GB2084606A - Treating crude oil - Google Patents

Abstract

A method of treating a crude oil comprises passing a solution of crude oil in a solvent through a plurality of ultrafilters arranged in series, to obtain a filtrate; and feeding solvent, solution or part at least of the filtrate into the solution which is passing between a pair of the ultrafilters to prevent build- up of the phospholipids on the filters. A concentrated phospholipid solution, and a substantially phospholipid-free filtrate are obtained; lecithin may be obtained from the former and degummed oil from the latter.

Description

SPECIFICATION Treating crude oil A crude oil generally contains phospholipids and other impurities which must be removed, by purification, before the oil is used as food or for industrial purposes. The phospholipids are generally removed in the first stage of purification. This treatment is generally known as "degumming". A common method of degumming comprises adding water to a crude oil, to insolubilise the phospholipids dissolved in the crude oil, and then removing the insolubles by, for example, centrifugal separation. In this method, materials such as phosphoric acid may be used which in fact require a second degumming step, since the removal of the phospholipids is incomplete in the first. However, phospholipids are often insufficiently removed even after a second degumming step.

Oil meal and/or waste water formed as the result of deacidification after degumming may still contain a high level of phospholipids. Consequently, the workability of the process is low and the waste water has to be rigorously treated.

Lecithin is usable as a foodstuff or industrially. It can be obtained from the phospholipids produced in the degumming of crude oil. Therefore, degumming using water and phosphoric acid is also undesirable from the viewpoint of lecithin production.

Japanese Patent Publication No. 153010/1975 discloses a method in which a solution of crude oil in a solvent is passed through an ultrafilter, in order to divide the materials into phospholipids having a relatively high molecular weight and crude oil having a relatively low molecular weight. By this method, the problems associated with the use of water and phosphoric acid can be substantially wholly overcome. However, if this method is carried out on a commercial scale, other problems are observed.

For example, the viscosity of the solution to be treated increases, and the phospholipids are deposited on the surface of the ultrafilter. The filtration rate is reduced, and the phospholipids are insufficiently concentrated. It is therefore difficult to obtain high quality lecithin.

Phospholipids produced in the degumming of oils may be added to oil meal used as feed or fertiliser. Such phospholipids are generally classed as "oil foots" and are usually obtained when degumming oils by the addition of water. The oil foots have a water content of around 50% and must therefore be dried, to remove water, after the oil foots are incorporated in oil meal. It is difficult to obtain a homogeneous mixture of oil foots having a high viscosity with oil meal, and the mixture is apt to be lumpy, making it difficult efficiently to evaporate water in drying.

According to the present invention, a method of treating an oil comprises passing a solution of crude oil in a solvent through a plurality of ultrafilters arranged in series, to obtain a filtrate; and feeding solvent, solution or part at least of the filtrate into the solution which is passing between a pair of the ultrafilters. The crude oil solution may thus be divided into a filtrate from which phospholipids have been removed, and a concentrated phospholipid solution. Degummed oil may be obtained from the filtrate and lecithin from the concentrated solution.

The concentrated phospholipid solution may be added to oil meal. The solvent may be removed to obtain a feed or fertiliser of high efficiency.

The ultrafilters are preferably of a solvent-resistant, oil-resistant, tubular module, made of a polysulfone or polyimide high molecular membrane. The fractional molecular weight of the membrane is preferably from 6,000 to 20,000.

Crude oils which can be treated by the method of the present invention include oils obtained from soy-beans, rapeseed, cotton seed, linseed, sunflower seed, safflower seed and sesame seed. The solvent may be, for example, a hydrocarbon or an alcohol. Specific examples of suitable solvents are ethanol, petroleum benzin, trichloroethylene and hexane (which is particularly preferred).

The preferred concentration of the crude oil in the solvent (the solution hereinafter referred to as a miscella) to be passed to the ultrafilters is from 20 to 40%. A higher concentration is generally impractical, since the filtration rate is adversely affected. Crude oil obtained by solvent extraction is in the form of a miscella having a concentration which is generally in the above range. Such a miscella may therefore be used as such in the method of the present invention.

By feeding a part of the solvent, miscella or filtrate which has passed through the ultrafilters in at least one connecting part between the ultrafilters, the viscosity and concentration of the miscella to be treated can be reduced, and the treatment efficiency can thus be improved. A suitable quantity of the liquid to be fed in is from 5 to 10 wt. %, based on the miscella to be treated. The liquid may be fed in all, some only, one or a part of the connecting parts between the ultrafilters. It is often preferred to introduce the feed in a connecting part positioned before the last ultrafilter in the sequence, where the viscosity and concentration of the miscella to be treated are high.

Apparatus which can be used for carrying out the present invention is provided with ultrafilters; a pump, pipes and tank for circulating a miscella through the ultrafilters under pressure; and a pump and pipes for feeding a part of the solvent, miscella or filtrate into the ultrafilter-connecting parts. The miscella circulating in the ultrafilters and the tank is successively contacted with the ultrafilters under pressure, thereby increasing phospholipid concentration in the circulating liquid which has not passed through the ultrafilters. The miscella from which the phospholipids have been removed is collected as the filtrate. A part of the solvent, miscella or filtrate is fed into at least one ultrafilter-connecting part and passes towards a downstream ultrafilter, together with the miscella to be treated.

In the operation, the temperature of the miscella is preferably from 40 to 650C. The pressure is preferably from 5 to 20 kg/cm2. If a lower temperature or pressure is employed, the filtration velocity of the filters, and the amount treated, may be reduced.

The degummed miscella which is obtained has the solvent removed; it is then purified, e.g. by conventional methods. Solvent is also removed from the concentrated phospholipid solution, to obtain lecithin which can be of high purity.

By use of the method of the present invention, the increase in viscosity and concentration of the liquid to be treated can be controlled and the phospholipids deposited on the surface of the ultrafilters can be washed away by feeding solvent or miscella into the appropriate ultrafilter-connecting part(s).

Accordingly, the filtration rate of the ultrafilters can be substantially maintained; a high treatment efficiency can be obtained. Thus, degumming by means of ultrafilters can be carried out on a commercial scale, and the process is simpler and cheaper than the conventional degumming method using water and phosphoric acid. Further, a high rate of phospholipid removal can be achieved. Crude oil to be degummed by the method of the present invention does not always require deacidification by alkali purification, but steam purification, in which the crude oil is decoloured with china clay and then deodorised and deacidified by steam distillation, may be employed.

The oil foots obtained by the alkali purification of the degummed crude oil can have a low phospholipid content, e.g. of less than 0.1% by weight. Therefore, there is little or no emulsification, when decomposing the oil foots into fatty acids, thereby giving good workability. Further, water discharged as waste from the alkali purification and decomposition steps is reasonably pure and can be easily treated. The treated water can be of satisfactory quality.

For the regeneration of the ultrafilters, any known method, such as back-washing, may be employed, to increase the treatment efficiency. The circulating liquid obtained by the degumming contains highly concentrated phospholipids. After the removal of the solvent, light-coloured lecithin having a purity equivalent or superior to that of commercially available lecithin can be obtained directly.

In another aspect of the present invention, the concentrated phospholipid solution is added as it is to oil meal, suitably in an amount of from 1 to 5 wt. %, based on the weight of the oil meal. The oil meal may be, for example, any such meal conventionally used as a feed or fertiliser such as the oil meal obtained from soy-beans, rapeseed, cotton seed, linseed, sunflower seed and safflower seed.

After addition of the concentrated solution, followed by the removal of the solvent, e.g. in conventional manner, an oil meal of the present invention is obtained. Since the phospholipids have substantially the same composition as that of oil foots conventionally added to oil meal, the oil meal of the present invention is substantially the same as known oil meal and can have high efficiency as a feed or fertiliser. Oil meal obtained by solvent extraction still contains a smali quantity of solvent, and a solvent removal step is necessary. However, if the concentrated solution is added to the oil meal from which the solvent has not been removed, the solvents in the oil meal and in the concentrated solution can be distilled out in one step.

Unlike conventional oil foots, the concentrated phospholipid solution of the present invention is free of water and, consequently, no drying step is required after its addition to oil meal. Further, the concentrated solution, having a low viscosity, can be mixed with the oil meal to form a homogeneous mixture without forming lumps, unlike known oil foots.

The following Examples illustrate the present invention. The phospholipid contents are given in terms of the acetone-insoluble matter. Oil chromaticity was determined using a Lovibond colorimeter with a 133.4 mm cell. Lecithin chromaticity was determined using a Gardner colorimeter.

EXAMPLE 1 A miscella (oil content: 22%, phospholipid content of the oil: 2.5%) obtained from rapeseed by solvent extraction with hexane, was treated in a device comprising three non-aqueous membranes for ultrafiltration NTU-4220 (fractional molecular weight: 20,000), module P-i 8, arranged in series. The respective membrane areas of the modules were 9.2 m2, 1.8 m2 and 0.8 m2, in order of oil flow. The miscella was passed into the modules at a rate of 1 550 I/hr under a pressure (at the inlet of the membrane) of 10 kg/cm2 at a temperature of 500 C, and at a linear velocity in the membrane of 2-4 m/sec. The miscella circulating in the modules was contacted with the ultrafilters. The phospholipids were concentrated in the circulating liquid which had not been passed through the ultrafilters. The miscella from which the phospholipids had been removed was collected as the filtrate.

69 I/hr of hexane were fed into a connecting part between the second and third modules. Flow rates in the respective modules are shown in the following Table.

First Second Third stage stage stage Circulating solution 222 61 60 (I /hr) Filtrate (I/hr) 1333 161 70 Filtrate (i/m2. hr) 90 60 100 The resulting filtrate had a phospholipid content of less than 0.1 wt. % and an acid value of 1.6.

The filtrate was treated in conventional manner to remove the solvent, and then subjected to alkali purification (deacidification, discolouration and deodorisation) to obtain the intended oil. The oil had a chromaticity of 3.4Y/0.3R, an acid value of 0.04, an AOM stability of 21.0 (peroxide value: 2.2), and good flavour.

For comparison, the procedure was repeated, except no hexane was fed into the moduleconnecting part. In this case, the filtration rate began to fall about five minutes after the start of the operation. Ten minutes after the start of the operation, the filtration flow had been reduced from 100 l/m2 to 30 l/m2, and the workability was adversely affected.

By way of further comparison, crude rapeseed oil obtained by removing the solvent from the same crude miscella as used in Example 1 was treated by a conventional degumming method using water and phosphoric acid. The resulting degummed oil had a phospholipid content of 0.2% which was higher than that observed after carrying out the method of the present invention, at a degumming rate lower than that of the present invention.

Phospholipid contents (excluding the solvent) of the circulating liquid were 20%, 40% and 65% in the respective stages. The solvent was then removed by means of a film evaporator ( 1 00 C/20 Torr) to obtain highly pure, light-coloured rapeseed lecithin. This product had a chromaticity of G 14, an acid value of 22, a water content of 0.1% and a phospholipid content of 65%.

EXAMPLE2 A miscella (oil content: 21%, phospholipid content: 2.5%) obtained from soy beans, by solvent extraction using hexane, was treated by means of ultrafilters in the same manner as in Example 1 , to obtain a filtrate from which the phospholipids had been removed, and a circulating liquid containing the concentrated phospholipids. The solvent was removed from the filtrate by conventional means, and the residue was subjected to steam purification (discolouration, steam distillation) to obtain the intended oil. The product had a chromaticity of 2.9Y/0.2R, an acid value of 0.03, an AOM stability of 1 7.5 (peroxide value: 1.9), and good flavour.

The solvent was removed from the latter in the same manner as in Example 1 to obtain highly pure, light-coloured soybean lecithin. This product had a chromaticity of G 13, an acid value of 25, a water content of 0.1% and a phospholipid content of 64%.

EXAMPLE 3 A miscella (oil content: 22%, phospholipid content of the oil: 2.5%) obtained from rapeseed by solvent extraction with hexane, was treated by means of the same ultrafiltration apparatus as in Example 1, under the same conditions as in Example 1. The miscella circulating in the modules was contacted with the ultrafilters. The phospholipids were concentrated in the circulating liquid which had not been passed through the ultrafilters. Hexane was fed at a rate of 69 I/hr into a connecting part between the second and third modules. Phospholipids contents (excluding the solvent) of the circulating liquid were 20%, 40% and 65% in the respective stages. The final phospholipid concentration in the third stage reached 65%.

220 kg of the product were added to 7,500 kg of soy-bean oil meal to obtain a homogeneous mixture. This was an easily-conducted procedure. The solvent was removed from the mixture in conventional manner, to obtain oil meal having a high feed efficiency.

For comparison, oil foots obtained by treating crude rapeseed oil (obtained by removing the solvent from said miscella) by a conventional degumming method, using water, were added to a soybean oil cake. It was difficult to mix them homogeneously and lumps were formed, since the oil foots had a high viscosity. Further, it was necessary to remove water from the oil foots, after mixing. The water evaporation efficiency in the drying step was low owing to the lumpy consistency.

Claims (8)

1. A method of treating a crude oil, which comprises passing a solution of crude oil in a solvent through a plurality of ultrafilters arranged in series, to obtain a filtrate; and feeding solvent, solution or part at least of the filtrate into the solution which is passing between a pair of the ultrafilters.

2. A method according to claim 1, wherein solvent, solution or filtrate is fed into the solution passing between the final pair of ultrafilters.

3. A method according to claim 1, wherein solvent, solution or filtrate is fed into the solution passing between each pair of ultrafilters.

4. A method according to claim 1, substantially as described in any of the Examples.

5. A concentrated phospholipid solution produced by a method according to any preceding claim.

6. Lecithin obtained from the phospholipid solution of claim 5.

7. Oil meal to which the phospholipid solution of claim 5 has been added, followed by removal of the solvent.

8. A degummed oil obtained from the filtrate produced by a method according to any of claims 1 to 4.