C6 Polyols Research Articles

PRODUCTION OF ESTERS BY ETERIFICATION OF FATTY ACIDS OF SUNFLOWER, OLIVE AND SOYBEAN OILS WITH MANNITOL, SORBITOL AND XYLITOL

Polyol esters are widely used in various fields of science and technology, food industry, sanitation, medicine, cosmetics, etc. In engineering, polyol esters are mainly used as high-temperature lubricating oils․Esters of polyols with a degree of substitution from 1:1 to 3:1 are used as emulsifiers, stabilizers, defoamers, dispersants and detergents. Esters of saturated carboxylic acids С12 – С18 – with a degree of substitution from 4:1 to 6:1 are thick or hard oils and are used in medicine, pharmacy and cosmetology. In our early studies, with the esterification of mannitol and other C4 – C6 polyols with some higher aliphatic acids in molar ratios of 1: 3÷6, various esters were obtained. The synthesized oil-like products were similar in their physicochemical and rheological properties to natural fats and oils and had melting points in the range of –10...64 °C. However, differing from artificial oils, natural fats and oils contains variety of saturated and unsaturated fatty acids C6 – C12. Therefore, in order to obtain more natural oil and fat substitutes, it seems appropriate to obtain esters of higher polyols with a complex of natural fatty acids. This paper presents data on obtaining a complex of fatty acids of sunflower, olive and soybean oils and further synthesis of esters with mannitol, sorbitol and xylitol in molar ratios of 1: 3...6. The studies were carried out according to the following scheme: A) hydrolysis of sunflower, olive and soybean oils with an alkali solution, with the formation of a mixture of carboxylic acids, consisting mainly of oleic, linoleic, stearic and palmitic acids; B) neutralization of alkali salts, isolation and drying of fatty acids mixtures; C) esterification of mannitol, sorbitol and xylitol with fatty acid complexes; D) purification and drying of non-glyceride oils; E) determination of the main physicochemical properties of the obtained artificial oils. The reaction progress is monitored by HPLC method on an Agilent Infinity II HPLC 1260 System instrument and by IR spectra method on an IKS 29 instrument. The completion of polyol esterification reactions with fatty acid complexes is determined by the disappearance of absorption bands in the IR spectra in the region of 1740 and 2500...2700 cm˗1. Outputs of artificial oils in optimal conditions reach 95-97%. Non-glyceride oils are intended for testing as substitutes for natural oils and fats.

Gold structures on 3D carbon electrodes as highly active nanomaterials for the clean energy conversion of crude glycerol

The electrochemical stability of gold nanomaterials and their ability to oxidize C2 and C3 polyols makes them suitable electrocatalysts for the oxidation of biofuels like crude glycerol. In this work, Au nanomaterials were electrodeposited by differential pulse amperometry (named as Au DPA 1&2) and cyclic voltammetry (Au CV 1&2) onto 3D porous carbon paper electrodes. X‒ray diffraction patterns indicated that DPA promoted the abundance of Au with {100} surface domains (Au DPA 2), and it was attributed to the formation of 3D hierarchical structures known to be rich in surface/crystalline defects. While, CV allowed to obtain hemispheres with small particle sizes. For the crude glycerol oxidation, Au DPA 2 was the most active material, displaying 56.2 mA cm−2 at 0.5 M crude glycerol + 3 M KOH at 20 mV s−1, and onset potential of −0.13 V vs. NHE (only 70 mV more positive than monometallic Pd). According to impedance studies, this activity was attributed to the decrease of the resistances to charge transfer (Rct) at different steps of the electrocatalytic process, suggesting a better renewal of actives sites, and a better tolerance to poisoning by intermediates. Differential pulse voltammetry (DPV) curves demonstrated that the abundance of {100} surface sites enhanced the OH− adsorption to form Au(OH)ads species lowering the potentials to start the reaction, boosting the activity and durability.

Total chemocatalytic cascade conversion of lignocellulosic biomass into biochemicals

Because of its complexity, selective conversion of lignocellulosic biomass into platform chemicals presents significant challenges. Herein, we converted birch wood into high-yield lignin-derived phenolic monomers and dimers and holocellulose-derived polyols and monocarboxylic acids via a two-step cascade reaction using 0.1 wt% Pd on N-doped carbon (Pd0.1/CNx) and passivated alumina-coated Ni on activated carbon (Ni2 @Al2O3/AC) catalysts. The catalytic fractionation of birch sawdust using Pd0.1/CNx produced 11.1 wt% monomers, 5.6% dimers, and 63.4 wt% pulp-rich solid (PRS) based on feed weight. The subsequent conversion of PRS over passivated Ni2 @Al2O3/AC produced 21.6 wt% C2–C6 polyols and 7.9 wt% monocarboxylic acids. After the whole biomass conversion reaction, the Pd0.1/CNx and Ni2 @Al2O3/AC catalysts were separated using their different magnetic responses and reused three times without activity loss. The structure–performance relationships of the Pd0.1/CNx catalysts synthesized using different methods and effect of passivation on the performance of the Ni2 @Al2O3/AC catalyst were analyzed.

Catalytic Hydrogenolysis of Biomass-derived Polyhydric Compounds to C2–C3 Small- Molecule Polyols: A Review

Biomass energy has attracted much attention because of its clean and renewable characteristics. At present, C2–C3 polyols such as glycerol, 1,2-propanediol, and ethylene glycol, widely used as platforms for downstream chemicals or directly used as chemicals in diversified industries, mainly depend on the petrochemical industry. In terms of the feedstock for C2–C3 polyol production, the C3-derived glycerol is a side product during biodiesel synthesis, whereas the C5-derived xylitol and C6-derived sorbitol can be mainly obtained by hydrolysis–hydrogenation of hemicellulose and cellulose from lignocellulosic biomass, respectively. In this review, we summarize the catalysts and catalysis for selective hydrogenolysis of these polyhydric compounds to C2–C3 polyols and introduce the reaction pathways for the target polyol formation based on the C3, C5, and C6 polyhydric alcohol hydrogenolysis. Finally, state-of-the-art technologies are described and the remaining challenges and further prospects are presented in view of the technical aspects.

Investigation of the mechanism of the selective hydrogenolysis of C O bonds over a Pt/WO3/Al2O3 catalyst

Abstract The hydrogenolysis of various polyols and ethers over a Pt/WO3/Al2O3 catalyst was investigated. The hydrogenolysis rate of a C O bond at a secondary carbon was higher than that at a primary carbon, indicating that a hydroxyl (OH) group at a primary carbon played an important role in the dissociation of a C O bond. Moreover, the dissociation position of the C O bond in alcohols and ethers strongly depended on the stability of the carbocation intermediate, and hydrogenolysis via a secondary carbocation as an intermediate proceeded preferentially to that via a primary carbocation. The kinetics of the hydrogenolysis of C3 polyols were also investigated. The reaction orders with respect to the concentrations of glycerol, 1,2- and 1,3-propanediol were almost the same. In contrast, different reaction orders with respect to the H2 pressure were observed for the hydrogenolysis of C3 polyols with or without vicinal OH groups, indicating that the dissociation of a C O bond at primary and secondary carbons proceeded via completely different mechanisms. These investigations suggested that both the structure and position of a substrate on the catalyst surface must be controlled for highly selective hydrogenolysis.

Influence of Lewis Acid on the Activity and Selectivity of Pt/MCM-41 (Al) Catalysts for Oxidation of C3 Polyols in Base-Free Medium

The nature of a solid support is crucial for the metal–support interaction, leading to tunable activity and selectivity on supported catalysts. We prepared the Lewis acidic MCM-41 (Al)-supported Pt catalysts for selective oxidation of C3 polyols in base-free medium. Catalyst characterizations (e.g., high-angle annular dark-field scanning transmission electron microscopy and X-ray photoelectron spectroscopy) and density functional theory calculations confirmed that the electron transfer from Pt to MCM-41 (Al) weakens the adsorption of reactants and products, and the enhanced metal–support interaction between Pt and Lewis acid of MCM-41 (Al) promotes the selectivity of carboxylic acids by preventing the cleavage of the C–C bond of polyols. The conversion of glycerol and the selectivity of glyceric acid were 72.2 and 77.9%, respectively, over 3 wt % Pt/MCM-41catalyst (Si/Al ratio, 70) at 60 °C and 1 MPa O2. In addition, the location and number of hydroxyl groups also affect the catalytic oxidation activity. The insights may provide new suggestions on design of the bifunctional Pt–Lewis catalyst for the selective oxidation of alcohols.

Adsorption of Biomass-Derived Polyols onto Metal–Organic Frameworks from Aqueous Solutions

Adsorption of biomass-derived polyols from dilute aqueous solutions as an alternative to energy-intensive distillation has a significant impact on the economics of biorefinery. A series of metal–organic frameworks (MOFs) which differ in chemical functionality and topology (SOD and RHO) are screened as adsorbents in this study. It has been demonstrated that SIM-1 (Zn(almeIm)2, SOD topology, almeIm = 4-methylimidazole-5-carbaldehyde) outperforms other studied MOFs, namely ZIF-8, ZIF-90, ZIF-93, and ZIF-97, in terms of the adsorption capacity. The hydrophobic/hydrophilic balance and aperture/pore size of adsorbents are two key factors controlling the adsorption capacity. The adsorption of C2–C3 polyols onto SIM-1 increased in the order of glycerol < ethylene glycol < 1,3-propanediol, which has a positive correlation with their octanol–water partition coefficients (Kow). In addition, SIM-1 exhibited preferential adsorption of 1,3-propanediol over glycerol, indicating the promising application of SIM-1 as adso...

Torulaspora delbrueckii produces high levels of C5 and C6 polyols during wine fermentations.

Non-Saccharomyces yeasts impact wine fermentations and can diversify the flavor profiles of wines. However, little information is available on the metabolic networks of most of these species. Here we show that unlike the main wine yeast Saccharomyces cerevisiae, Torulaspora delbrueckii and to a lesser extent Lachancea thermotolerans produce significant concentrations of C5 and C6 polyols under wine fermentation conditions. In particular, D-arabitol, D-sorbitol and D-mannitol were produced at significant levels. Their release into the extracellular matrix started when that of glycerol ceased. The data also show that polyol production is influenced by initial sugar concentration, repressed by acetic acid and induced in ethanol supplemented media. Moreover, unlike glycerol and sorbitol, mannitol was partially re-assimilated when populations started to decline. The findings suggest that polyol synthesis is a physiological adaptation to stressful conditions characteristic of alcoholic fermentation and that these polyols may serve a similar purpose as glycerol production in S. cerevisiae, including osmoadaptation and redox balancing.

Sustainable Synthesis of Oxalic and Succinic Acid through Aerobic Oxidation of C6 Polyols Under Mild Conditions.

The sustainable chemical industry encompasses a shift from the use of fossil carbon to renewable carbon. The synthesis of chemicals from nonedible biomass (cellulosic or oil) represents one of the key steps for "greening" the chemical industry. In this paper, we report the aerobic oxidative cleavage of C6 polyols (5-HMF, glucose, fructose and sucrose) to oxalic acid (OA) and succinic acid (SA) in water under mild conditions using M@CNT and M@NCNT (M=Fe, V; CNT=carbon nanotubes; NCNT=N-doped CNT), which, under suitable conditions, were recoverable and reusable without any loss of efficiency. The influence of the temperature, O2 pressure (PO2 ), reaction time and stirring rate are discussed and the best reaction conditions are determined for an almost complete conversion of the starting material and a good OA yield of 48 %. SA and formic acid were the only co-products. The former could be further converted into OA by oxidation in the presence of formic acid, resulting in an overall OA yield of >62 %. This process was clean and did not produce organic waste nor gas emissions.

Cooperative action of heteropolyacids and carbon supported Ru catalysts for the conversion of cellulose

Acid hydrolysis and hydrogenation/hydrogenolysis reactions can be combined for catalytic conversion of cellulose into renewable biorefinery feedstocks by using heterogeneous bifunctional catalysts. In the present study a cooperative effect of heteropolyacids (HPA) and Ru nanoparticles supported on two carbon materials is demonstrated. The process can be suitable for the one-pot tandem reaction, yielding the conversion of cellulose into alkanediols (mainly propylene glycol and ethylene glycol).From a mechanistic point of view the differences in the distribution of polyol products, obtained from the cellulose reaction over monometallic Ru catalysts or over bifunctional Ru-HPAs materials, seem to be strongly determined by the competitive reactions of the sucrose (glucose+fructose) intermediate. HPA not only promote, as solid acids, the efficient hydrolysis of cellulose to glucose, but also catalyze the selective cleavage of the CC bonds in glucose and fructose, leading to the formation of ethylene glycol and propylene glycol. These reactions are in competition with the sugar hydrogenation to the corresponding C6 polyols (e.g. sorbitol), which takes place on the single Ru surface sites. The strong dependence of the product distribution on both catalytic functions is clarified by the kinetic analysis of the three competitive reactions of glucose, including its hydrogenation, isomerization and CC bond cleavage.Finally, considering the applicability of this reaction, it should be raised that the ball-milling pretreatment of cellulose is compulsory. In fact, during this ball-milling the crystallinity and particle size of cellulose are reduced, which results in a much higher conversion of cellulose. Herein, mixed ball-milling of cellulose and solid catalysts together was presented, which remarkably accelerates the cellulose conversion into valuable products.

Upgrading Lignocellulosic Biomasses: Hydrogenolysis of Platform Derived Molecules Promoted by Heterogeneous Pd-Fe Catalysts

This review provides an overview of heterogeneous bimetallic Pd-Fe catalysts in the C–C and C–O cleavage of platform molecules such as C2–C6 polyols, furfural, phenol derivatives and aromatic ethers that are all easily obtainable from renewable cellulose, hemicellulose and lignin (the major components of lignocellulosic biomasses). The interaction between palladium and iron affords bimetallic Pd-Fe sites (ensemble or alloy) that were found to be very active in several sustainable reactions including hydrogenolysis, catalytic transfer hydrogenolysis (CTH) and aqueous phase reforming (APR) that will be highlighted. This contribution concentrates also on the different synthetic strategies (incipient wetness impregnation, deposition-precipitaion, co-precipitaion) adopted for the preparation of heterogeneous Pd-Fe systems as well as on the main characterization techniques used (XRD, TEM, H2-TPR, XPS and EXAFS) in order to elucidate the key factors that influence the unique catalytic performances observed.

Catalytic routes and oxidation mechanisms in photoreforming of polyols

Photocatalytic reforming of biomass-derived oxygenates leads to H2 generation and evolution of CO2via parallel formation of organic intermediates through anodic oxidations on a Rh/TiO2 photocatalyst. The reaction pathways and kinetics in the photoreforming of C3–C6 polyols were explored. Polyols are converted via direct and indirect hole transfer pathways resulting in (i) oxidative rupture of C–C bonds, (ii) oxidation to α-oxygen functionalized aldoses and ketoses (carbonyl group formation) and (iii) light-driven dehydration. Direct hole transfer to chemisorbed oxygenates on terminal Ti(IV)-OH groups, generating alkoxy-radicals that undergo ß-C–C-cleavage, is proposed for the oxidative C–C rupture. Carbonyl group formation and dehydration are attributed to indirect hole transfer at surface lattice oxygen sites [Ti⋯O⋯Ti] followed by the generation of carbon-centered radicals. Polyol chain length impacts the contribution of the oxidation mechanisms favoring the C–C bond cleavage (internal preferred over terminal) as the dominant pathway with higher polyol carbon number.

Insight into the function of base-promoted Cu-containing catalysts for highly efficient hydrogenolysis of cellulose into polyols

The Cu-containing catalysts were synthesized via thermal treatment of the CuMgAl hydrotalcite with a fixed metal ratio at various calcination temperatures. The bi-functional solid base catalysts exhibited high activity for the hydrogenolysis of highly concentrated cellulose. The hydrotalcite precursors and the calcined samples were characterized by means of X-ray diffraction (XRD), thermogravimetric analysis (TG), N2 adsorption–desorption, temperature-programmed reduction of H2 (H2-TPR), temperature-programmed desorption of CO2 (CO2-TPD) and dissociative N2O adsorption. The characterization results indicated that the transformation of structure was caused by the increasing calcination temperature, which could further influence the numbers of the base sites and metal active sites in the CuMgAl catalysts. The hydrogenolysis of cellulose was systematically investigated over different catalytic systems. With the CuMgAl-600 catalyst, complete conversion of cellulose can be accomplished and the highest yield obtained is 81.4%, with total polyols yields obtained are 59.1% for the C2–C3 polyols. In addition, either the in-situ hydroxyl or the hydrated OH− due to the “memory effect” of hydrotalcite as Brønsted bases, was proved to exhibit promotional effect on the hydrogenolysis of cellulose, which could effectively substitute the effect of ionizing alkali. Furthermore, it is noteworthy that the conversion of cellulose could maintain up to 90.2% with unobvious formation of coke-like precipitates when the cellulose concentration reached a high level of 18%.

Kinetic insight into the effect of the catalytic functions on selective conversion of cellulose to polyols on carbon-supported WO3 and Ru catalysts

Efficient conversion of cellulose, the most abundant biomass on Earth, to chemicals in high yields remains a formidable challenge. Here, we report the marked change in the distribution of polyol products in the cellulose reaction on Ru/C and WO3/C, strongly depending on the competitive reactions of the glucose intermediate. WO3 crystallites not only promote, as a solid acid, the efficient hydrolysis of cellulose to glucose, but also catalyze the selective cleavage of the C–C bonds in glucose and other C6 sugar intermediates, leading to the formation of ethylene glycol and propylene glycol, in competition with the sugar hydrogenation to the corresponding C6 polyols (e.g. sorbitol) on Ru/C. The basic C support, behaving similar to other solid bases (i.e. MgO), catalyzes the isomerization of glucose into fructose, leading to the favored formation of propylene glycol instead of ethylene glycol. Such strong dependence of the product distribution on the catalytic functions is clarified by the kinetic analysis of the three competitive reactions of glucose, including its hydrogenation, isomerization and C–C bond cleavage. Importantly, such kinetic analysis can predict the maximum selectivity ratio of propylene glycol to ethylene glycol, which is 2.5, for example, at 478K under the reaction conditions in this work, corresponding to a maximum yield of propylene glycol of ∼71%. These understandings shed new insights into the selective conversion of cellulose, which provides guidance for the rational design of catalyst functions and tuning of reaction parameters towards the controllable synthesis of specific products from cellulose.

Unravelling the Ru‐Catalyzed Hydrogenolysis of Biomass‐Based Polyols under Neutral and Acidic Conditions

The aqueous Ru/C-catalyzed hydrogenolysis of biomass-based polyols such as erythritol, xylitol, sorbitol, and cellobitol is studied under neutral and acidic conditions. For the first time, the complete product spectrum of C2 C6 polyols is identified and, based on a thorough analysis of the reaction mixtures, a comprehensive reaction mechanism is proposed, which consists of (de)hydrogenation, epimerization, decarbonylation, and deoxygenation reactions. The data reveal that the Ru-catalyzed deoxygenation reaction is highly selective for the cleavage of terminal hydroxyl groups. Changing from neutral to acidic conditions suppresses decarbonylation, consequently increasing the selectivity towards deoxygenation.

Sorbitol hydrogenolysis to glycerol and glycols over M-MgO (M = Ni, Co, Cu) nanocomposite: A comparative study of active metals

The activities and selectivities of MgO-supported Ni, Cu, and Co catalysts have been compared in aqueous-phase hydrogenolysis of sorbitol to glycerol and glycols. All catalysts effectively catalyzed the sorbitol conversion into C2 and C3 polyols like glycerol, 1,2-propylene glycol, and ethylene glycol, but with different product distributions. The differences in activities and selectivities are ascribed to their different dehydrogenation/hydrogenation activities. The influences of base promoter, temperature, H2 pressure, and reaction time were also studied. Added base promoter and prolonged reaction time enhanced sorbitol conversion for the three catalysts, but led to product degradation and decreased selectivity over Ni-MgO and Co-MgO, whereas selectivity maintained almost unchanged over Cu-MgO.

Production of C2 and C3 polyols from d-sorbitol over hydrotalcite-like compounds mediated bi-functional Ni–Mg–Al–Ox catalysts

Production of C2 and C3 polyols from d-sorbitol over Ni/MgxAlyOx+1.5y catalysts with different Mg/Al molar ratio were performed under mild conditions. It was found that this reaction proceeded effectively over these bi-functional catalysts prepared via thermal decomposition and reduction of Ni–Mg–Al hydrotalcite-like compounds. The detected conversion of d-sorbitol over Ni/Mg1.29Al0.06O1.38 reached 80.7% at 453K and further increased to 97.0% at 473K. Characterizations indicate that the performance of these catalysts depended mainly on its surface basicity.

Selective electrocatalytic oxidation of sorbitol to fructose and sorbose.

A new electrocatalytic method for the selective electrochemical oxidation of sorbitol to fructose and sorbose is demonstrated by using a platinum electrode promoted by p-block metal atoms. By the studying a range of C4, C5 and C6 polyols, it is found that the promoter interferes with the stereochemistry of the polyol and thereby modifies its reactivity.

Kinetic Study of Catalytic Conversion of Cellulose to Sugar Alcohols under Low‐Pressure Hydrogen

AbstractEfficient hydrolytic hydrogenation of cellulose to sugar alcohols under low H2 pressures has remained a challenge. This article deals with the conversion of cellulose by using a carbon‐supported Ru catalyst under H2 pressures as low as 0.7–0.9 MPa (absolute pressure at room temperature). Kinetic studies revealed that the Ru catalyst not only enhances the hydrolysis of cellulose to glucose and hydrogenation of glucose to sugar alcohols (sorbitol and mannitol), but also the degradation of sugar alcohols to C2–C6 polyols and gasses. The degradation path limits the total yield of sugar alcohols to less than 40 %. The yield of sugar alcohols is theoretically improved by increasing the ratio of the reaction rates of the cellulose hydrolysis, which is the rate‐determining step in the reaction, to the decomposition. Thus, a mix‐milling pretreatment of cellulose and the Ru catalyst together selectively accelerated the hydrolysis step and raised the yield up to 68 %, whereas the addition of acids in the cellulose conversion was less effective as a result of promotion of side‐reactions. These results demonstrate superior applicability of the mix‐milling treatment in the depolymerization of cellulose to its monomers.

Atom Economical Aqueous-Phase Conversion (APC) of Biopolyols to Lactic Acid, Glycols, and Linear Alcohols Using Supported Metal Catalysts

Conversion of renewable biopolyols to value-added chemicals such as lactic acid and glycols usually demands excess hydrogen/oxygen or harsh reaction conditions in strong alkaline medium (220–350 °C). This unfortunately promotes significant side reactions resulting in low carbon selectivity to liquid products, posing significant challenges for the development of sustainable technologies. We report here a new atom economical catalytic conversion of various biopolyols (glycerol, xylitol, mannitol, and sorbitol) to lactic acid with glycols and linear alcohols as co-products at much lower temperatures (115–160 °C) without external addition of either hydrogen or oxygen. Among various metal-based catalysts (Pt, Pd, Rh, Ru, Raney Ni, Raney Co, and Cu) evaluated, Pt/C catalyst gives the highest chemoselectivity (S > 95%) for lactic acid, glycols, and linear alcohols at 115–160 °C. An important finding is that approximately two-thirds of the hydrogen generated in situ via dehydrogenation of polyols over Pt/C catalyst is efficiently utilized for the conversion of the remaining polyols and intermediates to useful products (e.g., glycols and linear alcohols instead of gaseous products) with the remaining available hydrogen for use elsewhere in a biorefinery. The Pt/C catalyst is thus multifunctional facilitating tandem dehydrogenation/hydrogenolysis of polyols. Furthermore, it is observed that Ba2+ alkali ion promotes the activity of the Pt/C catalyst by almost 12-fold compared to other alkali promoters such as NaOH, KOH, and Ca(OH)2. In addition to being the first reported study on the conversion of C5∼C6 polyols (e.g., xylitol and sorbitol) to lactic acid at relatively low temperatures, the results also provide new insights into the mechanism of tandem catalysis of biopolyols conversion to value-added commodity chemicals.