Catalyst for selective hydrogenation

Details Catalyst for selective hydrogenation Catalyst for selective hydrogenation

2001-04-30

2003-09-30

Silverman, Stanley S. (Department: 1754)

Catalyst, solid sorbent, or support therefor: product or process

Catalyst or precursor therefor

Metal, metal oxide or metal hydroxide

C502S333000, C502S345000, C585S260000

Reexamination Certificate

active

06627578

ABSTRACT:

The present invention relates to a catalyst for hydrogenation, more particularly, it relates to a catalyst for the selective hydrogenation of alkynes in C
4
cuts. The present invention also relates to a process for the preparation of the said catalyst, its use in the selective hydrogenation and a regeneration method of the said catalyst.
The C
4
cuts produced in petrochemical industry represents a mixture of several alkanes and olefins containing 4 carbon atoms, in which 1,3-butadiene, deemed as one of the industrially valuable component, accounts to about 40-60 wt %, and the alkynes present as impurities, including methyl acetylene (MA), ethyl acetylene (EA) and vinyl acetylene (VA) etc., amounts to 0.5-2.5 wt %. Therefore, there is a need to hydrogenate alkynes in C
4
cuts to obtain 1,3-butadiene in high purity that meets the requirements of polymerization.
One of the methods for removing alkynes is based on catalytically selective hydrogenation of alkynes by means of catalysts in such a way as to convert the alkynes, such as VA, EA, MA etc. into butadiene, butene and butane although the latter form is in a relatively small amount, thus making the C
4
alkynes become valuable. The catalyst for hydrogenation used in such a alkyne-removing method should have high activity and selectivity and thereby can remove alkynes effectively while minimizing the 1,3-butadiene losses. In addition, it is desirable that the catalyst has a good running stability over time with low operation investment.
U.S. Pat. No. 4,101,451, filed on Jan. 19, 1977 and thereafter issued to The Dow Chemical Company, disclosed a process for improving the activity of a promoted copper catalyst suitable for selectively hydrogenating alkynes in liquid streams containing olefins. In the working examples of this parent, use was made of the catalyst in which the salts of Cu, Ni, Co, Cr, Mn or Ag were supported on the supporting material of &agr;-alumina containing Na
2
O.
JP57-185,228 disclosed a process for selective hydrogenation of alkyne compounds. The catalysts comprising Al
2
O
3
as a support, and palladium and copper or palladium and silver as active components were used in its examples to hydrogenate alkynes in C
4
cuts.
It appears that when the catalysts which are widely adopted in the prior art are used in the removal of alkynes from C
4
cuts through selective hydrogenation, problems arise from the impossibility of selective hydrogenation in an efficient way of alkyne-enriched C
4
cuts in which the alkyne content is, for example up to 2 wt % on the one hand, and unlikeliness of complete hydrogenation to obtain satisfactory removal of alkynes for example to the extent of 25 ppm, or even 15 ppm in alkyne content as required in the process specification in the art on the other hand. Therefore, it is necessary to seek for a catalyst which can remove alkynes from alkyne-enriched C
4
cuts through selective hydrogenation steadily and efficiently.
Accordingly, it is an object of the present invention to provide a novel catalyst, which can be used to remove alkynes from alkyne-enriched C
4
cuts through selective hydrogenation with high efficiency, good selectivity, prominent stability and a long life time.
It is another object of the present invention to provide a process for preparing a catalyst, which can be used to remove alkynes from alkyne-enriched C
4
cuts through selective hydrogenation with high efficiency, good selectivity, prominent stability and a long life time.
It is still another object of the present invention to provide a use of the said catalyst in respect of removal of alkyne, from alkyne-enriched C
4
cuts through selective hydrogenation.
It is yet a further object of the present invention to provide a process for regenerating the above-mentioned catalyst.
These and other objects are accomplished by providing in a surprising and unexpected manner a catalyst, comprising 1-30 wt % of copper as a first active component, 0.001-5 wt % of palladium as a second active component, 0.001-6 wt % of at least one metal selected from Ag, Pt, Pb, Mn, Co, Ni, Cr, Bi, Zr and Mo as a cocatalyst, and the balance of at least one support selected from alumina, silica and titania, all the percentage indicated hereinabove and hereinafter are calculated on the basis of total weight of the catalyst except those otherwise designated.
Preferably, the catalyst according to the present invention comprises 3-20 wt % of copper, 0.05-3 wt % of palladium, 0.01-4 wt % of at least one metal selected from Ag, Pt, Pb, Mn, Co, Ni, Cr, Bi, Zr and Mo as a cocatalyst, based on the total weight of the catalyst.
More preferably, the catalyst according to the present invention comprises 3-20 wt % of copper, 0.05-1 wt % of palladium, 0.01-1 wt % of at least one metal selected from Ag, Pt, Pb, Mn, Co, Ni, Cr, Bi, Zr and Mo as a cocatalyst, based on the total weight of the catalyst.
As a variant of the present invention, the weight ratio of Cu/Pd in the final catalyst is in the range of from 20~60.
As a variant of the present invention, the support used in the catalyst of the present invention is optionally treated with alkali metal salts, alkaline earth metal salts of mixtures thereof so as to enhance the catalyst selectivity and lower the surface acidity of the support and thereby control the polymerization of butadiene by reducing the possible buildup of polymers.
Preferably, the said alkali meal is selected from at least one of the group consisting of Li, Na, K, Rb and Cs, and the said alkaline earth metal is selected from at least one of the group consisting of Be, Mg, Ca, Sr and Ba.
More preferably, the said alkali metal is selected from at least one of the group consisting of Li, Na and K, and the said alkaline earth metal is selected from at least one of the group consisting of Dc, Mg and Ca.
Preferably, the amount of said alkali metal salts, alkaline earth metal salts or mixtures thereof expressed in terms of the elementary metal is 0.001-3 wt %, preferably 0.05-0.5 wt %, based on the total weight of the catalyst,
The catalyst according to the present invention has a specific surface area of 100-350 m
2
/g, as determined by means of model BC-
1
surface area measuring instrument.
The catalyst according to the present invention has an average pore diameter of 30-200 Å, as determined by means of Absorption Detector of the type Sorptomatic 1990 (Ex FISONS Corp.) in which N
2
is used as an absorption gas.
Preferably, alumina, titania or silica in the form of bars, strips, platelets, cylindrical granulae, granular powders or spheroidal particle is used as a support in the catalyst of the present invention.
More preferably, alumina, titania or silica in the form of spheroidal particle of &PHgr;2-5 mm is preferably used as a support in the present catalyst.
The present invention further relates to the process for preparing the catalyst according to the present invention, comprising the steps of;
(1) The support-forming substance selected from at least one of alumina, silica or titania is calcined at 200-900° C.;
(2) The support resulting from step (1) is impregnated in any order in a copper nitrate solution and a palladium nitrate, palladium chloride or palladium acetate solution to the extent that the copper content reaches 1-30 wt % and palladium content is 0.001-5 wt %, based on the total weight of the catalyst;
(3) The pH value of the palladium nitrate, palladium chloride or palladium acetate solution used in step (2) is adjusted to 3-6 with aqueous ammonia, sodium bicarbonate or sodium carbonate solutions;
(4) The support obtained from step (2) is calcined at 300-500° C. for 4-10 hours;
(5) The support is impregnated in any order with a solution of salt of at least one metal selected from Ag, Pt Pb, Mn, Co, Ni, Cr, Bi, Zr and Mo as a cocatalyst simultaneously with or independently of the copper salt solution in step (2).
In accordance with a variant of the process according to the present invention, the said support is formed into bars, strips, platelets, cylindrical granulae, granular powders or spheroidal particles,

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