A study has been made of the sorption of isopropyl methylphosphonofluoridate vapor (IMPF) by an air-permeable protective material consisting of powdered activated carbon bonded to a fabric substrate. The interactions of IMPF with individual components of the system have been studied prior to examination of the composite material. The solubility and diffusivity coefficients of IMPF in films formed from two different acrylic latex binders have been determined by gravimetric sorption methods. Sorption of IMPF vapor by the activated carbon and the fabric substrate has been measured gravimetrically. Experimental materials employing different binders and carbon loadings have been prepared, and the uptake of IMPF vapor determined.
Vapor sorption by these materials has been studied under dynamic conditions of flow through the material, and breakthrough profiles have been obtained. A mathematical model of dynamic vapor sorption has been developed that accurately reproduces the experimentally observed results. This model divides the adsorbent into regions of different prevailing sorption kinetics. The major region has a sorption rate that is determined solely by mass transport of vapor. The remaining “slow” region shows sorption kinetics that are consistent with a slow surface deposition or displacement reaction as the rate determining step. Even though all of the carbon particles are coated with a film of binder, permeation through this film is not rate-controlling step. The “dynamic” sorption capacity of carbon incorporated into the material is largely uninfluenced by the presence of the latex binder.
The mathematical model is successful in predicting the performance of multiple-layer assemblies from the results observed on single layers, and this provides a verification of the approach to the analysis of the sorption kinetics. The model is useful in providing guidelines to show how the material performance may be improved, and indicating the research avenues that are most likely to lead to useful developments.