Simultaneous Conversion of C₅ and C₆ Sugars into Methyl Levulinate with the Addition of 1,3,5‐Trioxane

Abstract

The simultaneous conversion of C 5 andC 6 mixed sugarsi nto methyl levulinate (MLE) has emerged as av ersatile strategy to eliminate costly separation steps. However,t he traditional upgradingo fC 5 sugars into MLE is very complex as it requires both acid-catalyzed and hydrogenation processes. This study concerns the development of ao ne-pot,h ydrogenation-free conversion of C 5 sugarsi nto MLE over different acid catalysts at near-critical methanolconditions with the help of 1,3,5-trioxane. For the conversion of C 5 sugars over zeolites without the addition of 1,3,5-trioxane, the MLE yield is quite low,o wing to low hydrogenation activity.T he addition of 1,3,5-trioxanes ignificantly boosts the MLE yield by providing an alternative conversion pathway that does not include the hydrogenation step. Ad irectc omparison of the catalytic performance of five differentz eolitesr eveals that Hb zeolite,w hichh as high densities of both Lewis and Brønsted acid sites, affords the highest MLE yield. With the addition of 1,3,5-trioxane, the hydroxymethylation of furfural derivativea nd formaldehyde is ak ey step. Notably,t he simultaneous conversion of C 5 and C 6 sugars catalyzed by Hb zeolite can attain an MLE yield as high as 50.4 %w hen the reaction conditions are fully optimized. Moreover,t he Hb zeolite catalystc an be reused at least five times withoutsignificant change in performance.Lignocellulosic biomass,a st he mosta bundant carbon-containing organic resource, can be depolymerized and hydrolyzed into C 5 and C 6 sugars. [1] These mixed sugars are difficult to separate, owing to their many similarities and lack of fixed boiling points. [2] An efficient approach is to convert them into volatile chemicals, such as C 5 -derived furfural (FAL) and C 6 -derived 5-(hydroxymethyl)furfural (HMF). [3] However,t he resultant prod-ucts of these conversion processes are usually different, leading to the occurrenceo fs ome costly separation processes. [1a] To avoid this situation, the simultaneous conversion of C 5 and C 6 sugars into the same platform chemical by furtherc onverting FALa nd HMFr epresents ap romising solution. [3e, 4] Brønsted acid (B acid) sites have been identified as the main active site for the production of FALa nd HMF from the hydrolysis of sugars;H MF can be easily converted into methyll evulinate (MLE). [5] The traditional upgrading of hemicellulose-derived C 5 sugars to MLE is very complex. [3e] This multistep conversion includes the hydrogenation of FALinto furfuryl alcohol (FOL) in addition to acid-catalyzed alcoholysis (Scheme 1, blue arrows). [6] The hydrogenation process, in particular,r equires high-pressure H 2 , hydrogenation-active sites, and other harsh reaction conditions that hinder the effectiveness of the conversion. [7] Established one-pot productions trategiesf or the conversion of C 5 sugars into MLE have shown only limited success. Hu et al.,f or example, reported ao ne-pot synthesis of MLE from xylose at 7MPa H 2 pressure over Amberlyst 70 (acid) and Pd/Al 2 O 3 (hydrogenat...

Novel One‐Step Process for the Production of Levulinic Acid from Furfural over Hierarchical Zeolites in a Microwave Reactor

“…The earlier studies utilize larger amounts of HM reagent, and/or obtain lower product and/or higher humins yields. [ 12–16 ] While, the present study utilizes a lower formaldehyde:furfural ratio and water as solvent, and reports lower humins yield at reasonably higher LA yields. Moreover, from the formaldehyde consumption data (Table S1, Supporting Information), it was evident that the formaldehyde consumed was relatively low at lower C F (2 wt%), and close to that required for the LA/HMF production.…”

“…obtained a maximum methyl levulinate (MLE) yield of 50.4% in the conversion of glucose and xylose over H‐β zeolite using 1,3,5‐trioxane/methanol mixture. [ 12 ] Zhang et al. [ 13 ] reported a maximum yield of 68% MLE at 97% furfural conversion using D008 solid acid resin in dimethoxymethane (DMM)/methanol solvent system.…”

Molecular Oxygen-Promoted Synthesis of Methyl Levulinate from 5-Hydroxymethylfurfural

“…To begin with, commercially available H-beta25, which has been applied for the synthesis of ML from sugars, , was chosen as the catalyst for the conversion of HMF to ML in methanol. The reaction condition was initially set at 170 °C for 50 min under 10 bar N 2 , and 52% yield of ML was obtained.…”

Levulinic acid production from furfural: process development and techno-economics

“…15 Lyu et al utilized a 1,3,5-trioxane/methanol mixture to convert C5/C6 sugars to MLE. The maximum MLE yields of 47.4 and 50.4% were obtained with xylose (1 wt%) and a glucose + xylose (1 wt%) mixture as feedstocks, respectively, over the Hβ zeolite at 160 °C and 18 h. 16 Zhang et al reported the production of an MLE and LA mixture using DMM/methanol in the transformation of furan (7.1 wt%) over the D008 resin. MLE was obtained in a maximum yield of 67.9% with 97.2% furan conversion at 170 °C and 90 min.…”