Cascade Production of Lactic Acid from Universal Types of Sugars Catalyzed by Lanthanum Triflate

Abstract

Lignocellulosic biomass conversion into value-added platform chemicals in the non-toxic, water-tolerant Lewis acid, and water solutions bears the hallmark of green chemistry. Lactic acid derived from biomass is an important chemical building block for biodegradable polymers such as polylactide. Herein, a universal method of converting lignocellulosic sugars into lactic acid using catalytic amount of water-stable Lewis acid La(OTf) is demonstrated. The lignocellulosic sugars studied in this work include 1) pyrolytic sugars from pyrolysis oil, and 2) sugars derived from ionic liquid (IL)-pretreated biomass. Under moderate conditions (250 °C, 1 h), levoglucosan (major pyrolytic sugar), glucose, and xylose were converted into lactic acid with carbon-based molar yields of 75, 74, and 61 %, respectively. Furthermore, roughly 49 mol % (based on levoglucosan) and 74 wt % (relative to pretreated biomass) of lactic acid were obtained from the conversion of pyrolytic sugars and sugar-rich fraction after lignin removal from switchgrass, respectively. To our knowledge, this is the first reported conversion of pyrolytic sugar into lactic acid by chemocatalysis and also lignocellulosic sugars are converted into lactic acid without hydrolysis. This approach could potentially be extended to other lignocellulosic sugars after simple removal of lignin from biomass pretreatment, rendering moderate to high yields of lactic acid.

Levoglucosan: a promising platform molecule?

“…139 Lactic acid was also prepared by a simple universal method using a La(OTf ) 3 water resistant Lewis acid. 140 They demonstrated that under moderate conditions (250°C, 1 h) levoglucosan was transformed to lactic acid with the total yield was 75%. This yield was comparable to that obtained with other sugars such as glucose and xylose (74 and 64% respectively).…”

Catalytic Processes from Biomass-Derived Hexoses and Pentoses: A Recent Literature Overview

“…To increase productivities, working with more concentrated feedstock, the catalytic strategy could be an alternative. Liu et al have recently proved that pyrolytic sugars (levoglucosan, glucose and xylose) can be converted in acceptable yields to LA (75, 74 and 61% based on C content) using lanthanum triflate, a Lewis acid catalyst [85]. This approach can be successfully extended to cellulose (73% C yield).…”

Chemocatalytic Production of Lactates from Biomass-Derived Sugars

“…Nevertheless, very few studies researched LA production directly from cellulosic biomass, due to the complexity of biomass structures (i.e., cellulose, hemicellulose, and lignin), along with the catalyst deactivation induced by lignin [89]. Interestingly, Liu et al presented a valuable work regarding LA production directly from lignocellulosic sugars including levoglucosan, glucose, and xylose with good yields [70]. Using a Lewis acid catalyst, La(OTf ) 3 which is stable in both aqueous and organic solvent, 61% LA yield for C 5 sugars and >70% LA yield from C 6 sugars could be obtained.…”