Acetaldehyde process improvements

Examples for necessary process improvements through catalyst research are the development of one-step processes for a number of bulk products like acetaldehyde and acetic acid (from ethane), phenol (from benzene), acrolein (from propane), or allyl alcohol (from acrolein). For example, allyl alcohol, a chemical which is used in the production of plasticizers, flame resistors and fungicides, can be manufactured via gas-phase acetoxylation of propene in the Hoechst [1] or Bayer process [2], isomerization of propene oxide (BASF-Wyandotte), or by technologies involving the alkaline hydrolysis of allyl chloride (Dow and Shell) thereby producing stoichiometric amounts of unavoidable by-products. However, if there is a catalyst... 

Dehydrogenation processes in particular have been studied, with conversions in most cases well beyond thermodynamic equihbrium Ethane to ethylene, propane to propylene, water-gas shirt reaction CO -I- H9O CO9 + H9, ethylbenzene to styrene, cyclohexane to benzene, and others. Some hydrogenations and oxidations also show improvement in yields in the presence of catalytic membranes, although it is not obvious why the yields should be better since no separation is involved hydrogenation of nitrobenzene to aniline, of cyclopentadiene to cyclopentene, of furfural to furfuryl alcohol, and so on oxidation of ethylene to acetaldehyde, of methanol to formaldehyde, and so on. 

Improvement of the One-Pot Multi-Step Enzymatic Process for Practical Production of 2 -Deoxyribonucleoside from Glucose, Acetaldehyde and a Nucleobase... 

To make the DERA-catalyzed process commercially attractive, improvements were required in catalyst load, reaction time, and volumetric productivity. We undertook an enzyme discovery program, using a combination of activity- and sequence-based screening, and discovered 15 DERAs that are active in the previously mentioned process. Several of these enzymes had improved catalyst load relative to the benchmark DERA from E. coli. In the first step of our process, our new DERA enzymes catalyze the enantioselective tandem aldol reaction of two equivalents of acetaldehyde with one equivalent of chloroacetaldehyde (Scheme 20.6). Thus, in 1 step a 6-carbon lactol with two stereogenic centers is formed from achiral 2-carbon starting materials. In the second step, the lactol is oxidized to the corresponding lactone 7 with sodium hypochlorite in acetic acid, which is crystallized to an exceptionally high level of purity (99.9% ee, 99.8% de). 

In the 1990s, BP re-examined the iridium-catalyzed methanol carbonylation chemistry first discovered by Paulik and Roth and later defined in more detail by Forster [20]. The thrust of this research was to identify an improved methanol carbonylation process using Ir as an alternative to Rh. This re-examination by BP led to the development of a low-water iridium-catalyzed process called Cativa [20]. Several advantages were identified in this process over the Rh-catalyzed high-water Monsanto technology. In particular, the Ir catalyst provides high carbonylation rates at low water concentrations with excellent catalyst stability (less prone to precipitation). The catalyst system does not require high levels of iodide salts to stabilize the catalyst. Fewer by-products are formed, such as propionic acid and acetaldehyde condensation products which can lead to low levels of unsaturated aldehydes and heavy alkyl iodides. Also, CO efficiency is improved. 

Improvements to the basic commercial process also involve modifications to the purification stage and implementation of chemical treatment applications within that section, such as treatment with ozone, peroxides, or hydrogen [116-126]. These improvements are designed specifically to remove low levels of iodides, acetaldehyde, and acetaldehyde-derived impurities (i.e., crotonaldehyde and 2-ethylcrotonaldehyde) to reduce the concentration of these impurities in the final product. Removal of these impurities improves the acetic acid product quality [116-126]. 

IMPROVEMENT OF THE ONE-POT MULTISTEP ENZYMATIC PROCESS FOR PRACTICAL PRODUCTION OF 2 -DEOXYRIBONUCLEOSIDE FROM GLUCOSE, ACETALDEHYDE, AND A NUCLEOBASE... 

Synthesis of vinyl acetate acetaldehyde + acetic anhydride = vinyl acetate improved safe process with high yields [21]... 

There were also improvements in acetaldehyde and acetic anhydride manufacture. Ag based catalysts for the partial oxidation of ethanol became available around 1940. When used to oxidatively dehydrogenate ethanol [14], the conversion of ethanol to acetaldehyde was no longer equilibrium limited since the reaction was now very exothermic. Fortunately, the process still displayed excellent selectivity (ca. 93-97%) for acetaldehyde. This technology replaced the older Cu-Cr processes over the period of the 1940-1950 and made ethanol a much more attractive resource for acetaldehyde. When ethylene became available as a feedstock in the 1940 s through 1950 s, ethanol became cheaply available via ethylene hydration (as opposed to traditional fermentation). With ethanol now cheaply available from ethylene, the advent of the Ag catalyzed oxidative dehydration to acetaldehyde rapidly accelerated the shutdown of the last remaining wood distillation units. 

Acetaldehyde oxidation was also marginally improved, especially for the manufacture of acetic anhydride. In 1935, workers at Shawingan Chemicals discovered that the oxidation of acetaldehyde, if conducted in the presence of cobalt, copper, or better yet, a mixture of the two catalysts, yielded a mixture of acetic anhydride and acetic acid providing the water co-product was rapidly separated by azeotropic distillation, normally with a compatible material such as ethyl acetate. It would not be until the 1940 s that this became widely practiced, but the process was eventually widely adopted. While experimental units produced ratios of acetic anhydride acetic acid as high as 4 1, it appears that the commercial process normally gave a 5 4 mixture of acetic anhydride acetic acid... 

For the same purpose, a Pt/Ti02 catalyst was used in the deep oxidation of ethanol and acetaldehyde with molecular oxygen in SCCO2 at 150 to 300°C, but no significant improvement compared to the gas-phase process was achieved. ... 

For emulsion polymers, the monomer devolatilization rate is often limited by the mass transfer through the interface between the aqueous phase and the gas phase [57]. For these systems, diffusion in the polymer particles is fast because the Tg of the polymer is low and the particle size is small. In addition, the mass transfer from the particles to the aqueous phase is fast because of the huge interfacial area. For water-soluble VOCs such as acetaldehyde and fert-butanol, the rate-limiting step is also the mass transfer through the liquid/gas interface. Therefore, all the process variables that increase the interfacial area between the aqueous phase and the gas phase, such as agitation, geometry of the sparger, or gas flow rate, would improve devolatilization [81]. 

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