Light Aromatics Research Articles

Hierarchical ZSM-5 nanosheets for production of light olefins and aromatics by catalytic cracking of oleic acid

The bolaform surfactant C6H13-N+(CH3)2-C6H12-N+(CH3)2-C6H12-O-C6H4-C6H4-O-C6H12-N+(CH3)2-C6H12-N+(CH3)2-C6H13 (BCPH-6-6-6) was synthesized and used to guide the synthesis of hierarchical ZSM-5 nanosheets (HZN) for use as zeolite catalysts.

Insight into the coke alleviation pattern over iron-based and boron-modified HZSM-5 bifunctional catalyst for direct CO2 hydrogenation to aromatics

Carbon dioxide (CO2) hydrogenation to aromatics is promising for reducing the burden of petroleum fuels. Herein, iron-based catalyst was mixed with boron modified HZSM-5 with pre-treatment and post-treatment method. The textural, acidic and element distribution properties over zeolite framework and external surface were studied. Combining with characterizations for internal and external coke, the element distribution-acidity-coke-stability relationship over boron-modified zeolite was put forward. Pre-treated zeolite witnessed reduced amount of external and total Brönsted acid sites (BAS) with similar degree, and increase paired Al (Alpair) fraction in the intersection site, leading to increased aromatics selectivity and reduced coke amount. While boron post-treatment significantly reduced external surface BAS and inhibited formation of condensed external coke. Afterwards, the mechanism of olefins aromatization was studied and found that PT-Z5-B greatly suppressed the overalkylation of light aromatics, thus alleviating the co-deactivation pattern generated by transformation of coke precursors from zeolite to iron-based catalyst.

Advances in Carbon Dioxide Catalytic Conversion and Applications

To achieve the global climate goals set out in the Paris Agreement, reducing carbon dioxide (CO2) emissions and utilizing resources have become key areas of focus within international energy technology research and development. CO2 can be converted into high-value chemicals, including hydrocarbons, alcohols and hydrocarbons, through the catalytic technology. This process can potentially address environmental issues while generating economic benefits. This paper presents a review of the principal products resulting from the catalytic conversion of CO2, together with an examination of their practical applications. These include hydrogenation of olefins, light aromatics, methanol, polyols, and synthetic bioconversion technologies. The development of catalysts with high conversion and selectivity represents a key area of current research. In the future, it will be necessary to combine physical, chemical, and biological technologies to establish an engineered heterogeneous carbon sequestration technology system to achieve the efficient conversion and utilization of CO2.

Gasification of olive tree pruning in a rotary kiln reactor integrated with radio frequency plasma torch

Olive tree pruning pellets are gasified by air in a bench-scale rotary kiln gasifier integrated with a radio frequency plasm torch. For the first time the technical suitability of the proposed configuration is herewith assessed. The effect of biomass flowrate (190–900 g/h), equivalence ratio (0.15–0.30), gasification temperature (650–900 °C), on syngas composition and yield is investigated. By increasing the biomass flowrate, from 190 to 900 g/h at 800 °C, both hydrogen and carbon monoxide mole fractions decreases, while the carbon dioxide mole fraction increase, with a drop in CGE from 76 % to 26 % increasing the biomass flowrate from 190 to 900 g/h at 800 °C. Higher temperature has a beneficial effect on syngas composition and CGE that increase from 20 % to about 64 % by increasing the temperature from 650 to 900 °C at a biomass flowrate of 450 g/h. The tar content shows a decreasing trend with equivalence ratio and temperature while it shows an increasing trend with biomass flowrate. The integration of the radio frequency plasma torch treatment of raw gas produced at 650 °C, with equivalence ratio of 0.15 and a biomass flowrate of 450 g/h shows good performance in hydrocarbons conversion, with a significant increase in terms of hydrogen yield. The H2/CO molar ratio increased by 104 % due to reforming reactions generating H2 and CO. A reduction of CO2 is also observed. With the RFPT treatment, gravimetric tar content was lower than the limit of detection while the concentration of light aromatics, i.e. benzene and toluene, decreases from 8.3 g/Nm3 to 2.2 g/ Nm3. The proposed post-gasification technology is worthy of further investigation for hydrogen production from biomass.

Reactivity and stability of Ni encapsulated hierarchical HZSM-5 for lignite-to-aromatics via catalytic pyrolysis

Metal-zeolite composite catalysts, as a special type via metallic encapsulation technology, hold great promise for lignite-to-aromatics conversion due to their high activity, shape-selectivity, and stability. However, the key issues lie in the location of the efficient metal sites and the nature of coke evolved in metal-encapsulated zeolites. Herein, we reported an efficient in situ encapsulation method to confine Ni species inside hierarchical channels and on the surface of HZSM-5 (i.e., Ni-HeZ5) assisted by water-soluble carbon black as hard template. Compared to core-shell Ni-impregnated hierarchical HZSM-5 (i.e., Ni@HeZ5), Ni-HeZ5 exhibited high activity, good stability and enhanced coke resistance in lignite-to-aromatics conversion via catalytic pyrolysis under an H2 atmosphere. The selectivity for light aromatics reached 93.6% in a single-pass reaction. The Ni species on the surface and within the zeolite were evidenced to facilitate, respectively, the cracking reaction of aliphatics and light oxygenates to produce olefins, and the secondary reaction of olefines to produce aromatics. The coke deposition and its influence on deactivation of Ni-HeZ5 and Ni@HeZ5 were studies based on coke location, chemical nature and formation mechanism. The principle of coke development in lignite-to-aromatics conversion is different from that in biomass-to-aromatics conversion. The heavy aliphatic coke deposits, which undergo chain-growth, play a more significant role in catalyst deactivation than the aromatic coke species. This work provides a facile strategy for designing metal-encapsulated zeolites (i.e., balancing the internal and external metallic sites on hierarchical channels) for lignite-to-aromatics conversion.

Catalytic upgrading of lignite pyrolysis volatiles to light aromatics under methanol atmosphere over Zr and/or Fe modified hollow ZSM-5 zeolites

Fe and Zr modified hollow ZSM-5 zeolites were prepared and their applications in upgrading of lignite pyrolysis volatiles coupling with methanol to light aromatics were investigated. The results demonstrated that hollow zeolites with larger voids and shorter diffusion length favored the production of light aromatics. Adding Fe and Zr into ZSM-5 zeolites further enhanced BTX yields due to the synergism between metals and acid sites for promoting hydrodeoxygenation reactions. Meanwhile, Zr-Fe/HZ-5 catalyst with increasing Lewis acid sites facilitated methylation leading to high selectivity of xylene under methanol atmosphere. Moreover, diffusion behaviors of xylene were quantified. Higher self-diffusion coefficient of molecules in hollow zeolites led to the formation of less coke, while the incorporation of Fe and Zr promoted the formation of catalytic coke due to the increase of alkylation resulting in partial conversion of BTX into PAHs on external surfaces although the total coke yields were further decreased.

Synthesis of Nanoscale ZSM-5 Zeolites for the Catalytic Cracking of Oleic Acid into Light Olefins and Aromatics

Synthesis of Nanoscale ZSM-5 Zeolites for the Catalytic Cracking of Oleic Acid into Light Olefins and Aromatics

Dual-engine-driven realizing high-yield synthesis of Para-Xylene directly from CO2-containing syngas

The direct synthesis of light aromatics, especially para-xylene (p-X), from syngas/CO2 is drawing strong interest, but improving the space-time yield (STY) of p-X is a significant challenge. Here, a dynamic “dual-engine-driven” (DED) catalytic system is designed by combining two partners of ZnCr and FeMn (named “dual-engine”) with Z5@SiO2 capsule zeolite. The DED catalyst of 1.0%FeMn&[ZnCr&Z5@SiO2] shows an extremely higher p-X STY of 36.1 gp-x·kgcat-1·h-1, about eight times higher than that of [ZnCr&Z5]. DED manipulates ZnCr engine for methanol formation and drives FeMn engine for light olefins generation together, and then the formed methanol and light olefins are coordinately converted in situ into p-X-rich aromatics over Z5@SiO2. The DED model boosts the driving force for syngas/CO2 conversion, simultaneously concerting the cooperation of “dual-engine” for p-X generation, resulting in extremely high STY of p-X. This study achieves non-petroleum p-X production at industrial-relevant level and advances knowledge in designing innovative heterogeneous catalysts.

Isolated Pt Atoms Stabilized by Ga2O3 Clusters Confined in ZSM-5 for Nonoxidative Activation of Ethane.

Selective activation of light alkanes is an essential reaction in the petrochemical industry for producing commodity chemicals, such as light olefins and aromatics. Because of the much higher intrinsic activities of noble metals in comparison to non-noble metals, it is desirable to employ solid catalysts with low noble metal loadings to reduce the cost of catalysts. Herein, we report the introduction of a tiny amount of Pt (at levels of hundreds of ppm) as a promoter of the Ga2O3 clusters encapsulated in ZSM-5 zeolite, which leads to ∼20-fold improvement in the activity for ethane dehydrogenation reaction. A combination of experimental and theoretical studies shows that the isolated Pt atoms stabilized by small Ga2O3 clusters are the active sites for activating the inert C-H bonds in ethane. The synergy of atomically dispersed Pt and Ga2O3 clusters confined in the 10MR channels of ZSM-5 can serve as a bifunctional catalyst for the direct ethane-benzene coupling reaction for the production of ethylbenzene, surpassing the performances of the counterpart catalysts made with PtGa nanoclusters and nanoparticles.

Integrated approach for co-production of bioethanol and light aromatics from lignocellulose through polyethylene glycol-aided acidic glycerol pretreatment

Acid-catalyzed glycerol organosolv (GO) pretreatment is a promising method for lignocellulosic biomass (LCB) fractionation. However, this method often leads to lignin repolymerization, intensifying lignin's inhibitory effects on subsequent enzymatic hydrolysis and limiting the production of highly active lignin, thereby hindering its valorization. This study explored incorporating polyethylene glycol (PEG) into acidic-catalyzed GO to improve bioethanol and bio-oil yields, with a focus on improving the yield of light aromatics, from LCB. Optimized PEG-aided GO pretreatment achieved a significantly higher bioethanol yield (23.7 g/L) compared to GO (17 g/L) and dilute acid (DA: 11.3 g/L) pretreatments. This improvement is attributed to the ability of PEG to mitigate lignin inhibition and modify the physicochemical properties of the pretreated substrate. Furthermore, thermal pyrolysis of PEG-aided GO lignin, obtained after the fermentation process, resulted in a substantially increased bio-oil yield (45.5 %) compared to GO (19 %) and DA (12 %). The enhanced bio-oil yield from PEG-aided GO lignin is ascribed to the promotion of β-O-4 linkages and the formation of β-O-4′ linkages. Characterization of the pyrolysis bio-oil revealed that light aromatic compounds were the dominant fraction, with their relative abundance significantly increasing from DA (5.9 %) to GO (9.7 %) and PEG-aided GO lignin (24.9 %). The PEG-aided GO method achieved an energy output of 8.85 MJ/kg, exceeding that of the GO and DA methods by 31 % and 57 %, respectively. The energy conversion efficiency of the PEG-aided GO method was 70 %, demonstrating a significant improvement compared to GO (57 %) and DA (51 %). This approach promotes the circular economy by upcycling LCB for bioethanol and valuable light aromatic compound production.

Catalytic pyrolysis of plastic waste using activated carbon from cotton waste

This study introduces a novel approach to plastic waste management and energy recovery by synthesizing highly porous activated carbon from an often-overlooked resource, waste cotton fabric (WCF), using H3PO4 as an activating agent. The synthesized waste cotton fabric activated carbon samples (WCF-AC) were utilized as a solid acid catalyst in the catalytic pyrolysis of low-density polyethylene (LDPE), with the aim of converting LDPE into fuel-range hydrocarbons. This research highlights the potential of bio-based waste materials in the synthesis of eco-friendly and cost-effective catalysts for feedstock recycling. The impact of the H3PO4 impregnation ratio and the carbonization/activation temperature on the physicochemical properties of the resulting WCF-AC samples was investigated, providing valuable insights into the optimization of activated carbon production. The catalytic activity of the synthesized WCF-AC samples was evaluated, demonstrating a reduction of 12°C in the LDPE degradation temperature. Furthermore, this work revealed a substantial increase in the formation of carbocyclic compounds, with light aromatics such as benzene, toluene, and xylene constituting up to 43 % of the pyrolysis output. In certain instances, a decrease in heavier hydrocarbons beyond C11 was observed, indicating the selective yield of specific range hydrocarbons. This study underscores the potential of bio-based acid catalysts, such as the synthesized activated carbon presented here, in plastic recycling. The approach adopted in this research aligns with the principles of the circular economy, promoting resource efficiency and sustainability.

Co-aromatization of methane and methanol over MoxZn/HZSM-5 to increase aromatic hydrocarbon yield: experimental and kinetic studies

Co-aromatization of methane and methanol over MoxZn/HZSM-5 was conducted to improve hydrocarbon yield and methane conversion. Natural gas, coalbed methane, and coke oven gas are rich in methane. The utilization of methane-rich gas is particularly important as energy demand continues to increase and environmental requirements continue to rise. The efficient conversion to light aromatics is obtained using a co-feed of methane and methanol under relatively mild conditions and catalyzed by MoxZn/HZSM-5. In general, Mo species promote the C-H bond breaking of methane to produce intermediates. Mo is transformed into Mo2C in the co-aromatization reaction as observed by FT-IR and XPS, which leads to the higher activity and aromatic selectivity of the catalyst and can also avoid carbon deposition of the catalyst. Furthermore, kinetic analysis results indicate that olefins play an important role during the co-aromatization of methane and methanol. Olefins are the key reaction intermediates to form aromatics and olefins initially formed in the transformation reaction of methanol perhaps promote the conversion of methane.

The effects of in situ-produced hydrogen on catalytic upgrading of lignite pyrolysis volatiles over ZSM-5 zeolites to produce light aromatics

The introduction of in situ hydrogen donors to obtain a high H/Ceff ratio is an effective way to upgrade coal pyrolysis volatiles to light aromatics. In this study, the influence of different in-situ hydrogen suppliers in catalytic reforming of coal pyrolysis vapors was explored. The abilities of active hydrogen donation were greatly corresponded to structures of hydrogen donors. Isopropanol showed the best catalytic performance due to the release of a large amount of active α-H as a result of negative inductive effect of hydroxyl. Whereas tertbutanol showed the poorest catalytic performance owing to the lack of α-H. Meanwhile, the effect of in-situ hydrogen production via steam reforming with different alcohols on light aromatic yields was investigated. The highest BTEXN yield was obtained under in-situ hydrogen production from isopropanol steam reforming. Two circumstances of hydrogen supply were further compared. Relatively higher BTEXN yield was presented in the reaction of methanol steam reforming than that of using methanol solely. However, higher BTEXN yield was contrarily obtained from sole isopropanol as a hydrogen donor despite lower H2 production was gained compared to the case of isopropanol steam reforming. The fact was probably ascribed that high electron-withdrawing effect of hydroxyl for isopropanol promoted the cleavage of α-C-H bond and favored the transfer of active hydrogen to reactants over acid sites.

Optimizing light and heavy aromatic ratios in fluid catalytic cracking slurry oil for mesophase pitch with wide-area optically anisotropic texture

Aromatics are the preponderant component of fluid catalytic cracking (FCC) slurry oil, with notable differences in molecular structure between the light and heavy aromatics. The effect of these differences on the formation and optically anisotropic texture of mesophase remains elusive, impeding the preparation of high-quality mesophase pitch. This paper aims to regulate the ratio of light to heavy aromatics in the FCC slurry oil for optimizing the optically anisotropic texture of mesophase pitch. The results show that the heavy aromatics possess higher aromaticity, longer alkane side chains, larger molecular size and more reactive structures (methylene bridges, n-alkane structures) compared with the light aromatics. As an “accelerator”, heavy aromatics can form mesophase quickly. Light aromatics not only served as a “diluent,” but also assumed the function of a “lubricant”, which facilitated the orderly arrangement of aromatic molecular lamellar. The system exhibits moderate reactivity that inhibits excessive condensation and modifies the structural orientation of pyrolysis products with the 2/5 ratio of light to heavy aromatics. Under these conditions, a high-quality mesophase pitch (d002 = 3.485 Å, Lc = 19.832 Å) with wide-area optically anisotropic texture, suitable softening point (262 °C) and short polymerization time (t = 5.5 h) was obtained. This work provides theoretical support for the preparation of high-quality mesophase pitch by regulating the components of slurry oil.

A porous media catalyst for waste polyethylene pyrolysis in a continuous feeding reactor

This study investigated the catalytic pyrolysis of waste polyethylene (PE) using a ZSM-5/Al2O3 porous media catalyst in a continuous feeding mode. The findings revealed that the porous media catalyst with 100 mm height and 40 PPI (pore per inch) pore size had the supreme catalytic performance, which could obtain the highest pyrolysis oil yield and the light fraction (<C12) and aromatics in the oil, and improve the catalytic stability of the porous media catalyst. The optimal operating conditions were the pyrolysis temperature of 460 °C, the carrier gas velocity of 65 mL/min, and the plastic feeding rate of 25 g/h, of which the light fraction and aromatics in the oil were up to 95.25 % and 97.33 %. Moreover, the catalytic cycling performance of the porous media catalyst was thoroughly investigated. The catalytic activity declined and the catalyst deactivation rate decreased after multiple regeneration cycles. This study presents a comprehensive investigation of waste PE catalytic cracking using the porous media catalyst in continuous feeding mode, which can provide insightful guidance on the industrialization of plastic waste valorization.

The application of Ni and Zr modified ZSM-5 nanosheet in upgrading of lignite pyrolysis volatiles coupling with methanol to light aromatics

Ni and Zr modified nanosheet ZSM-5 zeolites as tandem catalysts were designed using co-impregnation method (Zr-Ni/S-Z5) or combining in-situ hydrothermal synthesis of Ni@S-Z5 and sequential impregnation of Zr (Zr/Ni@ S-Z5). Their applications in upgrading of lignite pyrolysis volatiles coupling with methanol to light aromatics were investigated. The results demonstrated that nanosheet zeolites with larger surface areas and shorter b-axis length benefited the production of light aromatics due to exposing more active sites and improved diffusion limitation compared with conventional ZSM-5 zeolites. Adding Ni and Zr into tandem catalysts further enhanced BTEXN yields, which was attributed to the induction of oxyphilic ZrO2 for activating CAr-O bonds combining the promotion of Ni for hydrogenation. Comparing to Zr-Ni/S-Z5 catalyst, lower BTEXN yield was observed due to the decrease in exposing active sites over Zr/Ni@ S-Z5 catalyst. Moreover, enhancing diffusion behaviors in shorter b-axis length and the presence of more fractions of external coke indicated less effective in blocking pore channels, thus nanosheet zeolite series showed lower deactivation rates.

A quantitative investigation on pyrolysis behaviors of metal ion-exchanged coal macerals by interpretable machine learning algorithms

Generalizing the rules from complex processes such as catalytic pyrolysis to guide their process control is always a difficult but attractive task. The influences of ion-exchange of metal ions (Na+, K+, Ca2+, Mg2+, Co2+ and Ni2+) on the pyrolysis behavior of vitrinite and inertinite from Shendong coal were investigated by thermogravimetric analyzer-Fourier transform infrared spectrometer (TG-FTIR), fixed-bed reactor (FBR), gas chromatograph-mass spectrometer (GC-MS) and X-ray diffractometer (XRD). A set of machine learning models was successfully constructed based on random forest, support vector machine, and Gaussian process regression, to quantify the relationships between pyrolysis behaviors and the properties of metals and macerals. The leave-one-out-cross validation showed that there are considerable determination coefficients (R2 > 0.9) between predicted and experimental values for most responses (17 out of 29). By combining genetic programming-based symbolic regression with the black-box algorithm, 23 symbolic regression expressions with high confidence were successfully constructed. This work is a pioneering attempt of optimization in small-scale experiments. By utilizing the highly interpretable models, a demand-orientated (multi-)optimization coal pyrolysis can be achieved. The bi-objective optimization was conducted on the yield of tar and the content of light aromatics in tar, and the results show that Co is the optimal loading metal.

Selective aromatization of 1-hexene to BTX over core-shell structured Silicalite-1@ZSM-5 catalyst

The strong acidity on the external surface of ZSM-5 is a primary factor resulting in the low BTX selectivity and catalyst deactivation during the olefin aromatization. In this study, a membrane-restricted Silicalite-1@ZSM-5 core–shell structured catalytic catalyst was designed and constructed for 1-hexene aromatization using a hydrothermal coating method. TEM and NMR results confirmed the complete coverage of Silicalite-1 on the surface of ZSM-5, with a shell thickness of 50 nm. The further reaction of the TIPB (1,3,5-triisopropylbenzene) molecular probe reactions demonstrated the passivation of the acid sites on ZSM-5 external surface. The inert shell layer passivated the acid sites on the external surface, thereby suppressing the isomerization of PX and the side-chain alkylation reaction of light aromatics. Compared to ZSM-5, the Silicalite-1@ZSM-5 catalyst exhibited a 37.15 % increase in BTX selectivity, a 58.65 % increase in PX selectivity, significantly reduced coke deposition, and demonstrated better stability. This strategy of in-situ epitaxial growth of inert shell layers holds significant promise for enhancing the selectivity of shape-selective catalysts and extending catalyst lifetime.

Coke formation on different metal-modified (Co, Mo and Zr) ZSM-5 in the catalytic pyrolysis of cellulose to light aromatics

Catalytic pyrolysis of biomass is regarded as a promising method for preparing value-added products. However, the main factors limiting the development of the process at present are the low yield of value-added products and poor selectivity, especially for rapid catalyst deactivation due to coke deposition. The present study focuses on the catalytic pyrolysis of cellulose over metal Co-, Mo-, and Zr-loaded catalysts using a falling fixed bed at 600 °C to evaluate the type of coking of the catalysts as well as the effect of the different metal active sites on the formation of coke deposits. The introduction of Co and Mo metal sites increased the light aromatics yield of ZSM-5 from 128.9 mg/g to 147.2 mg/g and 143.0 mg/g. And the yield of coke deposits decreased from 8.3 to 6.8 and 5.1 wt%. The stability evaluation of the catalyst showed that the deactivation degree of ZSM-5 of the supported metal Co was lower than that of commercial ZSM-5, while the ZSM-5 of the supported metal Mo was rapidly deactivated. The deactivation of the catalysts depended more on the morphology or location of the accumulated coke than on the total amount deposited. The clogging of metal and acidic sites on the surface of the zeolite and the pore channels by the amorphous encapsulating coke was the main cause of catalyst deactivation. The metal Mo active sites promoted dehydrogenation coupling and hydrogen transfer during coke formation, forming a more highly disordered multiring structure, and the metal Co active sites were more capable of decomposing macromolecular compounds, olefins and alkanes, and promoted the formation of graphite-like structural carbon.

Conversion of Polypropylene into Light Hydrocarbons and Aromatics by Metal Exchanged Zeolite Catalysts.

Polyolefins can be converted into C2-C5 hydrocarbons and benzene-toluene-xylene (BTX) aromatics as high-demand petrochemical feedstocks via catalytic pyrolysis on acidic zeolites. Bro̷nsted and Lewis acid sites are responsible for cracking polyolefins into olefins and subsequent aromatic formation. In this study, we have subjected the parent HZSM-5 zeolite to postsynthetic partial metal exchange with Fe, Co, Ni, Cu, and Ce cations to perturb Bro̷nsted/Lewis acidity. We have investigated these metal-modified HZSM-5 on the catalytic pyrolysis of polypropylene (PP) in a micropyrolyzer connected to a two-dimensional gas chromatograph coupled to a time-of-flight mass spectrometer and flame ionization detector (Tandem Pyrolyzer-GC × GC-TOF-MS/FID setup). Whereas Fe-, Co-, Cu-, and Ce-exchanged zeolites (with 2.5, 2.3, 1.9, and 0.8 wt % metal, respectively) had comparable product yields with the parent zeolite, Ni-exchanged zeolites with Ni content of 0.5 to 2 wt % were associated with enhanced BTX formation (28-38 wt %) compared to that of the parent zeolite (22 wt %). Pyridine-FTIR indicated that the Bro̷nsted/Lewis acid ratio of the parent zeolite decreased upon metal ion exchange. According to Pyridine-TPD, the parent zeolite's medium-strength acid sites were redistributed into weak and strong acid sites in Ni-exchanged zeolites. The higher amount of carbon deposits on Ni-exchanged zeolites compared to the parent and other metal ion exchanged zeolites was attributed to the enhanced aromatization activity by the simultaneous decrease in the Bro̷nsted/Lewis acid ratio and emergence of strong acid sites.