Xylene Production Research Articles

Production of Xylenes from Toluene and 1,2,4‐Trimethylbenzene over ZSM‐5 and Mordenite Catalysts in a Fluidized‐Bed Reactor

AbstractThe production of various xylenes from toluene, heavy aromatics such as 1,2,4‐trimethylbenzene (1,2,4‐TMB) and their mixture was investigated over H‐ZSM‐5 (H‐Z), H‐mordenite (H‐M) and a dual zeolitic catalyst comprising ZSM‐5 and mordenite (H‐ZM). The experiments were conducted in a riser‐simulator reactor under different operating conditions to study the effect of temperature, reaction time and feed composition on conversion and product yields. At 400 °C, the conversion of toluene over the three catalysts yielded mainly benzene and xylenes with maximum conversion at 25 % and a xylene yield of 12.5 wt % over the H‐M catalyst. The transformation of 1,2,4‐TMB doubled the conversion level and xylene yield and suppressed benzene formation. However, a considerable portion of the 1,2,4‐TMB feed was isomerized into 1,2,3‐TMB and 1,3,5‐TMB accompanied by the formation of tetramethylbenzenes (TeMBs). The conversion of an equimolar mixture of toluene and 1,2,4‐TMB over the three catalysts resulted in higher toluene conversion and double xylene yield in comparison with 1,2,4‐TMB alone. The advantage of using a dual zeolitic catalyst was observed at an equimolar feed of toluene and 1,2,4‐TMB, exhibiting maximum toluene conversion, higher xylene yield and the formation of lower levels of undesirable products.

Para-Xylene Maximization. Part VIII: Promotion of H-ZSM-5 Zeolite by Pt and HF Doping for Use as Catalysts in Toluene Alkylation with Methanol

Toluene was alkylated with methanol in a flow type reactor at temperatures between 300 and 500℃ using H-ZSM-5 zeolite, 0.2%Pt/H-ZSM-5 and hydrofluorinated 0.2%Pt/H-ZSM-5 with HF concentrations of 1.0%, 2.0%, 3.0%, or 4.0%. Pt primarily enhances toluene conversion, total xylenes production, and p-xylene relative to its thermodynamic equilibrium. As the concentration of HF increases from 1.0% to 3.0%, the catalyst activity increases because of the increase in the number of acid sites and their strength. Additionally, the surface area and Pt dispersion also increases. An advantage of increased HF doping is that the formation of voluminous trimethylbenzene (TMB) byproducts is inhibited. However, at a HF concentration of 4.0%, Al and Si are partially leached and then deposited mostly in the wider catalytic pores. This was determined by evaluating the pore volume distribution and we determined that reactivity inhibition was obviously present and was due to diffusion restriction.

Effect of Hydrohalogenation of Metal/Zeolite Catalysts for Cyclohexene Hydroconversion ‐Part 3‐ Pd/H‐ZSM‐5 Catalysts

AbstractCyclohexene (CHE) hydroconversion was performed in a flow reactor at atmospheric pressure and temperatures of 50–400 °C using: Pd/H‐ZSM‐5, Pd/H‐ZSM‐5(HCl), and Pd/H‐ZSM‐5(HF) catalysts. These catalysts were characterized for acid site strength distribution via NH3 TPD, Pd dispersion via H2 chemisorption, TPR via reduction of the metal oxide in the catalysts and XRD for tracing crystallinity The hydroconversion steps proceeded as follows: CHE → Cyclohexane (CHA); CHE → Methylcyclopentenes (MCPEs) → Methylcyclopentane (MCPA); CHE → Cyclohexadienes (CHDEs) → Benzene → Alkylbenzenes; CHE and others → Hydrocrackedproducts.The overall hydroconversion of CHE was achieved in the catalyst order: Pd/H‐ZSM‐5 > Pd/H‐ZSM‐5(HF) > Pd/H‐ZSM‐5(HCl). CHE hydrogenation step was the major reaction at low temperatures which significantly inhibited via HCl treatment, but slightly enhanced via HF treatment. At medium temperatures, on all catalysts, isomerisation to MCPEs and MCPA increase to a maximum then a decline with a further increase of temperature. The overall isomerisation of CHE was highest on the untreated catalyst. During the higher temperature range, dehydrogenation, alkylation and hydrocracking were increased with temperature. Dehydrogenation of CHE always yielded larger amounts of 1,3‐CHDE than 1,4‐CHDE. These cyclohexadienes were produced in the catalyst order: Pd/H‐ZSM‐5(HF) > Pd/H‐ZSM‐5(HCl) > Pd/H‐ZSM‐5. In general, benzene alkylation to toluene exceeded that of xylenes, indicating that the second methylation is more difficult than the first. However, the catalytic activities for benzene and toluene production were in the order: Pd/H‐ZSM‐5 » Pd/H‐ZSM‐5(HCl) > Pd/H‐ZSM‐5(HF), whereas for xylenes production, Pd/H‐ZSM‐5 » Pd/H‐ZSM‐5(HF) > Pd/H‐ZSM‐5(HCl). Intrapore diffusion plays an important role during the dehydrogenation reactions as well as during the interconversion of individual aromatic hydrocarbons.

Manufacture of aromatic hydrocarbons from coal hydrogenation products

The manufacture of aromatic hydrocarbons from coal distillates was experimentally studied. A flow chart for the production of benzene, ethylbenzene, toluene, and xylenes was designed, which comprised the hydrogen treatment of the total wide-cut (or preliminarily depehenolized) fraction with FBP 425°C; fractional distillation of the hydrotreated products into IBP-60, 60–180, 180–300, and 300–425°C fractions; the hydro-racking of middle fractions for increasing the yield of gasoline fractions whenever necessary; the catalytic reform of the fractions with bp up to 180°C; and the extraction of aromatic hydrocarbons.

Benzene transalkylation with C9+ aromatics over supported 12-tungstophosphoric acid on silica catalysts

Abstract Silica-supported H 3 PW 12 O 40 (H 3 PW) catalysts (8, 15, 20 and 25 wt.% H 3 PW) were prepared and their catalytic activities were evaluated in benzene transalkylation with C9+ aromatics, using an industrial stream. This reaction is a convenient way to upgrade the low value of the stream produced in naphtha reforming and gasoline pyrolysis, by improving the production of xylenes. It was found that the activity and selectivity to xylenes changed with the acid loading and this was related to optimum acid strength and dispersion as well as specific surface area of the solids. The most active catalyst was the sample with 15 wt.% H 3 PW, which showed the adequate combination of the three parameters cited above. This solid was also the most stable, showing the lowest rate of deactivation under the reaction conditions, producing the least amount of coke. In addition, it presented the highest activity and selectivity to xylenes, even when compared to a mordenite commercial catalyst. Consequently, this catalyst represents a promising catalyst for industrial applications.

Improved selectivity in the toluene alkylation reaction through understanding and optimising the process variables

It has been demonstrated that it is possible to produce p -xylene with >99.9% selectivity by optimising the process variables of the toluene alkylation reaction over a B/ZSM-5 catalyst. This has been achieved specifically by minimising the undesirable isomerisation of p -xylene on the external acid sites of the catalyst by controlling the contact time. It has been demonstrated that it is possible to produce p -xylene with near-perfect selectivity by optimising the process variables of the toluene alkylation reaction over a B/ZSM-5 catalyst. This has been achieved specifically by minimising the undesirable isomerisation of p -xylene on the external acid sites of the catalyst by controlling the contact time. This offers a superior route to high selectivity compared to multiple pre-treatments of the catalyst to eliminate external acid sites (for example, by silanisation). Additionally, a high toluene:methanol feed ratio is beneficial because it minimises the methanol dehydration reaction. A further benefit is that the maximum theoretical conversion of toluene is limited, which diminishes p -xylene product inhibition. These findings confirm that toluene alkylation is best operated in a multistage reactor, but also highlight the need for removal of p -xylene as well as addition of methanol between stages. The method of catalyst preparation is not critical, provided that there is sufficient boron present (≥6.5 wt%) and any boron lost through sublimation during the reaction is replenished. It has been found that an active catalyst can be produced in situ by either loading a physical mixture of hydroboric acid and HZSM-5 into the reactor prior to reaction or even placing a bed of hydroboric acid upstream from a bed of HZSM-5. The in situ-formed catalyst readily achieves >99.9% selectivity to the desired p -xylene isomer, under optimised conditions.

H-MCM-22 zeolitic catalysts modified by chemical liquid deposition for shape-selective disproportionation of toluene

Catalysts were prepared by dealumination of H-MCM-22 zeolite with oxalic acid leaching, followed by shaping and liquid phase modification with siloxane. The catalytic performance was measured with selective disproportionation of toluene in a fixed-bed reactor. The unmodified H-MCM-22 zeolite exhibited much higher initial activity than H-ZSM-5 with a thermodynamic equilibrium distribution of xylene products. The oxalic acid treatment of H-MCM-22 improved the selectivity for para-xylene by 10–18%. The modification by siloxane of the oxalic acid treated H-MCM-22 turned out to be highly selective for para-xylene, however, with the expense of the conversion. It is proposed that the high para-selectivity was closely associated with the contraction of micropore windows and the elimination of acid sites at the external surface by the deposited silica. Therefore, the modified H-MCM-22 is a potential catalyst for the selective disproportionation of toluene with a high para-selectivity.

Xylene isomerization in a membrane reactor

Abstract A model and the simulation of a membrane reactor for xylene isomerization are presented. Kinetic parameters for the reaction carried out under industrial conditions are optimized using plant data with a conventional plug-flow model. In the membrane reactor, the characteristics of a ZSM-5 film supported on porous SS tubes, which was developed in our laboratory, are included to simulate the improvement in p -xylene production at 370 °C. The values used for the simulations correspond to ternary mixtures at 370 °C, and they are: 4.70 × 10 −8 , 8.44 × 10 −9 and 8.45 × 10 −9 mol s −1 m −2 Pa −1 for p -, o - and m -xylene, respectively. In this vein, while for the output of the conventional plug-flow reactor the ratio p -/ o -/ m -xylene is 1.000/0.936/1.940, in the case of the membrane reactor the rate is improved to 1.000/0.830/1.719, taking into consideration the contribution of the permeate and retentate sides. Consequently, an increase of 12% in p -xylene production is predicted by increasing permeation area and sweep gas flow, restricted to a reasonable pressure drop and whithin the physical and constructive feasibility of the SS tubes.

Ototoxicity in rats exposed to ethylbenzene and to two technical xylene vapours for 13 weeks

Male Sprague-Dawley rats were exposed to ethylbenzene (200, 400, 600 and 800 ppm) and to two mixed xylenes (250, 500, 1,000 and 2,000 ppm total compounds) by inhalation, 6 h/day, 6 days/week for 13 weeks and sacrificed for morphological investigation 8 weeks after the end of exposure. Brainstem auditory-evoked responses were used to determine auditory thresholds at different frequencies. Ethylbenzene produced moderate to severe ototoxicity in rats exposed to the four concentrations studied. Increased thresholds were observed at 2, 4, 8 and 16 kHz in rats exposed to 400, 600 and 800 ppm ethylbenzene. Moderate to severe losses of outer hair cells of the organ of Corti occurred in animals exposed to the four concentrations studied. Exposure to both mixed xylenes produced ototoxicity characterized by increased auditory thresholds and losses of outer hair cells. Ototoxicity potentiation caused by ethylbenzene was observed. Depending on the mixed xylene studied and the area of the concentration-response curves taken into account, the concentrations of ethylbenzene in mixed xylenes necessary to cause a given ototoxicity were 1.7-2.8 times less than those of pure ethylbenzene. Given the high ototoxicity of ethylbenzene, the safety margin of less or equal to two (LOAEL/TWA) might be too small to protect workers from the potential risk of ototoxicity. Moreover, the enhanced ototoxicity of ethylbenzene and para-xylene observed in mixed xylenes should encourage the production of mixed xylenes with the lowest possible concentrations of ethylbenzene and para-xylene.

Hydroisomerization of ethylbenzene over bimetallic bifunctional zeolite catalysts: Maximization of xylene production

Zeolite-β and mordenite were impregnated with 0.1 wt.% Pt and varying (0, 0.1, 0.3, 0.5 wt.%) amount of Ni and reduced at 475 °C. The line broadening in the XRD patterns reveals that the increasing Ni addition decreases the crystallinity of zeolites. The catalysts were also characterized by TEM, ESCA and TPD of ammonia and pyridine. The TEM results show that the average metal particle size increases with increasing Ni addition. ESCA studies clearly points to the maximum percentage of Ni reduction in the Pt loaded zeolite-β and mordenite catalysts. The acidity measurements by both TPD of ammonia and pyridine adsorbed FT-IR spectroscopy show that the number of the acid sites of the catalysts decreases upon the addition of the Ni species. Hydroisomerization of ethylbenzene over the Pt–Ni loaded zeolite and mordenite was carried out in the temperature range 250–400 °C. It has been found that the addition of Ni up to 0.3 wt.% over 0.1 wt.% Pt loaded zeolite-β and 0.1 wt.% over 0.1 wt.% Pt loaded mordenite greatly enhances the ethylbenzene conversion, isomerization selectivity and sustainability of the catalysts. Further addition of Ni above the threshold value leads to a drastic reduction in the activity and isomerization selectivity. Zeolite-β-based Ni–Pt catalysts show higher activity and selectivity than mordenite-based catalysts under the optimized reaction conditions.

Microkinetic modeling of propane aromatization over HZSM-5

Reaction kinetic studies of propane conversion to aromatics were conducted on an HZSM-5 zeolite at a pressure of 1 atm, temperatures in the range 793–823 K, and different space times (0–12 g cat h/mol). The rates of production of methane, ethane, ethene, propene, propane, butane, butene, benzene, toluene, and xylene are reported. A kinetic model has been postulated that considers surface species as neutral alkoxides, reactions of these alkoxide species by carbenium ion-like transition states, and alkane activation by carbonium ion-like transition states. The associated elementary steps, categorized within the reaction types adsorption, desorption, unimolecular protolytic cracking and dehydrogenation, β-scission, oligomerization, hydride transfer, alkylation, dealkylation, and cyclization, were parsed into reaction families based on an equal reactivity assumption. A total of 311 reaction steps were grouped into 37 reaction families, and the number of unknown parameters was reduced to 25 using adsorption parameters for n-alkanes and relative rates for β-scission and hydride transfer from the literature. It is proposed that this kinetic model describes the reaction behavior over an HZSM-5 catalyst in terms of relevant rate and equilibrium constants and activation energies.

Design and Development of Zeolite-Based Catalytic Processes for Aromatics Production

Processes for the production of xylenes, which occur in an integrated aromatic complex, are discussed. A brief overview of the work carried out at Indian Petrochemicals Corporation Limited for the development of zeolite-based catalytic processes for the production of aromatics is presented. This includes xylene isomerization, transalkylation and disproportionation of C7 and C9 aromatics for maximization of xylenes, selective disproportionation of toluene and selective alkylation of mono-alkylaromatics to p-dialkylbenzene. Achievements in the commercialization of zeolite-based catalysts and processes for isomerization of m-xylene to p- and o-xylene along with dealkylation of ethylbenzene, and for selective ethylation of ethylbenzene to produce p-diethylbenzene are highlighted.

TRANSFORMATION OF n-OCTANE INTO AROMATIC HYDROCARBON OVER ZSM-S ZEOLITES

ABSTRACT Conversion of n- octane over ZSM-5 zeolites are greatly enhanced by incorporation of 0.35 wt. % Fe, Zn, Zr metals. Hydroconversion rates were conducted at temperature range of 350-500 C, W/F of 14.8 g of catalyst / g. mole of feed / h, and hydrogen / feed = 5:1 (mole : mole). The product selectivity with total conversion was examined at the temperature range under study. The catalyst Zr / H25 M-5 gave the highest selectivity towards aromatization and production of xylenes.

100 Jahre Givaudan in Dübendorf [1] Ein Jahrhundert für Geruch und Geschmack

The activities of Givaudan in Duebendorf go back to July 1900 when the 'Chemische Fabrik Flora AG' started the production and sales of musk xylene. Having been acquired by L. Givaudan & Co. in Vernier in 1948, the company was subsequently bought by F. Hoffmann-La Roche & Co. in 1963. Activities were restructured and concentrated in two areas: the development, production and sales of flavours for the food and beverage industries, and the research and development for fragrances and flavours.Today, Givaudan Duebendorf is part of a global group with sales of over CHF 2000 million and a staff of 5000, and, as of June 2000, an independent company listed on the Swiss stock exchange. In addition to the history of Givaudan, the article illustrates the various facets of production, product development, and research.

Feasibility of Simultaneous Measurement of Xylene Isomers and other Hydrocarbons in p-Xylene Production Processes Using Near-Infrared Spectroscopy

The feasibility of simultaneous measurement of important components such as o-xylene, m-xylene, p-xylene, ethylbenzene, toluene, aliphatic hydrocarbons, and total C9–C10 aromatic hydrocarbons in the p-xylene production process is investigated. Mixtures of those components were prepared to simulate concentration levels in actual p-xylene processes, and near-infrared (NIR) spectra were collected from mixtures over the spectral range of 1100 to 2500 nm. Even with the very similar spectral features of xylene isomers and other aromatic compounds, the concentrations of each of the components in the mixtures are accurately predicted by using a partial least-squares (PLS) algorithm and show excellent correlation with conventional gas chromatographic analysis. The results clearly demonstrate the possibility of using NIR spectroscopy for monitoring the major components in an actual p-xylene production process for process control and optimization.

The cost benefit of near‐surface geophysics: A case study

This article describes conductivity and magnetic surveys at a convenience store/gas station in Phoenix, Arizona, which were undertaken to find the source of water contamination at the site. The geophysical surveys indicated that the origin of the contamination (benzene, toluene, ethylene, and xylene products, known as BTEX) was a different gas station, across the street from the contaminated site. The client, who had been paying for remedial action for about four years, estimates that at least $200 000 could have been saved had geophysical surveys been performed as part of the initial site investigation.

Slurry‐Based Biotreatment of Polyaryl Contaminants Sorbed onto Soil

Abstract Whole soil samples were obtained from a site immediately adjacent to an impoundment used for disposal of still bottoms residue from a benzene, toluene and xylenes (BTX) production process. Research examined the effects of other operating conditions on the biotreatment process such as inoculum source, temperature and suspended solids concentration. The effects of humic substances and humic acid metabolites on the biodegradation of polyaryl species and measurements of biological activity also were assessed. Uncontaminated whole soil, was fed to the active bioreactor to determine the contribution of humic material to measurements of the biodegradation process including UV absorbance of slurry extracts, aqueous total organic carbon (TOC), carbon dioxide evolution and acid production. Significant reductions of marker species concentrations, often to levels below detection limits, are observed with low, medium and some high molecular weight aromatic and polyaryl species.

Catalytic properties of high-silica zeolites synthesized in mixtures of water and organic solvent

The Catalytic properties of ISI-1, 3, 4, 5 and 6, synthesized in mixtures of water and organic solvent, have been studied. Although having acidic properties similar to a sample of ZSM-5 zeolite comprising small and aggregated crystallites, the five zeolites showed low selectivities for C 5 + product and fraction of aromatics in the C 5 + product in syngas-to-gasoline and methanol-to-gasoline reactions. Under methanol-to-gasoline reaction conditions, ISI-3, 4, 5 and 6 showed a high production of p-xylene in the xylene product. From the results of physicochemical measurements, the unique Catalytic properties of each ISI zeolite can be attributed to its crystal structure, pore size and large crystallite size.

Production and reactions of xylenes over H-ZSM5

Disproportion of toluene, isomerization of xylenes and alkylation of toluene with methanol were investigated over a series of H-ZSM5 zeolites varying in Si/Al ratio. The specific rates per unit cell of H-ZSM5 for disproportionation of toluene and isomerization of xylene were found to be directly proportional to the concentration of strong Brönsted acid sites for all temperatures investigated. For temperatures above 573 K, the corresponding specific rates for alkylation of toluene with methanol were found to be independent of the concentration of strong Brönsted acid sites. In contrast, at 473 K a significant dependence was observed. We explain this variation of the dependence of the specific rate upon the concentration of strong Brönsted acid sites by the contribution of two reaction pathways to the overall reaction rate.

Disproportionation of toluene and of trimethylbenzene and their transalkylation over zeolite beta

Zeolite Beta has been demonstrated as having the potential for catalysis in xylene production reactions, including toluene disproportionation, trimethylbenzene disproportionation, and toluene-trimethylbenzene transalkylation. It exhibits excellent catalytic stability and transalkylation selectivity. In trimethylbenzene disproportionation, blending toluene into feedstocks can shift the production selectivity of tetramethylbenzene to xylene, whereas in toluene disproportionation, mixing trimethylbenzene into feedstocks can not only reduce the reaction temperatures but also raise the xylene yield. The shift of reaction selectivity is discussed from the viewpoints of both thermodynamics and kinetics. A methyl group transfer model has been proposed to rationalize the enhancement of xylene production efficiency