Gas evolution measurement

It is important to measure the gas evolution rate during the normal reaction. This information is required to design the venting or scrubbing system so that the reactor does not become pressurized as the reaction proceeds. 

Gas evolution rate can be measured by very simple methods. The gas generated in a reaction can be collected in an upturned measuring cylinder filled with a suitable collecting fluid (water for insoluble gases, silicone oil for water-soluble gases). Timing the rate of gas collection gives a quick assessment of the evolution rate. 

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Figure 12-26. The SIMULAR reaction calorimeter. Features include pumped liquid feed, gas mass flow control, gas evolution measurement, and distillation equipment. (Source Hazard Evaluation Laboratory Ltd.)...

Lambert, P. G., G. Amery, and D. J. Watts (October 1992). "Combine Reaction Calorimetry With Gas Evolution Measurement." Chemical Engineering Progress, 53-59. 

Lambert, P., Amery, G. and Watts, D.J. (1992) Combine reaction calorimetry with gas evolution measurment. Chemical Engineering Progress, October, 53-59. 

With aliphatic azides, gas evolution did not usually begin until ca. 5 min had elapsed from the time of initial addition. In contrast, immediate gas evolution was observed after the addition of azido nitriles and phenoxy azides to the nitrosonium salt. Total gas evolution, measured on the closed sy.stem by water displacement from a calibrated gas burette, reflected the total amount of reacted azide and the different pathways for the production of gaseous products (nitrosative decomposition and Curtius rearrangement). The rate of production of gaseous products slowed markedly after the evolution of 40-60 mL gas (1 -2 mmol of reacted azide) with the exception of nitrosative reactions with 4-azidobutaticnitrile and... 

By comparison to peroxides, the azo compounds are generally not susceptible to chemically induced decompositions. It was shown,however, that it is possible to accelerate the decomposition of a,a -azobisisobutyronitrile by reacting it with bis(-)-ephedrine-copper(II) chelate. The mechanism was postulated to involve reductive decyanation of azobisisobutyronitrile through coordination to the chelate. Initiations of polymerizations of vinyl chloride and styrene with a,a -azobisisobutyronitrile coupled to aluminum alkyls were investigated. Gas evolution measurements indicated some accelerated decomposition. Also, additions of large amounts of tin tetrachloride to either a,a -azobisisobutyronitrile or to dimethyl-a,a -azobisis-obutyrate increase the decomposition rates. Molar ratios of [SnCl4]/[AIBN]= 21.65 and [SnCl4]/[MAIB] = 19.53 increase the rates by factors of 4.5 and 17, respectively. Decomposition rates are also enhanced by donor solvents, like ethyl acetate or propionitrile in the presence of tin tetrachloride. ... 

The data required can be derived directly from the pressure-time and temperature-time curves obtained from adiabatic calorimeters and gas evolution measurements. Calorimeters which use pressure compensation (Section 3.6.3, page 43) allow the use of test cells with extremely low Phi factors and yield data which requires little if any correction for Phi. in contrast to some of the other adiabatic calorimeters available which were designed for highly adiabatic operation. 

Nxylylene system, substituents affect it only to a minor extent. AH parylenes are expected to have a similar molar enthalpy of polymerization. An experimental value for the heat of polymerization of Parylene C has appeared. Using the gas evolution from the Hquid nitrogen cold trap to measure thermal input from the polymer, and taking advantage of a peculiarity of Parylene C at — 196°C to polymerize abmptiy, perhaps owing to the arrival of a free radical, a = —152 8 kJ/mol (—36.4 2.0 kcal/mol) at — 196°C was reported (25). The correction from — 196°C to room temperature is... 

The evaluation of ehemieal reaetion hazards involves establishing exothermie aetivity and/or gas evolution that eould give rise to inei-dents. Flowever, sueh evaluation eannot be earried out in isolation or by some simple sequenee of testing. The teehniques employed and the results obtained need to simulate large-seale plant behavior. Adiabatie ealorimeters ean be used to measure the temperature time eurve of selfheating and the induetion time of thermal explosions. The pertinent experimental parameters, whieh allow the data to be determined under speeified eonditions, ean be used to simulate plant situations. 

Measurements of product gas evolution, mass loss or evolved gas analysis may all be used to study the kinetics of a solid—solid interaction provided that there is strict adherence to the condition that gas evolution occurs concurrently with the solid state process. Clearly this approach is only applicable if there is direct experimental support for a single step process. For example, carbon dioxide release is identified [410] as being... 

Although there are experimental and interpretative limitations [189, 526] in the kinetic analysis of non-isothermal data, DTA or DSC observations are particularly useful in determining the temperature range of occurrence of one or perhaps a sequence of reactions and also of phase changes including melting. This experimental approach provides, in addition, a useful route to measurements of a in the study of reactions where there is no gas evolution or mass loss. The reliability of conclusions based on non-isothermal data can be increased by quantitatively determining the... 

If both steps are kinetically distinct, measurement of gas evolution (D) does not give any information concerning the rate of the subsequent interaction (formation of C). If E is produced in a finely divided state, it may be appreciably more reactive than alternative bulk preparations of the... 

Janssen and Hoogland (J3, J4a) made an extensive study of mass transfer during gas evolution at vertical and horizontal electrodes. Hydrogen, oxygen, and chlorine evolution were visually recorded and mass-transfer rates measured. The mass-transfer rate and its dependence on the current density, that is, the gas evolution rate, were found to depend strongly on the nature of the gas evolved and the pH of the electrolytic solution, and only slightly on the position of the electrode. It was concluded that the rate of flow of solution in a thin layer near the electrode, much smaller than the bubble diameter, determines the mass-transfer rate. This flow is affected in turn by the incidence and frequency of bubble formation and detachment. However, in this study the mass-transfer rates could not be correlated with the square root of the free-bubble diameter as in the surface renewal theory proposed by Ibl (18). 

However, the synthesis process, depicted in scheme 5, is rather idealized. In reality, the chemistry appears to be quite complex, resulting in a partially cross-linked rubber and the evolution of gaseous species other than chloromethane. Dietrich et al.17 reported that the progress of the polymerization at 116°C, as measured by gas evolution and polymer molecular weight, significantly slowed at around 50% conversion. The reaction could, however, be driven further forward by increasing the temperature to > 150°C. 

These experiments also show the value of NEXAFS as a technique for following the kinetics of surface processes. We have shown that experiments can be tailored so a specific reaction can be studied, even if gas evolution is not involved. This represents an advantage over thermal desorption experiments, where several steps may be required in order to desorb the products to be detected. Another advantage of NEXAFS is that rates are measured isothermally, so the kinetic parameters can be determined with accuracy. Finally, NEXAFS is not a destructive technique, so we need not to worry about modifying the surface compounds while probing the system, as would be the case with other techniques such as Auger electron spectroscopy. 

Screening techniques are relatively cost-effective and require only a small chemical sample however, they do not measure gas evolution or maximum pressure rise. A material is generally considered to be thermally stable if the temperature at which energy from reaction is first observed is at least 100 degrees Celsius (°C) above the maximum operating temperature of a process event under upset conditions (CCPS 1995b p. 93). 

Gas evolution from gunpowder measured at atmospheric pressure and 290 °C. 

Figure 3 System for gas chromatographic measurement of Oz evolution from superconductors dissolved in acid (29) (A) enlarged view of reaction flask, (B) circulating system including flask (G), NaOH U-tube (T), three-way valves (S), 1 mL loop (L), pulse pump (PP) and vacuum system (V), At the right is the gas chromatograph (G.C.). (From Reference 29. With Permission.)...

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