Preparation And Performance Evaluation Of N-hexane Isomerization Catalyst

Comparison with the octane number of n-alkane,the octane number of the isoparaffin with the same carbon atomic numbers is dozens of units higher,and the isomerized gasoline has the advantage of low content of sulfur,no existence of olefins,aromatics or benzene.Therefore,the conversion of n-alkanes into isoparaffins is an effective means of improving the quality of gasoline.However,the isomerization process of n-alkanes to isoparaffins needs to be carried out with catalyst.So it is necessary to develop a catalyst which can catalyze the isomerization of n-alkanes into isoparaffins.There is a certain time for the catalyst development of n-alkane isomerization at domestic and overseas,and some achievements have been achieved.At present,the mature method is using metallic Pt or Pd as the active component which is loaded on different type of molecular sieve carriers to obtain different kinds of catalyst.The representative catalysts are HS-10 type of Shell and I-7 type of UOP respectively.However,these catalysts are very expensive since the noble metals are used as the active components of the catalysts.In addition,Pt-based catalysts,particularly Pt and Pd catalysts,are easy to be poisoned and be inactivation by elements S,N and As.Therefore,these have been replaced by non-noble metals such as Ni in recent years.This kind of non-noble metal catalyst is represented by CI-154 non-noble metal isomerization catalyst developed by Jinling Petrochemical Company Refinery Research Institute of Sinopec.The cost of this kind of catalyst is only 25%of the noble metal catalyst,and the catalytic activity is also quite good.But when it is used to treat the sulfur-containing raw material,the performance is not satisfactory.The isomerization reaction of n-alkane is essentially consisted of the dehydrogenation and the isomerization,in which the dehydrogenation step takes place on the active site of catalyst.When more than one kind of metallic elements are used as the active components,there may exist an interaction between them,and the catalytic activity of the catalyst could be improved.The purpose of this paper is to develop a kind of non-noble metal catalyst with various metallic elements as active componenents,which can catalyze the isomerization of n-hexane,and has better catalytic activity,long service life and better stability.The MOR,?and ZSM-5 type catalyst carriers were prepared by the extruding method.The metallic elements Ni,Mo,Cu and Mo was respectively used as the active components,and the MOR type of zeolite was used as the carrier of catalyst,the Ni/MOR,Mo/MOR,Cu/MOR and Co/MOR types of catalysts were prepared by equivalent-volume impregnation.When the metallic elements Cu,Mo and Co was used as the co-catalyst to be loaded on Ni/MOR catalyst by equivalent-volume impregnation,respectively,the bimetallic active componenent catalysts,i.e,Ni-Mo/MOR,Ni-Cu/MOR and Ni-Co/MOR catalysts were prepared.The performance of the prepared catalyst was evaluated on a continuous flow fixed bed high pressure microreactor equipped with gas chromatograph.The structures of prepared catalyst were characterized by BET,XRD,SEM and so on,respectively.The catalytic activity of catalyst carrier,i.e.MOR,?and ZSM-5 had been investigated.Although the conversion of n-hexane was low,the selectivity of i-hexane was high and the liquid yield of reaction was high when using the MOR carrier as catalyst for the isomerization of n-hexane.Therefore,the MOR was an ideal catalyst carrier.The catalytic activity of Ni/MOR,Mo/MOR,Cu/MOR and Co/MOR catalysts had been evaluated by experiments.Among of above-mentioned four types of catalysts,the Ni/MOR catalyst was able to yield the high selectivity of i-hexane and liquid yield of reaction.Hence,it was an ideal monometallic catalyst.The proper loading amount of Ni on the MOR catalyst carrier was 5wt.%.The characterization results for Ni/MOR catalyst demonstrated that the disperse degree of element Ni on catalyst was better,the specific surface area was larger and the ratio of acid/metal center was the best when the loading amount of Ni is 5wt.%.Moreover,the catalytic activity of Ni-Mo/MOR,Ni-Cu/MOR and Ni-Co/MOR catalysts had been evaluated.When the Ni-Cu/MOR catalyst was used to catalyze the isomerization of n-hexane,the conversion of n-hexane,selectivity of i-hexane and the liquid yield of reaction was all higher.When the loading amount of Cu and Ni was both 5wt.%,the catalytic activity of the catalyst was the best.The stability of Ni-Cu/MOR catalyst with Ni and Cu loading amount of 5wt.%had also been investigated.The catalyst stability was better and the catalytic activity was almost unchanged during the 200 hours operating period.The effects of reaction conditions on n-hexane isomerization performance had been investigated by using the Ni-Cu/MOR catalyst with Ni and Cu loading amount of 5wt.%.Under the condition of reaction temperature of 280?,reaction pressure of 1.0MPa,reaction mass space velocity of 1.0h^-1 and hydrogen/oil ratio of 1.0,the conversion of n-hexane was 81.13%,the selectivity of i-hexane was 80.03%,and the liquid yield of reaction was 97.51%.These data were close to that of the noble metallic isomerization catalyst,but the cost of prepared non-noble metallic isomerization catalyst by this paper was much cheaper than that of the noble metallic isomerization catalyst.