Cobalt Shell 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 For propene hydroformylation, they have been replaced by rhodium (Union Carbide, Mitsubishi, Ruhrchemie-Rhone Poulenc).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. 

Phosphine modified cobalt catalysts the Shell process... 

Since Shell s report on the use of phosphines in the cobalt catalysed process, which included preliminary data for the use of rhodium as well [1], many industries started to apply phosphine ligands in rhodium catalysed processes [2], While alkylphosphines are the ligands of choice for cobalt, they lead to slow reactions when applied in rhodium catalysis. In the mid-sixties the work of Wilkinson showed that arylphosphines should be used for rhodium and that even at mild conditions active catalysts can be obtained [3], The publications were soon followed by those of Pruett, in which phosphites were introduced (Figure 8.1) [4],... 

Cobalt was the first catalyst used in commercial applications of the oxo-synthesis. In order to stabilize the HCo(CO)4 catalyst, high pressures are necessary with a maximum n/i ratio of 80/20. In the Shell process,324,325,393 cobalt catalysts modified with alkylphosphines e.g. ( )3 ( 4 9) are more selective towards linear products but exhibit high hydrogenation activity and are therefore mainly used for the direct synthesis of long chain alcohols. 

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). 

In the sixties it was recognized that ligand substitution on the cobalt carbonyl might influence the performance of the catalyst. It has been found that aryl phosphines or phosphites have little influence in fact they may not even coordinate to cobalt under such high CO pressures. Tertiary alkyl phosphines, however, have a profound influence [5] the reaction is much slower, the selectivity to linear products increases, the carbonyl complex formed, HCoL(CO)3, is much more stable, and the catalyst acquires activity for hydrogenation. This process has been commercialized by Shell. As a result of the higher stability of the cobalt complex, the Shell process can be operated at lower pressures and higher temperatures (50-100 bar vs 200-300 bar for HCo(CO)4, 170°C vs 140°C). 

The Shell process uses a cobalt/phospfaine catalyst for the homologation of methanol CH3-OH +CO + 2Ha CH3CH2OH H2O... 

Ligand modification and thus stabilization of cobalt carbonyl, product separation by distillation and recycling of the catalyst phase (Shell process). 

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 . 

Fresh cobalt is introduced into the Shell process in the form of carboxylate, e.g., octanoate. In the presence of phosphine (PR3) and carbon monoxide, a complex is formed to which the formal structure [Co(CO)3PR3]2 is ascribed [189]. Under carbon monoxide pressure this neutral complex is converted into an ionic complex [Co(CO)3(PR3)2]+[Co(CO)4], which can be precipitated (e.g., by addition of methanol) and separated by filtration [190]. In the case of the combined hydrofor-mylation/aldolization the precipitation may be achieved by slight acidification under carbon monoxide pressure (make-up section 7 in Figure 12) [185]. 

A variety of ligand-modified cobalt catalysts have been investigated and a commercial process known as the Shell Process was developed The Shell Process uses tributylphosphine as the modifier, which generates HCo(CO)3PBu3 as the active catalyst species and is substantially more stable than HCo(CO)4. This process gives a higher linear/branched ratio (7.3/1, i.e., 88% linear and 12% branched for the reaction of 1-propene), but the products are alcohols and not aldehydes, and ca. 15% of 1-propene is hydrogenated to propane. These... 

The Shell process is a variant of the cobalt-catalyzed process in which phosphine-modified catalysts of the type [HCo(CO)j(PR3)] are used. Such catalysts, which are stable at low pressures, favor the hydrogenation of the initially formed aldehydes, so that the main products are oxo alcohols. However, a disadvantage is the lower catalyst activity and increased extent of side reactions, especially the hydrogenation of the olefin starting material. The superiority of the low-pressure rhodium process can be seen from the process data listed in Table 3-3. 

Powell JB, Slaugh LH, Mullin SB, Thomason TB, Weider PR. (1999) Cobalt catalyzed process for preparing 1,3-propanediol from ethylene oxide. Shell Oil Company. U.S. Patent 5981808. 

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]. 

Generally, pressures of 80 to 300 atm are applied at reaction temperatures above 100 °C, with the exception of the Shell process which has been successfully applied in the last few years [148]. In the Shell process cobalt carbonyls modified by phosphine ligands are used as catalysts. They exhibit a high thermal stability and allow operations at pressures of 3 to 35 atm even at such high temperatures as 180—200 °C. 

Shell uses a special catalyst system (see chapter 3.6 on catalyst modifiers). Cobalt salts of organic acids (e.g. Co-2-ethylhexanoate), trialkyl phosphines (e.g. tributyl phosphine) and alkali, such as KOH, are fed to the 0X0 reactor as catalyst precursors. Under the conditions of the Shell process HCo(CO)3pR3 is formed from these compounds which is the catalyst active in the Shell method. Since this catalyst is thermally more stable than HCo(CO)4 the 0X0 reactor needs only a pressure around 100 atm, versus 200-300 atm in the other processes. However, compared with HCo(CO)4 the catalyst is less reactive. Thus at equal concentrations even at 180 °C... 

Ligand-Modified Cobalt Process. The ligand-modified cobalt process, commercialized in the early 1960s by Shell, may employ a trialkylphosphine-substituted cobalt carbonyl catalyst, HCo(CO)2P( -C4H2)3 [20161 -43-7] to give a significantly improved selectivity to straight-chain... 

When the Claus reaction is carried out in aqueous solution, the chemistry is complex and involves polythionic acid intermediates (105,211). A modification of the Claus process (by Shell) uses hydrogen or a mixture of hydrogen and carbon monoxide to reduce sulfur dioxide, carbonyl sulfide, carbon disulfide, and sulfur mixtures that occur in Claus process off-gases to hydrogen sulfide over a cobalt molybdate catalyst at ca 300°C (230). 

Shell Gas B.V. has constructed a 1987 mVd (12,500 bbhd) Fischer-Tropsch plant in Malaysia, start-up occurring in 1994. The Shell Middle Distillate Synthesis (SMDS) process, as it is called, uses natural gas as the feedstock to fixed-bed reactors containing cobalt-based cat- yst. The heavy hydrocarbons from the Fischer-Tropsch reactors are converted to distillate fuels by hydrocracking and hydroisomerization. The quality of the products is very high, the diesel fuel having a cetane number in excess of 75. 

Alkyldiphosphines turned out to be very useful in a different reaction, namely the carbonylation/hydrogenation of ethylene oxide to give 1,3-propanediol also using cobalt catalysts. Interestingly, the ligand contains two phobane units bridged by 1,2-ethenediyl. The process was commercialised by Shell [18]. 

Shell Chemical has a process that does both the Oxo reaction and hydroformyiation in one step in the same reactor. They use a special catalyst, thought to be cobalt modified with a trialkyl or triaryl phosphine ligand— but they are holding this one pretty close to the vest. Overall yields are 70-80%, with straight-chain alcohols representing greater than 80%. Major by-products are paraffins that are recovered and used to make olefins and then recycled back as feed. This process can also use internal olefins (with the double-bond somewhere besides the alpha position) and yield similar normakiso alcohol ratios. ... 

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