Low-temperature hydrothermal modification of waste paper fiber adsorbent to enhance removal benzothiophene sulfide efficiency from oil: kinetics and equilibrium study

Thiophene sulfide is difficult to be removed by hydrodesulfurization. In this study, ZnCl2-waste paper fiber activated carbon was used as adsorbent to remove thiophene sulfide from simulated oil by hydrothermal modification. Under the optimum condition of ammonia modification, the adsorption capacity of modified adsorbent to BT is 14.8 mg S/g, 2.98 times that of unmodified. BET, FTIR and Boehm analysis showed that the mesopore volume of ammonia modified adsorbent increased by 96.62% and the mesopore ratio increased from 12.58% to 43.40%, which was conducive to improving the adsorption rate. After modification, the basic groups on the surface of the adsorbent increased by 44.3 times, and –NH3+, –OH and –NH2 enhanced the electron attraction and hydrogen bonding force between the adsorbent and BT molecule. Adsorption isotherms, adsorption kinetics and adsorption thermodynamics show that the adsorption process is spontaneous, entropic and exothermic. The pseudo-second-order kinetic rate constant increases with the increase of adsorption temperature, indicating that the increase of temperature is beneficial to accelerate the adsorption rate. The adsorption desulfurization process follows the mechanism of single and multilayer adsorption mixing. The results of this study can help to reveal more clearly that biobased activated carbon can be modified to adsorb thiophene sulfide.