Article pubs.acs.org/IECR
Continuous Hydroformylation with Phosphine-Functionalized Polydimethylsiloxane Rhodium Complexes as Nanofilterable Homogeneous Catalysts Zhuanzhuan Xie,† Geoffrey R. Akien,†,§ Bibhas R. Sarkar,†,⊥ Bala Subramaniam,*,†,‡ and Raghunath V. Chaudhari*,†,‡ †
Center for Environmentally Beneficial Catalysis, University of Kansas, 1501 Wakarusa Drive, Lawrence, Kansas 66047, United States Department of Chemical and Petroleum Engineering, University of Kansas, 1530 W. 15th, Lawrence, Kansas 66045, United States
‡
S Supporting Information *
ABSTRACT: Commercially available polydimethylsiloxane (PDMS) was functionalized with phosphine and used to form a Rh complex catalyst. The PDMS-based Rh catalyst complex shows promise as an inexpensive, readily synthesized and nanofilterable homogeneous catalyst for performing continuous hydroformylation. Batch hydroformylation of several substrates including 1octene, 1-decene, 1-dodecene and styrene showed good activity and selectivity. For 1-octene hydroformylation, the observed catalyst activity with the PDMS-based Rh complex is 2-fold greater compared to that with a conventional Rh-triphenylphosphine complex under similar conditions. Continuous 1-octene hydroformylation for up to 120 h was demonstrated in a membrane nanofiltration system, showing stable conversion (∼60%) and high chemoselectivity (>95%). The total turnover number (TON) after 120 h was approximately 12 000 and the permeate Rh concentration was C4) is an atom-economical route for making the linear aldehydes needed for the manufacture of important chemical intermediates such as the aliphatic alcohols and acids used in plasticizers, surfactants, antifreeze and other everyday products.1 However, because of the exorbitant cost of Rh, nearly total catalyst recovery and recycle must be clearly demonstrated for practical viability of these catalysts. To address this problem, several strategies have been attempted including biphasic catalysis1−4 where the Rh catalyst complex is immobilized in an aqueous phase. However, biphasic systems are not applicable to C3+ olefins due to their limited aqueous solubility, necessitating the use of surfactants as phase-transfer agents.5 Suitably designed ionic liquids have also been employed to immobilize the catalyst phase.6 Thermomorphic solvent systems (TMS) exploit temperature-dependent miscibility of certain solvent mixtures to achieve phase separation, obviating the need for additives.7,8 With an appropriate combination of solvents, the reaction mixture can be made to exist as a single phase under reaction conditions. Upon lowering the temperature, the reaction mixture is separated into two phases, one containing the products and the other the catalyst. The TMS concept has been demonstrated for continuous hydroformylation of long chain alkenes in a miniplant scale and shows much promise.9 Various immobilization techniques to anchor Rh complexes to solid supports have also been attempted.10 Catalyst leaching is often the most significant problem with the supported catalysts. The tunable properties of scCO2 have been investigated to overcome the aforementioned issues. Solinas et al.11 demonstrated a batch cartridge system where scCO2 was used as a phase-switch trigger to recover organometallic catalysts. van © XXXX American Chemical Society
Received: August 14, 2015 Revised: October 10, 2015 Accepted: October 14, 2015
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DOI: 10.1021/acs.iecr.5b02990 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research supported biphephos-type ligand) has been reported to show stable activity [turnover frequency (TOF) ∼ 120 h−1] and regioselectivity (n/i = 3.5) during continuous Rh-catalyzed hydroformylation in a stirred reactor equipped with a nanofiltration membrane.23 During a 24 h continuous run, the Rh concentration in the permeate reached a steady-state value of
