Study On Preparation Of Industrial Hydrotalcite Aerogel Catalyst And Hydroxylation Performance Of Phenol

Catechol and hydroquinone have been widely used in many industries as high-value chemicals.At present,a large number of phenol hydroxylation catalysts have been developed.Hydrotalcite,as an environmentally friendly catalyst,has been favored by many researchers.Hydrotalcite（LDHs）is a layered composite metal hydroxide consisting of positively charged laminates,anions and water molecules filled between the laminates.The positively charged laminate is formed by an octahedral coordination of divalent and trivalent metal ions(M²⁺and M³⁺)with OH^-in a highly ordered arrangement.Under certain conditions,M²⁺can be replaced by M³⁺with similar ionic radius,so that the lamellar is positively charged.However,because most of the prepared hydrotalcite catalysts are powdery,it is difficult to recycle and meet the needs of industrial applications.Therefore,the research and development of hydrotalcite catalysts with high activity has become an important research direction.In this work,a hydrotalcite aerogel catalyst with high particle strength was developed and its phenol hydroxylation activity in a fixed bed was investigated.It mainly includes the following research contents:（1）Four different types of ternary hydrotalcite catalysts were prepared by microwave coprecipitate method.The physical and chemical properties of the prepared hydrotalcite catalysts were systematically characterized by Fourier transform infrared spectroscopy（FT-IR）,X-ray powder diffraction（XRD）,Nitrogen adsorption-desorption test and scanning electron microscopy（SEM）.Finally,using H₂O₂ as oxidant,the catalytic effect of hydrotalcite catalysts on hydroxylation of phenol was evaluated,and the best group of ternary hydrotalcite catalysts were optimized to be used as forming aerogel catalysts.（2）On the basis of the previous chapter,the hydrotalcite aerogel was formed by using different binkers,and the proportions of different binkers were adjusted.The hydrotalcite aerogel catalyst was characterized by Fourier transform infrared spectroscopy（FT-IR）,scanning electron microscopy（SEM）,thermogravimetric analysis（TGA）,particle compressive strength and phenol hydroxylation reaction.Optimize the best performance of the group,the fixed bed reaction kinetics of the catalyst study.（3）The macroscopic kinetics of phenol hydroxylation with hydrotalcite aerogel catalyst was studied in a fixed bed.The effects of different phenol concentration,hydrogen peroxide concentration,catalyst dosage and reaction temperature on phenol hydroxylation were investigated.The results showed that among the four ternary hydrotalcite catalysts,the Cu²⁺/Ni²⁺=3:1 catalyst had the best catalytic effect,the highest conversion rate of phenol was 69.2%,and the selectivity of catechol and hydroquinone was more than 90%.In addition,the weight of oxidized starch 4 g,gelatin 5 g,polyvinyl alcohol 2.5 g,hydrotalcite 4 g,formed hydrotalcite aerogel granule compressive strength is 97 N.The optimum reaction conditions were as follows:water as solvent,hydrogen peroxide as oxidant,molar ratio of phenol to hydrogen peroxide of 3:1,mass of catalyst of 25 g,reaction temperature of 343 K,the conversion rate of phenol reached 63.8%.