GB2122589A - Regeneration of spent adsorbents - Google Patents

Abstract

Adsorption agents used to refine fats and glyceride oils by adsorption of polar impurities are regenerated by contact with a heterogeneous azeotrope mixture of methanol and hydrocarbon for removing the adsorbed material. Preferably the mixture comprises hexane and methanol.

Description

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

The removal of impurities from fats and glyceride oils by adsorption on 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 and bleaching earth is discarded after use and no attempt is made to regenerate it. More recently however adsorption methods have been developed in which the fat or oil is diluted in non-polar solvent and the solution contacted with adsorbent alumina or silica-containing material, 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 reactivated. This process entails the removal of strongly adsorbed material from the absorbent and this 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, usually by a non-polar solvent, to reactivate the adsorbent. The present invention proposes the use of a heterogeneous azeotrope for removing adsorbed material from the adsorbent.

Hexane and methanol form an azeotrope at 27% volume/volume methanol which separates into two layers. The upper layer contains 85% hexane and 15% methanol and has a specific gravity of 0.675. The lower layer contains 42% hexane and 58% methanol and has a specific gravity of 0.724. The invention extends to immiscible mixtures of methanol with hydrocarbons generally, preferably having a boiling range between 40 and 120"C. The immiscible mixture is thoroughly mixed to ensure uniform concentration of the dispersed methanol in the hydrocarbon, immediately before percolation through the adsorption column.

Alternatively, the methanol rich layer is circulated first from store followed by hexane rich layer in proportions present in azeotrope. Alternatively the adsorbent may be removed from the column and agitated with the immiscible mixture.

The process is most efficient when operated using the azetrope proportions, but it can be operated away from this proportion, for example using equal volume proportions. Higher proportions of methanol, for example up to 50% by weight, can be used provided there is sufficient hydrocarbon present to prevent clogging.

The adsorbed material remains inactive even after removing the adsorbed impurities in accordance with the invention and may be regenerated to remove the alcohol adsorbed on the active sites of the adsorbent, by treatment with a hydrocarbon, for example in accordance with our co-pending Application HLL 113 using superheated hydrocarbon vapour.

The process of the invention is applicable to the reactivation of absorbents generally used in refining fats and glyceride oils in processes, for example, as described in British Patent Specifications 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. The process is applicable to naturally occurring and reacted clays and refractory materials. These are preferably used in columns in the form of particles which are smail 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-precipitates silica-aluminas which may be used.

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

Example 1 Sal fat, bleached and degummed but still retaining coloured material, in addition to 17% free fatty acid and 14% impurities, was dissolved in hexane to provide a 20% miscella percolated through a column containing Sarex adsorbent in a bed 50 cms high. The Sarexwas previously dried at 1200C but not sieve-graded and the ratio Sarex:sal was 0.8:1 by weight.

After recovery from the raffinate, the refined sal fat was analysed and showed only 3% impurities with 14% free fatty acid. The Sarex bed was then rinsed with hexane, followed by a hexane-methanol mixture. The runnings from the column were collected until colour-free. The volume collected was then measured and taken as the amount required for regeneration. Further particulares are given in Table I.

TABLE I Experiment 1 2 Sal used (gm) 225 3000 Sal in treated miscella (gm) 109 Sal in hexane rinse (gm) 92 2600 Sarex (gm) 120 2400 Methanol in azeotrope (%) 50 25 Eluentused (ml) 600 22000 MeOH required to remove colour ml/g Sarex 2.5 2.3 Eluent required vol/vol of Sarex 1.10 2.02 The data given in Table I clearly show a low volume ratio of eluent is required where an immiscibie mixture of a higher proportion of methanol and hexane is used in accordance with the invention.

Both samples were satisfactory and the silica-alumina precipitate was subsequently reactivated.

Example 2 The sequence of addition of the heterogeneous azeotrope during the elution of adsorbed impurities was studied in detail. Methanol and hexane are known to form azeotrope separating into two layers. Lower layer and upper layers will have 58% and 15% methanol respectively. However when technical grade solvents were used the compositions were different due to the presence of moisture. The methanol content of bottom and top layers were found to be 60% and 4% respectively.

The regeneration of adsorbed bed was tested with methanol hexane containing overall 15% methanol. In the pilot plant for the regeneration of 100 kg of adsorbent bed filled in a 100 cm diameter column 1400 litres of eluent was prepared. This contained 210 litres of methanol and 1190 litres of hexane. When mixed thoroughly and allowed to settle for 1 hour, 2 layers were formed. Bottom layer was 275 litres containing 60% methanol and top layer was 1125 litres containing 4% methanol.

The sequence and made of addition to the column were varied to get the best results.

i. Passing the solution from a tank where this was kept well agitated to get uniform dispersion.

ii. Pumping the top layer followed by bottom layer through the column.

iii. Pumping the bottom layer followed by top layer through the column.

The first option needed additional mixing during the entire elution cycle. The second option needed two separate tanks for layers so that the top layer could be pumped first. The third option was the easiest since pumping from the tank bottom outlet automatically gave the sequence required. The details are given in Table II.

TABLE II Adsorbent 100 kgs Bed diameter 100 cm Bed height 50 cm Volume of eluent 1400 litres Top layer 1125 litres of 4% methanol Bottom layer 275 litres of 60 % methanol Extent of regeneration Passing a mixture of top and bottom layers Incomplete ii. Passingtop layerfollowed by bottom layer Incomplete iii. Passing bottom layer followed by top layer Complete Data clearly indicates that the practically easiest option of bottom layer followed by top layer elution gives the best results in terms of impurities desorption. <

Claims (9)

1. Process for the regeneration of spent adsorbent material used for refining fatty material, comprising contacting the adsorbent with a heterogeneous azeotrope mixture of methanol and hydrocarbon and removing the azeotrope from the adsorbent.

2. Process according to Claim 1 in which the boiling range of the azeotrope is 40 to 120"C.

3. Process according to Claim 2 in which the azeotrope contains substantially equal proportions of methanol and hydrocarbon.

4. Process according to any of the preceding claims in which the azeotrope is removed by contact with hydrocarbon vapour.

5. Process according to Claim 4 in which the hydrocarbon vapour is superheated.

6. Process according to any of the preceding claims in which the adsorbent comprises refractory or clay material.

7. Process according to any of the preceding claims wherein the fatty material comprises a vegetable butter.

8. Process according to Claim 7 wherein the vegetable butter comprises sal fat.

9. Process for refining fatty material, including oils and fats, by contact with a solution of the fatty material with an adsorbent and recovering refined fatty material from the solution, wherein spent adsorbent is regenerated for re-use by a process as claimed in any of the preceding claims.