Beneficial Effect of Water on the Catalytic Conversion of Sugars to Methyl Lactate in Near-Critical Methanol Solutions

Abstract

Biomass comprises a certain amount of water, which affects the reactions in organic solutions. Generally, water facilitates the hydrolysis of methyl lactate resulting in a decrease of the yield. However, we observed that a certain water content is beneficial for the production of methyl lactate on the conversion of sugars with NiO as a catalyst in near-critical methanol solutions. With water, glycolaldehyde dimethyl acetal, the main side product, was hydrolyzed to glycolaldehye. Glycolaldehye could be transformed to sugars via the aldol condensation at relative higher temperatures, and the sugars were subsequently converted to methyl lactate. NiO could be regenerated by calcination, and water showed almost no adverse effect on the activity of NiO catalyst. The beneficial effect of a certain water content showed a great potential for the direct production of methyl lactate from raw biomass materials without drying.

Mesoporous Sn-In-MCM-41 Catalysts for the Selective Sugar Conversion to Methyl Lactate and Comparative Life Cycle Assessment with the Biochemical Process

“…As a result, the production of ML from fructose usually leads to higher yields than from glucose. 22,28,31 The experiments carried out with Sn-In-MCM-41 (run 1) reached a mean ML yield of 69.4 ± 1.6%, indicating that this catalyst is very selective for the formation of ML. This value of ML yield is an average of six tests carried out at the same conditions.…”

“…As a result, the production of ML from fructose usually leads to higher yields than from glucose. 22 , 28 , 31 …”

“…3 In this context, Holm et al 22 reported the conversion of sucrose to alkyl lactates using zeolites Ti-beta, Zr-beta, and Snbeta with a maximum yield of ML of 64% at 160 °C and 20 h. After that work, other authors reported the utilization of several heterogeneous catalysts: carbon−silica composite, 10 Sn-MWW-type zeolite, 13 Sn-MCM-41, 23,24 Mg-MOF-74, 25 Snbeta zeolite with different modifications, 24,26−29 γ-NiOOH, 30 or NiO. 31 In 2016, Nemoto et al 32 studied the activity of different metal chlorides as homogeneous catalysts in the transformation of sugars to ML. They reported that indium chloride had higher activity than tin chloride for the transformation of fructose, but lower activity if the sugar was dihydroxyacetone; as a result, the authors claimed that indium catalyzes the retro-aldol reaction and tin catalyzes the isomerization.…”

One-pot conversion of dihydroxyacetone into ethyl lactate by Zr-based catalysts

“…Inspired by these ndings, numerous Lewis acid-containing solid materials have been synthesized and used for the preparation of ALs, such as Sn-MCM-41, 12 Sn-MWW, 13 Sn-Mont, 14 SnPO, 15,16 ZrO 2 -TiO 2 , 17 Zr-SBA-15, 18 ZIFs, 19 montmorillonite-supported Pt(II) diphosphane complex 20 and NiO. 21,22 The reported catalysts containing single Lewis acid or base site are responsible for the efficient conversion of dihydroxyacetone (DHA) to lactic acid and its esters. 23 However, the reported catalysts still face a challenge for industrial application due to the complex catalyst preparation procedures or harsh reaction conditions.…”

Catalytic Production of Methyl Lactate from Fructose‐Based Carbohydrates Using Yttrium Modified ZSM‐5 Zeolite

“…Although these Lewis acid‐containing zeolites are active in the conversion of sugars to MLA, their preparation is complex and time‐consuming (more than 40 day for Sn‐ β zeolites), and some tin precursors are also toxic which may hinder their potential industrial applications. In addition, due to the special pore channels, the active zeolite sites are easily occupied by the formed humins and other carbonaceous species unavoidably, resulting in the required calcination for zeolite regeneration to regain activity [3a,9a] . Therefore, simple, active, environmentally benign, and stable solid catalysts should be designed for the conversion of carbohydrates to MLA.…”