Heat capacities 57 Formaldehyde

We have directly measured the heat capacity of formaldehyde at temperatures close to that of liquid helium (about 2 10 3 cal g 1 grad-1 at 6 to 7°K) and we can say that the average heating of our sample by radiation itself (at the dose rate of about 50 rad sec-1) could not exceed 0.1°K, whereas the average increase of temperature caused by the heat of polymerization (Q 0.4eV, length of polymerization chain v 103) was not larger than about 0.5°K. 

The critical points are the thermal conductivity and heat capacity of the formaldehyde crystal at the low temperature. If these parameters are low enough relative to the rate of reaction and heat release, the reaction may not be occurring at low temperatures. 

Experimental results for the effective specific heat capacity were obtained by DSC tests in [6]. MXB-360 (phenol-formaldehyde resin) with a 73.5% mass fraction of glass fibers was used in those tests. and were given in [6] as follows ... 

Figure 2.5. Quasi-isothermal cure of a melamine-formaldehyde (MF) resin (pH 9.5 F/M = 1.7) at 119°C in closed high-pressure steel (HPS) and open A1 pans (a) non-reversing heat flow and heat capacity (b) heat flow phase.

Figure 2.15. Comparison of the heat capacity change as a function of reaction conversion for an epoxy(/ = 2)-amine(/ = 4), epoxy-anhydride, unsaturated polyester and melamine-formaldehyde system.

Patience, G.S. and Cenni, R. (2007). Formaldehyde process intensification through gas heat capacity. Chemical Engineering Science, Vol. 62, pp. 5609-5612. 

Methane and oxygen react in the presence of a catalyst to form formaldehyde. Consider the heat capacity data for methane (CH4) as f (T) where T is in K. Calculate the amount of heat needed to heat up 100 moles of methane gas from 300 to 900 K at constant pressure. 

The molar feed rate of formaldehyde to the CSTR (Fpo) is 2000 mol/h. The temperature of the feed to the reactor is 32 °C. As a rough first approximation, you may assume that the molar heat capacity is the same for all species at 15 cal/mol-°C. All solutions are ideal. 

Specific Heat Capacity. Representative values of specific heat capacity are shown in Tables 3 and 6. The range of values is only about 850 to 2400 J/(kgK) or barely a factor of three. As a general rule, differences are usually associated with the molecular composition of the polymer and less with molecular architecture, although crystallinity may be important. For example, a comparison of three forms of polyethylene (Table 6) reveals little difference in heat capacity the high density, and hence more crystalline, form has a somewhat lower value. Similarly, no differences are observed between two grades of phenol-formaldehyde resin, or between them and phenol-furfural resin. However, in comparing isotactic and atactic (amorphous) polypropylene shown in Table 3 with values of 1790 and 2350 J/(kg K), respectively, a fairly substantial difference is observed the more ordered, denser isotactic form has the lower heat capacity, as is to be expected. However, comparable values of isotactic and atactic polystyrene have been reported to be 1264 and 1227 J/(kg-K), respectively (65) here the difference is small. 

Heat Capacity of Formaldehyde Gas. In the absence of any experimental data, we haA e calculated heat capacity figures for formaldehyde by the method described by Dobratz based on spectroscopic measurements This calculation leads to the following expres.sions for heat capacity at constant pressure in cal/gram mol formaldehyde gas as a function of its temperature in degrees centigi-ade and partial pressure in atmospheres. 

The most common adhesive system used for bonding continuous fibers and fabrics to rubber is resorcinol-formaldehyde latex (RFL) system. In general, RFL system is a water-based material. Different lattices including nitrile and SBR are used as the latex for the adhesive system. 2-Vinylpyridine-butadiene-styrene is the common latex used in the adhesive recipe. RFL system is widely being used in tires, diaphragms, power transmission belts, hoses, and conveyor belts because of its dynamic properties, adhesion, heat resistance, and the capacity to bond a wide range of fabrics and mbbers. 

The driving force in the use of these salts as hardeners is their capacity to release acid, which decreases the pH of the resin and thereby accelerates curing. The speed of the reaction between the ammonium salt and formaldehyde (or ammonia and formaldehyde when this is present) also determines, together with the amount of heat supplied, the rate of acid release and therefore the rate of curing ... 

Similarly, the commercial resins Wofatit K and Wofatit K.S. marketed by I. G. Farben are made by reacting benzaldehyde-2 4-di-sulphonic acid, resorcinol and formaldehyde. Phenol is also present in the production of Wofatit K.S. The final heating stage with formaldehyde is continued until a gel is formed. This is then cooled, washed and dried for several days at 80°C to 90°C, to give a resin which is fairly hard and has an exchange capacity of about 2-8 m-eq/g. ... 

Ion-exchangers with good heat and chemical stability were synthesized by incorporating cryptate groups in phenol-formaldehyde resins or by attaching them to chloromethylated polystyrene as in Scheme 18. Capacities of 1.0 to 1.3 mmol gr for alkali-metal salts were attained. 

Cellulose can be converted into a hemiacetal derivative, methylol cellulose , by reacting with formaldehyde in methyl sulphoxide. Other aprotic solvents, such as pyridine, AA-dimethylformamide, AA-dimethylacetamide, A-methyl-2-pyrrolidinone, and thiolane-1-oxide can be substituted for methylsulphoxide for this conversion. More concentrated solutions of methylol cellulose could be obtained when cellulose and paraformaldehyde were heated together in the solvent than when formaldehyde gas was bubbled through a suspension of cellulose in the solvent. Solutions of 10% cellulose in methylsulphoxide could be obtained by this method. During the swelling of cellulose in ethanolamine, ethylenediamine, and methyl sulphoxide, the solvent retention capacity of cellulose at 20—120°C decreased by 10—20%, depending on the solvent."... 

In the manufacture of solid and liquid resole resins, the reaction procedure makes use of the exothermic nature for heat production and vacuum dehydration for temperature control. After the alkaline catalyst (which is usually sodium hydroxide, but sometimes calcium hydroxide, barium hydroxide or ammonia) is added to the phenol and formaldehyde, the mixture is allowed to heat at 80-100°C for 1-3 hours. The size of the kettle batch, for example, 60,000-135,000 lb, is controlled by the exothermic nature of the reaction, which has been measured at 81.1 and 82.3 kJ/mole, the design of the reactor and the condenser cooling capacity. 

C in a heat exchanger, entered a scrubber. Absorption with water produced solutions containing 5—7% formaldehyde. The steel reactor was lined inside with ceramics. The production capacity was 18 tons of formaldehyde per month [35,174,267]. 

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