High Styrene Conversion Research Articles

Efficient epoxidation of styrene over single-atomic copper-doped ordered mesoporous alumina (Cu-OMA) composited with carbon nitride

The present study assessed the catalytic performance in epoxidation of styrene using tert‑butyl hydroperoxide (TBHP) as an oxidant over single-atomic copper-doped Ordered mesoporous alumina (Cu-OMA) composited with g-C3N4 (CN). The thermal treatment at three temperatures (300, 500, 700 °C) provided a facile mean to modify the texture and electronic structure of the Cu-OMA@CN composite. The X-Ray absorption spectroscopy proved the single-atomic Cu-O-Al and Cu-O-C in Cu-OMA@CN-500 catalyst. Catalytic reaction parameters, namely temperature (60–80 °C), catalyst amount (10–70 mg), substrate/oxidant ratio (1:1–1:3), and solvents (acetone, ethanol, acetonitrile, N, N-dimethylacetamide) were optimized to obtain high conversion of styrene and selectivity to styrene epoxide. Under the optimized reaction conditions (75 °C, 30 mg of catalyst, 1:2 of styrene/TBHP and acetonitrile as solvent), the conversion decreased in the order of Cu-OMA@CN-500 > Cu-OMA@CN-300 > Cu-OMA@CN-700. This sequence was related to the formation of electron-rich single-atom copper sites, high surface area, medium alkaline environment and high content of graphic nitrogen species in Cu-OMA@CN-500. This structure differed from the blocky structure of C3N4 in Cu-OMA@CN-300 and the destroyed tri-s-triazine ring in Cu-OMA@CN-700. The most active Cu-OMA@CN-500 catalyst displayed a high styrene conversion (87.2 %) and striking selectivity to styrene oxide (90.0 %). Its catalytic activity was retained after five recyclability tests. The possible catalytic mechanism for epoxidation of styrene over this catalyst was tentatively proposed.

Fenton-like Cerium Metal–Organic Frameworks (Ce-MOFs) for Catalytic Oxidation of Olefins, Alcohol, and Dyes Degradation

AbstractA metal–organic framework (MOF) of cerium (Ce) ions and 4,4′,4′′-nitrilotribenzoic acid linker was synthesized via a hydrothermal method. Ce-MOF consists of a Lewis acid moiety, i.e. Ce3+ and triphenylamine cores. It showed Fenton-like properties with excellent catalytic oxidation activity for olefins, primary/secondary alcohols, and water pollutants e.g., organic dyes. It displayed high oxidation conversion of cinnamyl alcohol and styrene of 100% and 53%, respectively. It offered good selectivity towards styrene oxide and benzaldehyde (i.e. 75% and 100%, respectively). It was applied for the oxidative degradation of dyes e.g. rhodamine B (RhB), methyl blue (MeB), Congo red (CR), and direct blue (DB) using hydrogen peroxide (H2O2) as an oxidant. It exhibited high efficiency in the oxidative degradation of these water pollutants. The mechanistic study of oxidation involves the formation of radical hydroxyl (•OH) species. This study revealed the possibility of enhancing the oxidative catalytic performance, including oxidative degradation of organic pollutants, by employing advanced oxidation processes (AOPs) using Ce-MOF. The catalyst is recyclable five times without significantly decreasing of the material’s catalytic performance.

SU-101: a Bi(III)-based metal-organic framework as an efficient heterogeneous catalyst for the CO2 cycloaddition reaction.

A non-porous version of SU-101 (herein n-SU-101) was evaluated for the CO2 cycloaddition reaction. The findings revealed that open metal sites (Bi3+) are necessary for the reaction. n-SU-101 displays a high styrene oxide conversion of 96.6% under mild conditions (3 bar and 80 °C). The catalytic activity of n-SU-101 demonstrated its potential application for the cycloaddition of CO2 using styrene oxide.

Polyoxometalate-Incorporated Metal-Organic Network as a Heterogeneous Catalyst for Selective Oxidation of Aryl Alkenes.

Selective oxidation of aryl alkenes is important for chemical synthesis reactions, in which the key lies in the rational design of efficient catalysts. Herein, four polyoxometalate (POM)-incorporated metal-organic networks, with the formulas of [Co(ttb)(H2O)3]2[SiMo12O40]·2H2O (1), [Co(ttb)(H2O)2]2[SiW12O40]·8H2O (2), [Zn(Httb)(H2ttb)][BW12O40]·9H2O (3) and {[Zn(H2O)3(ttb)]4[Zn3(H2O)6]}[H3SiW10.5Zn1.5O40]2·24H2O (4) (ttb = 1,3,5-tri(1,2,4-triazol-1-ylmethyl)-2,4,6-trimethylbenzene), were hydrothermally synthesized and structurally characterized. Structural analysis showed that compound 1 consists of a POM-encapsulated three-dimensional (3-D) supramolecular framework; compound 2 is composed of a POM-supported 3-D coordination network; and compounds 3-4 show POM-incorporated 3-D supramolecular networks. Using selective catalytic oxidation of styrene as the model reaction, compounds 1-4 as heterogeneous catalysts display excellent performance with the double advantages of high styrene conversion and benzaldehyde selectivity owing to the synergistic effect among POM anions and transition metal (TM) centers. Among them, compound 1 exhibits the highest performance with ca. 96% styrene conversion and ca. 99% benzaldehyde selectivity in 3 h. In addition, compound 1 also displays excellent substrate compatibility, good reusability, and structural stability. Thus, a plausible reaction pathway for the selective oxidation of styrene is proposed. This study on the structure-function relationship paves a way for the rational design of POM-based heterogeneous catalysts for important catalysis applications.

Impregnation Synthesized Cu@MIL‐101(Cr) Catalyzes the Oxidation of Styrene to Benzaldehyde with TBHP**

AbstractA series of M@MIL‐101(Cr) (M=Cu, Co, Ni and Mn) adopting impregnation method were fabricated as heterogeneous catalysts to oxidize styrene to benzaldehyde with tert‐butyl hydroperoxide (TBHP). The morphology of the MIL‐101(Cr) was nicely retained after the uniform dispersion of metals. In order to obtain the optimized reaction conditions, various in‐depth investigations were carried out to evaluate the effects of reaction time and reaction temperature on catalytic efficiency. Importantly, the Cu@MIL‐101(Cr) performed best in this study, the highest styrene conversion and the benzaldehyde selectivity can reach 97.45 % and 84.39 %, respectively, which revealed the synergetic effects of Cu2+ and Cr3+ in Cu@MIL‐101(Cr) on the styrene oxidation. Furthermore, the result of a three‐cycle experiment demonstrated the good recyclability of Cu@MIL‐101(Cr) without considerable structural deterioration and loss in activation. A possible mechanism of oxidation of styrene by using Cu@MIL‐101(Cr) and TBHP was also proposed.

Copper-complexed dipyridyl-pyridazine functionalized periodic mesoporous organosilica as a heterogeneous catalyst for styrene epoxidation.

A new heterogeneous catalyst has been synthesized by immobilization of a copper complex on dipyridyl-pyridazine functionalized periodic mesoporous organosilica (dppz-vPMO). This ordered support was first prepared by a co-condensation reaction between vinyltriethoxysilane and 1,2-bis(trimethoxysilyl)ethane and further post-functionalized through a hetero Diels-Alder reaction with 3,6-di-2-pyridyl-1,2,4,5-tetrazine. Techniques such as XRD, N2 isotherms, TEM, 13C NMR, XPS and DRIFT, among others, were employed to characterize the surface functionalized materials. These results have proven the ordered mesostructure of the materials as well as the presence of novel nitrogen-chelating heterocyclic compounds on the pore surface after the post-modification process. Additionally, the successful anchoring of a copper complex on the dipyridyl-pyridazine (dppz) ligands has been confirmed. The resulting material was evaluated as a heterogeneous catalyst in the epoxidation of styrene using tert-butylhydroperoxide (TBHP) as an oxidant. Under the optimized reaction conditions, Cu@dppz-vPMO showed a high styrene conversion (86.0%) and a remarkable selectivity to styrene oxide (41.9%). Indeed, this catalyst provided excellent catalytic results in terms of stability, reaction rate, conversion and selectivity compared to other bipyridine-like copper catalysts.

Efficient organocatalytic synthesis of styrene oxide from styrene and its kinetic study in a continuous-flow microreaction system

Alkene epoxidation, which consists an important reaction in the synthesis of various fundamental chemical compounds, has aroused increasing attention in the field of organic synthesis. Hydrogen peroxide that is often considered as a green oxidant for the epoxidation of olefins is relatively unstable when reacting in batch reactor. Microreactor system possesses the advantages of high mass and heat transfer performances as well as great controllability, making it a suitable pathway for the epoxidation of olefins. In this work, a highly efficient microreaction system for epoxidation of styrene is studied. Both high conversion of styrene and excellent product selectivity could be achieved. The effects of temperature, residence time, molar fraction of catalyst, molar ratio of MeCN/t-BuOH, flow rate of H2O2 and buffer solution were studied. According to the experiment data, kinetic equation was built, which will be in favor of verifying the rationality of the reaction mechanism and optimizing experimental conditions.

Syndiospecific Polymerization of Styrene Catalyzed by Half‐titanocenes Containing Monodentate Anionic Nitrogen Ligands

Main observation and conclusionStyrene polymerization catalyzed by the half‐titanocenes CpTiCl2[1,3‐R2(CH2N)2C=N] (6b: R= 2,6‐Me2C6H3, T4: R = 2,4,6‐Me3C6H2; T5: R = 2,6‐iPr2C6H3) was carried out in the presence of methylaluminoxane (MAO). Compared to the styrene conversion (31%) and syndiospecific index (45%) using reported 6b as precatalyst, T5 bearing ligand with isopropyl substitutes on the N‐aryl‐rings exhibits much higher styrene conversion (61%) and syndiospecific index (99%), indicating that the catalytic behavior could be improved obviously by the introduction of electronic donating and steric bulky substituents. One N atom in imidazolin‐2‐iminato ligand was replaced by O atom, affording half‐titanocenes CpTiCl2[3‐C6H5(CH2N)(CH2O)C=N (T1) and CpTiCl2[2,6‐Me2(C6H3O)(NiPr2)C=N] (T2). Compared to 6b, both higher styrene conversion and syndiospecific index are afforded by using half‐titanocene T1 containing 2‐imino‐3‐phenyloxazolidine ligand. All the results illustrate that both the chemical structure and the nature of substituents of the ligand have obvious influence on the styrene conversion and syndiospecific index in the polymerization of styrene. All the resulting syndiotactic polystyrenes (sPSs) are highly syndiospecific (rrr > 99%). Correspondingly, the sPS prepared using T5/MAO catalytic system exhibits high melting point and narrow molecular weight distribution. The results might show new light on designing more efficient half‐titanocenes for styrene polymerization with both high styrene conversion and high syndiospecific selectivity.

Silver(I) Dicyanonitrosomethanide, Ag[ONC(CN)2] Complex as Catalyst for the Selective Oxidation of Styrene to Benzaldehyde

Silver(I) dicyanonitrosomethanide, Ag[ONC(CN)2] represent a 3D interwoven coordination polymer organization in which all the donor atoms of the functional groups of ONC(CN)2- are coordinated to the Ag(I). Oxidation of styrene utilizing H2O2 as an oxidant in acetonitrile (CH3CN) was used as a model reaction to investigate the catalytic potential of the Ag(I) complex. The CH3CN was chosen as the solvent based on the data collected from Conductor like Screening Model for Real Solvents (COSMO-RS) study. The data indicate that the Ag[ONC(CN)2] complex was compatible and soluble in CH3CN. Different parameters such as styrene:H2O2 molar ratio, reaction time, catalyst mass, and reaction temperature were studied. Highest styrene conversion (36%) with 100% selectivity towards benzaldehyde (BZ) was achieved when 25 mg catalyst, 1:1 styrene to H2O2 molar ratio were used. The reaction was carried out at 303 K for 3 h. The catalytic conversion of styrene to BZ is proposed to take place via [Ag-H2O2] adduct with styrene oxide (StO) as an intermediate. Molecular Electrostatic Potential (MEP) shows that the Ag atom has the highest probability to coordinate with the oxygen atom of H2O2. The MEP data confirms the proposed mechanism.

Functional hexanuclear Y(III) cluster-based MOFs supported Pd(II) single site catalysts for aerobic selective oxidation of styrene

Oxidation of styrene is one of the significant reactions in organic synthesis. In this work, a serious of PdCl2 moiety-decorated Y6-MOFs adopting post-synthetic strategy were fabricated as applicable single-site catalysts for oxidation of styrene. Specifically, the functional organic linker, H2bpydc (2,2′-bipyridine-5,5′-dicarboxylic acid), was first incorporated quantitatively into Y6 clusters-based MOF, [(CH3)2NH2]2[Y6(μ3-OH)8(bpdc)6] (bpdc = 4,4′-biphenyl dicarboxylic acid) via post-synthetic ligand exchange. Then post-synthetic Pd(II) metalation was performed to enhance the density of isolated single sites. The obtained Pd(II)-Y-bpydcx/bpdc1-x can be used as highly efficient heterogeneous single-site catalysts to promote selective oxidative cleavage of styrene to benzaldehyde using O2 as a oxidant under solvent-free and mild reaction conditions (1 atm and 80 °C). Importantly, when using Pd(II)-Y-bpydc0.8/bpdc0.2 (0.024 mmol Pd) as catalyst, the high conversion of styrene and the selectivity for benzaldehyde can reach 88.7 % and 82.2 %, respectively.

Selective oxidation of styrene to benzaldehyde by cobalt phthalocyanine-multi-walled carbon nanotube composites

Novel tetrasubstituted cobalt phthalocyanine-multi-walled carbon nanotube composites ([4a(OPh-p-Cl)CoPc]-MWCNTs) were prepared to efficient catalytic oxidation of styrene to benzaldehyde. The [4a(OPh-p-Cl)CoPc]-MWCNTs composites were characterized by UV–vis spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. In order to achieve efficient and selective catalysis, the effects of solvent types, oxidant types, catalyst amount, temperature and reaction time on catalytic performance have been studied. It was found that the [4a(OPh-p-Cl)CoPc]-MWCNTs composites performed very high catalytic activity in the styrene oxidation reaction. The highest styrene conversion (99.17%) and benzaldehyde selectivity (88.93%) were obtained under the optimum conditions of 20 mg of [4a(OPh-p-Cl)CoPc]-MWCNTs, oxidant being TBHP for 2 mL, and in THF at 80 °C for 4h. Furthermore, the possible reaction mechanism for [4a(OPh-p-Cl)CoPc]-MWCNTs composites selectively oxidized styrene to benzaldehyde was also proposed.

Novel tetrasubstituted zinc phthalocyanine-attapulgite composites for efficient catalytic oxidation of styrene with tert-butyl hydroperoxide as oxidant

Novel tetrasubstituted zinc phthalocyanine-attapulgite ([ZnPc(OC10H14N)4]-ATP) composites were prepared by an ultrasonic impregnation method. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. The prepared [ZnPc(OC10H14N)4]-ATP composites are used as the catalyst for styrene oxidation reaction to obtain the major products of styrene oxide and benzaldehyde, and the effects of solvent, oxidant, temperature, time and catalyst dosage on the reaction were investigated. The results showed that the [ZnPc(OC10H14N)4]-ATP composites exhibited high catalytic activity in the styrene reaction with the solvent being DMF and the oxidant being TBHP. The highest styrene conversion (84.13%) was obtained under the optimum conditions of 6 h, 100 °C and 20 mg of catalyst. Additionally, the possible mechanism of selective oxidation of styrene by [ZnPc(OC10H14N)4]-ATP composites was also proposed.

Catalytic Role of Pd(II) Ions in Mg–Al Hydrotalcites for the Oxidation of Styrene

Pd(II) ions were introduced into Mg0.7Al0.3(OH)2(CO3)0.15·mH2O through the co-precipitation of the corresponding nitrate salts at a constant pH value. The presence of Pd in the brucite-like layers affects an increased surface area and decreased crystal domain of the Mg–Al hydrotalcite catalysts. Pd(II) ions may exist in both intra- and extra- brucite-like layers and exhibit different roles in the oxidation of styrene with t-BuOOH, depending on the amount of palladium. The insertion of Pd(II) into the hydrotalcite lattice has significantly improved the catalyst stability. The highest conversion of styrene is about 80% for the production of styrene oxide and benzaldehyde at low temperatures.

Degradation of Styrene from Waste Gas Stream by Advanced Oxidation Processes

Waste‐air treatment is experimentally investigated by advanced oxidation processes utilizing UV irradiation combined with ozone and hydrogen peroxide. The effect of operating parameters, such as an initial concentration of styrene and flow rate of gas, on the removal of styrene is studied in a photochemical pilot plant unit. The conversion of styrene decreases with an increasing initial styrene concentration and with a decreasing retention time (higher flow rate) of waste gas. The highest conversion of styrene (87%) is achieved under lower initial styrene concentration (100 ppm) and lower flow rate (42 m3 h−1). The energy per order is also calculated for the advanced oxidation process. Electrical energy per order is calculated for all the experimental conditions and it was found that the energy consumption is of about 0.070 kWh m−3 per order, for the 87% styrene removal at 100 ppm of initial styrene concentration and 42 m3 h−1 flow rate. The combination of UV irradiation and ozone is significantly more efficient with lower electrical energy need per order in comparison with combination of UV irradiation and hydrogen peroxide. Therefore, the advanced oxidation process represents a promising treatment technology for the management of waste‐air, and the pilot plant unit designed for high flow rates of waste‐gas streams is suitable for an industrial use.

Hierarchical hollow nickel silicate microflowers for selective oxidation of styrene

Developing heterogeneous non-precious metal catalysts that can achieve high catalytic activity and good product selectivity at the same time is still a challenging and interesting work for the selective oxidation of styrene into valuable chemicals from environmental and industrial points of view. Herein, hierarchical hollow nickel silicate (Ni3Si2O5(OH)4) microflowers assembled from well-defined Ni3Si2O5(OH)4 nanosheets have been prepared by a facile one-pot hydrothermal method. The intriguing structure endows the hollow Ni3Si2O5(OH)4 microflowers a high surface area of 177.4 m2 g−1 and an average pore size of 3.9 nm. When employed as a catalyst for the selective oxidation of styrene in the presence of hydrogen peroxide as a ecological sustainable green oxidant, the Ni3Si2O5(OH)4 exhibits an attractive catalytic performance with a remarkably high styrene conversion of 99.3% and a high selectivity of 81.1% to benzaldehyde.

Stable poly (ionic liquids) with unique cross‐linked mesoporous‐macroporous structure as efficient catalyst for alkylation of o‐xylene and styrene

In this work, using divinylbenzene (D), 1‐vinylimidazole (V) and 1‐vinyl‐3‐butylimidazolium bromide ([VBIM][Br]) as monomers, the binary‐monomer poly (ionic liquids) (PILs) and ternary‐monomer PILs were successfully synthesized, via hydrothermal polymerization and anion exchange, sequentially. Compared with each other, the ternary polymeric acidic IL catalyst has a clear spongy porous structure, while having a more stable macroporous structure, a larger specific surface area, more acidic groups and more active sites. Catalytic performance of catalyst was investigated through the alkylation of o‐xylene and styrene. The effect of the amount of IL added and the length of the cation chain on the ternary polymerization of acidic IL was systematically investigated. Under optimal reaction conditions (molar ratio of monomers was D:V:[VBIM][Br] = 2:1:1, the most suitable cation chain length was C4), the synthesized MPD‐[C4V]‐[VBIM][SO3CF3] has a larger specific surface area (89.47 m2/g), large pore volume (0.29 cm3/g), and abundant mesopores and macropores, which help to improve the contact between the active site and reactants. Moreover, the catalyst could maintain a relatively high conversion of styrene (99.0%), 1,2‐diphenylethane yield (98.7%) and high thermostability under reaction and be easily be divided from the solution, which is critical for heterogeneous solid catalysts.

Functional mesoporous poly (ionic liquid) derived from P123: From synthesis to catalysis and alkylation of styrene and o‐xylene

A novel strategy was proposed for the fabrication of high‐performance acidic mesoporous poly ionic liquids catalyst. In this work, mesoporous poly ionic liquids (MPILs) were synthesized with P123 (PEO20PPO70PEO20) served as pore‐forming agent. Then, MPILs were treated with PW3− anion exchange, thereby fabricating PW/MPIL‐S(x). MPIL and PW/MPIL‐S(x) were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), Thermogravimetric analysis (TA), N2 adsorption–desorption and Fourier transform infrared (FT‐IR) spectra and X‐ray photoelectron spectroscopy (XPS) spectra. The effect of solvent and concentration of P123 on the morphology and mesoporous structure of MPILs were investigated systematically. And the results show that MPILs were featured with mesoporous channel structure, high surface area (up to 737 m2/g) and large pore volumes (1.16 cm3/g), which benefit heterogeneous phase reaction (such as, alkylation of styrene with o‐xylene). In the alkylation reaction, under optimal reaction conditions, the catalyst PW/MPIL‐THF (4.0 g) shows high conversion of styrene (100%) and PXE yield (96.21%), demonstrating the excellent catalytic activities. Furthermore, PW/MPIL‐S(x) are easy to be separated from the catalytic system by filtration and show no obvious decrease in catalytic activity after 6 cycle runs. The obtained PW/MPIL‐S(x) catalyst exhibit high thermal and mechanical stability as well, indicating extensive application in high temperature acidic catalysis. This work might open up a new method for the synthesizing of porous polymer catalysts in the future.

Highly efficient CuCr-MMO catalyst for a base-free styrene epoxidation with H2O2 as the oxidant: synergistic effect between Cu and Cr.

The base-free styrene epoxidation with H2O2 as an oxidant was strongly in accordance with the requirements for a sustainable chemical industry. Aiming at the low efficiency of a non-noble metal catalyst system, we proposed utilizing the synergistic effect and manipulating the surface acid-basic property of materials to increase the catalytic performance in this reaction. Herein, to combine two promoting approaches, we synthesized a series of mixed metal oxide (MMO) materials to screen promising active components with a suitable acid-basic property for H2O2-styrene epoxidation. As a result, the highest styrene conversion (82.8%) and best styrene oxide selectivity (79.7%) were achieved over a CuCr-MMO catalyst. The catalytic performance was considerably enhanced compared with the CuO and CrOx references. Detailed characterizations were performed to investigate the dispersion, electronic structure, and acid-basic property to explain the structure-performance relationship. On one hand, the promoted dispersion of the Cu and Cr components contributed to more catalytic sites and the electron transfer between Cu and Cr improved the intrinsic activity, which were both responsible for the enhanced activity. On the other hand, the unique structure modulated the acid-basic properties to be suitable for this catalytic system. In particular, a suitable basicity was facilitated to selectively transform H2O2 into HOO˙ radicals, while a low acidity suppressed the epoxide ring opening to form phenylacetaldehyde. By combining the high accessibility, suitable basic-acid property, and fast electron transfer, CuCr-MMO exhibited a high styrene conversion and selectivity to styrene oxide.

Effect of graphitization degree of electrospinning carbon fiber on catalytic oxidation of styrene and electrochemical properties

Ag/carbon nanofibers and carbon nanofibers were prepared through electrospinning and high temperature carbonization. The catalyst was investigated through oxidation of styrene. The highest conversion of styrene respectively got to 98% and 70% when calcination temperature got to 1200 °C. CNFs (carbon nanofibers) have not only excellent catalytic performance but also relatively large accessible ion surface area to accommodate greater capacity and high graphitization degree to accelerate ion diffusion. CNFs exhibited excellent electrochemical performance for use as supercapacitors with high specific capacity of 271.1 F g−1 at current density of 0.5 A g−1, good rate capability and superior cycling stability over 3050 cycles.

High Conversion of Styrene, Ethylene, and Hydrogen to Linear Monoalkylbenzenes.

1-Alkylbenzenes as a precursor of surfactants, can be produced from ethylene, styrene, and hydrogen. These intermediates, lacking tertiary carbons, are environmentally more benign than commercial ones that bear the aromatic ring linked to an internal carbon of the aliphatic chain. The one-pot synthesis of highly linear 1-alkylbenzenes (LABs) through the homogeneous catalysis of olefin poly-insertion from cheap and largely available reagents can be carried out with a high turnover and selectivity. A purposely designed reactor that allows for the fine control of the three components feed, along with temperature, plays a key role in this achievement. A turnover of 194 g of LABs per mmol of catalyst per hour can be obtained with the simultaneous removal of polyethylene as a by-product.