Aromatic hydrocarbons are vital petrochemical feedstocks used in producing various materials, but these hydrocarbons often contain trace olefins that harm product quality. Modified bentonite-based structures serve as catalysts for the removal of olefins from aromatic compounds. To enhance the catalyst efficiency of this material, which is primarily found in montmorillonite, various modification methods can be employed. The objective of the present study was to develop a high-performance catalyst for the removal of olefins and to evaluate how the quality of water used during preparation influences the final performance of the catalyst. For this purpose, the effect of mass ratio of bentonite to acid on leaching was first investigated, and the optimal ratio was determined to be 0.8. Then, the combination of purification with sodium hexametaphosphate (NaHMP) and acid activation with sulfuric acid on Iranian bentonite was performed to acquire a highly active catalyst. The prepared catalysts were characterized using various analytical techniques, including nitrogen adsorption-desorption analysis (BET analysis), X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), and ammonia temperature-programmed desorption (NH3-TPD). In addition, the effect of urban and deionized water on the activity of the prepared samples was investigated. Analysis by XRD revealed that the sample purified with deionized water contained smaller amounts of impurity phases, such as quartz, dolomite, and calcium carbonate. Additionally, the catalytic performance of the samples was evaluated in the olefin-removal process at a temperature of 160°C and a pressure of 11 bar. According to the results, the sample purified and activated with deionized water displayed superior performance and greater stability compared with the unpurified and urban water-purified and activated bentonite. This catalyst maintained the bromine index of <20 mg per 100 g for 370 h, which indicates the stability and high performance of this catalyst in terms of olefin removal.

Bentonite is used as a catalyst in the removal of olefins from aromatic compounds and the present study was designed to investigate how its performance might be improved by various treatments. Bentonite from Semnan mine, Iran, was used in the study following initial characterization. In order to investigate the effect of acid and thermal treatments on the removal of olefins from aromatic compounds, bentonite samples were modified using HNO3 at different concentrations (0.15, 0.3, 0.5, 0.7, 1, and 2 M) and were also at temperatures between 100 and 340°C for 3 h. To examine the catalytic activity of bentonite-based catalysts, the samples were evaluated after running batch and continuous experiments. The optimum catalyst was characterized using thermo-programmed desorption (TPD) of NH3 to examine the acidic sites. Scanning Electron Microscopy (SEM) images, nitrogen adsorption-desorption isotherms (BET analysis), and X-ray diffraction (XRD) patterns were used to study the structural changes of the bentonite produced by the acid and thermal activation. The removal of olefins by the catalysts in batch and continuous systems revealed that the sample modified with 0.3 M Nitric acid at 150°C had superior catalytic activity, with olefin conversion remaining at >50% for up to 20 h. Nitrogen adsorption-desorption isotherms showed that acid treatment can produce a mesoporous structure. On the other hand, the TPD analysis indicated that during weak acid treatment, some cations, such as Al3+ and Fe3+, were leached from octahedral sheets and the interlayers of the clay mineral resulting in weak acid sites being generated. Finally, a novel method was proposed and tested for measuring the Bromine Index (BI) using potentiometric titration.

Acid-activated clays are inexpensive materials that are used extensively in the removal of unsaturated compounds on an industrial scale. The performance of bentonitic clays in removing these compounds relies heavily on the types of raw clays and acids used in the activation process. In this work, we report on the removal of olefins from aromatic streams by bentonitic clays activated via two different routes. After preliminary tests of four different natural clays, the best clay was selected in terms of it having high swelling index, cation-exchange capacity, specific surface area and suspension stability values. Activation was achieved with hydrochloric acid (HCl) and sulfuric acid (H2SO4), and olefin removal was evaluated after holistic clay characterization by means of X-ray diffraction, X-ray fluorescence, Brunauer–Emmett–Teller (BET) specific surface area analysis, ζ-potential analysis, Fourier-transform infrared (FTIR) spectroscopy after treatment with pyridine, scanning electron microscopy and transmission electron microscopy. The increased basal spacing, replacement of H+ with interlayer cations and retained structural stability of the clay after acid treatment contributed to the improvement of olefin removal for HCl-activated clay. The HCl-activated clay was more efficient in terms of olefin removal than its H2SO4-activated counterpart, removing up to 90% of olefin components after 40 h. Based on pyridine-FTIR spectra and quantitative measurement of the acidic properties of the samples, HCl treatment increased the total number acid sites (Brønsted and Lewis) by approximately ninefold compared to the pristine natural clay and by approximately fourfold compared to the H2SO4-activated clay.