GB2305185A - Dewaxing oil with a co-polymer - Google Patents

Abstract

A process for dewaxing a hydrocarbon oil includes the precipitation of the wax by a co-polymer of n-alkyl (meth)acrylates and maleic anhydride. Preferably the ratio of (meth)acrylate to maleic anhydride is 5:1, especially 1:1, the copolymer having a degree of alternation of at least 50%. Preferably the alkyl chain length of the (meth)acrylate is C 10 -C 30 and more preferably C 12 -C 24 . The oil is dissolved in a conventional solvent such as toluene and on addition of the copolymer the mixture is cooled, preferably to between -10{C to -45{C. The flow rate of the resulting oil is thus improved.

Description

DEWAXING PROCESS The present invention relates to a process for dewaxing a wax-containing hydrocarbon oil.

Dewaxing is an important process which is applied in the refining of hydrocarbon oils, since the removal of the wax leads to an oil with a considerably improved pour point. The process is usually carried out by cooling the oil to a temperature that is low enough to cause the wax to precipitate and then removing the wax from the oil by filtration. Usually, solvents are added to the oil which can disslove the oil and precipitate the wax. The precipitated wax has a tendency to block the filter during the filtration. As a consequence, the filtration rate is substantially reduced and the quantity of oil remaining behind in the filter cake increase considerably. These difficulties can be avoided by carrying out the dewaxing in the presence of certain polymers, which are referred to as dewaxing aids.An example of a class of polymers suitable for this purpose is formed by polymers from one or more olefinically unsaturated compounds which consist at least partly of alkylacrylates or alkylmethacrylates with at least 8 carbon atoms in the alkyl group, as for instance described in US 4,728,414.

In an investigation by the applicant into the application of polymers as dewaxing aids, a class of copolymers has now been found, which copolymers are well suited for this purpose.

Accordingly, the present invention provides a process for dewaxing a wax-containing hydrocarbon oil wherein the oil is dewaxed by precipitation of the wax and separation of the wax from the oil, characterized in that the precipitation of the wax is carried out in the presence of a copolymer of n-alkyl (meth)acrylates with maleic anhydride.

It should be noted that copolymers of n-alkyl (meth)acrylates with maleic anhydride are known to be used as flow improvers in gas oils and diesel oils since they promote in these oils the formation of many small parafin crystals, see for instance EP-A-0636637.

In this way filter blockage is avoided because the paraffin crystals are sufficiently small to pass through the filter. Since, it is well appreciated by those skilled in the art that flow improvers perform very poorly as dewaxing aids, because of their promotion to form small paraffin crystals, it is very surprising that in acccrdance with the present invention it has now been found that these copolymers perform very attractively as dewaxing aids.

Suitably, the copolymers of n-alkyl (meth)acrylates and maleic anhydride have a structure consisting of alternating (meth)acrylate and maleic anhydride monomeric units.

Preferably, the copolymer is a copolymer of at least one n-(Cg-C30-alkyl) (meth)acrylate with maleic anhydride, which contains alternating (meth)acrylate and maleic anhydride monomeric units, characterized in that the copolymer has a degree of alternation of at least 50%.

Preferred copolymers are those prepared from one or more n-(C10-C30-alkyl) (meth)acrylates, most preferably one or more n-(C12-C24-alkyl) (meth)acrylates.

Acrylates are most preferred.

The degree of alternation in the copolymers can be readily determined by quantitative C13 Nuclear Magnetic Resonance Spectroscopy (NMR). Thus, a sample of pure copolymer is dissolved in deuterated chloroform containing 0.15 M 2,2,6, 6-tetramethyl-l-piperidinyloxy (TEMPO) and is subsequently analysed by NMR. From the NMR spectrum obtained, the ratio a/b of the integrals in the carbonyl (CO) region at 172-174 ppm (a) and in the ester (OCH2) region at about 65 ppm (b) is calculated. In the case of a homopoly(meth)-acrylate, there is one carbonyl carbon for every OCH2 carbon, so that the ratio a/b is 1. By comparison, in the case of a perfectly alternating copolymer of n-alkyl (meth)acrylate with maleic anhydride, there are three carbonyl carbons for every OCH2 carbon, so that the ratio a/b is 3.In the case where a copolymer of nalkyl (meth)acrylate with maleic anhydride contains y perfectly alternating segments and l-y acrylate segments (y x 1008 represents the degree of alternation as a percentage), then there are 3y + (1-y), i.e.

2y + 1, carbonyl carbons for every y + (l-y), i.e. 1, OCH2 carbon, so that the ratio a/b is 2y + 1 (or y is (a/b-1)/2).

The latter expression is based on the understanding that maleic anhydride has an extremely low tendency to homopolymerise. This was confirmed in control experiments carried out under the same polymerisation conditions as used in the preparation of the copolymers according to the present invention, in which no oligomers or polymers of maleic anhydride were formed.

The above explanation of the calculation of the degree of alternation may be more readily understood by reference to the following structural representations:

"A" represents an acrylate monomeric unit in which "n" is an integer in the range from 6 to 28, and "M" represents a maleic anhydride monomeric unit.

For: AAAAAAAA , C=O/OCH2 = 1 AMAMAMAM , C=O/OCH2 = 3 (AM)y(A) (l-y)r C=O/OCH2 = 3y + (l-y) = 2y + 1 y + (l-y) The degree of alternation in the copolymers of the present invention is preferably at least 50%, more preferably at least 70, and especially at least 90%.

The n-(Cg-C30-alkyl) (meth)acrylates used in the process of the present invention are known compounds or can be prepared by processes analogous to known processes. Thus, the (meth)acrylates may conveniently be prepared by an esterification process in which (meth)acrylic acid is heated together with one or more Cg-C30 n-alkanols in an azeotropic solvent such as toluene, in the presence of an esterification catalyst, e.g. p-toluenesulphonic acid, and a polymerisation inhibitor, e.g. copper (II) acetate, with removal of water. The esterification reaction is typically carried out at a temperature in the range from 70 to 90"C under 20 kPa vacuum.

Preferred (meth)acrylates are those prepared from C12-C24 n-alkanols, e.g. 1-dodecanol, or a mixture of C12-C15 n-alkanols which is available from member companies of the Royal Dutch/Shell Group under the trade mark "DOBANOL 25", or a mixture of C16-C24 nalkanols which is available from Sidobre Sinnova (France) as "Behenyl Alcohol X5".

Examples of radical-forming initiators include benzoyl peroxide, di-tert-butyl peroxide, acetyl peroxide, acetyl benzoyl peroxide and a,ct '-azoiso- butyronitrile. Further examples of radical-forming initiators are mentioned in EP-A-485 773.

The radical-forming initiator is conveniently used in an amount from 1 to 10 mol%, preferably from 1 to 5 mol%, and most preferably from 1.5 to 3 mol%, based on (meth)acrylate. The radical-forming initiator may be added as a single portion, or, alternatively, may be divided into two or more portions which are added at different stages during the course of the reaction.

The initiator is conveniently added in two portions, the first portion containing 65 to 75, and the second portion containing 25 to 35%, of the total intake of initiator.

In the process of the invention, a predetermined molar amount of at least one n-(C8-C30-alkyl) (meth)acrylate is dosed to a predetermined molar amount of maleic anhydride at a dosage rate of 20 to 100 mol%, preferably 40 to 80 molE, and especially 60 mol%, (meth)acrylate per hour.

The ratio of the predetermined molar amount of (meth)acrylate to the predetermined molar amount of maleic anhydride is in the range from 1:1 to 1:5, preferably from 1:1 to 1:3, more preferably from 1:1 to 1:1.5, and is especially 1:1.

The number average molecular weights (Mn) of the copolymers which are eligible to be used as dewaxing aids in the process of the present invention may vary within wide limits. For example, the copolymers may have number average molecular weights up to 100,000, e.g. in the range from 500 to 100,000, preferably from 1,000 to 50,000, more preferably from 1,000 to 35,000, still more preferably from 1,000 to 20,000, and advantageously from 4,500 to 10,000. Such number average molecular weights may conveniently be determined by gel permeation chromatography (GPC) against polystyrene standards.

The present invention further relates to the hydrocarbon oils thus dewaxed and to the wax thus obtained.

The process of the invention can in principle be applied to dewaxing any wax-containing hydrocarbon oil.

The process is preferably applied to dewaxing waxy raffinates obtained from lubricating oil fractions by applying aromatic extraction to them.

As pointed out above, the dewaxing can very suitably be carried out by cooling the oil in the presence of a dewaxing solvent. Examples of solvents which can be used for this purpose are low molecular weight hydrocarbons such as ethane, propane, butane and isobutane, polar solvents such as acetone, methyl ethyl ketone, propanol, butanol and pentanol, diethyl ether, diisopropyl ether, ethylene dichloride and ethylene trichloride, as well as mixtures of the aforementioned polar solvents with an aromatic solvent such as benzene or toluene. As a dewaxing solvent, a mixture of methyl ethyl ketone and toluene is preferred, in particular such a mixture in which both components are present in approximately equal quantities. When using a dewaxing solvent, preferably just enough of it is used for the oil to remain in solution at the dewaxing temperature while as little wax as possible dissolves.The solvent/oil ratio to be used depends, amongst other things, on the wax content of the oil, the viscosity of the oil, the temperature and other conditions applied during the dewaxing. There is a preference for 1 to 10 volumes, and in particular 2 to 4 volumes of solvent per volume of wax-containing oil.

The dewaxing in the presence of a solvent can be carried out under application of a single-stage or multi-stage dilution. If the dewaxing is carried out using single-stage dilution, the dewaxing takes place in a single step by gradually cooling to the dewaxing temperature a mixture of the oil to be dewaxed and the total quantity of the solvent intended for the dewaxing, which mixture is at an elevated temperature.

If the dewaxing is carried out using a multi-stage dilution, the dewaxing takes place in two or more steps by gradually cooling to a temperature above the dewaxing temperature a mixture of the oil to be dewaxed and a part of the total quantity of solvent intended for the dewaxing, which mixture is at an elevated temperature, and then again adding a part of the total quantity of the solvent intended for the dewaxing and again cooling and, if desired, repeating these steps one or more times until all the solvent has been added and the dewaxing temperature has been reached. The dewaxing in the presence of a solvent is preferably carried out using a solvent/oil mixture at a temperature of 45-900C. Suitable dewaxing temperatures lie between -10 and -450C.. in the dewaxing process one or more copolymers can be used.

The present invention will be further understood from the following illustrative examples.

Example 1 Preparation of a highly alternating copolymer of C16-C24-alkyl acrylate and maleic anhydride 9.8 g (0.1 mol) maleic anhydride (MALA) and 50 g toluene were introduced into a double walled glass reactor equipped with an overhead stirrer, an argon inlet, a condenser and an inlet connection for a perfusion pump. The reactor was purged with argon and a slight flow of argon was maintained throughout the entire reaction. The mixture in the reactor was heated, with stirring, to a temperature of about 800C by circulating silicon oil from a thermostatted bath.

When all the maleic anhydride had melted and dissolved, a portion of a,a'-azoisobutyronitrile (AIBN) in toluene was introduced into the reactor using a syringe. This portion consisted of 75% of the total AIBN intake of 0.24 g (1.5 mol% based on acrylate intake) in 5.4 g toluene.

100 ml of a solution of 36.8 g C16-C24-alkyl acrylate (being the reaction product of acrylic acid and a mixture of C16-C24 n-alkanols) in toluene was subsequently dosed to the reaction mixture over a period of 100 minutes (molar ratio acrylate:MALA of 1:1; dosage rate of 60 mol% acrylate per hour). On completion of the acrylate addition, the remaining portion of AIBN solution (25%) was immediately introduced into the reactor and the reaction was left to continue for a further 4 hours. On cooling to below 600C, the crude reaction product containing the highly alternating copolymer of C16-C24-alkyl acrylate and maleic anhydride was collected and analysed by gel permeation chromatography (GPC) against polystyrene standards. The copolymer was found to have a number average molecular weight (Mn) of 9,050.Purification of the crude product by dialysis followed by analysis by Nuclear Magnetic Resonance (NMR) revealed the degree of alternation in the copolymer to be 100% (calculated on the purified product).

Example 2 Example 1 was repeated with the following exceptions: 9.8 g maleic anhydride in 20 g toluene was used and the C16-C24-alkyl acrylate was replaced by 36.8 g C20-alkyl acrylate (molar ratio acrylate: MALA of 1:1). The copolymer of C20-alkyl acrylate and maleic anhydride obtained had Mn 9,200 (determined by GPC on the crude product) and a degree of alternation of 100% (calculated on the purified product).

Example 3 Example 1 was repeated with the following exceptions: 9.8 g maleic anhydride in 20 g toluene was used and the C12-C15-alkyl acrylate was replaced by 39.7 g C22-alkyl acrylate and maleic anhydride obtained had Mn 10,900 (determined by GPC on the crude product) and a degree of alternation of 53% (calculated on the purified product).

Example 4 The following polymers were tested as dewaxing aids in the dewaxing of a waxy raffinate with a viscosity index of 130.

Additive 1: The copolymer prepared according to Example 1.

Additive 2: The copolymer prepared according to Example 2.

Additive 3: The copolymer prepared according to Example 3.

The polymers were introduced into the raffinate in the form of a solution of 25 %w solids in toluene. The results of the experiments are tabulated below. The additives are expressed in mg copolymer solution per kg wax-containing raffinate.

Experiment 1 In this experiment the raffinate was dewaxed using single-stage dilution. This consisted of adding to a sample of the raffinate heated to 60"C a mixture, also at 60"C, of equal parts by volume of methyl ethyl ketone and toluene, 3 parts by weight of the mixture being added per part by weight of raffinte. The mixture thus obtained was cooled at a rate of 30C per minute to -200C and filtered at this temperature.

Experiment 2 This experiment was carried out in substantially the same way as experiment 1, but with the difference that, before adding the solvent, 600 mg/kg of a polymer solution containing additive 1 was incorporated in the warm raffinate.

Experiment 3 This experiment was carried out in substantially the same way as experiment 1, but with the difference that, before adding the solvent, 600 mg/kg of a polymer solution containing additive 2 was incorporated in the warm raffinate.

Experiment 4 This experiment was carried out in substantially the same way as experiment 1, but with the difference that, before adding the solvent, 600 mg/kg of a polymer solution containing additive 3 was incorporated in the warm raffinate.

It will be clear from the results shown in Table 1 that the copolymers of n-alkyl (meth)acrylate with maleic anhydride can be suitably used as dewaxing aids.

Results of the dewaxing experiments

Experiment Filtration Additive Filtration Oil in No. temperature No. rate filter OC g/(sec.m2) cake 1 -20 - 198 67 2 -20 1 185 61 3 -20 2 197 60 4 -20 3 196 58

Claims (12)

1. CLAIMS 1. Process for dewaxing a wax-containing hydrocarbon oil wherein the oil is dewaxed by precipitation of the wax and separation of the wax from the oil, characterized in that the precipitation of the wax is carried out in the presence of a copolymer of n-alkyl (meth)acrylates with maleic anhydride.
2. 2. Process according to claim 1, wherein the copolymer is a copolymer of at least one n-(Cg-C30-alkyl) (meth)acrylate with maleic anhydride containing alternating (meth)acrylate and maleic anhydride monomeric units and having a degree of alternation of at least 50%.
3. 3. Process according to claim 2, wherein the at least one (meth)acrylate is selected from n-(C12-C24-alkyl) (meth) acrylates and mixtures thereof.
4. 4. Process according to claim 2 or 3, wherein the degree of alternation is at least 70%.
5. 5. Process according to claim 4, wherein the degree of alternation is at least 90%.
6. 6. Process according to any one of claims 1-5, wherein the hydrocarbon oil is a lubricating oil.
7. 7. Process according to any one of claims 1-6, which is carried out in the presence of a dewaxing solvent.
8. 8. Process according to claim 7. where the dewaxing solvent is used in a quantity of 1-10 volumes per volume wax-containg oil.
9. 9. Process according to any one of claims 1-8, which is carried out using single-stage or multi-stage dilution.
10. 10. Process according to any one of claims 1-9, substantially as described hereinbefore and in particular with reference to the Examples.
11. 11. Dewaxed hydrocarbon oils prepared according to a process described in any one of claims 1-10.
12. 12. Wax obtained in a process as described in any one of claims 1-10