CA1122553A

CA1122553A - Process for the separation of aromatic compounds from hydrocarbon mixtures

Info

Publication number: CA1122553A
Application number: CA311,125A
Authority: CA
Inventors: Guy Barre; Roland Quillet; Emmanuel Neel
Original assignee: Shell Canada Ltd
Current assignee: Shell Canada Ltd
Priority date: 1977-10-07
Filing date: 1978-09-12
Publication date: 1982-04-27
Also published as: DE2843536C2; DE2843536A1; IT7828461A0; GB2005299A; IT1099766B; BE870877A; JPS6210278B2; NL7810049A; FR2405290B1; FR2405290A1; JPS5461127A; GB2005299B

Abstract

A B S T R A C T
process for the separation of aromatic compounds from a hydrocarbon mixture by contacting said mixture in the liquid phase with a solid absorbent comprising an inorganic porous carrier on which a silver compound has been supported and subsequently separating the absorbed aromatic compounds from the absorbent This process enables oils of great purity, in particular medicinal oils, to be obtained.

Description

~.~Z~53 PROCESS FOR THE SEPARATION OF AROMATIC COMPOU~DS
FRO~ HYDROCARBO~ MIXTURES

The present invention relates to a process for the separation in the liquid phase of aromatic compounds from hydrocarbon mixtures.
Hydrocarbon oils which are to be used in the medical and related fields must meet high purity demands. ~his type of oils, which are often designated as medicinal oils, are used especially in the medical field as liquid paraffins and as constituents of pharmaceutical preparations. In addition, they are used as lubricating oil for food-processing machinery, where there is a risk of the lubricating oil coming into contact with the food.
Certain cosmetic products, such as skin ointments, lotions and sunburn lotions also contain medicinal oils.
Medicinal oils must be substantially free of aromatic com-pounds, and their purity in this respect must meet certain standard specifications, such as those according to the DAB VII test (of the Cerman pharmacopoeia) and the British sulphuric acid test (of the British pharmacopoeia~.
In order to remove aromatic compounds from hydrocarbon mixtures several methods have been described. From U.S. patent specification 2,548,502 it is known to remove unsaturated com-pounds, including aromatic compounds, from hydrocarbon mixturesin the gaseous phase with the aid of silica gel and activated carbon as adsorbents.

~2;~S53 In U.S. patent specification No.,2,754,3l~3 a process is described for the separation of aromatic compounds from non-aromatic compounds in the liquid phase, which is carried out by making use of adsorption. The adsorben-t which is preferably used in said process is silica gel. After the adsorption, a regeneration solvent, for example xylene or toluene, is used to separate the adsorbed aromatic compounds from the adsorbent.
This cycle of adso~ption and regeneration is repeated as long as no deactivation of the silica gel occurs.
In the German "Offenlegungsschrift" (published u~examined patent application) 2,364,333 there is described a process for the purification of slack wax by separating in particular the aromatic compounds therefrom by means of an ion-exchange macro-porous resin, which may contain a metal of Group Ib.
The methods mentioned are not very efficient.
It has now been found that it is possible to separate very efficiently, in the liquid phase~ aromatic compounds from a hydro-carbon mixture by means of adsorption with the aid of a solid adsorbent comprising an inorganic porous carrier on which a silver compound has been supported. It has, moreover, been found that it is possible to regenerate the loaded aasorbent without reducing its capacity for adsorption of aromatic compounds.
Accordingly, the invention relates -to a process for the separation of aromatic compounds from a hydrocarbon mixture which comprises contacting said mixture in the liquid phase with a solid adsorbent comprising an inorganic porous carrier on which a silver compound has been supported, and subsequently separating the adsorbed aromatic compounds from the adsorbent.
As inorganic porous carriers oxidic carriers are very suit-able, such as aluminas, silica-aluminas (amorphous and crystalline) and in particular silica.
The adsorbent according to the invention preferably contains from 10 to 30% by weight of silver. I-t is possible to support the silver in the form of a silver salt, for example silver nitrate, ~z~553 on the inorganic porous carrier, *or'example by impregnating the carrier (e.g., silica gel or alumina gel) with an aqueous solution of silver nitrate. Other methods, such as precipitation of silver salts or the supporting of silver in the vapour phase on a carrier, may also be used. Before using the adsorbent, the silver-containing (e.g., impregnated) carrier is preferably dried and calcined with an oxygen-containing gas at a temperature o~
from 350 to 500C.
The process according to the invention is very conveniently carried out by percolating the hydrocarbon mixture to be purified through a column which contains the inorganic porous carrier on which a silver compound has been supported. The contacting temper-ature is preferably from 70 to 150 C. The conditions are prefer~
ably chosen in such a way that the product obtained contains not 15 more than 0.00170wt of aromatic compounds. When the amount of aromatic compounds in the product obtained after the contact with the adsorbent exceeds the limits set, the contacting of the hydrocarbon mixture to be purified with the adsorbent is dis-continued and the adsorbent is regenerated by removing the aromatic compounds adsorbed thereon.
The aromatic compounds adsorbed on the adsorbent can readily be separated therefrom, for example by percolation with an organic solvent, which preferably comprises polar components.
By this removal of the arom tic compounds the adsorbent is regenerated.
Suitable solvents may comprise aliphatic alcohols, such as isopropyl ~lcohol and normal butyl alcohol, ethers, ketones, such as acetone, methyl ethyl ketone and methyl isobutyl ketone, and esters, such as ethyl acetate or mixtures of ethyl acetate and alkanes, for example a mixture of is~tane and ethyl acetate.
The regeneration is preferably carried out at a temperature of from 50 to 80 C. After the passage of the regeneration solvent, the adsorbent is dried and subsequently calcined by the passage of an oxygen-containing gas at an elevated temperature, prefer-35 ably between 350 and 500 C.

; ' ` : ' ~ ' -.

~ZZ553 Hydrocarbon feeds which are par~icularly suitable to be purified by separating aromatics therefrom according to the process of the present invention, are hydrocarbon mixtures preferably containing not more than 3% by weight of aromatics.
Hydrocarbon mixtures containing not more than 1% by weigh-t of aromatics are preferred in particular.
The process according to the invention is in particular suited for the preparation of medicinal oils from hydrocarbon mixtures which already have been purified to a great extent, but in which the content of aromatic compounds, and in particular polyaromatic compounds, is too high to meet the very stringent purity requirements set for medicinal oils.
Hydrocarbon mixtures from which medicinal oils can be manufactured may be prepared in several ways.
Very conveniently such a hydrocarbon mixture, from which aromatic compounds can very suitably be separated according to the invention, is prepared by hydrocracking and/or hydro-isomer-ization of a petroleum fraction. This conversion is very con-veniently carried out in two stages. In the first stage, a high-boiling hydrocarbon mixture, for example a distillation residue or a heavy fraction obtained by pyrolysis of coal, bituminous shale or tar sand is hydrocracked. Conveniently, use may be made as feed of petroleum fractions which at least partly have a boiling point lying above the boiling rangecf lubricating oils, for example a fraction obtained by vacuum distillation starting from a petroleum residue obtained during distillation at atl~ospheric pressure. Such a fraction has a boiling range lying between 350 and 500 C. Deasphalted residual petroleum fractions are preferred as feed for the hydrocracking.
The liquid product of the first stage of the hydrocracking treatment is dewaxed, if desired after distilling off hydro-carbons having a boiling point below a temperature in the range from 350 to 400 C. In the second stage, the resultant wax under-goes a hydroisomerization treatment. The part of the product - ~ , ~ . :

~- ~553 of the catalytic hydroisomeriga-tion h~ving a boiling point above a temperature in the range from 365 to 425C is dewaxed, yielding a hydrocarbon mixture with a very high viscosity index, of the order of 130 to 155.
For the hydrocracking and hydroisomerization use may be made of catalysts known as such, which, e.g., comprise alumina as a carrier, upon which there have been supported metals of Group VIII, e.g., cobalt and/or nickel and metals of Group VI B, e.g., molybdenum and/or tungsten and/or oxides or sulphides of the said metals, and if desired non-metals, such as fluorine and/or phosphorus and/or boron.
If the aromatic compounds are separated from the afore-mentioned hydrocarbon mixture having a viscosity index from 130 to 155 by means of the process according to the invention, products are obtained which meet the specifications set for medicinal oils.
The process according to the invention will further be elucidated by way of the following ~xamples.
EXAMPLE I
a. Feed:
In order to obtain a suitable aromatic-containing hydro-carbon feed, a residual petroleum fraction of a North A~rican crude, deasph~lted with propane, was subjected to a two-stage hydrocracking treatment. This fraction had the following properties:
speci~ic weight : o.896 viscosity at 100C: ~5 cS
The fraction was subjected to a catalytic hydrocracking treatment under the following reaction conditions:
temperature : 390C
pressure ~: 140 bar (absolute pressure) space velocity : 0.95 kg of oil per hour per litre of hydrogen/oil ratio: 1,520 n~ of H2 per kg catalyst of oil.

~t2;~SS3 Of the liquid product of the hy~rocracking treatment, 39% by weight, representing the fraction of which the boiling point was below 375 C, was separated by fractional distilla-tion.
The fraction of which the boiling point was above 375 C
(60% by weight) was dewaxed using a mixture of methyl ethyl ketone and toluene (in equal volumes), at a temperature o~ -27 C. The solvent/oil ratio was 3:1. During the process, 24 parts by weight of wax were separated from the fraction. The resultant lubricating oil had a viscosity index (VIE~ ASTM-D 2270) o~ 130.
The resultant quantity of this lubricating oil amounted to 32% by weight of the original deasphalted residual petroleum fraction.
The wax released during the dewaxing treatment was then sub-jected to a catalytic hydroisomerization treatment under the following reaction conditions:
temperature : 340C
pressure : 140 bar (absolute pre~sure) space velocity : 0.81 kg of wax per hour per litre of catalyst hydrogenloil ratio: 1,660 nl of ~2 per kg of oil.
From the product of the catalytic hydroisomerization con-version, that fraction having a boiling point b~low 400 C was separated by fractional distillation.
The resultant quantity of product having a boiling point above 400 C amounted to 49.4% by weight of the hydrocracking feed. This oil was dewaxed at -27C with a mixture of methyl ethyl ketone and toluene (in equal volumes), the sol~ent/oil ratio used being 8:1.
The resultant quantity of thus dewaxed lubricating oil amounted to 24.9% by weight ~ the hydrocracking feed.
This lubricating oil had the followillg properties:
viscosity index -(VIE~ ASTM-D 2270) : 150 kinematic viscosity at 100C: 5.97 cS

- ;

-- -, ~ : :

_ ~ Z2553 As regards this product of cata~ytic hydrocracking con-version, ultra-violet spectrometric analysis was -then used to determine what aromatic compounds the reed contained, and in what quantities.
Table I shows the results of this analysis.
TABLE I

aromatics, m.mol./100 g benzenes 0.18 naphthalenes 0.01 biphen~ls and phenanthrenes 0.007 pyrenes 0.008 benzoperylenes coronenes 0.011 In order to gain an insight into the pharmaceutical quality of the ~eed, the sulphuric acid test was carried out according to the test method of the British pharmacopoeia IP 17 and the U.V. absorption test according to the DAB VII test of the German pharmacopoeia.
Table II below shows the results of these tests. It also states the specifications applying to medicinal oils.
TABLE II
DAB VII Test (German pharmacopoeia) Speci~i- Result cations _ . ......................... ~ ~ _ absorption o~ 275 nm ultraviolet rays < o.8 1.75 absorption o~ 295 nm ultraYiolet rays < 0.4 11.96 absorption of 300 nm ultraviolet rays < 0.3 13.44 Sulphuric acid test (British pharmacopoeia) red < 2.5 11 yellow < 6.5 5o .~ .,: : . .

- . . : , :~ZZ553 b. Adsorbent:
The silver-containing adsorbent was prepared as follows.
Starting from an aqueous solution of silver nitrate, silver nitrate was impregnated on the porous silica gel having a specific surface area of 363 m2/g and a pore volume of o.g8 ml/g.
Subsequently, the impregnated silica gel was dried by the passage of a stream of hot nitrogen at a temperature of 120 C.
Then the adsorbent was calcined by the passage of a stream of oxygen at a temperature of 425 C and a space velocity of 20 l/h for two hours. The silver content of the adsorbent prepared ac-cording to the afore-mentioned process was 20%.
c. Adsorption:
The hydrocarbon feed containing aromatics, described above7 was percolated through a column filled with 100 g of adsorbent at a temperature of 70C and a space velocity of one part by volume of oil per part by volume of adsorbent per hour. Then the production of the column, expressed as the ratio between the volume of percolated oil and the volume of adsorbent, was measured. It was found that this ratio could be raised above 25, the volumesof oil leaving the column all corresponding to the specifications applying to medicinal oils. Table III below shows the results of the DAB VII test (absorption of ultra-violet rays) and of the sulphuric acid test for the 10th, 20th and 25th volume respectively. For greater clarity, it also shows the results of the analysis of the feed and the specifications which appl~ to medicinal oils.

: , . ~

-` ~lZZ553 TABLE III' Details vol of DAB VII Test H2S0 adsorbent i 275 nm 295 nm ¦ 300 nm feed _ l _ 11.96 13.44 red - 6.8 l yello~26 i - __ speci- , <o.8 <.4 ~ <0.3 I red < 2.5 fica- ! ! yellow<6.5 tions I I
. .
per- 10 0.20 1 0.115 0.15 red 1.5 colated , yellow 3.0 oil 20 0.30 0.25 0.20 0.45 ' 0.30 0.25 red 2.5 ~i yellow 6.o EXAMPLE Ia By means of a comparative test differing only from that in Example I by the use of non-impregnated silica gel, it was investigated what quantity by volume (in relation to the volume of adsorbent) corresponded to the specification of medicinal oils.
Table IV below shows how disappointing the results are if the adsorbent used is a silica gel not impregnated with silver nitrate. Even by bringing down the ratio to fol~ i-t was no longer possible to meet the specifications according to the DAB VII test.
TABLE IV

Details vol. of feed DAB VII
vol. of adsorbent 275 nm 295 nm 300 nm percolated oil 0.045 0.99 0.88 specifications <o.8 <0.4 <0.3 ~lZZ~53 EXAMPLE Ib By way of compa~ison, a series of adsorption tests were then carried out with an adsorbent consisting of an ion-exhange resin (Amberlyst-15)* charged with silver ions and known from the German "Offenlegungsschrift" 2,364,333. These tests also involve the determination of the maximum quantity by volu~e (in relation to the volume of adsorbent) still corresponding to the specifica-tion. Table V states the results of these tests.

TABLE_V

¦Details vol. of feed DAB VII
~ol. of adsorbent 275 mm 295 mm 300 mm _ percolated oil 7 ~0.30 0.48 0.4 specifications ~0.8 ~0.4 ~0.3 ... .. _ . ... .

From this Table it follows that the maximum ratio is low-er than 7.
EXAMPLE II
In order to investigate to what extent the activity of the adsorbent is influenced by repeated regenerations, 20 re~ener-ation testswere carried out with isopropyl alcohol as regeneration solvent. The space velocity of the regeneration solvent was 1 litre per litre per hour. Each regeneration comprised the passage of three volumes of solvent over one volume of adsorbent. Then the adsorbent was dried by the passage of a stream of air at 70 C, after which the adsorbent was calcined for 2 hours at 425 C by the passage of stream of air for 2 hours. Between the regeneration tests, adsorption was carried out each time by passing 25 volumes of feed over one volume of adsorbent : . ~ - . :

3L~LZZS53 As Table VI shows, the activity of the adsorbent did not diminish after repeated regeneration.

lQ~ -.~;

~: ..
- : :

:: :

~ZZ~53 TABLE VI ' Details DAB VII Test H2SO
275 nm 295 nm 300 nm Before the 1st regeneration 0. 45 0.30 0.25 After the 20th red = 2.4 regeneration 0. 45 0.30 0.25 yellow- 6 Specifications <O.o <0. 4 <0. 3 red =< 2.5 L l yell~ 6.5 EXAMPLE III
The influence o~ the silver content on the activity of the adsorbent was investigated at 70 C for three different adsorbents.
The activity of the adsorbent is expressed here, as in Examples IV and V, as the maximum ratio between the volume of feed and the volume of adsorbent, this maximum being established by the final volume of oil still corresponding to the DAB VII speci-fication. Apart from the variation in adsorbent, all the con-ditions of these tests are the same as those in Example I.
TABLE VII
. Adsorbent activity % by weight vol. of feed o~ silver vol. of adsorbent _ ~ilica gel, l6.5 5 specific surface area: 28.5 15 363 m2/g pore volume: o.98 ml/g 33.0 20 9.5 30 ~lu=ina 10. 4 5 specific surface area:
211 m2/g 19.8 15 pore volume: o.65 ml/g ! 13.0 20 alumina, 123. 7 10 specific surface area: ' 223 m2/g ' 23.1 15 pore volume: o.64 ml/g ¦ 19.4 20 EXAMPLE IV
The influence of the calcination temperature on the same maximum r~tio was investigated by using the test conditions described in Example I. Table VIII below shows the results o~
this investigation.
TABLE VIII
_ _ Adsorbent activity calcination vol. o~ feed temperature, vol. of adsorbent C
silica gel, 29.5 400 specific surface a~ea:
363 m~/g 24.4 450 pore volume: o.98 ml/g 19.9 5 % by weight of Ag:
12.5 15.8 55 EXA~LE V
The influence of the adsorption temperature on the activity was investigated, likewise by using the test conditions described in Example I. Table IX shows the results o~ this investigation.

TABLE IX

Adsorbent activity adsorption temperature, vol. of feed o vol. o~ adsorbent C
alumina 11.2 5o specific surface area:
223 m2/g 26.7 7o i pore volume: o.64 ml/g 31.2 90 % by weight of Ag:
12.5 ~6 6 130 : ' ~':

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE ARE CLAIMED AND DEFINED AS FOLLOWS:

1. A process for the separation of aromatic compounds from a hydrocarbon mixture which comprises contacting said mixture in the liquid phase with a solid adsorbent comprising an inorganic porous carrier on which a silver compound has been supported, and subsequently separating the adsorbed aromatic compounds from the adsorbent.

2. A process as claimed in claim 1, in which the inorganic porous carrier is an oxidic carrier.

3. A process as claimed in claim 2, in which the oxidic carrier is silica.

4. A process as claimed in preceding claim 1, in which the adsorbent contains from 10 to 30% by weight of silver.

5. A process as claimed in claim 1, in which the contacting temperature is from 70 to 150°C.

6. A process as claimed in claim 1, in which after the con-tacting the adsorbed aromatic compounds are separated from the adsorbent with an organic solvent.

7. A process as claimed in claim 6 in which the organic solvent to be used comprises at least one solvent selected from an aliphatic alcohol, an ether, a ketone and an ester.

8. A process as claimed in claim 6 in which the organic solvent is an aliphatic alcohol.

9. A process as claimed in claim 6 in which the organic solvent is an ether.

10. A process as claimed in claim 6 in which the organic solvent is a ketone.

11. A process as claimed in claim 6 in which the organic solvent is an ester.

12. A process as claimed in claim 6 or 7 in which the separation is effected at a temperature of from 50°C to 80°C.

13. A process as claimed in claim 1, in which the hydro-carbon mixture contains not more than 3% by weight of aromatic compounds.

14. A process as claimed in claim 13, in which the hydro-carbon mixture contains not more than 1% by weight of aromatic compounds.

15. A process as claimed in claim 1, in which the hydro-carbon mixture is prepared by hydrocracking a petroleum fraction.

16. A process as claimed in claim 1 in which the hydro carbon mixture is prepared by hydroisomerization of petroleum fraction.

17. A process as claimed in claim 1 in which the hydro-carbon mixture is prepared by both hydroisomerization and hydro-cracking a petroleum fraction.

18. A process as claimed in claim 17, in which the hydro-cracking and hydroisomerization is carried out in two stages;
in the first stage a paraffin-containing oil is obtained by hydro-cracking, which is dewaxed; in the second stage, the paraffin wax obtained is hydroisomerized and the resulting product is dewaxed yielding a hydrocarbon mixture having a viscosity index of the order of 130 to 155.