Methanol—continued oxidation

A solution of methacrolein in methanol and aqueous soda solutions were continuously oxidized by O2 at 5 bar and 80 °C in a reactor packed with Pd-Bi/ Si02-Mg0-Al203 catalyst. Methyl methacrylate was obtained with 90.8 % selectivity at 63.4 % conversion [93]. 

However, the intermediate product during the oxidation of methanol makes the catalysis complicated, and the reaction rate for making CO out of methanol solution is slow. Moreover, a second metal such as Ruthenium (Ru) is required, which is explained by the bifunctional mechanism. In other words, activation of water or surface oxides at lower potentials makes the CO absorption bond weaker on the PtRu alloy catalyst. In the meantime, oxidative methanol dehydrogenation occurs on Pt by oxygen-like species on Ru, so that species on Pt-Ru pair sites enables the continuous oxidation of CO to CO. ... 

Oxidation, (i) Dissolve 5 g. of potassium dichromate in 20 ml. of dil. H2SO4 in a 100 ml. bolt-head flask. Cool and add 1 ml. of methanol. Fit the flask with a reflux water-condenser and warm gently a vigorous reaction soon occurs and the solution turns green. The characteristic pungent odour of formaldehyde is usually detected at this stage. Continue to heat for 3 minutes and then fit the flask with a knee-tube (Fig. 59, p. 100) and distil off a few ml. Test the distillate with blue litmus-paper to show that it is definitely acid. Then apply Test 3 p. 350) for formic acid. (The reflux-distillation apparatus (Fig. 38, p. 63) can conveniently be used for this test.)... 

Historically, formaldehyde has been and continues to be manufactured from methanol. EoUowing World War II, however, as much as 20% of the formaldehyde produced in the United States was made by the vapor-phase, noncatalytic oxidation of propane and butanes (72). This nonselective oxidation process produces a broad spectmm of coproducts (73) which requites a complex cosdy separation system (74). Hence, the methanol process is preferred. The methanol raw material is normally produced from synthesis gas that is produced from methane. 

Jacobsen (1999) has carried out carbomethoxylation of asymmetric epoxides. Thus, the carbomethoxylation of (R)-propylene oxide with CO and methanol yields 92% of (3R)-hydroxybutanoic acid in greater than 99% ee. Similarly, the reaction of (/ )-epichlorohydrin gives 96% of 4-chloro-(3R)-hydroxybutanoic acid in greater than 99% ee. The catalyst consists of dicobalt octacarbonyl and 3-hydroxy pyridine. A continuous process for making enantiomeric 1-chloro-2-propanol has been suggested. With a suitable catalyst propylene reacts with O2, water, cupric and lithium chloride to give 78% of (S)-l-chloro-2-propanol in 94% ee. 

Poisoning of platinum fuel cell catalysts by CO is undoubtedly one of the most severe problems in fuel cell anode catalysis. As shown in Fig. 6.1, CO is a strongly bonded intermediate in methanol (and ethanol) oxidation. It is also a side product in the reformation of hydrocarbons to hydrogen and carbon dioxide, and as such blocks platinum sites for hydrogen oxidation. Not surprisingly, CO electrooxidation is one of the most intensively smdied electrocatalytic reactions, and there is a continued search for CO-tolerant anode materials that are able to either bind CO weakly but still oxidize hydrogen, or that oxidize CO at significantly reduced overpotential. 

In the following, after a brief description of the experimental setup and procedures (Section 13.2), we will first focus on the adsorption and on the coverage and composition of the adlayer resulting from adsorption of the respective Cj molecules at a potential in the Hup range as determined by adsorbate stripping experiments (Section 13.3.1). Section 13.3.2 deals with bulk oxidation of the respective reactants and the contribution of the different reaction products to the total reaction current under continuous electrolyte flow, first in potentiodynamic experiments and then in potentiostatic reaction transients, after stepping the potential from 0.16 to 0.6 V, which was chosen as a typical reaction potential. The results are discussed in terms of a mechanism in which, for methanol and formaldehyde oxidation, the commonly used dual-pathway mechanism is extended by the possibility that reaction intermediates can desorb as incomplete oxidation products and also re-adsorb for further oxidation (for the formic acid oxidation mechanism, see [Samjeske and Osawa, 2005 Chen et al., 2006a, b Miki et al., 2004]). 

In this section, we present results of potentiodynamic DBMS measurements on the continuous (bulk) oxidation of formic acid, formaldehyde and methanol on a Pt/ Vulcan catalyst, and compare these results with the adsorbate stripping data in Section 13.3.1. We quantitatively evaluate the partial oxidation currents, product yields, and current efficiencies for the respective products (CO2 and the incomplete oxidation products). In the presentation, the order of the reactants follows the increasing complexity of the oxidation reaction, with formic acid oxidation discussed first (one reaction product, CO2), followed by formaldehyde oxidation (two reaction products) and methanol oxidation (three reaction products). 

The adsorption and oxidation of the Ci molecules methanol, formaldehyde, and formic acid over a carbon-supported Pt/C fuel cell catalyst under continuous electrolyte flow have been investigated in a quantitative, comparative online DBMS study. 

A dissociative adsorption of methanol forming surface methoxy groups is suggested as the initial step. This is followed by the slow step, the formation of some form of adsorbed formaldehyde species. Evidence.for the bridged species is not available, experiments with °0 labeled methanol are expected to clarify this. Continued surface oxidation leads to a surface formate group and to carbon monoxide. All the byproducts can be obtained by combination of the appropriate surface species. 

An exceptionally short synthesis of grassularine-1 133 was reported recently by Horne and coworkers [95]. This approach utilized intermediate oxotryptamine 146, which had been prepared previously as part of another synthesis [96]. Condensation of 146 with dimethylcyanamide produced 147, which was prone to oxidation, and was only stable as its hydrochloride salt (Fig. 41). This sensitivity to oxidation was utilized in the key reaction step in which oxidative dimerization to give 148 was accomplished by stirring 147 in methanolic ammonia solution at room temperature for 1 day. Continued stirring under these conditions for another 5 days eventually resulted in the production of 149 in 60% yield directly from 147. Hydrolysis of 149, which required forcing conditions (12-h reflux in a mixture of ethanol and 6M HC1), but nevertheless proceeded in 95% yield, completed this synthesis of grassularine-1 133. 

Formox [Formaldehyde by oxidation] A process for oxidizing methanol to formaldehyde, using a ferric molybdate catalyst. Based on the Adkins-Peterson reaction, developed by Reichold Chemicals, and licensed by that company and Perstorp, Sweden. Acquired by Dyno Industries in 1989. The process uses formaldehyde produced in this way to make formaldehyde-urea resin continuously. A plant using this process was to be built in Ghent by 1991, owned jointly by Dyno and AHB-Chemie. Licensed to 35 sites worldwide. Several other companies operate similar processes. 

Skeletal catalysts are usually employed in slurry-phase reactors or fixed-bed reactors. Hydrogenation of cottonseed oil, oxidative dehydrogenation of alcohols, and several other reactions are performed in sluny phase, where the catalysts are charged into the liquid and optionally stirred (often by action of the gases involved) to achieve intimate mixing. Fixed-bed designs suit methanol synthesis from syngas and catalysis of the water gas shift reaction, and are usually preferred because they obviate the need to separate product from catalyst and are simple in terms of a continuous process. 

Synthetic studies of various cyclic phosphine oxides continue to be published. Thus a methanolic work-up leads to an 88% yield of 1-methylphospholen 1-oxides (6) from dichloro(methyl)phosphine, and detailed S1P n.m.r. and mass spectra have been described.10 The oxides (7) and (8) have been prepared11 as shown. Structural... 

To continue the process, the fatty methyl esters are phase-separated from the glycerin (or glycerol—same thing, just to keep you on your toes), washed with water to remove any trace amounts of methanol and glycerin and dried. In a second reaction, the methyl esters are hydrogenated to get the fatty alcohols (in the southeast corner of Figure 15—2). The catalyst is usually a mixture of cupric chromite and cupric oxide in the form of a finely divided powder. Conversion of the triglycerides is about 95%. 

The TPA process. The technology involves the oxidation of p-xylene, as shown already in Figure 18—2. The reaction takes place in the liquid phase in an acetic acid solvent at 400°F and 200 psi, with a cobalt acetate/ manganese acetate catalyst and sodium bromide promoter. Excess air is present to ensure the p-xylene is fully oxidized and to minimize by-products. The reaction time is about one hour. Yields are 90—95% based on the amount of p-xylene that ends up as TPA. Solid TPA has only limited solubility in acetic acid, so happily the TPA crystals drop out of solution as they form. They are continuously removed by filtration of a slipstream from the bottom of the reactor. The crude TPA is purified by aqueous methanol extraction that gives 99 % pure flakes. 

A fuel cell is an electrochemical conversion device that has a continuous supply of fuel such as hydrogen, natural gas, or methanol and an oxidant such as oxygen, air, or hydrogen peroxide. It can have auxiliary parts to feed the device with reactants as well as a battery to supply energy for start-up. 

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