US-12617739-B2 - Method for producing para-xylene

US12617739B2US 12617739 B2US12617739 B2US 12617739B2US-12617739-B2

Abstract

The method is for producing para-xylene using, as a main raw material, a mixed gas of carbon dioxide or carbon monoxide or both thereof and hydrogen. The method including: a reaction step of bringing a raw material mixed gas including the mixed gas into contact with a reaction catalyst under high temperature and high pressure to cause a reaction, to thereby obtain a product gas mixture containing para-xylene; a separation step of cooling the product gas mixture obtained in the reaction step to condense a high boiling point component, to thereby separate the product gas mixture into a water phase containing a water-soluble component, an oil phase containing a xylene mixture, and a gas phase containing an unreacted gas; and a circulation step of mixing at least part of the gas phase having been separated in the separation step into the raw material mixed gas.

Inventors

Osamu Hirohata
Tadashi Ito
Taichiro Masagaki
Yuria Watanabe

Assignees

CHIYODA CORPORATION

Dates

Publication Date: 20260505
Application Date: 20220323
Priority Date: 20210430

Claims (8)

1 . A method of producing para-xylene using, as a main raw material, a mixed gas of carbon dioxide or carbon monoxide or both thereof and hydrogen, the method comprising: a reaction step of bringing a raw material mixed gas including the mixed gas into contact with a reaction catalyst under high temperature and high pressure to cause a reaction, to thereby obtain a product gas mixture containing para-xylene; a separation step of cooling the product gas mixture obtained in the reaction step to condense a high boiling point component, to thereby separate the product gas mixture into a water phase containing a water-soluble component, an oil phase containing a xylene mixture, and a gas phase containing an unreacted gas; and a circulation step of mixing at least part of the gas phase having been separated in the separation step into the raw material mixed gas, wherein the separation step comprises first separating a gas-liquid mixture obtained by cooling the product gas mixture into a liquid phase and the gas phase, and then separating the liquid phase having been separated into the oil phase and the water phase by a separation method utilizing a difference in specific gravity, and wherein the circulation step comprises purging part of a circulation gas, followed by mixing hydrogen having been separated and recovered from the resultant purge gas, using pressure swing adsorption (PSA) or a hydrogen separation membrane for hydrogen from the purge gas, into the raw material mixed gas.
2 . The method according to claim 1 , wherein the reaction catalyst used in the reaction step is a mixed catalyst including a mixture of: a catalyst containing an oxide of at least one kind of metal selected from chromium, zinc, and copper; and a catalyst containing ZSM-5-based zeolite having a surface coated with a compound containing silicon.
3 . The method according to claim 1 , wherein the reaction step comprises bringing the raw material mixed gas into contact with the reaction catalyst at a reaction temperature of from 250° C. to 600° C. and a reaction pressure of from 1 MPaG to 10 MPaG.
4 . The method according to claim 1 , wherein the circulation step comprises purging part of a circulation gas to effectively utilize the resultant purge gas as a fuel gas.
5 . The method according to claim 1 , wherein the method comprises heat exchanging the raw material mixed gas and the product gas mixture, followed by transferring the raw material mixed gas to the reaction step.
6 . The method according to claim 1 , wherein the method comprises using, as at least part of carbon dioxide forming the raw material mixed gas, carbon dioxide separated from a combustion exhaust gas of a thermal power plant or a heating furnace, carbon dioxide separated in an ammonia production apparatus, an ethylene glycol production apparatus, or a hydrogen production apparatus, carbon dioxide separated from a product gas of a gasification furnace for coal, biomass, or garbage, carbon dioxide separated from a blast furnace of an ironworks, or carbon dioxide separated from air in an atmosphere.
7 . The method according to claim 1 , wherein the method comprises using, as at least part of hydrogen forming the raw material mixed gas, hydrogen generated through electrolysis of water with electric power generated by solar power, wind power, water power, geothermal power, biomass, or nuclear power.
8 . The method according to claim 1 , wherein the method comprises using, as at least part of the raw material mixed gas, a synthesis gas generated from a gasification furnace, an off-gas discharged from a blast furnace of an ironworks, an off-gas separated in a hydrogen production apparatus, a synthesis gas generated through co-electrolysis of water and carbon dioxide, or a synthesis gas generated through a reverse shift reaction between hydrogen and carbon dioxide.

Description

TECHNICAL FIELD The present invention relates to a method of producing para-xylene using, as a main raw material, a mixed gas of carbon dioxide or carbon monoxide and hydrogen. BACKGROUND ART Para-xylene, which is useful as a raw material for a polyester fiber or a polyethylene terephthalate (PET) resin, has hitherto been produced through a reforming reaction of naphtha in a petrochemical complex. However, this method requires fossil (petroleum) resources, and entails emission of carbon dioxide in a large amount in a production process. Meanwhile, as a method of producing para-xylene without use of fossil resources, there has already been a proposal of a method involving using a so-called synthesis gas formed of carbon monoxide and hydrogen as a raw material (Non Patent Literature 1 and Patent Literature 1). This method involves converting the synthesis gas into methanol with, for example, a catalyst having a ZnCr2O4 spinel structure, followed by converting methanol into an aromatic compound containing para-xylene with, for example, a catalyst in which an outer surface of H-ZSM-5 zeolite (proton-type ZSM-5 zeolite) is coated with silicalite-1. Moreover, para-xylene is synthesized from carbon monoxide and hydrogen through a one-stage reaction operation by using those catalysts as a mixture. In addition, there is also a proposal of a method involving synthesizing para-xylene in one stage by using carbon dioxide, which is used instead of carbon monoxide, and hydrogen as raw materials (Patent Literature 2). In the method of Patent Literature 2, while production efficiency of para-xylene is improved by using a chromium oxide catalyst and a catalyst in which H-ZSM-5 zeolite is coated with silicalite-1 as a methanol synthesis catalyst and a para-xylene synthesis catalyst, respectively, para-xylene is synthesized from carbon dioxide and hydrogen through a one-stage reaction operation by using the methanol synthesis catalyst and the para-xylene synthesis catalyst as a mixture. CITATION LIST Patent Literature PTL 1: Japanese Patent Translation Publication No. 2020-535966PTL 2: Japanese Patent Application Laid-Open No. 2019-205969 Non Patent Literature NPL 1: Peipei Zhang et al., Chemical Science, The Royal Society of Chemistry, October 2017, Vol. 8, 7941-7946 SUMMARY OF INVENTION Technical Problem In Example 1 of Patent Literature 2, para-xylene is synthesized at a high yield from a mixed gas of carbon dioxide and hydrogen by using a mixed catalyst of: a catalyst containing chromium oxide; and a catalyst containing H-ZSM-5 zeolite coated with silicalite-1. Meanwhile, a catalyst containing chromium zinc oxide is used instead of the catalyst containing chromium oxide in Comparative Example 1, and a catalyst containing a product in which acid sites of H-ZSM-5 coated with silicalite-1 are partially doped (ion exchanged) with zinc is further used in Comparative Example 2. However, the yield of para-xylene is 7.61% even in Example 1. The yield is higher than 3.42% of Comparative Example 1 and 5.06% of Comparative Example 2, but is not so different from those of Comparative Examples in that a CO2 conversion rate is low. Accordingly, it is required to achieve an increase in yield of para-xylene and a reduction in consumption energy in the whole process including reutilizing an unreacted gas. Solution to Problem According to the present invention, there is provided a method of producing para-xylene using, as a main raw material, a mixed gas of carbon dioxide or carbon monoxide or both thereof and hydrogen, the method including: a reaction step of bringing a raw material mixed gas including the mixed gas into contact with a reaction catalyst under high temperature and high pressure to cause a reaction, to thereby obtain a product gas mixture containing para-xylene; a separation step of cooling the product gas mixture obtained in the reaction step to condense a high boiling point component, to thereby separate the product gas mixture into a water phase containing a water-soluble component, an oil phase containing a xylene mixture, and a gas phase containing an unreacted gas; and a circulation step of mixing at least part of the gas phase having been separated in the separation step into the raw material mixed gas. Thus, the above-mentioned objects can be achieved. Advantageous Effects of Invention According to the method of the present invention, ZSM-5-based zeolite coated with a compound containing silicon (preferably silicalite-1) is used as the catalyst in the reaction step, and hence the ratio of para-xylene in the oil phase having been separated from the product gas mixture in the separation step is increased, and less energy is required for a purification step (distillation, adsorption separation, isomerization, or disproportionation). In addition, the unreacted gas (carbon dioxide, carbon monoxide, and hydrogen), which makes up the majority of (volume of) the gas contained in the gas phase having been separated in the se