Maltose hydrogenation to maltitol over industrial Raney Ni catalyst: Kinetics and mechanism

Abstract

The kinetics and mechanisms of selective maltose hydrogenation over Raney Ni remain poorly understood, which hinders the industrial advancement of maltitol production for biorefining. Herein, the impact of hydrogenation conditions and in-depth mechanistic characterizations were carefully investigated in this research. Optimization of reaction conditions illustrated that maltitol formation was favored by moderate reaction temperatures (≤130 C), high hydrogen pressures (>7 MPa), and nearneutral sodium phosphate buffer (pH = 6.47). Kinetic studies demonstrated the E a of 45.5 kJ/mol for the hydrogenation of maltose. The in situ IR revealed that the hydrogenation of maltose over Raney Ni occurs in the order of ring opening and adsorption via C O of the aldose form followed by hydrogenation. The UV-vis spectra demonstrated the near-neutral setting (pH = 6.47) promoted the production of open-chain aldose conformation and selective C O hydrogenation to the corresponding alcohols. The present study on concentrated-maltose hydrogenation paves the way for the industrial development of maltitol manufacturing.

Continuous Hydrogenation of Maltose over Raney Ni in a Trickle-Bed Reactor

“…According to the Arrhenius relationship ln k = Ea/RT + ln A, the activation energy (Ea) and pre-exponential factor (A) were obtained through linear regression of ln k versus 1000/T (Figure 7b). The data illustrated that the pre-exponential factor was 3.13 × 10 4 L mol −1 min −1 and the activation energy was 44.1 kJ/mol, which was in strong agreement with the previous batch setup results (45.5 kJ/mol) 16 and observations reported in other studies (32.0−58.5 kJ/mol), 9,38,51,52 as shown in Table S2.…”

“…The behavior of maltose hydrogenation catalyzed by Raney Ni was presumed to be a pseudo-first-order kinetic according to the previous study. 16 Therefore, the linear fitting result of −ln (1 − X) (where X represents the average conversion of maltose after 2 h on stream) vs residence time was plotted. As illustrated in Figure 4b, the substrate conversion was directly proportional to the residence time with R 2 > 0.99, which is a perfect validation of the first-order reaction approximation.…”

“…This result is consistent with the conclusion derived from our previous work conducted in batch setups that higher temperature favors side reactions (e.g., hydrolysis and hydrogenolysis), preferably leading to the generation of sorbitol and even glycerol. 16,43 Eventually, in order to balance the conversion of the reactant and the yield of maltitol and sorbitol, the reaction temperature was set at 130 °C for the following experiments.…”

“…Regarding the mechanism of maltose hydrogenation over Raney Ni has been preliminarily studied using experimental characterization (e.g., in situ IR and UV− vis techniques), 16 exploration of its underlying reaction pathways through theoretical modeling remains urgent for maltose upgrading in industrial applications. Herein, DFT calculations were applied to guide the optimization of the reaction route and promote productivity and selectivity.…”

“…Furthermore, the kinetic and mechanistic insights toward maltose hydrogenation over commercial Raney Ni were obtained in our previous work. 16 To date, batchwise technology is mature and well established due to its simple structure and ease of operation. 17 Nevertheless, traditional batch production still underperforms owing to several drawbacks, including limited production capacity, poor mass and heat transfer, and severe back mixing.…”