A spray reactor concept for catalytic oxidation of p-xylene to produce high-purity terephthalic acid

Facile Production of 2,5-Furandicarboxylic Acid via Oxidation of Industrially Sourced Crude 5-Hydroxymethylfurfural

The oxidation of 5-hydroxymethylfurfural (HMF) produces value-added chemicals such as 2,5-diformylfuran (DFF) and 2,5-furandicarboxylic acid (FDCA). In this work, FDCA production was achieved by oxidation of crude HMF solution containing around 45 % HMF and unwanted byproducts such as 5,5'-[oxy-bis(methylene)]bis-2-furfural (HMF dimer) and polymers. At optimized reaction conditions similar to the Mid-Century process, homogeneous oxidation of the crude HMF (up to 20 wt% in the feed) by Co/Mn/Br catalyst in acetic acid solution produced FDCA at >95 % yield. The solid FDCA product contained <4000 ppm 5-formyl-2-furancarboxylic acid (FFCA). Such high yields were observed because the impurities in crude HMF were also converted to FDCA, as confirmed by the facile oxidation of HMF dimer to FDCA under reaction conditions. The successful demonstration of crude HMF as feed, obviating the need for HMF purification, suggests potential for cost-effectively producing FDCA in existing terephthalic plants.

Manganese and Cobalt Doped Hierarchical Mesoporous Halloysite-Based Catalysts for Selective Oxidation of p-Xylene to Terephthalic Acid

Bimetallic MnCo catalyst, supported on the mesoporous hierarchical MCM-41/halloysite nanotube composite, was synthesized for the first time and proved its efficacy in the selective oxidation of p-xylene to terephthalic acid under conditions of the AMOCO process. Quantitative yields of terephthalic acid were achieved within 3 h at 200–250 °C, 20 atm. of O2 and at a substrate to the Mn + Co ratio of 4–4.5 times higher than for traditional homogeneous system. The influence of temperature, oxygen, pressure and KBr addition on the catalyst activity was investigated, and the mechanism for the oxidation of p-toluic acid to terephthalic acid, excluding undesirable 4-carboxybenzaldehyde, was proposed.

Intensified ozonolysis of lignins in a spray reactor: insights into product yields and lignin structure

A safe and efficient spray ozonolysis to valorize grass and hardwood lignins, selectively yielding aromatic aldehydes without their overoxidation or lignin bleaching.

Preparative microdroplet synthesis of carboxylic acids from aerobic oxidation of aldehydes

Single liquid-phase and liquid-liquid phase reactions in microdroplets have shown much faster kinetics than that in the bulk phase. This work extends the scope of microdroplet reactions to gas-liquid reactions and achieves preparative synthesis. We report highly efficient aerobic oxidation of aldehydes to carboxylic acids in microdroplets. Molecular oxygen plays two roles: (1) as the sheath gas to shear the aldehyde solution into microdroplets, and (2) as the sole oxidant. The dramatic increase of the surface-area-to-volume ratio of microdroplets compared to bulk solution, and the efficient mixing of gas and liquid phases using spray nozzles allow effective mass transfer between aldehydes and molecular oxygen. The addition of catalytic nickel(ii) acetate is shown to accelerate further microdroplet reactions of this kind. We show that aliphatic, aromatic, and heterocyclic aldehydes can be oxidized to the corresponding carboxylic acids in a mixture of water and ethanol using the nickel(ii) acetate catalyst, in moderate to excellent yields (62-91%). The microdroplet synthesis is scaled up to make it preparative. For example, aerobic oxidation of 4-tert-butylbenzaldehyde to 4-tert-butylbenzoic acid was achieved at a rate of 10.5 mg min-1 with an isolated product yield of 66%.

Biomass-Derived Renewable Aromatics: Selective Routes and Outlook for p-Xylene Commercialisation

Methylbenzenes are among the most important organic chemicals today and, among them, p-xylene deserves particular attention because of its production volume and its application in the manufacture of polyethylene terephthalate (PET). There is great interest in producing this commodity chemical more sustainably from biomass sources, particularly driven by manufacturers willing to produce more sustainable synthetic fibres and PET bottles for beverages. A renewable source for p-xylene would allow achieving this goal with minimal disruption to existing processes for PET production. Despite the fact that recently some routes to renewable p-xylene have been identified, there is no clear consensus on their feasibility or implications. We have critically reviewed the current state-of-the-art with focus on catalytic routes and possible outlook for commercialisation. Pathways to obtain p-xylene from a biomass-derived route include methanol-to-aromatics (MTA), ethanol dehydration, ethylene dimerization, furan cycloaddition or catalytic fast pyrolysis and hydrotreating of lignin. Some of the processes identified suggest near-future possibilities, but also more speculative or longer-term sources for synthesis of p-xylene are highlighted.