JPWO2020002142A5 - - Google Patents

Description

The stream at the top of the column contains the C8 aromatic isomer and is subsequently delivered to the separation process. This process is usually an adsorption separation step in a pseudo -moving bed.

The extract obtained as a result of the adsorption separation step in the simulated moving bed contains paraxylene. High-purity paraxylene can be obtained by further distilling this extract in an extraction column and then in a toluene column.

The raffinate obtained as a result of the adsorption separation step in the pseudo -moving bed contains high concentrations of metaxylene, orthoxylene and ethylbenzene. This mixture is introduced into the isomerization step through the desorption agent removal step by distillation, so that the xylene (ortho-, meta-, paraxylene) ratio is substantially in thermodynamic equilibrium and the amount of ethylbenzene is reduced. The resulting mixture can be obtained. The mixture is re-delivered to the "xylene column" with the new raw material.

Patent Document 1 describes a method for producing paraxylene from a hydrocarbon raw material. In this method, separation by a pseudo -moving bed is performed in two steps, and isomerization is also performed in two steps. The disadvantage of such a process is that it requires as many as two separation steps with a pseudo -moving bed, resulting in a substantial increase in manufacturing costs.

SMB represents a pseudo -moving floor.

-Step A is a single separation step in the quasi -moving bed, in which zeolite is used as the desorbent and adsorbent. Further, this step is carried out at a temperature of 20 ° C. to 250 ° C. and under a pressure between the bubble pressure of xylene and 2.0 MPa at the operating pressure. Further, in the separation unit in the pseudo moving bed, the volume ratio of the desorbing agent to the feedstock is set to a ratio of 0.4 to 2.5. At this stage, at least three fractions can be obtained.

Separation stage A in the simulated moving floor

The separation step of the raw material is performed in one unit. In this unit, the pseudo -moving floor is operated in at least one separation column. This separation column contains multiple interconnected beds and a desorbent, which is circulated within a closed loop. And three fractions are generated from this unit.

As the adsorbent used in the separation unit in the simulated moving bed, barium-exchanged zeolite X, potassium-exchanged zeolite Y, or barium-potassium-exchanged zeolite Y is preferable.

The desorbing agent used in the separation unit in the pseudo -moving bed is preferably selected from para-diethylbenzene, toluene, para-difluorobenzene or diethylbenzene, and can be used alone or as a mixture.

The volume ratio of the desorbing agent to the feedstock in the separation unit related to the simulated moving bed is 0.4 to 2.5, preferably 0.5 to 2.0, and more preferably 0.5 to 1.5. be.

The separation step A in the simulated moving bed is at a temperature of 90 ° C. to 210 ° C., more preferably 160 ° C. to 200 ° C., and under a pressure of 1.0 MPa to 2.2 MPa, preferably 1.2 MPa to 2.0 MPa. It is preferable to do it in.

The desorbing agent fraction B41 and the desorbing agent-based B42 lacking C8A are recovered at the bottom of each column when the desorbing agent is heavy and at each top when the desorbing agent is light. It is later mixed and returned to the adsorption step A of the pseudo -moving bed via stream B4.

The effluent C1 obtained in step C exhibits concentrations of PX, OX and MX isomers close to thermodynamic equilibrium and is reused in adsorption step A of the pseudo -moving bed.

According to the prior art of FIG. 1b, the C8A cut is supplied to the adsorption step A of the pseudo -moving bed. This pseudo -moving floor is divided into four zones, each containing a desorbing agent. The zone is partitioned by the inlet of the feedstock and the desorbent, and the outlet of the raffinate A2 and the extract A1. This adsorber consists of a 15-tiered bed and contains barium-exchanged zeolite X. The floor distribution is shown below.

Raffinate A2 was supplied to the 25th theoretical stage of distillation columns BC2. This column contains 47 theoretical stages, a capacitor, and a reboiler. The operating pressure was 0.2 MPa and the reflux ratio was 1.4, and this column gave a dichotomy. That is, 420 t / h raffinate B2 was obtained at the top of the column, and the desorbing agent was contained at 25 ppm. Further, at the bottom of the column, a desorbent B42 of 407 t / h was obtained, and 50 ppm of xylene was contained. The raffinate B42 was mixed with the stream B41 and then returned to the pseudo -moving bed after heat exchange to the extent required for adsorption. Then, as shown, Raffinate A2 was separated and purified on a Raffinate column. Riboyl required 80 G cal / h of energy. Raffinate B2 was also sent to the first isomerization step (C).

In carrying out the method of the invention shown in FIG. 2, the C8A cut was sent to the pseudo -moving bed of adsorption step A. This pseudo -moving floor contains a desorbing agent and is divided into 5 zones. The compartment is made up of an inlet for the feedstock and desorption agent (B4) and an outlet for the raffinates A21 and A22. The adsorber consists of an 18-tiered floor, and the floors are distributed as follows.

As a result of collecting raffinates A21 and A22 and adsorbing them on a pseudo -moving bed on each side of zone 3B in the unit A, the following composition was shown.

-At the apex, 420 t / h raffinate B21 was obtained, which contained MX, OX and EB, as well as 25 ppm of desorbent.
-At the bottom, a 407 t / h desorbent B42 was obtained, which contained 50 ppm xylene. After being mixed with the stream B41, B42 was returned to the pseudo -moving bed after undergoing the temperature heat exchange required for adsorption. And, in order to carry out the fractional distillation of raffinates A21 and A22 in the illustrated raffinate column, 74.4 Gcal / h of riboyl energy was required. Raffinate B2 was sent to isomerization stage C.

The following was clearly shown from this example. That is, in the separation step A, an adsorption unit with a pseudo -moving bed is used to obtain a raffinate rich in the desorbent and a raffinate rich in MX, OX and EB, and they are separately introduced into one distillation column. By adopting the combination, separation and purification could be easily performed, and therefore the heat load could be reduced.

Claims (11)

A process for obtaining para-xylene from a feedstock containing xylenes, ethylbenzene and C9+ hydrocarbons comprising:
The method includes the following steps A and B,
- Stage A is a single separation stage in a simulated moving bed, which uses zeolites as desorbent and adsorbent, at a temperature between 20 and 250°C and the xylene bubble pressure at the operating temperature . It is carried out under a pressure of ~2.0 MPa and with a volume ratio of desorbent to feed in the separation unit in a simulated moving bed between 0.4 and 2.5, this step yielding at least three fractions. It is possible,
- one fraction A1 contains a mixture of para-xylene and a desorbent,
the second fractions A21 and A22 contain ethylbenzene (EB), ortho-xylene (OX) and meta-xylene (MX) and desorbents;
Also,
- stage B is the fractionation by distillation of the fractions A21 and A22 resulting from stage A in one distillation column, into which said fractions are introduced separately, each at an independent injection point, Also, at this stage, a fraction B2 containing ethylbenzene, ortho-xylene and meta-xylene and a fraction B42 containing desorbents and lacking aromatic compounds having 8 carbon atoms can be obtained. 2. The process according to claim 1, wherein the distillation column used in step B has 30 to 80 theoretical plates. A process according to claim 1 or 2, wherein the distance between the injection points of said fractions A21 and A22 into the distillation column used in step B is 2 to 15 theoretical plates . Process according to any one of claims 1 to 3, wherein the distillation column used in step B is selected from a 2-cut column and a 3-cut column. A process according to any one of claims 1 to 4, wherein fraction A21 has a lower desorbent content than said fraction A22. Process according to any one of claims 1 to 5, wherein the separation stage A in the simulated moving bed is carried out at a temperature of 90-210°C and under a pressure of 1.0-2.2 MPa. Process according to any one of claims 1 to 6, wherein the separation unit (SMB) used in stage A has 10 to 30 beds . A process according to any one of claims 5 to 7, wherein the desorbent used in step A has a boiling point higher than that of xylene and the fraction A22 is introduced at a lower position than the fraction A21. . Process according to any one of claims 5 to 7 , wherein the desorbent used in step A is a compound with a boiling point lower than that of xylenes, and said fraction A22 is introduced at a position higher than A21. . Process according to any one of claims 1 to 9, comprising a gas phase isomerization stage C of fraction B2 containing ethylbenzene, ortho-xylene and meta-xylene obtained from fractionation stage B. the isomerization stage at a temperature greater than 300 ° C. and at a pressure of less than 4.0 MPa and a space velocity of less than 10.0 h ⁻¹ and a hydrogen-to-hydrocarbon molar ratio of less than 10.0 , and carried out in the presence of a catalyst,
Said catalyst comprises at least one zeolite and at least one metal, and the tubular pores exhibited by the zeolite are defined by rings whose openings have 10 or 12 oxygen atoms (10MR or 12MR), and the metal is VIII 11. The method according to claim 10, which is selected from the group and whose content is 0.1% to 0.3% by weight.