The role of impurities in the La2O3 catalysed carboxylation of crude glycerol

Abstract

The direct carboxylation of crude glycerol, obtained as a by-product of bio-diesel synthesis, with CO 2 has been investigated over lanthanum oxide as a heterogeneous catalyst for the irst time. Adiponitrile is employed as a dehydrating agent in order to shift the reaction equilibrium to the product side. The selectivity of the reaction towards glycerol carbonate when using crude glycerol is signiicantly reduced as compared to employing reined glycerol: 2.3% cf. 17% respectively. Glycerol conversion, however remains approximately constant: 54% cf. 58%. In order to understand the role of the impurities present in crude glycerol, model systems consisting of reined glycerol and one or more of water, methanol, methyl palmitate (as a model fatty acid methyl ester), and sodium methoxide have been prepared and used as reaction media to systematically evaluate their efect. All of these impurities are seen to reduce the selectivity towards glycerol carbonate, instead favouring the formation of 4-(hydroxymethyl)oxazolidin-2-one, with the exception of methanol where no detrimental efect is observed and the measured selectivity increases slightly to ca. 22%. This efect is ascribed, in part, to improved mass transfer as a consequence of an increased solubility of carbon dioxide in the liquid media when methanol is present. Additionally, adiponitrile is observed to play a crucial role in the reaction mechanism beyond its simple role as a dehydrating agent. These results provide insights into the required puriication steps for crude glycerol, and suggest the possibility of employing crude glycerol directly, and its use as a chemical feedstock; in both cases by minimising costly separation and puriication steps.

Influence of Biochar Composition and Source Material on Catalytic Performance: The Carboxylation of Glycerol with CO2 as a Case Study

“…The effectiveness of zeolites and lanthanum-based catalysts has also been studied [7,[11][12][13]. However, rhodium is a platinum group metal and is very expensive, whilst tin is moderately scarce, and could be depleted in the next 100-1000 years [13]. Carbonaceous catalysts could therefore improve the economic viability and sustainability of the process through the use of catalytic materials from a renewable resource.…”

“…Catalysts 2020, 10, x FOR PEER REVIEW 3 of 21 Catalysts used for glycerol upgrading are generally bases, e.g., metal oxides, such as tin and rhodium [2]. The effectiveness of zeolites and lanthanum-based catalysts has also been studied [7,[11][12][13]. However, rhodium is a platinum group metal and is very expensive, whilst tin is moderately scarce, and could be depleted in the next 100-1000 years [13].…”

A high performance barium-promoted cobalt catalyst supported on magnesium–lanthanum mixed oxide for ammonia synthesis

“…47 The hightemperature peak centred at 741 C could originate from the interaction of CO 2 with cubic La 2 O 3 . 47,59 In the case of the Bapromoted catalyst, two desorption peaks were distinguished. The medium-temperature peak at 362 C corresponded to the basic sites of hexagonal La 2 O 3 , while the high-temperature peaks located at 671 and 752 C could be attributed to the interaction of CO 2 with BaO and cubic La 2 O 3 , respectively.…”

H2‐free Synthesis of Aromatic, Cyclic and Linear Oxygenates from CO2

“…[2] Consequently,t he chemicals ector is the third largest industrial emittero fc arbon dioxide (CO 2 )a nd am ajor contributor to anthropogenic climate change. [3] This has stimulated investigations into carbon capture from power and chemical plants, [4] for example, as sodiumb icarbonate (NaHCO 3 ). [5,6] In this context,t he direct conversion of CO 2 to fuel and organic molecules presentsa n opportunity to utilise an abundant waste resource.…”

“…[19,20] Ad ecrease in dielectric constantf urtherm akes it ag ood solvent for organic and hydrophobic substances. [19] The primary focus of CO 2 reduction in hydrothermal mediah as been on the synthesis of short-chained hydrocarbons such as methane, CH 4 and formic acid, av ersatile platform molecule. The reduction of aqueous carbon dioxide by zero-valent iron at ambientc onditions in seawater solutionw as reported by Hardy and Gillham, who obtained hydrocarbons of chain length up to C 5 after 500 h. [21] At shorter reaction times of 40 days, conversion to CH 4 and short-chaina lkanesi nt he presence of Fe at ap ressure of 1bar was achieved by Deng et al [22] Increased yields of C 1-3 alkanes in the presence of iron-containing olivinea t3 00 8C and 500 bar after 69 days were reported by Berndt et al [17] At shorter reaction times of 20 h, Guan et al synthesised CH 4 and trace methanolo ver zero-valent Fe.…”