Acetic acid is the raw material for many key petrochemical intermediates and products including vinyl acetate monomer (VAM), purified terephthalic acid (PTA), acetate esters, cellulose acetate, acetic anhydride, monochloroacetic acid (MCA), etc. Acetic acid is produced commercially from several feedstocks and by several different technologies. Methanol carbonylation technology using syngas accounts for over 60 percent of global capacity. This share is growing because it is the preferred technology for most new plants. The objectives of this study are to examine the emerging technology for acetic acid production via direct ethane oxidation and compare it with the current key commercial technologies. Direct ethane oxidation to acetic acid has been an area of high interest to many chemical companies. During the last five years, there have been increasing numbers of World, U.S., European, and Japanese patents granted to corporations and research institutes concerning the catalyst system and the process for direct ethane oxidation to acetic acid. Among the many patent holders, the most active players in this area are Hoechst Research and Technology Deutschland GmbH & Company, Saudi Basic Industries Corporation, Mitsubishi Chemical Corporation, and BP Chemicals Limited and the Standard Oil Company which are now BP. The ethane oxidation reaction to acetic acid can be stoichiometrically described by the following equation: 
It should be noted that the concept of direct ethane oxidation to acetic acid is not new. In the 1980s, Union Carbide developed a process for the production of ethylene via oxidative dehydrogenation of ethane with co-production of acetic acid. Though not promoted as a primary route to acetic acid, the process, referred to as the Ethoxene Process, can be envisioned in this capacity. Union Carbide is not actively pursuing this technology due to limited market opportunity for the specific acetic acid/ethylene product mix. For comparison purposes, the current commercial technologies involving methanol carbonylation and direct ethylene vapor phase oxidation, as well as the Ethoxene Process, are also examined in this study. Hoechst has issued some recent patents describing catalysts that enable high acetic acid selectivities. The results disclosed in the patents show that ethane conversion ranges from 3 to 11 percent per pass while acetic acid selectivity is in the range of 77 to 91 percent. However, even with these good selectivities, our analysis shows that on a USGC basis ethane based acetic processes are not yet competitive with state-of-the-art methanol carbonylation processes such as Celanese's Acid Optimization process and BP's CATIVA process. However, when situated in an area with low ethane pricing, such as the Middle East, this route may provide an economic path for acetic production. Apparently, this scenario is driving SABIC's plans for an ethane-based process. A proprietary ethane based route is especially valuable when access to the latest methanol carbonylation process technology is quite limited, if available at all. SABIC has recently announced it has developed a proprietary process for converting ethane to acetic acid. SABIC's subsidiary, Ibn Rushd, is planing to build a 30,000 metric ton per year acetic acid semi-works plant over the next two years. In addition, SABIC plans to build a full scale 200,000 metric ton per year acetic acid plant once the technology is proven out in the smaller unit. |
