Co-reporter:Tian Xia, Zhenhao Xi, Tao Liu, Ling Zhao
Chemical Engineering Science 2017 Volume 168(Volume 168) pp:
Publication Date(Web):31 August 2017
DOI:10.1016/j.ces.2017.04.042
•The periodical CO2-renewing sorption operation was proposed in PET foaming process.•The CO2 concentration achieved 150–160 mg/g PET in 8 h.•The cell nucleation and growth were initiated after every depressurization.•The CO2-saturated PET expanded fully at the foaming temperature as low as 100 °C.•The crystallinity of PET foam was increased to 30% by annealing for only 1 h.The periodical CO2-renewing sorption process was applied in the solid state foaming of poly(ethylene terephthalate) (PET), in order to decrease the sorption time, increase the concentration of CO2 in PET matrix, and ultimately increase the expansion ratio of PET foams. The cell nucleation and growth were initiated after every depressurization in the sorption process, and the concentration of the dissolved CO2 was reduced by the consumption of cells nucleation and cells formation, which inhibited CO2-induced crystallization. As a result, the CO2 concentration of 150–160 mg/g PET was obtained, which was much higher than the reported CO2 solubility in PET matrix (∼110 mg/g PET). With different sorption temperatures and CO2-renewing periods, PET foams with the cell size between 5 and 22 μm, the cell density between 2.42 × 108 and 2.93 × 109 cells/cm3, and the expansion ratio between 3 and 6 times were controllably prepared. Only 1 h was required to enhance the crystallinity of PET foams to about 30% by the means of annealing treatment at 110–130 °C. And the cell morphology was still well kept during the annealing process.
Co-reporter:Minmin Zhou, Dehong Bai, Yuan Zong, Ling Zhao, Jeremy Nicholas Thornock
Chemical Engineering and Processing: Process Intensification 2017 Volume 122(Volume 122) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.cep.2017.09.017
•Designing a novel static mixer hollow cross-disk (HCD) to intensify the near-wall mixing level.•Sinusoidal wave structure of HCD generates a counter vortex pairs flow structure.•Identifying the mixing level by the spatial distribution of the mixture fraction and reaction product.In the fast reaction category, the turbulent reactive mixing strongly affects the reaction products yield and distribution. The present work adopts a high-efficiency vortex structure induced by a novel static mixer – hollow cross disk (HCD) to enhance the turbulent reactive mixing within the tubular turbulent flow. Specifically, the direct quadrature method of moments (DQMoM) coupled with the interaction-by-exchange-with-the-mean model (IEM) is utilized to simulate the consecutive competitive reactions system in this tubular turbulent flow. In order to quantitatively evaluate the enhanced mixing effect of the HCD, the turbulent reacting flows in the Kenics static mixer and coaxial jet mixer have also been studied. A combining analysis of turbulent flow field and the chemical species distribution indicates that the turbulent mixing enhancement mechanisms of these two static mixers. The simulation suggests that the sinusoidal wave structure in the HCD generate an important flow structure-counter vortex pairs (CVPs), which increases the momentum exchange between the near-wall region and the flow core. Moreover, the spatial distribution of the mixture fraction and reaction product concentration in these configurations agrees well with its turbulent flow field characteristics. The improved turbulent mixing initially is located at the jet periphery when at 0 < z/D < 2, which fits well with the HCD's longitudinal evolution of turbulent energy dissipation. Whereas at z/D > 2, CVPs of the HCD ameliorate the near-wall area's turbulent mixing and thus increase the reaction productivity and selectivity. Additionally, the effects of flow rate on segregation index are studied to suggest that the improvement of Xs for HCD is of about 35% relative to the original tubular flow.Download high-res image (155KB)Download full-size image
Co-reporter:Weizhen Sun, Shenglu Zhang, Junfeng Qiu, Zhimei Xu, Ling Zhao
Chemical Engineering Research and Design 2017 Volume 124(Volume 124) pp:
Publication Date(Web):1 August 2017
DOI:10.1016/j.cherd.2017.06.024
•Kinetic models of CHB oxidation at oxygen-rich conditions.•Kinetic models of CHB oxidation at oxygen-poor conditions.•Free radical chain reaction mechanism and pathway of CHB oxidation.•Determined rate constants are compared to those of cumene oxidation.The liquid phase autoxidation of cyclohexylbenzene (CHB) to CHB hydroperoxide (CHBHP) is the key step of green production of phenol. The CHB oxidation kinetics was originally investigated by semibatch experiments under various oxygen partial pressures. Kinetic models to deal with oxygen-rich and oxygen-poor conditions were developed on the basis of free radical chain mechanism. It was found that the activation energy of the rupture of the bond OO of molecule CHBHP was close to that of cumene hydroperoxide, while the activation energy of hydrogen abstraction from the tert-butyl carbon of CHB was reasonably larger than that of cumene due to the steric effect. The kinetic model involving the oxygen addition to R (Model II) can be used to deal with various oxygen partial pressure conditions. Based on the developed kinetic model, the simulation of well-mixed reactor operated under continuous conditions was performed, and the results were in good agreement with continuous experiments.Download high-res image (139KB)Download full-size image
Co-reporter:Tian Xia, Zhenhao Xi, Xuefeng Yi, Tao Liu, and Ling Zhao
Industrial & Engineering Chemistry Research 2015 Volume 54(Issue 27) pp:6922-6931
Publication Date(Web):June 26, 2015
DOI:10.1021/acs.iecr.5b01583
Exfoliated poly(ethylene terephthalate) (PET)/organoclay nanocomposites were prepared by extrusion blending method with different clay contents and molecular weights of raw PET. Pyromellitic dianhydride (PMDA) was extruded, together with PET and clay, to introduce long-chain branching to PET backbone and delaminate the clay layers. Although the molecular weights and viscoelastic properties of nanocomposites were much lower than those of foamable PMDA-modified PET, the melt foamability of nanocomposites was significantly improved by the well-dispersed clays due to the heterogeneous nucleation effect, enhanced nonisothermal crystallization rate, and so on. Foaming temperature windows with a width of 20–60 °C were explored for PET/clay nanocomposites with intrinsic viscosities of 0.67–0.94 dL/g, in which nanocomposites foams with cell diameters of 29–53 μm, cell densities of 6.5 × 107–6.9 × 108 cells/cm3, and expansion ratio of 10–50 could be controllably produced using supercritical CO2 as a blowing agent.
Co-reporter:Yang Xu, Tao Liu, Wei-kang Yuan, and Ling Zhao
Industrial & Engineering Chemistry Research 2015 Volume 54(Issue 28) pp:7113-7121
Publication Date(Web):June 29, 2015
DOI:10.1021/acs.iecr.5b01014
In this study, spherical, lamellar, and aligned lamellar types of polyethylene-b-poly(ethylene oxide) (PE-b-PEO) diblock copolymers were prepared and comparatively foamed with CO2 to understand the influence of microphase morphology and long-range ordering on foaming behavior. The experimentally measured melting point, CO2 solubility, and interfacial tension in the presence of CO2 indicated the potential of CO2-philic PEO block acting as bubble nuclei. Scanning electron microscopy results revealed that lamellar PE-b-PEO produced open cells all the way, whereas spherical PE-b-PEO created closed cells at low temperature and mesh-like openings at high temperature. Continuous PEO microdomains directly provide numerous potential opening channels and therefore induce the bursting of cells. The drastic biaxial stretching of cell walls at high temperature turns the embedded discrete PEO spheres into those channels responsible for the distinct mesh-like perforations. As for the flow aligned lamellar PE-b-PEO, submicron open cells were fabricated with a regular multilayered pattern. Long-range ordering not only suppresses the undesired coalescences but also preserves the self-assembled pattern. Foaming mechanisms, mainly focused on the bubble growth, were finally uncovered for different morphological PE-b-PEO block copolymers, complete understanding of which will be of importance in the block copolymer design to meet the requirement on foam structures.
Co-reporter:Tian Xia;Zhenhao Xi;Tao Liu;Xun Pan;Chaoyang Fan
Polymer Engineering & Science 2015 Volume 55( Issue 7) pp:1528-1535
Publication Date(Web):
DOI:10.1002/pen.23995
By reactive extrusion with pyromellitic dianhydride (PMDA), foamable poly(ethylene terephthalate) (PET) was obtained, which achieved a maximum intrinsic viscosity of 1.36 dL/g with PMDA content 0.8 wt%. Dynamic shear rheological properties were measured to characterize the structure evolution of modified PET. And the Avrami analysis was extended for the non-isothermal crystallization process of modified PET, which relates to cell stabilization in the melt foaming process. Based on the batch foaming process with supercritical carbon dioxide as blowing agent, broad foaming temperature windows were obtained for PETs modified with 0.8 and 0.5 wt% PMDA, in which PET foams with the expansion ratio between 10 and 50 times, the cell diameter between 15 and 37 μm, and the cell density between 6.2 × 108 and 1.6 × 109 cells/cm3 were controllably produced. POLYM. ENG. SCI., 55:1528–1535, 2015. © 2014 Society of Plastics Engineers
Co-reporter:Tian Xia, Ye Feng, Yunlong Zhang, Zhenhao Xi, Tao Liu, and Ling Zhao
Industrial & Engineering Chemistry Research 2014 Volume 53(Issue 47) pp:18194-18201
Publication Date(Web):2017-2-22
DOI:10.1021/ie5033606
The polycondensation of poly(ethylene terephthalate) (PET) in both melt and solid states was conducted with high pressure CO2 and ambient pressure N2 sweeping to remove the volatile byproducts, revealing that only the solid state polycondensation (SSP) of PET could be facilitated by high pressure CO2 due to the substantial increase of free volume. With the comparison of SSP processes of PET in dynamic and static CO2 supplying modes, a periodical supercritical CO2 renewing strategy for SSP of PET was proposed. The SSP process was promoted significantly, and only 6 h were required from the degree of polymerization of 100 to 150, while it takes nearly 20 hours in the industrial SSP process of PET. The effects of CO2 renewing period, CO2 pressure, reaction temperature, and initial molecular weight on the newly proposed SSP strategy were investigated, and a semiempirical kinetic model was applied to fit the experimental data well.
Co-reporter:Zhenhao Xi;Fanglin Zhang;Hua Zhong;Tao Liu;Lih-Sheng Turng
Polymer Engineering & Science 2014 Volume 54( Issue 12) pp:2739-2745
Publication Date(Web):
DOI:10.1002/pen.23824
The microcellular injection molding (commercially known as MuCell) of in situ polymerization-modified PET (m-PET) was performed using supercritical nitrogen as the physical blowing agent. Based on the design of experiment matrices, the influence of operating conditions on the mechanical properties of molded samples was studied systematically for two kinds of m-PETs, namely, n-m-PET and m-m-PET synthesized using pentaerythritol and pyromellitic dianhydride (PMDA) as modifying monomers, respectively. Optimal conditions for injection molding were obtained by analyzing the signal-to-noise (S/N) ratio of the tensile strength of the molded samples. The specific mechanical properties, especially the impact strength, of the microcellular samples under those optimal conditions increased significantly. Scanning electron microscope analyses showed a uniform cell structure in the molded specimens with an average cell size of around 35 µm. The m-m-PET modified with PMDA generated a slightly finer cell structure and a higher cell density than the n-m-PET. POLYM. ENG. SCI., 54:2739–2745, 2014. © 2013 Society of Plastics Engineers
Co-reporter:Jie Chen, Tao Liu, Ling Zhao, and Wei-kang Yuan
Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 14) pp:5100
Publication Date(Web):March 13, 2013
DOI:10.1021/ie303587r
The effects of the filler size and concentration on the solubility and diffusivity of CO2 in polypropylene (PP)/calcium carbonate (CaCO3) composites were investigated in this work. The apparent solubility of CO2 in PP and its composites containing 5 wt % and 10 wt % micro- or nano-CaCO3 was measured by using a magnetic suspension balance (MSB) at temperatures of 200 and 220 °C and CO2 pressures up to 22 MPa. Meanwhile, the swelling volume of the PP composites/CO2 solutions was experimentally measured at the same conditions by using a high-pressure view cell with direct visual observation. It was then used to correct the gas buoyancy acting on the PP composites in the MSB measurement so that the real solubility of CO2 in the PP composites was determined. Meanwhile, the diffusion coefficient of CO2 in the PP composites was estimated from the sorption lines at gas pressures ranged from 5 to 10 MPa. It was found that the experimental solubility and diffusivity of CO2 in PP/nano-CaCO3 composites were higher than those in PP/micro-CaCO3. Moreover, the solubility and diffusivity of CO2 decrease with increasing micro-CaCO3 concentration whereas they increase with increasing nano-CaCO3 loading in the PP composites. Two new models based on free volume theory considering the effects of micro-CaCO3 on the free volume and the diffusion path and the lubricant effect of nano-CaCO3 were proposed and used to well correlate the experimental diffusion coefficient of CO2 in PP/micro-CaCO3 and PP/nano-CaCO3 composites, respectively.
Co-reporter:Weizhen Sun, Yi Shi, Jie Chen, Zhenhao Xi, and Ling Zhao
Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 44) pp:15262-15269
Publication Date(Web):2017-2-22
DOI:10.1021/ie400415p
The alkylation kinetics of isobutane with butene using sulfuric acid as catalyst was investigated by batch experiments in the conditions of industrial interest. More than 16 alkylates were identified and quantified by GC-MS. On the basis of the classic carbonium ion mechanism, the kinetic model was established, which can predict the concentration change of three groups of key alkylates including trimethylpentanes (TMPs), undesirable dimethylhexanes (DMHs), and heavy ends (HEs). The agreement between experimental and model calculated data was quite satisfactory. The rate constants were found to be constant with the varied temperatures (276.2 to 285.2 K) except those accounting for the addition of H+ to isobutene and its reversible reaction. An anti-Arrhenius behavior was observed for the addition reaction of H+ to isobutene, in which the corresponding rate constant falls with the increasing temperatures. The kinetic model was confirmed by the simulation of the industrial alkylation reactor. Hopefully, the kinetic model developed in this work will be useful to the design and optimization of novel alkylation reactors.
Co-reporter:Jie Chen, Tao Liu, Wei-kang Yuan, Ling Zhao
The Journal of Supercritical Fluids 2013 Volume 77() pp:33-43
Publication Date(Web):May 2013
DOI:10.1016/j.supflu.2013.02.007
This work is aimed at studying the effects of the fillers and interface bonding condition between the fillers and polymer matrix on the solubility and diffusivity of CO2 in polypropylene (PP)/Micro-calcium carbonate (MicroCaCO3) composites. The solubility of CO2 in PP and its composites containing 5% and 10% MicroCaCO3 was determined precisely by using magnetic suspension balance (MSB) combined with experimental swelling correction at 200 and 220 °C and CO2 pressures up to 22 MPa. It was found that the solubility of CO2 in the PP/MicroCaCO3 composites without the interface compatibilizer increased with increasing the filler content, while the CO2 solubility remained almost unchanged in PP composites with compatibilizer. The Henry's law and a modified Henry's law were used to well correlate the solubility of CO2 in the PP composites with and without the interface compatibilizer, respectively. The diffusion coefficient of CO2 in the PP composites was found to decrease with increasing the filler content. The mutual diffusion coefficients of CO2 in the PP composites can be correlated within an average relative deviation of 10% by the free volume model proposed by Kulkarni and Stern with a parameter accounting for the barrier effect of the filler.Graphical abstractHighlights► The solubility of CO2 in PP/MicroCaCO3 composites was precisely determined. ► Henry's law was used to correlate the solubility data in PP composites with compatibilizer. ► A modified Henry's law correlated well solubility data in PP composites without compatibilizer. ► A modified free volume model correlated well the diffusion coefficients of CO2 in PP composites.
Co-reporter:Like Chen;Zhenhao Xi;Zhen Qin;Weikang Yuan
Macromolecular Symposia 2013 Volume 333( Issue 1) pp:151-161
Publication Date(Web):
DOI:10.1002/masy.201300051
Summary
Based on the kinetic and thermodynamic equations, a comprehensive mathematical model for the continuous synthetic process of polyester polyols was developed, which was carried out in two innovational bubbling reactive distillation towers (BRDTs). In this new type of reactor, condensation reactions among oligomers of polyester polyols were accomplished efficiently and rapidly. Two bench BRDTs with the height of 2 m were applied for the continuous process of poly(ethylene adipate) (PEA). In the first continuous esterification operation at atmospheric pressure, linear oligomers were discharged from the bottom of the column, while water and ethylene glycol (EG) passed a few column trays and a packing section and reached the top of the column. Then water was discharged as byproducts and EG was sent back to the first tray for further reaction. In the second continuous polycondensation operated in the second BRDT under partial vacuum, PEA was discharged from the bottom of the column, while water and ethylene glycol passed a few column trays, they were discharged as byproducts. The influence of major operating conditions on reactor performance was also simulated. Simulation results provided a strategy for developing and optimizing this process.
Co-reporter:Zhenhao Xi;Like Chen;Yong Zhao
Macromolecular Symposia 2013 Volume 333( Issue 1) pp:172-179
Publication Date(Web):
DOI:10.1002/masy.201300052
Summary
The main polycondensation reaction of poly(m-xylene adipamide) (PA-MXD6) is a reversible reaction strongly coupled with mass transfer in melt polycondensation process. In this work, a realistic model for melt polycondensation of PA-MXD6 has been proposed taking in to account the kinetics data, equilibrium data and diffusion process for major by-product water in the melts. The characteristics of reaction and the effects of mass-transfer of polycondensation process have been studied by using stagnant film experiments. It is observed that the apparent rate of the polycondensation process increases with higher temperature, lower degree of vacuum and thinner film thickness with reduced specific interfacial area. Based on the experimental data, the model parameters including the kinetics data, equilibrium data and mass transfer coefficient of volatile have been estimated by the nonlinear least squares method. The model predictions are in a quite satisfactory agreement with the experimental data that all of the relative deviations are almost less than 2%.
Co-reporter:Hao Tang;Yuan Zong;Zhenhao Xi
Macromolecular Symposia 2013 Volume 333( Issue 1) pp:305-310
Publication Date(Web):
DOI:10.1002/masy.201300055
Summary
Poly(p-phenylene terephthalamide) (PPTA), as a typical high performance fiber with excellent strength and modulus property, is usually synthesized by low temperature solution polycondensation with p-phenylenediamine(PPD) and terephthaloyl chloride(TPC) in twin screw extruders. Since the polycondensation during the process is a multicomponent reaction with high reactivity and wide viscosity range, the molecular weight and its distribution of PPTA are strongly influenced by mixing behavior of the extruder. In this paper, the polycondensation process in fully-filled conveying elements of twin screw extruder were analyzed by three-dimensional numerical simulation using the finite element method. The effects of conveying element geometry, rotating speed on mixing state were studied. In order to understand the mechanism behind the reactive extrusion process of PPTA, reaction extent and instantaneous efficiency of stretch in extruder were calculated simultaneously. The results indicate that the reaction process and mixing behavior of the PPTA flow are strongly interrelated. The increase of rotating speed promotes the reaction extent by enhancing the stretch effect, while larger screw pitch accelerates the reaction by rearranges the proportion of energy for stretch.
Co-reporter:Hua Zhong, Zhenhao Xi, Tao Liu, Zhimei Xu, Ling Zhao
The Journal of Supercritical Fluids 2013 Volume 74() pp:70-79
Publication Date(Web):February 2013
DOI:10.1016/j.supflu.2012.11.019
An integrated process of melt polycondensation modification and foaming of poly(ethylene terephthalate) (PET) was performed in a high pressure vessel assisted by supercritical carbon dioxide (scCO2). ScCO2 was firstly employed to sweep PET melt, i.e., high pressure CO2 continuously flows through the vessel at a fixed flow rate to remove small molecules for higher molecular weight PET, then this modified PET melt was directly foamed through a rapid depressurization process using scCO2 as blowing agent. In this integrated process, PET with high melt strength after polycondensation modification could be foamed directly in molten state. Therefore, re-molten process of solid modified PET pellets was canceled to avoid its degradation and CO2 saturation time could be saved in foaming process, thus processing time could be shortened and energy efficiency could be improved. The influences of scCO2 sweeping treatment time, pressure and flow rate on properties of the modified PETs and cell morphologies of the foamed PETs were investigated respectively. The results showed that CO2 sweeping treatment could effectively enhance PET melt polycondensation modification process, which was superior to that of N2 treatment. PET foams with average cell diameter of 32–62 μm and cell density of 1 × 107 to 4 × 107 cells/cm3 have been obtained in the integrated process. Compared with the process of only foaming modified PET by scCO2 or performing scCO2 assisted modified PET further melt polycondensation process and scCO2 foaming process separately, this integrated process produced better cell morphology.Graphical abstractHighlights► An integrated process of PET melt polycondensation and foaming is performed by CO2. ► The integrated process can reduce PET degradation and shorten processing time. ► The melt strength of the modified PET can be improved with CO2 sweeping. ► Better cell morphology can be obtained in the integrated process.
Co-reporter:Yang Xu, Tao Liu, Lei Li, Da-chao Li, Wei-kang Yuan, Ling Zhao
Polymer 2012 Volume 53(Issue 26) pp:6102-6111
Publication Date(Web):7 December 2012
DOI:10.1016/j.polymer.2012.10.049
Co-reporter:Jin-Biao Bao, Tao Liu, Ling Zhao, Guo-Hua Hu, Xiaran Miao, Xiuhong Li
Polymer 2012 Volume 53(Issue 25) pp:5982-5993
Publication Date(Web):30 November 2012
DOI:10.1016/j.polymer.2012.10.011
Polystyrene (PS) foams with isotropy cell morphology and oriented cell morphology were prepared to investigate the relationship between the cell morphologies and the mechanical properties (tensile and impact properties). For the isotropy cell morphologies, the tensile strength, tensile modulus and impact strength of PS foams all increase with the increase of relative density. When the relative density is constant, the cell size does not affect the tensile strength and modulus but has a modest effect on the impact strength. The solid area (cell walls) fraction on the fracture-surface and the cell walls finely dispersed by the bubbles are the main reasons for the toughening of isotropy PS foams. For oriented foams, the cell morphologies oriented perpendicular to the impact direction could significantly enhance the toughness of PS foams. The oriented bubbles and the matrix perpendicular to the fracture propagation direction are expected to absorbed large impact energy during the fracture process and make sample more ductile. The impact strength of the highly oriented PS foam in this work is about 1.5 times that of the unfoamed one while its relative density is 0.3. Small angle X-ray scattering (SAXS) measurements indicate that the molecular chains can be oriented by the shearing of the bubbles by oriented foaming, which leads to the improvement of tensile strength along oriented direction. In addition, the cells oriented parallel to the impact direction result in the poor impact properties.
Co-reporter:Gangsheng Tong, Tao Liu, Shenmin Zhu, Bangshang Zhu, Deyue Yan, Xinyuan Zhu and Ling Zhao
Journal of Materials Chemistry A 2011 vol. 21(Issue 33) pp:12369-12374
Publication Date(Web):18 Jul 2011
DOI:10.1039/C1JM11779C
Mesoporous silica nanoparticles (MSNs) with soft templates were readily fabricated using a sol–gel process under mild conditions. The soft templates were composed of an amphiphilic supramolecular star-copolymer from anionic monocarboxyl polydimethylsiloxane and cationic hyperbranched polyethyleneimine via the electrostatic interaction. Ascribed to the high accessibility of dendritic architecture for small molecules and the existence of plentiful amino groups, these supramolecular dendritic templates in MSNs could be used directly as the nanoreactors and reducing reagents for the in situ reduction of chloroauric acid (HAuCl4). The resultant Au@MSN nanocomposites showed excellent catalytic performance in a reduction reaction of 4-nitrophenol by sodium borohydride (NaBH4).
Co-reporter:Lei Li;Tao Liu
Macromolecular Rapid Communications 2011 Volume 32( Issue 22) pp:1834-1838
Publication Date(Web):
DOI:10.1002/marc.201100462
Abstract
The deformation of isotactic poly-1-butene (iPB-1) matrix, during the CO2-assisted foaming process, makes the iPB-1 melt crystallize into form I rather than form I′, which crystallizes after annealing under high-pressure CO2 without foaming. The result provides a new strategy to directly obtain porous iPB-1 with stable form I from iPB-1 melt.
Co-reporter:Da-chao Li, Tao Liu, Ling Zhao, Xiao-song Lian, and Wei-kang Yuan
Industrial & Engineering Chemistry Research 2011 Volume 50(Issue 4) pp:1997-2007
Publication Date(Web):January 10, 2011
DOI:10.1021/ie101723g
The nonisothermal crystallization behaviors of poly(lactic acid) (PLA) under ambient N2 and compressed CO2 (5−50 bar) at cooling rates of 0.2−2.0 °C/min were carefully studied using high-pressure differential scanning calorimetry. The presence of compressed CO2 postponed the crystallization peak to a lower temperature region while effectively reducing the half-crystallization time and enhancing the crystallinity of the PLA specimen. On the basis of these findings, a new foaming strategy was proposed and utilized to fabricate PLA foams using the ordinary unmodified PLA. The upper and lower temperature limits of this foaming strategy were 105 and 90 °C, which were determined by the melt strength and crystallization behavior of the unmodified PLA specimen, respectively. In this temperature range, PLA foams with interconnected structures, porosity of 67.9−91.4%, and expansion ratio of 15−30 times are controllably produced. The obtained PLA foams have widely distributed average bubble size of 80−270 μm and CO2 enhanced crystallinity of 32−38%.
Co-reporter:Weizhen Sun and Ling Zhao
Industrial & Engineering Chemistry Research 2011 Volume 50(Issue 5) pp:2548-2553
Publication Date(Web):May 19, 2010
DOI:10.1021/ie1005993
Secondary oxidation of p-xylene (PX) plays an important role in the production of purified terephthalic acid (PTA), including directly secondary oxidation (DSO) and nondirectly secondary oxidation (NDSO). Little is known about which kinds of kinetics, either PX oxidation or p-toluic acid (p-TA) oxidation, can be used to simulate these two types of secondary oxidation processes. In this work, the kinetic model of p-TA oxidation with only one parameter was first established, which exhibited good fitting accuracy to experiments. Next, semi-batch experiments were carried out to imitate the liquid phase oxidation in DSO and NDSO. The simulation results show that the direct prediction of liquor oxidation in DSO by PX oxidation kinetics has poor accuracy. But PX oxidation kinetics exhibits better prediction if choosing the free radical concentrations in the final phase of the primary PX oxidation process as the initial condition. And also, the kinetics of p-TA oxidation have a better capability of predicting liquor oxidation in DSO than the direct prediction by PX oxidation kinetics. Regarding the liquor oxidation in NDSO, the prediction given by p-TA oxidation kinetics was excellent, while that given by PX oxidation kinetics was unsatisfactory.
Co-reporter:Jin-Biao Bao, Tao Liu, Ling Zhao, and Guo-Hua Hu
Industrial & Engineering Chemistry Research 2011 Volume 50(Issue 16) pp:9632-9641
Publication Date(Web):June 30, 2011
DOI:10.1021/ie200407p
This study proposes a novel process for significantly toughening isotactic polypropylene (iPP) by finely tuning and controlling the structure and morphology of iPP. The toughness of injection-molded iPP specimens can be significantly improved by controlled shearing, CO2-induced recrystallization, and adequate cooling without loss of strength. The distribution and structure of the iPP samples before and after toughening were characterized by polarized optical microscopy, Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, small-angle X-ray scattering, scanning electron microscopy, and differential scanning calorimetry, to investigate the structure–property relationship. Under shear, a high degree of orientation can be obtained with “shish-kebab” crystals formed in the shear zone. During the subsequent CO2 treatment, a crystal network morphology can be formed as a result of an increase in the numbers of primary lamellae and crosshatched subsidiary lamellae, which leads to an increase in toughness. Wide-angle X-ray diffraction patterns indicate that quenching in ice–water of scCO2-treated iPP promotes the formation of nanosized mesomorphic phase domains in the shear zone, which further toughens the iPP. The impact strength of the best toughened iPP sample was found to be over 12 times that of the original sample without loss in tensile strength and modulus.
Co-reporter:Jin-Biao Bao, Tao Liu, Ling Zhao, Danielle Barth, and Guo-Hua Hu
Industrial & Engineering Chemistry Research 2011 Volume 50(Issue 23) pp:13387-13395
Publication Date(Web):October 26, 2011
DOI:10.1021/ie2018228
A highly oriented isotactic polypropylene (iPP) with a shish-kebab crystalline structure is used as a template to achieve nanocellular foams by CO2 foaming in the solid state. The shish-kebab crystalline structure is obtained by tuning injection-molding conditions. Nanocells are generated in amorphous domains confined by shish-kebab crystalline domains which cannot foam. The highly oriented iPP consists of both shish-kebab crystalline structure and spherulites structure and is used to investigate the effect of the crystalline morphology on the cell formation at a given CO2 saturation pressure (15 MPa) and various foaming temperatures (135, 140, 143, and 146 °C). When the foaming temperature is 143 °C, a uniform open nanocellular morphology is obtained. The cell size and cell density both increase with foaming temperature from 135 to 143 °C due to the fact that more crystals are molten, providing more space for cell nucleation and growth. However, when the foaming temperature is increased to 146 °C, the cell size abruptly increases from dozens of nanometers to dozens of micrometers, and the corresponding cell density decreases by several orders of magnitude.
Co-reporter:Lei Li, Tao Liu, Ling Zhao, Wei-kang Yuan
Polymer 2011 Volume 52(Issue 15) pp:3488-3495
Publication Date(Web):7 July 2011
DOI:10.1016/j.polymer.2011.05.042
In-situ high-pressure FTIR was used to investigate the polymorphous phase transition of isotactic poly-1-butene (iPB-1) with form III upon annealing at temperatures ranging from 75 to 100 °C and CO2 pressures ranging from 2 to 12 MPa. It was shown that the phase transition of form III changed from form III to II not through form III to I′ with increasing temperature and application of CO2 increased the content of generated form I′. Wide-angle X-ray diffraction (WAXD) measurement on the annealed iPB-1 with form III verified the phase transition of form III. The crystalline morphology of the annealed iPB-1 films was investigated using polarized optical microscopy (POM). The results implied that the phase transition of form III to I′ might process via a solid–solid transition, which did not affect the orientation of the lamellar stacks. The orientation of form II lamellar stacks depended strongly on the formation process. To obtain strong orientation, the formation process displayed the following order: melt crystallization at ambient condition > melt recrystallization under CO2 > phase transition upon annealing at ambient condition. Avrami equation could be well established to describe the phase transition of form III to I′ through a solid–solid phase transition.
Co-reporter:Lei Li, Tao Liu, Ling Zhao
Polymer 2011 Volume 52(Issue 24) pp:5659-5668
Publication Date(Web):10 November 2011
DOI:10.1016/j.polymer.2011.10.011
In this work, we found a new method to obtain isotactic poly-1-butene (iPB-1) with form I′ through direct melt-crystallization using high-pressure CO2. The non-isothermal melt-crystallization behaviors of iPB-1 under atmospheric N2 and 0.5–10 MPa CO2 at cooling rates ranging from 0.25 to 5 °C/min were carefully studied using high-pressure differential scanning calorimeter (DSC) and analyzed using the modified Avrami method. Wide-angle X-ray diffraction (WAXD) measurements showed that the crystal structure of non-isothermally melt-crystallized iPB-1 changed from form II under atmospheric N2 and 0.5–8 MPa CO2 to form I′ under 10 MPa CO2. In-situ high-pressure Fourier transform infrared (FTIR) was also used to investigate the non-isothermal melt-crystallization at CO2 pressure up to 18 MPa at the cooling rate of 1 °C/min. Likewise, it was found that form II crystallized under atmospheric N2 and 0.5–8 MPa CO2, and form I′ melt-crystallized directly at CO2 pressures higher than 10 MPa, which was confirmed by the followed DSC and WAXD characterizations on the iPB-1 films after FTIR measurements. The crystal morphology of the melt-crystallized iPB-1 films, characterized by using polarized optical microscopy (POM), showed that the Maltese cross pattern of iPB-1 spherulite became more diffuse with increasing CO2 pressure, and the spherulite size decreased abruptly at the CO2 pressure of 10 MPa.In-situ high-pressure FTIR was applied to detect the crystal modification change during the non-isothermal melt-crystallization process of isotactic poly-1-butene (iPB-1) in atmospheric N2 and high-pressure CO2 at the cooling rate of 1 °C/min. Under atmospheric N2 and low-pressure CO2, e.g., 6 MPa CO2, the characteristic band at 904 cm−1 generated at the start of crystallization, and its intensity increased with decreasing temperature, indicating that the form II crystallized directly. At 8 MPa, 904 cm−1 band appeared at 67 °C, and its intensity increased continuously with decreasing temperature until to 55 °C, at which the form I (or I′) characteristic band at 924 cm−1 appeared, indicating that the form II crystallized from the melt and then quickly transformed into the form I with the assistance of CO2. Under 10 MPa CO2, only was the IR characteristic band of form I (or I′) at 924 cm−1 detected during the cooling, indicating the form I (or I′) crystallized directly from the melt.
Co-reporter:Lei Li, Tao Liu, Ling Zhao, and Wei-kang Yuan
Macromolecules 2011 Volume 44(Issue 12) pp:4836-4844
Publication Date(Web):May 23, 2011
DOI:10.1021/ma200988y
This work is aimed at studying the effect of CO2 on the phase transition of isotactic poly-1-butene (iPB-1) with form III upon heating. The melting behaviors of form III under atmospheric N2 and compressed CO2 at different heating rates ranging from 1 to 20 °C/min were investigated using high-pressure differential scanning calorimetry (DSC). The results showed that the plasticization effect of CO2 promoted melting of form III and inhibited the phase transition of form III to II as a whole. By analyzing the melting parameters obtained from the DSC measurements, we deduced that the phase transition of form III to II might comprise another transition process besides the melt-recrystallization mechanism. In-situ wide-angle X-ray diffraction (WAXD) measurement on form III under atmospheric N2 at a heating rate of 0.25 °C/min verified that the phase transition of form III to II passed through the solid–solid phase transition before melt-recrystallization. In-situ high-pressure Fourier transform infrared (FTIR) was then used to detect the phase transition of form III under atmospheric N2 and compressed CO2 at the heating rate of 1 °C/min. It was also shown that the phase transition of form III to II passed through the solid–solid phase transition and melt-recrystallization under atmospheric N2, 1 and 2 MPa CO2. However, form II formed completely through the melt-recrystallization under 3 MPa CO2 and could not generate with further increasing CO2 pressure to 4 MPa. Moreover, more form I′ generated during heating through the solid–solid phase transition with increasing CO2 pressure. Besides carbon tetrachloride solution prepared form III, the other two solutions, i.e., dilute toluene and o-xylene, cast form III also exhibited the similar generation processes of form II upon heating under atmospheric N2 and compressed CO2 as measured by in-situ high-pressure FTIR.
Co-reporter:Jin-Biao Bao, Tao Liu, Ling Zhao, Guo-Hua Hu
The Journal of Supercritical Fluids 2011 Volume 55(Issue 3) pp:1104-1114
Publication Date(Web):January 2011
DOI:10.1016/j.supflu.2010.09.032
A two-step depressurization batch process is developed to produce bi-modal cell structure polystyrene (PS) foams by using supercritical carbon dioxide (SC-CO2) as the blowing agent. Bi-modal cell structure foams can be achieved by depressurization in two distinct steps and can be significantly affected by the process parameters. The process conditions at the holding stage between the two steps are the key to controlling the bi-modal cell structure. The findings of this study can help predict the bi-modal cell morphology of PS and other polymers prepared by a two-step depressurization bath process.
Co-reporter:Lei Li;Tao Liu
Macromolecular Symposia 2010 Volume 296( Issue 1) pp:517-525
Publication Date(Web):
DOI:10.1002/masy.201051068
Abstract
The CO2 plasticization effect on the isotactic poly-1-butene (iPB-1) form III with pre-existed minority form I' was investigated by using high-pressure differential scanning calorimetry (DSC). The results showed that the form III melting peak moved to a lower temperature and the melting peak area of form II generated during heating decreased with the increased CO2 pressure. The solid-solid transition of form III to I' in the iPB-1 was mainly studied by fourier transform infrared spectroscopy (FTIR). It was claimed that the phase transition was a thermodynamic process and the pre-existed form I' in form III inhibit the phase transition of form III into I'. The influence of the pre-existed form I' on the melting behavior of the iPB-1 was also studied by DSC. It was found that the form I' also suppressed the recrystallization of form II.
Co-reporter:Tao Liu, Dachao Li, Ling Zhao, Weikang Yuan
Particuology 2010 Volume 8(Issue 6) pp:607-612
Publication Date(Web):December 2010
DOI:10.1016/j.partic.2010.09.008
Co-reporter:Weizhen Sun, Wanbing Qu, and Ling Zhao
Journal of Chemical & Engineering Data 2010 Volume 55(Issue 10) pp:4476-4478
Publication Date(Web):August 17, 2010
DOI:10.1021/je100632c
The solid−liquid equilibrium data of 4-formylbenzoic acid in four solvents was measured by the steady-state method at temperatures ranging from (303.2 to 473.2) K, including ethanoic acid, water, and aqueous ethanoic acid with 0.8 and 0.9 mass fractions of ethanoic acid, respectively. The solubility model modified from the Apelblat equation was used to correlate the experimental data. The average relative deviations of these correlations are 0.06 and 0.04 for solubilities in ethanoic acid and water at temperatures above 403.2 K, respectively, and no more than 0.03 for those in aqueous ethanoic acid.
Co-reporter:Da-chao Li, Tao Liu, Ling Zhao and Wei-kang Yuan
Industrial & Engineering Chemistry Research 2009 Volume 48(Issue 15) pp:7117-7124
Publication Date(Web):June 23, 2009
DOI:10.1021/ie8019483
The solubility and diffusivity of carbon dioxide (CO2) in the solid-state isotactic polypropylene (iPP) were studied by using the pressure−decay method at temperatures of 373.15, 398.15, and 423.15 K and pressures ranging from 1 to 15 MPa. The solubilities of CO2 in the solid-state and amorphous regions of iPP were both obtained. They increased almost linearly with increasing pressure and decreased with increasing temperature. The Sanchez−Lacombe equation of state (S-L EOS) correlated the solubility in the amorphous regions of the solid-state iPP within 3% average relative deviation in conjunction with a temperature-dependent interaction parameter. The diffusion coefficient of CO2 in the solid-state iPP showed a weak concentration dependence and had an order of magnitude of 10−10−10−9 m2/s in the solid-state iPP.
Co-reporter:Lei Li, Tao Liu, Ling Zhao and Wei-kang Yuan
Macromolecules 2009 Volume 42(Issue 6) pp:2286-2290
Publication Date(Web):February 18, 2009
DOI:10.1021/ma8025496
Co-reporter:Xiu-Lei Jiang, Tao Liu, Zhi-Mei Xu, Ling Zhao, Guo-Hua Hu, Wei-Kang Yuan
The Journal of Supercritical Fluids 2009 Volume 48(Issue 2) pp:167-175
Publication Date(Web):March 2009
DOI:10.1016/j.supflu.2008.10.006
This paper aims to study, for the first time, the effect of crystal structure on the cell formation in an isotactic polypropylene (iPP) during a solid-state foaming process using supercritical carbon dioxide (scCO2) as a foaming agent. Results show that the spherulite structure exerted a significant impact on the cell morphology of foamed iPP. Very interestingly, under a relatively low pressure, microcells could appear at the centers of spherulites of iPP where the melting started proceeding first. They also appeared in the amorphous domains located in between spherulites and the interlamellar regions of spherulites of iPP. The larger the size of an amorphous area, the lower the CO2 saturation pressure needed to induce cell formation. When microcells were generated in the interlamellar regions, tie fibrils bridging lamellae could be stretched. γ-Crystals were formed at very high CO2 saturation pressure.The α-monoclinic is the most common crystal structure for isotactic polypropylene and is characterized by dominant radiating lamellae and a set of tangential lamellae. This feature is revealed by the cell structure obtained using scCO2 as a foaming agent. A cell starts nucleating and growing from the center of a spherulite. Microcells are also formed in the interlamellar regions.
Co-reporter:Tong Gang-sheng, Tao Liu, Ling Zhao, Hu Li-xia, Yuan Wei-kang
The Journal of Supercritical Fluids 2009 Volume 48(Issue 3) pp:261-268
Publication Date(Web):April 2009
DOI:10.1016/j.supflu.2008.11.017
This work was aimed at preparing polypropylene grafted acrylic acid (PP-g-AA) with high grafted content and small gel percent by using a supercritical carbon dioxide (scCO2)-assisted solid-state free radical grafting process. The effects of various factors on both the grafted acrylic acid content and gel percent in PP-g-AA were investigated. Those factors included the reaction time, reaction temperature, CO2 pressure, monomer and initiator concentrations. Results showed that self-polymerization of acrylic acid resulted in crosslinking of PP chains and production of gel in PP-g-AA. There exists an optimal reaction time to produce PP-g-AA with high grafted content and small gel percent at a certain temperature. Both the initial AA/PP mass ratio and CO2 pressure constituted very sensitive process parameters that could control the gel percent and grafted content in PP-g-AA to a significant extent and with ease. The crystallization temperature, melting temperature and crystallinity increased with the increasing of the grafted content of PP-g-AA. Moreover, the PP-g-AA removal of gel has a higher thermal stability than the blank PP.Self-polymerization of acrylic acid resulted in crosslinking of PP chains and production of gel in PP-g-AA. Both the initial AA/PP mass ratio and CO2 pressure constituted very sensitive process parameters that could control the gel percent and grafted content in PP-g-AA to a significant extent and with ease.
Co-reporter:Zhenhao Xi;Weizhen Sun
Frontiers of Chemical Science and Engineering 2009 Volume 3( Issue 1) pp:93-96
Publication Date(Web):2009 March
DOI:10.1007/s11705-009-0112-x
A new static mixer Cross-over-Disc has been invented to strip off the boundary layer and to make strong radial mixing. The pressure drop of Cross-over-Disc is 12-26 times as large as that of empty pipe with equivalent diameter and length. The mixing performance of Cross-over-Disc with 14 elements has been investigated in the viscosity range of 190–250 Pa·s by decoloration method, and the gray analysis of images shows that mixing inhomogeneity is about 7.5% and 9.4% for the mixing ratio of 5:1 and 10:1, respectively. Furthermore, mixing inhomogeneity for a combination of static mixing elements (four from Cross-over-Disc and three pairs from Sulzer-type) can be decreased to 2.1%–3.1% within a reasonable range of pressure drop.
Co-reporter:W. Sun;Y. Pan;L. Zhao ;X. Zhou
Chemical Engineering & Technology 2008 Volume 31( Issue 10) pp:1402-1409
Publication Date(Web):
DOI:10.1002/ceat.200800189
Abstract
The kinetic models based on complex free-radical mechanisms always involve lots of parameters, which result in model overparameterization. In this work, on the basis of free-radical reaction mechanisms, a simplified kinetics for liquid-phase catalytic oxidation of p-xylene (PX) to terephthalic acid (TPA) was developed. By assuming that different peroxy radicals have equivalent reactivity, all the initiation rate constants are identical, and the differences in the rates of termination between various peroxy radicals are neglected, the kinetic model is simplified to include only six parameters that are to be determined by experiment. The kinetic model established in this paper was shown to have satisfactory precision in predicting the concentration profiles. The kinetic model proposed is even simpler than the first-order kinetic model because the rate constants concerning chain propagation and termination are independent of temperature within the range investigated.
Co-reporter:Miaocan Chen;Tao Liu;Jiangwei Wu
Frontiers of Chemical Science and Engineering 2008 Volume 2( Issue 2) pp:
Publication Date(Web):2008 June
DOI:10.1007/s11705-008-0040-1
The solubility of CO2 in solid-state PET was measured using a pressure-decay method. In order to calculate the solubility of CO2 in the amorphous region of PET, the crystallinity of solid state PET dissolved in CO2 at different pressures and temperatures was measured by differential scanning calorimetry (DSC). The solubility increases with increasing pressure and it follows a linear relationship and obeys Henry’s law when the pressure is below 8 MPa. The effect of temperature on solubility is weak and the solubilities at different temperatures are almost the same under low pressures. At higher pressure, the solubility decreases with an increase in temperature. The solubility of CO2 in the amorphous region of PET at 373.15 K, 398.15 K and 423.15 K was correlated with the Sanchez-Lacombe equation of state with a maximal correlation error of 6.69%.
Co-reporter:Bin Li, Guo Hua Hu, Gui Ping Cao, Tao Liu, Ling Zhao, Wei Kang Yuan
The Journal of Supercritical Fluids 2008 Volume 44(Issue 3) pp:446-456
Publication Date(Web):April 2008
DOI:10.1016/j.supflu.2007.09.012
This work aims at using supercritical carbon dioxide (scCO2) to disperse a nucleating agent, sodium 2,2-methylene-bis (4,6-di-tert-butylphenyl) phosphate, denoted as NA40, in an isotactic polypropylene (PP) on the nanometer scale and at studying the nucleating efficiency of the nano-dispersed NA40 by differential scanning calorimeter (DSC) and polarized optical microscope (POM). The Avrami equation and a model combining Avrami equation and Ozawa equation were used to describe the isothermal and non-isothermal crystallization kinetics of the nucleated PP, respectively. The results showed a consistent trend: both the isothermal crystallization rate and the non-isothermal crystallization temperature of the PP in which NA40 was dispersed under scCO2 were higher than those of the virgin PP and the PP in which the same amount of NA40 was incorporated by a classical extruder compounding process. Moreover, the size of the spherulites and the haze of the former PP were smaller than those of the virgin PP and the latter. The trend was reversed in terms of flexural and tensile strengths.
Co-reporter:Zhi-Mei Xu, Xiu-Lei Jiang, Tao Liu, Guo-Hua Hu, Ling Zhao, Zhong-Nan Zhu, Wei-Kang Yuan
The Journal of Supercritical Fluids 2007 Volume 41(Issue 2) pp:299-310
Publication Date(Web):June 2007
DOI:10.1016/j.supflu.2006.09.007
This work is aimed at studying the foaming behavior of polypropylene (PP) with supercritical carbon dioxide (scCO2). The effects of saturation time, foaming temperature, saturation pressure and depressurization rate on the foam structure and volume expansion ratio were investigated. A likely foaming zone delimited by the upper and lower limits for foaming temperature and saturation pressure was determined. The upper limit for foaming was dictated by the melt strength of the PP while the lower one by the deformability of the PP. The maximum likely foaming temperature range was very narrow, only about 4 °C, whatever the saturation pressure, showing the poor foamability of PP. There was a sort of equivalence between increasing foaming temperature and increasing saturation pressure in terms of the foamability. However, a lower foaming temperature and a higher saturation pressure were more favorable for obtaining uniform foam than a higher foaming temperature and a lower saturation pressure. At given foaming temperature and saturation pressure, increasing depressurization rate led to an increase in cell density. However, both the cell size and the foam volume expansion ratio first increased with increasing depressurization rate, reached a maximum at some point and then decreased with a further increase in depressurization rate.
Co-reporter:Gang-Sheng Tong, Tao Liu, Guo-Hua Hu, Ling Zhao, Wei-Kang Yuan
The Journal of Supercritical Fluids 2007 Volume 43(Issue 1) pp:64-73
Publication Date(Web):November 2007
DOI:10.1016/j.supflu.2007.03.014
The work reported in this paper was aimed at exploring the advantages of using supercritical carbon dioxide (scCO2) as an environmentally benign solvent and swelling agent for carrying out the free radical grafting process of vinyl monomers onto isotactic polypropylene (PP) in the solid state. Methyl methacrylate (MMA) was chosen as a grafting monomer. Results showed several scientifically interesting and industrially relevant advantages of the scCO2-assisted solid-state grafting process over a classical solid-state or melt process. First, compared to a classical solid-state grafting process the overall reaction rate of the scCO2 assisted one became less diffusion-controlled and more reaction-controlled because of enhanced diffusion of MMA and the initiator in the PP. Second, the CO2 pressure itself constituted an additional and sensitive process parameter capable of significantly modifying the monomer grafting yield and the product quality. Third, the scCO2-assisted solid-state process produced much higher MMA grafting contents and longer MMA grafts than the classical solid-state and melt processes did.
Co-reporter:Zhaoyan Liu;Zhenghao Xi
Macromolecular Symposia 2007 Volume 259(Issue 1) pp:10-16
Publication Date(Web):11 DEC 2007
DOI:10.1002/masy.200751302
Summary: A grid falling film tower (GFFT) has been invented as an ideal polycondensation reactor. In this reactor, polymer melt flows through multi-layers grids from top to bottom to form falling film owing to gravity without agitation and shear; large gas-liquid interfacial area is generated; the grids are perpendicular between adjacent layers to ensure film renewal and to achieve uniformly flowing. The fluid flow in this reactor has little back-mixing and dead zone, which is near to plug flow. All melts are under the state of thin film which avoids the negative effect of hydrostatic head on the mass transfer impetus. Furthermore, the GFFT has wide operation flexibility as well as adjustable configuration parameters to meet different demands. A pilot scale GFFT with the height of 4.0 meters has been applied to polyester polycondensation process. The intrinsic viscosity of polyethylene terephthalate increased from 0.45 dl/g to 0.8–0.9 dl/g successfully. GFFT is supposed to be an universal apparatus for many devolatilization processes.
Co-reporter:Hao Tang, Yuan Zong, Ling Zhao
Chinese Journal of Chemical Engineering (September 2016) Volume 24(Issue 9) pp:1135-1146
Publication Date(Web):1 September 2016
DOI:10.1016/j.cjche.2016.04.040
To control the multicomponent reactions in extrusion, reactive-mixing flow in a co-rotating twin screw extruder was numerically studied in the present paper. Effects of initial species distribution, rotating speed and flow rate on a competitive-parallel reaction were investigated and the relationship between mixing and reactions was discussed from the view of chemical reaction engineering. The simulation results show the studied operational parameters, which determine residence time distribution, earliness of mixing and segregation degree of reactive-mixing flows, affect the local species concentration and reaction time and hence have significant influences on the reaction extent. Orthogonal test was adopted to clarify the significance of operational parameters. The analysis shows that initial species distribution and flow rate are the most important factors in the control of reaction extent, and effect of rotating speed is conditional depending on the micro-mixing status of the fluid.Feeding condition and rotational speed determine the local concentrations of reactants by controlling the earliness/lateness of mixing and the degree of segregation, respectively. Besides, rotational speed and flow rate also have effect on the RTD and duration of the reaction. The combination of local concentration and time accumulation restricts the reaction extents of multicomponent reactions during extrusion.Download full-size image
Co-reporter:Fenglei Bi, Jianqiang Shao, Zhenhao Xi, Ling Zhao, Di Liu
Chinese Journal of Chemical Engineering (September 2016) Volume 24(Issue 9) pp:1290-1297
Publication Date(Web):1 September 2016
DOI:10.1016/j.cjche.2016.04.003
Poly(m-xylylene adipamide)/poly(ethylene terephthalate) (MXD6/PET) copolymers are synthesized by melt copolycondensation with 1–5 wt% low molecular weight PET oligomers into the MXD6 oligomers at 260 °C. FR-IR and 1H NMR analysis results indicate that the interchange reaction has occurred between MXD6 oligomers and PET oligomers. The thermal behavior of copolymers shows that the melting temperature of MXD6/PET copolymers decreases with the increasing of amount of PET oligomers, while the crystallization temperature accordingly increases. And the equilibrium temperature Tm0 is evaluated to be 251.8 °C for the copolymers with 5 wt% PET oligomer adding, which is very close to that of neat MXD6. The tensile and impact strength of MXD6/PET copolymers are significantly improved than that of pure MXD6 by mechanical properties test, and the microfibril structure in the impact fracture sample's surface reveals the feature of ductile fracture.
Co-reporter:Like CHEN, Zhenhao XI, Zhen QIN, Ling ZHAO, Weikang YUAN
Chinese Journal of Chemical Engineering (March 2013) Volume 21(Issue 3) pp:246-252
Publication Date(Web):1 March 2013
DOI:10.1016/S1004-9541(13)60472-6
Based on the kinetic and thermodynamic equations, a comprehensive mathematical model for the continuous esterification process of polyester polyols was developed, which was carried out in an innovational bubbling reactive distillation tower (BRDT) at atmospheric pressure. In this new type of reactor, direct esterification between ethylene glycol and adipic acid was accomplished efficiently and rapidly. A bench BRDT with the height of 2 m was applied for the esterification process of poly (ethylene adipate) (PEA). In the continuous operation, linear oligomers were discharged from the bottom of the column, while water passed a few column trays and a packing section as a condensation byproduct. The influence of major operating conditions on reactor performance was also simulated. Simulation results were in good agreement with experimental data, providing a strategy for developing and optimizing this process.
Co-reporter:Zhenhao Xi, Jie Chen, Tao Liu, Ling Zhao, Lih-Sheng Turng
Chinese Journal of Chemical Engineering (January 2016) Volume 24(Issue 1) pp:180-189
Publication Date(Web):1 January 2016
DOI:10.1016/j.cjche.2015.11.016
Microcellular injection molding of neat isotactic polypropylene (iPP) and isotactic polypropylene/nano-calcium carbonate composites (iPP/nano-CaCO3) was performed using supercritical carbon dioxide as the physical blowing agent. The influences of filler content and operating conditions on microstructure morphology of iPP and iPP/nano-CaCO3 microcellular samples were studied systematically. The results showed the bubble size of the microcellular samples could be effectively decreased while the cell density increased for iPP/nano-CaCO3 composites, especially at high CO2 concentration and back pressure, low mold temperature and injection speed, and high filler content. Then Moldex 3D was applied to simulate the microcellular injection molding process, with the application of the measured ScCO2 solubility and diffusion data for iPP and iPP/nano-CaCO3 composites respectively. For neat iPP, the simulated bubble size and density distribution in the center section of tensile bars showed a good agreement with the experimental values. However, for iPP/nano-CaCO3 composites, the correction factor for nucleation activation energy F and the pre-exponential factor of nucleation rate f0 were obtained by nonlinear regression on the experimental bubble size and density distribution. The parameters F and f0 can be used to predict the microcellular injection molding process for iPP/nano-CaCO3 composites by Moldex 3D.
Co-reporter:Hua ZHONG, Zhenhao XI, Tao LIU, Ling ZHAO
Chinese Journal of Chemical Engineering (December 2013) Volume 21(Issue 12) pp:1410-1418
Publication Date(Web):1 December 2013
DOI:10.1016/S1004-9541(13)60543-1
Most of traditional linear poly(ethylene terephthalate) (PET) resins of relatively low molecular mass and narrow molecular mass distribution have low melt strength at foaming temperatures, which are not enough to support and keep cells. An in-situ polymerization-modification process with esterification and polycondensation stages was performed in a 2 L batch stirred reactor using pyromellitic dianhydride (PMDA) or pentaerythritol (PENTA) as modifying monomers to obtain PETs with high melt strength. The influence of amounts of modifying monomers on the properties of modified PET was investigated. It was found that the selected modifying monomers could effectively introduce branched structures into the modified PETs and improve their melt strength. With increasing the amount of the modifying monomer, the melt strength of the modified PET increased. But when the amount of PENTA reached 0.35% or PMDA reached 0.9%, crosslinking phenomenon was observed in the modified PET. Supercritical carbon dioxide (ScCO2) was employed as physical foaming agent to evaluate the foaming ability of modified PETs. The modified PETs had good foaming properties at 14 MPa of CO2 pressure with foaming temperature ranging from 265 °C to 280 °C. SEM micrographs demonstrated that both modified PET foams had homogeneous cellular structures, with cell diameter ranging from 35 μm to 49 μm for PENTA modified PETs and 38 μm to 57 μm for PMDA modified ones. Correspondingly, the cell density had a range of 3.5×107 cells·cm−3 to 7×106 cells·cm−3 for the former and 2.8×107 cells·cm−3 to 5.8×106 cells·cm−3 for the latter.
Co-reporter:Jie Chen, Tao Liu, Ling Zhao, Wei-kang Yuan
Thermochimica Acta (20 February 2012) Volume 530() pp:79-86
Publication Date(Web):20 February 2012
DOI:10.1016/j.tca.2011.12.006
Co-reporter:Gangsheng Tong, Tao Liu, Shenmin Zhu, Bangshang Zhu, Deyue Yan, Xinyuan Zhu and Ling Zhao
Journal of Materials Chemistry A 2011 - vol. 21(Issue 33) pp:NaN12374-12374
Publication Date(Web):2011/07/18
DOI:10.1039/C1JM11779C
Mesoporous silica nanoparticles (MSNs) with soft templates were readily fabricated using a sol–gel process under mild conditions. The soft templates were composed of an amphiphilic supramolecular star-copolymer from anionic monocarboxyl polydimethylsiloxane and cationic hyperbranched polyethyleneimine via the electrostatic interaction. Ascribed to the high accessibility of dendritic architecture for small molecules and the existence of plentiful amino groups, these supramolecular dendritic templates in MSNs could be used directly as the nanoreactors and reducing reagents for the in situ reduction of chloroauric acid (HAuCl4). The resultant Au@MSN nanocomposites showed excellent catalytic performance in a reduction reaction of 4-nitrophenol by sodium borohydride (NaBH4).
![Poly[iminomethylene-1,3-phenylenemethyleneimino(1,6-dioxo-1,6-hexanediyl)]](http://img.cochemist.com/ccimg/25900/25805-74-7.png)
![Poly[iminomethylene-1,3-phenylenemethyleneimino(1,6-dioxo-1,6-hexanediyl)]](http://img.cochemist.com/ccimg/25900/25805-74-7_b.png)
![Poly[oxy-1,2-ethanediyloxy(1,6-dioxo-1,6-hexanediyl)]](http://img.cochemist.com/ccimg/25000/24937-05-1.png)
![Poly[oxy-1,2-ethanediyloxy(1,6-dioxo-1,6-hexanediyl)]](http://img.cochemist.com/ccimg/25000/24937-05-1_b.png)
