(67c) A Modified Schlenk Line for Gas Phase Accelerating Rate Calorimetry, Capable of Quantitatively Sampling and Safely Handling Hazardous Gases

For gas phase accelerating rate calorimeter (ARC) testing, quantitatively charging gaseous sample into an ARC bomb remains a challenging issue. One conventional approach is to use a precision scale to measure the mass of gas container before and after the gas transfer. Obviously, it would be difficult to obtain a desired quantity in a controllable way, and the tubing attaching to the container for gas transfer may also exert an uncertain weight on the scale. Another approach is to use gas pressure to quantify the mass of gaseous sample. However, simply connecting the source gas to the ARC bomb and relying on the source pressure may either overcharge or undercharge the sample.

In this study, we have developed a method capable of accurately measuring the quantity of gas(s) charged to an ARC bomb using a modified Schlenk line, a common chemistry apparatus used to safely manipulate air/moisture sensitive chemical compounds. The modified Schlenk line consists of a dual manifold for vacuum and inert gas manipulation, sample ports, and a precision digital vacuum-pressure gauge for system leak checking and pressure reading. A key step is to measure the volume of gas line (and the gas storage tube if needed), which is achieved through calibration with a known volume of container and inert gas. Based on the ideal gas law, the volume of gas line (and gas storage tube) can be readily calculated. The assembly line allows to precisely control sample loadings by simply adjusting gas pressure via a needle valve. With the pressure, temperature, and volume data, this method enables measurement of gas sample mass with quantitative accuracy. Depending on the property of the gas and the loading quantity, repetitive charging steps with the aid of dry ice or liquid nitrogen may be necessary. The method conveniently allows loading a single gas or multiple gases for reaction and addition of pad gas as needed. It also provides dosing capability to add gaseous sample when necessary, a useful solution for a gas that is too reactive to be preloaded with other components before measurement starts.

The assembly line ensures a quick leak checking and enables safely handling toxic and extremely reactive gaseous chemicals, collecting gaseous products for further characterization or disposing the products into scrubbers after run. To aid safer venting of hazardous gases after a test when needed, an eductor is also incorporated into the line.

The utility of this method using a modified Schlenk line will be demonstrated in the thermal evaluation of the chlorination of toluene with chlorine and the polymerization of trans-1,2-difuoroethylene (E-1132) with 2,3,3,3-tetrafluoropropene (R-1234yf). The versatile method can also find application in other process safety testing, such as in a closed cell VSP2 test.