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Ruthenium Melt PRODUCING CHEMICALS FROM SYNTHESIS GAS By John F. Knifton Texaco Chemical Company, Austin, Texas

A range of commodity chemicals and fuels can be generated directly from synthesis gas by ruthenium melt catalysis. Careful selection of the catalyst components enables a wide range of oxygenates to be produced, while other advantages of this flexible process include high productivity and the ease with which the products may be recovered and the catalyst recycled.

In - catalysed organic syn- present a renewable surface may avoid many of thesis, the primary purpose is to produce pure the problems of deactivation seen with con- products in high yields, with good ventional heterogeneous catalysts (4). reproducibility and ease of product isolation. Frequently, the melt is called upon to play While both homogeneous and heterogeneous more than one role in a chemical process. It catalysis systems may fulfill these roles in may, for example, simply act as a solvent for laboratory or industrial processes, an alterna- reactants and products; it may be a catalyst; it tive approach, that has many of the inherent may supply one or more of the reactants, as well advantages of both systems, is the use of molten as aid in controlling the heat of reaction. The salts as catalyst and/or reaction media. salts may be used singly (for example molten Molten salts may be classified into simple Na2C03, ZnCL or AlC13), or as eutectic ionic salts (for example the alkali and alkaline mixtures (such as Li2C03-Na2C03-K2C03, earth metal halides), simple and polymeric CuC1-CuCl2-KC1, and AlC13-BuPyC1) where oxyanionic salts (such as metal nitrates, car- the lower liquidus temperatures may be bonates, phosphates, borates), and salts contain- advantageous. ing organic cations and/or anions (including the Molten salts have already found numerous quaternary phosphonium and salts) technical applications in industrial catalytic (I). The high thermal stability of many of these processes. Examples include the Transcat, melts, together with their low vapour pressure, Deacon and SO2 oxidation processes (I ,2). The good thermal and electrical conductivity, and literature illustrating the diverse uses of melt low viscosity provides them with a range of catalysis with the platinum important physical and chemical advantages includes applications in chlorination (z), oxida- over conventional homogeneous and tion (5) and selective (6) process- heterogeneous catalyst systems (2). Molten ing, as in Equation i: salts, such as the quaternary phosphonium n salts, dissolve a broad range of metals, and complexes; high reaction rates and yields are often possible (for example organic syn- U theses in molten tetrachloroaluminate solvents In the case of synthesis gas (carbon (3) and fused salts (4)) with ease of monoxide/) chemistry, Fischer- producdcatalyst separation and recovery. Tropsch production using Ir4(C0)12dissolved Where chemical synthesis occurs at a melt-gas in NaC1-AlC13 melts has now been demons- interface, as in gas reactions, the ability to trated (7); ethane is the major product fraction,

Platinum Metals Rev., 1985,29, (2), 63-72 63 see Equation ii or, under flow conditions, ease of product-catalyst separation, typical of isobutane and propane. A further examination, heterogeneous catalyst systems, once the reac- by Collman and his colleagues, implicates tion is complete. chloromethane (or methanol) as the primary Optionally, a second or third intermediate, with methane, ethane, and may be added to the ruthenium to further chloromethane the major carbon-containing modify its performance and to steer the product products (8). distribution toward specific aliphatic CO + 3H2 ->C~HL (major) + CH4 + oxygenates. These modifiers may be derivatives C3Hs (tr) + C4Hlo (tr) ii of , cobalt, , , Ruthenium Melt Catalysis zirconium and , in either -free In other, potentially far-reaching applica- or halogen-containing forms. tions of melt catalysis by the Some specific applications of this technology metals, we at Texaco have demonstrated the include (Equations iii to viii): synthesis of a range of commodity chemicals [I] Ethylene glycol synthesis directly from and fuels directly from synthesis gas by the use synthesis gas using ruthenium-rhodium catalysts of ruthenium-containing molten salt catalysis. or ruthenium alone (9). Products include ethylene glycol, C1-C4 [2] C1-G AlcohoVacetate ester fuel alcohols, acetic acid, acetate esters, C2+ olefins products, which are potential octane enhancers, and vicinal glycol esters. In its simplest form, using ruthenium in combination with cobalt, this new class of melt catalyst comprises one or titanium or zirconium (I 0). more ruthenium sources, including ruthenium [3] Selective methanol production with the carbonyls, oxides and complexes dispersed in a lowmelting (m.p.