Electron-withdrawing ability tunable polyphosphazene frameworks as novel heterogeneous catalysts for efficient biomass upgrading

A series of polyphosphazene nano-frameworks with electron-withdrawing capability have been produced and exhibited high activity as non-acidic heterogeneous catalysts for the dehydration of fructose to 5-hydroxymethylfurfural under mild conditions with good stability and recyclability. The unique cyclotriphosphazene unit and electron-withdrawing nature of the polymer backbone are essential for the catalytic performance

From Biomass to Sugar Alcohols: Purification of Wheat Bran Hydrolysates Using Boronic Acid Carriers Followed by Hydrogenation of Sugars over Ru/H-ZSM-5

Wheat bran is a lignocellulosic waste of milling industry. It contains hemicelluloses, which can be valorized into arabitol and xylitol via a few-step approach. It begins with extraction and hydrolysis of hemicelluloses to produce a solution of xylose and arabinose, along with proteins and inorganic salts. This work focuses on the purification of sugars of this hydrolysate and the subsequent catalytic production of sugar alcohols. A purification process based on the recovery of sugars by anionic extraction with a boronic acid, followed by back-extraction and a further refining step with ion exchange resins is described. After this process, a high purity sugars solution (∼90%) free of inorganic elements and proteins was obtained. The feasibility of the process was also highlighted by a successful recycling of the organic phase containing the boronic acid. The hydrogenation of purified sugars was then performed over Ru/H-ZSM-5. A high yield into pentitols of ∼70% with 100% selectivity was achieved. Importantly, the catalytic hydrogenation of sugars in the hydrolysate prior to purification did not occur. We determined that proteins caused the deactivation of the catalyst, and consequently, the inhibition of the production of sugar alcohols.Ministerio de Economía, Industria y Competitividad - Fondo Europeo de Desarrollo Regional (project CTQ2015-64892-R

Porous Tin-Organic Frameworks as Selective Epimerization Catalysts in Aqueous Solutions

Epimerization of sugars is a carbon-efficient route not only to produce rare carbohydrates but also to extend the product scope for chemical production in future biorefineries. Industrially available catalysts for epimerization are limited mainly to soluble Mo(VI) species as well as substrate-specific epimerases. Here we report highly active and selective tin-organic frameworks (Sn-OF) as solid catalysts for the epimerization of aldoses at the C-2 position, such as the conversion of glucose to mannose. The reaction proceeds via a carbon skeleton rearrangement, that is, through breaking of a C-2/C-3 carbon bond and formation of a C-1/C-3 bond. Partially hydrolyzed Ph₃Sn-OH sites were found to be the catalytically active centers. Our results suggest that the high catalytic activity of Sn-OFs for the epimerization is determined by (1) Lewis acidity of tin; (2) free Sn-OH groups; and (3) the high hydrophobicity of organic linkers applied in the aqueous solutions

Solvent effects on catalytic activity and selectivity in amine-catalyzed D-fructose isomerization

Rational catalyst design and optimal solvent selection are key to advancing biorefining. Here, we explored the organocatalytic isomerization of D-fructose to a valuable rare monosaccharide, D-allulose, as a function of solvent. The isomerization of D-fructose to D-allulose competes with its isomerization to D-glucose and sugar degradation. In both water and DMF, the catalytic activity of amines towards D-fructose is correlated with their basicity. Solvents impact the selectivity significantly by altering the tautomeric distribution of D-fructose. Our results suggest that the furanose tautomer of D-fructose is isomerized to D-allulose, and the fractional abundance of this tautomer increases as follows: water < MeOH < DMF ≈ DMSO. Reaction rates are also higher in aprotic than in protic solvents. The best D-allulose yield, 14 %, was obtained in DMF with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as the catalyst. The reaction kinetics and mechanism were explored using operando NMR spectroscopy

Alternative Monomers Based on Lignocellulose and Their Use for Polymer Production

Polymeric materials play a key role in modern industry. Owing to outstanding and very versatile properties of polymers, they have rather quickly occupied the great niche of commodities. World plastic production is continuously growing from 1.7 Mton/year in 1950 to 288 Mton/year in 2012. Fossil sources are still required for production of the major part of polymers, as only 5% of chemicals are currently produced from renewable feedstocks. Nevertheless, the application of natural chemicals as feedstocks for the manufacture of polymers is steadily increasing. Different motivations induce such a high interest toward new biobased materials. First of all, the global depletion of petroleum resources and their uneven spread over the world stimulate the rational use of biomass as a renewable and ubiquitous resource. Additionally, overwhelming of dumps with nondegradable plastics causes serious ecological problems, stimulating the developments toward new biodegradable materials. Here we have to point at the distinction between the terms “biobased” and “biodegradable”. Biobased products are manufactured from renewable sources, but several examples of biobased and nonbiodegradable products, e.g., biopolyethylene, biopolyamide 11, exist. It should be noted that each new material has to be tested for biodegradability before it can be claimed to be so. For example, linear polymers produced from itaconic acid are biodegradable, but cross-linking of the polymer chains slows down the biodegradatio

Anionic Extraction for Efficient Recovery of Biobased 2,3-Butanediol-A Platform for Bulk and Fine Chemicals

Drabo P, Tiso T, Heyman B, et al. Anionic Extraction for Efficient Recovery of Biobased 2,3‐Butanediol—A Platform for Bulk and Fine Chemicals. ChemSusChem. 2017;10(16):3252-3259.**Abstract** 2,3‐Butanediol (BDO) presents a promising platform molecule for the synthesis of basic and fine chemicals. Biotechnological production of BDO from renewable resources with living microbes enables high concentrations in the fermentation broth. The recovery of high‐boiling BDO from an aqueous fermentation broth presents a subsequent challenge. A method is proposed for BDO isolation based on reversible complexation with phenylboronate in an anionic complex. BDO can be recovered by back‐extraction into an acidic solution. The composition of the extracted species was determined by NMR spectroscopy, MS, and GC–MS methods. The conditions of extraction and back‐extraction were optimized by using commercial BDO and finally applied to different fermentation broths. Up to 72–93 % BDO can be extracted and up to 80–90 % can be back‐extracted under the optimized conditions. Purified bio‐BDO was used in the presence of sulfuric acid for the synthesis of methyl ethyl ketone, an established organic solvent and discussed tailor‐made biofuel

Binuclear and mononuclear active sites of porous tin-organic frameworks for selective epimerization of D-glucose into D-mannose

Porous tin-organic frameworks (Sn-OFs) are composed of Lewis acid Sn⁴⁺ sites connected via organic linkers by tin-carbon covalent bonds. Although high activity of Sn-OFs for selective epimerization of D-glucose into D-mannose has been reported, the roles of different active sites of the Sn-OFs in catalysis remain under debate. Herein, four Sn-OFs with different aromatic linkers were synthesized and characterized using elemental analysis, low-temperature N₂ adsorption, and SEM, along with ATR-IR, ¹H, ¹³C, and ¹¹⁹Sn MAS NMR, XANES and EXAFS spectroscopies. Comparative studies with organotin model molecules revealed tetraaryltin Ar₄Sn as major structural element of the Sn-OFs with additional sites including dimers Ar₃Sn[sbnd]O[sbnd]SnAr₃, alkylaryltin sites ⁿBuₓAr₍₄₋ₓ₎Sn, and SnO₂. Catalytic tests of the respective organotin molecules suggest Ar₄Sn and Ar₃Sn[sbnd]O[sbnd]SnAr₃ as active sites for the epimerization, whereas the activity of the latter binuclear sites appears to be superior. In contrast, ⁿBuₓAr₍₄₋ₓ₎Sn alkylaryltin sites and SnO₂ contributed to the formation of side products, converting D-glucose into D-fructose. The Sn-OFs with symmetrical linkers are more structured materials exhibiting higher catalytic activity than the Sn-OFs with asymmetrical linkers. These findings clarify the roles of various Sn sites in Sn-OFs, advancing understanding of their catalytic behavior

Green Pathways for the Enzymatic Synthesis of Furan-Based Polyesters and Polyamides

The attention towards the utilization of sustainable feedstocks for polymer synthesis has grown exponentially in recent years. One of the spotlighted monomers derived from renewable resources is 2,5-furandicarboxylic acid (FDCA), one of the most promising bio-based monomers, due to its resemblance to petroleum-based terephthalic acid. Very interesting synthetic routes using this monomer have been reported in the last two decades. Combining the use of bio-based monomers and non-toxic chemicals via enzymatic polymerizations can lead to a robust and favorable approach towards a greener technology of bio-based polymer production. In this chapter, a brief introduction to FDCA-based monomers and enzymatic polymerizations is given, particularly focusing on furan-based polymers and their polymerization. In addition, an outline of the recent developments in the field of enzymatic polymerizations is discussed. </p