Butane oxidation process development in a circulating fluidized bed Gregory S. Patience a, *, Richard E. Bockrath b a Department of Chemical Engineering, Ecole Polytechnique de Montre ´al, C.P. 6079, Succ. ‘‘CV’’, Montre ´al, QC, Canada H3C 3A7 b E. I. du Pont de Nemours, Central Research and Development Laboratories, Experimental Station, Wilmington, DE 19880, USA 1. Introduction The most common route to produce THF – an industrial solvent as well as a critical monomer for segmented polyurethanes (Lycra 1 ) and copolyester elastomers (Hytrel 1 ) – has been the Reppe process: acetylene reacts with formaldehyde forming butynediol followed by hydrogenation and an acid de-hydration step. DuPont developed a new environmental process to THF in which n-butane is partially oxidized to maleic anhydride and the acid is subsequently hydrogenated at high pressure [1,2]. The first step – partial oxidation of butane over a vanadium phosphorous oxide (VPO) – was accomplished through major innovations in reactor technology and catalyst morphology. The circulating fluidized bed reactor (CFB) transferred catalyst from a net oxidizing zone to a net reducing zone. In the oxidizing environment, a fraction of the vanadyl pyrophosphate (VPP) – (VO) 2 P 2 O 7 – was converted from a V 4+ oxidation state to V 5+ . In the reducing environment, the V 5+ phase was a source of oxygen to partially oxidize n-butane to maleic anhydride. In multi-tubular fixed beds the reactants are co-fed and operate under very oxidizing conditions below the lower explosion limit. Circulating catalyst from an oxidizing environment to a reducing environment has been shown to improve selectivity to maleic anhydride as well as activity—increased butane conversion [3–5]. Even in fixed bed operation, when the butane feed is temporarily interrupted and fed air, performance is improved when the butane is initiated. Schuurman and Gleaves [3] proposed that this may be evidence that more than one VPP phase may be active. Recently, Ballarini et al. [6] inferred the nature of the surface active phases by running transient experiments. They showed that both the P/V ratio and reaction conditions could alter the surface to form vanadium oxide and polyphosphoric acids or other non-selective active species. Together with higher selectivity and increased yield, the net throughput per kg of catalyst is improved in a CFB by operating with more than 10 vol% butane, which is 2–5 times as much as a turbulent fluidized bed and multi-tubular fixed bed, respectively. Hutchings [7] suggested that by increasing the butane concentra- tion, the maleic anhydride yields could be increased substantially. Centi et al. [8] reported higher selectivity to MA (as well as butenes, butadiene and other by-products) with 30% butane concentrations Applied Catalysis A: General 376 (2010) 4–12 ARTICLE INFO Article history: Received 13 August 2009 Received in revised form 8 October 2009 Accepted 13 October 2009 Available online 21 October 2009 Keywords: Butane oxidation Vanadyl pyrophosphate Circulating fluidized bed Lattice oxygen contribution Attrition resistance Maleic anhydride ABSTRACT DuPont designed and operated a circulating fluidized bed reactor (CFB) to produce maleic anhydride from n-butane using a vanadium pyrophosphate catalyst (VPP) encapsulated in a silica shell. A fraction of the pyrophosphate was oxidized to the V 5+ state from the V 4+ state in an air fed fluidized bed regenerator. The oxidized VPP was shuttled to a transport bed reactor with a high concentration of butane and oxygen. The gas carried the catalyst up through the bed at velocities of 0.8 m/s and, in the commercial plant, solids circulation rates exceeding 7 kt/h. Early development work was conducted on an experimental scale facility containing 1 kg of catalyst. The pilot plant catalyst inventory exceeded 2000 kg and there was 175 t in the commercial reactor. Throughout the program, significant advances in catalyst manufacture and process design were achieved. The CFB reactor configuration is being considered for several unrelated processes including chemical looping combustion, methanol-to-olefins and hot gas desulphurization. Improvements in spray drying technology reduced attrition losses by an order of magnitude versus expectation based on the pilot plant. Together with the low attrition losses and good stability, catalyst consumption was reduced by successfully re-spray drying used/attrited catalyst. By modifying the solids entrance and exit configurations, we were able to double initial plant capacity. Operability of the plant was excellent with a turn-down ratio of 5 demonstrated. At a production rate of 65,000 t/year of maleic acid – one of the largest single train reactors for a partial oxidation of an alkane – the maximum temperature difference within the bed was less than 20 8C. Heat transfer had been a major design consideration but even at this rate, only 1/3 of the total coil surface for cooling was activated. ß 2009 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +1 514 3404711/3439; fax: +1 514 340 4159. E-mail address: Gregory-S.Patience@polymtl.ca (G.S. Patience). Contents lists available at ScienceDirect Applied Catalysis A: General journal homepage: www.elsevier.com/locate/apcata 0926-860X/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2009.10.023