|Title of Invention||
"A PROCESS FOR PREPARING THE NOVEL CATALYST"
|Abstract||This invention is related to a novel catalyst for the dehydrogenaton of n-paraffins c6 to c!6. The catalyst has a nobel metal such as platinum group metal as the active metal component , a promoter metal component selected from tin, germanium and rhenium, at least a first modifier component selected from alkali or alkali earth metals, a support and optionally a second modifier component are selected from group IIIA metals and a halogen component. Further this invention relates to a process for the preparation of this novel catalyst. According to the process, a support is impregnated with a solution of an active metal component, at least a modifier component, a promoter metal component and optionally a modifier component and a halogen component. The impregnated support is dryed and calcined at a temperature of 450 to 600°C. The calcined support is dehalogenated and then redrying the dehalogenated support.|
|Full Text||FIELD OF INVENTION
This invention relates to a catalyst for the dehydrogenation of N-paraffins and to the
process of preparation thereof.
BACKGROUND OF THE INVENTION
In the process of dehydrogenation of hydrocarbons, and in particular of paraffins, the monolefins thus produced are required for production of a number of important chemical compounds like detergents, plastics, synthetic rubber, components for gasoline and pharmaceutical products.
The dehydrogenation of normal paraffins with 6-16 carbon atoms to give corresponding monolefins is of particular importance for production of detergents. Monolefins produced out of dehydrogenation process are used for alkylating aromatic compounds such as, for example benzene, to yield corresponding linear alkyl benzene.
As the dehydrogenation of n-paraffins involves various paralled reactions, the life cycle of the catalyst is relatively short. In order maximize selectively and increase catalyst life span, it is essential to suppress accompanying parallel undesirable reactions by limiting per pass conversion. It is the optimum combination of activity of moles of
paraffins converted per mole of paraffins passed, selectively of moles of n-monolefm formed per mole of paraffin converted and stability or life span of duration for which sustained activity and selectivity are maintained during on stream period or during the course of reaction. Hence besides operating parameters, it is the chemical components employed and the method of preparation of catalytic composite which are ultimately responsible for unique physico-chemical properties of the catalyst which enables to attain the optimum combination of activity, selectivity and stability as mentioned above.
Although pressure and fhiHC ratio are detrimental to conversion, they serve the purpose of limiting conversion and prolonging the life of the catalyst with n-monoencs (n-olefin) as the desired product. Under the reaction conditions a plurality of other reactions viz. secondary dehydrogenation, dehydrocyclisation, skeletal isomerisation, hydrogenolysis, cracking and cooking also occur, resulting in the formation of by products viz. diencs, aromatics, lightends and coke as shown in the reaction scheme below:
For this reason though the reaction is dehydrogenation, a little pressure as well presence of Hydrogen is required for carrying out the reaction.
The catalyst plays a key role in regulating product selectivity )n-monolefins) by minimizing hydrogenolysis, cracking and isomerisation. As regards the reaction in series to dehydrogenation (paraffins to monoene) viz. secondary dehydrogenation (monoenes to diences) and dehydrocyclisation (aromatics formation) and ultimately to coke lay down the catalysts operating conditions is to be regulated in such a manner that paraffin conversion is restricted in order to achieve good product selectivity. However till date a very selective catalyst could not be developed due to aforesaid reasons and the reaction is accompanied by considerable coke lay down leading for rapid catalyst deactivation.
Numerous catalyst composites are already known in the art. US pat no. 2602, 772 discloses addition of oxide of alkali metal or alkaline earth metal or Mg not exceeding 1 wt.% to a pt/AhOa catalyst containing 0.1-8 wt.% combined halogen. The effect of Mg is reportedly leasser coke formation.
US pat no. 2930,763 discloses a catalyst composition of Pt 0.1-1.0 wt.% combined halogen (calculated on cleantal basis) 0.1-1.0 wt.%, and alkali metal 0.1-1.0 wt.% for
use in reforming applications in which dehydrogenation is one of the predominant reactions.
Addition of elements of group IV A or group niA are disclosed in US patent no. 35131,543 which discloses a catalyst composition for dehydrogenation application 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 AhOs. The purpose of alkali metal addition is to obtain a relatively nautral support.
US pat no. 3745112 discloses a catalyst primarily for reforming application of a similar composition to that of US pat 3531.543 wherein the role of alkali metal is described as neutralising the acidic function of the catalyst. Sn is described as a good promoter.
Similarly US pat. 3909451 and US pat. 4329.258 and 4363.721 describe catalysts containing Pt, Sn and alkali metal and combined halogen wherein the atomic ratio of alkali metal to Pt is in the range 0.2 to 10.
US pat no. 3892657 discloses a catalyst consisting of Pt. In and one of Ge, Sn or Pt alongwith combined halogen, the halogen content as calculated on an elemental basis is 0.1 wt% for dehydrogenation application.
US pat. No. 5677260 discloses preparation of novel catalyst composite for use in the dehydrogenation of paraffins to corresponding monolefins, the said composite incorporating by weight basis a predetermined concentration gradient of a noble metal, a metal of group IV A, a metal of group III A, an alkali or alkaline earth metal element, a halogen and a metal of group VIE selected from Fe, Co, Ni on a high surface area mesoporous support and a process for the preparation thereof.
Indian patent no. 145594 describes a catalyst composition consisting of Pt. 0.2-1%, one of Ga, In, Ti, 0.2-1% an alkaline or alkaline earth element 0.2 to 2 wt.% and combined halogen 0.01 to 0.1 wt.%. The patent shows the superiority of such composition over prior art catalysts consisting of Pt/AhOa with alkali or alkaline earth metals with AS or Pb as promoters.
British Patent No. 1499297 reveals a catalyst similar in composition to that disclosed in Indian Patent 145594. The patent however claims that combined halogen content greater than 0.2% and an atomic ratio of alkali metal to pt greater than 10 lends improved activity and selectivity.
Indian patent no. 165513 describes a catalytic composition consisting of pt , one of group IV. A metal selected from Ge, Sn or pb and an alkali or alkaline earth metal in an amount whereby the atomic ratio of this letter metal component to pt is greater than 10, and a combined halogen content exceeding 0.2 wt.%. Such composition is shown to
exhibit better activity and selectivity than prior art catalysts with halogen content of less than 0.2 wt.%.
Indian patent no. 166585 discloses use of a combination of alkali and alkaline earth metals, K & Li to a catalyst which otherwise is similar in other composition to that disclosed in Indian patent no. 165513.
Indian patent specification no. 161974 discloses a catalyst for dehydrogenation application consisting of Pt, Sn, In an alkali or alkaline earth component and combined halogen, wherein the atomic ratio of In: Pt is greater than 1. The support in preferably an Sn-AhOs support. The patent discloses the promoting action of In.
US patent no. 3632661 discloses a catalyst consisting of pt or pd 0.1-5% alongwith 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% wt.% alkali/alkaline earth metals on a near neutral carrier. The preparation do not use halogenated salts for impregnation and preferably impregnates the promoter prior to the noble metal incorporation.
US patent nos. 2814599 & 2914464 describe catalysts containing one or more of Ga, In, So, Y, La, Ti & Ac as primary activitating agents along with optional addition of one or more of Hg, Zn or Cd as secondary activating agents for improved reforming activity.
US Patent No. 5849657 discloses a catalyst containing Mg as an additional modifier responsible for higher stability of the catalyst.
OBJECTS OF THE INVENTION
An object of this invention is to provide a novel catalyst for the dehydrogenation of n-paraffins.
Further object of this invention is to provide novel catalyst for the dehydrogenation of n-paraffins having high activity and stability.
Still further object of this invention is to propose a process for the preparation of the novel catalyst for the dehydrogenation of n-paraffins.
Another object of this invention is to propose a process of dehydrogenation n-paraffins using the novel catalyst of the present invention.
SUMMARY OF THE INVENTION
According to this invention there is provided a novel catalyst for the dehydrogenation of n-paraffins c6 to c!6 comprising a nobel metal such as platinum group metal as the active metal component, promoter metal component selected from tin, germanium and rhenium at least a first modifier component selected from alkali or alkali earth metals a support and optionally a second modifier component selected from group niA metals and a halogen component.
In accordance with this invention there is provided a catalyst for the dehydration of C6 to V16 paraffins comprising on an inorganic support 0.01 to 5 wt. % of atleast one nobel metal such as platinum 0.01 too 5 wt.% of atleast one promoter metal selected from the elements tin, germanium and lead, atleast one modifier component selected from the group consisting of alkali or alkali earth metals an optionally upto 5 wt.% of a second modifier component selected from group IIIA metals like gallium, indium and thallium and a halogen component.
Further, according to this invention there is provided a process of preparing the novel catalyst comprising impregnating the support with a solution of the active metal component, the promoter metal component, a modifier component and the halogen component drying the said impregnated support, calcining said support at a temperature between 400 to 600°C, dehalogenating the calcined support to Dehydrogenation of n-paraffins may be carried out in the presence of the novel catalyst of the present invention under dehydro-genation conditions in a fixed bed, a fluidized bed or in a moving bed. However, the fixed bed catalyst system is most preferred due to a number of reasons such as flexibility of operations and also for no make up catalyst or catalyst separation from products and unconverted reactants are required. In fixed bed, the n—paraffins to be hydrogenated is first preheated to the required reaction temperature and then passed over the
fixed bed catalyst. Paraffins are dehydrogenated in the vapour
o phase. The temperatures are usually in the range of 300 to 650 C.
The following examples are provided to further illustrate the present invention and are not to be conferred as limiting thereof . Example - I - Comparison Catalyst A
For comparisons sake with the catalysts of present invention, a conventional dehydrogenation catalyst A different from the invention was prepared.
For this 100 gms. of spherical alumina supper - 1 as described
thus impregnated was dried at 150 C and finally calcined in a
o programmed manner at 550 C for 3 hrs.. Thereafter, the catalyst
was impregnated with an aqueous solution of LiNO . The catalyst
st was again oven dried and calcined in a similar manner as in 1
step (after impregnation with Pt + Sn complex).
The catalyst composite was then subjected to dehalogenation
treatent. This was done at 70 C by washing with DM water containing 154 ammonium nitrate for two and a half hours followed
o with washing with DM water only at 60 C for one and a half hours.
The dehalogenated material is then dried and calcined when it is
ready for use in dehydrogenation reaction.
The composition of the catalyst thus prepared was : Pt - 0.3854;
Sn - 0.4554? Li - 0.5854 8 mono olefin selectivity of 8954 only. The yield was about 10.954 on
the average (see Table - 1 & Fig.l).
The active elements Pt and promoter Sn of this formulation as per
Scanning Electron Microscopy (SEM) were found to be surface
impregnated. On the other hand, the modifier element Li was found
to be uniformly impregnated - Fig.2.
If may be emphasized that scanning by electron microscopy is
useful for gauzing relative distribution profile of impregnated
metallic across the radius of the spheroidal catalyst in relation
to alumina level only.
Example - II - Catalyst composite of formulation B of the present invention
Support - 2 in which Sn is incorporated in Sol stage preparation of the support was used. In the first stage Ca as Ca (NO3)2 was impregnated in the support instead of Li & Pt as PtHiClr, in aqueous Hcl amounting to 1% Cl in 2nd stage. After each stage drying and calcination operations were carried out as described in EX-1I (formulation A) followed with dehalogenation and redrying to get the finished catalyst.
The composition of the catalyst composite thus obtained was Pt - 0.39%; Sn - 0.42%; Ca -0.75%; Cl-0.079%.
This catalyst exhibits a mono olefin selectivity of 93 - 94%. The results are presented in iuble l&Mg. I.
Jt appears that incorporation of Sn alongwith support preparation increases selectivity. Further, incorporation of alkaline earth metal Ca instead of alkali metal Li may be responsible for enhanced stability.
Similar Scanning Microscopy Examination of this catalyst composite of the present invention shows that all metallic components viz Pt, Sn & Ca are uniformly distributed in the catalyst pill in contrast to formulation A - see fig -3.
Example-111 - Formulation C
This catalyst composite was prepared with support 2 viz in which Sn was included in Sol Stage of carrier preparation by simultaneous impregnation of the support with a common solution containing all metallic components except Sn. Thus 100 gms. of support was impregnated with 140 ml. of an aqueous solution of HjPtClg + 3 wt.% Hcl + 2.8 gms. of Ca (NO3>2, 4 HiO. After impregnation the catalyst precursor was dried, calcined and dehalogenated as described in comparison example - 1. This catalyst C, prepared by one stage impregnation has good yield combined with exceptionally long term stability as can be seen from fig - 1 and table -1.
The concentration of components in this catalyst composite was Pt - 0.396; Sn - 0.45%; Ca - 0.82%; Cl-0.082%.
Like formulation B, Scanning microscopy pattern shows all elements to be uniformly distributed -seefig-4.
Example- IV - Formulation I)
A further catalyst composite D was prepared with support - 1 (no component incorporated in support preparative stage) was prepared in the same manner as Example-Ill. Thus apart from Pt & Ca, Sn was incorporated in the common solution as SnCb, 2HzO + 3% Hcl.
The average olefin content was found to be less than formulation C (Ex. - III) and also stability was found to be much less than formulation - C,2oDays as against 28 days for formulation C - fig - 1 & Table - 1.
Scanning electron microscopic examination of shows metallic component Sn to be surface impregnated only similar to comparison formulation - A but contrast to formulation - B & C wherein it is observed to be uniformly distributed.
Example - IV - Formulation E
As per a number of patents Indium was used as one of the modifiers (as described under Introduction & Background). It is believed that Indium contributes to the stability of the catalyst. Accordingly a preparation was made in the same way as in Example - III but also with Indium. Thus the aqueous solution used for impregnation besides Pt & Ca also contained 0.98 gms. of In (NO})} so as to have 0.38% Indium in the final catalyst. When compared to formulation A & D, Indium incorporations enhances the stability with little lower yield and the stability is comparable to that of formulation C. However comparative test with formulations B & C indicates that good stability can also be achieved without incorporation of Indium and therefore inclusion of Indium is not a must for imparting enhanced stability.
Comparison with Example - 111 - Effect of higher B.D. - Formulation F
A Comparison catalyst F based on support 5. which ad bulk density of 0.58, PV of 0.66 ml/gm. 100 gms of support were impregnated with H2 Pt C16 + 3% HC1 and CaNOa aqueous solution. The quantities of active component and modifiers were so chosen so as to have almost half wt% of components in Example 3 formulation C. Subsequent procedures were same as in Example -3
The lower Pt content of the catalyst as compared with other examples was amply compensated for by Us higher B.D. Accordingly the amount of catafytically active platinum in each of the application examples listed in this patent here was identical. With this formulation temperature was higher and olefin content low being only 5.1% against 11 -11.5% on the average. Even an increase in temperature to around 485° C did not reflect any improvement.
The poor results for this catalyst is attributed to its low porosity which makes access of the reactants to cataryticalry active components very different.
Comparison with Example 3 : Effect of chloride content
The alumina support used was same as 2. (Sn during preparative stage of support) aril single step impregnation method wherein the solution impregnation was a mixluic of solution of aU active elements.
Formulations G, H, I, J, K, L were made when the factor varied was the quantity of acid anion Cl in the impregnating solution. The factor was varied by addition of extra amount of HCl acid where reqd. to maintain high Cl concentration. The concentration of the anion in the impregnating solution were varied in the order 1, 2, 3, 5 and 8. It was observed that the minimum/optimum concentration Cl content required in impregnating solution is 3 - 5% whereby the active components are distributed uniformly. It is also seen from formulations A & B that the impregnating solution containing less percentage of HCl show lower % dispersion of pt then subsequent formulations C, D & E (containing 3% HCl). Uniform distribution of Sn required larger Cl content which however can be taken care of by cogelling Sn in the support. Moreover a larger chloride content exceeding 5% will require
long hours of washing with DJf water. It is seen from the preparations indicated in this patent that after impregnation with 3-4% HC1, drying and calcination, chloride can be brought down to £ 0.1 % level by washing with an aqueous solution of a weak base viz around 1% ammonium nitrate solution for .1-3 (ITS. at around 70° followed with 2 hrs. washing with DM water at 60° C.
Effect of residual acidic anion content in finished catalyst
Effect of residual acidic anion content in the formulations are essentially same as that of Example - 3 when following the same method by washing to a lesser extent a fonnulation K was prepared having 0.28% Cl as against 0.08% of formulation C. The results (see fig. 3) clearly show an inverse relation between stability and chloride content.
All catalyst reduced in a stream of H2 at 460°C for 3 hrs.
10 CC of catalyst volume charged in a reactor. The reactor was maintained atPSeudo Isothermal conditions at any temp with the help of P 1 D temp controllers.
The initial temp of 450°C was selected as most of catalyst compositions yielded an define content around 11% in the product «*Mth paraffin conversion level of 13.0 to 13.5% per pass. Since the catalyst deactivates, the temp is required to be raised at regular intervals during the course of the test to maintain the yield. For all testing final temperature was fixed at 500°C to maintain the initial yield % obtained at 450°C
The results obtained are as below:-
10.85% for 23 days
Brief Description of Table & Drawings.
Table-1 shows relative efficacies of Catalyst composites in terms of yields & days of stream & inferences thereof as per testing carried out.
Yield = wt percent of paraffin fed converted X % selectivity of monoolefins in paraffin
Fig-1 is the graphical representation of the performance in the paraffin dehydrogcnation process of comparison A & samples B, C, D & E of the invention. The figure is a graph of reactor temp to maintain a constant monoolefin yield (around 11%) as a function of days on stream of the tests, initial starting from 450°C upto 500°C.
Fig-2, 3 & 4 are graphical representations of Pt & modifier metals gradient across the radius of the catalysts of Examples A, B & C respectively. The metal distribution is presented as a ratio of particular metal concentration to the alumina concentration plotted against the distance in millimeter from the surface of the particle. The distributions were determined by 'Scanning Electron Microscopy* (SEM).
It may be noted that the plots do not represent actual metal content but only the approx relative concentration of the metal across the radius of a catalyst sphere.
Fig-5 is again comparative % yield of olefin against days on stream, similar to Fig-1, of 2 catalysts C (0.08% Cl) & Catalyst K (0.28% Cl).
1. A process for preparing a novel catalyst comprising of impregnating a support with a solution of a active metal component, at least a first modifier component, a promoter metal component and optionally a second modifier component and a halogen component, drying the said impregnated support, calcining said support at a temperature of 450 to 600°C, dehalogenating the calcined support with and redrying the dehalogenated support as herein described.
|Indian Patent Application Number||145/DEL/2002|
|PG Journal Number||08/2009|
|Date of Filing||25-Feb-2002|
|Name of Patentee||Sud-Chemie India Pvt. Ltd.|
|Applicant Address||402/403 MANSAROVAR, 90 NEHRU PLACE, NEW DELHI-110 019|
|PCT International Classification Number||B01J 23/40|
|PCT International Application Number||N/A|
|PCT International Filing date|