Shell hydroformylation process

FIG. 5 Hydroformylation of higher molecular weight olefins with a ligand-modified cobalt carbonyl catalyst [HCo(CO)3PR3] (Shell process). 

Cobalt carbonyls are the oldest catalysts for hydroformylation and they have been used in industry for many years. They are used either as unmodified carbonyls, or modified with alkylphosphines (Shell process). For propene hydroformylation, they have been replaced by rhodium (Union Carbide, Mitsubishi, Ruhrchemie-Rhone Poulenc). For higher alkenes, cobalt is still the catalyst of choice. Internal alkenes can be used as the substrate as cobalt has a propensity for causing isomerization under a pressure of CO and high preference for the formation of linear aldehydes. Recently a new process was introduced for the hydroformylation of ethene oxide using a cobalt catalyst modified with a diphosphine. In the following we will focus on relevant complexes that have been identified and recently reported reactions of interest. 

In the Shell process (SHOP) phosphine-modified cobalt-catalyzed hydrofor-mylation is one of the steps in the synthesis of linear alcohols with 12-15 carbon atoms (see Section 7.4.1). Two important characteristics of this reaction should be noted. First, the phosphine-modified precatalyst HCo(CO)3(PBu3) is less active for hydroformylation than HCo(CO)4 but more active for the subsequent hydrogenation of the aldehyde. In this catalytic system both hydroformylation and hydrogenation of the aldehyde are catalyzed by the same catalytic species. Second, the phosphorus ligand-substituted derivatives are more stable than their carbonyl analogues at higher temperatures and lower pressures (see Table 5.1). 

Phosphine-modified cobalt catalyst is applied commercially only in the Shell process to hydroformylate olefins of medium chain length (C7-C14). The resulting alcohols are sold under the brand name Dobanol . 

Hydroformylation (Oxo-process, O. Roelen, Ruhrchemie, 1938 worldwide there are three variants of the Oxo-process 1. the classical synthesis using HCo(CO)4 as catalyst 2. Shell s SHOP-process, based on a cobalt carbonyl - phosphine complex 3. UCC s process, using a rhodium catalyst). ... 

Depending on the reaction conditions, more or less of the aldehyde product is hydrogenated when the olefin hydroformylation is performed in the presence of unmodified cobalt catalyst see Table 3, for example. Trialkylphosphine modified cobalt catalysts are more active in this hydrogenation. By raising the temperature and the H2 CO ratio, the final product of hydroformylation is the alcohol instead of the aldehyde see the product of the Shell process in Table 1. 

The favorable effects of phosphine ligands in catalysis have been known for more than half a century. One of the first reports involves the use of triphenylphosphine in the Reppe chemistry, the reactions of alkynes, alcohols and carbon monoxide to make acryhc esters [2]. An early example of a phosphine-modified catalytic process is the Shell process for alkene hydroformylation nsing a cobalt catalyst containing an alkylphoshine [3]. 

These discoveries led finally to the establishment of large-scale processes in industry for hydroformylation-hydrogenation of olefins with short and longer alkyl chains (Shell process) [24]. 

Despite the fact that the Shell process operates at lower pressure and higher temperatures than the conventional processes, still higher n/iso ratios of the products formed are observed. Thus, in the hydroformylation of propylene an 88/12 ratio of n- over iso-product is obtained, whereas for comparison the distribution in the Ruhrchemie process is 80/20. This type of modified catalyst is not only a hydroformylation but also a hydrogenation catalyst. Thus, in the SheU process about 10-15 % of the olefin fed is lost through hydrogenation to the paraffin whereas the figures for the conventional 0X0 processes are only about 2-3 %. 

The 0x0 process is employed to produce higher alcohols from linear and branched higher olefins. Using a catalyst that is highly selective for hydroformylation of linear olefins at the terminal carbon atom. Shell converts olefins from the Shell higher olefin process (SHOP) to alcohols. This results in a product that is up to 75—85% linear when a linear feedstock is employed. Other 0x0 processes, such as those employed by ICI, Exxon, and BASE (all in Europe), produce oxo-alcohols from a-olefin feedstocks such alcohols have a linearity of about 60%. Enichem, on the other hand, produces... 

Shell higher olefin process (organic/organic) and the Ruhrchemie-Rhone Poulenc propene hydroformylation process (aqueous/organic). The diversity of the applications may confuse the newcomer but it is not easy to comprehend even by the more experienced. A guide to this field may help a lot, and this is why the book of Adams, Dyson and Tavener is most welcome. 

A very elegant solution to solve this problem is the introduction of either a permanent or a temporary phase boundary between the molecular catalyst and the product phase. The basic principle of multiphase catalysis has already found implementation on an industrial scale in the Shell higher olefin process (SHOP) and the Ruhrchemie/Rhdne-Poulenc propene hydroformylation process. Over the years, the idea of phase-separable catalysis has inspired many chemists to design new families of ligands and to develop new separation... 

Three commercial homogeneous catalytic processes for the hydroformyla-tion reaction deserve a comparative study. Two of these involve the use of cobalt complexes as catalysts. In the old process a cobalt salt was used. In the modihed current version, a cobalt salt plus a tertiary phosphine are used as the catalyst precursors. The third process uses a rhodium salt with a tertiary phosphine as the catalyst precursor. Ruhrchemie/Rhone-Poulenc, Mitsubishi-Kasei, Union Carbide, and Celanese use the rhodium-based hydroformylation process. The phosphine-modihed cobalt-based system was developed by Shell specih-cally for linear alcohol synthesis (see Section 7.4.1). The old unmodihed cobalt process is of interest mainly for comparison. Some of the process parameters are compared in Table 5.1. 

ALTAM A process for making caprolactam from butadiene and carbon monoxide. Developed by DSM in the late 1990s and subsequently improved by Shell Chemicals, which contributed catalyst know-how. In the first two steps of the process, butadiene undergoes two hydroformylations with carbon monoxide, followed by reductive animation with ammonia and then cyclization to caprolactam. First commercialization was expected in Taiwan. A joint venture with Chiyoda Corporation, to further develop and commercialize the process, was announced in 2002. 

---