Cracking Of Benzene Research Articles

Effects of steam and CO2 on gasification tar composition and evolution of aromatic compounds

The removal of tar is conducive to improving the energy efficiency of downstream equipment and reducing the damage caused to it. In this study, a two-stage continuous feeding apparatus was developed to explore the yield and characteristics of tar produced from the co-gasification of microcrystalline cellulose (MCC) and polyethylene (PE) under separate and mixed atmospheres of steam and CO2. The tar yield can effectively reduce to 2.27 % when the steam and feedstock mass ratio (S/F) is 0.8. CO2 can partially substitute the steam in the gasification process, which can effectively promote a decrease in benzofuran. Furthermore, Gaussian software was employed to analyze the evolution mechanism of aromatic compounds. When the temperature is more than 800 °C, hydrogen consumption in the benzene cracking process is reduced, which is instrumental in improving the quality of syngas. Naphthalene is prone to form through the recombination of two cyclopentadienyls. Controlling the cyclization of cyclopentadienyls is a critical step in reducing the formation of polycyclic aromatic hydrocarbons. H and OH radicals are critical in phenol and benzofuran cracking, respectively. Although radicals act differently on specific aromatic compounds, the gasification effect of CO2 is less than that of steam because steam can provide both H and OH radicals, whereas CO2 needs to consume H radicals to generate OH radicals. The results provide beneficial guidance for controlling tar formation.

In Situ Removal of Benzene as a Biomass Tar Model Compound Employing Hematite Oxygen Carrier

Tar is an unavoidable biomass gasification byproduct. Tar formation reduces gasification efficiency and limits the further application of biomass gasification technology. Hence, efficient tar removal is a major problem to be solved in the formation and application of biomass gasification technology. Chemical looping gasification (CLG), a novel and promising gasification technology has attracted extensive attention owing to its low tar generation. Active oxygen carriers (OCs), the reduced OC in CLG, are considered to be excellent catalysts for tar cracking. In this study, the use of benzene as a typical tar model compound for tar removal using the iron ore OC is investigated. In the blank experiment, where an inert material (SiO2) is used as the carrier, the benzene cracking is relatively low, and the benzene conversion, H2 yield, and carbon conversion are 53.65%, 6.33%, and 1.24%, respectively. The addition of hematite promotes benzene cracking. A large amount of oxygen-containing gases (CO and CO2) are generated. Additionally, the conversion degrees for benzene, H2 and carbon are about 67.75%, 21.55%, and 38.39%, respectively. These results indicate that hematite performs both oxidation and catalysis during benzene cracking. The extension of the residence time facilitates benzene removal, owing to the good interaction between the gas phase and solid phase. The addition of water vapor inhibits the benzene conversion and promotes the conversion of carbon deposition. The lattice oxygen reactivity of hematite OC shows an uptrend as the cycle number is increased during the benzene conversion cycle. The experimental results confirm that CLG has a low-tar advantage and that hematite is an effective OC for benzene removal.

Selective Synthesis of p‐Cresol by Alkylation of Phenol with Methanol over SiO2‐Modified HMCM‐22 Catalyst

AbstractA series of xSiO2/HMCM‐22 were prepared by chemical liquid deposition of HMCM‐22 with tetraethyl orthosilicate and evaluated in the catalytic synthesis of p‐cresol by alkylation of phenol with methanol. Several characterization techniques including N2 adsorption‐desorption, X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), Pyridine‐IR, temperature‐programmed desorption of NH3 (NH3‐TPD) as well as the probe reaction of m‐xylene isomerization and 1,3,5‐triisopropyl benzene (1,3,5‐TIPB) cracking have been used to analyze the physicochemical properties of xSiO2/HMCM‐22 catalyst. The conversion of phenol decreased with increasing SiO2 loading of xSiO2/HCM‐22 catalyst; while the selectivity for p‐cresol maximized at x=1 %. The 1 %SiO2/HMCM‐22 catalyst was identified as the most efficient catalyst, showing the highest p‐cresol selectivity for longer than 15 h under optimized reaction conditions. The high p‐cresol selectivity of the catalyst is attributed to the fact that SiO2 covered the acid sites of the external surface of the HMCM‐22 and preserved the acid sites in the micropores of zeolite.

Reactivity and deactivation mechanisms of pyrolysis chars from bio-waste during catalytic cracking of tar

The catalytic activity of pyrolysis chars from bio-waste was investigated for the cracking of model tar compounds (ethylbenzene and benzene). Two pyrolysis chars were produced at 700 °C from (1) used wood pallets (UWP), and (2) a 50/50 dry% mixture of food waste (FW) and coagulation-flocculation sludge (CFS). Steam activation at 850 °C was used to study the influence of the porous structure. While coke deposition is known to be responsible for the deactivation of carbonaceous chars and metal catalysts during tar cracking reactions, the deactivation of complex materials such as bio-waste chars has scarcely been studied. For this reason, special attention was paid on the relationships between the physicochemical properties of the chars, the operating conditions, and the deactivation mechanisms. To this aim, the cracking tests were performed over a wide temperature range: 400–650 °C for the ethylbenzene cracking, and 850–950 °C for benzene cracking. After the ethylbenzene cracking tests at 650 °C, the characterisations performed with SEM, BET, FTIR and Raman revealed that coke deposition was responsible for the char’s deactivation. The high specific surface area of activated chars explained their higher catalytic activity, and mesoporous catalysts were proved to be more resistant to coke deactivation than microporous catalysts. For these reasons, the higher ethylbenzene conversion (85.8%) was reached with the activated char from food waste and sludge (ac.FW/CFS). For benzene cracking at higher temperature (850 and 950 °C), the chars from food waste and sludge (FW/CFS) were the most active catalysts, despite their deactivation by the melting, diffusion and sintering of the inorganic species. This original deactivation mechanism, reported for the first time, led to the formation of an inorganic layer composed of P and Ca species at the char surface, with some areas rich in KCl and NaCl. Non-activated char from food waste and sludge (c.FW/CFS) was surprisingly proved to be more resistant to deactivation by inorganic species than the activated char (ac.FW/CFS) during the benzene cracking tests at 950 °C. This extended catalytic activity was explained by the activation of the non-activated char (c.FW/CFS) with the CO2 contained in the syngas which simultaneously developed the porosity and created new available active sites. This study marks a step forward in the understanding of the relationships between the deactivation mechanisms, the physicochemical properties of the chars, and the cracking temperature. Finally, a proposal for process integration is presented to consider the possibility to valorise the chars as catalysts to decompose the tar generated in the same pyro-gasification process.

Catalytic Oxidative Cracking of Benzene Rings in Water

Efficient degradation of harmful benzene rings in water is indispensable for achieving a clean water environment. We report herein unprecedented catalytic oxidative benzene cracking (OBC) in water ...

Microwave-induced cracking and reforming of benzene on activated carbon

This study was conducted to convert tar generated during biomass pyrolysis/gasification to fuel gas through microwave process. Benzene was selected as a model tar, and the benzene reduction and produced-gas conversion characteristics were investigated for benzene cracking and CO2/steam reforming.The benzene conversion was the highest value of 99% when benzene cracking was performed, 98.5% when CO2 was supplied and 94% when steam was supplied. The produced-gas heating value was highest at 15 MJ/m3 for cracking, lowest at 4 MJ/m3 when CO2 was supplied, and 8.7 MJ/m3 when steam was supplied.In the case of CO2 reforming, the benzene conversion of the catalyst carbon receptor slightly increased for both the nickel and iron catalysts. The H2/CO ratio decreased, but the heating value increased. In the case of steam reforming, the benzene conversion slightly decreased for both catalysts, but the H2/CO ratio and the heating value increased.

Decomposition of benzene as a tar analogue in CO2 and H2 carrier gases, using a non-thermal plasma

Cracking of benzene in a non-thermal plasma (NTP) dielectric barrier discharge reactor (DBD) was investigated in CO2 and H2 carrier gases. Benzene was acting as an analogue for gasification tar, and CO2 and H2 are abundant in gasifier product gas. A parametric study in terms of specific input energy (SIE), residence time, concentration and temperature was performed to determine the optimal conditions for tar conversion. It was found that almost complete removal of benzene (36 g/Nm3) was observed in each carrier gas above 30 kJ/L and at 4.23 s. Lower hydrocarbons (<C6) (LHC) and solid residue were common products in both carrier gases. The selectivity to LHC in H2 carrier gas was higher (12%) than CO2 (2%) carrier gas, and CO was the major gaseous product in CO2 carrier gas. However, the problem of solid formation in the reactor was completely eradicated by operating at elevated temperatures in H2 carrier gas. The selectivity to lower hydrocarbons increased with increasing temperature. At 400 °C in H2 carrier gas, the selectivity to LHC reached 91% with no formation of solid residue. The major lower hydrocarbons at these conditions were CH4 (82%) and C2 (C2H6 + C2H4) 6.6%.

Preparation of carbon molecular sieves and its impregnation with Co and Ni for CO2/N2 separation

The carbon molecular sieves (CMSs) prepared by carbonaceous materials as precursors are effective in CO2/N2 separation. However, selectivity of these materials is too low, since hydrocarbon cracking for developing the desired microporosity in carbonaceous materials has not been done effectively. Hence, in this study, cobalt and nickel impregnation on the precursor was conducted to introduce catalysts for hydrocarbon cracking. Cobalt and nickel impregnation, carbonization under N2 atmosphere, and chemical vapor deposition (CVD) by benzene were conducted on the extruded mixtures of activated carbon and coal tar pitch under different conditions to prepare CMSs. The best CMS prepared by carbon deposition on the cobalt-impregnated samples exhibited CO2 adsorption capacity of 54.79 mg/g and uptake ratio of 28.9 at 0 °C and 1 bar. In terms of CO2 adsorption capacity and uptake ratio, CMSs prepared by carbon deposition on non-impregnated and cobalt-impregnated samples presented the best results, respectively. As benzene concentration and CVD time increased, equilibrium adsorption capacity of CO2 decreased, and uptake ratio increased. Cobalt was found to be the best catalyst for benzene cracking in the CVD process.

An experimental and simulated investigation on pyrolysis of blended cyclohexane and benzene under supercritical pressure

The pyrolysis characteristics of blended cyclohexane and benzene mixture are investigated under supercritical pressure. The experimental results show that cyclohexane pyrolysis is greatly easier than thermal cracking of benzene, and the addition of cyclohexane can significantly promote the benzene pyrolysis, while the thermal cracking of cyclohexane itself is weakened by the addition of benzene. A simulation of the blended fuel is carried out by using Chemkin program, indicating that the chemical heat sink of cyclohexane pyrolysis can account for nearly 50% of its total heat absorption capacity, while benzene is inactive in thermal cracking process.

Influence of TiN coating on products distribution for hydrocarbon fuel cracking under high temperature and pressure

To understand the cracking behavior of hydrocarbon fuels when a passivation coating covers the metal substrate, the pyrolysis of n-hexane, cyclohexane and benzene in uncoated and titanium nitride (TiN) coated stainless steel 304 (SS304) continuous tubular reactors (3mm diameter, 700mm long) under high temperature and pressure were studied. The TiN coating was prepared on the inner surface of SS304 tubes by atmospheric pressure chemical vapor deposition (APCVD) using TiCl4-H2-N2 system. The solid, liquid and gaseous products distribution of the pyrolysis of n-hexane, cyclohexane and benzene for bare and TiN-coated tubes were analyzed and discussed. The results show that the influence of TiN coating on hydrocarbon fuels cracking is not a simple effect of promotion or inhibition. As a whole, the TiN coating has little effects on the distribution of the gas products for n-hexane cracking, but has great influence on that of cyclohexane and benzene cracking. For the liquid products distribution, the mass fractions of alkane for bare tubes reduce compared with those for TiN-coated tubes, while the alkene contents are higher than those for TiN-coated tubes. Moreover, the morphologies of carbon deposits are mainly filamentous and spherical on the inner surface of SS304 tubes, but no morphologies of carbon deposits are observed on TiN-coated tubes surface after thermal cracking of hydrocarbon fuels. Meanwhile, the amount and carbon deposition rate of cokes deposited in the system for TiN-coated tubes are higher than those of bare tubes, regardless of the hydrocarbon fuels are n-hexane, cyclohexane and benzene.

Carbon-based nanostructured catalyst for biodiesel production by catalytic distillation

A promising carbon-based nanostructured catalyst was prepared via the following four steps: (1) thermal decomposition of organometallic compound (C10H14CoO4) on 304 stainless steel substrate, (2) cracking of benzene to carbon nanotubes (CNTs) on the substrate using Co particle catalyst, (3) sulfurizing CNTs with Na2Sx, and (4) oxidating the sulfurized CNTs with hydrogen peroxide. The as-prepared carbon-based catalyst was characterized by spectroscopy, scanning electron microscopy, transmission electron microscopy etc. The monolithic catalyst can serve as appropriate filler for a catalytic distillation column. Catalytic activity was examined by catalyzing the transesterification of soybean oil and methanol to biodiesel in the catalytic distillation column.

THE PREPARATION OF ULTRAFINE TUNGSTEN CARBIDE NANOPARTICLES BY DC ARC DISCHARGE PLASMA PROCESS

Tungsten carbide nanoparticles were synthesized successfully by DC arc discharge plasma process with 23 A discharge current at atmospheric pressure, in which tungsten positive electrode reacted with carbon black produced from the benzene cracking. The XRD results indicate that the samples consist of carbon black, WC and W 2 C . The TEM micrographs show that the tungsten carbide particles range from 3 to 7 nm in size, and are composed of WC and W 2 C .

Characterization and catalytic performance of Fe3Ni8/palygorskite for catalytic cracking of benzene

Catalytic decomposition is a very attractive way to convert tar components into H2, CO and other useful chemicals. The performance of Fe3Ni8/PG (palygorskite, PG) reduced in hydrogen at different temperatures for the catalytic decomposition of benzene has been assessed. Benzene was used as the model biomass tar. The effects of calcination atmosphere, temperatures and benzene concentration on catalytic cracking of benzene were measured. The results of XRD (X-Ray Diffraction), TEM (Transmission Electron Microscope), TPR (Temperature Program Reduction), TPSR (Temperature Program Surface Reduction), TC (Total Carbon), the reactivity component and reaction mechanism over Fe3Ni8/PG for catalytic cracking of benzene are discussed. The results showed particles of awaruite (Fe, Ni) about 2–30nm were found on the surface of palygorskite by TEM when the calcination temperature was 600°C. Particles with size smaller than 30nm were obtained on all prepared Fe3Ni8/PG catalysts as shown by XRD. The nanoparticles proved to be the reactive component for catalytic cracking of benzene and the increase of active particle size caused the decrease in the reactivity of Fe3Ni8/PG. Fe3Ni8/PG annealed in hydrogen at 600°C was proved to have the best reactivity in experiments (45% hydrogen yield). High concentration benzene (448g/m3) accelerated the formation of carbon deposition. However, iron oxide decreases carbon deposition and increases the stability of catalyst for catalytic cracking of benzene. The application of Fe3Ni8/PG catalysts was proved a very effective catalyst for the catalytic cracking of benzene.

PREPARATION AND CATALYTIC ACTIVITY FOR ISOPROPYL BENZENE CRACKING OF Co, Mo AND Co/Mo-Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-PILLARED MONTMORILLONITE CATALYSTS

It has been prepared Co, Mo and Co/Mo-Al2O3-pillared montmorillonite catalysts using montmorillonite clay as raw material. The structure and porosity of the catalysts were determined using N2 adsorption-desorption and FT-IR spectroscopy analysis methods. Isopropyl benzene cracking using these catalysts were used to test the catalytic activity and performance of Co, Mo and Co/Mo-Al2O3-pillared montmorillonites. Characterization results showed that pillarization resulted in the increase of the total pore volume and specific surface area of the clay. Meanwhile, transition metals (Co, Mo and Co/Mo) loaded on Al2O3-pillared monmorillonites could increase the catalytic activity of the catalysts for isopropyl benzene cracking significantly. Keywords: pillared monmorillonite, isopropyl benzene and cracking catalyst

Photocatalytic activity of TiO2-based materials for the oxidation of propene and benzene at low concentration in presence of humidity

This paper complements previous studies devoted to the photocatalytic oxidation of a low-concentration propene gaseous stream in absence of humidity using agglomerated TiO2-based materials. These prepared agglomerated materials have shown very good oxidation activities and complete selectivity towards CO2. The present paper analyses the role of humidity on propene oxidation, which has not been studied before, and extends the use of the prepared agglomerated photocatalysts to low concentration benzene oxidation, both in absence and presence of humidity. The obtained results have shown that humidity must be totally avoided, or kept as low as possible, to achieve high propene conversions. In the case of benzene, some insight to controversial published results is given; very low conversions together with benzene cracking on the surface of the photocatalyst occur in absence of humidity. However, the introduction of humidity leads to high conversions and avoids benzene cracking. The performance of the agglomerated photocatalyst containing a high surface area activated carbon (TiO2/C1) must be underlined in terms of activity.

Carbon molecular sieves from palm shell: Effect of the benzene deposition times on gas separation properties

In the present work, an effort has been made to develop suitable process conditions for synthesis of carbon molecular sieve (CMS) from a locally available palm shell of Tenera type. The process involves three stages; carbonization, physical activation with steam, and carbon deposition by using benzene cracking technique. The highest micropore volume of activated carbon was obtained at 53.2% burn-off, which is then used as a precursor for CMS production. In order to narrow down the pore mouth size to a required size, benzene was cracked at 800 °C for 15–60 min. The characterization of the samples was assessed by physical adsorption of N 2 at 77 K. The adsorption kinetic of CO 2, CH 4, O 2 and N 2 were measured at room temperature in order to determine the sample behavior as CMS.

Preparation and Characterization of Molecular Sieving Carbon by Methane and Benzene Cracking over Activated Carbon Spheres

Molecular sieving carbon (MSC) for separating <TEX>$O_2-N_2$</TEX> and <TEX>$CO_2-CH_4$</TEX> has been prepared through chemical vapor deposition (CVD) of methane and benzene on activated carbon spheres (ACS) derived from polystyrene sulfonate beads. The validity of the material for assessment of molecular sieving behavior for <TEX>$O_2-N_2$</TEX> and <TEX>$CO_2-CH_4$</TEX> pair of gases was assessed by the kinetic adsorption of the corresponding gases at <TEX>$25^{\circ}C$</TEX>. It was observed that methane cracking on ACS lead to deposition of carbon mostly in whole length of pores rather than in pore entrance, resulting in a reduction in adsorption capacity. MSC showing good selectivity for <TEX>$CO_2-CH_4$</TEX> and <TEX>$O_2-N_2$</TEX> separation was obtained through benzene cracking on ACS with benzene entrantment of <TEX>$0.40{\times}10^{-4}\;g/ml$</TEX> at cracking temperature of <TEX>$725^{\circ}C$</TEX> for a period of 90 minutes resulting in a selectivity of 3.31:1.00 for <TEX>$O_2-N_2$</TEX> and 8.00:1.00 for <TEX>$CO_2-CH_4$</TEX> pair of gases respectively.

Synthesis of carbon molecular sieves from palm shell by carbon vapor deposition

A series of experiments were conducted to produce carbon molecular sieves (CMS) through carbon deposition from a locally available palm shell of Tenera type for separating gaseous mixtures. The process involves three stages; carbonization, physical activation with steam, and carbon deposition by using benzene cracking technique. Carbonization of the dried palm shells was occurred at 900°C for duration of 1 h followed by steam activation at 830°C for 30–420 min to obtain activated carbons with different degree of burn-offs. The highest micropore volume of activated carbon obtained at 53.2% burn-off was used as a precursor for CMS production. Subsequent carbon deposition of the activated sample at temperature range from 600 to 900°C for 30 min has resulted in a series of CMSs with different selectivities of CO2/CH4 and O2/N2. The kinetic adsorption isotherm of CO2, CH4, O2 and N2 at room temperature also presented in this work.

Green chemistry perspectives of methane conversion via oxidative methylation of aromatics over zeolite catalysts

Methane gas is known to be the most destructive greenhouse gas. The current world reserves of natural gas, which contains mainly methane, are also still underutilized due to high transportation costs. Thus, considerable interest is presently shown in conversion of methane to transportable liquid fuels and chemicals of importance to the petrochemical industry. The catalytic methylation of aromatics is one possible new route for converting methane to more valuable higher hydrocarbons. This paper provides a general overview of the recent work that we and other researchers have done on the utilisation of methane for catalytic methylation of aromatic compounds and for direct coal liquefaction for the production of liquid hydrocarbons. In particular, the paper presents a detailed description of more recent substantial experimental evidence that we have provided for the requirement of oxygen as a stoichiometry reactant for benzene methylation with methane over moderately acidic zeolite catalysts. The reaction, which has been termed “oxidative methylation”, was thus postulated to involve a two-step mechanism involving intermediate methanol formation by methane partial oxidation, followed by benzene methylation with methanol in the second step. However, strongly acidic zeolites can cause cracking of benzene to yield methylated products in the absence of oxygen. The participation of methane and oxygen, and the effective use of zeolite catalysts in this methylation reaction definitely have some positive green chemistry implications. Thus, the results of these previous studies are also discussed in this review in light of the principles and tools of green chemistry. Various metrics were used to evaluate the greenness, cost-effectiveness, and material and energy efficiency of the oxidative methylation reaction.

Anaerobic Immobilized Yeast Cell Fermentation and Anaerobic Remediation in Hybrid Reactor for Mineralization of Dicarboxylic Acid Solid Waste

The solid resinous product (SRP) containing unsaturated/saturated dicarboxylic acid residues, phthalic acid and maleic acid is discharged as a solid waste during cracking of benzene over vanadium at temperatures above 500°C in the dicarboxylic acid manufacturing industry. In the present study the solid waste was diluted with water to a concentration of 0.5% w/v for microbial degradation. The waste was fermented in a reactor containing mesoporous activated carbon on which was immobilized Saccharomyces cerevisiae at an optimum residence time of 24 h at pH 6.5. The immobilized-yeast-treated samples were further treated in an upflow anaerobic reactor at an hydraulic retention time (HRT) of 0.1038 days at a hydraulic flow rate of 7.34 × 10−3 m3/day and chemical oxygen demand (COD) loading rate of 2.19 kg/m3/day. The pathway followed in the degradation of dicarboxylic acid into end products by anaerobic metabolism in the yeast cell fermentor and in the upflow anaerobic reactor was confirmed through HPLC, Fourier transform infra red spectroscopy and proton and 13C NMR spectroscopy.