Preparation Of Modified KX Catalyst And Its Application To The Side Chian Alkylation Of Toluene And Methanol

As a basic industrial raw material,styrene is widely used in automobiles,packaging materials,medical equipment,daily necessities,etc.,and it occupies an important position in the chemical industry.The traditional process of styrene has the disadvantages of complicated process,long process,high energy consumption and high cost of raw materials.It is imperative to develop an economical,environmentally friendly and sustainable process for the preparation of styrene.It has been found that toluene-methanol side chain alkylation is an ideal method for the preparation of styrene.Although the process is relatively mature in the experimental theory and has many advantages,but decades of research has failed to achieve its industrialization,mainly due to:low styrene selectivity,toluene conversion is not high,the catalyst life is low.It is generally believed that good catalysts must have both acidity and alkalinity,so the research on the relationship between acidity and alkalinity and catalytic activity of the catalysts will also have important academic value.Based on the above background,the main research content of this paper is to adjust the acid-base properties of the catalyst by adding different modifying substances.Combined with a series of characterizations,the effects of catalyst structure and acid-base performance on the alkylation of side chains were explored.The main results of this paper are as follows:?1?The influence of preparation of KX on the reaction performance under different conditions was investigated.After a series of experiments,it was found that the optimal ion exchange conditions were as follows:KOH concentration 1 mol/L,exchanged two times.A series of metal oxide-doped KX catalysts were prepared by physical mixing.The effect of all catalysts on the alkylation performance of the toluene side chain of methanol was investigated.The conclusions are as follows:After the ZnO-modified KX acid is reduced in strength,strong alkali sites are weakened,and the toluene conversion rate and styrene selectivity of the catalyst ZnO/KX are all increased.The strength of KX base modified with MgO decreases,and the selectivity of styrene and ethylbenzene on Mg O/KX catalyst increases.The acid strength of the KX catalyst modified with NiO was increased,and the strong alkali site was weakened.The selectivity of ethylbenzene and the toluene conversion rate on the NiO/KX catalyst were all improved.The KX strong base sites modified with CeO₂ and La₂O₃ become stronger,and the toluene conversion rate and styrene selectivity both decrease.?2?The effect of K₂B₄O₇ modified KX on the reaction performance was studied.The addition of K₂B₄O₇ makes the KX acid-base performance change,effectively increase the alkylation performance of the side chain and increase the styrene yield.K₂B₄O₇ is added to neutralize or covers part of the acid sites on the catalyst,so that the amount of acid on the catalyst decreases,and the acid strength decreases.With the increase of K₂B₄O₇ content,the styrene selectivity gradually increased and reached the maximum when the K₂B₄O₇content was 4 wt%.At this time,the toluene conversion rate also reached the maximum,and then decreased with the increase of the K₂B₄O₇ content.?3?Explore the impact of AlCl₃ modified 4KB on the reaction performance.It shows that the addition of a certain amount of AlCl₃ can increase the styrene selectivity,but it also leads to a decrease in the conversion of Toluene.The selectivity of styrene was the highest when the content of AlCl₃ was 0.8%by weight,and decreased when the amount of Al Cl₃ continued to increase.After Al Cl₃ loading,the acid content and acid strength of the catalyst increased,and the alkali strength decreased.A decrease in the alkali strength resulted in a decrease in the amount of polarized toluene methyl groups and a decrease in the toluene conversion rate.At the same time,the amount of CO and H₂ decreased by methanol decomposition,which resulted in less hydrogenation of styrene to ethylbenzene,resulting in increased styrene selectivity and decreased ethylbenzene selectivity.?4?The effects of reaction temperature,reaction space velocity and molar ratio of toluene to methanol on the reaction performance were investigated.It shows that the temperature is below 600 K,the reaction is almost inactive,and no side chain alkylation product is produced.When the reaction temperature reached 698 K,the yield of styrene and ethylbenzene reached the maximum.Too high temperatures,or too low temperatures,are detrimental to the side chain alkylation reaction;When the space velocity is 1 h^-1,the total yield of styrene and ethylbenzene reaches the maximum;The yields of styrene and ethylbenzene in the side chain alkylation products increased gradually with the increase of the molar ratio of toluene to methanol.The toluene conversion rate gradually decreases with increasing molar ratio of toluene to methanol.