Selective Production Of Light Olefins Research Articles

Combined Strategies Enable Highly Selective Light Olefins and para-Xylene Production on Single Catalyst Bed.

Achieving multiple high-value-added chemical production through novel reaction processes and shape-selective catalytic strategy is the key to realizing efficient low-carbon catalytic processes. In this work, a methanol-toluene coreaction system was developed, and combined control strategies of reaction pathway guidance and shape-selective catalysis were applied for the successful production of light olefins and para-xylene on single HZSM-5 catalyst bed. Cofeeding toluene additionally provides reactive and flowing aromatic hydrocarbon pool species that change the dominant reaction pathway in the complex network of the methanol reaction on HZSM-5 and promote the formation of ethylene. For the first time, the key reaction intermediates methylmethylenecyclodiene are directly captured and identified by experimental and theoretical techniques. This helps to propose the catalytic cycle for the dominant generation of ethylene and, more importantly, enriches the methanol-to-hydrocarbons (MTH) chemistry and hydrocarbon pool mechanism. Furthermore, 0.4HZSM-5@S-1-CLD, an optimized HZSM-5 catalyst modified by the silicalite-1 epitaxial growth followed by silanization approach, realizes highly selective production of light olefins (especially ethylene) and para-xylene, while excellent reactant activity is maintained. This highly efficient coreaction route gives an important leading significance in synthesizing the raw materials for the polyolefin and polyester industries. The establishment of the combined control strategies provides a model for the joint production of multiple target chemicals in complex catalytic processes.

Insight into the synergistic effect of copper and sodium over metal organic framework-derived Fe-based catalyst for CO2 hydrogenation to aromatics

One-step hydrogenation of carbon dioxide (CO2) to aromatics is a promising strategy for relieving the stress of fossil fuels. Here, a copper and sodium co-modified Fe-based catalyst (3-NFC-5) was synthesized through the pyrolysis of Cu-doped MIL-101(Fe) and Na impregnation. After combining with HZSM-5, 42.11% CO2 conversion and 50.68% total aromatics selectivity was achieved. Through multiple characterization and DFT calculations, the synergistic promotion of Na and Cu on light olefins intermediate production was revealed. Na was crucial for COOH* formation as the intermediate for reverse water gas shift reaction (RWGS), whose concentration could be further enhanced after Cu modification. Controlled C-C coupling towards C2-C4 hydrocarbons was realized by the enhanced CO non-dissociative activation and the increased content of χ-Fe5C2 after Cu doping, which was responsible for the inhibited surface CHx* concentration and selective production of light olefins, respectively.

Effects of zinc on χ-Fe5C2 for carbon dioxide hydrogenation to olefins: Insights from experimental and density function theory calculations

Production of light olefins from CO 2 , the primary greenhouse gases, is of great importance to mitigate the adverse effects of CO 2 emission on environment and to supply the value-added products from non-petroleum resource. However, development of robust catalyst with controllable selectivity and stability remains a challenge. Herein, we report that Zn-promoted Fe catalyst can boost the stable and selective production of light olefins from CO 2 . Specifically, the Zn-promoted Fe exhibits a highly stable activity and olefin selectivity over 200 h time-on-stream compared to the unpromoted Fe catalyst, primarily owing to the preservation of active χ-Fe 5 C 2 phase. Structural characterizations of the spent catalysts suggest that Zn substantially regulates the content of iron carbide on the surface and suppresses the re-oxidation of bulk iron carbide during the reaction. DFT calculations confirm that adsorption of surface carbon atoms and graphene-like carbonaceous species are not thermochemically favored on Zn-promoted Fe catalyst. Carbon deposition by C—C coupling reactions of two surface carbon atoms and dehydrogenation of CH intermediate are also inhibited. Furthermore, the effects of Zn on antioxidation of iron carbide were also investigated. Zn favored the hydrogenation of surface adsorbed oxygen atoms to H 2 O and the desorption of H 2 O, which reduces the possibility of surface carbide being oxidized by the chemisorbed oxygen.

Two-Step Conversion of CO2 to Light Olefins: Laboratory-Scale Demonstration and Scale-Up Considerations

The highly selective production of light olefins from CO2 was demonstrated for the first time with a laboratory-scale process comprising consecutive reverse water gas shift (RWGS) and Fischer–Tropsch (FT) reactors. The RWGS reaction, catalyzed by rhodium washcoated catalyst at 850 °C yielded good quality syngas with conversion values close to the thermodynamic equilibrium and without experiencing catalyst deactivation from carbon formation or sintering. For the FT synthesis, a packed bed Fe-Na-S/α-Al2O3 catalyst was used. The highest light olefin selectivity observed for the FT-synthesis was 52% at 310 °C, GHSV of 2250 h−1 and H2/CO ratio of 1. However, the optimal conditions for the light olefin production were determined to be at 340 °C, a GHSV of 3400 h−1 and a H2/CO ratio of 2, as the CO conversion was markedly higher, while the light olefin selectivity remained at a suitably high level. In addition to the experimental results, considerations for the further optimization and development of the system are presented. The combined RWGS–FT process seems to work reasonably well, and initial data for basic process design and modeling were produced.

Selective production of light olefins over zeolite catalysts: Impacts of topology, acidity, and particle size

Compared to conventional steam cracking, catalytic cracking of naphtha and methanol-to-olefins (MTO) over zeolite catalysts have been proved as the most successful processes for producing light olefins. To achieve the maximum light olefins yield and the longest lifetime, zeolite catalysts with excellent catalytic performance should be designed, by choosing suitable structure and regulating their physicochemical properties. In this review, the impacts of topology, acidity, and particle size of zeolites on the catalytic performance of naphtha cracking and MTO reactions, especially the light olefins selectivity and lifetime are systematically discussed. We hope that this review can be helpful not only to deeply understand the structure–property-performance relationship of various zeolite catalysts, but also to design more excellent zeolite catalysts for these two processes.

Catalysts for the Conversion of CO2 to Low Molecular Weight Olefins-A Review.

There is a large worldwide demand for light olefins (C2=–C4=), which are needed for the production of high value-added chemicals and plastics. Light olefins can be produced by petroleum processing, direct/indirect conversion of synthesis gas (CO + H2) and hydrogenation of CO2. Among these methods, catalytic hydrogenation of CO2 is the most recently studied because it could contribute to alleviating CO2 emissions into the atmosphere. However, due to thermodynamic reasons, the design of catalysts for the selective production of light olefins from CO2 presents different challenges. In this regard, the recent progress in the synthesis of nanomaterials with well-controlled morphologies and active phase dispersion has opened new perspectives for the production of light olefins. In this review, recent advances in catalyst design are presented, with emphasis on catalysts operating through the modified Fischer–Tropsch pathway. The advantages and disadvantages of olefin production from CO2 via CO or methanol-mediated reaction routes were analyzed, as well as the prospects for the design of a single catalyst for direct olefin production. Conclusions were drawn on the prospect of a new catalyst design for the production of light olefins from CO2.

Effects of Ce/Al molar ratio in Ce-incorporated mesoporous SAPO-34 on the physicochemical property and catalytic performance in the selective production of light olefins via conversion of chloromethane

In this work, SAPO-34 and a series of meso-CeAPSO-34(mesoporous cerium incorporated silicoaluminophosphate, X = Ce/Al molar ratio, X = 0, 0.02, 0.05, 0.07, and 0.10) catalysts with different Ce/Al molar ratio(X) were applied for olefin generation, especially propylene. The chloromethane to olefin (CMTO) reaction at 450 °C demonstrated that meso-CeAPSO-34(0.05) catalysts showed stable chloromethane conversion, with the highest propylene selectivity. The CM conversion increased with the introduction of mesoporosity. The mesopore volume increased and the amount of active sites maintained sufficiently high with the incorporation of cerium. The structural stability of the catalysts and the diffusivity of products improved with the addition of proper amount of cerium. In summary, the enhancement of the physicochemical properties of the catalysts played a crucial role in catalytic stability and the selective production of propylene in the CMTO reaction, resulting in stably high CM conversion and the highest propylene selectivity over meso-CeAPSO-34(0.05) catalyst.

Hierarchical hollow Al-rich nano ZSM-5 crystals for highly selective production of light olefins from naphthenes

An Al-distribution regulated one-step desilication approach is developed to fabricate hierarchical hollow Al-rich nano ZSM-5 crystals (Si/Al molar ratio = 12.5) for highly selective production of light olefins from naphthenes.

Fine-tuning the surface acidity of hierarchical zeolite composites for methanol-to-olefins (MTO) reaction

The zeolite nanosheet composites, containing a high acidic density ZSM-5 and weak-acidic Silicalite-1 nanosheets (Si-NS) acting as a core and a shell, respectively, have been successfully fabricated by a one-pot hydrothermal synthesis. The shell thickness, textural properties, and acidity of synthesized composites can be easily adjusted by hydrothermal synthesis time and temperature. The uniform thickness of 9.4 ± 1.1 nm of Silicalite-1 shells can be observed when using the crystallization temperature of 110 °C, whereas the non-uniform distribution of zeolite shells becomes predominant with increasing the crystallization temperature due to its rapid growing rate. Interestingly, due to the different acidity of core and shell materials, the acid site distribution of the composites has been modified with respect to their isolated zeolites, and therefore the highly selective production of propylene in MTO process is greatly improved (>90% and 50% for the hierarchical composite and unmodified ZSM-5, respectively). In addition, a significantly lower coke formation could be achieved due to the suppression of further side reactions over the stacking-layered siliceous covering on high acidic density ZSM-5 surfaces. This example opens up perspectives for the development of hierarchical zeolite composites with the modified acid surfaces for highly selective production of light olefins.

Selective Production of Light Olefins from Fischer–Tropsch Synthetic Oil by Catalytic Cracking

Biomass is a potentially unlimited source of chemicals and energy for sustainable development. However, there are currently no effective methods to produce lower olefins from biomass-derived feedst...

Insight into the Intrinsic Active Site for Selective Production of Light Olefins in Cobalt-Catalyzed Fischer–Tropsch Synthesis

Selective production of light olefins remains a great challenge in cobalt-catalyzed Fischer–Tropsch synthesis (FTS). Understanding the nature of the active site and the structure–performance relati...

Propane to light olefins by one-pot cascade and series reactions

Propane is selectively converted to propylene via propane dehydrogenation (PDH) process for an on-purpose propylene usage. Due to regional market demands, olefin interconversion for propylene-to-ethylene (PTE) is required to control the supply-demand of light olefins. Our concern centers on combining the PDH and PTE reactions to achieve a simple catalytic process for selective production of light olefins from propane. Herein, converting propane to light olefins is investigated via cascade and series PDH-PTE reactions over highly selective two catalysts. From the catalytic results, selectively produced propylene over a PDH catalyst (Cr2O3/Al2O3) from propane was readily converted to other light olefins over a PTE catalyst (modified ZSM-5). The modified ZSM-5 as the PTE catalysts was further studied in the both cascade and series reactions with different reaction conditions in order to find an optimum reaction condition for high olefin yield and selectivity with low methane selectivity as well as to investigate the influence of process parameters on the catalytic activity. The AHFS treated ZSM-5 (AHFS-ZSM-5) as the PTE catalyst in PDH-PTE series reaction exhibited a superior light olefin yield (50.7 wt%) and olefin selectivities up to 76.7 wt% (26.9 wt% ethylene, 38.0 wt% propylene, and 11.8 wt% butenes) with low methane selectivity (4.27 wt%) at 550 °C, WHSV 7 h−1, and propylene partial pressure in the PDH model feed 0.025 MPa.

Comparison of HZSM-5 Zeolite and SAPO (-18 and -34) Based Catalysts for the Production of Light Olefins from DME

The catalytic transformation of dimethyl ether (DME) for the selective production of light olefins has been studied over HZSM-5 zeolite (with SiO2/Al2O3 = 280) and silicoaluminophosphate (SAPO-18 and -34) based catalysts in order to asses the effect of shape selectivity on the catalytic performance. The catalysts have been synthesized by agglomerating the active materials with bentonite (as a binder) and alpha-alumina (as inert filler). The runs have been carried out at a pressure of 1.5 bar in a fixed bed reactor, under the following reaction conditions: temperature, 350 and 400 °C; space time, 1.6 and 0.064 gcatalyst h molC −1; time on stream, 60 min. The results reveal the importance of the severity of the shape selectivity of the catalysts on the reaction indices (conversion, yield and selectivity of olefins, and catalyst stability). The HZSM-5 zeolite based catalyst has the best kinetic behavior, being stable at 350 °C, with a DME conversion of 4.5 % and selectivity to ethylene, propylene and butenes of 27, 50 and 16 %, respectively.

A selective catalyst for methanol conversion into light olefin with a high propylene to ethylene ratio

MSU-S catalyst, assembled from ZSM-5 zeolite seed (MFI), was synthesized with silica to alumina ratio 55 and characterized by XRD, NH3-TPD, BET and FT-IR techniques. It was tested in a vertical fixed bed reactor for selective production of light olefins from methanol (MTO) at temperatures of 400, 450 and 500 °C and WHSV of 1, 5 and 25 h−1. After thorough investigation, it was found that WHSV=5 h−1 and temperature of 500 °C are the optimum conditions for maximum light olefin yield, which was 52% with propylene to ethylene ratio of 4.57. Acidity of MSU-S was promoted by incorporation of phosphotungusticacid (HPW) and a direct method to reach high HPW dispersion and thermal stability. Maximum light olefin yield was observed over HPW-MSU-S at the optimum reaction conditions to be nearly 60% with propylene to ethylene ratio of 4.3.

Effect of preparation of Fe–Zr–K catalyst on the product distribution of CO2 hydrogenation

Small and uniform Fe–Zr–K particles with mesopores obtained by microwave assisted homogeneous precipitation show high catalytic activity and stability for the selective production of light olefins with low CO from CO2 hydrogenation.

Cracking of High Density Polyethylene Pyrolysis Waxes on HZSM-5 Catalysts of Different Acidity

High density polyethylene (HDPE) cracking has been carried out in a thermal-catalytic two-step unit for the selective production of light olefins. Continuous pyrolysis of HDPE has been conducted in a conical spouted bed reactor at 500 °C, and the volatiles formed (mainly waxes) have been transformed in a downstream fixed bed catalytic reactor at 500 °C. The effect of catalyst acidity on product yield and composition has been studied by using three catalysts based on HZSM-5 zeolites with a SiO2/Al2O3 ratio of 30, 80, and 280. The maximum light olefin yield (58 wt %) has been obtained using the most acidic catalyst (SiO2/Al2O3 ratio of 30), with the individual yields of ethylene, propylene, and butenes being 9.5, 32, and 16.5 wt %, respectively. The results are a clear evidence of the higher efficiency of the two-step reaction system compared to the in situ catalytic pyrolysis (single-step), which is explained by the suitable combination of operating conditions in each one of the steps.

Production of Light Olefins from Polyethylene in a Two-Step Process: Pyrolysis in a Conical Spouted Bed and Downstream High-Temperature Thermal Cracking

A two-step process has been used for the selective production of light olefins by the thermal cracking of high-density polyethylene. The plastic has been continuously fed into a conical spouted-bed reactor (CSBR) operating at 500 °C, which yields 93 wt % of waxes (C21+) and C12–C21 hydrocarbons. The volatile product stream has been cracked downstream in a multitubular (quartz tubes) reactor in the 800–950 °C range, with short residence times (0.016–0.032 s). A yield of 77 wt % of light olefins (C2–C4) has been obtained by operating at 900 °C in the second step. The maximum yields of ethylene, propylene, and butenes are 40.4, 19.5, and 17.5 wt %, respectively. Given the short residence time of the products in the reactor, the yield of aromatics is only 6.2 wt %. The high light olefin yield is due to the excellent performance of both steps. The CSBR allows maximizing the yield of waxes and avoiding defluidization problems. The operating conditions in the multitubular reactor (low concentration of the compou...

Selective conversion of bio-oil to light olefins: Controlling catalytic cracking for maximum olefins

Light olefins are the basic building blocks for the petrochemical industry. In this work, selective production of light olefins from catalytic cracking of bio-oil was performed by using the La/HZSM-5 catalyst. With a nearly complete conversion of bio-oil, the maximum yield reached 0.28±0.02kg olefins/(kg bio-oil), which was close to that from methanol. Addition of La into zeolite efficiently changed the total acid amount of HZSM-5, especially the acid distribution among the strong, medium and weak acid sites. A moderate increase of the number of the medium acid sites effectively enhanced the olefins selectivity and improved the catalyst stability. The comparison between the catalytic cracking and pyrolysis of bio-oil was studied. The mechanism of the conversion of bio-oil to light olefins was also discussed.