GB2122588A

GB2122588A - Regenerating spent adsorbents

Info

Publication number: GB2122588A
Application number: GB08224252A
Authority: GB
Inventors: Krishnamoorthi Chandrasekaran; Naganathan Viswanath Bringi; Shrinath Sheshgiri Kalbag
Original assignee: Unilever PLC
Current assignee: Unilever PLC
Priority date: 1982-06-26
Filing date: 1982-08-24
Publication date: 1984-01-18
Also published as: IN156362B

Abstract

Spent adsorption agents used for example in columns to refine glyceride oils and fats, are successively contacted with (1) an organic polar compound e.g. an alcohol such as isopropanol or a ketone to displace adsorbed impurities and (2) a superheated vapour of a hydrocarbon such as hexane, to reactivate the adsorbent by removing the adsorbed polar compound. The polar compound may be used in admixture with a hydrocarbon forming an immiscible azeotrope to facilitate solvent recovery. Silica and/or alumina or other adsorption agents may be repeatedly regenerated in accordance with the invention to refine fats such as palm, shea, sal and cottonseed oil.

Description

SPECIFICATION Refining of fats This invention relates to refining fatty material by adsorption. More particularly the invention relates to the regeneration of adsorbents which are used to remove impurities from fatty materials especially fats and glyceride oils.

The removal of impurities from fatty materials especially fats and glyceride oils by adsorption in inorganic bleaching materials such as Fullers Earth has long been practised, both to improve the colour of fats and oils and to remove odoriferous matter.

With such methods the bleaching earth is discarded after use and no attempt is made to generate it. More recently however adsorption methods have been developed in which the fat or oil is diluted in an organic solvent and the solution contacted with an adsorbent eg refractory oxide containing eg alumina or silica, usually packed in the form of sizeable particles in a column down which the solution is percolated.

With use the adsorbent loses its effectiveness and for reasons of economy is re-activated. This process entails the removal of stongly adsorbed material from the adsorbent and this desorption may be effected by elution of the adsorbent with a suitable alcohol or other strongly adsorbed polar organic liquid which displaces the impurities adsorbed on the adsorbent and washes them free. The adsorbed liquid must then be removed to reactivate the adsorbent, using a non-polar organic displacing agent. The present invention proposes for this purpose the use of superheated vapour of a nonpolar organic displacing agent.

According to the present invention therefore a process for regenerating spent adsorbent material used in refining glycerides comprises successively contacting the spent material first with an organic polar solvent, particularly an alcohol or a ketone to remove adsorbed impurities and a superheated hydrocarbon vapour to inactivate the adsorbent.

Preferably the reactivation stage is carried out at a su perheated temperature between 80 and 1 800C, particularly in the region of 1200C. Higher temperatures provide more efficient removal of the polar compounds but lower temperatures may be necessary for economic reasons. A superheat of from 20 to 50"C is preferred. A particular advantage of the process according to the invention is that the adsorbent used in percolation columns for refining fats and glyceride oils may be regenerated in situ.

The temperature of the superheated vapour is preferably at least 20"C above the boiling point of the alcohol or other polar substance used in the preceding desorption stage. In general, a superheattemperature from 10 to 500C above the boiling point of the polar solvent is preferred.

Afurtheradvantage of the invention is that super-heated vapour may be used at substantially atmospheric pressures and equipment is not required therefore to withstand high pressure.

Moreover, the vapour may be recycled directly from solvent recovery, achieving better heat economy.

Preferably desorption of adsorbed impurities is effected using an alcohol and more particularly, a mixture of alcohol and hydrocarbon solvent, isopropanol particularly in a mixture with hydrocarbon being particularly suitable, more especially an azeotrope of hexane and isopropanol to facilitate solvent recovery. Methanol may also be used, especially as described in our co-pending Application HLL 115, in an immiscible azeotrope with a hydrocarbon. This is conveniently the same hydrocarbon as used in the reactivation stage according to the invention. Generally, saturated aliphatic alcohols containing up to 6 carbon atoms are preferred, particularly in admixture from 20% to 80% by weight of non-polar solvent.The latter should preferably having a boiling point from 30 to 120"C, particularly paraffin hydrocarbons containing from 3 to 10 carbon atoms. It is convenient to use the same hydrocarbon or nonpolar solvent in both stages.

The process of the invention is applicable to the reactivation of adsorbents generally used in refining fats and glyceride oils in processes for example as described in British Patent Specification 865,807 and 1,476,307. Silica in the form of silica gels are suitable and mixtures of silica and alumina may also be used, as well as mixtures of silica or alumina with other adsorbents. These are preferably used in columns in the form of particles which are small enough to provide adequate column hold-up without being so small as to generate excessively low percolation rates. Suitable examples include aluminas such as Gibbsite and silicas such as silica gels marketed under the trade names Sorbsil and Kieselgel M.

Reference may also be made to our co-pending Application A.193 for specially co-precipitated silicaaluminas which may be used.

The invention may be applied to the regeneration of adsorbents used for refining a variety of glyceride oils and fats, including in particuiar edible oils and fats, eg soyabean, sunflower and palm oil and among vegetable butters, sal fat, shea oil and mango kernel oil, as wetl as semi-solid vegetable oils such as palm oil and cottonseed oil and lauricfats, eg coconut oil, palm kernel oil and babassu oil.

Example 250g of silica-alumina particles with an average particle size of -100 to +200 BSS mesh, were activated by heating for 3 hours at 120"C and packed in a vertical column 5 cms in diameter, giving a packing height of 50 cms. The bulk density of the packing was 0.26 gm/cm3.

The column was used to refine sal fat previously deodorised, neutralised and bleached and dissolved in hexane in a ratio 1:4 wt/volume. 1.25 litres of this miscella was percolated down the column at 30"C at a rate of 1176 mls/hr. The fat was recovered by evaporating a solvent from the raffinate and compared after 5 regeneration cycles as described below, with the feedstock.

Upon completion of the sal fat treatment the column was washed down with 1 litre of hexane and then percolated with 2 litres of a 25% isopropanol:hexane aceotrope mixture. 2 litres of hexane were then evaporated and the vapour heated further to 120"C before being passed through the column at a rate providing a velocity through the column of 2.5 to 3 cms/minute calcuiated as liquid. Fresh feedstock was then introduced into the column and the cycle repeated.

After 5 reactivation cycles the fat recovered from the raffinate still showed excellent characteristics compared with the feedstock, with a dilation at 30"C of 1430. Feedstock fat containing epoxy acid (1.5%) hydroxy glycerides (2.0%) and diglycerides (6.3%) gave a product fat free of these impurities.

Claims

1. Process for regenerating spent adsorbent used for refining fatty materials, comprising contacting the spent adsorbent first with a polar organic solvent to remove adsorbed impurities and then with a superheated vapour of a non-polar organic displacing agent to remove the solvent adsorbed and reactivate the adsorbent.

2. Process according to Claim 1, wherein the adsorbent is contacted with the vapour at 80 to 180"C.

3. Process according to Claim 2, wherein the adsorbent is contacted with the vapour in the region of 120 C.

4. Process according to any of the preceding claims, wherein a superheat temperature differential of 20 to 50"C is applied.

5. Process according to any of the preceding claims, in which the temperature of the vapour is from 10 to 50"C above the boiling point of the polar solvent.

6. Process according to any of the preceding claims, in which the adsorbent is contacted with the vapour at substantially atmospheric pressure.

7. Process according to any of the preceding claims including a solvent recovery stage from which the vapour is directly recycled.

8. Process according to any of the preceding claims in which the agent comprises a hydrocarbon.

9. Process according to Claim 8 in which the boiling point of the hydrocarbon is from 30 to 120 C.

10. Process according to Claim 9 in which the hydrocarbon comprises hexane.

11. Process according to any of the preceding claims in which the solvent is used in a mixture with a non-polar solvent.

12. Process according to Claim 11 in which the same hydrocarbon is used in both desorption and reactivation.

13. Process according to Claim 11 or 12 in which an azeotrope comprising isopropanol is used as solvent.

14. Process according to Claim 11 in which an immiscible azeotrope is used as solvent.

15. Process according to any of the preceding claims in which the adsorbent comprises a refractory oxide or prepared or treated clay containing silica or alumina.

16. Process for refining fatty materials, including glyceride oils and fats, by contact with a solution of the fatty material with an adsorbent, and recovery of the refined fatty material from the solution, wherein spent adsorbent is periodically regenerated by a process as claimed in any of the preceding claims.