Xylenes Plus process

The Xylene Plus process of ARGO Technology, Inc. (95,96) and the FINA T2BX process (97) also use a fixed-bed catalyst in the vapor phase for transalkylation of toluene to produce xylenes and benzene. The Mobil low temperature disproportionation (LTD) process employs a zeoHte catalyst for transalkylation of toluene in the Hquid phase at 260—315°C in the absence of hydrogen (98). 

Transalkylation processes operating conditions are given in Table 9.6. These conditions are similar to those of normal TDP except for the Xylenes-Plus process from ARCO-Lyondell which operates with a moving bed in absence of hydrogen. 

Fixed-bed reactor (except Xylenes-Plus process moving bed)... 

These processes are the Atlantic Richfield Co. (ARCO) xylene plus process, operated since 1968 in Houston, Texas, and Toyo Rayon s Tatoray process, commercialized with the assistance of UOP. 

The Xylene-Plus process developed by Atlantic Richfield also operates in the gas phase, but at low pressures (2 bar) and without hydrogen, and using Al203/Si02 catalysts. 

Amorphous silica-alumina was the first catalyst used for this disproportionation. The first industrial process using SiCh —AI2O3 was the Xylene —Plus process established by Adantic Richfield Co. ... 

In 1997, UOP announced the PX-Plus process which also uses a selectivated catalyst to convert toluene to para-rich xylenes. Pina commercialized a TDP process known as the (T2PX) process in 1984 (70). It uses a proprietary catalyst to react toluene at 42—48% conversion with selectivities to benzene of 42 wt % and to xylenes of 46 wt %. The xylenes produced are at equiUbrium. Typical commercial operating conditions of 390—495°C, H2 partial pressure of 4.1 Mpa, H2/hydrocarbon molar ratio of 4 1, and LHSV of 1—2/h. Pina s first commercial implementation occurred in 1985 at their Port Arthur refinery. 

Xylenes-plus A catalytic process for isomerizing toluene to a mixture of benzene and xylenes. A silica/alumina catalyst is used in a moving bed. It is unlike the related Tatoray process, in that no hydrogen is required. Developed by Sinclair Research in 1964 and then licensed by Atlantic Richfield. 

There are several commercial processes that produce xylenes via disproportionation or transalkylation. These include UOP s Tatoray and PX-Plus, ARCO s Xylenes Plus, and Mobil s MTDP and STDP. 

APU [Advanced Pygas Upgrading] A catalytic process for upgrading low-value pyrolysis gasoline, converting it to benzene, toluene, and xylenes, plus LPG. Developed by SK Corporation, South Korea, and licensed through Axens. 

After the cmde BTX is formed, by reforming in this case, a heart cut is sent to extraction. Actually, the xylenes and heavier components are often sent to downstream processes without extraction. The toluene produced is converted to ben2ene, a more valuable petrochemical, by mnning it through a hydrodealkylation unit. This catalytic unit operates at 540—810°C with an excess of hydrogen. Another option is to disproportionate toluene or toluene plus aromatics to a mixture of ben2ene and xylenes using a process such as UOP s Tatoray or Mobil s Selective Toluene Disproportionation Process (STDP) (36). 

Displacement-purge forms the basis for most simulated continuous countercurrent systems (see hereafter) such as the UOP Sorbex processes. UOP has licensed close to one hundred Sorbex units for its family of processes Parex to separate p-xylene from C3 aromatics, Molex tor /i-paraffin from branched and cyclic hydrocarbons, Olex for olefins from paraffin, Sarex for fruc tose from dextrose plus polysaccharides, Cymex forp- or m-cymene from cymene isomers, and Cresex for p- or m-cresol from cresol isomers. Toray Industries Aromax process is another for the production of p-xylene [Otani, Chem. Eng., 80(9), 106-107, (1973)]. Illinois Water Treatment [Making Wave.s in Liquid Processing, Illinois Water Treatment Company, IWT Adsep System, Rockford, IL, 6(1), (1984)] and Mitsubishi [Ishikawa, Tanabe, and Usui, U.S. Patent 4,182,633 (1980)] have also commercialized displacement-purge processes for the separation of fructose from dextrose. 

The process consists of a reactor section, continuous catalyst regeneration unit (CCR), and product recovery section. Stacked radial-flow reactors are used to minimize pressure drop and to facilitate catalyst recirculation to and from the CCR. The reactor feed consists solely of LPG plus the recycle of unconverted feed components no hydrogen is recycled. The liquid product contains about 92 wt% benzene, toluene, and xylenes (BTX) (Figure 6-7), with a balance of Cg aromatics and a low nonaromatic content. Therefore, the product could be used directly for the recovery of benzene by fractional distillation (without the extraction step needed in catalytic reforming). 

PX-Plus A process for disproportionating toluene to p-xylene and benzene. Developed by UOP in the 1990s. Competing technologies are Mobil s MSTDP and MTPX. Not commercialized as of 1997. 

The converse reactions dealkylation and hydrodealkylation are practiced extensively to convert available feedstocks into other more desirable (marketable), products. Two such processes are (1) the conversion of toluene or xylene, or the higher-molecular-weight alkyl aromatic compounds, to benzene in the presence of hydrogen and a suitable presence of a dealkylation catalyst and (2) the conversion of toluene in the presence of hydrogen and a fixed bed catalyst to benzene plus mixed xylenes. 

The feed to an aromatics complex is normally a C6+ aromatic naphtha from a catalytic reformer. The feed is split into Cg+ for xylene recovery and C7 for solvent extraction. The extraction unit recovers pure benzene as a product and C7+ aromatics for recycling. A by-product of extraction is a non-aromatic C6+ raffinate stream. The complex contains a catalytic process for disproportionation and transalkylation of toluene and C9+ aromatics, and a catalytic process for isomerization of C8 aromatics. Zeolitic catalysts are used in these processes, and catalyst selectivity is a major performance factor for minimizing ring loss and formation of light and heavy ends. The choice of isomerization catalyst is dependent on whether it is desired to isomerize ethylbenzene plus xylenes to equilibrium or to dealkylate ethylbenzene to benzene while isomerizing the xylenes. Para-selectivity may also be a desired... 

Derivation Ethylene polymerized by Ziegler catalysts at 1-100 atm (15-1500 psi) at from room temperature to 200F. Catalyst is a metal alkyl, e.g., triethylaluminum plus a metallic salt (TiCl4) dissolved in a hydrocarbon solvent. A vapor-phase modification of this process was developed in 1965. Another method uses such metallic catalysts as Cr203at 100-500 psi with solvents such as cyclohexane or xylene. 

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