Modified Catalyst With Structure Type Mtw, A Method For Its Preparation And Its Use In A Process For The Isomerization Of An Aromatic C8 Cut (IFP Energies Nouvelles)

CATEGORY: CATALYST-PARA-XYLENE 
Modified Catalyst With Structure Type Mtw, A Method For Its Preparation And Its Use In A Process For The Isomerization Of An Aromatic C8 Cut (IFP Energies Nouvelles)
United States Patent Application 20150321183
November 12, 2015
Assignee: IFP Energies Nouvelles
Abstract
The invention concerns a catalyst comprising at least one zeolite with structure type MTW, a matrix, at least one metal from group VIII of the periodic classification of the elements, said catalyst having a mesopore volume increased by at least 10% compared with its initial mesopore volume, which is generally in the range 0.55 to 0.75 mL/g, at the end of a treatment with steam at a partial pressure in the range 0.01 to 0.07 MPa and at a temperature in the range 300.degree. C. to 400.degree. C. for at least 0.5 hour. The invention concerns the process for the preparation of said catalyst as well as an isomerization process employing said catalyst.
FIELD OF THE INVENTION
[0001] The present invention relates to a catalyst comprising a zeolite with structure type MTW, modified by a treatment with steam.
[0002] The invention also relates to the preparation of the catalyst of the invention and to the use of said catalyst in a process for the isomerization of aromatic compounds containing 8 carbon atoms per molecule.
[0003] The isomerization process is of particular application to the isomerization of aromatic compounds containing 8 carbon atoms per molecule into para-xylene, and more particularly to the isomerization of ethylbenzene into para-xylene.
PRIOR ART
[0004] Isomerization of the aromatic C8 cut (aromatic compounds containing 8 carbon atoms per molecule) is the principal pathway to the formation of para-xylene, a product which is highly sought-after in the petrochemicals industry; it is primarily used for the manufacture of polyester fibres and films. The aromatic C8 cut obtained from catalytic reforming or steam cracking comprises meta-, para- and ortho-xylene as well as ethylbenzene. The cost of separating out the ethylbenzene by distillation is too high, and so only the para-xylene and possibly ortho-xylene are separated by selective separation over zeolites using various separation processes. The residual C8 cut comprising ethylbenzene is then transformed in an isomerization unit, the aim being to maximize the para-xylene fraction and to transform the ethylbenzene into xylenes or into benzene.
[0005] Xylene isomerization occurs in accordance with a mono-functional acid mechanism, the acid function generally being supplied by a zeolite. In contrast, ethylbenzene transformation requires a bifunctional catalyst having both an acid function and a hydrogenating function. In existing processes, the ethylbenzene is either isomerized into xylenes or dealkylated to form benzene. Thus, the isomerization is said to be either isomerizing or dealkylating.
[0006] The catalysts employed are generally bifunctional catalysts bringing together a zeolitic phase, at least one metal and a binder (also termed the matrix).
[0007] ZSM-12, a zeolite with structure type MTW, is one of the zeolites used for the isomerization of C8 aromatic cuts. These catalysts have been described in particular in patent applications WO 2010/000652 A1 and WO 2012/066012 A1.
[0008] An improvement to zeolitic catalysts for isomerizing isomerization to form xylenes would consist in increasing the ethylbenzene conversion; this step is the most difficult in this transformation. In particular, secondary side reactions such as dismutation and dealkylation of ethylbenzene limit upgrading of this compound into xylenes.
[0009] One pathway to improvement consists of modifying the catalyst using various treatments which can cause changes in the characteristics of the zeolite and/or the binder used. One particular treatment is steam treatment (also known as steaming).
[0010] U.S. Pat. No. 4,784,747 describes catalysts which have undergone steam treatment, which means that the catalytic activity can be increased, in particular for cracking and dewaxing. The best performances were obtained for steam treatment between 200.degree. C. and 500.degree. C.
[0011] Patent EP 034 444 B2 describes catalysts, in particular ZSM-5, which have undergone a steam treatment at a partial pressure of water of less than 100 mbar (1 bar=0.1 MPa) in order to increase their activity for n-hexane cracking.
[0012] The Applicant has discovered that a zeolitic catalyst comprising at least one MTW type zeolite which has undergone a particular treatment in the presence of steam exhibits a substantial improvement in ethylbenzene conversion and approach to thermodynamic equilibrium for para-xylene during its use in a process for the isomerizing isomerization of an aromatic C8 cut comprising at least ethylbenzene.
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