Cracking Of Butane Research Articles

Solvent-free synthesis of lamellar SAPO-18/34 intergrowth zeolite and the catalytic performance for 1-butene cracking

Lamellar SAPO-18/34 intergrowth zeolite has been successfully synthesized by solvent-free method employing N,N-diisopropylethylamine and tetraethylammonium hydroxide as co-template. Different framework structures (SAPO-34 or SAPO-18) could also be crystallized from identical gels under the guidance of a single template agent. The differences in structure, morphology, pore characteristics, chemical composition, and acidity of the prepared zeolite SAPO samples were investigated by XRD, SEM, N2 adsorption–desorption, XRF, and NH3-TPD. In comparison to SAPO-18 and SAPO-34, the lamellar SAPO-18/34 intergrowth zeolite with suitable acidity exhibited better catalytic conversion and enhanced catalytic stability in the cracking of 1-butene.

Kinetic analysis of monomolecular cracking of normal Alkanes (C4[sbnd]C6) over Brønsted Acid site of Zeolitic type catalyst with energetic evaluation of transition states using Quantum-Chemical modeling

The work aims to determine the kinetic parameters of reactions for production of light olefins via catalytic cracking reactions of C4–C6 n-alkanes based on the energy characteristics of the transition state using quantum chemical calculations. Cracking reactions of C4–C6 n-alkanes proceed via protolytic mechanism on the Brønsted acid sites of zeolite-containing catalysts. For kinetic studies in this work, the thermochemical parameters of the intermediate stages, including hydrocarbon adsorption and transition state were determined, then the activation energies and rate constants were determined over the temperature range of catalytic cracking process from 773 to 903 K (500–630 °C).The results showed that DFT method in combination with B3LYP and ωB97X-D functionals, and 3–21 G basis demonstrated quite high accuracy in determining thermochemical parameters, including enthalpy, entropy and Gibbs free energy at both energetic levels of adsorption and transition state. Then, modeling continued by calculations of activation energies and rate constants of reactions. Obtained kinetic parameters made it possible to determine the reactivity of hydrocarbons with different chain length. It was obtained that the rate constants of butane cracking reactions with the formation of ethylene are 54–90 times higher than the formation of propylene. The rate constants of pentane cracking reactions with the formation of butylene are on average 5 times higher than the formation of propylene. The rate constants for hexane cracking reactions with the formation of butylene are 2.9–3.7 times higher compared to the formation of propylene.

Improved Catalytic Performance on Post-Treated Zeolites SAPO-18 for 1-Butene Cracking

Improved Catalytic Performance on Post-Treated Zeolites SAPO-18 for 1-Butene Cracking

ECNU-13: A High-Silica Zeolite with Three-Dimensional and High-Connectivity Multi-Pore Structures for Selective Alkene Cracking.

A high-silica zeolite ECNU-13 (Si/Al=23) with a new three-dimensional (3D) pore system and a nanosized morphology has been developed, consisting of multitudes of 10-membered ring (10-R) medium pores and one set of 8-R small pores. A phase-discrimination strategy was proposed to synthesize ECNU-13 by regulating the gel compositions and nucleation processes that were used for preparing 12-R large-pore germanosilicate IM-20 with the known UWY topology. The crystallization was directed towards forming one set of single four-ring (s4r) composite building units together with one set of double four-ring (d4r) rather than two different types of d4r units in IM-20. The electron crystallographic investigations elucidated that the ECNU-13 structure was composed of two kinds of polymorphs as a result of distinct atomic positionings in s4r units. In catalytic cracking of 1-butene, ECNU-13 exhibited high propene selectivity (55.6 %) and propene to ethylene molar ratio (>4.7) superior to well-studied conventional ZSM-5 zeolite catalyst.

Cracking of Butane on a Pt/H-ZSM-5 Catalyst in the Presence of Hydrogen

Cracking of Butane on a Pt/H-ZSM-5 Catalyst in the Presence of Hydrogen

Reaction pathways of n-butane cracking over the MFI, FER and TON zeolites: Influence of regional differences in Brønsted acid sites

Three zeolites ZSM-5, ZSM-35 and ZSM-22 are applied in n -butane cracking to reveal the influence of regional differences in Brønsted acid sites on reaction pathways. The Brønsted acid sites located in the channels of ZSM-5 exhibit a higher catalytic activity and yields to light olefins (especially the ethylene), which can be attributed to more relative contribution of bimolecular pathway. In comparison, more Brønsted acid sites are situated on the external surface or micropore mouths of ZSM-35 and ZSM-22, which are beneficial to propylene production. Note-worthily, almost no propane production on the two zeolites implies the predomination of monomolecular pathway. In situ FTIR technique further discloses that the difference in the reaction pathways is tailored by adsorption configurations of n -butane at two types of Brønsted acid sites. Under comparable conditions, the ZSM-5 performs a relatively good catalytic stability through bimolecular pathway. Furthermore, the correlation between deactivation rate and light olefins reveals that the enhancement of propylene selectivity accelerates the deactivation of ZSM-35 and ZSM-22. While, promotion on the ethylene selectivity is a significant inducement for the deactivation of ZSM-5. Reaction pathways of n-butane cracking tailored by the influence of regional differences in Brønsted acid sites. • Three typical 10-member ring zeolites ZSM-5, ZSM-35 and ZSM-22 are prepared. • Reaction pathways of n -butane cracking over the zeolites are investigated. • Regional differences in Brønsted acid sites tailor the selectivities to propylene and ethylene. • ZSM-5 zeolite exhibits high catalytic activity and stability compared to ZSM-35 and ZSM-22. • Catalyst deactivation mechanisms are revealed on different reaction pathways.

Solvent-Free Synthesis of SAPO-34 Zeolite with Tunable SiO2/Al2O3 Ratios for Efficient Catalytic Cracking of 1-Butene

Solvent-free synthesis methodology is a promising technique for the green and sustainable preparation of zeolites materials. In this work, a solvent-free route was developed to synthesize SAPO-34 zeolite. The characterization results indicated that the crystal size, texture properties, acidity and Si coordination environment of the resulting SAPO-34 were tuned by adjusting the SiO2/Al2O3 molar ratio in the starting mixture. Moreover, the acidity of SAPO-34 zeolite was found to depend on the Si coordination environment, which was consistent with that of SAPO-34 zeolite synthesized by the hydrothermal method. At an SiO2/Al2O3 ratio of 0.6, the SP-0.6 sample exhibited the highest conversion of 1-butene (82.8%) and a satisfactory yield of light olefins (51.6%) in the catalytic cracking of 1-butene, which was attributed to the synergistic effect of the large SBET (425 m2/g) and the abundant acid sites (1.82 mmol/g). This work provides a new opportunity for the design of efficient zeolite catalysts for industrially important reactions.

Inhibition effect of Na+ form in ZSM-5 zeolite on hydrogen transfer reaction via 1-butene cracking

The Na+ and H+ of ZSM-5 having three Si/Al molar ratios (20, 35, and 50) were synthesized to investigate and illustrate 1-butene cracking mechanism. The physical and chemical properties of ZSM-5 were described by XRD, SEM-EDX, N2 physicsorption, FT-IR, pyridine-IR, 1H MAS NMR, TPO, and NH3-TPD techniques. For the characterization, the Na-ZSM-5 consisted of two main types of acid sites (weak and medium acid sites), whereas strong, medium, and weak acid sites were detected on H-ZSM-5. For H-ZSM-5, the Si-(OH)-Al site (strong Brønsted site) was an active site for 1-butene cracking reaction, while the active site of Na-ZSM-5 in the reaction was silanol nest (moderate Brønsted site). The 1-butene cracking reaction on H-ZSM-5 and Na-ZSM-5 was studied under the operating condition of temperature =500 °C, pressure =1 atm, and WHSV =3 h−1. The oligomerization, cracking, and hydrogen transfer were three main reactions in the 1-butene cracking mechanism. The alkenes excluding propylene occurred on weak acid site, while the formation of propylene underwent on medium acid site of ZSM-5 catalyst. The presence of strong acid site on ZSM-5 catalyst promoted the hydrogen transfer reaction, which provoked the alkane formation. The hydrogen transfer index in 1-butene reaction of Na-ZSM-5 was less than H-ZSM-5 in all Si/Al molar ratios because of the absence of strong acid. The Na-ZSM-5 (Si/Al molar ratio = 20) reached the highest propylene selectivity at 31.73 C-wt.% and the Na+ ion could block the strong acid site. At low Si/Al molar ratio, the stability of Na-ZSM-5 was higher than H-ZSM-5 because of the lower coke formation. Therefore, the Na-ZSM-5 was more suitable catalyst than H-ZSM-5 for propylene formation in 1-butene cracking reaction.

Selective dealumination of HZSM-5 zeolite boosts propylene by modifying 1-butene cracking pathway

An HZSM-5 zeolite was dealuminated by steaming with its self-adsorbed water at mild temperatures (300, 400 or 500°C), characterized and tested in the transformation of 1-butene into propylene. The structural, porous-surface and acidic properties of the catalysts (unmodified and steamed) were characterized using N2 adsorption-desorption isotherms, tert-butylamine adsorption-TPD, XRD, 29Si and 27Al MAS-NMR, and FTIR spectroscopies, and the results pointed to the following evidences: (i) dealumination took place transforming specific strong acid, framework tetrahedral Al sitings (located within the micropores) into distorted and extra-framework species; and (ii) the porous-surface properties were less sensible to the treatment. The acid site density was shifted towards the intersections of the zeolite micropores (of weaker acidity), resulting in the selective inhibition of hydrogen transfer pathway, thus lowering the selectivity of paraffins, aromatics and ultimately, coke deposition. Overall, the performance of the 500°C-steamed catalyst compared with the parent one was enhanced: propylene selectivity was boosted 69%, coke deposition dropped by 34%, whereas the initial conversion only fell 6%.

Phosphorus modified hierarchically structured ZSM-5 zeolites for enhanced hydrothermal stability and intensified propylene production from 1-butene cracking

Hierarchically structured ZSM-5 zeolites (HSZ) were synthesized by a mesoporogen-free procedure and subsequently modified with varied amounts of phosphorus (1–3 wt%) through impregnation of phosphoric acid solution. Materials characterization using various techniques showed that the hierarchical structures of HSZ were well preserved after phosphorus modification, and more interestingly, their hydrothermal stability were improved significantly and the main textural properties kept almost unchanged even after hydrothermally treated at 750 °C for 4 h in 100% steam. The strong acid sites of HSZ were found to be gradually eliminated by the phosphorus induced dealumination of tetrahedral framework aluminum (TFAL), however, weak acid sites remained almost intact. In the 1-butene cracking reactions, benefitting from the auxiliary mesopores and phosphorus modification, P-modified HSZ showed remarkably improved selectivity (∼52%) and yield (∼43%) of propylene as well as superior anti-deactivation ability. All these properties of P-modified HSZ made it a promising catalyst for industrial application.

On the synthesis and catalytic cracking properties of Al-ITQ-13 zeolites

Al-ITQ-13 zeolites with different Si/Al atom ratios above 25 were successfully synthesized in short crystallization time by using seeds in the gel. A variety of synthesis conditions were investigated in-depth and the resultant zeolite samples were characterized by XRD, SEM, N2 physisorption and FTIR spectra. Al-ITQ-13 zeolite samples synthesized with different Si/Al ratios exhibit similar textural properties. The amount and strength of acid sites decrease with increasing Si/Al ratio of Al-ITQ-13 zeolites. It was found that H-Al-ITQ-13 samples with low Si/Al ratios show a very high B/L ratio (such as 2.40) at a desorption temperature of 573 K. 1-Butene cracking reaction over proton form Al-ITQ-13 zeolites (Si/Al atom ratio from 47 to 179) was carried out in a continuous flow stainless steel reactor. It was found that the higher of the aluminium content in Al-ITQ-13 (i.e. lower Si/Al ratio), the better selectivity for ethylene and propylene yield. While the hydrogen transfer reaction and alkylation reaction were suppressed with increasing Si/Al ratio.

Catalytic cracking of 1-butene to propylene using modified H-ZSM-5 catalyst: A comparative study of surface modification and core-shell synthesis

Surface modification of ZSM-5 catalyst was carried out by silica deposition using chemical liquid deposition (CLD) method as well as core-shell silicalite composite material by hydrothermal method. The modified ZSM-5 catalyst was characterized using various physiochemical methods such as XRD, TPD, N2 adsorption-desorption and SEM analysis. Catalytic cracking of 1-butene was carried out using modified ZSM-5 catalysts. The propylene yield was higher for core-shell silicalite composite as compared to silica deposition through CLD method. Silica deposited using CLD method showed propylene-to-ethylene (P/E) ratio of 1.7, whereas core-shell silicalite composite resulted in P/E ratio of 3.0. The higher selectivity to light olefins using core-shell silicalite composite to be attributed to weak acid sites and effective control of external acid sites, which reduces the hydrogen transfer reactions that form alkanes and aromatics. The effective external surface passivation was verified using catalytic cracking of triisopropyl benzene. The core-shell silicalite composite showed excellent stability over 50h for the cracking of 1-butene stream.

Relationship between the Catalytic Activities of Acidic Protons in Aluminosilicate and Silicoaluminophosphate Molecular Sieves for n-Butane Cracking and Their 1H Chemical Shifts Measured at the Reaction Temperature

Zeolite materials are used as solid acid catalysts in petrochemical reactions, which typically occur at Bronsted acid sites located at bridging hydroxyl groups (Si–OH–Al). These sites have been investigated spectroscopically, albeit at room temperature; a proper understanding requires that such data be acquired at actual reaction temperatures. The influence of temperature on the 1H chemical shifts and dynamic properties of Si–OH–Al sites in proton-type aluminosilicate and silicoaluminophosphate molecular sieves was examined by variable-temperature 1H magic-angle spinning nuclear magnetic resonance spectroscopy, from 298 to 673 K. The chemical shifts and line widths of the peaks due to Si–OH–Al protons were strongly dependent on the temperature, whereas those due to P–OH protons in the silicoaluminophosphate were slightly dependent. The relationship between the 1H chemical shifts of the Si–OH–Al groups in both types of molecular sieves, (δ1H) and their catalytic activities for n-butane cracking were examin...

ZSM-5 with controllable acidity as an efficient catalyst for a highly adjustable propene/ethene ratio in the 1-butene cracking.

A facile strategy was proposed to realize the precise control of zeolitic acidity by selective cracking of a silane with an acid site. Modified ZSM-5 with controllable acidity brought about a highly adjustable propene/ethene (P/E) ratio in the 1-butene cracking.

Controlling coke deactivation and cracking selectivity of MFI zeolite by H3PO4 or KOH modification

The effect of the basic (KOH) or acid (H3PO4) treatment of the MFI (HZSM-5) zeolite has been studied comparing the structural and acidic features with the catalytic performance and deactivation of a set of unmodified and modified zeolites (SiO2/Al2O3=30–280, 0–3wt% of K or P). The properties of the catalysts have been elucidated using XRD, 27Al and 29Si NMR, N2 adsorption–desorption, and adsorption-TPD of tert-butylamine. The catalytic performance has been evaluated in the cracking of 1-butene by means of initial, 5h on-stream activity and coke formation. Our results point to the fact that using zeolites with high SiO2/Al2O3 ratio or neutralizing the strongest acid sites with KOH or H3PO4 increases propylene selectivity while decreases 1-butene conversion. The overall pathway of reaction involves propylene and other olefins as primary products that condensate in further steps to aromatics and ultimately to coke. This pathway can be controlled with less severe acidic features and by desilication with KOH or H3PO4 (particularly with the former).

Catalytic Property of SAPO-18/SAPO-34 Intergrown Molecular Sieve in 1-Butene Cracking

Abstract SAPO-18 (AEI)/SAPO-34 (CHA) intergrown molecular sieve (AC-HS) was prepared by hydrothermal synthesis. As evidenced by XRD, SEM, BET, and NH3-TPD analyses, AC-HS had unconventional physical and chemical properties such as crystal structure, crystal morphology, surface area, and acidity. Compared with SAPO-18 and SAPO-34 mechanical mixture (AC-MM), AC-HS showed better initial activity and higher selectivities of C3H6 and C2H4 + C3H6 in 1-butene cracking under the reaction conditions. The selectivities of C3H6 and C2H4 + C3H6 reached approximately 61.09% and 90.28%, respectively, when conversion was >70%. Regarding the SAPO-18/SAPO-34 intergrown molecular sieve, the relationship of acidity and catalytic performance was not close in 1-butene cracking, and the intergrowth structure should play a significant important role in the selectivity of olefins.

Catalytic cracking of 1-butene to propylene by Ag modified HZSM-5

Silver modified HZSM-5 (AgHZ) zeolite catalysts were prepared by ion exchange method and their catalytic properties in the 1-butene cracking reaction were measured. The catalysts were characterized by infrared spectroscopy with pyridine adsorption (Py-IR), N2 adsorption and X-ray diffraction (XRD). The effects of Ag loading and steaming treatment on catalytic performances were studied. It is found that the activity of HZSM-5 (HZ) catalyst significantly decreases with the steaming time, whereas AgHZ catalysts show stable activity in the steaming time of 24–48h and their activities increase with the Ag loading. When the steaming time is 24–48h, the yield of propylene over HZ catalyst significantly decreases, whereas it is stable over AgHZ catalysts. The AgHZ catalysts with Ag loadings of 0.28%–0.43% (by mass) show similar propylene yields (~30%), which are higher than that over the AgHZ catalyst with a Ag loading of 0.55% (by mass). These results indicate that the steam-treated AgHZ catalysts with optimum Ag loadings have higher yield of propylene and are more stable than the steam-treated HZ catalyst. The regeneration stability measurement in butene cracking also shows that the AgHZ catalyst steam-treated under a suitable condition has better stability than the HZ catalyst.

Effect of iron and phosphorus on HZSM-5 in catalytic cracking of 1-butene

HZSM-5 zeolites modified by phosphorus and/or iron were prepared. The physicochemical features of catalysts were characterized by XRD, N2 adsorption, 27Al MAS NMR, UV–vis, NH3-TPD, FTIR of adsorbed pyridine and CO2-TPD, and their performance for the cracking of 1-butene was measured. It was found that phosphorus modification significantly reduced the concentration of acid sites, especially strong ones. This suppressed hydrogen transfer reactions and enhanced the selectivity to propylene, while decreasing the butene conversion. Phosphorus modification also promoted the stability of the catalyst. Iron modification led to relatively little change on the acidity of the catalyst. However, the basicity increased after the introduction of iron. Accordingly, iron modification also suppressed hydrogen transfer reactions. After adding iron into phosphorus modified HZSM-5, the interaction between iron and phosphorus released some Brønsted acid sites which were previously neutralized by phosphate, increasing butene conversion and propylene selectivity compared with phosphorus modified HZSM-5. The presence of phosphorus promoted the dispersion of iron cations. Highest selectivity to propylene was observed on the catalyst co-modified by iron and phosphorus.

Preparation of Au Supported ZSM-5 Catalysts and its Special Performance in the Catalytic Cracking of Butane Reaction

Au/ZSM-5 was prepared by improved desorption-precipitation (DP) method using urea as precipitant. Au-samples were characterized by TEM, UV-Vis, XRD, pyridine-FTIR, FTIR and the other techniques. The catalytic performance of Au/ZSM-5 catalysts was carried out on the catalytic cracking of butane by mini-scale pulse reactor. Results showed that: 2.0wt% loading Au/ZSM-5 catalyst obtained the best activity that the n-butane conversion rate comes to 58% by weight,60% olefin selectivity and 10% aromatics selectivity; the i-butane conversion rate comes to 53%, 35% olefin selectivity and 15% aromatics selectivity.

Preparation of phosphorus-modified PITQ-13 catalysts and their performance in 1-butene catalytic cracking

A series of phosphorus-modified PITQ-13 catalysts was prepared by wet impregnation of NH4H2PO4 solution into an HITQ-13 parent. The catalysts were characterized using XRD, N2 adsorption, MAS NMR and NH3-TPD. Their catalytic performance in 1-butene catalytic cracking was evaluated in a fixed fluidized bed reactor. The results showed that the crystallinity, surface area and pore volume of P-modified PITQ-13 catalysts decreased with the increasing amounts of P. The number of weak acid sites increased, whereas that of strong acidity decreased. The selectivity to propylene in 1-butene cracking reactions increased because of the decrease in strong acidity. The yield of propylene achieved 41.6% over PITQ-13-2 catalyst with a P content of 1.0 wt%, which was 5.1% greater than that achieved over HITQ-13 catalyst.