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This paper demonstrates the application of near-infrared process analytical technology to investigate the kinetics as well as the interaction between adsorbate molecule and adsorbent surface during a gas-solid (isoamyl alcohol vapor-silica gel) adsorption process. The adsorption process took place in a differential adsorption bed, which was temperature-and mass-homogeneous, and was in-line monitored by a near-infrared spectrometer via an optical fiber probe. After pretreating near-infrared data with band selection and partial least squares, a calibration model of back propagation-artificial neural network has been constructed to quantitatively determine the amount of adsorbate onto the adsorbent surface at any time within the entire adsorption process, the prerequisite for studying adsorption kinetics. The interaction between adsorbate and adsorbent could be acquired from the near-infrared spectra of the adsorbent adsorbing the adsorbate continuously. What is perhaps more important, since the kinetics data and the information about interaction are synchronous, it is feasible to incorporate them together for understanding the adsorption process more thoroughly than any current method.

With an experimental setup of near-infrared process analytical chemistry, a competitive adsorption process of orthoxylene and aniline vapor onto silica gel has been revealed in the paper. The mixture vapor of orthoxylene and aniline has been introduced into a quartz adsorption bed, which was filled with adsorbent of silica gel and monitored continuously by a near-infrared spectrometer. Based on near-infrared spectra recorded during the adsorption process and chemometrics methodologies, the competitive adsorption process has been studied completely as well as clearly: 1) at about 62 minutes the adsorption achieved its equilibrium or stable state with aniline concentration of 0.22 g/g, and without any orthoxylene; 2) othoxylene was adsorbed first, but then rapidly replaced by aniline; 3) the adsorption of aniline resulted from the hydrogen bonds between aniline's amino groups and silica gel's silanol groups while that of orthoxylene was due to physical adsorption; 4) aniline was adsorbed vertically on the silica gel but orthoxylene laid evenly; 5) some surface of silica gel was more active for adsorption than others.