Abstract
Hydrodeoxygenation of para-methylguaiacol using silica supported Rh or Pt catalysts was investigated using a fixed-bed reactor at 300°C, under 4 barg hydrogen and a WHSV of 2.5h−1. The activity, selectivity and deactivation of the catalysts were examined in relation to time on stream. Three catalysts were tested: 2.5% Rh/silica supplied by Johnson Matthey (JM), 2.5% Rh/silica and 1.55% Pt/silica both prepared in-house. The Rh/silica (JM) showed the best stability with steady-state reached after 6h on stream and a constant activity over 3days of reaction. In contrast the other two catalysts did not reach steady state within the timeframe of the tests, with continuous deactivation over the time on stream. Nevertheless higher coking was observed on the Rh/silica (JM) catalyst, while all three catalysts showed evidence of sintering. The Pt catalyst (A) showed higher selectivity for the production of 4-methylcatechol while the Rh catalysts were more selective toward the cresols. In all cases, complete hydrodeoxygenation of the methylguaiacol to methylcyclohexane was not observed.
Highlights
Bio-oils upgrading can be performed using a variety of different approaches
In this paper we report on the HDO reaction of p-methylguaiacol (PMG) over silica-supported rhodium and platinum catalysts
By the end of the reaction, the metal surface area of the Rh/silica (A) was three times higher than that of the Rh/silica (JM) catalyst, yet the p-methylguaiacol conversion was lower, indicating that there was not a simple correlation between metal surface area and activity. Both Rh/silica catalysts showed both similar deactivation profiles with a fast deactivation at early time on stream followed with slow deactivation for the Rh/silica (A) or constant activity for the Rh/silica (JM)
Summary
Bio-oils upgrading can be performed using a variety of different approaches. In order to blend with crude oil, or to drop-in to existing petroleum processes, the oxygen content (30–50%) of the bio-oil has to be reduced. Amongst all the compounds present in the bio-oil, the phenolics are by far the most studied The reasons are their multiple functional groups, their high proportion in the bio-oil and their tendency to promote catalyst deactivation. Another reason of the extensive use of phenolics as model compounds for bio-oil upgrading relies on the higher bond dissociation energy required to break aryl-hydroxyl or aryl-methoxy linkages compared to alkyl hydroxyl or alkyl ether linkages [5]. A comparative study of Pt/Al2O3, Rh/Al2O3 and presulfided NiMo catalysts for the HDO of microalgae oil reported the better stability of the noble metal catalysts reaching a steady state after 5 h time on stream. Two 2.5% Rh/silica catalysts and a 1.55% Pt/silica catalyst were tested for this study
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