Catalytic Cracking Of Low-density Polyethylene Research Articles

Synthesis of ZSM-5 Zeolites from Quang Ninh Coal Ash Components and Activity for Catalytic Cracking of Low-density Polyethylene

Synthesis of ZSM-5 Zeolites from Quang Ninh Coal Ash Components and Activity for Catalytic Cracking of Low-density Polyethylene

Catalytic cracking of low-density polyethylene dissolved in various solvents: product distribution and coking behavior

Catalytic cracking of low-density polyethylene dissolved in various solvents: product distribution and coking behavior

The production and electrochemical performance of carbon nano-materials derived from plastics over nickel-based catalysts with different supports

This paper demonstrates a promising method for converting waste plastics into high-value carbon nano-materials as electrode materials. Therein, the catalytic performances of the three catalysts with different supports (Ni/γ-Al2O3, Ni/CaO and Ni/MgO) for carbon nano-materials derived from the catalytic cracking of low-density polyethylene in a two-stage reaction system were investigated. Compared with other carbon precursors, the hydrogen in the pyrolysis gas from plastics facilitated the growth of CNTs. Through the analysis of the physicochemical properties, the γ-Al2O3 support could improve the dispersion of NiO, which was beneficial to increasing the yield and uniformity of CNTs. The proper interaction of NiO with the γ-Al2O3 was conducive to improving the degree of graphitization of CNTs. The results showed that CNTs-A (from Ni/γ-Al2O3) obtained a specific capacitance of 32 F g−1 (0.5 A g−1, 6 M KOH), compared to CNTs-C (from Ni/CaO) and CNTs-M (from Ni/MgO) increased by 23% and 68%, respectively. It was demonstrated that CNTs-A with fewer defects, large specific surface area and high graphitization properties could achieve higher electrochemical performance by reducing the resistance during electron transfer.

Efficient Pyrolysis of Low-Density Polyethylene for Regulatable Oil and Gas Products by ZSM-5, HY and MCM-41 Catalysts

In this research, catalytic cracking of low-density polyethylene (LDPE) has been carried out in the presence of three kinds of typical molecular sieves, including ZSM-5, HY and MCM-41, respectively. The effects of different catalysts on the composition and quantity of pyrolysis products consisting of gas, oil and solid material were systematically investigated and summarized. Specially, the three kinds of catalysts were added into LDPE for pyrolysis to obtain regulatable oil and gas products (H2, CH4 and a mixture of C2–C4+ gaseous hydrocarbons). These catalysts were characterized with BET, NH3-TPD, SEM and TEM. The results show that the addition of MCM-41 improved the oil yield, indicating that the secondary cracking of intermediate species in primary pyrolysis decreased with the case of the catalyst. The highest selectivity of MCM-41 to liquid oil (78.4% at 650 °C) may be attributed to its moderate total acidity and relatively high BET surface area. The ZSM-5 and HY were found to produce a great amount of gas products (61.4% and 67.1% at 650 °C). In particular, the aromatic yield of oil production reached the maximum (65.9% at 500 °C) when the ZSM-5 was used. Accordingly, with the three kinds of catalysts, a new environment-friendly and efficient recovery approach may be developed to obtain regulatable and valuable products by pyrolysis of LDPE-type plastic wastes.

Selective Formation of p-Xylene in Catalytic Cracking of Low-density Polyethylene Using Simultaneously Generated ZSM-5 and Mesoporous Silica with Gel Skeletal Reinforcement

Silica-coated ZSM-5 with high crystallinity and related hierarchical catalysts using simultaneous generation of ZSM-5 and mesoporous silica with gel skeletal reinforcement exhibited high selectivity for p-xylene among a xylene mixture in catalytic cracking of low-density polyethylene, which reached more than 95%. A linear relationship appeared between mesoporous pore volume and the relative activity per acidic site calculated by the conversion and NH3-TPD, suggesting that the formation of hierarchical structure would increase the activity per active site.

Elucidating the structure-performance relationship of typical commercial zeolites in catalytic cracking of low-density polyethylene

Zeolite exhibits excellent catalytic performance in the catalytic cracking of polyolefins, but the reaction results are often controversial due to the differences in the lab-scale synthesized zeolites and the types of reactors selected. In this work, in order to eliminate the differences of catalysts synthesized by individual researchers, we studied the catalytic performance of four typical commercial zeolites (HZSM-5, Hβ, HY and SAPO-11) in the cracking of low-density polyethylene (LDPE) by self-designed batch reactor. By comparing the reaction performance of four zeolites under the same condition and correlating with the pore structure and acidity of the zeolites, it was found that the acid strength of zeolites was positively correlated with the cracking conversion. HZSM-5 and Hβ zeolites with high acid strength achieved a LDPE conversion of above 94%. Large micropore is beneficial to the formation of isomerized products, but promotes the formation of coke precursors, resulting in serious coking. By analyzing the product distribution over different zeolites, it was observed that Hβ achieved the highest yield of gasoline components. HZSM-5 and HY exhibited high yields of aromatization products. The high aromatization activity of HZSM-5 was attributed to its strong acidity which enhanced the hydrogen transfer process, while HY possesses high concentrations of both Brönsted and Lewis acid sites, and the synergistic effect of these two acid sites promotes the aromatization process.

Thermal Catalytic-Cracking Low-Density Polyethylene Waste by Metakaolin-Based Geopolymer NaA Microsphere.

Metakaolin-based geopolymer microspheres (MGM) with hierarchical pore structures were prepared by suspension dispersion method in dimethicone at 80 °C. The hydrothermal modification of MGM was carried out at a lower temperature of 80 °C, and a NaA molecular sieve converted from metakaolin-based geopolymer (NMGM) with good crystal structure was prepared and applied in thermal catalytic cracking of low-density polyethylene (LDPE) reaction. The one-pot two-stage thermal catalytic cracking of LDPE was carried out in a 100 mL micro-autoclave under normal pressure. In this work, the optimal proportions and optimal reaction conditions of catalysts for NMGM thermal catalytic cracking of LDPE waste to fuel oil were investigated. The NMGM catalyst showed high selectivity to the liquid product of thermal catalytic cracking of waste LDPE. Under the reaction conditions of reaction time of 1 h and reaction temperature of 400 °C, the liquid-phase yield of thermal catalytic cracking of LDPE reached a high of 88.45%, of which the content of gasoline components was 10.14% and the content of diesel components was 80.97%.

Fe-POM/attapulgite composite materials: Efficient catalysts for plastic pyrolysis.

This article describes the catalytic cracking of low-density polyethylene over attapulgite clay and iron substituted tungstophosphate/attapulgite clay (Fe-POM/attapulgite) composite materials to evaluate their suitability and performance for recycling of plastic waste into liquid fuel. The prepared catalysts enhanced the yield of liquid fuel (hydrocarbons) produced in cracking process. A maximum yield of 82% liquid oil fraction with a negligible amount of coke was obtained for 50% Fe-POM/attapulgite composite. Whereas, only 68% liquid oil fractions with a large amount of solid black residue was produced in case of non-catalytic pyrolysis. Moreover, Fe-POM/attapulgite clay composites showed higher selectivity towards lower hydrocarbons (C5-C12) with aliphatic hydrocarbons as major fractions. These synthesised composite catalysts significantly lowered the pyrolysis temperature from 375°C to 310°C. Hence, recovery of valuable fuel oil from polyethylene using these synthesised catalysts suggested their applicability for energy production from plastic waste at industrial level as well as for effective environment pollution control.

Catalytic cracking of low-density polyethylene over zeolite-containing hierarchical two-layered catalyst with different mesopore size using Curie point pyrolyzer

Zeolite-containing hierarchical two-layered (ZC2L) catalysts were prepared by the gel skeletal reinforcement method. Their reactivity was estimated in catalytic cracking of low-density polyethylene (LDPE) at 590°C using a Curie point pyrolyzer method. In addition, the “relative activity” per amount of zeolite in the catalyst was calculated, and the relationship between the pore and acid properties of each catalyst was investigated. The results suggested that the presence of both mesopores and the strong acid sites of zeolite would be closely related to the increase in activity. ZSM-5-ZC2L catalysts showed much higher aromatics selectivity especially for toluene and p-xylene than ZSM-5 single and kaolin-mixed catalysts. In contrast to the cases of ZSM-5-containing catalysts, β-zeolite-containing catalysts and Y-zeolite-containing catalysts selectively produced i-olefins and i-paraffins, respectively. The product selectivity of the ZC2L catalyst was influenced by the size of the micropores of the zeolite while the hierarchical ZC2L catalysts with a small amount (26 wt%) of zeolite exhibited the higher activity than zeolite single catalysts.

Opening up ZSM-5 Hierarchical Zeolite's Porosity through Sequential Treatments for Improved Low-Density Polyethylene Cracking.

An adequately tuned acid wash of hierarchical ZSM-5 zeolites offers a levelling up in the catalytic cracking of low-density polyethylene. Identification of crucial and limiting factors governing the activity of the zeolite was extended with studies about the accessibility of acid sites, nature of the realuminated layer and role of Lewis acid sites. The sequential treatment of a ZSM-5 zeolite offered enhanced activity in low-density polyethylene (LDPE) cracking at low and high conversions, as confirmed by a decrease in the temperatures needed to reach 20% and 80% conversion (T20 and T80, respectively). A linear dependence of the T80 on the coupled IHF (indexed hierarchy factor) and AFB (accessibility factor) highlighted the importance of the textural and acidic parameters in the catalytic cracking of LDPE. Operando FT-IR-GC studies confirmed a higher fraction of short-chain hydrocarbons (C3–C5) in the product distribution of hierarchical catalysts resulting from the effective polymer cracking in easily accessible pores.

Evaluation of the Textural Parameters of Zeolite Beta in LDPE Catalytic Degradation: Thermogravimetric Analysis Coupled with FTIR Operando Studies

Zeolite-based catalysts are globally employed in many industrial processes, such as crude-oil refining and bulk chemical production. In this work, the cracking of low-density polyethylene (LDPE) was thoroughly followed in a FTIR operando study to examine the catalytic efficiency of purely microporous zeolites β of various textural characteristics. To provide complementary and valuable information on the catalytic activity of the zeolite β studied, the thermogravimetric analysis results were compared with yields of the products generated under operating conditions. The reaction products were analyzed via GC–MS to determine the hydrocarbon chain distribution in terms of paraffin, olefins, and aromatics. The individual impact of textural and acidic parameters on catalytic parameters was assessed. The accumulation of bridging hydroxyls of high strength in the zeolite β benefited the decrease in polymer decomposition temperature. Through a strategic comparison of purely microporous zeolites, we showed that the catalytic cracking of LDPE is dominated by the acidic feature inherent to the microporous environment.

Chemical Crosslinking Assembly of ZSM-5 Nanozeolites into Uniform and Hierarchically Porous Microparticles for High-Performance Acid Catalysis.

Hierarchically porous zeolites combining the advantages of desirable mass transport of nanozeolites and easy separation and handling of micro-zeolites are ideal candidates in catalytic applications. Facile routes for the assembly of zeolite microparticles with hierarchical porosity and high mechanical strength are much expected. Herein, based on a microfluidic jet spray drying technology, we report a facile and scalable chemical crosslinking assembly strategy for the synthesis of hierarchical zeolite microparticles by directly using the conventional as-synthesized nanozeolite suspension as a precursor. This route not only avoids the energy-intensive centrifugal separation process of nanozeolites but also significantly increases the uniformity and mechanical strength of the microparticles. The soluble aluminosilicate species act as a stabilizer to improve the droplet stability during the drying process and then as a "cross-linker" to chemically bind and interconnect zeolite nanoparticles to form robust bodies after drying and calcination. Zeolite microparticles with variable morphologies (spherical, bowl-like, and dimpled) and uniform and controllable sizes (from 70 to 108 μm) can be obtained by adjusting the experimental parameters. The particle formation mechanism is discussed based on the zeolite microparticles obtained from the purified nanozeolite suspension as a control. The zeolite microparticles possess emerged uniform mesopores (∼6 nm) and a well-maintained high surface area, large pore volume, high microporosity, and strong acidity of the original nanozeolites. As a result, they exhibit excellent acid catalytic performances in acetolysis of epichlorohydrin and catalytic cracking of low-density polyethylene, far better than those of the commercial ZSM-5.

Operando Study Reveals the Superior Cracking Activity and Stability of Hierarchical ZSM-5 Catalyst for the Cracking of Low-Density Polyethylene.

A new theoretical and practical framework has been developed through operando study of the zeolite catalytic cracking of low-density polyethylene (as a model reaction) under reaction conditions. Results show that microporous ZSM-5 gives rise to less cracking products. Hierarchical ZSM-5 zeolites are more active cracking catalysts, rendering more C2 -C5 hydrocarbons, with a delayed deactivation due to the secondary porosity. This tool in combination with thermogravimetric analysis provides complementary and valuable information for the study, and design of advanced catalysts.

The catalytic cracking of sterically challenging plastic feedstocks over high acid density Al-SBA-15 catalysts

The catalytic cracking of polyolefinic waste materials over solid acid catalysts, such as zeolites, is a promising process for the production of useful fuels and chemicals. However, the inherent diffusional constraints of the microporous zeolites restrict the access of bulky polyolefin molecules to the active site, therefore limiting their effectiveness. To address this, a simple yet effective method of producing mesoporous Al-SBA-15 materials with a high density of Brønsted acid sites has been employed. These catalysts are shown to be very active for the catalytic cracking of low density polyethylene (LDPE), a common waste plastic. The acidic and textural properties of the catalysts were characterised by ICP-OES, XPS, XRD, N2 physisorption, propylamine-TPD, pyridine-FTIR and STEM and have been correlated with their catalytic activity. The product distribution from the catalytic cracking of LDPE has been shown to depend strongly on both the pore architecture and the Al content of the SBA-15 and thus the density and strength of Brønsted acid sites. Fine-tuning the Al content of the SBA-15 materials can direct the product distribution of the hydrocarbons. The Al-SBA-15 materials display increased cracking orientated towards aliphatic hydrocarbons compared to ZSM-5, attributed to the mesoporous nature of SBA-15, overcoming diffusional limitations.

Highly efficient catalytic degradation of low-density polyethylene Using a novel tungstophosphoric acid/kaolin clay composite catalyst

In order to take advantage of the Bronsted acidity of tungstophosphoric acid (TPA) and Lewis acidity of kaolin, TPA-loaded kaolin catalysts with varying percentages of TPA (10-50 wt.-%) were prepared by wet impregnation method. Fourier transform infrared spectrometer, X-ray diffractometer, Brunauer-Emmett-Teller surface area analyzer, and scanning electron microscope characterizations were performed to confirm the successful loading of TPA on kaolin. Catalytic cracking of low-density polyethylene (LDPE), by employing TPA-loaded kaolin as the catalyst, produced a higher percentage of fuel oil (liquid and gaseous hydrocarbons) with a negligible amount of semisolid wax (1.0 wt.-%). The wax amount was significantly lower compared to the thermal cracking, which produced $\sim $22 wt.-% solid black residue. Moreover, GC-MS analysis of oil showed that thermal cracking produced mainly higher hydrocarbons (C$_{22})$ as compared to the catalytic cracking where larger fraction of lower hydrocarbons were obtained. We purpose that the higher performance of prepared catalysts was due to the presence of both Bronsted and Lewis acid sites, which increase their catalytic efficiency and degraded LDPE at the relatively lower temperatures. These results suggest that prepared materials were effective catalysts with low cost and easily scalable production method, suitable for large-scale high performance catalytic cracking of polymers.

Catalytic Cracking of LDPE Dissolved in Benzene Using Nickel-Impregnated Zeolites

Among the various processes and reactor designs in polymer cracking, catalytic cracking of polymer dissolved in solvent offers interesting features. In the present research, catalytic cracking of low-density polyethylene (LDPE) dissolved in benzene in a fixed-bed reactor was studied. The catalysts used included three zeolites in original form and nickel (Ni)-impregnated forms. The LDPE conversions achieved were high (>98%) despite the short retention times. The catalytic cracking of LDPE produced liquid in the gasoline range, gases ranged from C1 to C4, and hydrogen gas. The increase in catalyst acidity improved gas yield at the expense of the liquid yield. Although high catalyst acidity had less influence toward liquid product composition, it led to higher degree of cracking of the gaseous products. The dissolution of LDPE in benzene led to high cracking rate despite short retention time and produced liquid products that can be used as fuels.

Bidimensional ZSM-5 zeolites probed as catalysts for polyethylene cracking

Lamellar and pillared ZSM-5 zeolites (L-ZSM-5 and PI-ZSM-5, respectively) were synthesized and tested in the catalytic cracking of low-density polyethylene (LDPE).

Catalytic cracking of LDPE over nanocrystalline HZSM-5 zeolite prepared by seed-assisted synthesis from an organic-template-free system

The catalytic cracking of low density polyethylene (LDPE) was accomplished using nanocrystalline HZSM-5 zeolites. Nanocrystalline ZSM-5 zeolites were synthesized by a seed-assisted method from an organic-template-free system employing three different seeding strategies: two of these strategies based on aqueous clear solutions containing the ZSM-5 precursors (silanized and non-silanized) and the third strategy based on a commercial ZSM-5 zeolite in powder form. The plastic cracking reactions were carried out at 380–420°C, employing really mild conditions (plastic to catalyst mass ratio of 100). Nanocrystalline HZSM-5 zeolites prepared by seed-induced synthesis based on liquid solutions exhibit a superior catalytic activity than the reference microcrystalline zeolite. Conversion values very close to 100% are achieved at 420°C, by using these catalysts, while significant conversion values (>50%) are still attained at 380°C. Moreover, these nanocrystalline HZSM-5 zeolites promote the production of a high proportion of light olefins (>60% at 380°C), propylene, 1-butene, isobutene, being the main products (∼50%). Nanocrystalline HZSM-5 synthesized from a clear solution containing an organic structure-directing agent (TPA+) exhibits a 100% conversion value at 380°C. However, the economic and environmental advantages of the seed-assisted synthesis from a TPA+ free system and the remarkable activity showed by the nanocrystalline zeolites obtained, makes of these materials interesting catalysts in the LDPE catalytic cracking.

Mesoporous materials with enhanced porosity and acidity to obtain clean fuels from low-density polyethylene (LDPE) cracking

Mesoporous materials with Si/Al ratio 7, 19 and 23 have been synthesized from ZSM-5 zeolite precursors prepared from tetrapropylammonium cations-containing clear aluminosilicate solutions, in the presence of the surfactant cetyltrimethylammonium bromide, and by employing different precursors of secondary mesoporosity or mesoporogen agents, such as nanometric carbon particles (BP700 and BP2000) and the biopolymer chitosan. The synthesized materials were characterized by X-ray diffraction, FT infrared spectroscopy, thermogravimetric analysis, electron microscopy, chemical analysis and nitrogen adsorption. It has been found that the effect of the pore-forming agents depends on the Si/Al ratio of the material, it is very small for Si/Al = 7, while for Si/Al above 19, there is a substantial increase of the secondary mesoporosity due to the mesoporogen agent, being this effect more evident for the sample with Si/Al = 23. For this material, in addition to the porosity associated to pores with a narrow size distribution centered at 3.7 nm due to the surfactant, secondary mesopores with a size distribution centered at 20–30 nm for carbon nanoparticles and in the range 4–10 nm for chitosan, are also detected. The acidity of the samples increases with their Si/Al ratio, and no significant effect of the porogen agent on the acidity has been found. The catalytic properties of these materials were tested in the conversion of m-xylene and in the cracking of low-density polyethylene (LDPE). Noticeable differences in the activity and selectivity of the gas/liquid products obtained in the catalytic cracking of LDPE were observed.

Stability of ZSM-11 and BETA zeolites during the catalytic cracking of low-density polyethylene

The stability of H-ZSM-11 (H-Z) and H-BETA (H-B) zeolites during the catalytic degradation of low-density polyethylene (LDPE) was studied using the same sample of catalyst in eleven consecutive cycles. The gaseous hydrocarbons, liquid hydrocarbons and waxes generated in each cycle were analyzed as well as the used catalyst. The zeolites were characterized by XRD, FTIR of adsorbed pyridine and N 2 adsorption, while the physical mixtures of LDPE/zeolites were subjected to TG-DTG analysis.The H-Z zeolite exhibited an important stability during the successive cycles of LDPE conversion. On the contrary, the behavior H-B zeolite was completely different; from the sixth cycle the yields of products changed progressively, approaching to that obtained in a purely thermal process. The yields of accumulated coke increased steadily throughout the cycles up to maximum values in the eleventh cycle of ∼6 and ∼15 wt% for H-Z and H-B, respectively. These results were confirmed by TG under air flow.