GB2084177A - Process for producing high- vacuum oils - Google Patents

Abstract

Aromatic hydrocarbons (such as naphthalene biphenyl, diphenylmethane and benzene) are alkylated by means of up to 5 moles of at least one normal secondary alkylchloride containing 8 to 12 carbon atoms at a temperature of from 20 to 100 DEG C in the presence of from 2 to 15 mol.% of aluminium chloride based on the amount of the employed alkylchlorides. The catalyst is separated from the resulting alkylate, the latter is subjected to a vacuum fractionation and the desired fraction which has its boiling temperature within the range of from 220 to 250 DEG C/0.2-0.3 mm Hg. is collected.

Description

SPECIFICATION Process for producing high-vacuum oils The present invention relates to a process for producing high-vacuum oils employed as working medium in super-high vacuum diffusion pumps.

Super-high vacuums of the order of 10 -10-8-10-9 10#mm Hg are widely employed in modern industry, especially in electronics and nuclear engineering. To obtain such a high vacuum, diffusion pumps are used with inorganic and organic liquids serving as the working medium in such pumps.

These working liquids should satisfy four basic requirements: a low proper vapour tension, a high thermo-oxidation stability, a relatively low viscosity at a temperature of 1 0-20 C, and a high ultimate vacuum produced, namely 2-5 X 10-8 mm Hg in unbaked systems without nitrogen traps and 2-5 X 109 mm Hg in baked systems without nitrogen traps.

The present invention provides a process for producing a high-vacuum oil, comprising effecting alkylation of an aromatic hydrocarbon by means of a normal secondary alkylchloride containing 8 to 12 carbon atoms or a mixture of said chlorides, the said alkylchloride(s) being employed in a molar ratio to the said aromatic hydrocarbon of from 2.5:1 to 5:1; the alkylation reaction being conducted at a temperature of from 20 to 1 00,C in the presence of 2 to 15 mol.% of aluminium chloride based on the amount of the alkylchloride(s) employed until discontinuation of evolution of hydrogen chloride occurs, followed by separation of the catalyst from the alkylate produced in the reaction, distillation of the said alkylate under vacuum, and collection of the desired fraction with a boiling range of from 220 to 250 C/0.2-0.3 mm Hg.

Thus there is provided a process for producing high-vacuum oils suitably by way of alkylation of condensed and/or non-condensed aromatic hydrocarbons by means of normal secondary alkylchlorides containing 8 to 12 carbon atoms or mixtures thereof, the alkylchloride and condensed and/or non-condensed aromatic hydrocarbon being employed in a molar ratio therebetween of from 2.5:1 to 5:1. The alkylation reaction is conducted at a temperature of from 20 to 1 00 C in the presence of 2 to 15 mol.% of aluminium chloride based on the amount of the alkylchloride employed until liberation of hydrogen chloride ceases, whereafter the catalyst is separated from the alkylate resulting from the reaction.The alkylate is subjected to a vacuum fractionation to collect the desired fraction with a boiling temperature within the range of from 220 to 250"C/0.2-0.3 mm Hg and the preceding fraction is recycled to the alkylation stage.

In order to increase the desired product yield, the fraction with a boiling range of from 170 to 220 C/0.2-0.3 mm Hg is preferably recycled to the alkylation reaction. To increase the yield and purity of the desired product, it is desirable to use naphthalene or biphenyl as the starting feed-stock.

The high-vacuum oils produced by the process according to the present invention may comprise a mixture of di-, tri- and tetralkylnaphthalenes with 8 to 12 carbon atoms in every hydrocarbon chain and ensure a vacuum of 3 X 10-8 mm Hg in unbaked systems without nitrogen traps and 2-5 x 10-9 mm Hg in baked systems without nitrogen traps.

High-vacuum oils produced by the process according to the present invention have certain advantages, one of which resides in the availability and low cost of the starting materials due to the use of alkylchlorides of different molecular weight (C8 to C,2). Alkylchlorides, in turn, can be produced by different methods such as chlorination of kerosene or, which is most preferable, by the addition of hydrogen chloride to readily available a-olefines containing 8 to 12 carbon atoms which are produced inexpensively on a large commercial scale.

Furthermore, high-vacuum oils produced by the process according to the present invention have a low congelation temperature and a relatively high flowability at room temperature and a low proper vapour tension of the order to 10-'0 mm Hg.

The process according to the present invention may be suitably effected in the following manner.

To a condensed or a non-condensed aromatic hydrocarbon there is added 2-15 mol.% of aluminium chloride based on the amount of alkylchloride to be subsequently added and then, under stirring at a temperature of from 20 to 30 C, there is added an alkylchloride containing 8 to 12 carbon atoms or a mixture of such alkylchlorides for a period of two hours. The alkylchloride and hydrocarbon are taken in a molar ratio of from 2.5:1 to 5:1.

After the addition of the total amount of alkylchloride, the mixture is heated to a temperature of from 60 to 1 00 C for one hour. The completion of the reaction is detected by the stoppage of hydrogen chloride evolution. At a temperature of from 50 to 60 C the alkylation products are separated from the liquid complex of aluminium chloride insoluble therein. Afterwards, the alkylation products are subjected to vacuum distillation at a temperature of from 0.1 to 0.5 mm Hg to recover, as the desired product, the fraction with a boiling range of from 220 to 250 C/0.2-0.3 mm Hg.

The yield of the desired product is 25 to 60% by weight. The best yield of the desired product of 50 to 60% by weight is ensured by the use of naphthalene and biphenyl in the alkylation reaction. The resulting high-vacuum oils have a iodine number of from 0.6 to 1. This low iodine value indicates the desired product purity and ensures long operational use. The preceding fraction comprises a mixture o mono- and dialkylnaphthalenes. This mixture may be either used for producing a vacuum of the order of from 10-5 to 10-8 mm Hg, or additionally alkylated to the desired product. Therefore, the yield of the desired product may be increased to 75-80% by weight.

The bottoms comprise a viscous liquid with a light-brown to dark brown colour consisting of a mixture of polyalkylnaphthalenes or polyalkylbiphenyls with a boiling temperature above 250=C/0.2-0.3 mm Hg. The bottoms per se can be used in different industries. Therefore, the process according to the present invention for the production of vacuum oils is substantially waste-free.

To produce high-vacuum oils with the best properties, it is advisable to make use of naphthalene as the condensed aromatic hydrocarbon, while the non-condensed aromatic hydrocarbon should be diphenyl, diphenylmethane or benzene, most preferably diphenyl.

Experiments have shown that the amount of AICI3 necessary for the production of high-quality products depends on the iodine number of the alkylchlorides employed. For high quality alkylchlorides (defined by their iodine number below 1), the amount of aluminium chloride may be reduced by 2-3 times, thus substantially lowering the quantity of the production wastes.

The best results are obtained in the case where alkylchlorides having an iodine number of not more than 1 are employed. It has been experimentally found that the best quality of the highvacuum oils is obtained according to the present invention with the use of alkylchlorides produced by the addition of hydrogen chloride to a-olefines prepared by the Ziegler-Natta method, for example olefines available from Mitsubishi Co. (Japan) or Gulf Oil (USA).

The advantage of the use of alkylchlorides formed upon the addition of hydrogen chloride to olefines is that hydrogen chloride evolving during alkylation can be used directly without purification for the synthesis of alkylchlorides by way of hydrochlorination of the next fraction of olefines. Therefore, hydrogen chloride is utilized in a closed production cycle.

The invention will be further described with reference to the following illustrative Examples.

EXAMPLE 1 Into a 100 I glass reactor (available from '#Simax", Czechoslovakia) prodiced with a stirrer, a coil and a pipe for the removal of evolving hydrogen chloride there were charged 12.8 kg of naphthalene (140 moles) and 1.2 kg (9 moles) of aluminium chloride and alkylchlorides were gradually added thereto under stirring. The reaction mass temperature was 25 C. The evolving hydrogen chloride was directly used in the hydrochlorination of olefines. The addition of alkychlorides was conducted for 1 hour 40 minutes. There were added altogether 56 kg (240 moles) of alkylchlorides including the following alkylchlorides with the content of carbon atoms, per cent by weight, as specified hereinbelow.

C8 3 The average molecular weight C9 6 assumed for the calculations C,O 13 is 200.

C1, 40 C12 23 (chlorine atom is in the second position of the molecular chain).

Furthermore; the alkylchlorides contained 15% by weight of alkane which did not take part in the reaction. The molar ratio of the alkylchlorides to naphthalene was 2.68 and was calculated after taking account of the weight of alkanes (the weight of alkanes was substracted from the total weight of the alkylchlorides charged into the reactor).

After the addition of the total amount of the alkylchlorides the reaction mixture was heated to 1 00 C for one hour. After doing so, the evolution of hydrogen chloride completely stopped.

Then the reaction mixture was allowed to stand for 40 minutes at a temperature within the range of from 80 to 503C (the temperature was slowly decreased due to natural cooling).

The mixture of the resulting alkylnaphthalenes was separated from the complex of aluminium chloride with alkylchlorides. To completely remove the complex of aluminium chloride with alkylchlorides, the mixture of allcylnaphthalenes was stirred with 3 kg of silica gel at a temperature of from 50 to 60 c and the silica gel was then separated by centrifugation.

Alkanes were separated from the reaction product by distillation under a residual pressure of 12 mm Hg The thus-treated alkylnaphthalenes were subjected to vacuum fractionation under a vacuum of from 0.3 to 0.5 mm Hg into three fractions which were collected: Fraction I with a boiling temperature of up to 1 70'C/0.3-0.5 mm Hg; Fraction II with a boiling range of from 170 to 220#C/0.3 mm Hg; Fraction Ill-the desired product with a boiling temperature within the range of from 220 to 250 C/0.3 mm Hg.

The yield of each fraction was as follows: Fraction I - 4 kg; Fraction II - 7 kg; Fraction III - 29 kg; Bottoms - 8 kg.

The yield was calculated after taking account of the weight of alkanes (the weight of alkanes incorporated in the alkylchlorides was substracted from the total weight of the alkylchlorides introduced into the reaction).

Fraction II comprising mono- and alkylnaphthalenes was collected from several operations and additionally alkylated.

Tests of the vacuum performance of the resulting desired product showed that when used in diffusion pumps the resulting vacuum oil ensures the following order of vacuum without the use of nitrogen traps: (a) in unbaked systems~3 X 10-8 mm Hg; (b) in baked systems - 3 X 10-9 mm Hg.

EXAMPLE 2 Into a reactor similar to that described in Example 1 there were charged 41 kg of the combined fraction II after six alkylation operations. 0.7 kg of aluminium chloride was added thereto. The reaction mixture was heated to a temperature of 30 C and 27 kg of alkylchlorides were added thereto under stirring over a time period of one hour.

After the addition of the total amount of the alkylchlorides the mixture was heated to a temperature of 80 C under continuous stirring for one hour. Afterwards, the mixture was treated as described in Example 1 above.

The fraction with a boiling range of from 220 to 250 C was collected during vacuum fractionation.The desired product yield was 43 kg (70% by weight). The yield is calculated in a manner similar to that described in Example 1 above.

The total yield of the desired product taking account of the post-alkylated product was 65% by weight. The iodine number was 0.6 to 1.

EXAMPLE 3 Into a three-neck glass flask provided with a stirrer, a dropping funnel and a gas-outlet tube there were placed 56 g of naphthalene, 40 ml of decane and 3 g of aluminium chloride.

2-Chlorodecane was uniformly added from the dropping funnel at a temperature of 20 C under stirring. There were added 204 g of 2-chlorodecane altogether.

After the addition of the entire amount of 2-chlorodecane, the mixture was heated for 40 minutes to a temperature of 60 C.

Then the reaction mixture was treated in a manner similar to that described in Example 1 above.

The following fractions were collected by vacuum fractionation under a vacuum of 0.3 to 0.5 mm Hg: Fraction I with a boiling point of up to 170rC/0.3-0.5 mm Hg; Fraction II with a boiling range of 170-230 C/0.3 mm Hg; Fraction Ill with a boiling range of 230-250 C/0.3 mm Hg; Bottoms with a boiling point above 250rC/0.3 mm Hg.

The yield of the fractions was as follows: Fraction I - 8 g; Fraction II - 26 g; Fractionlll 169 g; Bottoms - 18 g.

The yield of fraction Ill, the desired product, was 75% by weight.

According to PMR-spectroscopy data, the number of alkyl groups per one molecule of naphthalene in fraction Ill was equal to 2.4.

The vacuum characteristics of the resulting desired product were similar to those of the vacuum oil produced in Example 1.

EXAMPLE 4 Into a three-neck flask provided with a stirrer, a dropping funnel and a gas-vent pipe there were charged 123 g (0.8 mole) of diphenyl and 16 g (0.12 mole) of aluminium chloride.

There were added under stirring over a period of two hours and at a temperature of the reaction mixture of 20'C 420 g (2.1 moles) of alkylchlorides (having a composition similar to that of Example 1 above). After the addition of the entire amount of chloroalkanes the mixture was heated under continuous stirring for one hour at a temperature of 80 C.

Then the reaction mixture was subjected to a treatment following the procedure of Example 1, followed by distillation.

Alkanes were first distilled-off under vacuum; a vacuum of 12 mm Hg was ensured by means of a waterjet pump. The residue was distilled under a vacuum of 0.3-0.5 mm Hg.

The following fractions were thus obtained: Fraction I with a boiling point of up to 180#C/O.3-0.5 mm Hg; Fraction II with a boiling range of 180-220rC/0.3 mm Hg; Fraction Ill with a boiling range of 220-250rC/0.3 mm Hg; Bottoms with a boiling point of above 250'C/0.3 mm Hg.

The yield of the thus-obtained fractions was as follows: Fraction I ~ 35 g; Fraction II - 90 g; Fraction Ill - 215 g; Bottoms - 50 9.

The yield of Fraction Ill. the desired product, was 53% by weight. The iodine number was 0.6-1.

Tests of the vacuum properties of the desired product showed that upon its use in diffusion pumps the following vacuums were obtained without using nitrogen traps: (a) in non-heated systems 2.10-7 mm Hg; (b) in heated systems -- 5.10-9 mm Hg.

With the use of nitrogen traps in a heated system the attained vacuum was 7.10-'0 mm Hg.

EXAMPLE 5 Alkylation of 0.6 mole of naphthalene with 3 moles of 2-chloroctane was conducted under the conditions specified in Example 1 above. For the alkylation use was made of 75.5 g of naphthalene, 438 g of 2-chloroctane and 1.3 g of aluminium chloride. The reaction resulted in a mixture of octylnaphthalenes having an average molecular weight of 550. The yield of the desired product having a boiling temperature of from 220 to 250on/0.3 mm Hg was 250 g (65% by weight). The iodine number was 0.6.

This condensation product consisted of a naphthalene nucleus having, as substituents, 3.75 octyl radicals on average, i.e. it consisted mainly of tetraoctylnaphthalene with contaminating amounts of trioctylnaphthalene. When used in diffusion pumps, the product ensured a vacuum of 10-8 mm Hg in unbaked systems without nitrogen traps.

EXAMPLE 6 Into a reaction vessel provided with a stirrer there were charged 123 g (0.8 mole) of biphenyl and 25 g (0.16 mole) of aluminium chloride.

There were uniformly added for 45 minutes under continuous stirring and at a temperature of 20 to 25 C 420 g of alkylchlorides having the composition specified in Example 1. To complete the reaction, the mixture was heated to a temperature of 80 C for 30 minutes. After cooling and settling for 45 minutes the reaction mixture was separated from a lower layer of the complex of aluminium chloride with alkylchlorides and passed through a thin layer of silica gel.

Under a vacuum of 10-12 mm Hg alkanes were distilled-off from the reaction mixture, while the alkylation products were fractionated under a vacuum of 0.2-0.3 mm Hg.

The following fractions were collected in the fractionation: Fraction I with a boiling point of up to 190 C/0.3 mm Hg; Fraction II with a boiling rang of 190-220 C/0.3 mm Hg; Fraction ill with a boiling range of 220-230 C/0.3 mm Hg; Fraction IV with a boiling range of 230-250 C/0.3 mm Hg.

The yield of the fractions was as follows: Fraction I - 35 g; Fraction II - 65 g; Fraction III - 87 g; Fraction IV - 92 g; Bottoms 50 g.

Fractions Ill and IV comprised the desired product with an iodine number of 0.5. This was a colourless viscous liquid which when used in diffusion pumps ensured a vacuum of 2.10-7 mm Hg in unbaked systems; in baked systems it ensured a vacuum of 5.10-9 mm Hg without nitrogen traps and a vacuum of#7.1O-10 m Hg with nitrogen traps. The congelation point was -41 C.

EXAMPLE 7 In a flask provided with a stirrer there was effected condensation of 134 g (0.8 mole) of diphenylmethane with 400 g (1.8 mole) of alkylchlorides having the composition specified in Example 1 in the presence of 20 g (0.14 mole) of aluminium chloride under the conditions of Example 1. After treatment of the reaction mixture described in Example 1 it was fractionated under a vacuum of 0.2-0.3 mm Hg.

As a result of the fractionation, the following fractions were collected: Fraction I with a boiling point of up to 80'C/0.3 mm Hg; Fraction II with a boiling range of from 180 to 220 C/0.3 mm Hg; Fraction III with a boiling range of 220-250 C/0.3 mm Hg.

The yield of the fractions was as follows: Fraction I - 86 g; Fraction II - 80 g; Fractionlll 76 g; Bottoms - 35 g.

Fraction Ill comprised a high-vacuum oil with an iodine number of 1.3. When used in diffusion pumps, this oil ensured a vacuum of 10-7 mm Hg in unbaked systems which, as a rule, corresponds to a vacuum of 10-9 mm Hg in baked systems. The congelation temperature was -46'C.

EXAMPLE 8 In a flask provided with a stirrer there was effected condensation of 46.8 g (0.6 mole) of benzene with 460 g (2.2 moles) of alkylchlorides prepared from a-olefines with the boiling temperature within the range of from 210 to 240 C in the presence of 20 g of aluminium chloride. The reaction was carried out as described in Example 1 above.

The resulting alkylbenzenes were fractionated under a vacuum of from 0.2 to 0.5 mm Hg. As a result, the following fractions were obtained: Fraction I with a boiling range of from 140 to 195 C/0.2-0.5 mm Hg; Fraction II with a boiling range of 195-215'C/0.3 mm Hg; Fraction III with a boiling range of 220-250 C/0.3 mm Hg.

The fractions were obtained in the following yield: Fraction I - 65 g; Fraction Il - 47 g; Fraction Ill - 66 g.

Fraction Ill is the desired product. When used in diffusion pumps as the working fluid it ensured a vacuum of 3.10-8 in a heated system, without nitrogen traps; with the use of nitrogen traps it ensured a vacuum of 7.10-9 mm Hg. The congelation point of the highvacuum oil was - 52"C.

EXAMPLE 9 The synthesis was effected as described in Example 4, using 77 g of biphenyl, 265 g of 2chlorodecane, 4 g of aluminium chloride and 75 ml of decane.

Decane was distilled-off under vacuum by means of a water-jet pump; the residual pressure was 12 mm Hg.

The following fractions were collected in the vacuum fractionation process: Fraction I with a boiling temperature of up to 180 C/0.3 mm Hg-15 5 g; Fraction II with a boiling range of from 180 to 220 C/0.25 mm Hg-29 g; Fraction Ill with a boiling range of from 220 to 250 C/0.25 mm Hg-218 g; Bottoms with a boiling point above 250 C/0.2 mm Hg-16 g.

The yield of Fraction Ill (the desired product) was 76% by weight. The iodine number of the desired product was 0.6 to 1.0.

EXAMPLE 10 The synthesis was effected as described in Example 4, using 77 g (0.5 mole) of biphenyl, 340 g (2.3 moles) of 2-chloroctane, 10 g (0.075 mole) of aluminium chloride and 75 ml of decane.

Decane was distilled off under vacuum. A vacuum of 12 mm Hg was ensured by means of a water-jet pump.

The following fractions were thus obtained: Fraction I with a boiling point of up to 1 70#C/0.25 mm Hg-23 g; Fraction II with a boiling range of 170-220"C/0.25 mm Hg-55 g; Fraction Ill with a boiling range of 220-250 C/0.25 mm Hug~220 g; Bottoms with a boiling point above 250#C/0.2 mm Hg-1 7 g.

The yield of Fraction Ill was equal to 66%. The average molecular weight was 590.

EXAMPLE ii The synthesis was effected as described in Example 4, using 77 g (0.5 mole) of biphenyl, 255 g (1.25 mole) of 2-chlorodecane, 4 g (0.03 mole) of aluminium chloride and 75 ml of decane.

Decane was distilled off under vacuum. A vacuum of 12 mm Hg was ensured by means of a water-jet pump.

The following fractions were thus obtaind: Fraction I with a boiling point of up to 180to/0.2 mm Hug~17 g; Fraction II with a boiling range of 180-220GC/0.2 mm Hg-32 g; Fraction Ill with a boiling range of 220-2509C/0.2 mm Hg-208 g.

The yield of Fraction III was equal to 72%. The properties of the desired product were similar to those described in Example 4.

Claims (6)

1. A process for producing a high-vacuum oil, comprising effecting alkylation of an aromatic hydrocarbon by means of a normal secondary alkylchloride containing 8 to 12 carbon atoms or a mixture of said chlorides, the said alkylchloride(s) being employed in a molar ratio to the said aromatic hydrocarbon of from 2.5:1 to 5:1; the alkylation reaction being conducted at a temperature of from 20 to 100 C in the presence of 2 to 15 mol.% of aluminium chloride based on the amount of the alkylchloride(s) employed until discontinuation of evolution of hydrogen chloride occurs, followed by separation of the catalyst from the alkylate produced in the reaction, distillation of the said alkylate under vacuum, and collection of the desired fraction with a boiling range of from 220 to 250'C/0.2-0.3 mm Hg.

2. A process as claimed in Claim 1, wherein a remaining fraction with a boiling temperature within the range of from 170 to 220 C/0.2-0.3 mm Hg is recycled to the alkylation stage.

3. A process as claimed in Claim 1 or 2, wherein the said aromatic hydrocarbon comprises at least one condensed and/or non-condensed hydrocarbon.

4. A process as claimed in Claim 3, wherein the condensed aromatic hydrocarbon comprises naphthalene.

5. A process as claimed in Claim 3 or 4, wherein the non-condensed aromatic hydrocarbon comprises biphenyl, diphenylmethane or benzene.

6. A process according to Claim 1 for producing a high-vacuum oil, substantially as herein described in any of the foregoing Examples.