Partial pressure Formaldehyde

The reactors were thick-waked stainless steel towers packed with a catalyst containing copper and bismuth oxides on a skiceous carrier. This was activated by formaldehyde and acetylene to give the copper acetyUde complex that functioned as the tme catalyst. Acetylene and an aqueous solution of formaldehyde were passed together through one or more reactors at about 90—100°C and an acetylene partial pressure of about 500—600 kPa (5—6 atm) with recycling as required. Yields of butynediol were over 90%, in addition to 4—5% propargyl alcohol. 

Oxidation of cumene to cumene hydroperoxide is usually achieved in three to four oxidizers in series, where the fractional conversion is about the same for each reactor. Fresh cumene and recycled cumene are fed to the first reactor. Air is bubbled in at the bottom of the reactor and leaves at the top of each reactor. The oxidizers are operated at low to moderate pressure. Due to the exothermic nature of the oxidation reaction, heat is generated and must be removed by external cooling. A portion of cumene reacts to form dimethylbenzyl alcohol and acetophenone. Methanol is formed in the acetophenone reaction and is further oxidized to formaldehyde and formic acid. A small amount of water is also formed by the various reactions. The selectivity of the oxidation reaction is a function of oxidation conditions temperature, conversion level, residence time, and oxygen partial pressure. Typical commercial yield of cumene hydroperoxide is about 95 mol % in the oxidizers. The reaction effluent is stripped off unreacted cumene which is then recycled as feedstock. Spent air from the oxidizers is treated to recover 99.99% of the cumene and other volatile organic compounds. 

Methanol oxidation on Pt has been investigated at temperatures 350° to 650°C, CH3OH partial pressures, pM, between 5-10"2 and 1 kPa and oxygen partial pressures, po2, between 1 and 20 kPa.50 Formaldehyde and C02 were the only products detected in measurable concentrations. The open-circuit selectivity to H2CO is of the order of 0.5 and is practically unaffected by gas residence time over the above conditions for methanol conversions below 30%. Consequently the reactions of H2CO and C02 formation can be considered kinetically as two parallel reactions. 

Bufalini, J. J., and,K. L. Brubaker. The photooxidation of formaldehyde at low partial pressures, pp. 225-238. In C. S. Tuesday, Ed. Chemical Reactions in Urt)an Atmospheres. Proceedings of the Symposium held at General Motors Research Laboratories, Warren, Michigan, 1%9. New York American Elsevier. 1971. 

Figure 23 3 ami 23-4 present data on the pressures of aqueous lormaldchyde solutions.1 Figure 23-3 shows fntul system pressure Figure 23-4 gives partial pressure of the formaldehyde in the solution. m page ... 

FIGURE 25 Partial pressure of formaldehyde as a function of the subsurface oxygen peak area for the spectra in Figure 22A (open circles), and for a different experiment (black squares) in which the temperature of a copper foil was varied in the range from 420 to 720 K at a constant CH30H 02 molar ratio of 3 1 (the total pressure was the same as for the spectra in Fig 22A. The partial pressure of formaldehyde is linearly correlated with the abundance of subsurface oxygen in the near-surface region. The dashed line is a linear fit of the data points. 

The question remains open as to whether the surface complexes as proposed in (36)- (39) can be formed under FT conditions, especially at the higlt temperatures and (he low- CO partial pressures used [4], The search for surface chemisorbed formyl species has been unsuccessful 1114], Tlius, the interaction of formaldehyde, glyoxa) and CO/Hj with Al Oi supported rhodium gave no IR-detectahle traces of formyl species [ 169]. The insertion mechanism proposed by Hcnrici-Oliv and Olive is closely related to the Pichler Schul/. mechanism [40]. A reaction sequence based on the oxidative addition of hydrogen and reductive elimination of water is assumed Only one metal center is required, however, the mechanism of water elimination is not explained in detail,... 

For completeness, we mention that SFG was able to detect the final product of CH3OFI decomposition (CO), whereas the frequency range of intermediate products such as formaldehyde was not accessible. Similarly, HP-XPS carried out with a laboratory X-ray gun cannot accurately differentiate CO from CH , 0. In contrast, the wider frequency range of PM-IRAS allowed the identification of, for example, CH2O (in addition to CO) at elevated methanol partial pressures on a strongly CH c-poisoned surface (177). As these PM-IRAS investigations are relevant to methanol oxidation, they are discussed below. 

All the simple hydrocarbons are able to suppress the low pressure ignition of the H2 + O2 system. However, there are major differences of behaviour between methane and neopentane on the one hand, and most other hydrocarbons and related materials on the other [329—332]. With formaldehyde [333], ethane [334—336], propane [329, 337], and n- and i-butane [338] the second limit in KCl coated vessels falls more or less linearly with increasing partial pressure of additive. In the experiments of Baldwin et al. [333—338], the mole fractions, x and y, of H2 and O2, respectively, could be varied independently of each other by working with H2 + N2 + O2 mixtures and adjusting the nitrogen content appropriately. The rate of fall of the second limit at constant x was almost inversely proportional to y while at constant y and not too small x, it was almost independent of x. The limit did not change much with vessel size. The observations may be accounted for by adding reactions (1)—(lii)... 

It can be seen (Fig. 16) that the rate of formaldehyde polymerization increased rapidly with increasing formic acid partial pressure up to 40 torr with 500 torr of formaldehyde. In the kinetic scheme developed the initiation rate was proportional to the partial pressure of formic acid and... 

In contrast, toluene and methanol coadsorbed on Rb-X do not form a bimolecular precursor complex and both reactants seem to be independently adsorbed at the surface. It should be noted, however, that after equilibration of the catalyst with equal partial pressures of both reactants, toluene was the main adsorptive. During toluene methylation, sorbed toluene was again the main surface species, the reaction rate, however, was proportional to the surface concentrations of both chemisorbed species (toluene, formaldehyde). The onset of the reaction was observed at much higher temperatures than in the ring alkylation which is at large ascribed to the indispensable conversion of methanol to a formaldehyde (or formate) species. 

Kinetics of the reaction were determined by varying the partial pressures of oxygen, water, and methanol as well as the temperature. Other partial pressures were kept nearly constant nitrogen was the diluent. Kinetic observations also were similar as previously reported( 0 as is Illustrated in Figures T, 8 and 9 for different phases. The methanol reaction rate was nearly independent of the oxygen partial pressure, except at very low oxygen pressures in the reactor in which case the catalyst begins to be reduced. It was shown previously(6) that a reduced catalyst is much less active. The reaction rate has a positive dependence on methanol partial pressure, but the reaction is inhibited by the addition of water. Water does however increase selectivity to formaldehyde at the expense of dimethoxymethane, methylformate and dimethylether. 

The solubility of carbon dioxide in aqueous and non-aqueous solutions depends on its partial pressure (via Henry s law), on temperature (according to its enthalpy of solution) and on acid-base reactions within the solution. In aqueous solutions, the equilibria forming HCO3 and CO3 depend on pH and ionic strength the presence of metal ions which form insoluble carbonates may also be a factor. Some speculation is made about reactions in nonaqueous solutions, and how thermodynamic data may be applied to reduction of CO2 to formic acid, formaldehyde, or methanol by heterogenous catalysis, photoreduction, or electrochemical reduction. 

Methanol oxidation experiments were carried out in order to determine if methanol was an intermediate in the production of formaldehyde from methane. To this end a methanol saturator was placed upstream of the reactor. The saturator was submerged in an ice/acetone bath (at -16 to - 20 °C) keeping the saturated methanol partial pressure at 5 kPa. This was approximately equivalent to the total carbon containing products generated during standard reaction conditions. The gas feed stream to the saturator consisted of 81 kPa helium and 20 kPa air. The flow rate was varied from 6.25 - 100 ml min. ... 

For methane rich feeds, formaldehyde and carbon monoxide production increased with increasing oxygen partial pressure (Figure 3b). 

The condensation of formaldehyde on acetylene requires an extremely active and highly selective catalyst system to prevent explosions due to the use of excessively high acetylene partial pressures and the undesirable formation of cuprene, a polymer of acetylene. The catalyst used today is copper acetylide, deposited on a magnesium silicate support containing bismuth. Operations are -conducted at low pressure (0.1.10 Pa -absolute) and at relatively moderateiemperature (95°C) in a continuously fed system. 

Zhen et al. examined the use of VjOj-SiOj as a catalyst. Again, large amounts of N2O and H2O in the feed were necessary. The formaldehyde selectivity was higher than that of the methanol. Solymosi et al. examined a catalyst of Bi203-Sn02 and found 84-95% selectivity to formaldehyde at 1.7-2.7% conversion at 550 "C. No methanol was detected when dry feeds were used. The methanol selectivity increased with increasing H2O partial pressure. 

Both intermediates could conceivably decompose to MCPK by oxidative decarboxylation to give COx and water or by a concerted decarboxylation reaction to acetaldehyde starting from the first intermediate, or to formaldehyde starting from the second intermediate. However, neither intermediate, nor their dehydration products, nor acetaldehyde, formaldehyde, or CO were found even in trace quantities. Therefore, it appears that in this case as well the ketone is not being produced by an aldol reaction, but rather by a decarboxylative condensation reaction of the aldehyde and acetic acid, using oxygen from the surface as needed. When water was added, an increase in ketone formation was observed when comparing runs performed at the same CCald partial pressures. The reaction order for water was estimated to be 0.2. 

P(Tri), P(FA) = equilibrium partial pressure oftrioxane and formaldehyde, respectively, can be expressed [Busfield 1969] as ... 

Oscillations in the methanol-oxygen-copper-system were observed for the first time by H. Werner et al. [8]. They observed with stoichiometric methanol/oxygen mixtures (2 1) over Cu chip s in a tube reactor at 660 K rate oscillations with a cycle duration of ca. 3.5 min. Characteristic were sharp maxima (several seconds) of the methanol conversion leading to maxima in the formaldehyde and the CO2 productions, followed by a decline of the methanol conversion and the CO2 partial pressure whilst the formaldehyde partial pressure showed a slow decrease to the next period. 

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