Production Of Light Olefins Research Articles

Neat dimethyl ether conversion to olefins (DTO) over HZSM-5: Effect of SiO2/Al2O3 on porosity, surface chemistry, and reactivity

This study investigates the unique effect of the SiO2/Al2O3 ratio (30, 80, and 280) on the physicochemical and reactivity properties of the HZSM-5. This catalyst can be used for light olefin production using neat dimethyl ether (DTO). Crystallinity and porosity of the HZSM-5 samples as measured by XRD and N2 isotherms, show minimal effect of the SiO2/Al2O3 ratio. Acidity measurements by NH3-TPD, on the other hand, exhibit weak and strong acid sites, with both their ratio and total acidity being reduced with increasing SiO2/Al2O3. Experiments in the Berty reactor allow analyzing the changes of dimethyl ether (DME) conversion, light olefin selectivity and catalyst stability with SiO2/Al2O3 ratio. Moreover, these studies show that from the three HZSM-5 catalysts considered, the one with the SiO2/Al2O3=280 gives the highest light olefin selectivity. A maximum performance of 59% DME conversion at 1.16% coke load, and 50% light olefins selectivity (5% ethylene, 21% propylene, 24% butane) are observed at 450°C. In addition, this thermal level leads not only to find a promising catalyst performance for the SiO2/Al2O3=280 ZSM5 catalyst but to establish also its unchanged activity with time-on-stream. On the basis of the experimental data obtained it is postulated that an “in series” reaction network is adequate to describe the chemical changes with formed olefins undergoing eventually further transformation to paraffins and heavier aromatic hydrocarbons.

Reactivities of C6–8 hydrocarbons and effect of coexistence of another hydrocarbon in cracking on H-ZSM-5 catalyst at high temperatures

The cracking of C6–8 hydrocarbons on H-ZSM-5 (Si/Al=51) at high temperatures was carried out as a model reaction of naphtha cracking to produce light olefins. The reactivity of n-paraffin increased with an increase in carbon number, while the selectivities for light olefins were almost constant. In the cracking of cycloparaffin, the selectivity for the corresponding aromatics was very high, indicating that the dehydrogenation occurred directly without C-C bond cleavage. In the case of cycloparaffin cracking, the deactivation of H-ZSM-5 with time-on-stream (TOS) was fast due to high BTX (benzene, toluene, and xylene) selectivity. The deactivation of H-ZSM-5 in the cracking of methylcyclohexane was especially fast due to very high toluene selectivity. Coexistent 1-hexene did not affect the cracking rate of n-heptane, cyclohexane, or methylcyclohexane, indicating that monomolecular cracking was predominant at as high a temperature as 923K. In contrast, coexistent cyclohexane and methylcyclohexane considerably affected the cracking rate of n-heptane because of their slow diffusion in the pores of H-ZSM-5.

Elucidating the olefin formation mechanism in the methanol to olefin reaction over AlPO-18 and SAPO-18

The mechanism of the methanol to olefin (MTO) reaction over AlPO-18 (without Bronsted acid sites) and two SAPO-18 (with different Bronsted acid site densities) catalysts has been investigated. The Bronsted acid site density of AlPO-18 and SAPO-18 catalysts was determined by 1H MAS NMR spectroscopy. Methanol conversion over the catalysts showed that the catalytic activity of the catalysts was strongly influenced by their Bronsted acid site density. Using 13C magic angle spinning (MAS) NMR, we directly observed the pentamethylcyclopentenyl cation (pentaMCP+) over SAPO-18 under real MTO reaction conditions, but no carbenium ion was detected over AlPO-18. Furthermore, analysis of confined organics by 13C MAS NMR and GC-MS clearly demonstrated that higher Bronsted acid site density improved the formation and accumulation of some important and reactive hydrocarbon pool species, such as pentaMCP+ and polymethylbenzenes. With the aid of the 12C/13C-methanol switch technique, the detailed olefin formation mechanism was elucidated. During the MTO reaction, light olefin generation over SAPO-18 mainly followed the aromatic-based hydrocarbon pool mechanism; however, the olefin methylation and cracking mechanism accounted for the production of light olefins over AlPO-18.

Direct production of light olefins from syngas over potassium modified Fe–Mn catalyst

A series of potassium promoted Fe–Mn catalysts for light olefin synthesis from CO hydrogenation were prepared by the co-precipitation-calcination-impregnation method. The impact of potassium promoter on the textural properties, reduction behavior, adsorption of hydrogen, bulk phase composition and their correlation with Fischer–Tropsch synthesis (FTS) performances were emphatically studied. As revealed by N2 physisorption, the increasing of potassium had no distinct effect on the size of α-Fe2O3 and surface area. H2 temperature-programmed reduction/desorption showed that potassium inhibited the reduction and hydrogen adsorbability of catalysts. CO temperature-programmed desorption showed that potassium enhanced the CO adsorption of catalysts. X-ray photoelectron spectroscopy indicated the enrichment of promoter atoms on the surface of catalysts. The X-ray diffraction and Mossbauer effect spectroscopy results revealed that potassium made carburization easy. After reduction with syngas (H2/CO = 20) for 48 h, FTS test was performed with the syngas (H2/CO = 3.5) in the high temperature Fischer–Tropsch synthesis process. The maximum of CO conversion and selectivity to light olefins was noted on increasing K content (2.8 mol% K/Fe), followed by a significant decline at the excessive potassium level. At the point, the selectivity of light olefins and olefin/paraffin (C2–C4) was 27.75 mol% and 8.54. The results indicated that potassium promoter could inhibit the water gas shift reaction, suppress hydrogenation ability, which promoted the production of light olefins via suppressing the secondary hydrogenation reaction.

The production of light olefins by catalytic cracking of the microalga Isochrysis zhanjiangensis over a modified ZSM-5 catalyst

This study investigated the catalytic cracking of the microalga Isochrysis zhanjiangensis over a modified ZSM-5 catalyst with the aim of producing C2–C4 light olefins. Compared with the thermal cracking process, the catalytic cracking of this microalga displayed higher selectivity for and greater yield of these olefins. The catalytic cracking of extracted lipids and the corresponding residues of the microalga was also examined, and the results showed that the lipids could be efficiently converted to light olefins. The catalytic cracking of lipids extracted by different solvents demonstrated that neutral lipids gave the highest yield of light olefins at 36.7%. The yields of light olefins obtained from catalytic cracking of the extraction residues were much lower than the yields obtained from lipids, and thus the lipids, especially the neutral lipids, are the primary contributors to the generation of light olefins. Isochrysis zhanjiangensis with an elevated neutral lipid content will therefore give the highest yield of light olefins through catalytic cracking. The catalytic cracking of a microalga resulted in an 11.0% yield of light olefins. When the neutral lipid content in the microalga was increased to 33.9%, the yield of light olefins was improved to 16.4%.

Production of Light Olefins from Biosyngas by Two-stage Catalytic Conversion Process via Dimethyl Ether

NiSAPO-34 and NiSAPO-34/HZSM-5 were prepared and evaluated for the performance of dimethyl ether (DME) conversion to light olefins (DTO). The processes of two-stage light olefin production, DME synthesis and the following DTO, were also investigated using biosyngas as feed gas over Cu/Zn/Al/HZSM-5 and the optimized 2%NiSAPO-34/HZSM-5. The results indicated that adding 2%Ni to SAPO-34 did not change its topology structure, but resulted in the forming of the moderately strong acidity with decreasing acid amounts, which slightly enhanced DME conversion activity and C2=-C3= selectivity. Mechanically mixing 2%NiSAPO-34 with HZSM-5 at the weight ratio of 3.0 further prolonged DME conversion activity to be more than 3 h, which was due to the stable acid sites from HZSM-5. The highest selectivity to light olefins of 90.8% was achieved at 2 h time on stream. The application of the optimized 2%NiSAPO-34/HZSM-5 in the second-stage reactor for DTO reaction showed that the catalytic activity was steady for more than 5 h and light olefin yield was as high as 84.6 g/m3syngas when the biosyngas (H2/CO/CO2/N2/CH4=41.5/26.9/14.2/14.6/2.89, vol%) with low H/C ratio of 1.0 was used as feed gas.

Modified HZSM-5 as FCC additive for enhancing light olefins yield from catalytic cracking of VGO

HZSM-5 with varying Si/Al2 ratios were modified with Mn and alkaline treatment and tested as FCC catalyst additives to enhance the yield of light olefins (in particular, propylene) from catalytic cracking of hydrotreated Arab Light vacuum gas oil (VGO). The performance of the Mn/HZSM-5 and alkaline treated HZSM-5 additives were assessed using a commercial equilibrium USY FCC catalyst (E-Cat) in a fixed-bed micro-activity test unit at 550°C and various catalyst/oil ratios. The yield of light olefins over E-Cat containing parent HZSM-5 increased to 18.1, 25.4 and 27.4wt% for Si/Al2 of 30, 80 and 280, respectively, compared with 15.4wt% over E-Cat (at 75wt% conversion). Further increase in light olefins yield was achieved upon using Mn modified HZSM-5 as an additive. The highest light olefins yield of 29.2wt% was achieved over E-Cat-Mn/HZSM-5 (Si/Al2=80, 2.0wt% Mn). The enhanced production of light olefins over the Mn/HZSM-5 additive is mainly attributed to the decrease in the acid density and the amount of strong acid sites, and (possibly) the partial narrowing of ZSM-5 micropore. Alkaline treated HZSM-5 also exhibited high light olefins yield compared with parent HZSM-5, due to the formation of hierarchical micro-meso topology. The highest light olefins yield of ∼28.3wt% was obtained over E-Cat-containing alkaline treated HZSM-5 (Si/Al2=80–280, using the appropriate desilication conditions).

Catalysis for biomass and CO2use through solar energy: opening new scenarios for a sustainable and low-carbon chemical production

The use of biomass, bio-waste and CO2 derived raw materials, the latter synthesized using H2 produced using renewable energy sources, opens new scenarios to develop a sustainable and low carbon chemical production, particularly in regions such as Europe lacking in other resources. This tutorial review discusses first this new scenario with the aim to point out, between the different possible options, those more relevant to enable this new future scenario for the chemical production, commenting in particular the different drivers (economic, technological and strategic, environmental and sustainability and socio-political) which guide the selection. The case of the use of non-fossil fuel based raw materials for the sustainable production of light olefins is discussed in more detail, but the production of other olefins and polyolefins, of drop-in intermediates and other platform molecules are also analysed. The final part discusses the role of catalysis in establishing this new scenario, summarizing the development of catalysts with respect to industrial targets, for (i) the production of light olefins by catalytic dehydration of ethanol and by CO2 conversion via FTO process, (ii) the catalytic synthesis of butadiene from ethanol, butanol and butanediols, and (iii) the catalytic synthesis of HMF and its conversion to 2,5-FDCA, adipic acid, caprolactam and 1,6-hexanediol.

Effect of calcination conditions on the structure and catalytic performance of MgO supported Fe–Co–Ni catalyst for CO hydrogenation

The Fe–Co–Ni catalysts prepared using co-precipitation procedure, were tested for production of light olefins via Fischer–Tropsch synthesis. The effect of a range of calcination conditions such as temperature, time and atmosphere of calcination on the structure and catalytic performance of MgO supported Fe–Co–Ni catalyst was investigated. It was found that the catalyst calcined at 500 °C for 6 h under air atmosphere has shown the best catalytic performance for CO hydrogenation. Characterization of catalyst precursors and calcined samples (fresh and used) was carried out using powder X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Brunauer–Emmett–Teller (BET) measurements. It was observed that all of different investigated variables influenced the structure, morphology and catalytic performance of the catalysts.

The sol-gel derived Co-Mn/TiO2 catalysts for light olefins production

In this research work, two 30%(Co-Mn)/TiO2 catalysts were prepared using sol-gel (catalyst A) and co-precipitation (catalyst B) methods. The activity and selectivity to C2–4 light olefins in Fischer-Tropsch synthesis (FTS) has been studied in a fixed-bed reactor under different operational conditions. These operational conditions were: temperature 220–280°C, and total pressure from 0.1–0.6 MPa. The optimum operating conditions were investigated after steady state. As the results shown, the catalyst A was more selective to C2–4 olefins (58.7% in 260°C) and catalyst B was more selective to C5+ hydrocarbons. Characterization of both catalysts was carried out by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and N2 adsorption-desorption measurements methods.

Catalytic Cracking of C<SUB>5</SUB> Raffinate to Light Olefins Over Phosphorous-Modified Microporous and Mesoporous ZSM-5

Phosphorous-modified microporous and mesoporous ZSM-5 catalysts (XP/C-ZSM5) were prepared with a variation of phosphorous content (X = 0.17, 0.3, 0.7, 1.4, and 2.7 wt%), and they were applied to the production of light olefins (ethylene and propylene) through catalytic cracking of C5 raffinate. The effect of phosphorous content on the physicochemical properties and catalytic activities of XP/C-ZSM5 catalysts was investigated. It was revealed that physicochemical properties of XP/C-ZSM5 catalysts were strongly influenced by phosphorous content. Strong acidity of XP/C-ZSM5 catalysts decreased with increasing phosphorous content. In the catalytic cracking of C5 raffinate, both conversion of C5 raffinate and yield for light olefins (ethylene and propylene) showed volcano-shaped curves with respect to strong acidity. This result indicates that strong acidity of XP/C-ZSM5 catalysts played an important role in determining the catalytic performance in the catalytic cracking of C5 raffinate. Among the catalysts tested, 0.3P/C-ZSM5 catalyst with moderate strong acidity showed the best catalytic performance.

Effect of support and promoter on the catalytic performance and structural properties of the Fe–Co–Ni catalysts for CO hydrogenation

Co-precipitated Fe–Co–Ni catalysts were tested for production of light olefins via Fischer–Tropsch synthesis. The effects of different supports such as Al2O3, SiO2, TiO2 and MgO and subsequently the effect of optimum support loading and also the effect of different promoters including Li, Cs, K, Rb and Ru on the catalytic performance and structure of Fe–Co–Ni catalyst were investigated. It was found that the Fe–Co–Ni catalyst containing 10 wt% MgO has shown the better catalytic performance for FTS. The yield of methane, ethylene, propylene and C4+ olefins were calculated and reported. Characterization of the catalyst precursors and calcined samples was carried out using XRD, SEM, EDS and BET.

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.

Effect of support and promoter on the catalytic performance and structural properties of the Fe–Co–Mn catalysts for Fischer–Tropsch synthesis

Co-precipitated Fe–Co–Mn catalysts were tested for production of light olefins via Fischer–Tropsch synthesis. The effects of different supports such as Al2O3, SiO2, TiO2 and MgO and subsequently the effect of optimum support loading and also the effect of different promoters including Li, Cs, K, Rb and Ru on the catalytic performance and structure of Fe–Co–Mn catalyst were investigated. It was found that the Fe–Co–Mn catalyst containing 10wt% MgO has shown the better catalytic performance. Characterization of the catalyst precursors and calcined samples was carried out using XRD, SEM, EDS, BET, TPR, TGA and DSC.

Effect of sulfur on the catalytic performance of Fe–Ni/Al2O3 catalysts for light olefins production

The effects of sulfur (S) on the catalytic behavior of alumina supported iron–nickel catalysts for the conversion of synthesis gas to the light olefins were studied. Catalytic evaluation results indicated that the CO conversion, CH4 and light olefins selectivity were affected by level of sulfur in the composition of catalyst. The catalytic performance of modified catalysts with sulfur has been investigated in different operational conditions such as H2/CO molar feed ratios, gas hourly space velocity (GHSV), reaction temperature and reaction total pressure. The results showed that the best operational conditions for Fe–Ni/Al2O3 catalyst promoted with 0.15wt% of K2S are 340°C, GHSV=3000h−1, H2/CO molar ratio 2/1 under atmospheric pressure. The catalysts were characterized by X-ray diffraction (XRD), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and N2 physisorption methods.

Catalytic conversion of C4 fraction for the production of light olefins and aromatics

The catalytic conversion of the C4 fraction from a fluid catalytic cracking (FCC) unit over a commercial FCC equilibrium catalyst was investigated using a confined fluidized bed reactor system. Butenes were easier to convert than butanes, and 1-butene was the easiest to convert among the butene isomers. The ethene and propene yields increased with increased reaction temperature and decreased with increased weight hourly space velocity (WHSV). The formation of propene involved two successive steps: butene dimerization and large hydrocarbon cracking. Aromatics were formed by the aromatization of the intermediate large olefins. A mechanism parameter RCA was proposed to describe the relative function of the cracking reaction to the aromatization reaction. RCA increased with increased reaction temperature and decreased with increased WHSV. The cracking reaction predominates on the aromatization reaction at high reaction temperatures.

3D Numerical Simulation of a Large Scale MTO Fluidized Bed Reactor

The methanol to olefins (MTO) process has been successfully commercialized in China and will potentially become an important route for light olefins production. In this work, a modeling approach is presented for MTO fluidized bed reactor design and operation optimization. The two-fluid model (TFM) where the solid phase shear viscosity and solid phase pressure are derived from kinetic theory of granular flow has been used to model the solid–gas two-phase flows. The interphase drag force is calculated by either the traditional Gidaspow model or a recently developed EMMS-bubble model. The simulation study has been performed for a fluidized bed reactor in a 16 kt/a DMTO unit. It has been shown that the Gidaspow model cannot predict a stable dense bed, while the EMMS-bubbling model could simulate the solid fraction distribution in the reactor reasonable well. A reaction model based on the simple MTO reaction kinetics has been implemented to test the effectiveness of the model approach. The simulation results show that the methanol is converted rapidly just above the gas inlet. The selectivity of ethylene and propylene however are underpredicted, while the selectivity of CO2 and other products are overestimated. It is suggested that a further extension of the EMMS model to a turbulent fluidized bed is important in order to get more quantitative results. Also the MTO reaction kinetics for a commercial DMTO catalyst, in which the coke formation kinetics should be included, is highly desired.

Production of Low-carbon Light Olefins from Catalytic Cracking of Crude Bio-oil

Low-carbon light olefins are the basic feedstocks for the petrochemical industry. Catalytic cracking of crude bio-oil and its model compounds (including methanol, ethanol, acetic acid, acetone, and phenol) to light olefins were performed by using the La/HZSM-5 catalyst. The highest olefins yield from crude bio-oil reached 0.19 kg/(kg crude bio-oil). The reaction conditions including temperature, weight hourly space velocity, and addition of La into the HZSM-5 zeolite can be used to control both olefins yield and selectivity. Moderate adjusting the acidity with a suitable ratio between the strong acid and weak acid sites through adding La to the zeolite effectively enhanced the olefins selectivity and improved the catalyst stability. The production of light olefins from crude bio-oil is closely associated with the chemical composition and hydrogen to carbon effective ratios of feedstock. The comparison between the catalytic cracking and pyrolysis of bio-oil was studied. The mechanism of the bio-oil conversion to light olefins was also discussed.

Catalytic pyrolysis of microalga Chlorella pyrenoidosa for production of ethylene, propylene and butene

This paper investigated the process of catalytic pyrolysis of lipid-rich microalga Chlorella pyrenoidosa for the production of light olefins (ethylene, propylene and butene). A modified ZSM-5 zeolite catalyst was used in the reactions, and it had high selectivity for the light olefins production. The catalytic pyrolysis performances of microalga Chlorella pyrenoidosa in nitrogen and steam reaction atmospheres were investigated. The catalytic pyrolysis performances in one-step and two-step processes were investigated and compared. The effects of reaction temperatures and water flow rates on the catalytic pyrolysis performances were also explored. The results showed that higher yield of light olefins was obtained in the steam reaction atmosphere as compared with that in the nitrogen atmosphere. The carbon yield of light olefins obtained from two-step catalytic pyrolysis was nearly three times that from one-step catalytic pyrolysis. The two-step catalytic pyrolysis process also facilitated the production of aromatic hydrocarbons in the liquid products. The maximum carbon yield of light olefins could reach 31.9% in the two-step process under the reaction temperature of 923 K and water flow rate of 30 ml h−1.

Catalytic conversion of rapeseed oil for the production of raw chemicals, fuels and carbon nanotubes over Ni-modified nanocrystalline and hierarchical ZSM-5

Catalytic conversion of rapeseed oil has been investigated over nanocrystalline and hierarchical ZSM-5 zeolites aimed to the production of both raw chemicals and fuels. Ni has been added to some of the samples in order to induce bifunctional properties in the catalysts. Almost total rapeseed conversion and deoxygenation degree were achieved with all the catalysts. The main products were gaseous olefins (mostly ethylene and propylene) and aromatic compounds (benzene, toluene and xylenes), which have high interest as raw chemicals. Likewise, high hydrogen contents are found in the gaseous stream since the operating conditions employed (high reaction temperature and atmospheric pressure) favor the occurrence of dehydrogenation reactions. The introduction of hierarchical porosity in ZSM-5 increases the production of light olefins at the expense of aromatic compounds, showing the close relationship between these two types of hydrocarbons. Hierarchical zeolites exhibit enhanced accessibility and diffusion rates, which hinders secondary reactions of the primary cracking products. Ni-containing catalysts show an enhanced dehydrogenation activity as denoted by the increased hydrogen, light olefins and coke production. Important changes were observed in the catalytic activity along time on stream, with a progressive increase in the fraction of aliphatic hydrocarbons. Interestingly, the coke formed over the Ni-containing ZSM-5 samples is in the form of carbon nanotubes, which grow causing a segregation of the Ni particle from the zeolite support. This effect is attenuated in the hierarchical zeolites because the secondary porosity stabilizes the metal particles. In summary, rapeseed oil can be transformed into valuable products (hydrogen, light olefins, aromatic hydrocarbons and carbon nanotubes) by using tailored Ni-containing nanocrystalline and hierarchical ZSM-5 zeolites.