Effects of chemical structure of phenolic antioxidants on Ziegler–Natta catalyst performance during propylene polymerization

Present work studied the synthesis of in-reactor stabilization of polypropylene via introducing antioxidant into polymerization media. Special attention was dedicated to assess the efficiency of antioxidant in catalyst deactivation. Three different types of antioxidants (Irganox 1076, Irganox 1010 and Irganox 1330) which contain ester and/or phenolic OH functional groups were chosen to investigate their impact on Ziegler–Natta catalyst performance during slurry propylene polymerization. Our Results indicated that not only phenolic OH groups but also esteric bond of antioxidants are capable of interacting with active center of catalyst and consequently decreasing the catalyst activity. Our propylene polymerization results showed that determining factors such as antioxidant chemical structures and its steric hindrance effect and the number of functional groups (phenolic and esteric groups) affected on the Ziegler–Natta catalyst performance. Therefore, effects of these three types of antioxidants on polymer characteristics such as particle size distribution, morphology, T _m , T _c , X _c , and isotacticity were evaluated. Morphological analysis using scanning electron microscopy (SEM) showed that introducing antioxidant during propylene polymerization did not destroy the spherical morphology of the polypropylene particles. Conclusively, due to the negative effect of esteric bond of antioxidant on Ziegler–Natta catalyst performance, the use of antioxidant without ester groups (Irganox 1330) is more recommended during propylene polymerization.     

Modeling and optimization of operating parameters for abrasive waterjet turning alumina ceramics using response surface methodology combined with Box–Behnken design

Abrasive waterjet turning is a newly emerging non-traditional technology for machining ceramics. In the present study, an attempt has been made to investigate the effect of operating parameters on depth of penetration and surface roughness (Ra) in turning of alumina ceramics using abrasive waterjet. The quadratic regression models were developed to predict the depth of penetration and Ra by experiments using Response Surface Methodology. The influence of each operating factors has been studied through analysis of variance technique. Key parameters and their interactive effects on depth of penetration and surface roughness have also been presented in graphical contours which are useful for choosing operating parameter preciously. The operating parameters for depth of penetration and surface roughness were simultaneously optimized by RSM with desirability function. The absolute average error between the experimental and predicted values at the optimal combination of parameter settings for depth of penetration and surface roughness were calculated as within 5%. Thus the developed model can be effectively used to predict the depth of penetration and surface roughness in the machining of alumina ceramics.     

Control of molecular weight distribution for polypropylene obtained by commercial Ziegler–Natta catalyst: effect of temperature

Polymerization of propylene was carried out by using MgCl₂-supported TiCl₄ catalyst in conjunction with triethylaluminium (TEA) as cocatalyst. The effect of polymerization temperature on polymerization of propylene was investigated. The catalyst activity was influenced by the polymerization temperature significantly and the maximum activity of the catalyst was obtained at 40 °C. With increasing the polymerization temperature, the molecular weight of polypropylene (PP) drastically decreased, while the polydispersity index (PDI) increased. The effect of the two-stepwise polymerization procedure on the molecular weight and molecular weight distribution of PP was studied and the broad PDI of PP was obtained. It was also found that the PDI of PP could be controlled for propylene polymerization through regulation of polymerization temperature. Among the whole experimental cases, the M _w of PP was controlled from 14.5 × 10⁴ to 75.2 × 10⁴ g/mol and the PDI could be controlled from 4.7 to 10.2.     

Effective modeling and optimization of PVDF–PTFE electrospinning parameters and membrane distillation process by response surface methodology

Ploy(vinylidene fluoride)–polytetrafluoroethylene nanofibrous membrane fabrication and direct contact membrane distillation (DCMD) process were simulated and optimized by response surface methodology (RSM). Analysis of variance was applied to develop and verify the models that predict the objectives. The three-dimensional response surfaces of different objectives were obtained. Results showed that the membrane with thickness of 70.7 μm, contact angle of 146.2°, and liquid entry pressure of 53.5 kPa was obtained within investigated experimental range under the optimum electrospinning conditions. Rejection rate of 99.99% and the permeate flux of 67.5 kg m⁻² h⁻¹ were gained under the optimum membrane distillation (MD) process parameters. The actual and predicted values show good consistency verifying the accuracy of the models. In addition, an overall investigation of the influence of heat-press temperature on the morphological and mechanical properties of electrospun membrane was carried out. Results indicated that electrospinning process and MD performance can be enhanced after the corresponding variables were optimized by RSM. This study provides a scientific way to optimize the electrospinning and DCMD parameters. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47125.     

Dimerization of 1‐butene via zirconium‐based Ziegler–Natta catalyst

A zirconium‐based Ziegler–Natta catalytic system has been tested in the dimerization of 1‐butene. It was found that the concentration of Et₂AlCl, Ph₃P and PhONa as well as the reaction temperature had great influences on the activity and selectivity of the catalyst. Under the optimum reaction conditions, the conversion of 1‐butene is 91.9%, and the selectivity of dimers is 76.7%. Basic ligands such as Ph₃P and PhONa can inhibit isomerization of 1‐butene to 2‐butene effectively. In addition, the metal hydride mechanism was also suggested and some indirect evidence was obtained in favor of this mechanism. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cr(Ⅲ) removal from simulated solution using hydrous magnesium oxide coated fly ash:Optimization by response surface methodology(RSM)

Hydrous magnesium oxide coated fly ash(MFA) has environmental remediation potential by providing a substrate for the adsorption of aqueous Cr(Ⅲ). Aqueous Cr(Ⅲ) adsorption onto MFA was examined as a function of MFA dosage, p H and initial Cr(Ⅲ) concentration with the Box–Behnken approach used for experimental design and optimization using response surface methodology(RSM). p H and dosage(dosage and concentration) have significant interactive effects on Cr(Ⅲ) adsorption efficiency. Analysis of variance shows that the response surface quadratic model is highly significant and can effectively predict the experimental outcomes. Cr(Ⅲ) removal efficiency of 98% was obtained using optimized conditions of MFA dosage, p H and initial Cr(Ⅲ) concentration of 1.57 g·L~(-1), 4.11 and 126 mg·L~(-1), respectively. Cr(Ⅲ) adsorption onto MFA is mainly attributed to the interaction between Cr(Ⅲ) and the functional group OH of the hydrous magnesium oxide, in all probability caused by chemisorptions. The results of this study can conduce to reveal the interactions between Cr(Ⅲ) pollutant and MFA characteristics, posing important implications for the cost-effective alternative adsorption technology in the treatment of heavy metal containing wastewater.     

Enrichment of hazelnut oil with long-chain n−3 PUFA by lipase-catalyzed acidolysis: Optimization by response surface methodology

Response surface methodology (RSM) was used to determine optimal conditions for the lipase-catalyzed enrichment of hazelnut oil by incorporating n−3 PUFA from menhaden oil. A four-factor, five-level central composite design was used, and hazelnut oil containing n−3 PUFA was successfully produced. The effects of incubation time, temperature, substrate molar ratio, and water content on the incorporation ratio were investigated. From the evaluation of response surface graphs, the optimal conditions for incorporation of long-chain n−3 PUFA into hazelnut oil were identified as 45–60°C for temperature, 30–40 h for reaction time, 1∶1–2∶1 (mol hazelnut oil/mol menhaden oil concentrate) for substrate molar ratio, and 3–5% (w/w) for water content. Experiments conducted at optimized conditions predicted by the model equation obtained from RSM yielded structured lipids with 19.6% n−3 PUFA. This value agreed well with that predicted by the model. This structured lipid containing PUFA may be nutritionally more beneficial than unmodified hazelnut oil.     

Application of response surface methodology for optimization and determination of palladium by in-tube ultrasonic and air-assisted liquid–liquid microextraction coupled with flame atomic absorption spectrometry

A highly sensitive, simple and rapid in-tube ultrasonic and air-assisted liquid–liquid microextraction (IT-UAA-LLME) coupled with flame atomic absorption spectrometry was developed for preconcentration and determination of palladium (Pd) in soil and water samples. The effective parameters were optimized by the Plackett–Burman (P–B) and Box–Behnken design (BBD) methods. Under the optimum conditions, the calibration graph was linear over the range of 5–800 μgL^?1 (R² = 0.998). Detection limit, relative standard deviation (RSD) and the enrichment factor were 0.94 μgL^?1, 2.64% (n = 7, C = 40 μgL^?1) and 156, respectively. The proposed method was successfully applied for the determination of trace amounts of Pd in the soil and water samples.     

Morphology and mechanical properties of polypropylene/poly (propylene-1-octene) in-reactor alloys prepared by Metallocene/Ziegler–Natta hybrid catalyst

A series of isotactic polypropylene/poly(propylene-1-octene) (iPP/PPOc) in-reactor alloys were synthesized by a one-step polymerization process, using Metallocene/Ziegler–Natta hybrid catalyst. The alloys were characterized by FT-IR, DSC, optical microscopy and SEM. The results suggested that the spherical morphology was maintained during one-step polymerization process, which provided a potential application for one-step polyolefin in-reactor alloys. A characteristic “shell–core” structure of the nascent alloy particles was observed for the first time. This phenomenon may be due to the difference between the homopolymerization and copolymerization rate at different active centers. It was also found that the majority of the elastomers in the matrix were homogeneously distributed in the alloys. The introduction of the relatively long 1-octene branches could effectively reduce the crystal size and the crystallinity of the obtained iPP/PPOc alloys and made it possible to vary their rigidity and elasticity in a wide range. The crystallization kinetics of the alloys with pure iPP was also investigated. With the increase of elastomer content, an increase of nucleation density (the nuclei number per unit area) and the decrease of crystal perfection could be clearly observed. In comparison with pure PP, the overall crystallization rates and the growth rates of the spherulites of the alloys decreased obviously. These results indicated that the growth rate of the spherulites was the decisive step for the overall crystallization rate in this case, which can be explained on the basis of dilution effect and obstruction effect on the mobility of PP chains in the propylene–octene copolymer. Investigation of the mechanical properties indicated that notched Izod impact strength of iPP/PPOc alloys have obviously increased in comparison with that of pure iPP. The improvement of impact strength can be mainly attributed to the increase of random copolymer content. Based on the understanding of microstructure and phase morphology, the correlation between morphological structure and mechanical properties has been established.     

Optimization of the vulcanization parameters for ethylene–propylene–diene termonomer (EPDM)/ground waste tyre composite using response surface methodology

The utilization of waste tyre in a green way would definitely mitigate the possible risks of the waste tyre accumulation. A green way to solution for the waste tyre problem is recycling. However, it is necessary to optimize the recycling process parameters to come up with the optimum conditions for the effective reuse of the waste tyre. In this study, response surface methodology (RSM) was used to model and optimize the parameters of curing of EPDM and waste tyre composite for the purpose of waste tyre recycling. EPDM with different loadings of ground waste tyre composites were prepared. Mechanical, thermal, and Soxhlet extraction tests were carried out for the samples. RSM was applied and process parameters were optimized. It was seen that the most effective parameter was the curing temperature. The optimal values of the parameters were determined as curing temperature of 172.1 °C, curing pressure of 15.0 MPa and ground waste tyre content of 14.8% by weight. To test the parameters determined from optimization study, the samples were prepared under optimum conditions, and it was shown that the samples prepared according to the optimum conditions have better thermal, mechanical, and curing properties. The results were heartening to pursue the waste tyre recycling option with a considerable amount of ground waste tyre content within the final composite material.     

PE/clay nanocomposites produced via in situ polymerization by highly active clay-supported Ziegler–Natta catalyst

The synthesis of polyethylene/clay (PE/clay) nanocomposites by means of in situ polymerization was achieved using the clay/BOM/chloroform/EtOH/TiCl₄/TEA catalyst system where butyl octyl magnesium (BOM) and triethyl aluminum (TEA) were a modifier for the clay and cocatalyst, respectively. It was found that the catalyst had high activity in ethylene polymerization. The microstructure of the resulting PE/clay nanocomposites was characterized by X-ray diffraction, transmission electron microscopy, and scanning electron microscopy. The examinations evidenced the nanocomposite formation with exfoliated clay in the PE matrix. The thermal properties of the produced nanocomposites were studied by differential scanning calorimetry, oxidation induction time, and thermal gravimetric analysis. Furthermore, the mechanical properties of the nanocomposites were evaluated by the impact and tensile tests. The examinations indicated the improved thermal stability and mechanical properties. Meanwhile, a wide range of molecular weights were produced in the presence of hydrogen.     

Ziegler–Natta catalyst sonofragmentation for controlling size and size distribution of the produced polymer particles

The size of the Ziegler–Natta catalyst (ZNC) particles can have a strong impact on their activity and the size and size distribution (SD) of the final polymer particles. In this work, we apply sonofragmentation to break the ZNC particles dispersed in hexane. Our main goals are first to monitor the breakage induced by the ultrasonic power to understand the kinetics and the effect of sonofragmentation on the colloidal stability of the ZNC particles. Second, we explore the effect of sonofragmentation on the polymerization performance of the ZNC particles. It is found that sonofragmentation can not only reduce the size but also narrow the SD of the ZNC particles. From the tests of ethylene polymerization, we observed that the catalyst yield of the sonofragmentation-treated ZNC is substantially higher than that of the untreated one and that the obtained polymer particles exhibit a smaller average size and a narrower SD.     

Aqueous two-phase extraction of punicalagin (α+β) from pomegranate peel by response surface methodology

In order to enhance the recovery of punicalagin from pomegranate peel, extraction of punicalagin (α + β) was studied using aqueous two-phase system. Box Behnken design of response surface methodology was used as a tool to study the effect of Poly Ethylene Glycol (PEG) concentration, PEG molecular weight, salt concentration, solute amount and pH on the extraction yield of punicalagin. The optimal conditions were found to be 18% (w/v) PEG concentration, 8000 PEG molecular weight, 16% (w/v) salt concentration, 0.5 g solute amount and 6 pH. Under these conditions, experimental yield and predicted yield was found to be 43% and 48%, respectively.     

Estimation of the chain propagation rate constants of propylene polymerization and ethylene-1-hexene copolymerization catalyzed with MgCl2-supported Ziegler–Natta catalysts

In olefin polymerization with MgCl₂-supported Ziegler–Natta (Z–N) catalysts, the apparent propagation rate constant (k_p)_a calculated by R_p = (k_p)_a [C*] C_Me (C_Me is equilibrium monomer concentration in the reaction system) declines with reaction time for gradually developed monomer diffusion limitation in the polymer/catalyst particles. In this work, a simplified multi-grain particle model was proposed to build correlation between (k_p)_a and other kinetic parameters that can be determined experimentally. Rate profiles of propylene polymerization and ethylene-1-hexene copolymerization by three MgCl₂-supported Z–N catalysts were determined, and the (k_p)_a data was calculated using [C*] determined by quench-labelling the propagation chains with acyl chloride. Decline of (k_p)_a in each polymerization process was precisely fitted by the linear correlation between lg(k_p)_a and [(ρ_catm_p)/(ρ_pm_cat) + 1]^1/3 developed on the particle model. Real propagation rate constant (k_p) was estimated by extrapolating the fitting line to the starting point of polymerization, where no concentration gradient exists. According to the particle model, the slope of the lg(k_p)_a versus [(ρ_catm_p)/(ρ_pm_cat) + 1]^1/3 line (lgd) represents the degree of monomer diffusion limitation. Variations of parameter d found in the studied reaction systems can be reasonably explained based on the knowledge of olefin diffusion in the polymer phase.     

Microfunnel magnetic stirring-assisted liquid–liquid microextraction method for determination of trace amounts of gold after optimization employing response surface methodology

ABSTRACT

A rapid, sensitive and simple technique was proposed for the preconcentration and determination of gold in the presence of N-methyl-N,N,N-trioctylammonium chloride (Aliquat 336) as ion pair forming agent employing microfunnel magnetic stirring-assisted liquid–liquid microextraction (MF-MSA-LLME) and flame atomic absorption spectrometry. Parameters were optimized by full factorial and Box-Behnken design. Under the optimum conditions, the calibration graph was linear in the range of 2.5–800.0 ng mL?¹ (r² = 0.998). Detection limit, enrichment factor and relative standard deviation were 0.6 ng mL?¹, 240.0 and 1.4% (n = 7, C = 100 ng mL^?1), respectively. This technique was successfully applied for the determination of gold in soil and water samples.     

Modeling and operating conditions optimization of Fischer–Tropsch synthesis in a fixed-bed reactor

The effect of a range of operation variables such as pressure, low temperature and H₂/CO molar feed ration the catalytic performance of 80%Co/20%Ni/30 wt% La₂O₃/1 wt% Cs catalyst was investigated. It was found that the optimum operating conditions is a H₂/CO = 2/1 molar feed ratio at 260 °C temperature and 2 bar pressure. Reaction rate equations were derived on the basis of the Langmuir–Hinshelwood–Hougen–Watson (LHHW) type models for the Fischer–Tropsch reactions. The activation energy obtained was 59.69 kJ/mol for optimal kinetic model.     

Counting the number of active centers in MgCl2-supported Ziegler–Natta catalysts by quenching with 2-thiophenecarbonyl chloride and study on the initial kinetics of propylene polymerization

Using 2-thiophenecarbonyl chloride (TPCC) as a quenching agent, the number of active centers in propylene polymerization with MgCl₂-supported Ziegler–Natta catalysts were determined by measuring the sulfur content of the quenched polymer. Under suitable conditions, the thiophenecarbonyl-labeled polymer chains were stable in the reaction system when TPCC/Al > 1. The number of active centers was found to increase in the first 5 minutes of propylene polymerization, accompanied by rapid decrease of the propagation rate constant k_p. Diffusion barrier from the polymer covering the catalyst fragments is thought as the main reason of the rapid decay of k_p in the initial stage.