Apparatus and method to measure a molecular diffusion coefficient in a porous powder

摘要

An apparatus and method for measuring molecular diffusivity in porous powders or minerals, e.g., the microporous synthetic minerals used for gas separation and chemical catalysis, were invented that allows a varying pressure in the gas around the powder during the measurement. This obviates the need for the pressure to be constant and the attendant complicated component parts. A mass balance model equation of the sample cell with the diffusivity as an adjustable parameter is used to deduce the sample cell pressure change versus time (uptake curve) until the equilibration of gas diffusion into the powder. A numerical analysis method is used to solve the mathematical model to compute a simulated uptake curve. Curve fitting of the simulated and measured uptake curves is used to optimize the diffusivity parameter, which gives the measured diffusivity. The apparatus and method are simple, easy to use, and automation is also simple.

主权项

1. A method and apparatus for measuring a molecular diffusion coefficient in a porous powder comprising:
(a) providing a sample cell that has a weighed amount of the porous powder and a supply container of known volumes isolated by a gas flow control means, placing the sample cell in a constant temperature bath and treating the porous powder into a known chemical state, keeping the sample cell in the constant temperature bath at a fixed temperature and evacuating the sample cell and supply container by vacuum pump means and then isolating the supply container and sample cell; (b) supplying a gas to the supply container, then using the gas flow control means to allow communication between the supply container and the sample cell for a period between one second to thirty seconds, and measuring the pressure decrease and temperature in the supply container and the pressure and temperature in the sample cell as a function of time until equilibration thereby determining a curve of sample cell pressure versus time; (c) using numerical analysis means to provide a computer program further comprising a mass balance equation of the sample cell with the diffusion coefficient as a parameter, and using a computer with the computer program and an estimated value of the diffusion coefficient and the measured pressure decrease, temperature and volume of the supply container and measured volume, temperature and weight of powder in the sample cell to compute a curve of sample cell pressure versus time; (d) repeating the computation in step (c) to optimize the diffusion coefficient parameter by finding the best fit between the computed curve of sample cell pressure versus time and the corresponding curve measured in step (b), and using the optimized diffusion coefficient as the measured diffusion coefficient.