Syngas acetic

Eastman-Halcon A process for making acetic anhydride from syngas. The basic process is the carbonylation of methyl acetate. Methanol is made directly from the carbon monoxide and hydrogen of syngas. Acetic acid is a byproduct of the cellulose acetate manufacture for which the acetic anhydride is needed. The carbonylation is catalyzed by rhodium chloride and chromium hexacarbonyl. 

Commercialization of the novel syngas-to-alcohol-ester fuels (7), syngas acetic acid (125), and SFA processes (96,97) described in this review will hinge primarily upon projected 1990 s economics, particularly the relative feedstock values of petroleum and natural products, versus synthesis gas derived from coal or natural gas. 

The process begins with a gasification process that converts coal into carbon monoxide and hydrogen. Part of this gas is sent to a water-gas shift reactor to increase its hydrogen content. The purified syngas is then cryogenically separated into a carbon monoxide feed for the acetic anhydride plant and a hydrogen-rich stream for the synthesis of methanol. 

Several other important commercial processes need to be mentioned. They are (not necessarily in the order of importance) the low pressure methanol process, using a copper-containing catalyst which was introduced in 1972 the production of acetic add from methanol over RhI catalysts, which has cornered the market the methanol-to-gasoline processes (MTG) over ZSM-5 zeolite, which opened a new route to gasoline from syngas and ammoxidation of propene over mixed-oxide catalysts. In 1962, catalytic steam reforming for the production of synthesis gas and/or hydrogen over nickel potassium alumina catalysts was commercialized. 

Where acetic is the starting acid (eq. 1), homologation selectively yields the corresponding C3+ aliphatic carboxylic acids. Since acetic acid is itself a "syngas" chemical derived from methanol via carbonylation (2,3), this means the higher MW carboxylic acids generated by this technique could also be built exclusively from C0/H2 and would thereby be in-depent of any petroleum-derived coreactant. 

Effect of Operating Conditions. Yield data, summarized in Figures 1 and 2, point to acetic acid homologation activity being sensitive to at least four operating variables, viz. ruthenium and methyl iodide concentrations, syngas composition and operating pressure. 

Figure 2. Acetic acid homologation (%) acetic acid, propionic acid, (A) butyric acids, and (Y) valeric acids, ( Z ) ethane A, effect of syngas composition (operating conditions acetic acid, 833 mmol Ru(IV) oxide, 4.0 mmol Mel, 40 mmol 220°C 272 atm initial pressure) B, effect of operating pressure (operating conditions acetic acid, 417 mmol Ru(IV) oxide, 2.0 mmol Mel, 20 mmol 220°C constant pressure CO/H2 = 1/1)...

Deuteration studies with acetic acid-d4 (99.5% atom D) as the carboxylic acid building block, ruthenium(IV) oxide plus methyl iodide-d3 as catalyst couple and 1/1 (C0/H2) syngas, were less definitive (see Table III). Typical samples of propionic and butyric acid products, isolated by distillation in vacuo and glc trapping, and analyzed by NMR, indicated considerable scrambling had occurred within the time frame of the acid homologation reaction. 

Syngas Homologation of Acetic Acid. To a N2-flushed liquid mix of acetic acid (50.0 gm) and methyl iodide (5.67 gm, 40 mmole), set in a glass liner is added 0.763 gm of ruthenium(IV) oxide, hydrate (4.0 mmole). The mixture is stirred to partially dissolve the ruthenium and the glass liner plus contents charged to a 450 ml rocking autoclave. The reactor is sealed, flushed... 

ENSOL A combined process for converting syngas to methanol and then to ethanol. Acetic acid is an intermediate. Developed by Humphries Glasgow, in conjunction with BASF and Monsanto. 

Unlike SRE, the POE reaction for H2 production has been reported so far only by a few research groups.101104-108 While Wang et al. os and Mattos et r//.104-106 have studied the partial oxidation of ethanol to H2 and C02 (eqn (18)) at lower temperatures, between 300 and 400 °C using an 02/EtOH molar ratio up to 2, Wanat et al.101 have focused on the production of syngas (eqn (19)) over Rh/Ce02-monolith catalyst in a catalytic wall reactor in millisecond contact time at 800 °C. Depending on the nature of metal catalyst used and the reaction operating conditions employed, undesirable byproducts such as CH4, acetaldehyde, acetic acid, etc. have been observed. References known for the partial oxidation of ethanol in the open literature are summarized in Table 6. 

The influences of the ligand-to-metal ratio, reaction temperature and syngas pressure on the enantioselectivity and regioselectivity were also studied. A multi-substrate screening approach has recently been used by Dow Chemical Company to identify the best catalyst for the hydroformylation of vinyl acetate. Here, the chiral phosphite Kelliphite, 5 (Fig. 1) gave enantioselectivity up 88% ee and excellent regioselectivity for the branched isomer [24,25]. 

The overall reaction represents an all syn-gas route to acetic acid and acetic anhydride. At present, in Europe, syn-gas is being produced from natural gas, but eventually it will represent a route from coal, the future feedstock for syngas. 

A mixture of H2 and CO is an important chemical intermediate as are pure H2 and pure CO, and this mixture is called syngas or synthesis gas. These intermediates are used for production of gasoline, ammonia, methanol, and acetic acid. 

Also of great attractiveness is the direct synthesis of acetic acid from syngas, which would circumvent the two step process of Monsanto. Selectivities of up to 50 % are claimed. An economic analysis by Hoechst A.G. indicates (1/7) that this process is already economically feasible at a 80 % C2 Oxygenate selectivity. 

Acetic acid has been generated directly from synthesis gas (CO/H2) in up to 95 wt % selectivity and 97% carbon efficiency using a Ru-Co-I/Bu4PBr "melt" catalyst combination. The critical roles of each of the ruthenium, cobalt and iodide catalyst components in achieving maximum selectivity to HOAc have been identified. Ci Oxygenate formation is observed only in the presence of ruthenium carbonyls [Ru(C0)3l3] is here the dominant species. Controlled quantities of iodide ensure that initially formed MeOH is rapidly converted to the more reactive methyl iodide. Subsequent cobalt-catalyzed carbonylation to acetic acid may be preparatively attractive (>80% selectivity) relative to competing syntheses where the [00(00)4] concentration is optimized that is, where the Co/Ru ratio is >1, the syngas feedstock is rich in 00 and the initial iodide/cobalt ratios are close to unity. 

Data in Table I illustrate the production of acetic acid from 1/1 syngas catalyzed by ruthenium-cobalt halide bimetallic combinations dispersed in tetrabutylphosphonium bromide (m.p. 100°C). 

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