LLDPE synthesis via SiO2–Ga-supported zirconocene/MMAO catalyst

In this present study, the linear low-density polyethylene (LLDPE) was synthesized via ethylene/1-octene copolymerization with the zirconocene/MMAO catalyst by in situ impregnation of different silica (SiO₂) supports. The SiO₂ supports used were small-pored (SP) and large-pored (LP) sizes with and without Ga modification. It was found that the SP-SiO₂ support exhibited higher polymerization activity (～1.5 times) than that obtained from the LP-SiO₂ one. This can be attributed to the lower amount of MMAO being present inside the SP-SiO₂ support resulting in higher content of MMAO at the external surface. The higher activity in ethylene/1-octene copolymerization was also found with the supported catalyst having Ga modification onto both SP-and LP-SiO₂ supports_. The results demonstrated that the introduction of Ga may improve ability of supports to immobilize metallocene catalyst. Based on ¹³C NMR measurement, it indicated that all synthesized polymers were typical LLDPE having random distribution of comonomer.     

Copolymerization of ethylene and 1-octadecene with the Cp2ZrCl2/MAO and Cp2HfCl2/MAO catalyst systems

Summary The comparison of the copolymers obtained with the Cp₂ZrCl₂/MAO and Cp₂HfCl₂/MAO catalyst systems showed that the catalyst having hafnocene was much more reactive towards 1-octadecene than zirconocene. The comonomer concentration had to be three times higher in the zirconocene copolymerization than in the hafnocene copolymerization when the level of 6 mol-% was reached. Although the hafnocene catalyst was more reactive towards 1-octadecene, the molecular weights were higher than in the copolymers obtained with the zirconocene catalyst.The total activity of the zirconocene was 10 times higher than with the hafnocene catalyst. With the zirconocene catalyst the activity towards ethylene was constantly increasing by increasing the comonomer concentration but stayed nearly constant with the hafnocene catalyst. It seemed that there is no rate enhancement effect upon comonomer addition with the hafnocene catalyst.     

Hydrogen production by oxidative methanol reforming on Pd/ZnO: Catalyst preparation and supporting materials

Pd and Pd–Zn alloy were supported on various supporting materials using impregnation, co-precipitation and microemulsion methods, and their catalytic performances in oxidative methanol reforming (OMR) were investigated. Pd/ZnO exhibited much higher selectivity than either Pd/Al₂O₃ or Pd/ZrO₂ in the OMR for hydrogen production. This was attributed to the presence of Pd–Zn alloy on the ZnO support. Elemental Pd on Al₂O₃ or ZrO₂ promotes methanol decomposition reaction and increases CO formation. Using a microemulsion method, a highly selective Pd/ZnO can be obtained with much lower Pd loading than that in samples prepared by co-precipitation. Modification of Al₂O₃ with ZnO produced a ZnAl₂O₄ phase, which was found to be a good support for the Pd/ZnO catalyst. Highly active and selective Pd/ZnO/ZnAl₂O₄ catalysts for the OMR reaction, containing much lower Pd loadings have been developed by impregnation of the supports with an aqueous solution of Pd(NO₃)₂ + Zn(NO₃)₂.     

Synthesis of linear low density polyethylene with a nano-sized silica supported Cp2ZrCl2/MAO catalyst

A nano-sized silica supported Cp₂ZrCl₂/MAO catalyst was used to catalyze the copolymerization of ethylene/1-hexene and ethylene/1-octene to produce linear low-density polyethylene (LLDPE) in a batch reactor. Under identical reaction conditions, the nano-sized catalyst exhibited significantly higher polymerization activity, and produced copolymer with greater molecular weight and smaller polydispersity index than a corresponding micro-sized catalyst, which was ascribed to the much lower internal diffusion resistance of the nano-sized catalyst. Copolymer density decreased with the increase of polymerization temperature, probably due to the decrease of reactivity ratio r ₁ and ethylene solubility with increasing temperature. Polymerization activity of the nano-sized catalyst increased rapidly with increasing comonomer concentration. Ethylene/1-octene exhibited higher polymerization activity and had a stronger comonomer effect than ethylene/1-hexene.     

Role of titania in TiO2–SiO2 mixed oxides-supported metallocene catalyst during ethylene/1-octene copolymerization

The present study showed enhanced activities of ethylene/1-octene copolymerization via TiO₂–SiO₂ mixed oxides-supported MAO with a zirconocene catalyst. It was proposed that titania was decorated on silica surface and acted as a spacer to anchor MAO to the silica support resulting in less steric hindrance and less interaction on the support surface.     

Side chain liquid crystalline polyether macromonomers and their polymerization

Summary Copolymers of ethylene and 1-octene, 1-tetradecene and 1-octadecene were synthetized in order to study the effect of the comonomer chain length and amount on density, melting temperature and heat of fusion. They were also compared with the properties of the copolymers obtained with the heterogeneous titanium catalyst.It could be seen that the density/melting-area of the copolymers obtained with the zirconocene catalyst was much broader than with the titanium catalyst. It could also be seen that with the same comonomer content 1-tetradecene gave lower density of the copolymers than 1-octene. However, no difference were seen between the densities of the copolymers obtained with 1-tetradecene and 1-octadecene.The melting temperature of the copolymers was seen to be the lower the longer the comonomer was. In the area of the high branching amount the linear correlation was not in work. It was also shown that the differences in the heat of fusions could only be seen at high amount of branches (>15 branches/1000C): the longer the comonomer the lower amount of heat was needed to melt the copolymer.     

Hydrogen production by oxidative methanol reforming on Pd/ZnO catalyst: effects of Pd loading

Catalytic performances of Pd/ZnO in oxidative methanol reforming reaction were studied as a function of Pd loading. It was confirmed that the formation of Pd–Zn alloy is essential to the selective production of hydrogen. High active Pd/ZnO, comparable to commercial Cu-Zn catalyst, was obtained with higher Pd loading. Selectivity of the reaction was greatly increased by increasing Pd loading on ZnO. At higher Pd loadings (>5%), co-precipitation was superior to impregnation for the catalyst preparation. The catalytic performances were also discussed based on results from X-ray diffraction (XRD) characterization.     

Ce掺杂的蛋壳型CuO/ZnO/SiO2颗粒催化剂的制备和表征

用添加表面活性剂的两步沉淀法制备了以蛋壳型纳米空心SiO2为载体的CuO/ZnO催化剂和掺杂Ce的CuO/ZnO催化剂,初步考察了两组催化剂用于一氧化碳加氢合成甲醇的催化性能,并采用TEM, BET, XRD, XPS等方法对催化剂的结构进行了表征. 结果表明,以纳米空心SiO2为载体的CuO/ZnO催化剂具有较大的比表面积,活性成分在载体表面分散均匀,粒径在13 nm左右. 加入掺杂剂Ce能有效提高催化剂的活性和选择性：一方面,Ce可以降低Cu 2p3/2和Zn 2p3/2的表面结合能, 使氧化铜更容易被氢气还原成铜;另一方面,Ce也能增强铜锌之间的相互作用,抑制铜粒子的烧结,改善活性成分的分散.     

The effect of the ethylene pressure on its reaction with 1-hexene, 1-octene and 4-methyl-1-pentene

Summary Copolymers of ethylene and 1-hexexe, 1-octene and 4-methyl-1-pentene were obtained using Et[In]₂ZrCl₂/MAO catalyst at various pressures. The increase of 1-hexene and 1-octene concentration in the feed increases catalyst activity(g/nZr.h.bar) and productivity(g/nZr.h). For 4-methyl-1-pentene the activity is independent on comonomer concentration. Increasing the ethylene pressure the productivity of the copolymerization increases and the activity shows a weak decay. Characterization of the copolymer shows that at higher pressure the cristallinity of the copolymers is higher due to lower comonomer incorporation. There is a good linear correlation of cristallinity with comonomer concentration in the feed for 1-hexene and 1-octene at a fixed pressure, but not for 4-methyl-1-pentene.     

Copolymerization of ethylene and 1-octene by homogeneous and different supported metallocenic catalysts

In this work, the performance of the homogeneous catalyst system based on Et(Flu)₂ZrCl₂/MAO was evaluated on the copolymerization of ethylene and 1-octene. Characteristics of some of the produced polymers were also investigated. A study was performed to compare this system with that of Cp₂ZrCl₂/MAO. The influence of different support materials for the Cp₂ZrCl₂ was also evaluated, using silica, MgCl₂, and the zeolite sodic mordenite NaM. An increase in activity was observed in relation to the comonomer addition for the two homogeneous catalysts. The copolymers produced by the Et(Flu)₂ZrCl₂/MAO system showed higher molecular weight and narrower molecular weight distribution. We verified that the catalyst supported on SiO₂ was the most active one, although the copolymers produced with the catalyst supported on NaM showed higher molecular weight and lower molecular weight distribution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 724–730, 2001     

Preparation of Cu/ZnO/Al2O3 catalyst under microwave irradiation for slurry methanol synthesis

Cu/ZnO/Al₂O₃ catalysts with Cu/Zn/Al ratios of 6/3/1 were precipitated and aged by conventional and microwave heating methods and tested in the slurry phase reactor for methanol synthesis. The effect of technological condition of precipitation and aging process under microwave irradiation on the catalytic performance was investigated to optimize the preparing condition of Cu/ZnO/Al₂O₃ catalyst. The results showed that the microwave irradiation during precipitation process could improve the activity of the catalyst, but had little effect on the stability. While the microwave irradiation during aging process has a great benefit to both the activity and stability of the catalyst, the catalyst aged at 80°C for 1 h under microwave irradiation possessed higher methanol space time yield (STY) and more stable catalytic activity. The activity and stability of the catalyst was further enhanced when microwave irradiation was used in both precipitation and aging processes; the optimized condition for the catalyst precursor preparation was precipitation at 60°C and aging at 80°C under microwave irradiation.     

Effect of Zr-Modified SiO2-Supported Metallocene/MAO Catalyst on Copolymerization of Ethylene/1-Octene

The study revealed enhancement (four to seven times) of catalytic activities for ethylene/1-octene copolymerization via the Zr-modified SiO₂-supported the metallocene/MAO catalyst. Increased activity can be attributed to an increase in absorption ability of MAO on the modified support. In addition, the strong interaction between MAO and the support was also considered.     

α-二亚胺镍溴化物/凹凸棒黏土负载催化剂催化乙烯聚合研究

A nickel-diimine catalyst [N, N'-bis(2,6-diisopropylphenyl)-1,4-diaza-2,3-dimethyl-1, 3-butadiene nickel dibromide, DMN] was supported on palygorskite clay for ethylene slurry polymerization. The effect of supporting methods on the catalyst impregnation was studied and compared. Pretreatment of the support with methylalumi-noxane (MAO) followed by DMN impregnation gave higher catalyst loading and catalytic activity than the direct impregnation of DMN. Catalyst activity as high as 5.42×105g PE·molNi-1·h-1 was achieved at ethylene pressure of 6.87×105 Pa and polymerization temperature of 20℃. In particular, the morphological change of the support during MAO treatment was characterized and analyzed. It was found that nano-fiber clusters formed during the support pretreatment, which increased the surface area of the support and favored the impregnation of the catalyst. The investigation of polymerization behavior of supported catalyst revealed that the polymerization rate could be kept at a relatively h     

Preparation of Cu/ZnO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst under microwave irradiation for slurry methanol synthesis

Cu/ZnO/Al₂O₃ catalysts with Cu/Zn/Al ratios of 6/3/1 were precipitated and aged by conventional and microwave heating methods and tested in the slurry phase reactor for methanol synthesis. The effect of technological condition of precipitation and aging process under microwave irradiation on the catalytic performance was investigated to optimize the preparing condition of Cu/ZnO/Al₂O₃ catalyst. The results showed that the microwave irradiation during precipitation process could improve the activity of the catalyst, but had little effect on the stability. While the microwave irradiation during aging process has a great benefit to both the activity and stability of the catalyst, the catalyst aged at 80°C for 1 h under microwave irradiation possessed higher methanol space time yield (STY) and more stable catalytic activity. The activity and stability of the catalyst was further enhanced when microwave irradiation was used in both precipitation and aging processes; the optimized condition for the catalyst precursor preparation was precipitation at 60°C and aging at 80°C under microwave irradiation.     

废轮胎热解炭低温催化焦油重整制备富氢气体的研究

以全钢型废旧轮胎为原料,通过热解、活化、浸渍、焙烧的流程制备了三种热解炭催化剂,分别为轮胎热解炭（Raw char）、轮胎热解活性炭（AC）和负载Zn的活性炭（Zn/AC）。采用N₂吸/脱附、SEM、EDS、XRD等表征方法对催化剂进行了一系列表征和分析,发现CO₂/H₂O活化可显著提高催化剂BET比表面积,最高可达380 m²·g^-1,有效改善催化剂表面结构性质,同时浸渍法使催化剂表面负载大量ZnO活性位。对三种催化剂在纤维素热解焦油重整制氢过程中的催化性能进行了研究,发现Raw char（600℃）具有最佳催化效果,相较于空白组（500℃）,热解气中H₂体积分数提高了12.4%,达到19.3%,其次为Zn/AC（500℃）组的17.8%,实现了低温下催化纤维素焦油热解制得高产率H₂。     

Copolymerisation von butadien mit 1-octen und 1-dodecen mit einem neodymkatalysatorsystem

The catalyst system neodym octoate/ethylaluminium sesquichloide/aluminium triisobutyl was used for the copolymerization of butadiene with 1-octene and 1-dodecene. The ratio of the catalyst compounds optimum for the butadiene polymerization was chosen. The effect of comonomer ratio on the copolymer composition, the conversion, the microstructure, the number-average molar mass and on the molar mass distribution was evaluated. The copolymers show a distinctly higher chain branching than polybutadiene. The copolymerization parameters determined according to Kelen-Tüdßos are very different for both copolymerizations (r_butadiene ≫ r_olefin). Copolymerization was confirmed by ¹H NMR spectroscopy and olefin metathesis.     

Study on copolymerization of ethylene/1‐hexene catalyzed by a novel polystyrene‐supported metallocene catalyst

Ethylene/1‐hexene copolymerization was carried out with polystyrene‐supported metallocene catalyst. It was found that the kinetic of the copolymerization was strongly influenced by the steric hindrance of carrier. The influences of 1‐hexene concentration in the feed on catalyst productivity and comonomer reactivity were investigated. The microstructure of resultant copolymer was analyzed by ¹³C NMR. It was found that the different carriers have slight effect on the composite of copolymer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1574–1577, 2006     

Study of the compositional heterogeneity of ethylene/1–hexene copolymers produced over supported catalysts of different composition

Separation into narrow MWD fractions (liquid–liquid fractionation) and preparative TREF (temperature rising elution fractionation) with subsequent analysis of fractions by GPC, FTIR, and ¹³C NMR spectroscopy were used to study the comonomer distribution of ethylene/1–hexene copolymers produced over highly active supported titanium‐ and vanadium‐magnesium catalysts (TMC and VMC) and a supported zirconocene catalyst. These catalysts produce PE with different MWD: M_w/M_n values vary from 2.9 for zirconocene catalyst, 4.0 for TMC, and 15 for VMC. 1‐Hexene increases polydispersity to 25 for copolymer produced over VMC and hardly affects MWD of the copolymer produced over TMC and zirconocene catalysts. The most broad short chain branching distribution (SCBD) was found for ethylene/1–hexene copolymers produced over TMC. VMC and supported zirconocene catalyst produce copolymers with uniform profile of SCB content vs. molecular weight in spite of great differences in M_w/M_n values (22 and 2.5 respectively). TREF data showed that majority of copolymer produced over supported zirconocene catalyst was eluted at 70–90°C (about 85 wt %). In the case of VMC copolymer's fractions were eluted in the broad temperature interval (40–100°C). Accordingly, TREF data indicate a more homogeneous SCBD in copolymer, produced over supported zirconocene catalyst. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Is isoprene capable of being a comonomer under metallocene catalysis to reach side chain-unsaturated isotactic polypropylene?

Isoprene (2-methyl-1,3-butadiene) was attempted as a comonomer in metallocene-catalyzed propylene polymerization to prepare side chain-unsaturated isotactic polypropylenes (i-PP). Hydrogen was added into the sluggish copolymerization of propylene and isoprene mediated by a highly isospecific metallocene complex rac-Me₂Si(2-Me-4-Ph-Ind)₂ZrCl₂/MAO. Catalyst activity was restored due to breaking by hydrogen of the stable π-allyl zirconocene species caused by 1,4-isoprene insertion. Stunningly, it was found that the generated Zr-H species had been able to take the accompanying vinylidene-terminated polymer chain for insertion as a preemptive mode of re-initiation. With a consecutive action of chain release followed by in situ reinsertion, the hydrogen-induced catalyst reactivation was not accompanied by chain termination. With the smooth occurrence of the copolymerization, the 1,2-insertion of isoprene led to the preparation of i-PP bearing pendant vinylidene groups.     

ZnO对CuO-ZnO/Al2O3催化剂催化甘油氢解性能的影响

以氧化铝为载体,采用浸渍法制备了负载型CuO-ZnO/Al2O3催化剂,通过XRD、XPS、TPR手段表征催化剂上CuO和ZnO的分布和化学形态。结果表明,CuO-ZnO/Al2O3催化剂催化甘油氢解反应中,CuO是活性组分,ZnO的引入可以降低CuO与载体氧化铝的相互作用强度,有利于CuO的还原,提高催化剂甘油氢解活性;催化剂表面呈缺电子状态的Cu物种是甘油氢解的活性中心。当活性组分CuO质量分数为12%,n(Cu)∶n(Zn)=1∶1.5时,CuO-ZnO/Al2O3催化剂催化甘油氢解活性最高,甘油转化率可达97.82%,对1,2-丙二醇选择性达94%。