Reformulated Red Mud: a Robust Catalyst for In Situ Catalytic Pyrolysis of Biomass

Abstract

Biomass feedstocks contain inorganic compounds generally classified as ash. The ash consists of compounds of potassium, calcium, magnesium, silicon, phosphorus. and other elements. These elements have been reported to influence both the pyrolysis reactions as well as the destabilization of the pyrolysis oils during storage. The inorganic elements have also been reported to deposit on catalyst surfaces during in situ catalytic pyrolysis leading to the eventual deactivation of acidic catalysts such as zeolites. The deposition of inorganic elements and their effects on formulated red mud (FRM) catalyst during in situ catalytic pyrolysis of pinyon juniper wood was investigated. The inorganic elements were measured for the fresh, coked, and regenerated catalysts. The BET specific surface area of the FRM catalyst decreased from 76 m2/g for the fresh catalyst to 53 m2/g for the stable regenerated catalyst. After three regenerations, the BET specific surface area stabilized at 53 m2/g and remained constant after all other regenerations. Potassium, calcium, magnesium, and phosphorus were deposited on the catalyst. Potassium deposition was linear with the number of regenerations while magnesium and calcium depositions were initially rapid but leveled-off after three regenerations of the catalyst. Phosphorus deposition was almost linear, but the data were more scattered compared to that of potassium. The potassium deposition was attributed to physical phenomenon whereas calcium and magnesium depositions were more akin to chemical reactions related to the loss of BET surface area of the catalyst. The deposition of these elements on the surface of the catalyst did not deactivate it. After each catalyst regeneration, the oil yield was not significantly affected and the oil oxygen content and viscosity decreased slightly. This clearly showed that formulated red mud is a robust catalyst suitable for in situ catalytic fast pyrolysis of biomass.

Progress in understanding the coking behavior of typical catalysts in the catalytic pyrolysis of biomass

“…The yield of bio-oil at 400 C and 500 C was measured to be 44.2 and 42.6 wt%, respectively. These results were similar to the results reported by Agblevor et al 26,126 and Vesess et al 125 However, the yield of coke was relatively lower during the pyrolysis of sun ower cake, which may be due to the shorter run time of the pyrolysis. 2.5.1.…”

“…The results of using red mud as a catalyst during the pyrolysis of biomass are shown in Table 5. 26,47,[125][126][127] Vesess et al 125 studied the pyrolysis of pine wood chips (maximum particle size of 15 mm) in an auger reactor at 400-500 C using the catalyst : biomass mass ratio of 0.16-3. Sepiolite, bentonite, attapulgite and red mud with a particle size of 300-1000 mm.…”

“…In the following study, Agblevor et al 126 studied the deactivation of red mud (180–450 μm). In this case, the pyrolysis of pinyon juniper wood was conducted in a fluidized-bed reactor at 450 °C and the biomass feeding rate was 2 kg h −1 .…”

A Review of Recent Research on Catalytic Biomass Pyrolysis and Low-Pressure Hydropyrolysis

“…Finally, multiple works tested red mud, ,,− − which is a waste product from bauxite refining of aluminum, for CFP. Red mud’s main component is Fe 2 O 3 (∼40–60 wt %), but it also contains many other metal oxides such as TiO 2 , Cr 2 O 3 , Na 2 O, and CaO in varying compositions. ,,− ,− Red mud contains both acidic and basic sites and was found to be active in ketonization.…”

“…Finally, multiple works tested red mud, ,,− − which is a waste product from bauxite refining of aluminum, for CFP. Red mud’s main component is Fe 2 O 3 (∼40–60 wt %), but it also contains many other metal oxides such as TiO 2 , Cr 2 O 3 , Na 2 O, and CaO in varying compositions. ,,− ,− Red mud contains both acidic and basic sites and was found to be active in ketonization. The iron-oxides present in red mud will be reduced to a certain extent by the H 2 and CO produced under reaction conditions, and reduction to magnetite (Fe 3 O 4 ) showed improved activity and increased surface area (+57%) .…”