Impact of Water on Condensed Phase Ethanol Guerbet Reactions

Abstract

The effect of water on higher alcohol and noncondensable gas formation in condensed-phase ethanol Guerbet chemistry over Ni/La 2 O 3 /γ-Al 2 O 3 catalysts is investigated. Addition of 10 wt % water to anhydrous ethanol has a modest effect on conversion rate but significantly reduces both n-butanol and C 6+ alcohol yields and increases noncondensable gas yields. Removal of water formed during Guerbet condensation reactions was accomplished by installing a recirculating loop that passed the reacting solution through a bed of 3 Å molecular sieves at low temperature. Removal of reaction water further reduces gas selectivity to less than 10% and increases alcohol selectivity to greater than 75% at 50% ethanol conversion. Water present in reaction is postulated to adsorb on the nickel surface as −OH, increasing C−C bond breakage of the adsorbed acetaldehyde intermediate, and also interact with basic sites responsible for the condensation reaction, weakening their activity.

Catalytic Upgrading of Ethanol to n‐Butanol: Progress in Catalyst Development

“…In addition, raising the reaction temperature has a positive effect on improving the catalytic performance of the Pd 5 MgAlO catalyst. The ethanol conversion and n ‐butanol selectivity increased from 4.2 and 72.7 % to 17.5 and 78 %, respectively, as the reaction temperature increased from 473 to 533 K. It should be mentioned that water produced in the reaction system has a negative effect on the catalytic performance, probably due to the transformation of uncoordinated Lewis basic O 2− , which is the active site for the aldol condensation of acetaldehyde, into weaker basic OH − . Therefore, an attempt should be made to remove water from the reaction system (probably by raising the reaction temperature); thus enhancing the catalytic activity and further facilitating the investigation of the mechanism of the acid–base catalyzed reaction.…”

“…Based on a previous study, the aldol condensation of acetaldehyde is considered to be the rate‐determining step, whereas the adjacent Lewis acid–base pairs are responsible for this key step. Thus, interest in exploring rare‐earth‐metal oxides (La 2 O 3 and CeO 2 ) as basic modifiers of catalysts for the conversion of ethanol into n ‐butanol has increased considerably in recent years . However, attention should also be paid to the development of suitable Lewis acid sites because the requirement for the presence of strong base sites can be alleviated, if Lewis acid centers are present.…”

“…Thus, interesti ne xploring rare-earth-metal oxides( La 2 O 3 and CeO 2 )a sb asic modifiers of catalysts for the conversion of ethanol into n-butanol has increased considerably in recent years. [30,46,49,53,55,56] However,a ttention should also be paid to the development of suitable Lewis acid sites because the requirementfor the presence of strong base sites can be alleviated, if Lewis acid centers are present. Moreover,t he Lewis acidbase pairs, if introduced by the modifierors upport in the catalysts, would be affected by the properties of the metal loaded.…”

“…Moreover,t he effect of water as ar eaction mediumo nt he product distribution, and even the reaction mechanism, shouldb ef urther discussed. In previous reports, the stability of CuÀMgÀAl mixed oxide catalysts derived from hydrotalcite precursors [24] and Ni/La 2 O 3 /g-Al 2 O 3 [30] catalysts in ethanol-water upgrading was discussed. These catalysts experiencedr apid deactivation with the addition of water to the pure alcohol feedstock.…”

Recent advances in selective C-C bond coupling for ethanol upgrading over balanced Lewis acid-base catalysts

“…In the upgrading process of ethanol to value-added chemicals such as 1-butanol (potential gasoline additives), gasoline (C 8 -C 12 hydrocarbons mixtures) and even diesel (C 9 -C 25 hydrocarbons mixtures), the formation of C-C bond is the key reaction step [9][10][11][12]. However, the efficiency and selectivity to the desired products are always the major challenges due to the complexity of C-C bond coupling between oxygenates.…”