Catalyst – solid sorbent – or support therefor: product or process – Zeolite or clay – including gallium analogs – And additional al or si containing component
Reexamination Certificate
1997-01-17
2001-01-23
Dunn, Tom (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Zeolite or clay, including gallium analogs
And additional al or si containing component
C502S071000, C502S077000, C423S705000, C423S713000, C423SDIG002
Reexamination Certificate
active
06177374
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a novel porous crystalline synthetic material comprising oxides of silicon, zinc and aluminium useful as a catalyst for the preparation of liquified petroleum gas (LPG) and high octane aromatics and a process for the preparation of such catalyst.
The catalyst material prepared by the process of the present invention is given the name zinc-aluminosilicate or Zn—ZSM-5 molecular sieve catalyst. Hence, more specifically, the present invention relates to a process for the preparation of a catalyst consisting of Zn—ZSM-5 which is useful for the preparation of LPG and high octane aromatic hydrocarbons such as benzene, toluene, ethyl benzene and xylenes (BTX) from low value, low octane petroleum feed stocks.
BACKGROUND OF THE INVENTION
New gasoline specifications and changing markets have led to large and rapid variations of feed stocks and availability of the gasoline. The key factor to boost the profitability is to take advantage of these variations and produce high demand, high value products such as LPG, hydrogen and aromatics.
In addition, because of the population, many countries in the world are in a peculiar situation with great demand for LPG, which cannot be met by conventional resources such as cracking processes employing naphtha, gas oil and the like. The deficit between demand and production of LPG at the end of Indian 8 th plan (1996-97) is expected to be 2.8 million metric tones per annum which is likely to increase to 5.8 million metric tones per annum at the end of Indian 9 th plan (2001-02). Similarly, deficit between demand and production of motor gasoline at the end of 9 th plan is expected to be 1.5 million metric tonnes per annum. Hence, good amount of foreign exchange has to be spent for meeting the demand of LPG as the demand cannot be met by indigenous resources.
Natural gas condensate (NGC), aromatic extraction raffinate and light naphtha are considered as some of the few non economically viable feed stocks in the petroleum market today. As these feed stocks are being non-reformable by conventional catalytic reforming process, they have been considered only as a fuel for long periods. These feed stocks can be converted into valuable products like LPG and Benzene, Toluene and Xylenes (BTX aromatics), utilising the shape selective features of medium pore zeolite molecular sieve.
The aromatic hydrocarbons can be used as high octane blending feed stocks for the production of high octane gasoline. They are also used as feed stocks for the preparation of chemical and petrochemical products.
Aromatic chemicals constitute about one third of the total organic compounds known today. They are important chemical precursors for the production of detergents and polymers among others.
Hence, there is a need to develop a versatile process of the preparation of a novel catalyst which will be able to process cheaper, sometimes unwanted and variably available feed stocks to produce LPG and high octane aromatics.
Therefore, the present invention relates to a process for the preparation of a novel catalyst consisting of Zn—ZSM-5 molecular sieve useful for the conversion of petroleum feed stocks into value added products such as LPG and high octane hydrocarbons.
PRIOR ART PUBLICATION
An article published in the literature [Ind. Eng. Chem. Process Design Dev., 25,(1986), 151 ] describes a process proposed by Mobil Research and Development for the preparation of aromatics from variety of feed stocks such as pyrolysis gasoline, unsaturated gases from catalytic cracker, praffinic naphtha and LPG. The process describes the use of purely acidic H—ZSM-5 catalyst. Another report (Hydrocarbon processing, September 1989, p-72) describes a process developed jointly by UOP INC and British Petroleum company, based on gallium doped zeolite catalyst. In this process, LPG was converted into BTX aromatics and the process has been demonstrated in a large scale pilot plant of the British Petioleum's Graigemouth Refinery in Scotland. U.S. Pat. No. 5,124,417 dated June 1992 describes the use of Pt—Sn—ZSM-5 Catalyst for the production of mono alkyl aromatics from C
8
n-paraffins containing feed stocks. U.S. Pat. No. 5,026,938 dated Jun. 25, 1991 describes a process for converting gaseous feed stocks containing C
3
-C
5
paraffins into aromatic hydrocarbons by contacting the feed with galliosillicate molecular sieve catalyst.
Zeolite ZSM-5 is a crystalline aluminosillicate whose preparation was first claimed in 1972 and is described in a U.S. Pat. No. 3,702,886. Thre frame work structure is well established and the catalyst is reported to have many catalytic applications. “Silicalite” having a similar zeolite structure constituted by pure crystalline SiO
2
, has been described by E. M. Flanigen [Nature 271(1978), 512]. The highly ordered rigid structure with three dimensional rigid lattice can accommodate MeO
4
tetrahedra. Me being for example Al, Fe, Ga, Ti or B.
Conventionally, Benzene, Toluene and Xylenes (BTX) aromatics are obtained by catalytic reforming process of naphtha. In the catalytic reforming process of naphtha, the catalyst used is Pt/Al
2
O
3
monometallic or Pt—Re/Al
2
O
3
monometallic or Pt—Re/AI
2
O
3
bimetallic catalyst. Although these processes are used all over the world, there are number of limitations in the use of these catalysts for the above mentioned process.
These limitations are:
i) These catalysts are not effective in promoting aromatisation of C
5
hydrocarbons. Hence, it can not be used for the aromatisation of feed stocks like natural gas condensate (NGC), light naphtha or aromatic extraction raffinate, which contains appreciable amount of n-pentane and iso-pentane.
ii) These catalysts are also not very effective in promotion of the aromatisation of straight chain paraffins such as n-hexane and n-heptane. Hence, large amount of straight chain paraffins such as n-hexane and n-heptane present in the feed remain uncoveited.
iii) All catalytic reforming units employing these catalysts require an Organic Chloride additive to provide the proper balance between acid and metal function. The Organic Chloride is broken down during reforming process in to hydrochloric acid, a waste product which is difficult to dispose off and targeted for stricter environmental regulations.
iv) These processes result in the formation of gasoline in the range of 75-95 research octane number and hence require use of tetra ethyl lead to boost the octane number. The use of tetra ethyl lead in gasoline has toxic effects of lead emitted from exhausts and is being banned all over the world including India.
SUMMARY AND OBJECTS OF THE INVENTION
The main objective of the present invention relates to a novel porous crystalline synthetic catalyst having the general formula expressed in the form of oxides: wherein M represents a proton and/or a metallic cation, n is the valency of the cation, x, y and z represent the number of moles Al
2
O
3
, SiO
2
, and ZnO, respectively, Y/x is a number ranging from 5 to 1000 (SiO
2
/Al
2
O
3
molar ratio),and optionally comprising metals such as sodium, potassium, gallium, tin, iron and rhenium.
The preferred catalyst comprising 0.8 wt % of Al (as Al
2
O
3
), 1.7 or 3.3 wt % of Zn (as ZnO) and 97.5 or 95.9 of Si (as SiO
2
) on anhydrous basis.
Another object of the invention is to provide a process for the production of novel Zn—ZSM-5 Catalyst useful for the production of LPG and high octane aromatic hydrocarbons from non economically viable petroleum feed stocks. The catalyst prepared by the process of the present invention can be used for the production of Benzene, Toluene, Xylenes (BTX) aromatics using feed stocks like natural ,as condensate (NGC) and light naphtha. Production of LPG carries significance in view of much demand for LPG in many third world countries.
Zn—ZSM-5 catalyst prepared by the process of the present invention contains Zn, in addition to Al and Si, and possesses MFl structure.
Accordingly, the present invention provides a process for the preparation of a porous cys
Pradhan Ajit Ramchandra
Rao Turaga Sundara Rama Prasada
Ray Nirmalya
Shanker Uma
Suresh Surendranath
Council of Scientific & Industrial Research
Dunn Tom
Morgan & Finnegan , LLP
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