Liquid Phase Aldol Condensation Of Formaldehyde And Acetaldehyde

The use of low-cost aqueous formaldehyde solutions as starting materials to synthesize high valued products will have a huge impact on the entire formaldehyde industry.In this dissertation,aldol condensation from formaldehyde and acetaldehyde solutions was investigated to achieve green production of aldol intermediates.First of all,the activities of different catalysts in the synthesis of 3-hydroxy-2,2-bis?hydroxymethyl?propanal with formaldehyde?FA?and acetaldehyde?AC?in an aqueous environment were investigated,and the effects of ratio of raw materials,reaction temperature,amount of catalyst,water content,reaction time,and the method of acetaldehyde addition on the yield of products and conversion of raw materials were studied.The results showed that the catalytic activity was Triethylamine>Trimethylamine>N,N-diisopropylethylamine>N,N-dimet-hylethylamine>Tripropylamine>Tributylamine>Triethanolamine.When Triethylamine?TEA?was used in this reaction,the optimal reaction conditions?reaction time 60 min,reaction temperature 35oC,nFA:AC:TEA=5:1:0.1,water content 55%?,the highest molar yield of 3-hydroxy-2,2-bis?hydroxymethyl?propanal was 63.66%,and the conversion of formaldehyde?FA?and acetaldehyde?AC?were 29.56%and 86.69%,respectively.Furthermore,it was found that the existence of methanol in the system had an adverse effect in the yield of 3-hydroxy-2,2-bis?hydroxymethyl?propanal.Infrared analysis and GC-MS analysis showed that the main condensation product of formaldehyde and acetaldehyde was 3-hydroxy-2,2-bis?hydroxymethyl?propanal.Secondly,the feasibility of the direct‘one-step'synthesis of pentaerythritol from formaldehyde and acetaldehyde was investigated.The results indicated that when reaction time was 2 h,reaction temperature was 70oC,nFA:ACE:TEA=5:1:1.3,total water content was 42%,the molar yield of pentaerythritol was 72.29%,the conversion of formaldehyde and acetaldehyde were 47.76%and 97.31%,respectively.Finally,the Yoneda group contribution method was used to estimate the enthalpy change,reaction entropy,Gibbs free energy and standard equilibrium constant of the reaction of formaldehyde and acetaldehyde with 15-95oC.The results showed that the aldol condensation reactions between formaldehyde and acetaldehyde were exothermic.The reaction for the synthesis of pentaerythritol was less than-116.11 kJ?mol^-1,which was a strong exothermic reaction.In the experimental temperature ranges,reactions 5-1,5-2 and 5-4 can proceed spontaneously and the Gibbs free energy for reaction 5-3 changed from minus to plus values around 35oC,indicating that the high temperature was unfavorable to the synthesis of 3-hydroxy-2,2-bis?hydroxymethyl?propanal.Considering the synthesis reaction of pentaerythritol Gibbs free energy was large,the coupling of the two reactions was helpful to the formation of3-hydroxy-2,2-bis?hydroxymethyl?propanal,and it can be predicted that both 3-hydroxy-2,2-bis?hydrox-ymethyl?propanal and pentaerythritol exist simultaneously in the reaction system.