CA1171810A

CA1171810A - Process for dewaxing waxy oils produced by hydrotreating

Info

Publication number: CA1171810A
Application number: CA000382122A
Authority: CA
Inventors: Takatoshi Kunihiro; Yozo Iwao; Jiro Nishimiya
Original assignee: Idemitsu Kosan Co Ltd
Current assignee: Idemitsu Kosan Co Ltd
Priority date: 1980-07-30
Filing date: 1981-07-21
Publication date: 1984-07-31
Also published as: JPS5730792A; KR830006405A; KR840001852B1; JPS5917154B2

Abstract

ABSTRACT OF THE DISCLOSURE

An improved process for dewaxing waxy oils which have been produced by hydrotrcating to produce a base oil suitable for the production of high-quality lubri-cating oil. The dewaxing process is carried out utilizing a solvent and a dewaxing aid. The dewaxing aids are alkyl acrylate polymers which improve the characteristics of the filtration stage of the dewaxing operation resulting in improved filtration rate and yield. The preferred alkyl acrylate polymers contain an alkyl group containing the number of carbon atoms "n" defined by the following equation 6.4 + 0.235t ? n ? 7.4 + 0. 235t.

Description

1 !l~7~

"P}~OCESS FOR DEW7~XING WAXY
OILS PRODUCED BY IIYDROTRF.ATING"

BACXGROUND OF THE INVENl'ION
The present invention relatcs to an im~roved process for dewaxing waxy oils produced by hydrotrcating.

In general, oils such as vacuum distillate, deasphalted oil, etc., from which aromatics and undesirable constituents have been removed by solvent extraction using a solvent such as furfural have been used as base oils for the production of lubricating oils, etc. The removal of these components improves the viscosity index, color and other properties of base oils to produce high quality lubricating oil.

Recently, the hydrotrcating process has becn employed in place o~ the~ solvent extraction proccss to obtain the desired base oil since the hydrotreating proce~s is more economical than the solvent extraction process. oils produced by the lS hydrotreatin~ process are waxy oils and are introduced into a dewaxing unit where tho wax is rcmoved to provide base oil~.
It is known to use dewaxing aids in the dewaxing unit for the purpose of increasing the filtration rate.

The waxy oils produced by thc hydrotreating process are quite different in composition from the conventional waxy oils r~
''" ~

7~ 0 produced by solvent extractiOn. In ~articular, the isoparaffin content of the wax component in the waxy oils produced by the hydrotreating process is high.
The properties of the wax component in the waxy oils differ from the properties of the conventional waxy oils produced by prior processes.

It haY been found that when t:h~ conventional dewaxing aid~ are used in the dewaxin~ of waxy oils produced by hydrotreating, the amount of wax removed was low, or it has been necessary to increase th~ amount of the dewaxing aid to very high levels.

SUMMARY OF THE INVENTION
The present invention provides an efr:icient dewaxing proces~ for treatment of waxy oils prcduced by hydrotreating.
The dewaxing efficiency can be markedly increased by using specific dewaxing aids, particularly when correlated to the boiling point of the waxy oil.

The pre5ent invention, thereforc, provides a process for dewaxing waxy oils produced by hydrotreating, which is char-aaterized in that a waxy oil produced by treating a feed oil ; under hydro-cracking condition9 to rcmove undesirable con-stituent9 for use as a lubricatinc3 oil is brought into contact with a dewaxing solvent in the prcsence of an alkyl acrylate polymer.

sRIEF DESCRIPTION OF THL r)Rl~wINGs i Figs. l to 3 are ~raplls sllowirlg ~he rcsults in Example 1.

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:., . ~ ' ' ' - ~ ~7~ ~10 Fig. 1 is a graph illustrating the relationship between the filtration rate for a light Neutral oil and the numb,er of carbon atoms contained in the alkyl portion of the alkyl acrylate polymers used as the specific dewaxing aid~7 Fig. 2 is a graph illustrating the relationship between the filtration rate for a medium Neutral oil and the number of carbon atoms contained in the alkyl portion of the alkyl acrylate polymers used as the specific dewaxing aids;

Fig. 3 is a graph illustrating the relation between the filtration rate for a heavy Neutral oil (as Bright stock) and the number of carbon atoms contained in the alkyl portion of the alkyl acrylate polymers used as the specific dewaxing aids;

In Figs. 1 to 3, the number in the brackets shows dewaxing yield.

Figs. 4 and 5 are graphs showing the results in Comparative Example 2;

Fig. 4 is a graph illustrating the relation between the filtration rate for a light Neutral oil and the number of carbon atoms contained in the alkyl portion of the alkyl acrylate polymers used as the specific dewaxing aids; and Fig. S is a graph illustrating the relation between the filtration rate for a medium Neutral oil and the number of carbon atoms contained in the alkyl portion of the alkyl acrylate polymers used as the specific dewaxing aids.

~ L71810 DETAILED DESCRIPTION OF T~IE INVENTION
The feed oils which have heretofore been used as the chargestocks for the production of lubricating oils can be used as the feed oil for the hydrotreating process in the process of this invention. Such feed oils include heavy gas oil, vacuum distillates, and deasphalted oil.

These feed oils are treated under hydrocracking conditions, that is, are subjected to the hydrotreating process to remove undesirable constituents to produce oil for use as lubricating oil. This hydrotreating process may be performed under usual conditions that result in removal of undesirable constituents, such as aromatic components, which are contained in the feed oil. Processes which can be employed for the hydrotreating process include the Gulf lubricating oil hydrotreating process and the IFP lubricating oil hydrotreatinq process (O. & G.J., June 12, 1972, pages 94-94; Auffray, R. et al. (IFP report No. 20992-A).

The dewaxing of the waxy oil produced by the hydrotreating process is performed by the use of any of various known dewaxing solvent~. Examples of dewaxing solvents which can be used include propane, a mixture of ~ropane ancl butane, a mixture of methyl ethyl ketone (MEK) and toluene, and mixture of MEK and methyl isobutyl ketone (MIBK). Nonc of these dewaxing solvents inhibits the action of the dewaxiny aids described hereinafter.
Of these dewaxing solvents, a mixture o MEK and toluene (about 3:7 to 6:4) is particularly preferred. In the dewaxing stage, the volume ratio of dewaxing solvent to waxy oil is usually about 0.5:1 to 10:1 and preferably about 2:1 to 4:1.
, .

1.~7~ 10 In accordance with the process of th~ invention, the foregoing dewaxing treatment is pcrformed in the presence of an alkyl acrylate polymer~ This al]cyl acrylate polymer acts a~ a dewaxing aid and is added to the waxy oil or a mixture of the waxy oil and dewaxing solve~nt.

Various alkyl acrylate polymers can be used a~ dewaxing aids for use in the invention. The oL)timum alkyl acrylate polymers in specific instances vary depending on the boiling point of the waxy oil to be dewaxed. The choice of such optimum alkyl acrylate polymers provided markedly preferred results, and these optimum alkyl acrylate polymers can be determined by the following equation:

6.4 + 0.0235t ~ n ~ 7.4 + 0.0235t wherein n is the nurnber.of carbon atoms contained in the alkyl portion of an alkyl acrylate monomer constituting the alkyl acrylate polymer which is an averag~ number of carbon atoms because a mixture of alkyl a~rylate monomers having diferent alkyl portion9 is usually uscd for the production of the alkyl acrylate polymer altholl(3h a specif ic alkyl acrylate monomer having the samo n value carl be used, and t (C~ is the hoi.ling polnt of the waxy o.il to be dewaxed.

For example, when the boil.inr3 point of the waxy oil is 450C, the nwmber of carbon atoms ~ontai.ned i.n the alkyl portion of the alkyl acrylate polymer i~ between 17 and 18 ~17.0 ~ n ~ 18.0), and when the waxy oil has a boiling point of 650C, 21.7 ~ n < 22.7.

~ 11 71t~

Based on the value of n, the optimum dewaxing aid can be easily determined. When the waxy oil is a fraction having a wide boiling point range, an a~erage boiling point is employed as the value of t. This average boiling point is determined on the basis of molecular weight and specific gravity with reference to Ind. Eng. Chem., 27, 1460 (Nelson).

The alkyl acrylate polymer preferably has a weight average molecular weight of about 140,000 to 300,000 and a number average molecular weight of about 30,000 to 75,000.
More preferred are alkyl acrylate polymers having a weight average molecular weight of 150,000 to 270,000 and a number average molecular weight of 45,000 to 70,000.

In carrying out the process of the invention, the amount of the dewaxing aid used depends on filtration conditions and so forth. It is usually about 50 to 700 ppm (by weightl and preferably about 125 to 500 ppm (by weight) based on the weight of the waxy oil. When the amount of the dewaxing aid added is more than about 700 ppm, the addition effect of the dewaxing aid cannot be obtained. In much greater amounts, the filtration rate i8 lower than when no dewaxing is added.

The alkyl acrylate polymer used as a dewaxing aid in the process of the invention can be produced by various known methods.
For example, 70 parts of a specific alkyl acrylate monomer lor mixture of alkyl acrylate monomers) is mixed with 30 parts of kerosene and 0.14 part of azobisisobutyronitrile as a catalyst, and if necessary, with 0.017 part of dodecylmercaptan, and the resulting mixture is heated at 70C for 7 hours in a stream of nitrogen to produce the polymer dewaxing aid.

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1..~71.~310 The process of the invention can b~ applied to various dewaxing processes. An illustrative proces.s is described as follows: A specific dewaxing aid of the invention and a MEK-toluene mixed solvent are added to a waxy oil which S had been produced by a hydrotreating process, and are uniformly dissolved therein by heatlng. The resulting solution is chilled to a dewaxing temperature by the use of heat exchangers and chillers, and it is then filtered in vacuum to separate wax. The wax is washed with a MEK-toluene mixed solvent to recover the oil from the wax. The filtrate containing the dewaxed oil and the wax containing the solvent are separately sent to solvent recovery zones where the wax and the dewaxed base oil for lubricating oil are obtained.
A typical example of this illustrative process is the Texaco process (Petroleum Refiner, Vol. 15, No. 6, June, 1936, pages 205-209).

The process of the invention accelerates the cooling rate and filtration rate in the dewaxing stage. This produces a number o~ advantages. Some major advantages of the invention are given below:

~ 1) The amount of the chargestock being treated in the dewaxing stage can be increased because df the high ~iltration rate, and productivity can be marke~dly increased with the existing production equipment.

(2) Since the viscosity of the filter feed mixture is lowered, the amount of solvent being added to control the viscosity can be reduced.

(3) Since the amount of the oil component contained in the wax which is being removed is small, the dewaxing yield can be greatly increased.

1..~ J ~ O

The process of the invention can be effectively utilized in the field of the production of lubricating oils, etc.

The invention is described in greater detail with reference to the following examples and comparative examples.

Example 1 Three types of waxy oils produced by hydrotreating respective feed oils, i.e., (i) light Neutral oil (10%
point: 388C; 90% point: 470C; average boiling point:
450C); (ii) medium Neutral oil (10~ point: 468C; 90% point:
561C; average boiling point: 550C); and (iii) heavy Neutral oil as Bright Stock (10% point: 552C; average boiling point:
650C); were mixed with a MEK-toluene mixed solvent (volume ratio of 4:6) in a volume ratio of 2.5:1, 3.0:1 and 4.0:1 (ME~-toluene mixed to solvent to waxy oil), respectively. To each of multiple samples of each of these solutions was added 250 ppm of respective alkyl acrylate polymers each having an alkyl portion containing a different predetermined number of carbon atoms. The resulting mixture was heated to 60C, and was then chilled to -27C ~ 1C at a chilling rate of 3.5 to 7.0C/min. with moderate stirring in a low temperature bath maintained at -29C. The mixture was allowed to stand at that temperature for 30 minutes. Then, the mixture was filtered by the use of a leaf filter produced by providing a ~iltering cloth on a frame having a diameter of ~0 millimeters, and the amount of the mixture filtered per unit time, i.e., the filtration rate, was measured. The results are illustrated in Figs. 1 to 3.

li71~

Comparative Example 1 The procedure of Example 1 was repeated using the same Neutral oils as used in Example 1 except that no alkyl acrylate polymer was added. The results are illustrated in Figs. 1 to 3.

Comparative Example 2 Waxy oil which had been solvent extracted with furfural to provide light Neutral oil ~10% point: 388C; 90% point:
470C; average boiling point: 450C) and a waxy oil which had been solvent extracted with furfural to produce medium Neutral oil (10~ point: 468C; 90% point: 561C; average bolling point: 550C) were each mixed with a MEK-toluene mixed solvent in a volume ratio of 2.5:1 or 3.0:1 (MEK-toluene mixed solvent to waxy oil), respectively.

The operation other than described above was carried out in the same manner as in Example 1. The results are illus-trated in Figs. 4 and 5.

Examples 2 and 3 The procedure of Example 1 was repeated except that an eicosyl acrylate polymer was added in an amount of 125 ppm or 500 ppm. The results are shown in Table 1.

Table 1 Example 2Example 3 Dewaxing aid Eicosyl acrylate ibid polymer Amount (ppm) 125 500 25 Filtration Rate (ml/sec) 0.8 0.9 _ g _ ~ t7~iO

Comparative Examples 3 to 9 The procedure of Example 1 was repeated except that various dewaxing aids were used in place of the alkyl acrylate polymer. The result~ are shown in Table 2.

Table 2 Cornparative Dewaxing aid ~mount Filtrat o R t 3 Polyacryl methacrylate -based Dewaxing aid 250 0.52

4 ibid 500 0.65 ibid l,000 0.75 6 Polyolefin-based 250 0.56 Dewaxlng aid 7 ibid 500 0.59 8 Alkylnaphthalene-base~l Dewaxing aid 250 0.51 9 ibid 500 0.53 Example 4 In this example, the proccss o~ the inv~ntion was performed on a bench scale. Forty liters of a Illcdiuin Ncutral oil (10% point:
468C; 90~ point: 561C; average boilincJ point: 550C) produced by the hydrotreating process was mixed with a MEK-toluene mixed solvent in a ratio (by volumc) of ts)c mixcd solvcnt to the oil of 3:l, and 250 ppm of as~ cicosyl ~-srylatc polym~r was addcd thereto. The resulting mixture was fcd to a chiller at a rate 1.~7~
1 of 10 liters/hr. and then was filtered throuyh an Oliver filter to carry out dewaxing on a continuous basis.
30.4 liters of dewaxed oil was obtained with a yield of 70%. The filtration rate was 10 liters/hr. (2.8 milli-liters/sec).

Comparat-ive Example 10 The procedure of Example 4 was repeated except that no alkyl acrylate polymer was added. The yield was 64%, and 25.6 liters of a dewaxed oil was obtained with a filtration rate of 7.5 liters/hr. (2.1 milliliters~sec).

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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An improved process for dewaxing waxy oil produced by hydrotreating by admixing said waxy oil and a dewaxing solvent and then cooling until the wax precipitates and then separating the wax from the remaining oil by filtration, the improvement comprising admixing an alkyl acrylate polymer with said waxy oil and said solvent as a dewaxing aid, and wherein said alkyl acrylate polymer is in an amount of between about 50 ppm to 700 ppm by weight based on the weight of the waxy oil, and wherein the number of carbon atoms, n, contained in the alkyl portion of the alkyl acrylate polymer satisfies the following equation 6.4 + 0.0235t ? n ? 7.4 + 0.0235t wherein t in °C is the boiling point of said waxy oil which is being dewaxed.

2. The process of claim 1 wherein said alkyl acrylate polymer has a weight average molecular weight of between about 140,000 and 300,000 and a number average molecular weight of between about 30,000 and 75,000.

3. The process of claim 2 wherein the ratio of said dewaxing solvent to said waxy oil is between about 2:1 and 4:1.

4. The process of claim 1, 2 or 3 wherein the ratio of said dewaxing solvent to said waxy oil is between about 0.5:1 and 10:1.
5. The process of claim 1, 2 or 3 wherein said dewaxing solvent is a solvent selected from the group consisting of

Claim 5 continued ....

propane, a mixture of propane and butane, a mixture of methyl ethyl ketone and toluene, and a mixture of methyl ethyl ketone and methyl isobutyl ketone.

6. The process of claim 1 wherein said dewaxing aid is in an amount between about 125 and 500 ppm by weight.

7. The process of claim 3 wherein said dewaxing aid is in an amount between about 125 and 500 ppm by weight.

8. The process of claim 7 wherein said dewaxing solvent is a mixture of methyl ethyl ketone and toluene.

9. The process of claim 1, 3 or 8 wherein said alkyl acrylate polymer has a weight average molecular weight of 150,000 to 270,000 and a number average molecular weight of 45,000 to 70,000.