfate are employed. In thiε process the starch milk is boiled with about 20% dry substance in a jet boiler at about 140^s C. Thereafter the starch gel must be relieved in a large relief tank at about 95^aC.

Starch gel and/or starch solution, and a solution formed from the salts, are separately passed to a jet reactor into which the agglutinated starch is sprayed through a multitude of nozzles into the salt solution. These reactors have the disadvantage that the resulting fibers vary in a wide range, e.g. between 25 and 600 my/m.

In a following reactor the precipitate forms which must then be subjected to a post-reaction in which it must ripen for a time up to two hours.

This dimensioning feature complicates the further treatment of the fibers. The treatment is further complicated by the fact that about 50% of the fibers are smaller than 75 my/m. After the ripening period the fibers are washed in a filter step and dehydrated.

Known systems operate with a capacity of about 75 kg/h of fibers. Although the output is very low it requires the installation of large filtering capacities. To this end vacuum belt filters, disk filters, drum filters or drum pressure filters are employed.

The invention deals with the problem of increasing the capacity of the known plants with a lower investment volume and, at the same time, to reduce the power input and to improve the environmental stress.

This problem is solved in that the boiled starch, with simultaneous addition of the salt solution is passed axially with respect to the shear area to a rotor-stator stage in which the components are comminuted into minutest quantita¬ tive units, and under the action of high shearing forces and high frequency alternating stress are intensely mixed and treated, and the starch treated in the shear area is passed to the post-reaction step.

With this mode of operation it is possible that the precipitation of the boiled starch within a shear area results in fibers having a narrower distribution, 80 % being within a range of 75 to 500 my/m. Furthermore it has been found that with the use of different tools known per se fibers of different length can be produced.

Within the shear area immediate precipitation occurs. The fibers are more uniform than those obtained with hitherto known processes. The treatment in a shear area had the effect that the post-reaction could be reduced from hitherto 2 hours to 15 minutes, which cuts down investment costs. Also the amount of solution required for the reaction is substantially less, so that less waste water is produced and thus the evironmental stress is reduced.

The precipitation within a shear area permits higher fiber concentration and improved fiber structure. On account of these fibers the filter performance can be increased from hitherto 75 kg/h to 400 kg/h.

This permits less investment for the filtration equipment; moreover, instead of the vakuum belt filters a disk filter, a drum filter, a drum pressure belt filter or paring centrifuges can be employed.

The investment costs can be further reduced by using, instead of the hitherto known jet boiler having a boiling temperature of 140°C an additional rotor-stator stage. In this case steam is added to the starch milk, and this mixture is also passed axially to the shear area of a rotor- stator stage, in which the components are comminuted into minutest quantitative units and under high shearing action and high frequency alternating stress are intensely boiled, and the starch gel prepared in the shear area is passed to the reaction rotor-stator stage.

Owing to these treatment the starch milk can be boiled at temperatures below 100°C - preferably at 95°C - so that a pressure relief is not necessary and thus the large relief tanks may be forgone. This further cuts down investment costs. The special advantage of this process step may be seen in the fact that the starch is completely dissolved, which is not εo in the known processes.

An example of the invention is illustrated in a drawing and will be explained in more detail hereafter:

In a storage tank 1 equipped with a stirrer 2 through a conduit 3 starch milk is kept in store, which through a conduit 4 and a pump 5 is passed to a first rotor-stator machine 6. At the same time steam is filled in through a conduit 8. The machine 6 driven by a motor 7 may be a rotor- stator machine, for example, as is shown in the EP-OS 87 10 85 684.

The starch dissolved and boiled in the shear area of the machine 6 is passed through a conduit 9 to a second rotor- stator machine 10, into which - by means of a pump 12 - through a conduit 11 a salt solution is added. The starch precipitation formed in the shear area is added through a conduit 13 to a storage tank 14, in which a brief post- reaction occurs.

By means of a pump 15 and a conduit 16 the material is passed to a belt filter 21, and the material, after withdrawal of the processing liquid in a scrubbing zone 19 with scrubbing water 20, is scrubbed and thereafter dehydrated in a dehydrating zone 18. The waste water is removed through a conduit 22.

The treated fibers are removed from the filter 17 at 23 and are passed on via a means 24.

Claims

1. A process for precipitating starch from a starch milk from which, after a boiling step, a reaction step with addition of a salt solution, and a post-reaction step the resulting fibers are withdrawn via a filter stage; characterized in that the boiled starch, with simultaneous addition of the salt solution axially with respect to the shear area is passed to a rotor-stator stage in which the components are com¬ minuted into minutest quantitative units and under the action of high shearing force and high frequency alter¬ nating stress intensely mixed and treated and the starch treated in the shear area is passed to the post-reaction step.

2. Process according to claim 1, characterized in that steam is added to the starch milk and this mixture is axially passed to the shear area of the rotor-stator stage, in which the components are comminuted into minutest quan¬ titative units and intensely boiled under the influence of high shearing force under high frequency alternating stress.

3. Process according to claim 2, characterized in that the starch milk is treated at temperatures below 100°C in the shear area.

4. Process according to claim 1 to 3, characterized in that the post-reacted product is scrubbed in the filter step and dehydrated.