Separation process

Details Separation process Separation process

1995-07-21

1998-04-21

Barts, Samuel

Organic compounds -- part of the class 532-570 series

Organic compounds

Carboxylic acids and salts thereof

C07C 5142

Patent

active

057419272

DESCRIPTION:

BRIEF SUMMARY
This application is a 371 of PCT/GB94/00248 filed Feb. 9, 1994.


FIELD OF THE INVENTION

This invention relates to a separation process, particularly for use in the separation of crystals from a slurry thereof in a mother liquor essentially comprising an impurity-containing solvent from which the crystals have been precipitated in the course of a crystallisation process carried out at elevated pressure.


BACKGROUND OF THE INVENTION

One application of the present invention is in the separation of terephthalic acid crystals from an aqueous mother liquor following the purification of crude terephthalic acid by contacting an aqueous solution thereof with a source of hydrogen under reducing conditions. The purification process may of the type well known in the art; EP-A-498591 for instance may be referred to for details of one such process.
In EP-A-498591, it is recognised that conservation of water used in the purification process is desirable and EP-A-498591 teaches how this may be achieved. The present invention addresses more specific ways in which conservation of water (or other solvent) may be achieved in separation processes involving the separation of crystals from mother liquors especially in circumstances where the slurry of crystals in mother liquor arises under elevated pressure conditions.


SUMMARY OF THE INVENTION

According to the present invention there is provided a process for the separation of crystals from a slurry thereof with an impurity-containing mother liquor, said process comprising: primary separation process to produce a mass containing said crystals and residual mother liquor; wash liquor to reduce the residual mother liquor content of said mass; washed mass in an aqueous medium and transferring the slurry to a lower pressure zone; secondary separation process to recover the crystals and also the aqueous medium employed in step (c); between step (d) and step (c) whereby said recovered aqueous medium is repeatedly used in step (c).
Preferably the aqueous medium used in step (c) is at a lower temperature than the temperature prevailing in said elevated pressure and temperature zone. This eliminates the need to re-heat the aqueous medium to a temperature corresponding to the temperature residing in said elevated pressure and temperature zone. Thus, for example, prior to transfer to the lower pressure zone, the aqueous medium used in step (c) my be at a temperature which is at least 20.degree. C., more preferably at least 50.degree. C., below the temperature prevailing in the elevated pressure zone. However, we do not exclude the possibility of re-heating the aqueous medium to a temperature intermediate the temperatures prevailing in the recirculating flow and in the elevated pressure zone respectively.
According to a particularly preferred feature of the present invention, the primary separation of step (a) and the wash of step (b) are carried out using an integrated separation and washing process such as can be achieved using a belt filter apparatus or pressure drum filter apparatus. Because the separation and washing can be carried out with high efficiency by means of such apparatus, a low level of contamination can be maintained in the recirculating flow of aqueous medium used to reslurry the crystals for transfer from the elevated pressure zone to the lower pressure zone.
The level of contamination in the recirculating flow is conveniently maintained within desired, predetermined limits by taking a purge from the recirculating flow and introducing fresh aqueous medium into the flow.
Where, in step (c), the washed crystals are reslurried using relatively cold aqueous medium, the aqueous medium is conveniently combined with the washed crystals in a vessel in which a pressurised blanket of inert gas such as nitrogen is established.
Preferably the transfer from said elevated pressure and temperature zone to the lower pressure and temperature zone is effected by means of a flash vessel in which flashing off of aqueous medium occurs, the aqueous medium flashed off in this way advanta

REFERENCES:
patent: 2815288 (1957-12-01), Mckay

Affiliated with

Also associated with

Rating

Separation process does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Separation process, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Separation process will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2059068