Study On Solid Catalysts For The Production Of Trioxane From Formaldehyde

Vigorously developing the C1 chemical industry chain is a major energy strategic demand in my country at present.Formaldehyde,as an important C1 raw material,can use anhydrous formaldehyde to produce polyoxymethylene,polyoxymethylene dimethyl ether and a series of fine chemicals,thereby extending the C1 chemical industry chain.However,because formaldehyde is relatively active,formaldehyde monomer cannot be stored,and a series of reactions in the industrial chain need to use trioxane as a raw material instead of formaldehyde.At present,the mainstream production process of trioxane uses concentrated H2SO4 as a catalyst.Problems such as low selectivity,easily corroded equipment,and difficult product separation have always restricted the development of this industrial chain.In this paper,the catalyst for the synthesis of formaldehyde from formaldehyde was taken as the research goal,and a solid acid catalyst that could replace sulfuric acid was searched to optimize the synthesis method of trioxane.A series of SO₄^2-/M_xO_y solid acid catalysts were synthesized by impregnation method.Combining the characterization and performance evaluation results,the effects of different oxide supports,different active component precursors and different preparation conditions on the surface structure and catalytic performance of solid acids were investigated,and different acid center types,strengths and The effect of acid amount on the pointer reaction;the solid acid is modified by introducing rare earth element Ce and changing the active component of the solid acid to solve the problem that the solid acid is easily deactivated in the aqueous system.A series of solid acid catalysts such as SO₄^2-/Fe₂O₃,SO₄^2-/Zr O₂,SO₄^2-/Ti O₂,SO₄^2-/Sn O₂,SO₄^2-/Al₂O₃,SO₄^2-/Cr₂O₃ and SO₄^2-/Nb₂O₅ were prepared by co-precipitation method,and The catalytic activity of the pointer reaction is relatively high.Through characterization and performance evaluation experiments,we can understand the influence of different preparation conditions on the surface acid centers and catalytic effects of solid acids.The results show that the greater the acid content of the medium strong acid and strong acid,the greater the catalytic effect of the pointer reaction.The better the effect;with the solid acid under the best preparation conditions as the catalyst,the reaction conditions of the pointer reaction were optimized through single factor experiments and response surface design;through comparison,it can be known that the conversion rate of the solid superacid catalyst to the pointer reaction is comparable to that of sulfuric acid Equivalent,but there are fewer by-products in the generated liquid,the selectivity of trioxane is obviously higher than that of liquid acid catalyst,and its final yield is relatively high.Aiming at the problem that SO₄^2-/M_xO_y solid acid is easy to deactivate in water,Ce-modified Ce-SO₄^2-/Fe₂O₃ was prepared.Through the characterization of catalysts with different Ce contents,it is understood that the introduction of Ce affects the surface structure of solid acid and the acid center.The mechanism of Ce modification to improve the water resistance of SO₄^2-/Fe₂O₃ was explored,and the differential charge density of SO₄^2-/Fe₂O₃solid acid was calculated by first principles,and the generation process of solid acid acid center was visualized.The results showed that the introduction of Ce not only enhanced the number and strength of the acid centers on the surface of the solid acid,but also reduced the hydrogen bonding between the surface of the solid acid and water molecules,improving the stability of the solid acid during the reaction.On the whole,the comprehensive performance of SO₄^2-/Fe₂O₃ solid acid catalyst with 3%Ce content is better,and after five times of repeated use,it can still maintain a high catalytic activity in the catalytic reaction.The active component on the surface of SO₄^2-/Zr O₂ is changed from SO₄^2-,which is easily soluble in water,to WO₃,which is insoluble in water,so as to improve its water resistance.A series of WO₃/Zr O₂ solid acid catalysts were prepared by co-precipitation method.The influence of WO₃ loading and calcination temperature on the catalytic effect of solid acid was investigated through characterization and performance evaluation experiments.The oxide carrier before and after WO3 loading was calculated by first principle The differential charge density on the surface further explains the mechanism of acid center generation in solid acids.The results show that the WO₃/Zr O₂ solid acid prepared at a calcination temperature of 700°C with a loading of WO₃ of 15%,the carrier Zr O₂ is a complete and stable tetragonal crystal phase,and the amorphous phase of WO₃ is in a highly dispersed state on the surface of the carrier.The surface of the solid acid has the most acidic sites,the largest specific surface area,and the best catalytic performance for the pointer reaction,and the catalyst can still have a good catalytic effect after being reused five times,indicating that it also has good catalytic stability.