Towards efficient and greener processes for furfural production from biomass: A review of the recent trends

As mentioned in several recent reviews, biomass-based furfural is attracting increasing interest as a feasible alternative for the synthesis of a wide range of non-petroleum-derived compounds. However, the lack of environmentally friendly, cost-effective, and sustainable industrial procedures is still evident. This review describes the chemical and biological routes for furfural production. The mechanisms proposed for the chemical transformation of xylose to furfural are detailed, as are the current advances in the manufacture of furfural from biomass. The main goal is to overview the different ways of improving the furfural synthesis process. A pretreatment process, particularly chemical and physico-chemical, enhances the digestibility of biomass, leading to the production of >70 % of available sugars for the production of valuable products. The combination of heterogeneous (zeolite and polymeric solid) catalyst and biphasic solvent system (water/GVL and water/CPME) is regarded as an attractive approach, affording >75 % furfural yield for over 80 % of selectivity with the possibility of catalyst reuse. Microwave heating as an activation technique reduces reaction time at least tenfold, making the process more sustainable. The state of the art in industrial processes is also discussed. It shows that, when sulfuric acid is used, the furfural yields do not exceed 55 % for temperatures close to 180 °C. However, the MTC process recently achieved an 83 % yield by continuously removing furfural from the liquid phase. Finally, the CIMV process, using a formic acid/acetic acid mixture, has been developed. The economic aspects of furfural production are then addressed. Future research will be needed to investigate scaling-up and biological techniques that produce acceptable yields and productivities to become commercially viable and competitive in furfural production from biomass.

Recognizing soft templates as stimulators in multivariate modulation of tin phosphate and its application in catalysis for alkyl levulinate synthesis

Soft template tunes and controls explicitly both morphology and nature of active sites during the synthesis of tin phosphate catalyst. This synthesis strategy helped in producing alkyl levulinate in high yields from one-pot alcoholysis of furfuryl alcohol.

One-pot conversion of alginic acid into furfural using Amberlyst-15 as a solid acid catalyst in γ-butyrolactone/water co-solvent system

One-pot conversion of alginic acid, which was derived from brown algae, to furfural was investigated using various solid acid catalysts. Among the solid acid catalysts tested, Amberlyst-15 showed the highest activity in furfural production in aqueous media. When the effect of reaction media was examined by applying various organic solvent mixtures, it was found that γ-butyrolactone/water co-solvent system was selected as the most appropriate system for the reaction. Maximum furfural yield of 32.2% was obtained using Amberlyst-15 in the γ-butyrolactone/H₂O at 210 °C for 20 min. Catalyst showed gradual deactivation behavior as the reaction proceeded, although the catalyst recovered its activity upon the simple treatment with sulfuric acid. N₂ adsorption-desorption experiments, Fourier-transform infrared spectroscopy (FT-IR), back titration, and CHNS analysis were applied to investigate the physicochemical property of post-reaction samples, confirming that the leaching of the active sulfonic acid group and decrease in acid density was the major cause of deactivation.

Catalytic Upgrading of Biomass-Derived Sugars with Acidic Nanoporous Materials: Structural Role in Carbon-Chain Length Variation

Shifting from petroleum-based resources to inedible biomass for the production of valuable chemicals and fuels is one of the significant aspects in sustainable chemistry for realizing the sustainable development of our society. Various renowned biobased platform molecules, such as 5-hydroxymethylfurfural, furfural, levulinic acid, and lactic acid, are successfully accessible from the transformation of biobased sugars. To achieve the specific reaction routes, heterogeneous nanoporous acidic materials have served as promising catalysts for the conversion of bio-sugars in the past decade. This Review summarizes advances in various nanoporous acidic materials for bio-sugar conversion, in which the number of carbon atoms is variable and controllable with the assistance of the switchable structure of nanoporous materials. The major focus of this Review is on possible reaction pathways/mechanisms and the relationships between catalyst structure and catalytic performance. Moreover, representative examples of catalytic upgrading of biobased platform molecules to biochemicals and fuels through selective C-C cleavage and coupling strategies over nanoporous acidic materials are also discussed.

Hydrolysis of Hemicellulose and Derivatives-A Review of Recent Advances in the Production of Furfural

Biobased production of furfural has been known for decades. Nevertheless, bioeconomy and circular economy concepts is much more recent and has motivated a regain of interest of dedicated research to improve production modes and expand potential uses. Accordingly, this review paper aims essentially at outlining recent breakthroughs obtained in the field of furfural production from sugars and polysaccharides feedstocks. The review discusses advances obtained in major production pathways recently explored splitting in the following categories: (i) non-catalytic routes like use of critical solvents or hot water pretreatment, (ii) use of various homogeneous catalysts like mineral or organic acids, metal salts or ionic liquids, (iii) feedstock dehydration making use of various solid acid catalysts; (iv) feedstock dehydration making use of supported catalysts, (v) other heterogeneous catalytic routes. The paper also briefly overviews current understanding of furfural chemical synthesis and its underpinning mechanism as well as safety issues pertaining to the substance. Eventually, some remaining research topics are put in perspective for further optimization of biobased furfural production.

ZrMn Oxides for Aqueous-Phase Ketonization of Acetic Acid: Effect of Crystal and Porosity

Aqueous-phase ketonization of bio-based acetic acid is important to improve the conversion efficiency of biomass resources. In this study, ZrMn mixed oxides (ZrMnO_x ) with high aqueous-phase ketonization activity are synthetized through a carbonization/oxidation method (COM) and solvothermal method (STM). The results show that ZrMnO_x prepared by COM possesses tetragonal ZrO₂ , and hausmannite Mn₃ O₄ is observed only at a high oxidation temperature of 750 °C. Low-temperature and long oxidation results in decreased crystallinity and crystallite size, which is related to highly dispersed Mnⁿ⁺ species. The catalysts with improved acid sites possess high ketonization activity. Surface areas and pore size of ZrMnO_x synthetized by STM are controlled by the solvents for thermal treatment. Compared with water as solvent, ethanol increases the surface area and pore size, resulting in high ketonization activity.

Aqueous Phase Synthesis of 5-Hydroxymethylfurfural from Glucose over Large Pore Mesoporous Zirconium Phosphates: Effect of Calcination Temperature

For a solid acid-catalyzed dehydration of biomass-derived carbohydrates into useful furan derivatives, a suitable porous solid acid catalyst having an optimum acidic density and its strength is required to avoid cascade reactions in biomass conversion processes. A large-pore mesoporous zirconium phosphate (m-ZrP) was prepared hydrothermally using P123 as a template in water solvent, which resulted in a higher pore diameter (>9 nm) having wormhole-like pore structures with balanced Lewis (L) to Brönsted (B) acid sites. The effects of calcination temperature (500-800 °C) on the textural, acidic/basic, and structural properties of the m-ZrP with its catalytic performance for glucose dehydration to 5-hydroxymethylfurfural (HMF) were investigated in a pure water media as a green and sustainable alternative solvent. The larger number of L and B acid sites and basic sites with their appropriate strengths were clearly related with a better catalytic performance in terms of glucose conversion and HMF yield. The strong L acid and basic sites in the m-ZrP efficiently promoted the glucose isomerization to fructose, which dehydrated exclusively on the weak B acid sites resulting in a maximum conversion of glucose (83.8%) and HMF yield (46.6%). The adjusted acidic and basic sites with large mesopore sizes make the m-ZrP yield a higher reaction rate (2.78 mmol g_cat ^-1 h^-1) and turnover frequency (11.68/h) for conversion of glucose to HMF, which showed higher catalytic activity than those of a small-pore m-ZrP and other mesoporous heterogeneous and homogeneous acid catalysts.

Convenient isolation of strictinin-rich tea polyphenol from Chinese green tea extract by zirconium phosphate

Zirconium phosphate (ZrP) was prepared and employed to separate strictinin-rich tea polyphenol from Chinese green tea extracts. The influences of ZrP calcination temperatures, green tea extraction conditions, and the amounts of ZrP on the isolation of strictinin-rich tea polyphenol were evaluated; the absorption and desorption dynamics of strictinin on ZrP were also determined. Our results revealed that the HPLC content of strictinin increased from 4.96% in 70% ethanol extract of green tea to 58.2% in isolated strictinin-rich tea polyphenol obtained by ZrP-900 (ZrP calcined at 900°C). Furthermore, the suitable time for both strictinin absorption and desorption was 4 hours at 37°C. The method developed here consisted of easy steps such as ZrP absorption, water washing, and 0.4% phosphoric acid solution desorption, which may facilitate the detection and isolation of strictinin from different samples.

Lamellar zirconium phosphates to host metals for catalytic purposes

In the present study a porous lamellar zirconium phosphate heterostructure (PPH) formed from zirconium(iv) phosphate expanded with silica galleries (P/Zr molar ratio equal to 2 and (Si + Zr)/P equal to 3) was prepared to host noble metals.

Heterogeneously Catalyzed Hydrothermal Processing of C5-C6 Sugars

Biomass has been long exploited as an anthropogenic energy source; however, the 21st century challenges of energy security and climate change are driving resurgence in its utilization both as a renewable alternative to fossil fuels and as a sustainable carbon feedstock for chemicals production. Deconstruction of cellulose and hemicellulose carbohydrate polymers into their constituent C₅ and C₆ sugars, and subsequent heterogeneously catalyzed transformations, offer the promise of unlocking diverse oxygenates such as furfural, 5-hydroxymethylfurfural, xylitol, sorbitol, mannitol, and gluconic acid as biorefinery platform chemicals. Here, we review recent advances in the design and development of catalysts and processes for C₅-C₆ sugar reforming into chemical intermediates and products, and highlight the challenges of aqueous phase operation and catalyst evaluation, in addition to process considerations such as solvent and reactor selection.

Heterogeneous Catalytic Conversion of Biobased Chemicals into Liquid Fuels in the Aqueous Phase

Different biobased chemicals are produced during the conversion of biomass into fuels through various feasible technologies (e.g., hydrolysis, hydrothermal liquefaction, and pyrolysis). The challenge of transforming these biobased chemicals with high hydrophilicity is ascribed to the high water content of the feedstock and the inevitable formation of water. Therefore, aqueous-phase processing is an interesting technology for the heterogeneous catalytic conversion of biobased chemicals. Different reactions, such as dehydration, isomerization, aldol condensation, ketonization, and hydrogenation, are applied for the conversion of sugars, furfural/hydroxymethylfurfural, acids, phenolics, and so on over heterogeneous catalysts. The activity, stability, and reusability of the heterogeneous catalysts in water are summarized, and deactivation processes and several strategies are introduced to improve the stability of heterogeneous catalysts in the aqueous phase.

Catalytic cleavage of C–O linkages in benzyl phenyl ether assisted by microwave heating

Hybrid catalyst of ZrP–Pd/C performed effectively for promoting the cleavage of C–O linkages in benzyl phenyl ether forming phenol.