Nanocrystalline HZSM-5 Zeolite Research Articles

Moderate pressure boosts the aromatization activity of HZSM-5 zeolite during catalytic pyrolysis of lignocellulosic materials

Lignocellulose pyrolysis has been deeply investigated in the past years as a potential route for the production of advanced biofuels and biochemicals from residues and wastes. However, the effect of pressure has rarely been addressed in catalytic pyrolysis processes. Accordingly, the current work reports a comprehensive study on the pressure influence during the catalytic pyrolysis of different lignocellulosic materials (oak wood, cellulose, hemicellulose, and lignin) using nanocrystalline HZSM-5 zeolite as a catalyst and a downflow fixed-bed reactor. In thermal pyrolysis tests, pressure increase affects negatively the bio-oil* (organic components in the liquid products) since it reduces its yield in favor of the production of char and gases. However, in the case of the catalytic pyrolysis tests, working under moderate pressure (10 bar) has very positive effects on bio-oil upgrading, minimizing its oxygen concentration (< 10 wt.%) and sharply increasing the carbon yield of aromatic hydrocarbons, while the undesirable coke deposited on the catalyst surface can be even reduced. This finding denotes the occurrence of a remarkable synergistic effect between the pyrolysis pressure and the catalyst loading. These outstanding results are attributed to a more efficient activity of the zeolite under mild pressurization since both oxygenated species and light olefins are more strongly adsorbed over the catalyst surface, facilitating their subsequent transformation into aromatic hydrocarbons. The sharp enhancement of the deoxygenation and aromatization activity does not involve higher coke deposition over the zeolite surface, thus attenuating one of the major limitations of the lignocellulose catalytic pyrolysis process.

Effect of the Si/Al Ratios of Nanocrystalline HZSM-5 Zeolite on the Performance in Catalytic Conversion of Ethanol to Propylene

Effect of the Si/Al Ratios of Nanocrystalline HZSM-5 Zeolite on the Performance in Catalytic Conversion of Ethanol to Propylene

Enhanced Production of Aromatic Hydrocarbons by Rapeseed Oil Conversion over Ga and Zn Modified ZSM-5 Catalysts

Rapeseed oil conversion has been investigated over catalysts based on Ga- and Zn-modified nanocrystalline HZSM-5 zeolite aimed to the production of hydrocarbons that could be used as both raw chemicals and/or fuels. The reactions have been carried out in a fixed bed reactor operating under nitrogen at 550 °C and atmospheric pressure. The incorporation of the metallic species to the parent zeolite was carried out by wetness-impregnation, resulting in a good metal dispersion, which is facilitated by the relatively high external surface area available in the nanocrystalline zeolitic support. This metal addition causes significant changes in the textural and acidic properties of the ZSM-5 zeolite. In all cases, a high deoxygenation degree of the raw oil was achieved through the formation of CO, CO2, and H2O, whereas the main products obtained were light olefins (mainly ethylene and propylene) and aromatic hydrocarbons (BTX). The incorporation of Ga and Zn in the parent zeolite increased the formation of gasol...

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.

Catalytic upgrading of pyrolytic vapors from the vacuum pyrolysis of rape straw over nanocrystalline HZSM-5 zeolite in a two-stage fixed-bed reactor

This investigation involved the vacuum pyrolysis of biomass (rape straw) and the online catalytic upgrading of pyrolytic vapors in the second stage of the reactor. Based on the previous study on vacuum pyrolysis of biomass, effects of the operating factors including catalyzing temperature, biomass to catalyst mass ratio and catalyst Si/Al ratio on product yields and qualities have been studied using nanocrystalline HZSM-5 zeolite. Optimization of the oil phase yield was further conducted by employing response surface methodology (RSM). The statistical analysis showed that the operating factors significantly affected the product yields. The optimal conditions for the maximum oil phase yield were obtained at catalyzing temperature of 491.2°C, biomass to HZSM-5 mass ratio of 0.302 and catalyst Si/Al ratio of 53.3. Confirmation runs gave 9.82% and 9.80% of the oil phase yield compared to 9.90% of predicated value. The H/C, O/C molar ratios (dry basis), density, pH value, dynamic viscosity and high heat value of the oil phase obtained at optimal conditions were 1.518, 0.195, 0.96g/cm3, 5.15, 5.12mm2/s and 33.80MJ/kg, respectively. Liquid product compositions were examined using gas chromatography/mass spectrometry (GC/MS). A large amount of aromatic hydrocarbons and light phenols were detected in the oil phase which contributed to a relatively low polydispersity of 1.35 (M¯n=218.14 g/mol and M¯w=293.73 g/mol). The aqueous phase also contained a large number of light aromatics. The use of nanocrystalline HZSM-5 caused a remarkable increase of the desirable compounds including aromatic hydrocarbons, light phenols and alcohols, and a significant decrease of the unstable and corrosive compounds (e.g., acids, aldehydes and ketones). Besides, thermo-gravimetric analysis of the oil phase was conducted within air atmosphere. It was indicated that the oil phase had higher yield and qualities which might be used as an engine fuel.

Direct Synthesis of Nanocrystalline HZSM-5 Zeolite via Varying-Temperature Hydrothermal Synthesis

A nanocrystalline HZSM-5 zeolite was directly synthesized by two-stage varying-temperature synthesis method. The effects of second stage time and temperature on the particle size and morphology were of interest. The morphology of particles were specified by scanning electronic microscopy (SEM) and crystallinity of the samples were recorded by X-ray diffraction (XRD) test results. It was observed that second stage time had a strong effect on crystallinity and morphology; a highly crystalline ZSM-5 zeolite with twinned crystals was synthesised at 180 °C, 60h (second stage time and temperature ). The HZSM-5 particles synthesised at 180 °C, 18h (second stage time and temperature ) were 300600 nm in size and constructed by primary HZSM-5 nanocrystals of 20~30 nm.

A Study of HZSM-5 Membrane Synthesis on α-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Supports

Porous α-alumina supports were seeded with monodisperse nanocrystalline HZSM-5 zeolite and calcined. The supports were treated in a synthesis solution to grow the seeds into HZSM-5 membrane with aluminum nitrate (Al (NO3)3), tetraethyl orthosilicate (TEOS), and tetrapropyl ammonium hydroxide (TPAOH) as raw materials. X-ray diffraction (XRD) characterization results showed that the membranes consisted of well-crystallizedH ZSM-5. The influence of crystallization time on morphology of HZSM-5 membranes was represented by scanning electronic microscopy (SEM) characterization: the HZSM-5 zeolite membranes on the supports were defect free and the membrane thickness was increased with the crystallization time prolonged.

The Influence of Surfactants on Crystallization of Nanocrystalline HZSM-5 Zeolite

With addition of surfactants, a nanocrystalline HZSM-5 zeolite was prepared by hydrothermal synthesis method. X-ray diffraction (XRD) characterization results showed that surfactants can constraint the crystallization of HZSM-5. Scanning electronic microscopy (SEM) characterization revealed that nanocrystalline HZSM-5 with more regular morphology and smaller particle size can be prepared with suitable surfactants as additives. The HZSM-5 particles were 200-800 nm in size and constructed by primary HZSM-5 nanocrystals of 3050 nm. The average particle size will grow up to 800 nm with a cationic surfactant, and decrease to 200 nm with a anionic surfactant.

Synthesis and Characterization of Monodisperse Nanocrystalline HZSM-5 Zeolite

A monodisperse nanocrystalline HZSM-5 zeolite was prepared by varying-temperature synthesis method with aluminum nitrate (Al (NO3)3), tetraethyl orthosilicate (TEOS), and tetrapropyl ammonium hydroxide (TPAOH) as raw materials. X-ray diffraction (XRD) characterization results showed that the crystallinity of HZSM-5 prepared by varying-temperature synthesis method was higher than constant-temperature synthesis . The influence of crystallization temperature and time on morphology and particle size of HZSM-5 is represented by scanning electronic microscopy (SEM) characterization: nanocrystalline HZSM-5 with more regular morphology and smaller particle size can be prepared by varying-temperature synthesis method. The minimum average particle size is 0.3μm. The particle size will grow up to 3.0μm with the crystallization time prolonged.

Modification of nanocrystalline HZSM-5 zeolite with tetrapropylammonium hydroxide and its catalytic performance in methanol to gasoline reaction

Nanocrystalline ZSM-5 zeolite was modified with tetrapropylammonium hydroxide (TPAOH) solution. The effect of the TPAOH treatment time on the catalytic performance of HZSM-5 was investigated in methanol to gasoline (MTG) reaction. The modified samples were characterized using X-ray diffraction, scanning electron microscopy, 27 Al and 29 Si magic-angle spinning nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, N 2 adsorption, and NH 3 temperature-programmed desorption. The HZSM-5 structure was basically unchanged after modification, but the relative crystallinity increased and the crystal morphology was more regular. The Brunauer-Emmett-Teller surface area, the micropore surface area, the surface Si/Al ratio, and the amount of strong acid sites increased; this might be caused by desilication and dealumination, and secondary crystallization of the zeolite during the treatment. The stability of the catalyst was significantly improved after modification, as reflected by the increased lifetime from 70 h to above 170 h in MTG reaction. The catalyst lifetime increased with increasing TPAOH treatment time. Hydrogen transfer reactions became faster and led to more isoparaffins and less olefins in the liquid products. 采用四丙基氢氧化铵(TPAOH)溶液对纳米ZSM-5分子筛进行改性, 运用X射线衍射/扫描电镜/ 27 Al和 29 Si固体核磁/X射线光电子能谱/N 2 物理吸附脱附法和NH 3 程序升温脱附等手段对所制样品进行了表征, 并评价了其催化甲醇制汽油反应性能. 结果表明, 改性后的HZSM-5相对结晶度增加, 晶体形貌更加规整, 表面硅铝比增加, 比表面积和微孔表面积增大, 强酸位酸量增多. 同时, TPAOH改性不仅可以使分子筛脱硅脱铝, 而且伴有二次晶化补硅补铝, 改变了分子筛的硅铝分布. 改性的HZSM-5在甲醇制汽油反应中的稳定性大幅度提高, 其寿命由70 h增至170 h以上, 随着TPAOH处理时间的增加, 催化剂寿命增加, 氢转移反应加快, 导致油相产品中异构烷烃增多, 烯烃减少. Tetrapropylammonium hydroxide treatment of the HZSM-5 zeolite improved the diffusion capacity and coke tolerance through desilication, dealumination, and secondary crystallization, reflected by the significantly increased catalyst lifetime.

Synthesis of Dimethyl Ether from Methanol over Heteropoly Acid/Nanocrystalline HZSM-5 Complex Solid Acidic Catalyst

Exploiting the catalysts with higher activity and stability for methanol dehydration at low temperature has become the central part of research dimethyl ether from synthesis gas or methanol. The crystal size of HZSM-5 zeolite is 50~100 nm. The nanocrystalline HZSM-5 zeolite is thought to be an ideal material for the encapsulation of heteropoly acid (HPA) molecules having a Keggin or Dawson structure since they have the intergranular secondary pores. A HPA/nanocrystalline HZSM-5 complex solid acidic catalyst was prepared by an impregnation method and characterized by FT-IR, UV-Raman, XRD and 31 P MAS-NMR. The 12-phosphotungstic acid (HPW) loaded on nanocrystalline HZSM-5 zeolites was prepared by the following steps. The strip (ф 1 mm×2 mm) nanocrystalline HZSM-5 (Si/Al=4.2) catalyst was prepared by the procedure that reported in the literature. 1.00 g HPW was dissolved in 15 mL deionized water. 10.0 g of the strip nanocrystalline HZSM-5 zeolite were added into the solution and steeped the mixture for 12 h. The slurry mixture was calcined at 350 ℃ for 4 h. This catalyst is denoted HPW-HZSM-5. The FT-IR spectroscopy, UV-Raman spectroscopy and 31 P MAS-NMR of HPW-HZSM-5 characterization results show that the Dawson type structure was well preserved after calcination of the cata- lysts. The reaction was carried out in a continuous flow fixed-bed reactor (diameter 10 mm). Reaction conditions are listed as following: temperature 200 ℃, WHSV=1.6, FRH (methanol flow rate)=0.08 mL/min; FRH (N2 flow rate)=8.0 mL/min; catalyst 2.05 g; system pressure 0.8 MPa. The composition of the products was analyzed by a GC-8820 gas chromatograph equipped with FID and a GDX-403 (2 m×4 mm). The reaction performance results, including methanol conversion and di- methyl ether selectivity were subsequently calculated. Under steady state conditions, the catalyst shows good stability, and the conversion of methanol maintains above 87.0 mol% (90.9 mol%) during 300 h, it also shows the selectivity (99.0 mol%) of dimethyl ether under the experimental conditions. Keywords 12-phosphotungstic acid; nanocrystalline HZSM-5 zeolite; methanol dehydration; dimethyl ether

Nitrogen and sulphur poisoning in alkene oligomerization over mesostructured aluminosilicates (Al-MTS, Al-MCM-41) and nanocrystalline n-HZM-5

Abstract Oligomerization of 1-hexene in the presence of model poisons such as thiophene (700–7000 ppm of sulphur) and n -butylamine (25–250 ppm of nitrogen), either alone or in combination, were tested at 200 °C, 50 bar and using n -octane as solvent, over three catalysts: two uniformly mesostructured silica–alumina (Al-MTS, Al-MCM-41) and a nanocrystalline HZSM-5 zeolite. A content of 700 ppm of sulphur (adding thiophene) or/and 25 ppm of nitrogen (adding n -butylamine) after a TOS = 240 min led towards roughly 10–20% decrease in conversion over nanocrystalline HZSM-5, without significant changes in selectivity. On the contrary, a feeding of 1-hexene with 7000 ppm of sulphur and 250 ppm of nitrogen showed a drastic drop of conversion (from 90 to 27%) over n-ZSM-5 zeolite with a significant increase in the selectivity towards lighter oligomers (dimers, C 7 –C 8 isomers). This fact suggests that the strong acid sites of the zeolite are deactivated by poison adsorption and heavy oligomers/coke deposition both inside the micropores and over the external surface. In contrast, neither Al-MTS nor Al-MCM-41 catalysts were meaningfully affected by the poisons (especially Al-MTS), even for high concentration conditions, due to its high surface area, mesoporosity and medium acid strength distribution. TG analyses of the mesoporous catalysts indicate weight losses of ∼20–25%, with a contribution of 6–8% at 400–500 °C, assigned to the removal of deposited coke. Oligomerization of a FCC effluent under the same conditions over Al-MTS catalyst leads to a remarkable 58% conversion with a oligomer selectivity over 90% (32% of them C 13 –C 18 ).

In situ nanocrystalline HZSM-5 zeolites encaged heteropoly acid [formula omitted] and Ni catalyst for hydroconversion of n-octane

The heteropoly acid H 3 PMo 12 O 40 (PMo) and Ni in situ encaged in the secondary pore of nanocrystalline HZSM-5 zeolites was prepared from molybdenum oxide and phosphoric acid and nickel nitrate, in a slurry mixture of nanocrystalline HZSM-5 zeolite crystals and deionized water. Catalysts were characterized by ICP, FT-IR, XRD, 31P MAS-NMR, ESR, Py-IR, NH 3 -TPD, BET, SEM and TEM. PMo cannot enter the interior pores of the zeolite, but becomes encaged in the secondary pore of nanocrystalline HZSM-5 zeolite. The hydroconversion of n-octane over various catalysts was investigated in order to obtain light isomers of alkanes and aromatics products with high octane number. From the results presented in the paper, it is clear that the catalytic properties of the “in situ encaged” PMo–Ni and impregnated PMo–Ni properties are similar, and the number and distribution of Brønsted and Lewis acid sites in these two catalysts are similar, too. It is concluded that both the aromatization of n-octane and the ability of producing light iso-alkanes are enhanced over the PMo and Ni ‘in situ encaged’ and impregnated catalysts than other catalysts. The effects of the acidity and temperature on the activity of n-octane hydroconversion over investigated catalysts are demonstrated.

Catalytic degradation of high density polyethylene over nanocrystalline HZSM-5 zeolite

High density polyethylene (HDPE) was catalytically degraded using a laboratory fluidised bed reactor in order to obtain high yield of gas fractions at mild temperatures, between 350 and 550 °C. The catalyst used was nanocrystalline HZSM-5 zeolite. High yields of butenes (25%) were found in the gas fractions, which were composed mainly of olefins. Waxes were wholly composed of linear and branched paraffins, with components between C 10 and C 20. The effects of both temperature and polymer to catalyst ratio on the product yield were studied. Gas conversion was dramatically decreased when the operation temperature was low (below 450 °C) or when the polymer to catalyst ratio was greatly increased (9.2). Gas and wax compositions significantly altered over 500 °C, showing that a part of the HDPE was degraded thermally, increasing the olefin concentration in the waxes. The same variation was observed in the experiments carried out at high polymer to catalyst ratios, obtaining a 50% olefinic concentration in the waxes. The differences observed in product distributions can be attributed to both thermal and catalytic degradations.

Influence of nanocrystalline HZSM-5 external surface on the catalytic cracking of polyolefins

Catalytic cracking of both LDPE and HDPE has been studied using three different samples of nanocrystalline HZSM-5 zeolite as catalysts. The zeolite samples were synthesized under different conditions in order to obtain materials with different crystal sizes in the nanometer range (10–60 nm) and high external surface areas (78–242 m 2/g). The plastic cracking reactions were carried out at 340 °C for 2 h using a plastic/catalyst mass ratio of 100. Despite these really mild conditions, high activities were observed over the three catalysts. The plastic conversion and the turnover frequency increased strongly with the amount of external surface area of the catalysts, showing the importance of the non-sterically hindered external acid sites for the conversion of the bulky plastic molecules. The main products obtained in the cracking reactions over the three catalysts are light hydrocarbons (C 3–C 5 fraction) with a considerable amount of olefins, which indicates the possibility of addressing the zeolite selectivity towards hydrocarbons useful as raw chemicals. These products are formed via an end-chain cracking pathway of the polymer molecules over the zeolite acid sites. The occurrence of this mechanism has been confirmed by DSC analysis of the LDPE and HDPE residues remaining within the reactor after the catalytic tests, showing they still consist of plastic molecules with melting temperatures similar to those of the raw polymers.

WITHDRAWN: Influence of nanocrystalline HZSM-5 external surface on the catalytic cracking of polyolefins

Abstract Catalytic cracking of both LDPE and HDPE has been studied using three different samples of nanocrystalline HZSM-5 zeolite as catalysts. The zeolite samples were synthesized under different conditions in order to obtain materials with different crystal sizes in the nanometer range (10–60 nm) and high external surface areas (78–242 m 2 /g). The plastic cracking reactions were carried out at 340 °C for 2 h using a plastic/catalyst mass ratio of 100. Despite these really mild conditions, high activities were observed over the three catalysts. The plastic conversion and the turnover frequency increased strongly with the amount of external surface area of the catalysts, showing the importance of the non-sterically hindered external acid sites for the conversion of the bulky plastic molecules. The main products obtained in the cracking reactions over the three catalysts are light hydrocarbons (C 3 –C 5 fraction) with a considerable amount of olefins, which indicates the possibility of addressing the zeolite selectivity towards hydrocarbons useful as raw chemicals. These products are formed via an end-chain cracking pathway of the polymer molecules over the zeolite acid sites. The occurrence of this mechanism has been confirmed by DSC analysis of the LDPE and HDPE residues remaining within the reactor after the catalytic tests, showing they still consist of plastic molecules with melting temperatures similar to those of the raw polymers.

Feedstock recycling of agriculture plastic film wastes by catalytic cracking

Feedstock recycling by catalytic cracking of a real plastic film waste from Almeria greenhouses (Spain) towards valuable hydrocarbon mixtures has been studied over several acid catalysts. The plastic film waste was mostly made up of ambient degraded low-density polyethylene (LDPE) and ethylene-vinyl acetate (EVA) copolymer, the vinyl acetate content being around 4wt.%. Nanocrystalline HZSM-5 zeolite (crystal size ∼60nm) was the only catalyst capable of degrading completely the refuse at 420°C despite using a very small amount of catalyst (plastic/catalyst mass ratio of 50). However, mesoporous catalysts (Al-SBA-15 and Al-MCM-41), unlike it occurred with virgin LDPE, showed fairly close conversions to that of thermal cracking. Nanocrystalline HZSM-5 zeolite led to 60wt.% selectivity towards C1C5 hydrocarbons, mostly valuable C3C5 olefins, what would improve the profitability of a future industrial recycling process. The remarkable performance of nanocrystalline HZSM-5 zeolite was ascribed to its high content of strong external acid sites due to its nanometer dimension, which are very active for the cracking of bulky macromolecules. Hence, nanocrystalline HZSM-5 can be regarded as a promising catalyst for a feasible feedstock recycling process by catalytic cracking.

Thermal and catalytic cracking of a LDPE–EVA copolymer mixture

Catalytic cracking of a plastic mixture consisting of LDPE and ethylene–vinyl acetate (EVA) copolymer (86/14 w/w) over mesoporous Al-SBA-15 and Al-MCM-41 materials as well as nanocrystalline HZSM-5 zeolite (crystal size ∼35 nm) has been carried out in a batch reactor at 400–420 °C. The release of acetic acid formed from the EVA decomposition was observed within the temperature range 350–400 °C. The most active catalyst was nanometer size HZSM-5 that led to complete conversion of the plastic mixture at 420 °C whereas both Al-MCM-41 and Al-SBA-15 were meaningfully less active. In addition, the polymer mixture was more difficult to be cracked both thermally and catalytically than pure LDPE. This result has been ascribed to the occurrence of cross-linking reactions leading to a fast deactivation by coke fouling especially over mesoporous catalysts (Al-MCM-41 and Al-SBA-15) because of their open structure. A high selectivity towards C 1–C 5 hydrocarbons (∼75%) was attained over nanometer size HZSM-5, most of them being valuable C 3–C 4 olefins. PIONA analyses of the C 6–C 12 hydrocarbon fraction obtained at 420 °C indicates that olefins were the main components whereas a significant amount of aromatics was also obtained both thermally and catalytically (>15%).