Papers by Author: Li Fang Chen

Abstract: We report the thermal and catalytic decomposition of low density polyethylene (LDPE) as a recycling route of plastic solid waste. The reaction system consisted of a fixed-bed reactor at a 450 °C reaction temperature and a 40 min reaction time. Tungstophosphoric acid (H3PW12O40)-functionalized ordered mesoporous materials MCM-41 were employed as catalysts. Results show that using this technical approach, on one hand, environmentally unfriendly waste can be disposed and, on the other hand, valuable and widely used fuels can be obtained.

Abstract: Effects of ytterbia for Pt-SO42-/ZrO2-Al2O3-Yb2O3 (PSZAY) catalysts in n-hexane hydroisomerization were investigated. It was elucidated that the introduction of ytterbia into Pt-SO42-/ZrO2-Al2O3 (PSZA) increased both the surface area and the number of active sites, resulting in a higher n-hexane isomerization activity. At the same time the catalyst stability has also been markedly increased by alleviating the sulfur loss and by stabilizing ZrO2 tetragonal crystalline structure.

Abstract: Transition metal-modified carbon-based adsorbents were prepared by impregnating activated carbon with solutions of copper, cobalt or nickel chloride or nitrate. The mixtures were dried and then calcined under nitrogen stream. The surface metal species were analyzed by XRD technique and the surface oxygen-containing groups were characterized by FTIR. Their adsorption capacities for dibenzothiophene (DBT) were measured by using DBT-containing n-octane solution as model oil. Experimental results show that the metal species on the carbon surface could be controlled by the calcination process under nitrogen atmosphere. Both the transition metal precursors and kinds of metal species on the carbon surface have significant effects on DBT adsorption capacity.

Abstract: Rice hull (designated with RH) was activated by phosphoric acid to prepare an adsorbent for the removal of sulfur-containing compounds from diesel fuel. Adsorption tests for both, a 300 µg.g-1 dibenzothiophene (DBT)-containing n-octane solution using as model oil and a commercial hydro-treated diesel fuel, were performed to elucidate the effect of varying phosphoric acid to RH ratio, treating temperature and the removal of silica from the adsorbent on the combination of the textural structure, surface chemical property and adsorption capacity. It was indicated that high surface area and micro-pore volume of the adsorbent favored the adsorption of DBT and its derivatives. Richening of oxygen-containing compounds on the adsorbent surface was advantageous to the adsorption and removal of DBTs. At a phosphoric acid and RH weight ratio of 3:1 by using a two-step treatment, a satisfactory adsorbent with an adsorption capacity of 28.89 mg S/g was successfully prepared. If the silica in the adsorbent was further removed, the product exhibited the highest performance, reaching 30.43 mg S/g for the model oil and 21.79 mg S/g for the commercial diesel fuel. Both the textural structure and the surface chemical property like acidic groups of a RH-based adsorbent play important roles in its adsorption behaviors, and the formation of donor-acceptor complexes between surface acidic groups and DBT may probably benefit DBT adsorption capacity.

Abstract: Phosphotungstic acid (HPW) supported on activated carbon (AC) combined with hydrogen peroxide formed an oxidative desulfurizaiton (ODS) system to oxidize sulfur-containing compounds in diesel fuel. Dibenzothiophene (DBT) dissolved in n-octane was selected as a model feedstock for studying this new ODS system. The HPW/AC catalysts were characterized with XRD, FTIR and N2 adsorption-desorption measurements. HPW was highly dispersed on the surface of carbon support. It was found that the DBT adsorption capacity decreased from 42 mg S/g to 33.13 mg S/g as HPW loading amount increased from 0 to 15 wt.%. Oxidative removal of DBT in the model oil significantly increased with increasing HPW loadings on the support from 0 to 10 wt.%. 100 % DBT was removed by using the catalysts with HPW content higher than 10 wt. %. At 80 °C, oxidative removal of DBT reached 100 % after 40 min of reaction when O/S molar ratio ranged from 4 to 10.

Abstract: Two types of mesoporous Si-MCM-41 materials were synthesized via a cationic surfactant template method using different Si-precursors. The materials obtained were characterized by FTIR, XRD, BET, TEM and 29Si MAS-NMR techniques. When fumed silica was used as Si precursor, a Si-MCM-41-I solid with wormhole-like pore topologies was obtained. However, when tetraethylorthosilicate (TEOS) was used as Si precursor, a mesoporous Si-MCM-41-II solid with hexagonal arranges and a long-range ordered structure could be obtained. These two kinds of mesoporous materials had a uniform pore size distribution with an average pore diameter within 2.3-2.8 nm. Rather weak Lewis acid sites were formed on both the Si-MCM-41 samples prepared by the two methods.