Effect of Poly(vinyl alcohol) on Catalytic Performance of Al-Pillared Clay in Alkylation of Aromatic Hydrocarbons with Olefins

Abstract

It is vital to design and synthesize efficient catalysts for removing olefins from aromatics and prolonging reaction time. The catalytic properties of pillared clay for olefin removal from aromatic compounds can be enhanced noticeably by grafting organic polymer molecules due to modification of the clay porosity in the pillaring reaction. In the present work, a series of catalysts are prepared by pillaring raw bentonite and acid-treated bentonite with aluminum and poly(vinyl alcohol) (PVA) intercalation. Prepared samples are evaluated in the olefin removal process and characterized by X-ray diffraction patterns (XRD), temperature-programmed desorption (TPD) of NH3, and nitrogen adsorption–desorption isotherms. The BET results reveal that the pillaring reaction in an aqueous solution of PVA increases the clay’s surface area to greater than 200 m2.g–1. The pore volume of alumina-pillared acid-activated clay (Al-PAAC) is enhanced from 0.278 to 0.321 and 0.416 cm3.g–1 at the PVA concentrations of 30 and 50 wt %, respectively. The samples modified with PVA, as a precursor in the pillaring reaction, show an enhanced catalytic activity compared to the other samples due to a higher number of active sites. The olefin conversion of the pillared sample remains above 50% in the presence of 50 wt % PVA for more than 26 h. Furthermore, PVA could facilitate the reactant’s access to the active acid sites in the interlayer of the pillared clay. The adsorption of aromatic compounds and olefins by the pillared samples follows the intraparticle diffusion kinetic model. In addition, the Langmuir model fits the adsorption isotherm data well.

Olive stone as an eco-friendly bio-adsorbent for elimination of methylene blue dye from industrial wastewater

“…The maximum adsorption capacity is q max (mg g −1 ), and the Langmuir constant is b (L (mg/g) −1 ) 32 Freundlich K f 1/n (mg g −1 )/(mg L −1 ) : MB's adsorption capacity, n is the factor of heterogeneity 33 Dubinin–Radushkevich ƹ D 2 q D is the maximum adsorption capacity in (mg g −1 ), B D is the free energy coefficient of the adsorption (mol 2 /kJ 2 ), ƹ D is the Polanyi potential (kJ mol −1 ) 34 Temkin K t is the constant referring to the equilibrium (l g −1 ), B is the heat of adsorption (expressed in kJ mol −1 ), R is the universal gas constant (8.314 J mol −1 K −1 ), and T is the absolute temperature in Kelvin. B (J kJ −1 ) is a Temkin constant equal to ( RT/B ) 35 Kinetic Pseudo-first-order q e (mg g −1 ) is the equilibrium adsorption uptake, q t (mg g −1 ) is the amount of the removed MB at time t , and K 1 (min −1 ) is the rate constant of the first-order adsorption 36 Pseudo-second-order Second-order adsorption rate constant, K 2 (g (mg min) −1 ) 37 Elovich model A is the adsorption constant, and B is the initial rate of adsorption (mg g −1 ...…”

“…Adsorption, a mass transfer process, is the phenomenon of gases or solutes sticking to solid or liquid surfaces. Due to unequal forces, the molecules or atoms on the solid surface adsorb because they have excess surface energy 36 , 37 . The adsorption of contaminants on the adsorbent surface occurs in three steps 40 : (1) contaminants move from the liquid film's boundary layer to the adsorbent surface as explained by the extra-particle diffusion model, (2) molecules diffuse either within the pores, below the surface, or both as explained by the intra-particle diffusion theory, and (3) contaminants adsorb through electrostatic interaction and hydrogen bonding in a surface chemical reaction.…”