| As one of most effective approaches to improve gasoline performance,increase gasoline yield,and reduce environmental pollutions,the etherification technology of FCC light gasoline can synchronously realize multiple purposes such as reducing olefin,reducing saturated vapor pressure,and increase octane value and oxygen content of gasoline within one step reaction.Molecular sieve catalyst has become a focused research object as etherification catalyst for its advantages over resin catalyst.However,it still suffers defects such as poor etherification activity at low temperature,to solve this problem,our research was conducted.In this research,we first selected molecular sieve for preparing basal catalyst.After that we conducted fine adjustment of the pore structure and acid property by respectively using several single modification methods and compound modification methods to select out etherification catalyst,and compared it with industrial resin for testing the stability and renewability of the catalyst.Finally,we explored the deactivation reason and mechanism of catalyst 1.1CA/HBC.In addition,we performed comparative research on the influencing mechanisms of different modification methods on physical and chemical properties of the catalyst using the system characterization method,and thus explored proper pore structure and aci range for etherification in the hope of providing experimental basis for further improvement of later etherification catalysts.The etherification evaluation results showed that H? had a higher etherification activity over USY and HZSM-5.By mixing H? with 40?t% binder and 5?t% peptizer,it can gain a proper basal catalyst;Single modification methods can improve low-temperature activities of basal catalysts in different degrees,wherein the acid treatment method was superior over lanthanum ion exchange method and low temperature steam treatment.After citric acid treatment,the temperature where the highest activity located moved forward to 60?;In constrast,the etherification activities of basal catalysts after compound modification method were slightly lower than sample 1.1CA/HBC,but still significantly higher than sample 0.1La/HBC and 400-3/HBC;samples 1.1CA/HBC has the highest etherification activity,was the most suitable etherification catalyst.Under the condition where alfin ratio was 1.0,reaction temperature was 60?,volume space velocity was 1h-1 and reaction pressure was 2.0MPa,C5 active olefin conversion reached 68.3%,C6 active olefin conversion reached 46.84%,and the total conversion of tertiary olefin reached 61.44%;C5 ether content was 14.02% in etherified gasoline,C6 ether content was 5.33%,and the total content of olefin dimer only 0.14%;the olefin reduction rate reached 32.36%.The etherification activity and low temperature activity of 1.1CA/HBC were significantly higher than that of industrial resin catalyst,and with extremely low yield of by-product.After operation with this catalyst for 1272 h,the total conversion of tertiary olefin still maintained over 50%,showing sound stability.After conducting coke burning regeneration of deactivated catalyst,tertiary olefin conversion can reached to 61.35% etherification activity being recovered,showing that this catalyst has renewability.The characterization results of catalyst physical and chemical properties showed that all modification methods in this experimental made less influence on crystal structures,skeletal structures and microstructures of catalysts,but made significant influence on the pore structures and acid properties.Through combining the etherification activity and the characterization results,following conclusions can be reached:(1)the pore structure and pore size of molecular sieve are the precondition for determining the low-temperature etherification activity,while the pore volume and pore diameter are the parameters of influencing the etherification activity of molecular sieve.A large pore diameter and wide pore distribution can improve the absorption capacity of the catalyst,which is helpful to the diffusion of reactants and products between pore canals,to the increase of catalytic efficiency,and specifically to the improvement of low temperature etherification activity.However,an over large pore diameter may reduce the shape selectivity of molecular sieve.It is suggested to select pore diameter of around 11 nm.(2)The silicon aluminum bridge hydroxyl of molecular sieve may be main activity site where etherification reaction and side reactions.Etherification reaction needs moderate acid environment,and the acid content,acid strength and B acidity will all create impact to the etherification activity,this three factors are mutually constrained and cooperated in determining etherification activity,instead by any side of them.When total acidity was low,it was suggested to moderately increase the proportion of dium-strong acid as well as B acidity,however a too high or too low level of these two factors will damp etherification reaction.Through characterizing the physical and chemical properties of deactivated and regenerated catalyst as well as the analysis of sediment's composition,it and infer that the massive amount of low-temperature carbons deposited on the active center,which is the major cause for catalyst deactivation.In the early stage of reaction,the etherified products and olefin polymers deposited at the active centers inside and outside of catalyst pore canals,which increased the resistance for products desorption and diffusion of.As the reaction went on,the polymerization degree of olefin increased,generated macromolecular saturated alkane sediment through hydrogen transfer process.while less amount of polymerized olefin was dehydrocyclized into alkylbenzene.There even larger molecules continued to cover on the surfaces of active center,and gradually blocked orifices,and finally led to deactivation of etherification catalyst. |
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