Nickel Catalyst Stability toward Carboxylic Acids

Abstract

Reduced (unsulfided) nickel catalysts can be used for hydroprocessing sulfur-free Fischer−Tropsch derived feed materials, but catalyst deactivation by metal leaching can be a problem in the presence of carboxylic acids. Leaching of reduced nickel catalysts by carboxylic acids takes place by the formation of nickel carboxylates. Carboxylic acid leaching of nickel can be prevented by operating above the carboxylate decomposition temperature, which was found to be in the range 280−305 °C for the C2−C5 nickel carboxylates. Unfortunately this is not industrially practical, because of the hydrogenolysis propensity of reduced nickel catalysts at these conditions. It was also found that nickel leaching did not monotonically increase with temperature, but was inhibited at >200 °C, probably due to polymerization of the nickel carboxylates.

Patent Literature

“…29 In practice, promoting the H-ZSM-5 with Ni would require sulfided operation, since metal leaching will take place under unsulfided conditions with HTFT light oil feed. 30,31 The benefit of hydrogenating the heavier FT syncrude before fractionation and/or acid-catalysed conversion was realised and Mobil claimed a benefit of hydrogenating the FT material boiling above 150 1C before refining it. 32 This avoids the separation problems associated with atmospheric distillation of FT syncrude due to thermal decomposition in the reboiler (thermal cracking of oxygenates) and downstream carbon number broadening (oxygenate hydrogenation shifts the boiling point distribution).…”

Catalysis in the Upgrading of Fischer–Tropsch Syncrude

“…538 It was speculated that this may have been caused by acid leaching of the Ni, which was confirmed by a later study. 395 Leaching of reduced Ni/Al 2 O 3 catalysts by carboxylic acids resulted in the formation of nickel carboxylates. Carboxylic acid leaching can in principle be prevented by operating at a temperature above the nickel carboxylate decomposition temperature, which was found to be in the range 280-305 1C for the C 2 -C 5 nickel carboxylates.…”

“…The leaching of reduced metals from catalysts by short-chain carboxylic acids in Fischer-Tropsch syncrude has been documented. 395 Oxygenates can also preferentially adsorb on either metal or acid sites, thereby changing the metal-to-acid site ratio of bifunctional catalysts. 396 Although this does not result in deactivation, carboxylic acids can lower the effective metalto-acid site ratio, which may cause an increase in the rate of deactivation by the formation of carbonaceous deposits.…”

“…Reduced (unsulfided) metal-promoted catalysts can be deactivated by carboxylic acid leaching of the active metal. 395 Leaching is a problem because the oil products from FTS may contain corrosive short-chain carboxylic acids. Although the short-chain carboxylic acids preferentially dissolve in the Fischer-Tropsch aqueous product, C 3 -C 4 carboxylic acids are amphiphilic and may dissolve in the oil product from FTS.…”

Exploring the decomposition pathways of iron asymmetric transfer hydrogenation catalysts

“…The TON is an important metric for the chemical industry, where an extremely active catalyst with poor TON is often less desirable than a less active catalyst that can produce more product, or even potentially be reused for multiple applications. [33][34][35] Herein, we report several unexpected deactivation pathways observed for complexes 1a-b and 2a-b under catalytic conditions. These decomposition pathways were examined using experimental techniques and density functional theory (DFT) calculations.…”