Study On The Synthesis Of Neopentyl Glycol From Isobutyraldehyde And Formaldehyde

Neopentyl glycol（NPG）is an important fine chemical,and it is mainly produced from condensation hydrogenation method.This method mainly involves condensation reaction of formaldehyde with isobutyraldehyde（IBA）,and hydrogenation reaction of the condensation product hydroxypivaldehyde（HPA）.Currently,the condensation reaction process mainly uses liquid alkali catalyst,which has the disadvantages of difficult recovery and environmental pollution.For the hydrogenation process,there are some problems,such as high cost of noble metal catalyst,low activity of copper catalyst due to copper particles agglomeration,and harsh reaction conditions of nickel catalyst.Based on this consideration,acid-base bifunctional condensation catalyst was designed,and nickel-based catalyst suitable for mild conditions was developed in this study.The above-mentioned catalysts were applied to the reaction process of condensation and hydrogenation for NPG synthesis.For the condensation reaction process,Si O₂was selected as catalyst support,and a series of catalysts 15%X/Si O₂（X=Mg O,Ca O,Sr O,Ba O）were prepared by impregnation method.The catalysts were characterized by XRD,BET,CO₂-TPD and NH₃-TPD.The results showed that the conversion of isobutyraldehyde first increased,and then decreased with the increase of alkali content.The selectivity of HPA was positively correlated with the acid amount of catalyst and the ratio of acid amount to base amount.Moreover,the catalyst 15%Mg O/Si O₂showed the best catalytic activity,with large specific surface area,pore volume and pore diameter,large surface acid content（mainly weak acid and medium-strong acid）,relatively small alkali content（large proportion of medium-strong alkali）,and large acid-base ratio.Over this catalyst,the optimal reaction conditions were as follows.Molar ratio of formaldehyde to isobutyraldehyde was 1.2:1,catalyst dosage was 8 wt.%,reaction temperature was 80°C and reaction time was 16 h.Under this reaction conditions,IBA conversion was 89.3%and HPA selectivity was 91.5%.After three times usage,the reaction performance of the catalyst was nearly the same.The crystal structure and acid-base properties remained essentially unchanged.For the hydrogenation process,Ni/Al₂O₃catalysts were prepared by co-precipitation method and impregnation method.The catalytic performance of Ni/Al₂O₃catalysts was investigated under mild reaction conditions for the hydrogenation of hydroxypivaldehyde to neopentyl glycol.The results of XRD,BET,H₂-TPR and CO pulse adsorption showed that20%Ni/Al₂O₃catalyst prepared by impregnation method had good reaction performance.The catalyst has a large specific surface area（200 m²/g）and good metal dispersion.The nickel species in the catalyst were easily reduced to Ni.Under relatively mild conditions(reaction temperature 103°C,pressure 3 MPa,space velocity 1 h^-1,hydrogen to aldehyde ratio 10),HPA conversion was 100%and NPG selectivity was 99.3%.At the same time,catalyst aging testing showed that the conversion of HPA and the selectivity of NPG had little fluctuation in the long-term evaluation process of 1000 h,indicating that the catalyst had stable performance and good industrial application value.