Yuan-Yuan Xu

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.

Heterogeneous modeling for fixed-bed Fischer-Tropsch synthesis: Reactor model and its applications

Abstract A comprehensive one-dimensional heterogeneous reactor model is developed to simulate the performance of fixed-bed Fischer–Tropsch reactors for hydrocarbon production. The detailed mechanistic kinetics is combined into the reactor model along with considering the fact that the catalyst pores are filled with liquid wax under realistic conditions. The equilibrium between the gases in the bulk and the wax in the catalyst pores is correlated by using a modified SRK equation of state (MSRK EOS). The model is solved by using Gear method to integrate the reactor model with the embedded pellet model discretized by orthogonal collocation on finite elements. The validity of the reactor model is tested against the measured data from different-scale demonstration processes. Satisfactory agreements between model predictions and experiment results are obtained. Detailed numerical simulations are performed to investigate the effect of major process parameters on the reaction behavior of fixed-bed FTS systems with recycle operation.

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.

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.

Density functional investigation on copper carbonyl complexes

Abstract The structure and bonding of copper carbonyl complexes, [Cu(CO) n ] 0/+/− , have been investigated at density functional levels of theory. It was found that the bond parameters and CO bond dissociation energy are very sensitive to the size of the employed basis set. The best agreement between theory and the available experimental data has been achieved at the B3LYP level with the cc-pVTZ/TZV2P basis set.

Analysis of Liquefaction Product Oils from Fischer-Tropsch Synthesis Using Column Liquid Chromatography/Gas Chromatography

Abstract A two-step pretreatment method for analysis of Fischer-Tropsch cold trap oils by column liquid chromatography was developed. The first step was the separation of Fischer-Tropsch cold trap oils into paraffin-olefin fraction and oxygenates fraction by column liquid chromatography with silica gel of 80–100 mesh as a stationary phase and dimethylsulfoxide (DMSO) as the eluent. The second step was similar to the first one except that the pore diameter of silica gel was smaller (100–200 mesh), and the paraffin-olefin fraction was further separated into paraffins and olefins. Through this pretreatment, the cold trap oils were separated into three different groups, namely, paraffins, olefins and oxygenates. All preparation fractions were resolved by high-resolution-capillary column gas chromatography, respectively. Using pure reagents as standards, components of all the three separated groups were identified by comparing gas chromatography retention time and carbon number rule of samples with corresponding pure reagents. The components were then quantified by correction factor normalization method. On the basis of the above research, the results of 63 components were given in this article, which accounted for 80% of total peaks detected by GC. The results will benefit the development of Fischer-Tropsch synthesis process.