Dealuminated Hβ zeolite for selective conversion of fructose to furfural and formic acid

The fructose-to-furfural transformation is facing major challenges in the selectivity and high efficiency. Herein, we have developed a simple and effective approach for the selective conversion of fructose to furfural using Hβ zeolite modified by organic acids for dealuminization to regulate its textural and acidic properties. It was found that citric acid-dealuminized Hβ zeolite possessed high specific surface areas, wide channels and high Brønsted acid amount, which facilitated the selective conversion of fructose to furfural with a maximum yield of 76.2% at433 K for 1 h in the γ-butyrolactone(GBL)-H_(2)O system, as well as the concomitant formation of 83.0% formic acid. The^(13)C-isotope labelling experiments and the mechanism revealed that the selective cleavage of C1–C2 or C5–C6 bond on fructose was firstly occurred to form pentose or C5 intermediate by weak Brønsted acid, which was then dehydrated to furfural by strong Brønsted acid. Also this dealuminized Hβ catalyst showed the great recycling performance and was active for the conversion of glucose and mannose.

Co-Production of High-Grade Dissolving Pulp,Furfural,and Lignin from Eucalyptus via Extremely Low Acid Pretreatment and Pulping Technologies and Catalysis

Hemicellulose and lignin are not reasonably utilized during the dissolved pulp preparation process.This work aimed to propose a process for the co-production of dissolving pulp,furfural,and lignin from eucalyptus.High-grade dissolving pulp was prepared from eucalyptus using a combination of extremely low acid(ELA)pretreatment,Kraft cooking,and elementary chlorine-free(ECF)bleaching.The obtained pre-hydrolysate was catalytic conversion into furfural in a biphasic system,and lignin during Kraft cooking and ECF was recovered.The process condition was discussed as well as the mass flow direction.The results showed that ELA pretreatment could effectively remove 80.1%hemicellulose.Compared with traditional hydrothermal pretreatment,the ELA pretreatment significantly increased the xylose yield from 5.05 to 14.18 g/L at 170℃ for 2 h,which had practical significance for furfural production.The 82.7%furfural yield and 82.9%furfural selectivity were obtained from xylose-rich pre-hydrolysate using NaCl as a phase modifier in a biphasic system with 4-methyl-2-pentanone(MIBK)as an organic phase by ion exchange resin catalysts at 190℃ for 2 h.Subsequently,the pretreated eucalyptus was subjected to Kraft cooking,and the optimal alkali amount was 14%.Then,the Kraft pulp was bleached using the O-D1-EP-D_(2) sequence,and dissolving pulp was obtained with an ISO brightness of 86.0%,viscosity of 463 mL/g,andα-cellulose content of 95.4%.The Kraft lignin which has a potential application was investigated by 2D-HSQC NMR and 31P NMR.The results showed that the S/G ratio of Kraft lignin was 1.93,and the content of phenolic hydroxyl groups was 2.53 mmol/g.Moreover,based on the above proposed process,30.5 g dissolving pulp,5.5 g furfural,and 21.2 g lignin per 100 g eucalyptus chips(oven dry)were produced.This research will provide new catalysis and pulping technical routes for dissolving pulp,furfural,and Kraft lignin products,which are in great demand in the chemical industry.

Biochar-based Solid Acids as Catalysts for Carbohydrate Hydrolysis: A Critical Review

Recently, increasing interest has been focused on the hydrolysis of carbohydrates to monosaccharides, among which, glucose and xylose as typical platform sugars can be used to produce chemicals and biofuels. As heterogeneous catalysts, solid acids have gained extensive attention for biomass biorefinery and could replace the conventional process owing to their excellent properties, including acceptable acidity and easy separation. In particular, biochar-based solid acids derived from biomass are promising for biomass conversion owing to the low-cost of feedstocks and the simple preparation procedure. Herein, we attempt to provide a critical overview of biochar-based solid acids for hydrolysis of carbohydrates into glucose and xylose. The preparation methods and properties of biochar-based catalysts as well as the influence of their properties on catalytic performance were discussed in detail. We also highlight the major challenges facing the use of biochar-based solid acids for carbohydrate hydrolysis.

Triethylamine-catalyzed Isomerization of Glucose to Fructose under Low Temperature Conditions in Aqueous Phase

Isomerization of glucose derived from lignocellulosic biomass is an important step in biorefinery.Fructose isomerized from glucose,is used as a highly attractive sweetener in the food and beverages industries.However,the prevalence of side reactions at high glucose concentrations is a serious issue,leading to a significant reduction in the fructose yield,especially in the aqueous phase.In this study,an efficient method for the conversion of highly concentrated glucose into fructose under low temperature conditions using triethylamine as the catalyst was developed.It was demonstrated that high fructose yield could be maintained at high glucose concentration.At 60℃,fructose yield of 38.7%and fructose selectivity of 80.6%were achieved in 1 mol/L(approximately 17 wt%)glucose.When glucose concentration was increased to 2 mol/L(approximately 31 wt%),the fructose yield and selectivity were maintained at 34.7%and 77.4%,respectively.13C nuclear magnetic resonance(NMR)spectrometer was used to examine the glucose isomerization reaction.Compared to the NaOH catalytic system,triethylamine acted as a buffer to provide a stable alkaline environment for the catalytic system,further maintaining a high level of catalytic efficiency for the isomerization of glucose to fructose.