KR20170117551A - Top Separation Wall Type Distillation Column Technology to Improve Processing of Xylene - Google Patents

Abstract

(TDWC) separating a number of feedstocks to produce xylene mixtures having different compositions from the top of the TDWC. TDWC allows the production of xylene mixtures having different compositions to be separated and fed to different locations within the para-xylene recovery zone. Different feedstocks are fed to either side of the TDWC depending on the composition or isomer ratio of the feedstock. The xylene mixtures produced at the top of both sides of the distillation tower will have different isomer ratios, but these isomer ratios are equal to the isomer ratios of their respective feedstocks.

Description

Top Separation Wall Type Distillation Column Technology to Improve Processing of Xylene

Cross reference of related application

This application claims the benefit of 35 U.S.C. U.S. Provisional Application No. 62 / 117,151, filed Feb. 17, 2015, which is hereby incorporated by reference in its entirety, in accordance with § 119 (e).

Xylene isomers, ortho xylene (OX), meta xylene (MX), and para xylene (PX), and ethyl benzene (EB) are C8 aromatics derived from the reforming process or other petrochemical processes. The refined individual xylene products are used on a large scale as industrial solvents and intermediates in many products. The most important isomer, PX, is used in the production of terephthalic acid (TPA) and dimethyl terephthalate (DMT) for use in fiber, film and polyethylene terephthalate (PET) bottles. High purity (> 99.7%) PX is required for this use. The demand for high purity PX has increased significantly over the past few years to meet the rapidly growing market.

Typical feedstocks for aromatics and para-xylene production are catalytic reformate or pyrolysis gasoline (pygas). Catalytic cracking or flow catalytic cracking (FCC), which includes various modifications such as advanced catalytic cracking (DCC), high strength flow catalytic cracking (HS-FCC), residual flow catalytic cracking (RFCC), is catalytic naphtha or cat naphtha , A light olefin and similar C6 to C10 + aromatic rich streams. Generally, the product distribution in the equilibrium xylene mixture is about 40% MX, 20% PX, 20% OX and 20% EB. These quantities can vary by up to ± 10%.

There are other xylene production techniques that make the xylene mixture content different from conventional equilibrium xylene mixtures. Aromatization is a known technique for producing benzene, toluene and xylene (BTX) using an olefinic hydrocarbon stream. Aromatics take aromatic olefins in the C4-C8 range as raw materials and produce aromatic compounds. By-products of aromatization are hard paraffin and LPG offgas. The product of aromatization has a lower ethylbenzene content than conventional equilibrium xylene mixtures.

It is known to produce xylenes by methylation of toluene and / or benzene, for example methylation of toluene over catalysts using methanol. The feedstock may be a mixture of toluene, benzene, toluene and benzene, pyrolysis gasoline feedstock, or reformed gasoline feedstock. The methylated product has a higher paraxylene content and / or a lower ethylbenzene content than conventional equilibrium xylene mixtures.

Such as benzene / C9-C10 transalkylation, toluene / C9-C10 transalkylation, benzene / toluene / C9-C10 transalkylation using benzene, toluene, C9-C10 aromatics, There are other xylene production techniques well known in the industry such as toluene disproportionation (TDP) and selective toluene disproportionation (STDP), which have higher para-xylene content and / or lower ethylbenzene content than conventional equilibrium xylene mixtures Will produce different product streams.

All of the xylene production techniques described above may produce other products in which the content of C9 or heavier components is different.

In a conventional para-xylene production complex, the C8 + aromatic stream is fed to a C8 / C9 separation column, which is also referred to as a xylene distillation column. The C8 aromatic stream is separated from the xylene distillation column overhead and sent to the downstream para-xylene recovery unit for para-xylene production. If there are multiple sources, the feed C8 + aromatic stream may have different ethylbenzene, para-xylene, non-aromatics and / or C9 + contents. In a conventional para-xylene complex with only one xylene distillation tower, all feedstocks are mixed and then separated to produce a xylene mixture having a single composition. Multiple xylene distillation columns are used when production of multiple xylene mixture streams having different ethylbenzene and / or para-xylene contents is required, adding additional capital costs to the process.

However, it is advantageous to maintain different ethylbenzene and / or para-xylene contents or ethylbenzene / para-xylene ratios present in the feedstock. For example, ethylbenzene is the C8 isomer that is most difficult to remove from the extract in a para-xylene purification unit through adsorption. The concentration of ethylbenzene has a great influence on the number of beds of purification zone required to produce high purity para-xylene. Although it is convenient to be a single feed stream, the mixing of feed streams requires several theoretical steps to reform the separation that existed prior to mixing the feed streams. Similarly, it is advantageous to separate the para-xylene-rich feedstock from the equilibrium feedstock, such as feedstock derived from the STDP feedstock or the optional toluene methylation unit, in a para-xylene refining unit by crystallization. The equilibrium feedstock requires deep cooling at very low temperatures, while the condensed feedstock can be sent for product refinement without the hassle of cooling, thus significantly saving refrigeration energy.

The present system does not disclose a practical process for producing separate xylene mixture streams having different compositions in a single distillation column.

In the present invention, a top divided wall distillation column (TDWC) is disclosed for separating a plurality of feedstocks to produce xylene mixtures having different compositions. The xylene feedstock is produced from the top of the TDWC. By using TDWC, xylene mixtures with different composition and isomer ratios can be separated and fed to different locations within the para-xylene recovery zone.

In various embodiments, a TDWC separation system for producing xylene mixtures from different sources is disclosed. The TDWC system includes a distillation tower having a vertical separation wall that divides the upper portion of the distillation column into two halves. Different feedstock can be fed to either side of the TDWC depending on the composition of the feedstock or the difference in isomer ratio. The xylene mixtures formed at the top from both sides of the TDWC have different compositions, but at the bottom of the TDWC a common composition of heavy products using TDWC is produced. The xylene mixtures comprise an isomer ratio equal to the isomer ratio of their respective feedstocks.

The foregoing has outlined rather broadly the features of this disclosure so that the following detailed description can be better understood. Additional features and advantages of forming the subject matter of this disclosure will be described below.

For a more complete understanding of the present disclosure and advantages thereof, reference is now made to the following description, taken in conjunction with the accompanying drawings, illustrating a specific embodiment of the present disclosure:
1 shows a process schematic diagram according to an embodiment of the present invention for a TDWC design for separating equilibrium xylene feedstock from a para-xylene-rich feedstock.

In the following description, specific details are set forth, such as specific feedstocks, amounts, temperatures, etc., in order to provide a thorough understanding of the embodiments disclosed herein. It will be apparent, however, to one skilled in the art that the present disclosure may be practiced without such specific details. In many instances, the details of such considerations are not necessary to obtain a full understanding of the disclosure, but are omitted within the skill of those skilled in the art.

Reference is now made to Fig. 1, which is a schematic diagram 10 of a process for a TDWC 12 for separating equilibrium xylene feedstocks derived from para-xylene-rich feedstocks. The process scheme of the claimed invention is designed to separate C8A + feedstocks with high ethylbenzene content and STDP C8A + feedstocks (para-xylene-rich feedstocks) with moderate C9 + content and low ethylbenzene and C9 + content.

The process schematic 10 of FIG. 1 includes a TDWC 12. The TDWC 12 includes a first side 16 and a second side 18. The equilibrium feedstock 14 is sent to the first side 16 of the TDWC 12 and the para-xylene-rich feedstock 20 is sent to the second side 18. Vertical separation wall 22 divides the top portion of TDWC 12 into two halves (i.e., into first side 16 and second side 18). In the upper portion of the TDWC 12, the first side 16 is connected to the condensation system 24 and the second side 18 is connected to the condensation system 26. Each condensing system 24 and 26 includes a condenser, a receiver, a reflux pump, and other necessary equipment.

The C8 vapor fraction 25 from the equilibrium feedstock 14 is fed to a condensation system 24 and the C8 vapor fraction 27 from the para-xylene rich feedstock 20 is fed to the condensation system 26 Where the C8 vapor fractions 25 and 27 are condensed, cooled, and collected in the receiver of condensation systems 24 and 26, respectively. The liquid xylene mixture 28 is pumped out of the receiver of the condensation system 24 via a reflux pump and the liquid xylene mixture 30 is pumped out of the receiver of the condensation system 26 via a reflux pump. A portion of the liquid xylene mixture 28 is sent back to the top portion of the first side 16 at reflux and the remainder is recovered to the first xylene mixture 29 for further processing in the first para xylene recovery unit. Similarly, a portion of the liquid xylene mixture 30 is sent back to the top portion of the second side 18 at reflux and the remainder is returned as the second xylene mixture 31 for further processing in the second para- Is recovered. Thus, the first and second xylene mixtures 29 and 31 exiting the top of the TDWC 12 retain the isomer ratio in the C8 fraction originally present in their respective raw materials. The heavy product common composition 32 is produced from the bottom of the TDWC 12 distillation tower.

In some embodiments, an additional feed stream can be directed to either side of the distillation column depending on the inherent isomer ratio of the feedstock. For example, a reduced ethylbenzene xylene mixture derived from a xylene isomerization unit can be sent to the equilibrium feed side. A para-xylene-enriched xylene mixture derived from the optional toluene methylation unit can be sent to the STDP feed side.

In some embodiments of the present invention, the feedstock may be separated according to the content of the non-aromatics or C9 + content.

Feeds having different contents of C9 < + > may be fed at a higher or lower height in the TDWC 12 depending on the source of the feed. Optimization of the height of the feed inlet into the TDWC 12 reduces the energy demand.

An overall aspect of the present invention relates to a method for reducing capital and operating costs in a distillation process using a top separation wall-type distillation column, and a method for reducing the number of equipment for obtaining a desired effect.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the disclosure without departing from the spirit and scope of the invention, and will make various changes and modifications to adapt it to various usages and conditions . The above-described embodiments are illustrative only and should not be taken as limiting the scope of the present disclosure as defined in the following claims.

Claims (16)

A method for preparing two xylene mixtures from a top separating column-type distillation column,
The method comprising:
Supplying a first feedstock into the first side of the top separating column-type distillation column;
Feeding a second feedstock into a second side of the top separating column-type distillation column; And
Separating a first xylene mixture from the first feedstock and a second xylene mixture from the second feedstock through the top separating column type distillation column wherein the composition of the first xylene mixture is the same as that of the second xylene mixture Different from composition;
Wherein the top separating wall type distillation column includes a separating wall extending from the top of the top separating wall type distillation tower toward the bottom of the top separating wall type distillation tower. The method according to claim 1,
Wherein the first feedstock comprises an equilibrium feedstock and the second feedstock comprises a para-xylene-enriched feedstock. The method according to claim 1,
Wherein the first feedstock comprises an equilibrium C8A + feedstock having a high ethylbenzene content and the second feedstock comprises a STDP C8A + feedstock having a moderate C9 + content and a low ethylbenzene and C9 + content. Way. The method according to claim 1,
Wherein the first feedstock and the second feedstock are separated according to ethylbenzene content. The method according to claim 1,
Wherein the first feedstock and the second feedstock are separated according to the para-xylene content. The method according to claim 1,
Wherein the first feedstock and the second feedstock are separated according to an ethylbenzene: para-xylene ratio. The method according to claim 1,
Wherein the first feedstock and the second feedstock are separated according to the non-aromatics content. The method according to claim 1,
Wherein the first feedstock and the second feedstock are separated according to the C9 + content. The method according to claim 1,
Wherein the first feedstock comprises reformed gasoline or pyrolysis gasoline. The method according to claim 1,
Wherein the second feedstock comprises a feedstock derived from an aromatization unit, a transalkylation unit, a xylene isomerization unit or a non-selective toluene methylation unit. The method according to claim 1,
Wherein the first feedstock comprises a feedstock derived from an STDP unit or an optional toluene methylation unit. The method according to claim 1,
Feeding the first xylene mixture to a first condensing system to produce a first condensed xylene mixture and feeding the second xylene mixture to a second condensing system to produce a second condensed xylene mixture Way. 13. The method of claim 12,
Feeding a first portion of the first condensed xylene mixture to a first side of a top separating wall distillation column and feeding a second portion of the first condensed xylene mixture to a first para-xylene recovery unit; And
Feeding a first portion of the second condensed xylene mixture to a second side of the top separating wall distillation column and feeding a second portion of the second condensed xylene mixture to the second para- xylene recovery unit . The method according to claim 1,
The first xylene mixture comprises an isomer ratio equal to the isomer ratio of the first feedstock; Wherein the second xylene mixture comprises an isomer ratio equal to the isomer ratio of the second feedstock. 3. The method of claim 2,
Further comprising feeding a reduced ethylbenzene xylene mixture derived from a xylene isomerization unit to the first side of the top separating wall distillation column. 3. The method of claim 2,
Feeding a para-xylene-enriched mixture derived from a selective toluene methylation unit to the second side of the top separating column-type distillation column.

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