Low-carbon Olefins Research Articles

Hydrogen transfer reaction in butene catalytic cracking over ZSM-5

Hydrogen transfer reaction (HTR) is the pivotal side reaction in the catalytic cracking process of low carbon olefins. The intricate reaction pathways and product diversity of HTR directly impact the selective formation of ethylene and propylene. Therefore, elucidating the key HTR in various reaction pathways and defining the hydrogen transfer index (HTI) as a criterion lay a scientific foundation for precisely regulating HTR during olefin catalytic cracking process. Herein, the influence of the acid strength of ZSM-5 zeolites on the HTR degree was analyzed in butene catalytic cracking. Results showed that isobutane was the predominant component of HTR products, mainly derived from HTR during the dimerization-cracking of pentene (butene primary cracking product). Subsequent pentene catalytic cracking experiments validated this conclusion. Thus, the HTI in butene or pentene cracking process was defined as follows: for butene cracking process, HTI = Si–C4H10/SC5H10; for pentene cracking process, HTI = Si–C4H10/SC4H8. The HTI accurately reflected the extent of HTR with respect to the acid properties of the catalysts. Moreover, the reaction network of butene catalytic cracking process was optimized, providing a comprehensive explanation for the intriguing phenomenon of decreasing butene conversion with increasing reaction temperature when the acid strength of ZSM-5 was weak. Finally, a high-performance butene catalytic cracking catalyst, De-TS-1-0.25%P, was developed, exhibiting high olefin selectivity (92.33 %) and outstanding stability (307 h) in the conversion of butene.

Effect of fast heating rate and alkaline catalyst on composition and characteristic of volatile products during catalytic upgrading of oil sand bitumen

The study was devoted to exploring the fundamental study on the upgrading of Buton oil sand bitumen (OSB) via fast alkaline catalytic pyrolysis based on the fluid pyrolysis technology. The effect of fast heating rate on the composition and molecular distribution of volatile products from the high-temperature fast pyrolysis of OSB was investigated by Py-GC/TOF-MS that could simulate the fast heating rate of industrial fluid pyrolysis process. The results showed that the volatile products of OSB under heating rates ranging from 10 to 1000 °C/s had the similar species composition. It was found that there were the highest relative content of low-carbon alkenes (C2-C4) and light aromatics (C6-C8) in volatile products under the 1000 °C/s, indicating that the fast heating rate favored the production of light alkenes and aromatics. Subsequently, a laboratory-scale fluidized bed apparatus was employed to further gain insight into fast alkaline catalytic pyrolysis behaviors of OSB. The investigation on the yield distribution, fractional- and molecular-level chemical characteristic of volatile products obtained from the fast alkaline catalytic upgrading of OSB over calcium aluminate was carried out with the aid of the comparison with that over Y zeolite-based FCC catalyst and silica sand. The results revealed that three-phase products over calcium aluminate possessed the larger selectivity of C2−C4 alkenes, larger yield of light oil and the lower coke output, which were 51.88%, 45.49% and 7.96%, respectively. On basis of the chemical structure analysis of liquid products, the alkaline catalytic upgrading of OSB over calcium aluminate could heighten the content of chain alkyl structures as well as alkyl-substituents attached to aromatic ring in liquid products. This indicated that the fast heating rate and alkaline catalyst that adopted in catalytic upgrading process of OSB could play an energetic role in optimizing the composition of volatile products. The alkaline catalytic upgrading of OSB based on fluid pyrolysis technology with the fast heating rate could heighten the yield of low-carbon olefins and light oil and lessen coke yield, meanwhile modify the chemical structure characteristics of liquid products that were conducive to the generation of valuable chemicals (light alkanes and BTX) during secondary processing of liquid products.

Introducing of Cu(I) in MOFs by In Situ Reduction with Ni as the Catalyst for Efficient Olefin/Paraffin Separation.

Olefins can be cracked to provide more low-carbon olefins than paraffins; therefore, separation of olefin/paraffin mixtures is essential for arranging hydrocarbon molecules for directed conversion. In this article, a simple approach for reducing copper atoms in Cu-BTC has been developed to improve olefin/paraffin adsorption capacity and selectivity. Considering that Cu-BTC shows adsorption benefits, its olefin/paraffin adsorption and separation performance were improved further by in situ reduction of Cu(II) to Cu(I) in Cu-BTC using ethanol as the reducing agent and nickel ions as the catalyst. The results revealed that during the reduction process, Cu ion conversion from tetra-ligand to diligand considerably increased their specific surface area, resulting in more active adsorption sites inside the modified sample. The ratio of Cu(I)/Cu(II) in the modified samples varied from 0.57 to 0.96. When Cu(II) of Cu-BTC was reduced to Cu(I), the adsorption capacities of 1-hexene increased from 145.97 to 243.65 mg/g, whereas n-hexane adsorption increased only slightly from 8.18 to 11.43 mg/g, resulting in an acceptable increase in selectivity from 17.84 to 21.32. Cu-BTC, due to its own Cu atoms, minimizes the substantial requirements for the synthesis process as well as the oxygen avoidance conditions for storage when monovalent copper is introduced, compared to other porous materials. Experimental results found that when Cu(I) was introduced, the Lewis acidic sites of the modified Cu-BTC material were increased, and Cu(I) has an electrical structure that makes it susceptible to both accepting and donating too many d electrons, resulting in a stronger adsorption of olefins containing π-electrons to them. Materials Studio simulation revealed that the isosteric heats of modified Cu-BTC increased by 2.7 kJ/mol, indicating that it has a stronger adsorption capacity for olefins.

Carbon-neutral light olefins production for energy decarbonization: Process development and techno-econo-environmental analysis

Low-carbon olefins, as important platform molecules, are generally produced by limited fossil energy, resulting in massive carbon emissions and intensive energy consumption inevitably. Therefore, it is necessary to develop clean and sustainable alternatives. With this in mind, three low-carbon olefin production processes using waste CO2 and green H2 were proposed, including the methanol-mediated (Option A) and Fischer-Tropsch synthesis (FTS)-based CO2-to-olefin (CTO) processes. Herein, the FTS-based CTO processes are classified into the direct (Option B) and indirect routes (Option C) without/with the reverse water–gas-shift unit. Meanwhile, rigorous process models were established, and detailed mass and energy balances of three processes were obtained with the aid of the process simulator. Moreover, in order to evaluate the feasibility and compare the differences in process performances of three proposed processes quantitatively, comprehensive techno-econo-environmental assessments of three processes were conducted at the system level. The results indicate that, firstly, from a technical perspective, the FTS-based processes are more competitive than the methanol-mediated process due to their higher energy efficiency (67.93%) and carbon utilization efficiency (84.22%). Secondly, from an economic perspective, the methanol-mediated process has a better economic prospect in the minimum olefin selling price (2527.08 $/tonne C2–C4 olefins). Lastly, from an environmental perspective, the methanol-mediated process is more environmentally friendly owing to its lower CO2-eq emissions (61.13 kg CO2-eq/tonne C2–C4). Moreover, for two FTS-based processes, the direct route is favorable in energy efficiency and minimum olefin selling price, whereas the indirect route is preferable in the carbon utilization efficiency and environmental impacts. Overall, the study provides novel approaches for the production of low-carbon olefins, and is of significant importance for reducing carbon footprint and achieving carbon neutrality.

Low-carbon conversion of crude oil to C2-C4 olefins by micro Py-GC/MS and a small-scale fluidized-bed reactor

Green utilization of crude oil has become an important way for energy transformation in the petrochemical industry. Crude oil to aimed low-carbon (C2-C4) olefins had been conducted by micro pyrolysis-gas chromatograph/mass spectrometer (Py-GC/MS) and a small-scale fluidized-bed reactor. Fe-modified Al2O3/USY catalysts were used in the catalytic pyrolysis of crude oil. The results showed that product distribution altered hugely after Fe incorporation. Suitable incorporation of Fe can promote the conversion of crude oil, while excessive Fe incorporation could reduce the yield of light olefins. Bifunctional 1%Fe/USY catalyst showed good catalytic dehydrogenation pyrolysis activity in light olefin production, which could guide the clean and low-carbon conversion of crude oil.

Industrial Regenerator Model for SMTO Technology.

In order to alleviate the current domestic oil shortage, China has studied the technology of using coal as the source to produce low carbon olefins, among which methanol to olefin (MTO) is an important process. Since the coke deposition of MTO catalyst is inevitable, the deactivated MTO catalysts need to be regenerated by continuous coke combustion to recover the activity. This paper used the actual industrial data to study the gas-solid two-phase fluidized bed of a SMTO regenerator and the coke combustion kinetics of the deactivated SAPO-34 catalyst, and established the mathematical model of the SMTO industrial regenerator. The kinetic parameters in the model were obtained and validated with different data, which showed that the model is reliable and can accurately predict the industrial reaction results and provide guidance for the SMTO production operation.

Tetrahedrally coordinated W(VI) species induced Lewis acid for stable catalytic cracking of 1-hexene to propene

Reasonable regulation of the acidity of ZSM-5 could fundamentally improve the catalytic performance for the cracking of low-carbon olefins to propene. Herein, a series of ZSM-5 catalysts with highly dispersed tetrahedrally coordinated W(VI) species were prepared for the catalytic cracking of 1-hexene to propene by a simple “top-down” method. Multi-characterizations revealed that the introduction of W enhanced the stability of the Si-O-Al structure in W-ZSM-5 by eliminating the non-skeleton aluminum and excessive Brønsted acid sites, leading to a superb resistance to carbon/coke deposition. Moreover, the Lewis acid sites originated from the active tetrahedrally coordinated W (VI) species improved the propene selectivity via inhibiting the polymerization of products. In addition, through the optimization of various parameters (such as Si/Al ratio, temperature and weight hourly space velocity), high 1-hexene conversion (>97%) and propene selectivity (>40%) could be maintained at 575 °C over the W-ZSM-5(60) catalyst during 30 h long period reaction. This work may provide some new insights for the effect of W-based catalysts on acid composition in the cracking of light olefins to propene.

Seeds induced Beta zeolite synthesis with low SDA for n-heptane catalytic cracking reaction

Due to higher thermal and hydrothermal stability, suitable acidity properties, Beta zeolite is considered as promising catalyst for naphtha catalytic cracking process. However, high cost and environmental pollution issue limit its industrial application by using high content of N-containing organic structural directing agent (SDA). In this paper, different SiO2/Al2O3 ratios of Beta zeolites were prepared assisting by seeds induced method with low SDA and cheap industrial silica sol as the silicon source. Physical and chemical properties of as-prepared Beta zeolites were characterized by XRD, N2 adsorption-desorption, NH3-TPD, Py-FTIR and SEM. N-Heptane was used as model compound for catalytic cracking performance evaluation. The results showed that Beta zeolite with high SAR was successfully synthesized, which had well defined crystallinity, proper specific surface area and pore structure, high B/L ratio and strong acid site. n-Heptane catalytic cracking performance showed high yield of low-carbon olefins with relative low activity on hydrogen transfer reaction and coke formation.

Synthesis and catalytic behavior of nickel heterogenized in covalent organic frameworks as precatalysts in ethylene oligomerization

Two covalent organic frameworks (COFs), as the supports of transition metal catalysts, were prepared and coordinated with nickel to synthesize two precatalysts for ethylene oligomerization. The chemical structure of sub-constructing unit had a significant influence on the specific surface area and the catalytic performance of covalent organic frameworks supported nickel(Ⅱ) catalysts. Two COFs were stacked in lamellae, and the specific surface area and the pore volume of COF with p-phthalaldehyde as sub-constructing unit were far larger than those of COF with butanedione as sub-constructing unit. The catalyst with a larger specific surface area had a higher catalytic activity and a higher selectivity of low carbon olefins in ethylene oligomerization because of a higher specific surface areas and larger pore structure for ethylene diffusion and mass transfer. Two catalysts can be reused at least three times without considerable loss in the catalytic activity and the selectivity toward short-chain α-olefins.

Coordinated Control of PM2.5 and O3 in Hangzhou Based on SOA and O3 Formation Potential

A continuous observation campaign was carried out with the Syntech Spectras GC955 volatile organics online monitoring system from March 1, 2019 to May 31, 2019 in Hangzhou. The constituent features of VOCs, the preferred VOCs species, and VOCs characteristic pollutant ratios were analyzed. The results showed that alkanes were the most important component in the volume fraction of VOCs, accounting for 62.40%. C2-C6 alkanes, benzene series, ethylene, and acetylene were the key species of VOCs. Olefins and aromatics were the main contribution components of OFP, with contribution rates of 41.35% and 37.50%, respectively. Aromatics were the main contributors to SOA, with a contribution rate of more than 90%. Low carbon alkanes, low carbon olefins, and benzene series were the key contributing species of OFP. Controlling toluene, m/p-xylene, and o-xylene is the key to the coordinated control of O3 and PM2.5. VOCs in the atmosphere of the sampling point were not only affected by motor vehicle exhaust but were also significantly affected by industrial emissions, such as solvents.

Design of highly stable metal/ZSM-5 catalysts for the shape-selective alkylation of toluene with methanol to para-xylene

The co-existence of (Pt + Ni) effectively inhibits the formation of low-carbon olefins during the alkylation of toluene with methanol via the dehydrogenation of methanol to carbon oxides and also the hydrogenation of olefins to paraffins.

Industrial application of swirl regenerating micro-channel separation (SRMS) for fine catalysts removal from methanol-to-olefin quench water

Methanol to olefin (MTO) process is a chemical technology for producing low-carbon olefins from coal-based or natural gas-based methanol, which has changed the pattern of low-carbon olefins relying on petroleum cracking. However, a large amount of fine catalyst powders circulating in the water system of the MTO plant threats the sustainability of the process severely. Previously, a pilot-scale study about swirl regenerating micro-channel separation (SRMS) technology to remove the fine waste catalyst powders from MTO quench water was reported. In this study, the SRMS equipment was scaled up to an industrial level with a processing capacity of 400 m3/h based on the results of pilot-scale experiments, and the performance of the industrial unit was monitored for over 6 months. The results obtained directly from the industrial site showed that the SRMS unit based on deep-bed filtration and swirling flow enhanced washing and desorption could effectively remove the fine catalyst particles in the quench water, and the effluent particle concentration was maintained below 20 mg/L. Furthermore, the total oil content in the quench water reduced from 43.2 mg/L to 22.8 mg/L after being processed by the SRMS unit, which demonstrates that the SRMS unit also has an appreciable ability for oil pollutants removal. After the long-term operation of the SRMS unit, the equilibrium concentration of particulate matter in the quench water was reduced to under 50 mg/L, which significantly improved the performance of the quench water heat exchanger and effectively reduced the cleaning frequency of the heat exchanger, air cooler, and other equipment in the water system. Through the industrial-scale technical comparison, this technology outperforms the other common quench water treatment methods in equipment investment, maintaining cost, freshwater supplement, and energy consumption.

Selective ethylene oligomerization based on Fe-containing metal-organic coordination polymer catalysts

One-dimensional, two-dimensional and three-dimensional Fe-containing metal-organic coordination polymer (1D/2D/3D-Fe-MOCP) catalysts have been solvothermally synthesized and evacuated at different temperatures to give a series of 1D-Fe, 2D-Fe and 3D-Fe catalysts used for ethylene oligomerization performed in slurry batch mode. Their catalytic performances were investigated with the aid of AlEt2Cl cocatalyst, and moderate catalytic activities and high selectivities to low carbon olefins C4, C6, C8, and C10 were observed. Moreover, the oligomerization product distributions differed depending on various factors such as the structural dimension, ligand type, framework flexibility, distances between metal atoms, et al. 1D-Fe catalyst evacuated at 150 °C for 8 hours showed high C8 olefin selectivity up to 94.90% with the catalytic activity of 6.28 × 105 g/mol(Fe)•h•atm. However, 2D-Fe and 3D-Fe catalysts showed relatively low catalytic activity and low selectivity for C8 olefin.

Modulating the Interaction of NiSO4 and Nb2O5 Boosts the Dimerization of Propylene

Propylene dimerization is an attractive way to branch out the bulk chemicals to high-value-added fine chemicals. Based on the coordinatively unsaturated surface sites of nickel and solid acid sites for boosting highly selective dimerization of propylene, a series of NiSO₄/Nb₂O₅ catalysts were synthesized by tuning the synergistic effect through adjusting the calcination temperatures. Under the conditions of 70 °C, 2.5 MPa, and LHSV = 3 h–¹ in a fixed-bed reactor, the NiSO₄/Nb₂O₅-400 catalyst exhibits the highest propylene conversion of ca. 89% with 75% selectivity to C6 products (mainly including 4-methyl-2-pentene and 3-hexene). A possible Cossee–Arlman pathway has been proposed for the dimerization of propylene. In the long-term stability testing, an induction period has been observed, which may be attributed to the coordination of propylene molecules to unsaturated Ni²⁺ cations generating some active nickel species. Subsequently, the NiSO₄/Nb₂O₅-400 catalyst presents a stability up to 30 h. The interesting results inspired us to modulate the interaction of metal (salt) and acid sites to strengthen the selective dimerization of low-carbon olefins.

A periodic density functional theory study on methanol adsorption in HSAPO-34 zeolites

Methanol-to-olefins is a successful alternative route to produce the low-carbon olefins. The methanol adsorption in HSAPO-34 was investigated by the periodic density functional theory method. Several possible adsorption conformations were obtained, as well as the spatial orientation and the free energy. Methanol could be adsorbed on the Brönsted acid (BA) site in either the hydrogen bonding or in the protonation. The adsorption configurations coexist, slightly varying with the channel. When two CH3OH molecules were considered, they were likely located at both ends of the eight-ring window via the strong and the weak hydrogen bonding.

The tuning of TiO2-Al2O3 composite support for the fabrication of PtSn-based catalysts with superior catalytic performance in the propane dehydrogenation

Low-carbon olefins are considered as important chemical building blocks for the synthesis of various chemicals. Many pioneer works have developed novel processes or catalysts for satisfying their steadily increased demand. In this study, the PtSn-based catalysts were prepared by the TiO2-Al2O3 composite supports for the subsequent catalytic tests in the propane dehydrogenation (PDH) reaction. The prepared supports and corresponding catalysts were intensively characterized by X-ray diffraction (XRD), low-temperature N2 adsorption-desorption, high-resolution transmission electron microscopy (HRTEM), NH3 temperature-programmed desorption (NH3-TPD), and H2 temperature-programmed reduction (H2-TPR), etc. The results of catalytic tests and characterizations revealed that the high dispersion of Pt, the proper acidity, and the enhanced metal-support interaction were responsible for the improved catalytic performance over the prepared catalysts in PDH reaction. Especially, the catalyst prepared with 20 wt.% TiO2-Al2O3 composite support exhibited the stable and highest propylene selectivity (>88 %) under the investigation time.

Metal-organic framework-based composite Ni@MOF as Heterogenous catalyst for ethylene trimerization

MIL-125(Ti)-NH2 has been post-synthetically modified by reaction of pyridine with the terephthalate amino groups to form pyridine-imine that act as ligands of nickel(II). Ni@MOF showed moderate catalytic activity and high selectivity to low carbon olefins C4 and C6. Upon activation with MAO, the catalytic activity could achieve 1.81 × 105 g/mol Ni h, and the selectivity toward C6 was about 76.7 %, of which the 1-C6= occupied 91.5 % under the reaction condition of 50 °C, 1.0 MPa, Al/Ni = 800. Compared with homogenous pyridine-imine nickel complex, the selectivity toward C6 of Ni@MOF composite was greatly enhanced, which could be attributed to confinement effect of pore wall of MOF structure. Moreover, the Ni@MOF could be reused for at least two more catalytic runs without significant loss of activity or selectivity, indicating Ni@MOF had good catalytic stability and recyclability. A possible ethylene oligomerization mechanistic pathway involving reaction intermediates is proposed based on the Cossee mechanism.

UU-type parallel mini-hydrocyclone group for oil-water separation in methanol-to-olefin industrial wastewater

Methanol to olefin (MTO) process is a chemical technology for producing low-carbon olefins from coal-based or natural gas-based methanol. It has changed the pattern of low-carbon olefins relying on petroleum cracking, and opened a new process for producing low-carbon olefins. However, the wastewater generated in the MTO process is difficult to handle. Numbering-up of mini-hydrocyclone is often used to enhance the processing capacity of wastewater treatment when mini-hydrocyclone is used for oil-water separation in methanol-to-olefin process. In this paper, the efficiency and pressure drop distribution of a single mini-hydrocyclone were studied in the laboratory. In addition, according to the UU parallel configuration model, 150 mini-hydrocyclones arranged in parallel were established and used for the oil-water separation process of methanol-to-olefin reaction wastewater. The industrial operation results show that the average flow rate of long-period operation is 282 m3/h, the average pressure drop was 0.31 MPa, and the average separation efficiency of the mini-hydrocyclone group was 90 %. Especially for heavy components such as alkanes and aromatics, it had a good separation effect. Thus, it is shown that the mini-hydrocyclone group has good applicability in oil-water separation.

Synthesis of FER/MFI composite zeolite using isopropylamine as a structure-directing agent

Abstract A comprehensive investigation into the synthesis of the FER/MFI composite zeolite based on the isopropylamine-silica sol-NaAlO2-H2O system has been carried out. Parameters such as the Na2O/SiO2 molar ratio, SiO2/Al2O3 molar ratio, water concentration, and structure-directing agent (SDA) concentration were of great importance in the crystal phase transition and the morphology control. FER/MFI composite zeolites could be successfully prepared under the conditions of the SiO2/Al2O3 molar ratio ranging from 20 to 30 in the gel mixture. SEM and TEM images showed that the two different crystals (FER and MFI frameworks) in FER/MFI composite zeolites had a state of co-existence and staggered growth, which was typical of composite zeolites. Among these factors influencing the synthesis process, adjusting the Na2O/SiO2 molar ratio was easy to control the relative contents of each phase in the composite zeolites. The higher Na2O/SiO2 molar ratio was, the more content of the FER phase was. NH3-TPD and FT-IR of adsorbed pyridine results showed the acidity properties of composite zeolites were significantly different from those of corresponding physical mixtures. Interestingly, the distribution of aluminum between the FER and MFI structures in the composite zeolites was unequal, and aluminum atoms tended to enrich in the phase predominating in the FER/MFI composite zeolites. The catalytic performance in the cracking of olefins like butene and pentene of the FER/MFI composite zeolite was superior to that of the pure ZSM-5 zeolite. The FER/MFI composite zeolite after further modification is expected to become an excellent catalyst for the catalytic cracking of low carbon olefins to ethylene and propylene.

Preparation of low carbon olefins on a core-shell K-Fe5C2@ZSM-5 catalyst by Fischer-Tropsch synthesis.

In this study, a core–shell catalyst based on Fe5C2@ZSM-5 (ZSM-5 capped Fe5C2 as active phase) is prepared by the coating-carbonization method for Fischer–Tropsch synthesis (FTS). Further, the designed ZSM-5 zeolites are utilized to screen the low carbon hydrocarbons from the products generated on the iron carbide active centre, and for catalytic disassembly of the long-chain hydrocarbons into low carbon olefins. Prior to utilization, the physical–chemical properties of the prepared catalysts are systematically characterized by various techniques of X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Fourier transform infrared (FT-IR), and scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM) observations, in addition to the effects of coating-carbonization, molecular sieve coating amount, and K-doping on core–shell iron-based catalysts. Next, the performance of Fischer–Tropsch synthesis is investigated in a micro-fixed bed reactor. The results manifest that, comparing with Fe5C2 and a supported Fe/ZSM-5 catalyst prepared by the traditional impregnation method, the core–shell Fe5C2@ZSM-5 catalysts show higher CO conversion rate, reaction activity and selectivity to low-carbon olefins. Comparatively, the Fe5C2@ZSM-5C catalyst prepared by carbonization after the coating method exhibited more surface area, smaller average pore size, and more reactive active sites, resulting in the improvement of screening of high carbon hydrocarbons and the enhancement of selectivity to low carbon olefins, in comparison to those prepared by the carbonization-coating method. In conclusion, the K-doping catalyst had significantly improved the reactive activity of the core–shell Fe5C2@ZSM-5 catalyst and the selectivity to low carbon olefins, while the CO conversion on K–Fe5C2@ZSM-20C still remained good.