Production Of Light Olefins Research Articles

Influences of the confinement effect and acid strength of zeolite on the mechanisms of Methanol-to-Olefins conversion over H-ZSM-5: A theoretical study of alkenes-based cycle

Methanol-to-Olefins (MTO) conversion over acidic zeolite catalysts has become the most important non-petrochemical route for the production of light olefins. The ‘dual-cycle’ mechanism (i.e., alkenes-based cycle and aromatics-based cycle) over H-ZSM-5 zeolite has been generally accepted for olefins generation from methanol conversion. However, the relationship between the catalytic performance and the confinement effect/acid strength of the catalyst is still unclear. Herein, the methylation, isomerization and cracking processes involved in the alkenes-based cycle are discussed in-depth by density functional theory (DFT) calculations. The calculation results predicted that the transition states can be considerably stabilized by the van der Waals (vdW) interactions from the zeolite framework, resulting in the reduction of the activation barriers. And acid strength can also enhance the reaction activities. However, the catalytic reactivity of all elementary steps in the alkenes-based cycle can be improved at a different degree with increasing the acid strength. In addition, the ethene formation, transformation and the precursor of ethene formation need higher energy. And increasing acid strength can sharply decrease the activation barriers of ethene formation of cracking reaction, indicating that ethene formation may need strong acid strength.

Incorporation of mixed metals into SAPO-34 frameworks by the dry-gel conversion method using mixed templates: investigating catalysts characterisation and performance

ABSTRACTThe crystallisation of the MeAPSO-34 material was studied under dry-gel conversion conditions and using two and three templates. This study has been focused on the effect of the incorporation of a mixture of Ni and Mn into the SAPO-34 framework. The MeSAPO-34 samples were characterised by X-ray diffraction, energy-dispersive X-ray spectrometer, scanning electron microscope, temperature-programmed desorption and Brunner–Emmett–Teller. The influence of metal incorporation into the framework of SAPO-34 (MeAPSO-34) on methanol conversion was investigated in this study. The performances on methanol conversion for these catalysts were different according to the properties of metals incorporated into the SAPO-34 structure. The catalytic performance demonstrated high activity and light olefins selectivity for the prepared catalysts. Among the light olefin products, Mn and Ni incorporation is helpful for propylene generation, but samples with a mixture of Ni and Mn favour the ethylene production.

Thermodynamic equilibrium distribution of light olefins in catalytic pyrolysis

Catalytic pyrolysis is a promising technology to produce light olefins. Gibbs free-energy minimization method was used to study the thermodynamic equilibrium distribution of olefins in catalytic pyrolysis with Aspen Plus software. The result showed that olefin systems with different carbon numbers demonstrated a similar thermodynamic equilibrium distribution. The ethene equilibrium composition increased with increasing reaction temperature and decreased with increasing total hydrocarbon pressure. By contrast, the propene equilibrium composition reached a maximum of 40wt% at 850–950K under 0.1MPa. Ethene yield and propene yield of thermodynamic equilibrium, catalytic pyrolysis and thermal pyrolysis were compared. The use of catalyst greatly increased the yields of ethene and propene, but the yields were still lower than the equilibrium data. Catalytic pyrolysis was carried out in the interaction zone where both catalytic conversion and thermal conversion were important. Propene yield was close to ethene yield at about 950K from the thermodynamic view. Given the shape-selective effect of the catalyst on branched olefins with large carbon number, the equilibrium carbon number distribution of olefins possibly shifted from large carbon numbers to low carbon numbers, resulting in enhanced ethene and propene yields.

Design and Optimization of the Methanol‐to‐Olefin Process. Part I: Steady‐State Design and Optimization

AbstractThe steady‐state design and optimization for a methanol‐to‐olefin (MTO) process is studied. The MTO process is a novel route for light olefin production, especially ethylene and propylene. Comparing with the traditional way to produce olefins by steam cracking, this process offers benefits such as a more flexible range of ethylene‐to‐propylene ratio, higher selectivity toward light olefin, and mild reaction conditions. The design of the overall MTO process is divided into four sections, namely, reaction section, conditioning section, first separation section, and second separation section. After the design of each sub‐part, optimization is performed, in which the design and operating variables are thoroughly investigated. By rigorous simulation, a more economically competitive design flowsheet of the overall MTO process is proposed.

Effects of zinc on Fe-based catalysts during the synthesis of light olefins from the Fischer-Tropsch process

Fe-based catalysts for the production of light olefins via the Fischer-Tropsch synthesis were modified by adding a Zn promoter using both microwave-hydrothermal and impregnation methods. The physicochemical properties of the resulting catalysts were determined by scanning electron microscopy, the Brunauer-Emmett-Teller method, X-ray diffraction, H2 temperature-programed reduction and X-ray photoelectron spectroscopy. The results demonstrate that the addition of a Zn promoter improves both the light olefin selectivity over the catalyst and the catalyst stability. The catalysts prepared via the impregnation method, which contain greater quantities of surface ZnO, exhibit severe carbon deposition following activity trials. In contrast, those materials synthesized using the microwave-hydrothermal approach show improved dispersion of Zn and Fe phases and decreased carbon deposition, and so exhibit better CO conversion and stability.

Ex-situ catalytic pyrolysis of citrus fruit peels over mesoporous MFI and Al-MCM-41

The thermal and ex-situ catalytic pyrolysis of different citrus peels, Citrus paradisi peel, Citrus sinensis peel, Citrus unshiu peel, and Citrus limon peel, were studied by thermogravimetric, evolved gas analysis–mass spectrometry and tandem micro-reactor–gas chromatograph/mass spectrometry analyses. Kinetic analysis revealed more complicated reaction steps and a wider range of activation energies of citrus peels than those of wood powder due to the presence of pectin in the citrus peels. Large amounts of methanol formation from each citrus peel were also recorded by evolved gas analysis–mass spectrometry and fast pyrolysis–gas chromatograph/mass spectrometry analyses at the main decomposition temperature of pectin, between 150 and 250°C. Mesoporous MFI was found to be a more effective catalyst for the production of mono aromatic compounds (benzene, toluene, ethylbenzene, and xylene; 3.06–4.17C%) and light olefins (ethene, propene, butene, and butadiene; 8.13–9.13C%) than Al-MCM-41 (mono aromatic compounds 0.67–0.93C% and light olefins 3.61–4.58C%) because of its higher catalytic activity in deoxygenation and aromatization due to the stronger acidity of mesoporous MFI. The yield of mono aromatic compounds over mesoporous MFI was highest from C. paradisi peel (4.17C%), followed in order by C. sinensis peel (3.83C%), C. unshiu peel (3.61C%), and C. limon peel (3.06C%), due mainly to the different contents and properties of pectin in each citrus peel. The higher activities of mesoporous MFI than Al-MCM-41 were also maintained during the 7 times sequential catalytic pyrolysis of C. paradisi peel, demonstrating the stability of mesoporous MFI catalyst.

Speeding up CFD simulation of fluidized bed reactor for MTO by coupling CRE model

The methanol to olefins (MTO) process opens an economical and important route to produce light olefins. The design of MTO reactor borrows ideas from the reaction–regeneration configuration of the modern fluid catalytic cracking (FCC) units. However, their hydrodynamic behaviors are quite different in the sense that the fluidized bed for MTO reactions operates in different flow regime from that of FCC, calling for new modeling for scale-up. In addition, the coke deposited on catalysts greatly affects the MTO reaction while its generation is very slow. It normally takes tens of minutes or even hours for catalysts to reach the desired level of coke content. Time-dependent computational fluid dynamics (CFD) simulation of such a long process poses a big challenge to reactive multiphase flow modeling. To speed up it, we try to integrate the classic chemical reaction engineering (CRE) model with CFD. In particular, the continuous stirred tank reactor (CSTR) model is established to estimate the steady state distribution of coke content, which is then set as the initial distribution for CFD simulation to shorten the time to reach the steady state of reactive flows. Comparison with experimental data shows good agreement and also great speed-up ratio compared to traditional CFD simulation.

The Fabrication of Ga2O3/ZSM-5 Hollow Fibers for Efficient Catalytic Conversion of n-Butane into Light Olefins and Aromatics

In this study, the dehydrogenation component of Ga2O3 was introduced into ZSM-5 nanocrystals to prepare Ga2O3/ZSM-5 hollow fiber-based bifunctional catalysts. The physicochemical features of as-prepared catalysts were characterized by means of XRD, BET, SEM, STEM, NH3-TPD, etc., and their performances for the catalytic conversion of n-butane to produce light olefins and aromatics were investigated. The results indicated that a very small amount of gallium can cause a marked enhancement in the catalytic activity of ZSM-5 because of the synergistic effect of the dehydrogenation and aromatization properties of Ga2O3 and the cracking function of ZSM-5. Compared with Ga2O3/ZSM-5 nanoparticles, the unique hierarchical macro-meso-microporosity of the as-prepared hollow fibers can effectively enlarge the bifunctionality by enhancing the accessibility of active sites and the diffusion. Consequently, Ga2O3/ZSM-5 hollow fibers show excellent catalytic conversion of n-butane, with the highest yield of light olefins plus aromatics at 600 °C by 87.6%, which is 56.3%, 24.6%, and 13.3% higher than that of ZSM-5, ZSM-5 zeolite fibers, and Ga2O3/ZSM-5, respectively.

An Fe–Mn–Cu/SiO2@silicalite-1 catalyst for CO hydrogenation: the role of the zeolite shell on light-olefin production

The silicalite-1 coated catalyst presents a unique temperature-dependent performance due to the zeolite shell’s diffusion limitation on reactants and products and suppression of secondary reactions on downstream catalysts.

Process for production of xylenes and light olefins

Activation of the immune system due to infection or aging is increasingly linked to impaired neuropsychological function. Toll-like receptors 2 and 4 (TLR2, TLR4) are well-characterised for their role in inflammatory events, and their combined activation has been implicated in neurological diseases. We therefore determined whether TLR2 and TLR4 double gene knockout (GKO) mice showed modified behaviour and cognitive function during a 16-day test sequence that employed the automated IntelliCage test system. The IntelliCage features a home cage environment in which groups of mice live and where water reward is gained through performing various tasks centred on drinking stations in each corner of the apparatus. All mice were tested twice, one month apart (the first sequence termed “R1”and the second “R2”). There were fewer corner visits and nosepokes in TLR2/4 GKO compared to wild-type mice during early exploration in R1, suggesting elevated neophobia in GKO mice. Reduced exploration persisted over subsequent test modules during the dark phase. TLR2/4 GKO mice also displayed increased corner visits during drinking sessions compared to non-drinking sessions, but this was not associated with increased drinking. In subsequent, more complex test modules, TLR2/4 GKO mice had unimpaired spatial learning, but showed markedly poorer performance in a visual discrimination reversal task compared to wild-type mice. These results indicated subtle impairments in behaviour and cognitive functions due to double deficiency in TLR2 and TLR4. These finding are highly relevant to understanding the combined actions of TLR2 and TLR4 on neurological status in a range of different disease conditions.

Nine-Lump Kinetic Study of Catalytic Pyrolysis of Gas Oils Derived from Canadian Synthetic Crude Oil

Catalytic pyrolysis of gas oils derived from Canadian synthetic crude oil on a kind of zeolite catalyst was conducted in a confined fluidized bed reactor for the production of light olefins. The overall reactants and products were classified into nine species, and a nine-lump kinetic model was proposed to describe the reactions based on appropriate assumptions. This kinetic model had 24 rate constants and a catalyst deactivation constant. The kinetic constants at 620°C, 640°C, 660°C, and 680°C were estimated by means of nonlinear least-square regression method. Preexponential factors and apparent activation energies were then calculated according to the Arrhenius equation. The apparent activation energies of the three feed lumps were lower than those of the intermediate product lumps. The nine-lump kinetic model showed good calculation precision and the calculated yields were close to the experimental ones.

The Statistical Experimental Design for Chemical Reactors Modeling

The Statistical Experimental Design techniques are the most powerful tools for the chemical reactors experimental modeling. Empirical models can be formulated for representing the chemical behavior of reactors with the minimal effort in the necessary number of experimental runs, hence, minimizing the consumption of chemicals and the consumption of time due to the reduction in the number of experimental runs and increasing the certainty of the results. Four types of nonthermal plasma reactors were assayed seeking for the highest efficiency in obtaining hydrogen and ethylene. Three different geometries for AC high voltage driven reactors, and only a single geometry for a DC high voltage pulse driven reactor were studied. According to the fundamental principles of chemical kinetics and considering an analogy among the reaction rate and the applied power to the plasma reactor, the four reactors are modeled following the classical chemical reactors design to understand if the behavior of the nonthermal plasma reactors can be regarded as the chemical reactors following the flow patterns of PFR (Plug Flow Reactor) or CSTR (Continuous Stirred Tank Reactor). Dehydrogenation is a common elimination reaction that takes place in nonthermal plasmas. Owing to this characteristic, a paraffinic heavy oil with an average molecular weight corresponding to C15 was used to study the production of light olefins and hydrogen.

Insight into mechanism and selectivity of propane dehydrogenation over the Pd-doped Cu(111) surface

The Pd/Cu(111) surface demonstrates good balance between the activity, selectivity, thermal stability and the maximum use of the noble metal, showing great potential in the catalytic production of light olefins.

Thorough study of the effect of metal-incorporated SAPO-34 molecular sieves on catalytic performances in MTO process

SAPO-34 and MeAPSO-34s (Me=Fe, Co, Ni, La and Ce) molecular sieves were synthesized and used as catalysts for conversion of methanol to light olefins. X-ray diffraction, scanning electron microscopy, nitrogen adsorption–desorption inductively coupled plasma mass spectrometry, Fourier transform infrared spectroscopy and temperature programmed desorption techniques were used to characterize the synthesized catalysts. Thermogravimetric analysis was used to investigate the amount of coke deposited on the spent catalysts during the reaction. The synthesized MeAPSO-34s had the same chabazite topology structure, while metal incorporation gave rise to the different micropore area and acidity. All the SAPO-34 and MeAPSO-34 molecular sieves were very active and selective catalyst for light olefins production. Metal incorporation improved the catalyst lifetime and favored the ethylene and propylene product. Concerning the yield of light olefins at 425°C and 1bar, NiAPSO-34 favored ethylene production and CeAPSO-34 and LaAPSO-34 were helpful for propylene production. Light olefins yield decreased with time on stream for all the samples; although, this decrease rate is lower for MeAPSO-34 than for the parent SAPO-34. The catalyst lifetime increased in an order as follows: Ce->La->Co->Ni->Fe->SAPO-34. The rare earth modified catalysts exhibited lower methanation than parent SAPO-34 and transition metal modified catalysts.

Optimization using response surface methodology and kinetic study of Fischer–Tropsch synthesis using SiO2 supported bimetallic Co–Ni catalyst

Catalyst using bimetallic Ni–Co on SiO2 as support was prepared, characterized and tested for Fischer–Tropsch synthesis. RSM (Response surface methodology) and the CCD (Central composite design) were employed in determining the optimal condition for light olefin production. The process parameters of syngas ratio, operational pressure, and reaction temperature were chosen as independent variables in CCD. The quadratic model was developed for process optimization and statistical experimental designs. It is found that the syngas ratio, operational pressure, and reaction temperature are significant to CO conversion and light olefin (C2–C4) selectivity. The combination of temperature and pressure is found to be significant to CO conversion, while the combination of syngas ratio and pressure is found to be only significant to alkene selectivity. The optimal conditions with setting maximum CO conversion and alkene selectivity are the following: syngas ratio 2, total pressure 36 bar, reaction temperature 302 °C. At optimal condition, the predicted CO conversion and alkene selectivity reach 20% and 29%, respectively. Thirty different models derived from 10 different mechanisms according to LHHW (Langmuir–Hinshelwood–Hougen–Watson) type rate expressions were tested against experimental data. The CO insertion mechanism is found to yield the best fit with activation energy being 98.5 kJ/mol. The literature comparison of activation energy and light alkene selectivity among different supports were made.

Preparation and characterization of promoted Fe–Mn/ZSM-5 nano catalysts for CO hydrogenation

In the present work, a series of iron based catalysts supported on ZSM-5 were prepared using incipient wetness method and tested for C2–C4 light olefins production from syngas (CO + H2). The effects of Fe and Mn loading, calcination conditions, different promoters, wt.% K as an optimal promoter and operational conditions on the catalytic performance of the optimal catalyst were investigated. It was found that the catalyst containing 8% Fe/2.4%Mn/ZSM-5 promoted with 2 wt.%K had the best catalytic performance for light olefins production. The best operational conditions were H2/CO = 2/1 M feed ratio, T = 270 °C, gas hourly space velocity (GHSV) = 2600 h−1 and 1 bar pressure. Catalysts and precursors were characterized by X-ray diffraction (XRD), transmission electron microcopy (TEM), thermal gravimetric analysis (TGA), temperature program reduction (TPR), Scanning electron microcopy (SEM), differential scanning calorimetry (DSC) and N2 adsorption–desorption measurements. The TPR spectrum for 8% Fe/2.4%Mn/ZSM-5 showed lower reduction temperatures respect to similar Fe–Mn catalysts.

Production of Light Olefins Through Catalytic Cracking of C5 Raffinate Over Surface-Modified ZSM-5 Catalyst.

Surface modification of phosphorous-containing porous ZSM-5 catalyst (P/C-ZSM5-Sil.(X)) was carried out by a chemical liquid deposition (CLD) method using tetraethyl orthosilicate (TEOS) as a silylation agent. Different amount of TEOS (X = 5, 10, 20, and 30 wt%) was introduced into P/C-ZSM5il.(X) catalysts for surface modification. The catalysts were used for the production of light olefins (ethylene and propylene) through catalytic cracking of C5 raffinate. It was found that external surface acidity of P/C-ZSM5-Sil.(X) catalysts significantly decreased with increasing TEOS content. In the catalytic reaction, both conversion of C5 raffinate and yield for light olefins showed volcano-shaped curves with respect to TEOS content. Among the catalysts tested, P/C-ZSM5-Sil.(20) catalyst exhibited the best catalytic performance in terms of conversion of C5 raffinate and yield for light olefins. Thus, an optimal TEOS content was required for CLD treatment to maximize light olefin production in the catalytic cracking of C5 raffinate over P/C-ZSM5-Sil.(X) catalysts.

SnxOy/SAPO-34 as catalysts for catalytic dehydration of bio-ethanol: impacts of oxidation state, interaction, and loading amount

Light olefins are primarily used for the production of petrochemicals and polymers. The increases in the price of naphtha feedstock and light olefins are often observed with the shortage of petroleum. Together with the green concept, the production of light olefins from renewable resources has received wide attention. SAPO-34 is a potential catalyst for the catalytic dehydration of ethanol to light olefins, especially propylene due to its mild acidity and suitable pore size. Tin oxide-doped SAPO-34 was found to enhance the production of propylene, and its oxidation state can also alter the product distribution. Besides propylene, light aromatic hydrocarbons and oxygenates were also co-produced. Therefore, in this work, further studies were made on tin oxide-doped SAPO-34 catalysts in order to observe the changes of product distribution upon the changes of oxidation state, interaction with the support, and the amount of Sn loading. All supported catalysts were prepared by solid–solid interaction method, and characterized by using SAA, XPS, and XRD. The reaction was carried out in an isothermal fixed bed reactor at 400 °C and 1 atm. The gaseous and liquid products were analyzed by an online-GC, SIMDIST-GC and GC × GC-TOFMS. As a result, unsupported Sn0 catalyst was found responsible for the formation of cooking gas (hereby defined as the mixture of propane and butane), whereas SnO2 enhanced hexane, cyclohexane and benzene formation. SnO gave the high selectivity of oxygenate compounds. Owing to the Sn-support interaction, metallic Sn-doped SAPO-34 exhibited significantly higher selectivity of cooking gas that of using the unsupported metallic Sn, possibly due to the higher dispersion of metal oxide on the support and the interaction between the metal and the support. Furthermore, the impacts of tin oxides and their interaction with the SAPO-34 support were more pronounced at a high loading percentage. Propylene and cooking gas were more highly produced at a higher Sn loading.

Iron catalyst encapsulated in carbon nanotubes for CO hydrogenation to light olefins

Fe-based catalyst is an outstanding candidate for the Fischer-Tropsch reaction to get light olefins from syngas directly. However, exposed Fe species are susceptible to sintering and coking, which lead to deactivation. Here, we demonstrate that Fe nanoparticles encapsulated in pod-like carbon nanotubes (Pod–Fe) can be used as an efficient Fischer-Tropsch catalyst to produce light olefins. It gave a higher selectivity of light olefins (45%) and high stability over 120 h reaction (P = 0.5 MPa, T = 320 °C, CO:H2 = 1:2, gas hourly space velocity = 3500 h−1). A catalyst with exposed Fe particles on the outside of the Pod-Fe (FeOx/Pod-Fe) catalyst showed a selectivity of light olefins of 42%, but had a significantly lower stability due to the agglomeration of Fe nanoparticles and carbon deposition. These results indicated that the graphene shell of Pod-Fe played an important role in protecting the Fe particles and provided a rational way to enhance the activity and stability of Fe-based catalysts in high temperature reactions.

Reprint of “Ethanol to higher hydrocarbons over Ni, Ga, Fe-modified ZSM-5: Effect of metal content”

The effect of metal content on catalyst properties was studied by comparing unmodified HZSM-5 and 0.5–7wt.% Ga, Fe and Ni modified HZSM-5 in the ethanol conversion to hydrocarbons at 623K by combining detailed catalyst characterization (XRD, TEM, N2 adsorption, H2-TPR and NH3-TPD) and catalytic testing. Low metal amounts (<1wt.%) were found to have a positive effect on the production of light olefins, C2–C4 paraffins, aromatics and C5+ hydrocarbons. Increasing the amount of metal leads to a decreased production of these hydrocarbons, which is attributed to bulky metal clusters formation. These clusters decrease the accessibility of the acid sites due to pore blockage. For the first time, catalyst performance in ethanol conversion have been assessed at similar conditions, i.e. same conversion, showing that the selectivity towards the various product classes was not altered by the metal introduction. The site time yields of the metal modified HZSM-5 catalysts, based on the total concentration of accessible acid sites, exhibit a decreasing trend as function of metal content. This can be attributed to a lower acid strength of the accessible acid sites.