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 h as been studied using different palladium-supported catalysts. With 1% Pd/C catalyst, the major product formed was 1,4-butanediol, along with other si de products such as butenediol, gamma -hydroxy butyraldehyde, n-butyraldehy de and n-butanol. Role of supports and ammonia was very significant in achi eving a high selectivity to the intermediate, 2-butene-1,4-diol. A selectiv e hydrogenation of 2-butyne-1,4-diol to give cis-2-butene-1,4-diol was achi eved using 1% Pd/CaCO3-NH3 catalyst system. Effects of catalyst pretreatmen t with both 2-butyne-1,4-diol and H-2 on the catalyst activity and selectiv ity were investigated. It was found that the catalyst activity increased su bstantially, while the selectivity to 2-butene-1,4-diol decreased slightly with hydrogen-pretreated catalyst. The effects of hydrogen pressure, cataly st 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 tem perature range of 323-353 K. All the data obtained were in the kinetic regi me under the conditions of the present work, based on which a Langmuir-Hins helwood (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 wa s also developed. The agreement between the predicted concentration vs. tim e profiles with the experimental results was excellent. (C) 2001 Elsevier S cience B.V. All rights reserved.