Methanol homogeneous processes

Most authors consider acetaldehyde as the primary product of methanol hydro-carbonylation which, depending on the reaction conditions and catalyst system, can be hydrogenated to yield ethanol. The potential of cobalt hydrocarbonyl to reduce aldehydes to alcohols in a homogeneous process in the presence of syngas, was recognized by Wender et al, in 1950 [78]. A mechanism according to Equations (29) and (30) was proposed involving an ethoxy cobalt imermediate. 

The pseudo-homogeneous two-dimensional dispersion model, consisting of (11.11) to (11.18) and the pressure drop relations (11.3) and (11.4), was solved for the methanol production process under non-adiabatic conditions. 

Besides the "immobilized" CF3SO3H, another homogeneous catalyst is anionic [Rh(00)212]. This was the first active rhodium catalyst for the carbonylation of methanol to acetic acid. Recently, Chiyoda and UOP introduced the Acetica process, a novel technology based on an "immobilized" [Rh(CO)2l2] on a polyvinyl pyridine resin. Compared with the existing homogeneous process, immobilization increases catalyst concentration in the reaction mixture. 

The first commercialized homogeneous methanol carbonylation route to acetic acid was established at BASF in 1955, using a homogeneous Ni catalyst. In 1960 BASF developed an improved process it used an iodide-promoted CO catalyst and operated at an elevated temperature (230 °C) and pressure (600 bar) [2]. In 1970, Monsanto commercialized an improved homogeneous methanol carbonylation process using a methyl-iodide-promoted Rh catalyst [3-5]. This process operated at much milder conditions (180-220 °C, 30-40 bar) than the BASF process and performed much better [6]. Celanese and Daicel further improved the Monsanto... 

Inherent in the homogeneous system, however, are drawbacks relating to catalyst solubility hmitations and the loss of expensive Rh metal due to precipitation in the separation sections. Therefore, inmiobilization of the Rh complex on a support has been the topic of significant research as its heterogeneous catalyst properties. Moreover, Chiyoda and UOP have jointly developed a heterogeneous Rh catalyst system for the methanol carbonylation process to produce acetic acid [14-16]. 

From the industrial point of view one of the major achievements of homogeneous catalysis has been the introduction of acetic acid processes via the carbonylation of methanol. These processes allow not only the use of methanol as a cheaper feedstock as compared to ethylene, but are also characterized by an extremely high selectivity. 

Polymerizations were performed homogeneously in benzene as solvent at 6QOC in the presence of 0.3 wt% of AIBN for 7 hours with stirring rate of 75 rpm. The reaction mixture was poured into methanol. The precipitate was filtered off, redissolved in benzene and reprecipitating from methanol. This process was repeated three times. It was then dried in vacuo overnight at 60 C. 

Conversion of ethylene to acetaldehyde with a soluble palladium complex was one of the early applications of homogeneous catalysis. As most of the acetic acid-manufacmring processes were based on acetaldehyde oxidation, the easy conversion of ethylene to acetaldehyde by the Wacker process was historically a significant discovery. With the advent of the methanol carbonylation process for the manufacture of acetic acid, the industrial importance of the Wacker process has diminished. 

Tailor-made surface catalysts are required to improve the technical performance of known homogeneous processes as in alkene dimerization, alcohol homologation, and methanol carbonylation. 

Acetic Acid and Anhydride. Synthesis of acetic acid by carbonylation of methanol is another important homogeneous catalytic reaction. The Monsanto acetic acid process developed in the late 1960s is the best known variant of the process. 

The original catalysts for this process were iodide-promoted cobalt catalysts, but high temperatures and high pressures (493 K and 48 MPa) were required to achieve yields of up to 60% (34,35). In contrast, the iodide-promoted, homogeneous rhodium catalyst operates at 448—468 K and pressures of 3 MPa. These conditions dramatically lower the specifications for pressure vessels. Yields of 99% acetic acid based on methanol are readily attained (see Acetic acid Catalysis). 

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