Thermal Decomposition of Acetic and Formic Acid Catalyzed by Red Mud—Implications for the Potential Use of Red Mud as a Pyrolysis Bio-Oil Upgrading Catalyst§Dedicated to Prof. Ulf Schuchardt on the occasion of his retirement.

Abstract

Acetic and formic acid impart a high acidity on pyrolysis bio-oil (obtained by fast pyrolysis of lignocellulosic biomass), which is one of the factors preventing its direct use as a fuel. At temperatures g 330 °C, Red Mud, a waste byproduct of the aluminum industry produced at >70 million tons p.a., is a good catalyst for thermal decomposition of these acids. Formic acid can serve as an internal source of hydrogen through the formation of synthesis gas and the water gas shift reaction. The formation of C 6 -C 10 hydrocarbons in the nonpolar phase of the resulting product mixture and the identification of C 3 and C 4 hydrocarbons and CO 2 in the gas phase and acetone in the polar liquid phases can be rationalized through mechanisms involving ketene as the intermediate formed by acetic acid dehydration, with subsequent formation of acetone. Higher hydrocarbons, mostly alkanes and alkenes, are then formed through iterative aldol condensation, hydrogenation, hydrogenolysis, and deoxygenation reactions of the primary products. During the reaction, the Red Mud used in these reactions undergoes a distinct color change to gray, yielding a nonalkaline magnetic material containing Fe 3 O 4 and metallic iron rather than Fe 2 O 3 . Dedicated to Prof. Ulf Schuchardt on the occasion of his retirement.

Pyrolytic Conversion of Olive Mill Wastewater Sludge to Biofuels Using Red Mud as Catalyst

“…Catalytic applications of red mud have been extensively reviewed by [16]. This material has been investigated by several researchers for catalytic applications such as hydrodechlorination [17], hydrogenation of anthracene [18,19], pyrolysis of waste plastics and waste oils [20,21], hydrogenation and liquefaction of rye straw [22], upgrading of hemp-seed pyrolysis oils [23], and acetic acid [24]. In most of these applications red mud was activated through acid treatment and other modifications.…”

A survey of catalysts for aromatics from fast pyrolysis of biomass

“…The red mud was sourced as slurry from the Rio Tinto Alcan mining facility in Canada and contained about 50% w/w iron oxide. The slurry was water washed and dried at 120 • C [19].…”

“…Of the six catalysts, red mud generated the most CO 2 (∼13-15% of biomass weight). The cracking activity of red mud is due to the presence of silica and alumina which provide the acidic functionality [17,19]. CO 2 yields have been related to Al content in the catalyst which enhances the decarboxylation reactions by Bronsted acid catalysis [20].…”

“…The silica:alumina ratio (SAR) in red mud is <1.3, which is very low compared to other catalysts such as HZSM-5 (SAR = 23). Red mud had much higher Al content compared to all other catalysts and produced more CO 2 from the decarboxylation of acids in the pyrolysis product [19]. Thus, red mud may be used as an inexpensive catalyst to remove corrosive acids and upgrade pyrolysis vapor.…”

“…The disposal of red mud is an environmental concern [17,18]. Red mud is composed of many transition metal oxides, favors hydrogenation reactions and may prove to be an inexpensive catalyst for biofuel applications [17,19] .…”