EP0573446A1

EP0573446A1 - Adsorbent material

Info

Publication number: EP0573446A1
Application number: EP92903933A
Authority: EP
Inventors: Roger Skelton 26 Bembridge Close Taylor; Mary Elizabeth 41 St. Bridgets Close Davies; Philip James Turner
Original assignee: Laporte Industries Ltd
Current assignee: Evonik LIL Ltd
Priority date: 1991-02-27
Filing date: 1992-02-11
Publication date: 1993-12-15
Also published as: ZA921407B; JPH06504946A; WO1992015396A1; BR9205682A; TR25894A; GB9104056D0

Abstract

Matériau adsorbant approprié destiné à éliminer les composés phosphoreux et autres contaminants présents dans des huiles, comprenant un minéral des argiles réfractaires en couches traité à l'acide, présentant une surface spécifique d'au moins 250 m2/g, une teneur en silicium, calculée en tant que SiO2, de 80 % à 99 %, une teneur en alminium lié, calculée en tant que Al2O3, de 0,1 % à moins de 3,0 %, toutes deux en poids sec, et ayant de préférence une acidité Hedley de 0,1 % à 5,0 %. On peut produire ledit matériau adsorbant en traitant une argile appropriée en couches, par exemple une kaolinite, une actapulgite, une sépiolite ou une smectite, avec un acide fort dans des conditions contrôlées suivies par un lavage à un degré contrôlé.Suitable adsorbent material for removing phosphorous compounds and other contaminants from oils, comprising acid-treated layered refractory clay mineral, having a specific surface area of at least 250 m2 / g, a calculated silicon content as SiO2, from 80% to 99%, a bound alminium content, calculated as Al2O3, from 0.1% to less than 3.0%, both by dry weight, and preferably having Hedley acidity from 0.1% to 5.0%. Said adsorbent material can be produced by treating a suitable clay in layers, for example kaolinite, actapulgite, sepiolite or smectite, with a strong acid under controlled conditions followed by washing to a controlled degree.

Description

Adsorbent Material

This invention relates to an adsorbent material comprising an acid-treated clay mineral, to a process for the production of the same and to the purification of oils using the same.

Oils of animal or vegetable origin are produced in large quantities for use in the food industry. These oils, for example the triglyceride oils of vegetable origin such as sunflower seed oil, soya oil, rapeseed oil, coconut oil, palm oil and groundnut oil contain, as extracted, a variety of constituents which affect the colour, stability, taste or smell of the oil, and which require to be removed before the oil is saleable as an acceptable product.

One major type of contaminant of triglyceride oils are phosphorous compounds of widely varying compositions. Some of these compounds are complex esters of phosphoric acid, glycerides and a nitrogenous base. These esters may vary in composition depending on the identity of their constituent glycerides, which may be di-or tri-glycerides based on any of a wide variety of the naturally occurring fatty acids, and of the constituent base which may be, for example, choline, ethanolamine or inositol. Such compounds are often referred to as phospholipids. Other phosphorous compounds, sometimes referred to as phosphatides, may contain no nitrogenous base but may otherwise be of somewhat similar composition. The contaminating phosphorus compounds may also include simple glycerophosphoric acids, inorganic phosphates and products of phosphatide or phospholipid hydrolysis.

Other contaminants of as extracted or partially treated oils include trace metals, soaps and pigments such as the carotenoids and chlorophylls which are naturally present to characteristic levels in particular oils.

There have been a number of patented proposals for the purification of oils by the adsorption of phosphorus compounds from the oils onto icroporous solid materials such as precipitated amorphous silicas. The use of the term adsorption or adsorbent herein is merely as an indication of ability to remove some or any of the aforesaid phosphorus compounds or other contaminants from the oil and is not intended to imply that the compounds or contaminants removed are at any particular sites on or in the adsorbing solid. Suitable amorphous silicas are, for example, those produced by destabilisation of aqueous silicate solutions by acid neutralisation. Examples of such proposals are found in European Patent Specification No. 247411, in which the precipitated amorphous silica has at least 50% of its pore volume in pores having diameters greater than 60 Angstroms, in European Patent Specification No. 295418 in which the precipitated amorphous silica has supported on it an acid having a pKa of about 3.5 or lower, such as sulphuric acid, and in European Patent Specification No. 361622 in which the precipitated amorphous silica has a surface area of at least 400 m2/g in pores with a diameter of at least 2 nm.

There have also been proposals to purify oils by adsorption of phosphorus compounds from the oils onto precipitated metal oxide silica adsorbents. One such proposal is found in European Patent Specification No. 269173 in which the precipitated metal oxide silica adsorbent has at least 40% of its surface area in pores with a radius of at least 2 nm. The metal oxide silica adsorbent is prepared either by coprecipitation or by stepwise precipitation of the metal ions, e.g. aluminate ions, and silicate ions followed by prolonged ageing, washing, drying and calcination. A further similar proposal is found in European Patent Specification No. 376406 in which the adsorbent is a precipitated alumina silica having a surface area of at least 150 m^ g and a pore volume of at least 0.6 ml/g in pores having a diameter of from 4 to 20 nm.

It has long been the practice to treat oils with various clay mineral products referred to as bleaching earths. Such products may be, for example, naturally occurring clay minerals which have been treated with a strong acid to increase their surface area and porosity, for example to from 50 to 500 m^ g or more, and washed to remove residual acid and acidic salts formed by the reaction of the acid with aluminium and/or other metallic constituents of the clay mineral so as to form a product containing up to about 70% of silicon calculated as Siθ2, a substantial quantity, for example more than about 10%, of aluminium calculated as AI2O3 and at least some crystallinity. Such acid treated clays have been found to have a fairly substantial capacity for the removal of hosphorus comounds such as phospholipids from oils.

The present invention provides a new class of adsorbent materials, derived from acid-treated clays, which can show greatly enhanced activity in the removal of phosphorus compounds from oils, together with efficacy in the removal of other impurities. These new adsorbent materials comprise clays which have been acid treated under particularly severe but controlled conditions. The present invention therefore provides a process for the production of an adsorbent material suitable for use for the purification of oils comprising treating a layered clay mineral with a suitable strong acid to achieve a surface area of at least 250 m^ g and washing the acid treated clay mineral product to remove residual acid and acidic salts therefrom, the process being characterised in that the acid treatment is controlled to achieve a silicon content of from 80% to 99% by dry weight calculated as Siθ2 and a bound, i.e. non-water leachable, aluminium content, calculated as AI2O3 of from 0.1% to below 3.0% in the washed acid-treated clay mineral product.

The invention also provides the use for the treatment of oils and particularly for the removal.of phosphorus compounds therefrom, of an adsorbent material comprising an acid-treated layered clay mineral having a surface area of at least 250 m²/g, a silicon content, calculated as Siθ2, of from 80% to 99% by dry weight and a bound aluminium content, calculated as AI2O3, of from 0.1% to below 3.0% by weight.

The invention further provides, as a composition of matter, an adsorbent material comprising an acid-treated layered clay mineral having a surface area of at least 250 ι2/g, a silicon content, calculated as Siθ2 of from 80% to

99% by dry weight and a bound aluminium content, calculated as AI2O3, of from 0.1% to below 3.0% by dry weight.

The acid treated layered clay mineral products of the present invention possess unusual characteristics not found, for example, in a precipitated silica adsorbent. Whereas the highest possible surface area is generally regarded as being beneficial their optimum performance does not occur at the highest surface area but at an intermediate surface area. Similarly, their optimum performance does not occur at the highest silicalaluminiuma ratio. It is also noted that the optimum performance attainable by the products of this invention can exceed that attained by commercial precipitated silica adsorbents in respect of oil purification despite a possibly lower surface area and a lower content of silica. The mechanistic reasons for these differences are not known but could relate to structural features resulting from severe acid treatment of layered clay minerals.

The layered clay minerals utilised according to this invention may be two layer minerals, for example kaolins, such as the halloysite-endellite minerals, ribboned clay minerals containing a layered structure such as attapulgite or sepiolite or, preferably, three layer sheet structure clay minerals such as the smectite clays. While natural clay minerals are primarily envisaged analogous synthetic materials are not excluded.

Smectite clay minerals may be defined as a group of phyllosilicates of the 2:1 layer type having the general formulae:

(M*⁺ _x+y nH₂0)(R3+₂_y R²⁺ _y) (Si₄__xAl_x)O₁₀(OH)₂ m (dioctahedral)

(Mm+_χ+y nH₂0)(R²⁺ ₃__y Li+_y)(Si4__xAl_x)0₁₀(OH) m (trioctahedral)

(M ⁺χ-y nH₂0)(R2+₃_y R3+_y)(Si₄__xAl_x)O₁₀(OH)2 m (trioctahedral)

where M^m+ represents exchangeable cations such as Ca⁺⁺, Mg⁺⁺, having a valency m, necessary to satisfy the negatively charged lattice, R²⁺ represents magnesium or iron and R3⁺ represents aluminium or iron. The smectite group of minerals includes the mineral sub-groups montmorillonite, beidellite, nontronite, saponite, hectorite and sauconite. Minerals belonging to the mont orillonite (dioctahedral) , or the saponite or hectorite (trioctahedral) groups are particularly preferred for use according to the present invention. Fullers earth, commonly used for oil bleaching, is a montmorillonite containing predominantly Ca⁺⁺ and Mg⁺⁺ exchangeable cations which may provide a suitable raw material for the present invention.

The acid-treatment has a fundamental effect on the structure of layered clay minerals as well as causing the partial or complete replacement of calcium or magnesium cations by hydrogen cations. The smectite minerals, for example, have a layered structure composed of octahedral alumina sheets bonded via shared -0- bonds to adjacent tetrahedral silica sheets to form clay platelets, the crystallographic repeat distance or basal spacing of which is of the order of 10 Angstroms in the dry clay mineral and somewhat increased in the water-wet clay mineral. When a layered clay mineral is treated with a strong acid, i.e. an acid having a pKa value below 3.0, for example a mineral acid such as sulphuric acid, nitric acid or hydrochloric acid or an organic acid such as oxalic acid, the alumina layer is attacked at the platelet edges to leach out aluminium and other structural constituents and to generate pores having a diameter in excess of 15 Angstroms, usually from 20 to 50 Angstroms, in the platelets. As the severity of the acid treatment increases the clay mineral structure may be envisaged to be increasingly converted into one in which separate sheets of silica tetrahedra are linked together by the quantity of residual aluminium retained in bound form in the structure according to the invention. This may be expected to give a very open and characteristic high silica aluminosilicate structure with a wide pore size distribution which may be responsible for the observed altered adsorption characteristics in the clay mineral and which is quite different to the structure of either precipitated silicas or precipitated alumina silicas.

The silicon content of a natural clay mineral such as a smectite, calculated as Siθ2, may be in the region of about 50% to 60% by dry weight. An effect of acid- treatment according to the invention is to increase the overall content of silicon in the acid-treated product as an increasing proportion of the aluminium and other constituents such as magnesium are leached out and removed by washing in the form of soluble salts. In normal acid- treatment the content of silicon in the clay mineral may be increased from about 60% by dry weight to up to about 70% by dry weight calculated as Siθ2• In such products there remains a substantial quantity of aluminium, bound into the clay structure, which is not removable by water washing, usually amounting to more than 10% by dry weight of the clay, calculated as I2O3 with the effect that the original clay structure is to an extent retained. A number of other clay constituents for example up to about 5% of iron calculated as Fβ2θ3 may also be present. The acidic salts which are formed in the course of the acid treatment are conventionally removed by water-washing. In contrast the acid-treatment of the layered clay mineral according to the present invention is controlled to achieve a higher Siθ2 content which may even be above 85% or even above 90% by dry weight without allowing complete destruction of the aluminosilicate structure, as evidenced, using MASNMR techniques, by a residual content of bound aluminium. This acid treatment may be accomplished by digesting the clay mineral in aqueous slurry of a strong acid. An increasing severity of acid-treatment may be applied, for example, by increasing the duration, temperature, pressure or acid concentration utilised in the acid-treatment The acid is suitably a strong mineral acid, preferably sulphuric acid, which may have an initial concentration of, for example 77% to 100% by weight and a concentration in the aqueous slurry of about 10% to 40% preferably 15% to 30% by weight. An acid:clay ratio of from 0.25 to 2.0 by weight, calculated as 100% acid, is preferably used. The digestion may be conducted for from about 5 to 25 hours, preferably 10 to 16 hours if atmospheric pressure digestion is used or from 1 to 8 hours when pressure digestion is used. Pressure digestion may suitably be conducted at a pressure of up to about 200 psig (about 13.5 bars) but preferably of up to about 150 psig (about 10 bars) and is preferably conducted at a temperature suitable to generate the required pressure. Atmospheric pressure digestion may suitably be conducted at a temperature of about 70°C to 100°C preferably about 85°C to <100°C. The digestion may be terminated at the desired point by quenching with cold water after which the slurry of acid-treated clay mineral may be pumped to a suitable filter press where it may be water-washed to a desired residual acidity and dried to a desired residual water content to produce a powder which may be in the 10-40 micron or preferably in the 15 to 25 micron range. It is an advantageous feature of the invention that the drying of the product, although not essential, is conducted to achieve a free moisture content of from 8% to 30% by weight, preferably from 17% to below 25% by weight for optimum effectiveness for oil treatment.

The adsorbent produced according to the present invention may preferably contain at least 0.2% and up to

1.5% of bound non-water-leachable aluminium, and/or below

0.5% but usually at least 0.05%, for example at least 0.1% and up to 0.3% of non-water-leachable iron, calculated as I2O3 or Fe2θ3, respectively together with small quantities of other non-water-leachable constituents which may have been present in the clay structure. The adsorbent has a wide pore size distribution, often ranging from 20 Angstroms to 200 Angstroms diameter pores.

According to a preferred feature of the present invention the washing out of the soluble acidic salts formed in the course of the acid treatment is controlled so as to leave a residual quantity thereof and/or of the treating acid in the acid treated clay mineral product. Preferably the water-washing is controlled to give a Hedley Acidity in the washed product of from 0.1% to 5%.

The Hedley Acidity of a clay may be defined as % free acidity and may be measured by the following procedure. Weigh accurately a 4.9 g to 5.1 g sample of the clay mineral, add 100 ml distilled water to the weighed sample, boil for 2 minutes, filter, wash with 3 x 50 cm3 of boiling distilled water and titrate the combined filtrate and washings against 0.1M sodium hydroxide using a phenolphthalein indicator. The result is expressed as the % weight of sulphuric acid based on the weight of the clay sample.As a result of this controlled washing the product of this invention may preferably contain, in addition to the bound aluminium and/or iron referred to above 0.05% to 3% of water leachable aluminium calculated as AI2O3 and/or from 0.05 to 1% of water leachable iron calculated as Fe2θ3 together with small quantities of other water leachable salts corresponding to other constituents of the clay mineral. The products of such controlled washing are particularly effective in the removal of phosphorus compounds from oils.

The adsorbent produced according to the invention may be used to treat oils by methods well known in the art. It may be utilised on its own or in a blend, or added sequentially to the oil, with one or more other adsorbents which may be, for example, but not limited to, a bleaching earth for colour removal, an onium-exchanged or pillared clay for the removal of pigments or polyaromatic hydrocarbons, or amorphous silica. A suitable treatment would be with about 0.1 to about 3.0 parts of adsorbent according to the invention per 100 parts of oil, each by weight, for a duration of about 15 to about 40 minutes with agitation at a temperature of from 70 to 110°C. The adsorbent may then be removed from the oil by filtration. Other conditions such as a greater or lesser quantity of adsorbent, a shorter or longer duration or an elevated temperature may of course be used as dictated by the particular oil to be treated, the above stated conditions being merely illustrative.

Treatment with the adsorbent according to this invention may be carried out on raw extracted vegetable oils, either before or after alkali refining or degumming, on liquid animal fats, on fish oils, or on mineral or technical oils. Treatment according to the invention may avoid or reduce the need for alkali refining or degumming of vegetable oils the purpose of which is to reduce the residual level of phospholipids. Besides being suitable for adsorption of phospholipids the products of this invention have activity for the removal of trace metals or soaps or of pigments from oils.

The invention will now be described with reference to the following examples which are non-limitative and intended to be merely illustrative. Examples 2 to 6 and 10 to 16 are according to the invention aid Examples 1 and 7- 10 are comparative therewith.

A mixed calcium magnesium montmorillonite clay mineral obtained from Los Trancos, Spain, was heated with sulphuric acid at a 1:1.25 clay:acid (100%) ratio in an aqueous medium at a temperature of 95°C for a time of 16 hours at atmospheric pressure with agitation. The slurry was quenched and the clay was separated from the acid by filtration and washed to a preferred residual acidity and dried to a preferred water content. Some samples of the treated clay were again washed, to reduce the acidity still further. The products, or some of them, after drying to a water content of about 20%, were subjected to elemental analysis for certain constituents, to an acidity determination and to certain physical measurements and were used to treat a sample of water degummed soya bean oil containing a known quantity of phospholipids. The reduction in the phospholipid content of the oil was measured by X-ray fluorescence and expressed as parts per million phosphorus removed/grams adsorbent over a range of ratios of parts of adsorbent:parts of oil, indicated in the following Tables as the "K" value. The higher the "K" value the more effective the phosphorus removal performance.

The samples so produced had the following composition and properties.

Table 1 Ex Siθ2 AI2O3 Fβ2θ3 Tiθ2 MgO CaO a 0 K2O Surface Hedley

No < (w/w %) > Area Acidity m²/g % Before acid treatment 1 61.82 25.71 3.94 0.27 5.60 1.05 1.45 0.16 72

After acid treatment and washing

0.75 0.14 0.66 0.51 0.20 0.10 0.23 0.11 0.11 2.06 0.15 0.11 0.20 0.07 0.26 1.24 0.12 - 0.21 0.11 0.28 2.72 0.14 0.11 0.59 0.16 0.78 1.04 0.50 0.11

After further washing

7 98.56 0.54 0.16 0.10 0.14 0.27 0.10 0.10 - 0.3

When used to treat the water degummed soya bean oil the samples were found to give the following "K" values. Table 2 K value :us 175 ppm phosphorus

* Trisyl is a trade name for an amorphous silica adsorbent.

In the following tests the Siθ2 content as shown by the Siθ2:Al2θ3 ratio and as varied by varying the acid:clay mineral ratio is shown to be related to the "K" value in a standard treatment of a triglyceride oil. The surface area of the acid-treated clay mineral was found to have some relationship to phosphorus removal in that removal was relatively low when using clays having low surface areas, but the surface area was found to peak and to fall before maximum Siθ2 Al2θ3 and phosphorus removal were attained.

Table 3 S.A " * Si0₂: m²/g A1₂0₃

214 13 5.4 310 16 6.4 374 28 7.6 455 25 10.8 473 24 16.6 443 36 44.6 399 32 65.6 373 40 139.0 At very high Siθ2JAl2θ3 ratios, for example above about 300:1, or even above about 275:1 to an extent, there is a tendency for the "K" value to decline.

Claims

1. A process for the production of an adsorbent material suitable for use for the purification of oils comprising treating a layered clay mineral with a suitable strong acid to achieve a surface area of at least 250 m²/g and washing the acid treated clay mineral product to remove residual acid and acidic salts therefrom, the process being characterised in that the acid treatment is controlled to achieve a silicon content of from 80% to 99% by dry weight calculated as Siθ2, and a bound aluminium content, calculated as AI2O3 of from 0.1% to below 3.0% by dry weight, in the washed acid-treated clay mineral product.

2. A process as claimed in claim 1 wherein the layered clay mineral is a kaolinite, attapulgite, sepiolite or smectite.

3. A process as claimed in claim 1 or 2 wherein the strong acid is one having a p a value below 3.0.

4. A process as claimed in claim 3 wherein the layered mineral is treated by forming an aqueous slurry containing strong acid at a concentration of 10% to 40% by weight and at an acid:clay mineral weight ratio of from 0.25 to 2.0 calculated as 100% acid.

5. A process as claimed in any preceding claim wherein the acid treatment is conducted to give a bound aluminium content of at least 0.2% calculated as A1₂0₃.

6. A process as claimed in any preceding claim wherein the acid treated clay mineral is washed so as to give a Hedley acidity in the washed product of from 0 . 1% to

5% .

7. A process as claimed in claim 6 wherein the acid treated clay mineral is washed so as to give a Hedley acidity in the washed product of at least 1%.

8. An adsorbent material suitable for use for the purification of oils comprising an acid-treated layered clay mineral the absorbent being characterised by the following combination of features, namely a surface area of at least 250 m²/g, a silicon content calculated as Siθ2 of 80% to 99% by dry weight and a bound aluminium content calculated as AI2O3 of from 0.1% to below 3.0% by dry weight.

9. An adsorbent material as claimed in claim 8 having a bound aluminium content calculated as AI2O3 of at least 0.2% by dry weight.

10. An adsorbent material as claimed in claim 8 or 9 additionally characterised by having a Hedley Acidity of from 0.1% to 5.0%.

11. An adsorbent material as claimed in claim 10 wherein the adsorbent has a Hedley acidity of at least 1%.

12. An adsorbent material as claimed in any one of claims

8 to 11 additionally containing at least 0.05% of water leachable aluminium calculated as AI2O3 or of water leachable iron calculated as Fe2θ3.

13. A process for the removal of phosphorus compounds or other contaminants from oil by contacting the oil the an adsorbent material as claimed in claim 8.

14. A process for the removal of phosphorus compounds or other contaminants from oil by contacting the oil with an adsorbent material produced as claimed in claim 1.

15. A process as claimed in claim 13 or 14 wherein the adsorbent material is used in combination with one or more of a bleaching earth, an onium exchanged clay, a pillared clay or amorphous silica.

16. A process as claimed in any one of claims 13 to 15 wherein the oil is treated with from about 0.1 to about 3 parts fo the adsorbent material per 100 parts of oil by weight.