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1.
Particle‐resolved CFD simulations of multilayered packed beds containing 30 particles of different particle shapes (trilobe, daisy, hollow cylinder, cylcut, and 7‐hole cylinder) with a tube to particle diameter ratio of 5, were performed to understand the effect of particle shape on pressure drop (ΔP), dispersion, CH4 conversion and effectiveness factors for methane steam reforming reactions. The effect of different boundary conditions and particle modeling approaches were analyzed in detail. The empirical correlations (Ergun and Zhavoronkov et al.) over‐predicted the ΔP and a modified correlation was developed to predict ΔP for the particles with different shapes. Overall, the externally shaped particles (trilobe and daisy) offered lower ΔP and higher dispersion because of the lower surface area and higher back flow regions, whereas the internally shaped particles (cylcut, hollow, and 7‐hole cylinder) offered higher CH4 conversion and effectiveness factors because of the better access for the reactants. The cylcut‐shape offered the highest CH4 conversion/ΔP. © 2018 American Institute of Chemical Engineers AIChE J, 64: 4162–4176, 2018  相似文献   

2.
Free radical solution copolymerization of acrylonitrile (AN) and itaconic acid (IA) was performed with DMSO‐d6 as the solvent and 2,2′‐azobisisobutyronitrile (AIBN) as the initiator. Weight ratio of the monomers to solvent and molar ratio of initiator to monomers were constant in all experiments. The initial comonomer composition was the only variable in this study. On‐line 1H NMR spectroscopy was applied to follow individual monomer conversion. Mole fraction of AN and IA in the reaction mixture (f) and in the copolymer chain (F) were measured with progress of the copolymerization reaction. Overall monomer conversion versus time and also compositions of monomer mixture and copolymer as a function of overall monomer conversion were calculated from the data of individual monomer conversion versus time. Total rate constant for the copolymerization reaction was calculated by using the overall monomer conversion versus time data and then kp/kt0.5 was estimated. The dependency of kp/kt0.5 on IA concentration was studied and it was found that this ratio decreases by increasing the mole fraction of IA in the initial feed. The variation of comonomer and copolymer compositions as a function of overall monomer conversion was calculated theoretically by the terminal model equations and compared with the experimental data. Instantaneous copolymer composition curve showed the formation of alternating copolymer chain during copolymerization reaction. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3253–3260, 2007  相似文献   

3.
A methodology is presented to obtain a kinetic model for curing reactions, from conversion against time and the glass‐transition temperature versus conversion data. Isothermal runs for a cyanate ester resin from 140 to 190°C, reported previously, were evaluated. The approach utilizes the conversion measurement time derivatives that allow following the estimated parameters' trends: the rate constant and the reaction order, in this case. An autocatalytic model was found, and the rate constants were truly constant along the experiments; thus, their Arrhenius parameters were evaluated. The methodology allowed constructing a master curve relating the variable reaction order with a temperature difference (reaction and glass transition) explained by the Williams–Landel–Ferry (WLF) equation. Four parameters describing the reaction order variation, two related to an exponential‐like behavior and two required by the WLF equation, allowed describing the whole experimental set accurately. POLYM. ENG. SCI., 54:1900–1908, 2014. © 2013 Society of Plastics Engineers  相似文献   

4.
The curing reaction of a well‐defined glycidyl methacrylate‐co‐butyl acrylate statistical copolymer, prepared by atom transfer radical polymerization, and a commercial linear diamine (Jeffamine D‐230) was studied with the objectives of constructing and discussing a time–temperature–transformation isothermal curing for this system. Thermal and rheological analyses were used to obtain the gelation and vitrification times. Differential scanning calorimetry data showed a one‐to‐one relationship between the glass‐transition temperature (Tg) and fractional conversion independent of the cure temperature. As a result, Tg was used as a measurement of conversion. We obtained a kinetically controlled master curve for isothermal curing temperatures from 50 to 100°C by shifting Tg versus the natural logarithm time data to a reference temperature of 80°C. We calculated the apparent activation energy by applying two different methods, gel time measurements versus shift factors, suggesting a good agreement between them. Isoconversion contours were calculated by the numerical integration of the kinetic model. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011  相似文献   

5.
Head‐to‐head experimental performance comparisons for flow through pleated microfibrous structures (flat‐, V‐, and W‐shaped) were made with wash‐coated monolith of different cells per square inch (230 and 400). Microfibrous entrapped catalyst (MFEC) was prepared by entrapping support particles (γ‐Al2O3, 150–250 μm diameter) into nickel microfibers. Pleated structures of MFECs and wash‐coated monoliths containing Pd‐Mn/γ‐Al2O3 were investigated systematically for volatile organic compound (e.g., ethanol) removal at various face velocities (ca. 3–30 m/s) and at low temperatures (≤473 K). The experimental studies showed that pleated MFEC (W‐shaped) had shown significantly improved performance in VOC removal in terms of conversion and pressure drop than tested monolith for high face velocity system. The flexibility of pleating lowered the effective velocity inside the media that resulted lower pressure drop and higher conversion. Furthermore, a reaction kinetic model was developed for pleated MFEC considering the Peffer's model to substantiate the experimental results. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3814–3823, 2014  相似文献   

6.
Summary: This work deals with modeling the terpolymerization of styrene, α‐methylstyrene and methyl methacrylate in the presence of an inhibitor. The model used is a “tendency model” based on the kinetics of the complex elementary chemical reactions both in the aqueous phase and in the particles. It considers the reversible propagation of α‐methylstyrene and the main physical phenomena occurring during the process, i.e., (i) partitioning of monomers, surfactant and inhibitor between the aqueous phase, polymer particles, monomer droplets and micelles; (ii) homogeneous and micellar nucleation; (iii) radical absorption and desorption; (iv) gel and glass effects. The main kinetic parameters of the model are estimated on the basis of batch experimental data in order to be able to describe the complete picture of this complex process. The model can be used to predict (with good precision) the global monomer conversion, number and weight‐average molecular weight, the average diameter and number of polymer particles and the glass transition temperature, and consequently to study the effects of AMS on conversion and terpolymer and latex characteristics.

Comparison of experimental and simulated results of the weight‐average molecular weight versus conversion for the emulsion terpolymerization of styrene, alpha methylstyrene and methyl methacrylate at 60 °C.  相似文献   


7.
Nanosized poly(methyl methacrylate) (PMMA) particles with a high molecular weight of 106 g mol?1 and a polydispersity index of about 1–2 were synthesized, for which 2,2′‐azobisisobutyronitrile was used as the initiator and a differential microemulsion polymerization technique was employed. The kinetics of the polymerization, the glass transition temperature, tacticity, the particle size distribution, and the morphology of the nanosized PMMA synthesized were investigated. The dependence of the number of the polymer particles (Np) and the number of the micelles (Nm) on the concentration of the surfactant was discussed. The molecular weight distribution was found to be nearly constant over the polymerization time, which was attributed to the significance of micellar polymerization. The resultant nanosized PMMA has a rich syndiotactic configuration (53–57% rr triads) with a glass transition temperature of about 125°C. A beneficial operation condition was discovered where the conversion reached a maximum at a high monomer‐to‐water ratio. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009  相似文献   

8.
Temperature, pH, and reduction triple‐stimuli‐responsive inner‐layer crosslinked micelles as nanocarriers for drug delivery and release are designed. The well‐defined tetrablock copolymer poly(polyethylene glycol methacrylate)–poly[2‐(dimethylamino) ethyl methacrylate]–poly(N‐isopropylacrylamide)–poly(methylacrylic acid) (PPEGMA‐PDMAEMA‐PNIPAM‐PMAA) is synthesized via atom transfer radical polymerization, click chemistry, and esterolysis reaction. The tetrablock copolymer self‐assembles into noncrosslinked micelles in acidic aqueous solution. The core‐crosslinked micelles, shell‐crosslinked micelles, and shell–core dilayer‐crosslinked micelles are prepared via quaternization reaction or carbodiimide chemistry reaction. The crosslinked micelles are used as drug carriers to load doxorubicin (DOX), and the drug encapsulation efficiency with 20% feed ratio reached 59.2%, 73.1%, and 86.1%, respectively. The cumulative release rate of DOX is accelerated by single or combined stimulations. The MTT (3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide) assay verifies that the inner‐layer crosslinked micelles show excellent cytocompatibility, and DOX‐loaded micelles exhibit significantly higher inhibition for HepG2 cell proliferation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46714.  相似文献   

9.
A straightforward strategy is described to synthesize poly(?‐caprolactone)‐graft‐poly(N‐isopropylacrylamide) (PCL‐g‐PNIPAAm) amphiphilic graft copolymers consisting of potentially biodegradable polyester backbones and thermoresponsive grafting chains. PCL with pendent chlorides was prepared by ring‐opening polymerization, followed by conversion of the pendent chlorides to azides. Alkyne‐terminated PNIPAAm was synthesized by atom transfer radial polymerization. Then, the alkyne end‐functionalized PNIPAAm was grafted onto the PCL backbone by a copper‐catalyzed azide–alkyne cycloaddition. PCL‐g‐PNIPAAm graft copolymers self‐assembled into spherical micelles comprised of PCL cores and PNIPAAm coronas. The critical micelle concentrations of the graft copolymers were in the range 7.8–18.2 mg L?1, depending on copolymer composition. Mean hydrodynamic diameters of micelles were in the range 65–135 nm, which increased as the length of grafting chains grew. PCL‐g‐PNIPAAm micelles were thermosensitive and aggregated upon heating. © 2014 Society of Chemical Industry  相似文献   

10.
Semibatch emulsion copolymerization was carried out to prepare poly(butyl acrylate‐co‐glycidyl methacrylate) latexes at 75°C, using potassium persulfate as an initiator, sodium dodecylbenzene sulfonate as an emulsifier and sodium bicarbonate as a buffer. The reaction was conducted in three stages; a further stage (called the steady stage, 2 h) was added to the traditionally stages (i.e., feed and seed stages) to improve considerably the monomer conversion. The monomer conversion and particle size distribution were studied by gravimetric and laser light scattering methods, respectively. The effects of variables such as agitation speed, emulsifier concentration, initiator concentration, feeding rate and comonomers ratio were fully investigated based on the monomer conversion‐time profiles and the particle size distribution to find the optimized copolymerization conditions. Increasing the agitation speed had a negative effect on the monomer conversion, but reduced coagulation of polymer particles. Monomer conversion could be improved by increasing the initiator or emulsifier contents. Feeding rate increased the polymer particle size sharply; however, it showed no significant effect on conversion. The final conversions were as high as 97–99% and they were recognized to be independent of the comonomers ratios employed. Morphological studies by scanning electron microscopy showed nano‐sized isolated particles which were partially aggregated. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010  相似文献   

11.
Novel amphiphilic star‐shaped terpolymers comprised of hydrophobic poly(?‐caprolactone), pH‐sensitive polyaminoester block and hydrophilic poly(ethylene glycol) (Mn = 1100, 2000 g mol?1) were synthesized using symmetric pentaerythritol as the core initiator for ring‐opening polymerization (ROP) reaction of ?‐caprolactone functionalized with amino ester dendrimer structure at all chain ends. Subsequently, a second ROP reaction was performed by means of four‐arm star‐shaped poly(?‐caprolactone) macromer with eight ‐OH end groups as the macro‐initiator followed by the attachment of a poly(ethylene glycol) block at the end of each chain via a macromolecular coupling reaction. The molecular structures were verified using Fourier transform infrared and 1H NMR spectroscopies and gel permeation chromatography. The terpolymers easily formed core–shell structural nanoparticles as micelles in aqueous solution which enhanced drug solubility. The hydrodynamic diameter of these agglomerates was found to be 91–104 nm, as measured using dynamic light scattering. The hydrophobic anticancer drug curcumin was loaded effectively into the polymeric micelles. The drug‐loaded nanoparticles were characterized for drug loading content, encapsulation efficiency, drug–polymer interaction and in vitro drug release profiles. Drug release studies showed an initial burst followed by a sustained release of the entrapped drug over a period of 7days at pH = 7.4 and 5.5. The release behaviours from the obtained drug‐loaded nanoparticles indicated that the rate of drug release could be effectively controlled by pH value. Altogether, these results demonstrate that the designed nanoparticles have great potential as hydrophobic drug delivery carriers for cancer therapy. © 2015 Society of Chemical Industry  相似文献   

12.
This work deals with the resolution of DL ‐menthol with propionic acid by Candida cylindracea lipase (Ccl) in organic solvent reaction systems and a reverse micelles system of sodium 1,4‐bis (2‐ethylhexyl) sulfosuccinate (AOT). The activity and stability as well as enantioselectivity of the lipase in two systems were studied. The results indicate that the lipase showed higher stability in reverse micelles than in organic solvent, which proved that the reverse micelles system has potential application for maintaining the activity of the enzyme for a long time. This is because lipase molecules can be entrapped in water‐containing micro‐drops of reverse micelles, avoiding direct‐contract with unfavorable organic medium. The enantioselectivity (E > 30, eep = 92.5) in the two systems is relatively high, although the conversion is moderate. The influence of the characteristic parameters of the two systems, such as pH, temperature, w0 (molar ratio of water to AOT in reverse micelles systems) and water content (organic solvent) on the conversion of DL ‐menthol was also investigated. Copyright © 2005 Society of Chemical Industry  相似文献   

13.
Dispersion polymerization of acrylamide (PAM) has been successfully carried out in aqueous ammonium sulfate media by using poly(acryloyloxyethyl trimethylammonium chloride) (PAOTAC) as the polymeric stabilizer and 2,2′‐azobis(2‐methyl propionamidine) dihydrochloride (AIBA) as the initiator. The polymerization behaviors with varying concentrations of acrylamide, PAOTAC, AIBA, and ammonium sulfate were investigated. The reaction conditions for stable dispersion were concentrations of 5–10% for acrylamide, 0.6–1.8% for the stabilizer, 0.92–1.84 × 10?4 mol/L for the initiator, and 24–30% for the salt. The resulting conversion–time curves were S‐shaped, as is typically observed in polymerization. Polydisperse spherical particles were formed in the system. An image analyzer photographed the size of the dispersed particles and their distribution was measured. The mechanism and kinetics for the dispersion polymerization were discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1397–1405, 2002  相似文献   

14.
The atom transfer radical polymerization (ATRP) of lauryl methacrylate (LMA) with an ethyl 2‐bromobutyrate/CuCl/N,N,N,N,N″‐pentamethyldiethylenetriamine initiation system was successfully carried out in toluene, and poly(lauryl methacrylate) with a low polydispersity (1.2 < weight‐average molecular weight/number‐average molecular weight < 1.5) was obtained. Plots of ln ([M])0/([M]) versus time and plots of the molecular weight versus conversion showed a linear dependence, indicating a constant number of propagating species throughout the polymerization. The rate of polymerization was 0.56‐order with respect to the concentration of the initiator and 1.30‐order with respect to the concentration of the Cu(I) catalyst. In addition, the effect of the solvent on the polymerization was investigated, and the thermodynamic data and activation parameters for the solution ATRP of LMA were reported. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1117–1125, 2003  相似文献   

15.
Star‐shaped amphiphilic polymeric surfactants comprising a hydrophobic polyhedral oligomeric silsesquioxane (POSS) core and hydrophilic poly(ethylene glycol) (PEG) arms with various chain lengths are successfully synthesized using copper(I)‐catalysed azide–alkyne cycloaddition (CuAAC) click reaction. Their chemical structures and molecular characteristics are clearly confirmed using Fourier transform infrared and 1H NMR spectroscopies and gel permeation chromatography, and no homopolymer is found after CuAAC click reaction. Aqueous solutions of these star‐shaped polymers have been investigated using atomic force and transmission electron microscopies and dynamic light scattering studies and it is found that they can self‐assemble into micelles. The sizes of the micelles can be adjusted by the length of the PEG arms, where longer chains not only lead to increased micelle sizes, but also reduce the contact angle values. Moreover, the melting points and root mean square roughness of the obtained star‐shaped polymers are slightly increased on increasing the chain length of the PEG arms. © 2017 Society of Chemical Industry  相似文献   

16.
A novel, fast‐swelling superabsorbent polymer (SAP2) was fabricated with an anionic–nonionic surfactant [poly(oxy‐1,2‐ethanediyl)–(3‐carboxy‐1‐oxo‐3‐sulfopropyl)–(nonylphenoxy) sodium salt] as the stabilizer by inverse suspension polymerization. The microstructure, chemical structure, and gel strength of the superabsorbent polymers (SAPs) were characterized by scanning electron microscopy, porosity, and specific surface area analysis, Fourier transform infrared spectroscopy, and rheometry. The results show that SAP2 had irregularly shaped particles with a large number of pores and presented a greater specific surface area, pore volume, and gel strength than the prepared SAP1 with a nonionic surfactant (Span 60) as the stabilizer. The amount of residual monomer and the gel fraction of SAP2 were 202 mg/kg and 80.6%, respectively. Meanwhile, SAP2 demonstrated a faster swelling and deswelling rate as well as greater water absorbency than SAP1. The fast swelling rate mainly resulted from the capillary effect of the pores in the irregularly shaped particles. Superfast swelling SAPs should possess outstanding potential for healthcare products, communication cables, and the biomedical field. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46142.  相似文献   

17.
The oil/water microemulsion polymerizations of alkyl (methyl (MA), ethyl (EA), butyl (BA), hexyl (HA) and 2-ethylhexyl (EHA)) acrylates initiated by a water-soluble (ammonium peroxodisulphate (APS)) initiator were investigated. The rate of polymerization versus conversion curve shows two inconstant intervals. The maximum rate of polymerization of MA, EA, BA and EHA is found to be proportional to the 0·53, 0·17, 0·46 and 0·59 powers of the APS concentration and to the first power of the monomer (MA, BA and EHA) concentration. Homogeneous (solution) radical polymerization is operative in the MA, BA and EHA systems. The strong rate dependence on the EA monomer concentration is assumed to be caused by both the polymerization within the micelle core and the gel effect. The particle size was observed to increase with conversion in the EA and BA runs and to decrease in the EHA and HA runs. The number of particles increased with conversion during the whole polymerization. The polymer particles grow by recruiting monomer and emulsifier from the free monomer-swollen micelles and dead particles. © 1997 SCI.  相似文献   

18.
A mixed micellar system of novel function was designed and synthesized by co‐assembling TAT (cell penetrating peptide)‐modified poly (ethylene glycol)‐poly(l ‐lactide) (PEG‐PLA) copolymer with the drug‐conjugated poly(ethylene glycol)‐b‐poly(l‐ lactide‐co‐2‐methyl‐2‐carboxyl‐propylene carbonate) (mPEG‐b‐P(LA‐co‐MCC)) copolymer. UV‐Vis, Matrix‐assisted laser desorption/ionization time‐of‐flight, and XPS were used to ensure the successful modification of the copolymers with TAT and anti‐tumor drugs. The size of spherical nanomicelles increased from 50 to 60 nm as of empty polymeric micelles to 100–150 nm as of drug‐loaded ones, determined by dynamic light scattering and TEM. Daunorubicin was selected as model drug for in vitro evaluations on different cell lines. 3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay clearly indicated an improved cell growth inhibition of the TAT‐modified mixed micelles. While green fluorescent protein was used as a marker for the mixed micelle, small amount of DMSO was necessary to enhance the accumulation of the mixed micelles in cell lines Caski. Mediated by TAT, mixed micelles containing Apoptin (a tumor‐specific apoptosis drug) showed higher level of tumor cell internalization and growth inhibition than that of mixed micelles without TAT modification. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4598–4607, 2013  相似文献   

19.
Amphiphilic linear–hyperbranched polymer poly(ethylene glycol)–branched polyethylenimine–poly(?‐caprolactone) (PEG‐PEI‐PCL) was synthesized by progressively conjugating PEG (one chain) and PCL (multi‐chains) to PEI (hyperbranched architecture) with a yield of 87%. PEG‐PEI‐PCL forms nano‐sized uniform spherical micelles by self‐assembly in water. The micelles had an average diameter of 56 nm determined using dynamic light scattering and 35 nm observed from transmission electron microscopy images. PEG‐PEI‐PCL was used as a stabilizer of platinum nanoparticles (PtNPs) for the first time. The particle diameter of PEG‐PEI‐PCL‐stabilized PtNPs was 7.8 ± 1.4 nm. Amphiphilic (hydrophilic–hydrophilic–hydrophobic) and hyperbranched (linear–hyperbranched–grafted) structures enabled PtNPs to effectively stabilize and disperse in liquid‐phase synthesis. The highly disperse PtNPs in PEG‐PEI‐PCL micelles improved the catalytic activity for the reduction of 4‐nitrophenol with a catalytic yield of near 100%. © 2016 Society of Chemical Industry  相似文献   

20.
Uniform polymersomes (polymer vesicles) made of poly(2‐methyloxazoline)15b‐poly(dimethylsiloxane)68b‐poly(2‐methyloxazoline)15 (PMOXA15–PDMS68–PMOXA15) can be formed in miniaturized‐stirred tank reactors by the aid of a recently published process. In this study, the occurring self‐assembly mechanism was elucidated by using transmission electron microscopy. Subsequent to the initial formation of small spherical micelles and the following fusion to worm‐like micelles, two simultaneously occurring pathways, describing the transformation of further intermediate structures to the desired vesicles, were found. The resulting particle increase was followed by dynamic light scattering. Thus, the vesicle formation rate was judged by the linear increase of the particle diameter over time. While temperature showed no influence, higher initial polymer concentrations and lower final solvent concentrations accelerated the polymersome formation. Besides, the process was crucially dependent on the agitation speed. While spherical micelles did not transform into polymersomes when no stirring or too slow stirring is applied, the self‐assembly process was accelerated by increasing the agitation speed. Uniform polymeric vesicles can be formed under vigorous stirring in stirred‐tank reactors in short process times. In this study, the underlying mechanisms of vesicle formation were elucidated, showing that the polymer forms small micellar structures before undergoing two separate pathways to form the desired vesicular structures. The formation rate of the polymer vesicles was mainly dependent on the agitation speed but also on the polymer and solvent concentrations, highlighting the need for controlled formation conditions. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46077.  相似文献   

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