Chapter 8 - Acetic acid and co-chemicals production from syngas

Abstract

Acetic acid (AA) is a versatile chemical that is used as a reactant or solvent in various process industries. In this chapter, we have discussed the production of AA and other co-chemicals using syngas as a feedstock. Several syngas pretreatments techniques are also highlighted that enables it to be used as a feedstock for AA synthesis. Moreover, different routes of AA formation via syngas are briefly elaborated that includes both biological and chemical processes. Low gas solubility and AA production inhibition are some of the major challenges of biological AA synthesis. Among the chemical methods, direct conversion of syngas into AA suffers from low AA yield and selectivity over heterogeneous metal-supported catalysts because by-products like hydrocarbons, alcohols, acetaldehyde, and other oxygenates are simultaneously produced. However, methanol carbonylation route is the most promising method for AA manufacturing. Several methanol carbonylation processes, which includes Monsanto, Cativa and Acetica, are commercially available for AA synthesis in the presence of homogeneous and heterogeneous noble metal-based catalysts with iodide promoter. In Monsanto process, the oxidative addition of CH3I to rhodium complex is the rate determining step and 14–15wt% excess water presence is proposed for stability and high catalytic performance of Rh-based homogeneous catalyst. Recently, methanol hydrocarboxylation over noble metal-based homogeneous catalysts and co-catalysts have been proposed as an alternative AA production process to replace CO with CO2. However, downstream AA purification steps requiring azeotropic water-AA separation is highly energy intensive process in all these methods.