Formaldehyde conversions

As with resoles, the central issue in design of novolacs is molecular weight. The effects of formaldehyde-to-phenol molar ratio and formaldehyde conversion on molecular weight of novolacs has been well studied and reported [192,193]. The effects of molecular weight on most of the important properties are also available [193]. These include Tg, melt viscosity, gel time, hot-plate flow, glass-plate flow. 

Also, 1,3-dioxolane was obtained from the reaction of ethylene glycol (EG) and aqueous formaldehyde in high yield using an ion-exchange resin catalyst. In a batch mode of operation, with 50% excess EG, the conversion of formaldehyde is limited to 50% due to equilibrium limitation, whereas in batch reactive distillation, formaldehyde conversion greater than 99%... 

Figure 8.2. Vibrationally adiabatic potential for formaldehyde conversion in excited electronic (a) A A2 and (b) a3A2 states. The levels of the vt vibration are indicated. (From Jensen and Bunker [1982].)...

Let us apply Eq. (3.86) to phenol - formaldehyde polymers synthesized in an acid medium with a phenol excess (novolacs). Phenol is a trifunctional reactant (A3), the functional groups being the aromatic hydrogens located in positions 2, 4, and 6 of the phenolic ring. Formaldehyde acts as a bifunctional monomer (B2), forming methylene bridges between the reactive positions of phenol. Novolacs are synthesized with a phenol excess, such that gelation does not occur at full formaldehyde conversion. From Eqs (3.83) and (3.86), we obtain... 

Scleclivitics of around 90% at formaldehyde conversions of over 80% are claimed. Commercial developments require the building of an integrated complex, since neither of the two fccd-siocks, methyl propionate and formaldehyde dimethyl acetal,are available in the market. 

Methanol disproportionation includes two sites of A/xNa" generation (1) Methanol reduction generates a secondary AftNa from a primary A/IH" by the activity of the Na /H antiporter. This was concluded from the finding that CH4 formation from H2/CH3OH in Methanosarcina barkeri was coupled with Na extrusion, which was sensitive to Na /H antiporter inhibitors and protonophores [108]. (2) The oxidation of methylene-H4MPT to CO2 and 4[H] is coupled with the generation of a primary A/INa as indicated from the fact that Na translocation associated with formaldehyde conversion to CO2 and 2H2 was not sensitive towards Na /H antiporter inhibitors and protonophores [105]. 

The mechanism of A/iNa -driven methanol oxidation to the level of formaldehyde is not known. CH3-H4MPT H-S-CoM methyltransferase has been identified to be the site of primary A/iNa generation during formaldehyde conversion to the methanol level... 

Mueller, L.L. Griffin, G.L. Formaldehyde conversion to methanol and methyl formate on copper/ zinc oxide catalysts. J. Catal. 1987,105 (2), 352-358. 

Another example is monolithic-type reactors, which have found their main application in the field of combustion. A monolith bed allows better autothermic operations with a minimal pressure-drop. This concept was used to improve performances in commercial methanol into formaldehyde conversion by adding a... 

Venuto and Landis (1966) studied the condensation of phenol and formaldehyde on different zeolitic materials. The activity at 182°C decreases as follows H-Y>R-Y> H-Mordenite > R-X > Ca-X. However, although the highest selectivity to 2,4 -bis(hydroxy-phenyl)methane was obtained on H-Y, the greatest selectivity to the isomer 2,2 -bis-(hydroxyphenyl)methane was observed on R-X and Ca-X at low formaldehyde conversions. Only traces of dypione were observed during the aldol condensation of acetophenone on R-X zeolite. 

Figure 3. Formaldehyde conversion (7), dihydroxydiphenylmethane yield (a) and selectivity (o) upon condensation with phenol for 4V6 h at 180 C, vs. phenol/formaldehyde-molar ratio. Catalyst SAPO-5.

Figure 4. Formaldehyde conversion upon condensation with phenol for 4V4 h at 180 C, vs. reaction time. ALPO-5-P (o) and SAPO-5 (a) were used as catalysts. Phenol/formalde-hyde molar ratio 2/1.

Table 1. Formaldehyde conversion and dihydroxydiphenylmethane selectivities upon condensation with phenol, for 4Vfe h at 180 C (phenol/formaldehyde molar ratio 2/1).

Fig. 6.— Total Formaldehyde Conversion Bate at 60° Shown to be Independent of Concentration of Organic Species at Intermediate Conversion Levels when Plotted Against Concentration of Ca(OH)s Instead of Total Calcium Concentration. [Rate of feed of HCHO (mole.liter .min ) —O—. 0.94 — —, 0.86 —%—, 0.78 (CH3OH stabilized) —A—, 0.3S —V—, 0.15.]...

In this work conducted to establish the kinetics, experimentation was terminated when the formaldehyde conversion-rate approached the feed rate of formaldehyde to the reactor, because the reaction rate in a continuously stirred tank-reactor cannot exceed the feed rate to the reactor. Subsequent experiments were made at higher severities of reaction, that is, past the concentration levels of calcium hydroxide catalyst that were required for complete conversion of formaldehyde. ... 

At low formaldehyde conversion-levels, the first-order dependency of the Cannizzaro reaction on formaldehyde and calcium hydroxide can be explained as follows. In March s mechanism for the Cannizzaro reaction. 

The formaldehyde conversion-level has a definite effect on the product distribution. Most evident is the fact that the product obtained at complete conversion is markedly different from that obtained at intermediate conversion levels. Figure 16 shows the distribution, by number of carbon atoms, of the C3 and higher species produced in the formose reaction at 60° as a function of conversion of formaldehyde. Weight percents are regarded as identical to area percents of the gas-liquid chromatograms of the reduced sugars. No direct dependence on formaldehyde feed-rate is apparent. Three- and four-carbon compounds preponderate at low conversion levels at complete conversion, the terminal products are C4, 10% Cr 30% Co, 55% and C, 5%. 

A remarkably selective conversion of formaldehyde into glucose was reported by Weiss and co-workers.The reaction, carried out at 98°, was initiated by adding aqueous sodium hydroxide to a calcium chloride-formaldehyde solution. Under these conditions the induction period was IS seconds, and at 18% formaldehyde conversion level hexoses were formed with 84.3% selectivity. Analysis by glc of the products [in the form of trimethyl silyl (TMS) derivatives] revealed that no branched sugars were formed and glucose constituted about 90% of the reaction mixture. It should be noted that analysis—gas chromatography-mass spectrometry (gc-ms) of the corresponding alditol acetates—of the mixtures obtained in the formose reaction carried out under normal conditions revealed the presence of 33-37 components. ... 

Using RhCl(CO)(PPh3)2 as a catalyst precursor, together with amine promoters, both formaldehyde conversion and glycolaldehyde selectivity are in the range 80-90% at 120-200 bar and 110°C. However, a major disadvantage of this system is the cost penalty associated with the requirement for anhydrous formaldehyde if the cheaper and more readily available aqueous formaldehyde is used, the major product is methanol. The product glycolaldehyde also inhibits the reaction, and low concentrations have to be maintained in the reactor. 

More recently Kumar and Katiyar [56] have modeled the batch polymerization of melamine-formaldehyde reactions and determined the rate constants. They found that the rate constants are a function of temperature only. Their work suggests ten proposed reactive species and takes into account the reactivity of the hydrogens at primary and secondary amide positions (the reactivity was said to be independent of its substituents). The polymerizations of melamine with formaldehyde under conditions existing in an industrial reactor were studied. The polymerization was carried out in a special T-shaped reactor, and the conversion of formaldehyde was measured as a function of temperature. The reaction temperature and the formaldehyde (F) to melamine (A) ratio (F/A) and the pH were carried in a systematic manner and its effect on the course of the reaction followed by formaldehyde conversion. Melamine dissolves slowly in the reaction mass and also partially ionizes. The experiment suggests that it is the un-ionized species that play a major role in the polymerization. 

The methanol conversion increases with the oxygen concentration, obeying, like formaldehyde conversion, the first-order law in the reactant concentration, whereas the overall sequence of the formation of the products is described by the scheme ... 

The Ti02 and Z1O2 supports catalyze conversion of formaldehyde to metltyl formate. Methyl formate and methanol are the main products of formaldehyde conversion on Y-AI2O3. Si02 is inactive in both reactions. 

Supported vanadium on Y-AI2O3 does not provide a notable increase in activity, which is explained by low dispersion of vanadium over the surface of support. Increasing activity of VAlw is related to the presence of monomeric VOx species in sample. Low selectivity to formic acid in the oxidation of formaldehyde on VAl sample is caused by a low coverage of the surface with vanadia species and by a large fraction of free areas of support that are active in formaldehyde conversion to methyl formate. 

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