Aqueous phase hydrogenolysis of glycerol to bio-propylene glycol over Pt-Sn catalysts

Heterogeneous Catalysts for Glycerol Biorefineries: Hydrogenolysis to 1,2-Propylene Glycol

Research on the use of biomass resources for the generation of energy and chemical compounds is of great interest worldwide. The development and growth of the biodiesel industry has led to a parallel market for the supply of glycerol, its main by-product. Its wide availability and relatively low cost as a raw material make glycerol a basic component for obtaining various chemical products and allows for the development of a biorefinery around biodiesel plants, through the technological integration of different production processes. This work proposes a review of one of the reactions of interest in the biorefinery environment: the hydrogenolysis of glycerol to 1,2-propylene glycol. The article reviews more than 300 references, covering literature from about 20 years, focusing on the heterogeneous catalysts used for the production of glycol. In this sense, from about 175 catalysts, between bulk and supported ones, were revised and discussed critically, based on noble metals, such as Ru, Pt, Pd, and non-noble metals as Cu, Ni, Co, both in liquid (2-10 MPa, 120-260 °C) and vapor phase (0.1 MPa, 200-300 °C). Then, the effect of the main operational and decision variables, such as temperature, pressure, catalyst/glycerol mass ratio, space velocity, and H₂ flow, are discussed, depending on the reactors employed. Finally, the formulation of several kinetic models and stability studies are presented, discussing the main deactivation mechanisms of the catalytic systems such as coking, leaching, and sintering, and the presence of impurities in the glycerol feed. It is expected that this work will serve as a tool for the development of more efficient catalytic materials and processes towards the future projection of glycerol biorefineries.

Selective Production of 1,2-Propanediol or 1,3-Propanediol from Glycerol Hydrogenolysis over Transition Metal Doped Pt/TiO2

Selective hydrogenolysis of biomass-derived glycerol to propanediol is important for producing high value-added chemicals from renewable resources but faces a huge challenge. Here we report a transition metal doped Pt/TiO₂ catalyst with incorporated Cr, Mo, or W oxides, which exhibits the selective formation of 1,2-propanediol or 1,3-propanediol with a yield from 51.2% to 82.5% toward glycerol hydrogenolysis. In situ experimental studies verify that the surrounding CrO_x decreases the hydrogenating ability of Pt, leading to the formation of 1,2-propanediol, while the MoO_x or WO_x brings the Brønsted acid, giving 1,3-propanediol. This modification based on the catalyst compositions alters the reaction pathway with a different adsorption and bond scission mechanism, which can be extended to other sustainable catalytic systems.

Production of Propanediols through In Situ Glycerol Hydrogenolysis via Aqueous Phase Reforming: A Review

Production of 1,2-propanediol and 1,3-propanediol are identified as methods to reduce glycerol oversupply. Hence, glycerol hydrogenolysis is identified as a thermochemical conversion substitute; however, it requires an expensive, high-pressure pure hydrogen supply. Studies have been performed on other potential thermochemical conversion processes whereby aqueous phase reforming has been identified as an excellent substitute for the conversion process due to its low temperature requirement and high H2 yields, factors which permit the process of in-situ glycerol hydrogenolysis which requires no external H2 supply. Hence, this manuscript emphasizes delving into the possibilities of this concept to produce 1,2-propanediol and 1,3-propanediol without “breaking the bank” with expenses. Various heterogenous catalysts of aqueous phase reforming (APR) and glycerol hydrogenolysis were identified, whereby the combination of a noble metal, support, and dopant with a good amount of Brønsted acid sites are identified as the key factors to ensure a high yield of 1,3-propanediol. However, for 1,2-propanediol, a Cu-based catalyst with decent basic support is observed to be the key for good yield and selectivity of product. The findings have shown that it is possible to produce high yields of both 1,2-propanediol and 1,3-propanediol via aqueous phase reforming, specifically 1,2-propanediol, for which some of the findings achieve better selectivity compared to direct glycerol hydrogenolysis to 1,2-propanediol. This is not the case for 1,3-propanediol, for which further studies need to be conducted to evaluate its feasibility.

Catalytic Transfer Hydrogenolysis of Glycerol over Heterogeneous Catalysts: A Short Review on Mechanistic Studies

Catalytic transfer hydrogenolysis, using liquid H-donors in the absence of pressurized H₂ under mild temperatures, is regarded as the most important technology to substitute traditional hydrogenation processes in industry. Despite decade development with several breakthroughs in catalyst design, the reaction mechanism involved in H₂ generation and subsequent hydrogenolysis reactions is still under debate. In this review, transfer hydrogenolysis of glycerol, as a representative example, on metallic catalysts is revised critically with respect to surface reaction mechanism and catalyst design. The detailed reaction pathways for propanol, methanol, formic acid and ethanol for H₂ generation have been discussed systematically. In particular, reaction mechanism for catalytic C-H cleavage, H spillover/transfer and C-O cleavage reaction steps will be critically revised with experimental and theoretical results in literature. Insights into reaction pathways, mechanism and H₂ transfer efficiency and structure-performance relation for Pd, Cu and Ni catalysts will be provided for future development of catalyst manufacture and process development. The outcome of this work is useful for successful implementation of bio-refinery.

Probing supported bimetallic Pt–In sites in glycerol hydrogenolysis

This work studied platinum and indium supported on alumina and silica as monometallic and bimetallic catalysts for the aqueous phase hydrogenolysis of glycerol towards 1,2-propanediol (1,2-PDO).

PtRu/Zn3Ce1Ox catalysts with Lewis acid–base pairs show synergistic performances for the conversion of glycerol in the absence of externally added H2

Enhanced Lewis acid–base pairs and weaker PtRu–H hydride bonding synergistically enhance catalytic activity.

Magnesium hydroxide–supported ruthenium as an efficient and stable catalyst for glycerol-selective hydrogenolysis without addition of base and acid additives

Ru/Mg(OH)₂(S) exhibited high catalytic activity and selectivity to 1,2-propanediol for glycerol hydrogenolysis without any base and acid additives.

Selective Catalytic Transfer Hydrogenolysis of Glycerol to 2-Isopropoxy-Propan-1-Ol over Noble Metal Ion-Exchanged Mordenite Zeolite

This study investigated the selective conversion of glycerol to 2-isopropoxy-propan-1-ol over noble metal ion-exchanged mordenite zeolites (RuMOR, RhMOR, and PdMOR) as heterogeneous catalysts via catalytic transfer hydrogenolysis (CTH) using propan-2-ol as the solvent, hydrogen supplier, and reactive coupling reagent with glycerol. The catalytic reactions were performed at 140 °C under inert conditions with a 0.5 MPa initial pressure of N2. A single product, 2-isopropoxy-propan-1-ol, was catalytically generated without any appreciable by-products. The catalytic results were reproducible, and the catalysts exhibited good recyclability.

The Promoting Effect of Ni on Glycerol Hydrogenolysis to 1,2-Propanediol with In Situ Hydrogen from Methanol Steam Reforming Using a Cu/ZnO/Al2O3 Catalyst

Production of green chemicals using a biomass derived feedstock is of current interest. Among the processes, the hydrogenolysis of glycerol to 1,2-propanediol (1,2-PD) using externally supplied molecular hydrogen has been studied quite extensively. The utilization of methanol present in crude glycerol from biodiesel production can avoid the additional cost for molecular hydrogen storage and transportation, as well as reduce the safety risks due to the high hydrogen pressure operation. Recently the hydrogenolysis of glycerol with a Cu/ZnO/Al2O3 catalyst using in situ hydrogen generated from methanol steam reforming in a liquid phase reaction has been reported. This paper focusses on the effect of added Ni on the activity of a Cu/ZnO/Al2O3 catalyst prepared by an oxalate gel-co-precipitation method for the hydrogenolysis of glycerol using methanol as a hydrogen source. It is found that Ni reduces the conversion of glycerol but improves the selectivity to 1,2-PD, while a higher conversion of methanol is observed. The promoting effect of Ni on the selectivity to 1,2-PD is attributed to the slower dehydration of glycerol to acetol coupled with a higher availability of in situ hydrogen produced from methanol steam reforming and the higher hydrogenation activity of Ni towards the intermediate acetol to produce 1,2-PD.

Treatment of de-icing contaminated surface water runoff along an airport runway using in-situ soil enriched with structural filter materials

Airport surface runoff during wintertime contains high concentrations of pavement de-icing fluids (PDFs). Uncontrolled discharge of this runoff poses a potential environmental hazard for the terrestrial and aquatic ecosystem. Several technologies for collection, transportation and treatment of contaminated runoff water are available, mainly technical systems, which require high operation and maintenance efforts. For moderately contaminated runoff, the discharge to a wastewater treatment plant is usually applied. In this study, a passive soil-based filter is proposed to treat the contaminated surface water runoff. The degradation of two PDFs was under investigation, namely Safeway® KA-Hot based on potassium acetate, and urea. The main research objective was to determine the capability of the in-situ soil and a soil based filter using zeolite and perlite as additional filter media to degrade the organic pollutants in the runoff. Column experiments at temperatures between 3 °C and 5 °C were carried out to determine the degradation potential when using 50% in-situ soil mixed with zeolite and perlite. Besides TOC, the nitrogen degradation was also under investigation. Due to the low temperatures, available nutrients are a key factor for the TOC degrading microorganisms. Overall TOC reduction rates were found from 76% up to 98%, with TOC effluent concentrations in the range of 18 to 870 mg·L^-1, depending on the influent concentration. Based on the results, the use of a soil-based filter is a promising, passive, natural based solution for the treatment of de-icing runoff.

Nanostructured Metal Catalysts for Selective Hydrogenation and Oxidation of Cellulosic Biomass to Chemicals

Conversion of biomass to chemicals provides essential products to human society from renewable resources. In this context, achieving atom-economical and energy-efficient conversion with high selectivity towards target products remains a key challenge. Recent developments in nanostructured catalysts address this challenge reporting remarkable performances in shape and morphology dependent catalysis by metals on nano scale in energy and environmental applications. In this review, most recent advances in synthesis of heterogeneous nanomaterials, surface characterization and catalytic performances for hydrogenation and oxidation for biorenewables with plausible mechanism have been discussed. The perspectives obtained from this review paper will provide insights into rational design of active, selective and stable catalytic materials for sustainable production of value-added chemicals from biomass resources.

Kinetic study of liquid phase glycerol hydrodeoxygenation under inert conditions over a Cu-based catalyst

The kinetic model of a liquid phase glycerol hydrodeoxygenation-methanol reforming tandem reaction cycle, over a Cu:Zn:Al catalyst.

Comparative study of WCx-based catalysts for aqueous phase hydrogenolysis of glycerol into bioadditives

Metal-loaded WC_x catalysts were synthesized and investigated in hydrogenolysis of glycerol.

Significance of isomeric reaction intermediates in the hydrogenolysis of glycerol to 1,2-propanediol with Cu-based catalysts

The 2,3-enediol isomer was identified as the most favorable isomer to give 1,2-PDO.

Glycerol hydrogenolysis over a Pt–Ni bimetallic catalyst with hydrogen generated in situ

Pt–Ni catalyst significantly promotes the conversion and selectivity of 1,2-PDO due to a strong interaction between Pt and Ni.

Glycerol hydro-deoxygenation aided by in situ H2 generation via methanol aqueous phase reforming over a Cu–ZnO–Al2O3 catalyst

Methanol APR–glycerol HDO reactions were successfully coupled to produce 1,2-propanediol at high yields over an efficient CuZnAl catalyst.

Conversion of biomass-derived sorbitol to glycols over carbon-materials supported Ru-based catalysts

Ruthenium (Ru) supported on activated carbon (AC) and carbon nanotubes (CNTs) was carried out in the hydrogenolysis of sorbitol to ethylene glycol (EG) and 1,2-propanediol (1,2-PD) under the promotion of tungsten (WO_x) species and different bases. Their catalytic activities and glycols selectivities strongly depended on the support properties and location of Ru on CNTs, owning to the altered metal-support interactions and electronic state of ruthenium. Ru located outside of the tubes showed excellent catalytic performance than those encapsulated inside the nanotubes. Additionally, the introduction of WO_x into Ru/CNTs significantly improved the hydrogenolysis activities, and a complete conversion of sorbitol with up to 60.2% 1,2-PD and EG yields was obtained on RuWO_x/CNTs catalyst upon addition of Ca(OH)₂. Stability study showed that this catalyst was highly stable against leaching and poisoning and could be recycled several times.

Catalytic hydrogenolysis of glycerol to propanediols: a review

This study summarizes the most significant reports regarding the catalytic hydrogenolysis of glycerol to propanediols.

Production of acetol from glycerol using engineered Escherichia coli

Escherichia coli Lin43 is a strain which has some mutations in glycerol kinase (GlpK) and the repressor for the glycerol 3-phosphate regulon (GlpR). When exposed to glycerol, it quickly accumulates lethal levels of methylglyoxal, which is a precursor of acetol; acetol is important for the manufacture of polyols, acrolein, dyes, and skin tanning agents. This work reports the engineering of E. coli Lin 43 for the conversion of glycerol into acetol. First, the glyoxalase system was interrupted by deleting the gloA gene, which increased the acetol yield by 32%. In addition, the aldehyde reductase YqhD was overexpressed which led to an increase of acetol production by 11.4-fold. Acetol production was optimized by varying the cell density, glycerol concentration, supplemental carbon source, pH and temperature. Under the optimal conditions (OD600=20, 20 g/L glycerol, 2g/L succinate, pH 7.0, and 28°C), we obtained 5.4 g/L acetol in 21 h.