Modification Of TS-1 And Its Catalytic Performance For Ammoximation Of Butanone

Oxime is an important chemical product,which is usually obtained by oximation of aldehydes or ketones.The traditional oximation method is hydroxylamine method,which is the non-catalytic oxidation of aldehydes or ketones with hydroxylamine salt（such as（NH₂OH）₂·H₂SO₄ or NH₂OH·HCl）.However,there are many disadvantages in hydroxylamine method,such as high toxicity of raw material hydroxylamine,strong corrosiveness of sulfuric acid and hydrochloric acid,and a large number of low value by-products such as ammonium sulfate or ammonium chloride are produced in this method.Compared with traditional hydroxylamine method,the ammoximation with titanium silicalite TS-1 as catalyst and H₂O₂ as oxidant is a new method for preparing oxime developed in recent years.This method has many advantages,such as high atom utilization,mild reaction conditions,and only water as by-product.It conforms to the basic concept of"green chemistry".In recent years,TS-1 with MFI topological structure has been studied more in catalytic oxidation.In the aspect of aldehydes or ketone ammoximation,TS-1 was first large-scale applied to the ammoximation of cyclohexanone to prepare cyclohexanone oxime.At present,it has been industrialized.The conversion of cyclohexanone and the selectivity of cyclohexanone oxime are higher than 98%.The process greatly simplifies the traditional production process,reduces the production cost,significantly reduces the emissions of three wastes,and effectively promotes the production of nylon 6 in China.However,TS-1 catalyst,which is suitable for cyclohexanone ammoximation,has a poor catalytic effect on the ammoximation of butanone（MEK）.In order to improve the selectivity of TS-1 in MEK ammoximation,TS-1 was modified and its catalytic performance was studied.The details are as follows:（1）A series of TS-1 with different silicon-titanium ratios were prepared by traditional hydrothermal method.The TS-1 with different silicon-titanium ratios were characterized by XRD,FT-IR,SEM,UV-Vis and so on.The results show that the change of silicon-titanium ratio in the range of 15-65 will not affect the MFI topology of TS-1.As the silicon-titanium ratio decreases,the content of skeleton titanium gradually increased to almost unchanged,and the non-framework titanium gradually appears and increases.And the particle size of TS-1 also gradually increases.The catalytic performance of TS-1 with different silicon-titanium ratios for MEK ammoximation was studied.The results show that when the silicon-titanium ratio decreases from 65 to 35,the conversion of MEK increases from 81.6%to over 98.0%,the silicon-titanium ratio decreases again,the conversion is basically unchanged,and the selectivity of MEKO increases first and then decreases.The reason may be that the amount of titanium is too little,the active center is insufficient,and too much titanium leads to non-framework titanium which is not conducive to the production.When the silicon-titanium ratio is 25,the catalytic effect of TS-1 is better,the conversion of MEK is 98.2%,and the selectivity of MEKO reaches79.0%.This shows that only changing the silicon-titanium ratio of TS-1 is difficult to achieve the ideal effect of MEK ammoximation.（2）TS-1 with silicon-titanium ratio of 25 was subjected to alkali modification treatment with different concentrations of tetrapropylammonium hydroxide（TPAOH）.The alkali modified TS-1 was characterized by XRD,SEM,UV-Vis,N₂ adsorption-desorption and so on.The results show that alkali modification does not affect or destroy the framework structure in the concentration range of 0.05-0.25 mol/L TPAOH.There are obvious mesopores in TS-1,and the specific surface area increased slightly,and the micropore volume decreased slightly.When TPAOH concentration is too high,part of the skeleton structure of TS-1 collapses.The catalytic performance of TS-1 modified by alkali with different concentration for MEK ammoximation was studied.The results show that with the increase of alkali concentration,the etching effect of organic alkali is more obvious.In the ammoximation of MEK,the conversion of MEK remains basically unchanged,and the selectivity of MEKO is gradually increases to stable.When the concentration of TPAOH was 0.15 mol/L,the structure of TS-1 is well maintained,and the number of mesopores is large.The catalytic effect of MEK ammoximation is the best.The conversion of MEK is 98.4%and the selectivity of MEKO reaches 93.3%.（3）The transition metal modification of TS-1 was studied.Five kinds of transition metals（Fe,Co,Ni,Cu,Ce）modified TS-1 catalysts（M-TS-1）were prepared by ultrasonic impregnation method.The catalytic performance of M-TS-1 in MEK ammoximation was studied.The results show that the catalytic activity of M-TS-1modified by different transition metals in MEK ammoximation is quite different.Under the same reaction conditions,Ni-TS-1 has the best catalytic performance.Among the Ni-TS-1 with different Ni content,3wt%Ni-TS-1 is the best.In the ammoximation of MEK catalyzed by 3wt%Ni-TS-1,the conversion of MEK is 99.0%and the selectivity of MEKO reaches 99.3%.In addition,the catalyst has good recoverability.The catalyst used five times is regenerated,its catalytic activity is basically unchanged.The M-TS-1 was characterized by XRD,FT-IR,UV-Vis,XPS,ZPC and so on.The results show that after nickel modification,the skeleton structure of TS-1 remains basically unchanged.The electronic environment of the Ti active center changes,the electron cloud density goes down and the ZPC increases significantly.The mechanism analysis shows that the electrophilicity of Ni-TS-1 increases and the surface acidity decreases,thereby optimizing the adsorption and activation of H₂O₂,which is conducive to the generation of titanium peroxide,promoting the generation of hydroxylamine,and inhibiting the deep oxidation of oxime.So the selectivity of MEKO is greatly improved.