Stable and selective dehydrogenation catalyst and a process...

Details Stable and selective dehydrogenation catalyst and a process... Stable and selective dehydrogenation catalyst and a process...

2001-04-10

2003-10-21

Wood, Elizabeth D. (Department: 1755)

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

Catalyst or precursor therefor

Halogen or compound containing same

C502S224000, C502S227000, C502S229000, C502S230000, C502S231000

Reexamination Certificate

active

06635598

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a stable and selective dehydrogenation catalyst and a process for its preparation. The novel catalyst formulation of the invention consists of a noble metal component, a group IV A component, a rare earth group component, a group III A component, a group VIII component, an alkali component, a halogen component on an alumina support with a specific pore size distribution. The present invention also relates to a process for the production of unsaturated hydrocarbons from saturated hydrocarbons using the novel catalyst of the invention.
BACKGROUND OF THE INVENTION
Dehydrogenation of saturated hydrocarbons or paraffins specifically C2-C20 paraffins, is an important petrochemical process through which a number of useful unsaturated hydrocarbons are manufactured. These unsaturated hydrocarbons are olefin monomers such as ethylene, propylene butenes, butadiene, styrene and straight chain mono olefins of carbon number range C6-C20, which find extensive applications in the production of variety of plastics, synthetic rubber, detergents and a wide range of chemicals/intermediates of high utility. Furthermore, dehydrogenation of naphthenes and paraffins are the most important reactions during catalytic reforming processes, practiced worldwide for the production of aromatics (BTX) and high octane gasoline.
Dehydrogenation of C10-C16 n-paraffins is a reaction of prime importance particularly to the detergent industry for the manufacture of the active ingredients. The dehydrogenation process comprises of a complex series—parallel reaction network involving primary dehydrogenation, accompanied by a number of side chain reactions, like secondary dehydrogenation, aromatization, isomerisation, cracking and coking. The desired product, n-mono olefin, is formed in the first step, i. e. primary dehydrogenation. Selectivity towards n-mono olefins is of paramount importance in the whole process. An additional drawback of prior art processes is the relatively short catalyst life of 4 to 6 weeks due to active metal sintering and coking.
It is known to suppress accompanying reactions in order to maximise selectivity and increase catalyst life by thermodynamically limiting per pass conversion by the application of pressure and adding one of the reaction products, hydrogen. However, the overall performance in terms of activity, selectivity and stability as exhibited by the catalyst that actually dictate the optimum feasibility of this process. Activity can be defined in terms of per pass conversion as the ‘moles of paraffin converted per mole of paraffin fed’, the term selectivity as ‘moles of n-mono olefin formed per mole of paraffin converted’ and the term stability as ‘duration for which economically viable activity and selectivity are maintained during the course of the process’. Hence, it is the nature of the support (non-acidic and highly porous), chemical components employed in making the catalyst and the method of preparation of the catalyst composite with unique physico-chemical properties, which enables it to evince these virtues. Hence, catalyst support, catalyst composition as well methods of catalyst preparation are of vital importance.
Prior art catalyst compositions used for the dehydrogenation of paraffins consist primarily of the following metals or their combinations supported on a suitable porous, high surface area support such as gamma Al
2
O
3
.
1. Noble metal (Pt, Re, Pd, Ir, Au, Os)
2. Noble metal+Group IV A metal (Ge, Sn, Pb)
3. Noble metal+Group IV A metal+Group III A metal (Ga, In, Ti)
4. Noble metal+Other Group VIII metals (Fe, Co, Ni) and/or alloys thereof
5. 3 above+Group III A metal or Group III B metal (Sc, Y, La, Ac) as primary active agents, with Group II B metal (Zn, Cd, Hg) as optional secondary activating agent.
6. Noble metal+Group VA metal (As, Sb, Bi) or VI A element (S, Se, Te).
7. 1, 2, 3, 4, 5, or 6 above+Group VII A element (such as halogen in combined form).
8. 1, 2, 3, 4, 5, 6, or 7 above+Group I A metal or Group II A metal such as alkali or alkaline earth metals.
9. Any of 1 to 8 above+sulphur
The references to Groups are based on the CAS version of the Periodic Table.
U.S. Pat. Nos. 2,479,109; 2,602,772; 2,930,763; 3,531,543; 3,745,112; 3,632,661; 3,909,451; 3,892,657; 4,329,258; 4,486,574; EP-A -0-183861 D1; 4,786,625; 4,608,360; 3,892,657; 4,197,416; 4,078,743; 3,951,868; 4,136,064; 3,939,059; 4,003,957; 4,025,418; 4,179,405; 5,258,567; 5,358,920; 5,667,260; 5,536,695; 5,849,657; 5,912,394; British Patents 1,499,297; Indian Patents 41667; 128185; 136459; 128349; 140805; 145594; 163412; 163513; 166585; 161974; 179524; 179877; 181623; Chinese Patent CN 87101513A describe the use of catalyst formulations and processes for the preparation with such combination of elements for use in dehydrogenation of saturated normal paraffins.
U.S. Pat. Nos. 2,814,599 and 2,914,464 describe catalysts containing one or more of Ga, In, Sc, Y, La, Ti, and Ac as primary activating agents along with the optional addition of one or more of Hg, Zn or Cd as secondary activating agents for improved reforming activity
U.S. Pat. No. 2,930,763 discloses a catalyst composition consisting of Pt 0.1-1.0 weight percent, combined halogen (calculated on elemental basis), 0.1-1.0 weight percent, and alkali metal 0.01-1 weight percent for use in reforming applications in which dehydrogenation is one of the predominant reactions.
U.S. Pat. No. 3,632,661 discloses a catalyst consisting of Pt or Pd 0.1-5% along with Fe 0.01-10% or oxides/alloys thereof as promoters. The catalyst includes optionally Group I B metals as secondary promoters, 0.002-5% or one of Co or Zn 0.1-4% with 0.2-2% weight percent alkali/alkaline earth metals on a near neutral carrier. This method avoids the use of halogenated salts for impregnation and preferably impregnates the promoter prior to the noble metal.
Addition of elements of Group IV A or Group III A are disclosed in the following patents.
U.S. Pat. No. 3,531,543 discloses a catalyst composition for dehydrogenation applications containing Pt, Sn, alkali metal and combined halogen, wherein the alkali metal is added to the support in a first step to yield a support like lithiated Al2O3. The purpose of alkali metal addition is to obtain a relatively neutral support.
U.S. Pat. No. 3,745,112 discloses a catalyst primarily for reforming applications of a similar composition to that disclosed in U.S. Pat. No. 3,531,543 wherein the role of the alkali metal is described as killing of the acidic function of the catalyst. Sn is described as a good promoter.
U.S. Pat. No. 3,909,451 also describes a catalyst of similar composition for dehydrogenation wherein the combined halogen content as calculated on an elemental basis, is less than 0.2 weight percent. Similarly, U.S. Pat. Nos. 4,329,258 and 4,363,721 describe catalysts containing Pt, Sn, and an alkali metal and combined halogen wherein the atomic ratio of alkali metal to Pt is in the range of 0.2 to 10.
U.S. Pat. No. 3,892,657 discloses a catalyst consisting of Pt, In, and one of Ge, Sn, or Pb along with combined halogen, the halogen content calculated on an elemental basis, being variable depending on the application of the catalyst, namely, 0.1 weight percent for dehydrogenation, 3.5 weight percent for reforming and 10 weight percent for isomerisation. In is described as a good promoter when the atomic ratio of In:Pt is 0.1-1:1. A combination of Pt, Sn, In, Cl or Pt and one of Ge, Sn, Pb plus In is described as suitable for reforming reactions while a combination of Pt, In, and alkali or alkaline earth metals is stated to be suitable for dehydrogenation. The combination of Pt, Sn, In, and an alkali/alkaline earth element is not specifically disclosed.
U.S. Pat. No. 3,909,451 teaches the preparation of catalyst composite with platinum, tin and lithium on r-Al2O3 for the function of dehydrogenating of n-paraffins.
U.S. Pat. No. 3,951,868 demonstrates a catalyst composite comprising the support with 0.5wt % of Sn in the form

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