Junjie Liao

Removal behaviors of moisture in raw lignite and moisturized coal and their dewatering kinetics analysis

ABSTRACT To investigate the dewatering kinetics and mechanism of low-rank coal, the dewatering behaviors of the Chinese lignite and its moisturized sample (prepared from dewatered coal moisturized under relative humidity of 75% at 303 K for 48 h) in nitrogen and the temperature range of 333–433 K were tested. Physical structure changes of raw coal and moisturized coal before and after drying were determined. The results indicate that drying process of lignite could be divided into four stages, which are increasing rate stage, constant rate stage, relatively fast decreasing rate stage, and relatively slow decreasing rate stage. Jander model and first-order kinetics model are favorite to describe the relatively fast decreasing rate stage and relatively slow decreasing rate stage, respectively, and the corresponding dewatering mechanism equations are and y = −ln(1 − α). The effective diffusion coefficients and diffusion activation energy were calculated by Fick’s second law. The diffusion activation energy of the dewatering stages, related to the relatively fast and slow decreasing rate stages, was 35.80, 40.75 kJ/mol for raw coal and 27.80, 37.34 kJ/mol for moisturized coal, respectively. The effective diffusion coefficient was significantly affected by drying temperature through the pore structure change of coal when other drying operation parameters were fixed. These prove that the forms of readsorbed water are not entirely the same as that in raw lignite, in which the former is relatively simple and the latter is more complex.

A process for desulfurization of coking benzene by a two-step method with reuse of sorbent/thiophene and its key procedures

Pure benzene is an important chemical feedstock, and coking benzene is one of its sources. However, the industrialized coking benzene refining processes are not green and sustainable. To solve this problem, a green two-step process for the desulfurization of coking benzene with the advantages of easy operation, low environmental pollution and solid waste (sorbent/thiophene) recyclability was evaluated. The thiophene in coking benzene was first alkylated by the olefins present in it using a suitable AlCl3/silica gel catalyst to produce alkylthiophenes, which can be easily separated by distillation. The AlCl3/silica gel catalyst obtained by a novel green process was effective in catalyzing the alkylation of thiophene by 1-hexene with an efficiency of removing thiophene up to 94.2%. AlCl3 was grafted onto silica gel by reacting with hydroxyls on its surface, which could prevent the dissolution problem of AlCl3 in benzene. The residual thiophene with its concentration range of 100–1000 mg L−1 in benzene was then almost completely removed by adsorption using an ion-exchanged zeolite. The CeY zeolite sorbent showed excellent performance in deeply removing the residual thiophene in the benzene, in which the adsorption desulfurization over the CeY sorbent fits a Langmuir isotherm. The product met the requirements for a chemical feedstock, in that no thiophene was measured in the purified benzene by gas chromatography with a flame photometric detector. The CeY zeolite with adsorbed thiophene was used to prepare polythiophene–CeY composites by chemical oxidative polymerization using anhydrous FeCl3 as an oxidant at 0 °C. The decomposition temperature of the polythiophene–CeY composites is 480 °C, which is 60 °C higher than that of polythiophene.

The Adsorptive Removal of Thiophene from Benzene over ZSM-5 Zeolite

Abstract ZSM-5 zeolites with different Si/Al ratio (25, 38, 50) were selected for the research of adsorptive removing thiophene from benzene and the desulfurization behavior of H-ZSM-5(25) sorbent acid-modified and ion-exchanged was studied. The experimental results show that the sorbent H-ZSM-5(25) from acid-modified ZSM-5 zeolite with a Si/Al ratio of 25 is the best sorbent with the largest amount of Brönsted acidic sites, which plays an important role in the adsorption of thiophene. The results of the sorbents from H-ZSM-5(25) ion-exchanged with Ag+, Ni2+, Ce3+, and La3+ show that the desulfurization efficiency is increased for all ion-exchanged zeolites, because thiophene can be adsorbed via π-complexation over Ag-ZSM-5(25) and Ni-ZSM-5(25) zeolites, while through the S–M bond on Ce-ZSM-5(25) and La-ZSM-5(25) zeolites. Benzene can bring the effect of competitive adsorption with thiophene via π-complexation, so the efficiency of Ce-ZSM-5(25) and La-ZSM-5(25) removing thiophene from benzene by the selective S–M bond is better than that of Ag-ZSM-5(25) and Ni-ZSM-5(25), which can respectively reach to 92.7 and 93.9%.

Preparation of M/γ-Al2O3 sorbents and their desulfurization performance in hydrocarbons

M/γ-Al2O3 sorbents with different metals (Ag, Cu, Ni, Zn) as the active component loaded on a γ-Al2O3 support were prepared by the incipient wetness impregnation method, and their adsorption behavior for thiophene was investigated. The results show that all these metals can obviously promote the desulfurization activity of the prepared sorbents, and Ag is the best one. Then silver was selected to modify γ-Al2O3 with a different loading amount, and the desulfurization behavior of Ag/γ-Al2O3 series sorbents in a thiophene–benzene solution was evaluated. It was found that the silver content has a significant impact on desulfurization efficiency, and the A15 sorbent with 13.7 wt% silver has the best adsorption desulfurization performance. XRD results show that the simple Ag0 is the main active component in Ag/γ-Al2O3 sorbent. SEM/EDS and BET characterization show that the specific surface area and pore volume decrease obviously when the silver loading amount is more than 13.7 wt%, because of the agglomeration of silver. The desulfurization mechanism of the Ag/γ-Al2O3 sorbent was explored by using thiophene which has both a conjugated pi bond and sulfur, tetrahydrothiophene which has sulfur but no conjugated pi bond, benzene which has a conjugated pi bond but no sulfur, cyclohexane which has no conjugated pi bonds or sulfur as the model compounds. The desulfurization efficiencies of A15 sorbent in thiophene–benzene, thiophene–cyclohexane, thiophene–tetrahydrothiophene–benzene and thiophene–tetrahydrothiophene–cyclohexane solutions were compared. The results indicate that the thiophene adsorption on Ag/γ-Al2O3 sorbent is mainly dominated by two kinds of connection between thiophene and silver. One is the connection between the conjugated pi bond and silver (π-complexation), and the other one is the connection between sulfur and silver (S–metal bond). This is also the main reason that benzene has the competitive adsorption behavior on thiophene.

Preparation and characterization of poly(3-methylthiophene)/CeY zeolite composites

Poly(3-methylthiophene)/CeY zeolite nanocomposites (P3MT/CeY) were prepared by chemical oxidative polymerization using anhydrous FeCl3 as the oxidizing agent. The physical and chemical properties of the prepared samples were measured using various characterization techniques, such as conductivity measurements, Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and carbon–sulfur analysis. The prepared P3MT/CeY composites retained the crystalline structure of Y zeolite, which also enhanced thermostability. A 2000-fold increase in conductivity relative to a blank prepared using P3MT was observed for the composite prepared using a 3:1 g mL−1 ratio of CeY and P3MT.

Effect of carbon dioxide on pore structure characteristics of dewatered lignite and the relevance to its moisture-adsorbing capacity

Lignite with a high moisture content is needed to effectively remove water and maximally restrain the re-adsorption capacity of dewatered coal. The ambient gas during lignite drying is an important factor influencing the physical properties of dewatered samples. CO2 is the main component of exhaust gas, which has been reused in flash drying technology. The relationship between the drying characteristics of a typical Chinese lignite and the pore structure changes of dewatered coal in a CO2 atmosphere, and the effect on the behavior of re-adsorbing moisture were studied. Drying experiments of lignite samples under an Ar atmosphere were also carried out for comparison. The moisture re-adsorption experiments of dewatered coal samples were conducted at 30 °C under relative humidity of 75%. The results show that the drying efficiency of coal samples under a CO2 atmosphere is higher than that under an Ar atmosphere due to the swelling effect caused by the adsorption of CO2, but this difference between CO2 and Ar becomes gradually smaller with increase in the drying temperature. The dewatered coal sample obtained under a CO2 atmosphere shows a stronger ability to re-adsorb moisture caused by the swelling effect, which could be attributed to the changes of the structure of the coal sample in this atmosphere and the increase of the surface area where the moisture is primarily absorbed. The total moisture content in the coal sample after re-adsorbing moisture follows a linear relationship with the specific surface area of dewatered lignite.