DE1165004B - Process for the stabilization of water-containing, lower glycols to be used as extraction agents for the extraction of organic compounds from their solutions at elevated temperature. - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school Class: C 07 c

German class: 12 ο - 5/03

Number:
File number:
Registration date:
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S66794IVb / 12o
January 26, 1960
March 12, 1964

The extraction of organic compounds from hydrocarbons with the aid of glycols is known.

Examples of compounds used as extractants are diethylene glycol and dipropylene glycol. However, glycol-containing solvents are very sensitive to oxidation and must be handled under certain precautionary measures to avoid decomposition.

Phenothiazine and substituted phenothiazines are particularly effective antioxidants for Extraction liquids containing glycol at high and low temperatures. Liquids containing glycol, which can contain no water or only a small amount of water are used in the extraction of aromatic Hydrocarbons, such as petroleum fractions, are particularly advantageous, but they have the disadvantage that they are very sensitive to oxidation, so that you can only work with them under certain conditions in which an oxidative decomposition is completely or practically completely avoided. In some cases, those for the extraction and / or for the recovery of the aromatics are from the Extraction phase most advantageous temperatures above the temperature at which the glycol in question to oxidation by oxygen, which is unavoidable due to possible leakage and the like. is always present, is still permanent. In these cases it would be of particular advantage to use glycol against To stabilize oxidation and in some cases this significantly increases the economics of the process, since the applicable temperature range can be expanded.

The stabilization of polyglycols is generally known, but it was surprising that phenothiazines are particularly suitable for this purpose. These substances have a better stabilizing effect than the amines that are chemically related to them, such as monoethanolamine or diethylaniline. The same amount of oxygen that was absorbed by the glycol in 42 hours with the addition of 0.5% phenothiazine could be absorbed in less than 1 hour each time with the addition of the same amounts of the above-mentioned amines and under the same conditions. A similar rapid absorption was also observed when no stabilizer was present. However, the phenothiazines to be used according to the invention are also more effective than other, chemically incomparable antioxidants which, like the stabilizers according to US Pat. No. 2,665,312, are phenol derivatives. If you namely under the above-mentioned same conditions process for the stabilization of water-containing, lower, as an extractant for the
Extraction of organic compounds from
their solutions at elevated temperature
using glycols

Applicant:

Shell Research Limited, London

Representative:

Dr.-Ing. F. Wuesthoff, Dipl.-Ing. G. Pulse and

Dipl.-Chem. Dr. rer. nat. E. Frhr. v. Bad luck man,

Patent Attorneys, Munich 9, Schweigerstr. 2

Named as inventor:

Philip James Garner, Hooton, Wirral, Cheshire

(Great Britain)

Claimed priority:

Great Britain January 28, 1959 (No. 3050)

0.7 ° / o of that sold under the trade name Octylformol 185 C «adds the known phenol derivative, the same amount of oxygen was absorbed in 1 hour. On the other hand, this amount of oxygen (under somewhat modified conditions) with an addition of 1.5 per cent of phenothiazine only absorbed in 63 hours. This time was reduced to 32 hours when 0.5% of the phenothiazine was replaced by the last-mentioned antioxidant.

Phenothiazines have already been used as stabilizers, but only for substances that are not related to the glycols to be stabilized according to the invention. There is also a very important difference between the known and the present method. The former deal with the stabilization of highly viscous lubricating oil-like materials, while with the invention it is the glycols customary as solvents and therefore essentially only the lower compounds of this class, about their stabilization from the state of the art not the slightest hint is known. The operating conditions for which the stabilization is necessary are also for both cases are fundamentally different. In one case it is z. B. a lubrication process when present method, however, a solvent extraction at high temperature, wherein im

409 538/514

Solvent system also still water is present, which is known to make the extraction particularly is strongly promoted.

In contrast, the process for stabilizing water-containing, lower ones, as extraction agents for the extraction of organic compounds glycols to be used from their solutions at elevated temperature, according to the invention in that the glycols are substituted with a small amount of phenothiazine and / or one or more Phenothiazines of the general formula

P _n

Pn

where Y is an alkyl group with up to 3 carbon atoms, but the total number of carbon atoms in the substituents does not exceed 12, P is a polar group, m is an integer from 0 to 4, η is an integer from 0 to 1 and m + n is not greater than 4 on a single aromatic ring.

The term "glycol" also refers to polyoxyalkylene glycols and their ethers or esters.

Typical substituted phenothiazines are 2,8-dimethylphenothiazine, 4,7 - dihydroxyphenothiazine, 2-aminophenothiazine, 3 - aminophenothiazine and 2,8-dimethyl-4-aminophenothiazine.

Phenothiazine is preferred, and among the substituted phenothiazines are those alkyl-substituted phenothiazines particularly well.

Phenothiazines and substituted phenothiazines can be used in any amount up to the solubility limit, preferably between 0.05 and 1 percent by weight can be used.

The liquid hydrocarbon mixture can have a wide or narrow boiling range. The invention is particularly used in processes for the separation of aromatic hydrocarbons from catalytically reformed Petroleum, such as hydroformats and platforms, or fractions thereof are used. At such processes the extraction zone is normally at an elevated temperature and at maintained at a pressure high enough to keep the mixture liquid in the extraction zone.

The extraction phase that comes from the glycol solvent and consists of the dissolved aromatic hydrocarbons, is removed from the extraction zone transferred to the extractant recovery zone, which can consist of both a stripping zone and a distillation zone. In the stripping zone is usually operated at a pressure which is slightly lower than that in the extraction zone and at a temperature at which virtually all non-aromatic hydrocarbons, at least one Part of the water that may be present along with a small amount of glycol solvent and aromatic hydrocarbons can be removed from the top of the stripping zone. Of the Major part of the glycol and aromatic hydrocarbons is drawn into the bottom of the stripping zone Brought distillation zone, which usually operates at a pressure which is below that of the stripping zone. Some processes do not use a stripping zone.

The aromatic hydrocarbons are separated from the glycol in the distillation zone. Because of the quite high boiling points must be in the distillation zone when working under atmospheric pressure fairly high soil temperatures are used, e.g. B. 200 ° C, a temperature at which the glycol decomposes extremely quickly even in the presence of air. On the other hand, steam can also be used directly in the bottom, the distillation zone at lower temperatures, z. B. 150 to 160 ° C, are introduced, then a larger amount of water in the recovered Solvent is present. This mixture of recovered solvent and water is returned to the extraction zone, the water then entering the extraction phase and, as already mentioned, is distilled off in the stripping zone. The addition of steam in the Distillation zone and its subsequent removal in the stripping zone makes this process in which is carried out practically under atmospheric pressure in the distillation zone, economically very disadvantageous.

The amount of steam required can of course be achieved by using a sufficiently low one

The reduced pressure in the distillation zone, whereby the process can be carried out at such a low temperature that thermal decomposition of the solvent is not to be feared. Theoretically, the pressure can be reduced to such an extent that the steam can only be fed in at the overflow of the distillation zone. However, these processes with negative pressure have the disadvantage that air can penetrate into the distillation zone through any leakage, whereby the glycol is contaminated by any decomposition products that may be present and corrosion of the materials by the decomposition products is to be feared.
However, the glycol solvents stabilized according to the invention enable a process in which the glycol can be separated from the aromatic hydrocarbons at reduced pressure and temperatures of, for example, 150 ° C. without oxidation of the solvent.

When the raw material to be extracted is a fraction from a catalytic reforming process is, it is preferred to work with a fraction with an ASTM final boiling point of at most 220 ° C.

If reformates are used, the upper boiling point of this fraction should preferably not exceed 160 ° C and advantageously equal to the upper boiling point limit of the fraction of the starting material for the Be reforming process. The lower limit of the boiling range of the starting material should be advantageous be at about 75 ° C or at about 100 ° C.

Advantageous solvents for this process are, for example, diethylene glycol and triethylene glycol and / or dipropylene glycol, of which diethylene glycol is particularly advantageous. The solvent may contain a small amount, up to 15 percent by weight, but advantageously not more than 2% water. However, the use of a dry solvent with a water content is less cheaper than 0.1 percent by weight.

If there is negative pressure in the distillation zone, the volume ratio of the solvent is to the hydrocarbons used advantageously 3: 1

and 20: 1 and in particular between 3: 1 and 8: 1. The ratio of the amount of top product that is returned from the stripping zone to the extraction zone, to the amount of hydrocarbons used is advantageously between 0.2: 1 and 2.5: 1 and in particular between 0.2: 1 and 0.7: 1.

The extraction system can be a multi-stage countercurrent extraction system, e.g. B. with a Column containing packing or sieve plates, or a column with rotating disks or a variety of mixer-separator combinations. The number of theoretical levels should be advantageous be at least five. The hydrocarbons used can also be used in the extraction system intermediate point are introduced. However, in some cases it is preferred to use the starting materials at the end of the extraction system where the extraction phase is taken.

The stream of hydrocarbons and solvent that is overhead in the stripping zone is obtained after the condensation, and after practically all of the water second liquid phase has been separated in the condensation process, returned to the extraction system.

The temperature in the extraction system is preferably between 80 and 170 ° C. Usually it is operated in the stripping zone at a pressure which is lower than that in the extraction system. The top product contains practically all of the water and non-aromatic hydrocarbons present in the Extraction phase are present and in addition a small amount of solvents and aromatic Hydrocarbons.

The bottoms from the stripping zone, which consists mainly of the solvent and the aromatic Hydrocarbons, is advantageously brought into a distillation zone, which at negative pressure, advantageously at about 0.2 to 0.5 atm. Section. is working. Steam can be in the lower TeU of the distillation zone introduced to the temperature required to obtain one of aromatic hydrocarbons practically free solvent is necessary to keep as low as possible. Usually it becomes so the more steam introduced at the lower the negative pressure. The solvent is usually brought in back to the extraction zone. At the same pressure allows the presence of phenothiazine or a substituted phenothiazine in the solvent has a higher working temperature because this reduces the oxidative decomposition at a certain temperature of the solvent is, so that considerably less steam is needed and the economy of the process is considerable is increased.

The progressiveness of the use according to the invention is evident from the following comparative experiment emerge:

Unstabilized diethylene glycol was in contact with iron (Simon-Martin-Stahl) at 150 ° C for 30 hours. held; Using a Fehling's solution, the presence of Aldehydes, i.e. tested by oxidation products of glycol. The evidence was positive.

The experiment was then repeated with a diethylene glycol containing 0.1 percent by weight Phenothiazine was added. In this case, no aldehyde formation was found even after 50 hours will; the same was true for a 24-hour experiment in which air was constantly flowing through the in the ίο same way stabilized glycol passed through became.

Claims (5)

Patent claims: 1. Process for the stabilization of water-containing, lower, as an extractant for the Extraction of organic compounds from their solutions at elevated temperature to be used Glycols, characterized in that the glycols with a small amount of phenothiazine and / or a or more substituted phenothiazines of the general formula where Y is an alkyl group with up to 3 carbon atoms, but the total number of carbon atoms in the substituents does not exceed 12, P is a polar group, m is an integer from 0 to 4, η is an integer from 0 to 1 and m + nan a single aromatic ring is not larger than 4. 2. Use according to claim 1, characterized in that one alkyl-substituted phenothiazines used. 3. Use according to claim 1 or 2, characterized in that a total of 0.05 up to 1 percent by weight of phenothiazine and substituted phenothiazines in the extraction liquid used. 4. Use according to claim 1 to 3, characterized in that one is to be extracted organic compounds reformed gasoline or a fraction thereof is used. 5. Use according to claim 1 to 4, characterized in that there is a glycol with a Water content of up to 15 percent by weight, in particular up to 2 percent by weight, preferably less than 0.1 weight percent is used. Considered publications:
U.S. Patent No. 2,665,312;
British Patent No. 717,725;
Chemisches Zentralblatt, 1951, pp. 3587, 3588;
Industrial and Engineering Chemistry, 42 (1950), pp. 2479 to 2489. 409 538/514 3.64 © Bundesdruckerei Berlin