FR2569695A1 - PROCESS FOR THE PURIFICATION OF SULFOLANE USE FROM A PROCESS FOR OBTAINING TERTIO-BUTYLSTYRENE - Google Patents

Abstract

THE INVENTION RELATES TO A PROCESS FOR RECOVERING SULFOLANE. IN A PROCESS FOR THE PRODUCTION OF TERTIO-BUTYLSTYRENE BY OXYDESHYDROGENATION OF TERTIO-BUTYLETHYLBENZENE, SULFOLANE IS RECOVERED WITH A VIEW TO ITS RECYCLING BY EXTRACTION 2 OF AQUEOUS SULFOLANE WITH A HYDROCARBIDE HYDROCARBIDE OR AROMYLBURIDE HYDROCARBIDE HYDROCARBIDE 2 HYDROCARBIDE OR AQUEOUS SULFOLULLANE SULFOLANE. THE REFINATE IS THEN DISTILLED 6 TO RECOVER SULFOLANE CONTAINING ONLY SMALL QUANTITIES OF WATER AND PRACTICALLY FREE OF ORGANIC IMPURITIES. SULFOLANE IS USED AS A SOLVENT IN OBTAINING PURIFIED TERTIO-BUTYLSTYRENE.

Description

The present invention relates in its entirety to

  a solvent recovery process and in particular relates to the recovery of sulfolane used

  in the purification of t-butylstyrene.

  Tertiarybutylstyrene (tBS) is a compound which is advantageously prepared by catalytic oxidationhydrogenation of tert-butylethylbenzene (tBEB). It has many applications, for example as an intermediate chemical compound, as a monomer or comonomer in the production of polymeric materials, etc. Tertiarybutylstyrene has often replaced styrene in some applications because of the interesting physical and chemical properties of the product resulting from such substitution. In addition, there are processes in which styrene is unsuitable, but where

  tert-butylstyrene works well.

  Because tBS belongs to the same family

  as styrene, there are similarities in their chemistry.

  One of the common properties is the tendency of styrenic compounds to polymerize each time they are

  activated by chemical substances or by heat.

  Some of the techniques used for purification

  styrene can be used to purify tBS.

  However, since the boiling point of tBS is about 70 C higher than that of styrene, the tendency of tBS to polymerize is much greater than that of styrene.

  that of styrene in all industrial purification processes.

styrene.

  Some of the differences between styrene and

  tBS come from compounds of the family of dialkenyl-

  benzenes that are present in tBS but not in

  styrene. These crosslinking compounds can polymerize

  by giving a type of polymer that interferes with the operation of the refining equipment. The

  crosslinked polymer tends to accumulate in the

  to resist attempts to dissolve.

  U.S. Patent Application No. 646,266, filed Aug. 31, 1984, discloses a process for separating tBS from a charge of unreacted tBEB, while minimizing the operational problems due to fouling of the equipment. This process involves distillation by extraction under reduced pressure, using sulfolane as a solvent, and removal of sulfolane by dilution with water and separation. Sulfolane containing small amounts of unsaturated and saturated hydrocarbon is then recovered by distillation to remove water and can be recycled.

in the process.

  Similarly, the US patent application

  United States of America N 646 267 filed Aug. 31, 1984 discloses a tBS refining process in which

  the concentrations of the dialkenylbenzenes mentioned above

  above, in particular isopropenylstyrene and butenyl-

  styrene, are reduced to very low values. The process also involves distilling off a feed of tBS with sulfolane under reduced pressure, recovering the refined tBS as overhead product and the sulfolane bottoms product, containing the divinyl impurities, small amounts of tBS as well. other high-boiling hydrocarbons. The sulfolane tails are recycled in the process and preferably at least a portion of these tails is treated by periodic or continuous distillation

  for the removal of impurities in order to prevent their accumu-

  excessively in this loop of the process.

  However, it has been found that even though it is carried out with great care, the distillation of the sulfolane used, whether aqueous or non-aqueous, is not sufficient to sustain prolonged undisturbed operations in recovery and purification. tBS. In fact, after a relatively small number of passages in the circuit, the sulfolane takes on a dark hue and becomes more viscous and the yield of the extractive distillation process in which it is used is not as strong as with new sulfolane . It is therefore an object of the present invention to provide a process for recovering sulfolane

  used in the recovery of tBS.

  The single figure of the accompanying drawing illustrates an embodiment of the method of recovering the

  sulfolane of the present invention.

  According to the present invention, there is provided a process for purifying spent sulfolane from a tert-butylstyrene recovery process,

  wherein the spent sulfolane contains polyurethane impurities

  and other hydrocarbon impurities, which method comprises introducing the spent sulfolane as an aqueous solution into an extraction zone to bring said solution into intimate contact in the extraction zone with a liquid hydrocarbon solvent. , to separate from the solvent an aqueous solution of sulfolane exhausted into polymeric impurities and other hydrocarbon impurities, to distil in a distillation zone the separated sulfolane to remove the water and to collect

  purified sulfolane from the distillation zone.

  Various other features of this

  invention will emerge from the detailed description which

  will follow, made with reference to the attached drawing whose single figure is a schematic representation of the apparatus

  wherein the process of the invention is carried out.

  In a representative operation, the aqueous sulfolane in the conduit 1 may come from a treatment zone (not shown) for recovering tBS from an oxidation-hydrogenation effluent containing also

  tBEB as well as hydrocarbon by-products containing

  mantle of divinyl aromatic impurities. The spent sulfolane contains these compounds as impurities at low concentrations. However, the main impurity is a polymer that has accumulated, coming from the previous treatment zone. Also, spent sulfolane contains water, typically between about 25 and about 75% by weight, used to separate the tBS from the stream of tBS and sulfolane exiting the treatment zone. Alternatively, the stream passing through the conduit 1 may be a stream obtained prior to dilution with water, from a treatment zone in which a stream of tBS is purified to reduce the impurity content.

  divinyl aromatics. Again, such a current

  holds the same type of polymeric and aromatic impurities

  divinyls than those described above.

  Obviously, the stream in the conduit 1 can also be a mixture of effluents coming from the two treatment zones

mentioned above.

  The spent sulfolane is contacted in

  the extraction zone 2 with a hydrocarbon solvent introduced

  3. Suitable solvents are liquid aliphatic or aromatic hydrocarbons such as pentanes, hexanes, heptanes, octanes, etc., or benzene, ethylbenzene, xylene, toluene, tBEB and the like. than others that are liquid under the conditions of extraction. The solvent must

  preferably be aromatic. Extraction is advantageous-

  by a counter-current operation in which a volumetric ratio of the solvent is used

  aqueous sulfolane from about 1:10 to about 10: 1. The ex-

  traction can be performed in a wide range of conditions; however, for practical reasons, the temperature is usually limited to about 20 to about 90 ° C. When desired, the refined product may be further extracted (not shown) similar to that described herein. -above. The extract containing at least a portion of the impurities present in the sulpholane charge used in the duct 1 is withdrawn into the duct 4. The aqueous sulpholane depleted in impurities is introduced via the duct 5 into a

  distillation zone 6 equipped with conventional means

  both a reflux 7 and a reboiler indicated in 8. Water is withdrawn from the top condenser via a conduit 9 and is advantageously returned in the overall process

  recovery of tBS at a point where water is needed.

  to separate the sulpholane from hydrocarbons, by

example of tBS.

  The distillation operating conditions must be chosen so that the temperature of the sulfolane can not rise above 220 ° C and preferably does not exceed 200 ° C. The pressure is regulated by the temperature of the cooling water available

  for the condensation of water collected at the head and

  fluent at the top of the distillation zone.

  The sulfolane stream recovered as tails in line 10 contains negligible amounts of undesired impurities; however, further reduction of these amounts of impurities can be achieved, if desired, by redistillation of the tails. Similarly, if necessary, anhydrous sulfolane can be filtered

  to remove any insoluble matter that may be

  feel. In addition, any residual quantities of water may

  be removed by treatment with desiccants.

  The following example illustrates the invention.

EXAMPLE

  A volume of a used solution of sulfolane containing about 50% by weight of water, about 0.8% by weight of hydrocarbon impurities, mainly under

  the form of tBS, and 0.3% by weight of polymeric

  intimate contact twice in

  an extraction vessel equipped with a stirrer, with

  glass, with a capacity of 380 liters, with a

  half volume of ethylbenzene in each step. The temperature

  After the final separation between the ethylbenzene phase and the aqueous sulfolane phase, the latter is distilled in an apparatus.

  vacuum distillation system equipped with a distillation column

  3 meters, with a diameter of 7.6 cm.

  The operating conditions include a reflux ratio of 1:10, a maximum booster temperature of 170 ° C and a pressure of about 12 kPa. The bottoms product consists of pure sulfolane containing about

0.1% by weight of water.

  Integrating the above purification as a step in a comprehensive recovery process

  tBS resulted in continuing operations

  of the extractive distillation column used to separate the tBS from tBEB

  not reacted in a program lasting about 2 months.

  However, after a small number of repetitions of the operating cycle, when the extraction step was not incorporated in the sulfolane purification, the sulfolane took a dark hue and became viscous, and the distillation column yield extractive has been reduced. By letting operations continue,

  there was strong evidence of a similar risk of clogging

plete of the reboiler.

  It goes without saying that the present invention

  described only for explanatory purposes, but in no way

  tative, and that many modifications can be

  made without departing from its scope.

Claims (10)

  1. Process for purifying spent sulfolane from a process for obtaining tertiary butylstyrene   in which the sulfolane contains polymeric impurities   and other hydrocarbon impurities, characterized in that it comprises: (a) introducing spent sulfolane in the form of an aqueous solution into an extraction zone (2); (b) intimately contacting said solution in the extraction zone (2) with a liquid hydrocarbon solvent; (c) separating from the solvent an aqueous solution of sulfolane depleted in polymeric impurities and other impurities; (d) distilling in a distillation zone (6) the separated sulfolane to remove the overhead water; and (e) to collect purified sulfolane as tails of the distillation zone.   2. The process of claim 1, wherein   characterized in that the sulfolane separated from step (c) is subjected to a second extraction prior to distillation of step (d).   3. The process of claim 1, wherein   in that the liquid hydrocarbon solvent is   an aliphatic hydrocarbon selected from the group consisting of   pentanes, hexanes, heptanes and octa- nes.   4. The process of claim 1, wherein   characterized in that the liquid hydrocarbon is an aromatic hydrocarbon selected from the group consisting of benzene,   ethylbenzene, toluene, xylene and t-butyl- ethylbenzene.   5. The process of claim 1, wherein   characterized in that the volumetric ratio of solvent to aqueous sulfolane is from about 1:10 to about 1. 6. The process of claim 1, wherein   in that the temperature of step (b) is now   in the range of about 20 C to about 90 C.   7. The process of claim 1, wherein   in that the tails of the distillation zone are maintained at a temperature not exceeding about 220 C.   8. The method of claim 7, wherein   in that said temperature is equal to or less than than about 200 C.   9. The process of claim 1 wherein   in that the pressure of the distillation step   (d) is between about 4 kPa and about 20 kPa.   10. The process of claim 1, wherein   characterized in that the water content of the aqueous sulfolane   is between about 25 and about 75% by weight.