Selective hydrogenation of 2-butyne-1,4-diol to 2-butene-1,4-diol: roles of ammonia, catalyst pretreatment and kinetic studies

The selective hydrogenation of 2-butyne-1,4 diol to cis-2-butene-1,4 diol has been studied using different palladium-supported catalysts. With 1% Pd/C catalyst, the major product formed was 1,4-butanediol, along with other side products such as butenediol, gamma -hydroxy butyraldehyde, n-butyraldehyde and n-butanol. Role of supports and ammonia was very significant in achieving a high selectivity to the intermediate, 2-butene-1,4-diol. A selective hydrogenation of 2-butyne-1,4-diol to give cis-2-butene-1,4-diol was achieved using 1% Pd/CaCO3-NH3 catalyst system. Effects of catalyst pretreatment with both 2-butyne-1,4-diol and H-2 on the catalyst activity and selectivity were investigated. It was found that the catalyst activity increased substantially, while the selectivity to 2-butene-1,4-diol decreased slightly with hydrogen-pretreated catalyst. The effects of hydrogen pressure, catalyst loading, initial concentrations of 2-butyne-1,4-diol and ammonia on the initial rate of hydrogenation were also studied in a batch reactor in a temperature range of 323-353 K. All the data obtained were in the kinetic regime under the conditions of the present work, based on which a Langmuir-Hinshelwood (L-H) type rate model was proposed. To verify the applicability of the kinetic model over a wide range of conditions, a batch reactor model was also developed. The agreement between the predicted concentration vs. time profiles with the experimental results was excellent. (C) 2001 Elsevier Science B.V. All rights reserved.