Glycerol as a Source for Fuels and Chemicals by Low‐Temperature Catalytic Processing

Abstract

In this era of diminishing petroleum reserves, it is imperative that industrialized society should develop ways to utilize more effectively the abundant and renewable biomass resources available to provide new sources of energy and chemical intermediates.[1] To this end, various processes have been developed to convert biomass and biomass-derived molecules into specialty chemicals (methanol), light alkanes (C 1 -C 6 ), liquid fuels (ethanol and C 7 -C 15 alkanes), and synthesis gas.[2]As a new direction, we show herein that glycerol can be converted over platinum-based catalysts into gas mixtures of H 2 and CO (synthesis gas) at temperatures from 498 to 620 K. These temperatures are lower than those for conventional gasification of biomass (e.g. 800-1000 K).[3, 4] Synthesis gas can be used to produce fuels and chemicals; therefore, the endothermic conversion of glycerol into synthesis gas can be combined with exothermic Fischer-Tropsch and methanol syntheses to provide low-temperature and energy-efficient routes for the production of these compounds. The glycerol used can be sourced from waste glycerol streams that are currently generated as by-products from the production of biodiesel. This heat-integrated catalytic process could also be a less energy-intensive alternative to current methods of converting carbohydrates into fuel-grade ethanol.Synthesis gas production methods for conventional Fischer-Tropsch plants require either an O 2 plant or a large Fischer-Tropsch reactor to process the synthesis-gas stream diluted with N 2 from air, thereby increasing the capital costs of such facilities.[5] Furthermore, Hamelinck et al. showed that nearly 50 % of the cost of producing Fischer-Tropsch liquids from biomass is related to capital cost, [6] of which 50 % stems from biomass gasification, gas cleaning, and synthesis-gas processing. The method we present herein may allow for economic operation of a small-scale Fischer-Tropsch reactor by producing an undiluted H 2 /CO gas mixture. Indeed, our method reduces the capital cost of the Fischer-Tropsch plant by eliminating the O 2 plant or biomass gasifier and subsequent gas-cleaning steps. The conversion of glycerol into CO and H 2 takes place by Equation (1). The endothermic enthalpy change of thisreaction (350 kJ mol À1 ) corresponds to about 24 % of the heating value of the glycerol (À1480 kJ mol À1 ). The heat generated by Fischer-Tropsch conversion of the CO and H 2 to liquid alkanes such as octane (À412 kJ mol À1 ) corresponds to about 28 % of the heating value of the glycerol. Thus, combining these two reactions results in the following exothermic process, with an enthalpy change (À63 kJ mol À1 ) that is about 4 % of the heating value of the glycerol:

Liquid‐Phase Catalytic Processing of Biomass‐Derived Oxygenated Hydrocarbons to Fuels and Chemicals

“…In this respect, we have shown that whereas water gas shift is significant during the conversion of glycerol and water at 620 K over a catalyst consisting of Pt supported on ceriazirconia, the rate of water gas shift is negligible at these conditions over Pt supported on carbon. [7] The production of synthesis gas from oxygenated hydrocarbons over a supported metal catalyst such as Pt/C may be limited at low temperatures (e.g., below 570 K) by the desorption of CO from the metal surface. In particular, the heat of CO adsorption on Pt is high (e.g., 130-180 kJ mol À1 , depending on the CO coverage), and unless the CO is converted into CO 2 by the water gas shift reaction, its pressure in the reactor accumulates, leading to high coverages of CO on the Pt surface.…”

“…[62] Indeed, we have found that PtRu and PtRe alloys supported on carbon are excellent catalysts for the conversion of glycerol in water into synthesis gas at temperatures below 570 K, at which temperatures Pt/C catalysts exhibit low catalytic activity. [7] Another pathway outlined in Scheme 6 involves the formation of organic acids by dehydrogenation followed by rearrangement reactions. As noted in Section 3, a hydroxyaldehyde is less stable than a carboxylic acid (e.g., glyceraldehyde is less stable than lactic acid).…”

“…As an example, the conversion of synthesis gas to alkanes (along with CO 2 and water) is highly exothermic (e.g., À110 kcal mol À1 ), such that the overall conversion of glycerol to alkanes by the combination of reforming and Fischer-Tropsch synthesis is mildly exothermic, with an enthalpy change of about À30 kcal per mole of glycerol. [7] A useful synthetic reaction that can be employed to produce C À C bonds between biomass-derived molecules is the aldol condensation. For example, aldol condensation of HMF with acetone leads to a C 9 species (3-hydroxybutenyl)-hydroxymethylfuran (BH-HMF).…”

Carbodeoxygenation of Biomass: The Carbonylation of Glycerol and Higher Polyols to Monocarboxylic Acids

“…Preliminary results on the carbonylation of erythritol C 4 H 6 (OH) 4 have shown the formation of pentanoic acid and 2-methylbutyric acid. Furthermore, the reaction of sorbitol C 6 H 8 (OH) 6 with HI has been reported to generate 2-iodo hexane. 39 Nakamura reported the carbonylation of ethylene glycol to give propionic acid and of sorbitol to give heptanoic acid and 2-methyl hexanoic acid.…”

“…As a consequence, research into new conversion processes for glycerol as a C 3 platform chemical into value-added products is therefore, both from an economical and from an environmental point of view, of considerable importance. 5 Besides gasification to syngas, 6 several conversions of glycerol are already being explored, for example hydrogenolysis to 1,2-and 1,3-propanediol or the oxidation to dihydroxyacetone. [7][8][9][10][11] Other potential products that are being considered are acrylic acid, glycerol carbonate and epichlorhydrin.…”