Abstract
We report on a study of the key reaction parameters in glycerol oxidehydration into acrylic acid over W–V–Nb mixed oxides with a hexagonal tungsten bronze structure. This investigation demonstrated that the optimal control of the two consecutive steps of acid-catalysed glycerol dehydration into acrolein and aldehyde oxidation into acrylic acid, and of the parallel reaction of acrolein transformation into by-products (ketals and oligomers), was achieved in the presence of a defined glycerol-to-oxygen inlet ratio. Indeed, oxygen played the fundamental role of accelerating the oxidation of the intermediately formed acrolein into acrylic acid, by allowing a greater concentration of the oxidizing V5+ sites. In fact, an unprecedented higher yield to acrylic acid and acrolein compared to W–V bronzes was registered (maximum acrylic acid yield 50.5%) together with an increase of more than one order of magnitude in productivity, because of both the greater concentration of glycerol used in the inlet feed and the lower contact time needed. Further experiments were carried out by reacting acrolein and methanol in oxidative conditions, the latter as a model molecule for the determination of surface acid and redox properties.
Highlights
With the aim of reducing the carbon footprint of fuels, bio-diesel represents one of the most important options, theoretically providing neutral CO2 balance and significant reduction of greenhouse gas emission.[1,2,3] The increasing trend of biodiesel production goes hand-in-hand with the availability of large volumes of glycerol that is co-produced in the conventional transesterification reaction exploited to synthesize the bio-fuel.[2,4] Since the late 90s, this abundance of glycerol has significantly impacted the glycerin market resulting in a decline of its price,[5,6] and making glycerol a low-cost raw material desirable to be converted into different chemicals with higher economic value
We report here about an investigation of the key catalyst features and reaction parameters in glycerol oxidehydration into acrylic acid over W-V-Nb mixed oxides with the hexagonal tungsten bronze structure
With the aim of demonstrating the general conclusions drawn on W-V-Nb catalysts, showing superior performance compared to W-V, we report here the catalytic results obtained on Mo-V-(W) laminar oxide, which is a catalyst for the selective oxidation of acrolein into acrylic acid [REF]
Summary
With the aim of reducing the carbon footprint of fuels, bio-diesel represents one of the most important options, theoretically providing neutral CO2 balance and significant reduction of greenhouse gas emission.[1,2,3] The increasing trend of biodiesel production goes hand-in-hand with the availability of large volumes of glycerol that is co-produced in the conventional transesterification reaction exploited to synthesize the bio-fuel.[2,4] Since the late 90s, this abundance of glycerol has significantly impacted the glycerin market resulting in a decline of its price,[5,6] and making glycerol a low-cost raw material desirable to be converted into different chemicals with higher economic value. In order to fully investigate the catalyst activity of the best performing tri-component sample (reported as WVNb-1 sample)[41], we report here a complete study of the catalyst behavior as a function of the inlet feed composition. It is here reported about the methanol gas-phase transformation into formaldehyde and dimethyl ether (DME) on both W-V and W-V-Nb catalysts; methanol is known to be a suitable probe to explore the acid and redox properties of metal oxides.[45,46] The results obtained allow to draw important and general conclusions on the catalyst features needed to convert oxygenated molecules by means of direct processes, using a single multifunctional catalyst. In order to obtain a complete picture of the catalysts behavior, the acrolein oxidation reaction was studied on both HTBs and laminar-type oxides
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