Hongwei Xiang

Study on methanolytic depolymerization of PET with supercritical methanol for chemical recycling

Abstract Methanolytic depolymerization of polyethylene terephthalate (PET) was carried out in a stainless stirred autoclave at temperatures of 523–543 K, pressures of 8.5–14.0 MPa, and with a weight ratio of methanol to PET from 3 to 8. The solid products mainly composed of dimethyl terephthalate and small amounts of methyl-(2-hydroxyethyl) terephthalate, bis (hydroxyethyl) terephthalate, dimers and oligomers were analyzed by high performance liquid chromatography (HPLC). The liquid products composed of ethylene glycol and methanol were analyzed by gas chromatography (GC). It was found that both the yield of dimethyl terephthalate and the degree of PET depolymerization were seriously influenced by the temperature, weight ratio of methanol to PET, and reaction time, whilst the pressure has insignificant influence when it is above the critical point of methanol. The optimal depolymerization conditions are temperature of 533–543 K, pressure of 9.0–11.0 MPa, and the weight ratio (methanol to PET) from 6 to 8. The depolymerization of several PET wastes collected from the Chinese market was investigated under the optimal conditions.

Effect of reaction conditions on the product distribution during Fischer–Tropsch synthesis over an industrial Fe-Mn catalyst

Abstract The product distributions of Fischer–Tropsch synthesis (FTS) over an industrial Fe-Mn catalyst are investigated under different reaction conditions in an integral fixed bed reactor. The typical non-ASF distributions of the FTS products are analyzed in terms of the competitive steps of the surface reactions, and the desorption, diffusion and re-adsorption of alkenes under these broad reaction conditions. It is found that alkene selectivities are significantly higher than those for alkanes in a broad chain length range from C2 to about C20 over the Fe-Mn catalyst under most reaction conditions. Under the operation conditions of the catalyst, alkenes with carbon number larger than 27 cannot be detected in the wax products. Consequently, the contents of heavy alkanes have a slight increase at about C27, implying that primary alkenes with chain longer than C27 are dominantly hydrogenated to alkanes due to the long residence time of the products in the catalyst pores.

A new strategy for the efficient synthesis of 2-methylfuran and γ-butyrolactone

A novel process involving the coupling of the hydrogenation of furfural and the dehydrogenation of 1,4-butanediol has been studied in the vapor phase for the synthesis of 2-methylfuran (2-MF) and γ-butyrolactone (γ-BL) over the same Cu-based catalyst. It was found that hydrogen and heat energy are utilized with high efficiency in this process.

Study of Manganese Promoter on a Precipitated Iron-Based Catalyst for Fischer-Tropsch Synthesis

Abstract The effects of Manganese (Mn) incorporation on a precipitated iron-based Fischer-Tropsch synthesis (FTS) catalyst were investigated using N2 physical adsorption, air differential thermal analysis (DTA), H2 temperature-programmed reduction (TPR), and Mossbauer spectroscopy. The FTS performances of the catalysts were tested in a slurry phase reactor. The characterization results indicated that Mn increased the surface area of the catalyst, and improved the dispersion of α-Fe2O3 and reduced its crystallite size as a result of the high dispersion effect of Mn and the Fe-Mn interaction. The Fe-Mn interaction also suppressed the reduction of α-Fe2O3 to Fe3O4, stabilized the FeO phase, and (or) decreased the carburization degree of the catalysts in the H2 and syngas reduction processes. In addition, incorporated Mn decreased the initial catalyst activity, but improved the catalyst stability because Mn restrained the reoxidation of iron carbides to Fe3O4, and improved further carburization of the catalysts. Manganese suppressed the formation of CH4 and increased the selectivity to light olefins (C=2–4), but it had little effect on the selectivities to heavy (C5+) hydrocarbons. All these results indicated that the strong Fe-Mn interaction suppressed the chemisorptive effect of the Mn as an electronic promoter, to some extent, in the precipitated iron-manganese catalyst system.

Effect of A12O3 Binder on the Precipitated Iron-Based Catalysts for Fischer-Tropsch Synthesis

Abstract A series of iron-based Fischer-Tropsch synthesis (FTS) catalysts incorporated with Al 2 O 3 binder were prepared by the combination of co-precipitation and spray drying technology. The catalyst samples were characterized by using N 2 physical adsorption, temperature-programmed reduc-tion/desorption (TPR/TPD) and Mossbauer effect spectroscopy (MES) methods. The characterization results indicated that the BET surface area increases with increasing Al 2 O 3 content and passes through a maximum at the Al 2 O 3 /Fe ratio of 10/100 (weight basis). After the point, it decreases with further increase in Al 2 O 3 content. The incorporation of Al 2 O 3 binder was found to weaken the surface basicity and suppress the reduction and carburization of iron-based catalysts probably due to the strong K-Al 2 O 3 and interactions. Furthermore, the H2 adsorption ability of the catalysts is enhanced with increasing content. The FTS performances of the catalysts were tested in a slurry-phase continuously stirred tank reactor (CSTR) under the reaction conditions of 260 °C, 1.5 MPa, 1000 h −1 and molar ratio of H2/CO 0.67 for 200 h. The results showed that the addition of small amounts of Al 2 O 3 affects the activity of iron-based catalysts to a little extent. However, with further increase of Al 2 O 3 content, the FTS activity and water gas shift reaction (WGS) activity are decreased severely. The addition of appropriate Al 2 O 3 do not affect the product selectivity, but the catalysts incorporated with large amounts of Al 2 O 3 have higher selectivity for light hydrocarbons and lower selectivity for heavy hydrocarbons.

The Nature of Cu/ZrO2 catalyst: experimental and theoretical studies

The catalytic performance of Cu/ZrO2 calcined at different temperatures was investigated with XRD and XPS. It was found that the activity of Cu/ZrO2 depends on the interaction between copper and zirconia, rather than on their crystal sizes. The XRD and XPS results illustrated that the reinforced interaction between copper and zirconia can hinder the increase of the copper crystal size in the reaction process. In addition, B3LYP/LACVP density functional calculation revealed electron transfer from copper to zirconia and weakening effect of surface hydroxyl on zirconia near copper center.

The new simple extended corresponding-states principle: vapor pressure and second virial coefficient

Abstract A new simple extended corresponding-states principle has been developed to represent and predict the thermophysical properties of fluids. The extended corresponding-states principle only requires the substance-dependent critical parameters and acentric factor which enhances the corresponding-states principle of Pitzer et al. to include the behavior of substances whose force fields deviate strongly from spherical symmetry. The additional corresponding-states parameter defined in terms of the deviation of the critical compression factor of a real molecule from that of spherical molecules is independent of experimental data for any specific property. The new simple extended corresponding-states principle presented here remarkably improves the representation of the vapor pressure from the triple point to the critical point and the second virial coefficient from the triple point to the highest temperatures over which experimental data exist. Accurate results for these two well-understood properties are given for simple, normal, polar, hydro-bonding and associating compounds. The results also show that the new simple extended corresponding-states principle is more reliable and accurately predicts the vapor pressure and second virial coefficient of a strongly nonspherical fluid than any other existing methods.

Isothermal Kinetics Modelling of the Fischer-Tropsch Synthesis over the Spray-Dried Fe-Cu-K Catalyst

Abstract The isothermal kinetics of the Fischer-Tropsch synthesis (FTS) over Fe-Cu-K spray-dried catalyst was studied in a spinning basket reactor. The experiments were carried out at a constant temperature of 523 K, n (H 2 )/ n (CO) feed ratios of 0.8–2.0, reactor pressures of 1.1–2.5 MPa, and space velocity of 0.556×10 −3 Nm 3 /kg cat ·s. Kinetic model for hydrocarbon formation was derived on the basis of simplified carbide mechanism to reduce the number of parameters. Two individual rate constants for methane and ethene were considered. Furthermore, the model was modified empirically by non-intrinsic effect, such as physisorption and fictitious olefin pressures that were taken into account, and the influences of secondary reaction of α-olefins on product distribution. The simulation results showed that the experimental phenomena of FTS and the deviations from ASF distribution, such as the relatively high yield of methane and low yield of ethene observed experimentally could be depicted basically.

Effect of manganese on the catalytic performance of an iron-manganese bimetallic catalyst for light olefin synthesis

A systematic study was carried out to investigate the promotion effect of manganese on the performance of a coprecipitated iron-manganese bimetallic catalyst for the light olefins synthesis from syngas. The catalyst samples were characterized by N2 physisorption, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), Mossbauer spectroscopy, H2-differential thermogravimetric analysis (H2-DTG), CO temperature-programmed reduction (CO-TPR) and CO2 temperature-programmed desorption (CO2-TPD). The Fischer-Tropsch synthesis (FTS) performance of the catalyst was measured at 1.5 MPa, 250 °C and syngas with H2/CO ratio of 2.0. The characterization results indicated that the addition of manganese decreases the catalyst crystallite size, and improves the catalyst BET surface area and pore volume. The presence of manganese suppresses the catalyst reduction and carburization in H2, CO and syngas, respectively. The addition of manganese improves the catalytic activity of water-gas shift reaction and suppresses the oxidation of iron carbides in the FTS reaction. The incorporation of manganese improves the catalyst surface basicity and results in a significant improvement in the selectivities to light olefins and heavy hydrocarbons (C5+), and furthermore an inhibition of methane formation in FTS. The pure iron catalyst (Mn-00) has the highest initial FTS catalytic activity (65%) and the lowest selectivity (17.35 wt%) to light olefins (C=2−C=4). The addition of an appropriate amount of manganese can improve the catalyst FTS activity.

Activation pressure studies with an iron-based catalyst for slurry Fischer-Tropsch synthesis

Abstract Fischer-Tropsch synthesis (FTS) was carried out with an industrial iron-based catalyst (100Fe/5Cu/6K/16SiO 2 , by weight) under the baseline conditions in a stirred tank slurry reactor (STSR). The effects of activation pressure on the catalyst activity and selectivity were investigated. It was found that iron phase compositions, textural properties, and FTS performances of the catalysts were strongly dependent on activation pressure. The high activation pressure retards the carburization. Mossbauer effect spectroscopy (MES) results indicated that the contents of the iron carbides clearly decrease with the increase of activation pressure, especially for the activation pressure increasing from 1.0 MPa to 1.5 MPa, and the reverse trend is observed for superparamagnetic Fe 3+ (spm). The higher content of Fe 3+ (spm) results in the higher amount of CO 2 in tail gas when the catalyst is reduced at higher pressure. The catalyst activity decreases with the increase of activation pressure. The high quantity of iron carbides is necessary to obtain high FTS activity. However, the activity of the catalyst activated in syngas can not be predicted solely from the fraction of the carbides. It is concluded that activation with syngas at the lower pressure would be the most desirable for the better activity and stability on the iron-based catalyst.