Quartz Glass Reactor Research Articles

Using Low Energy-Consuming Microwave Technology to Regenerate High Carbon-Containing Pt Catalyst

In this research, the high carbon-containing (coke, >20 wt%) Pt catalyst wasted from a full-scale petrochemical plant are regenerated in quartz and borax glass reactors by applying 250 W microwave irradiation for 18 hours. When irradiated with microwave substances of various dielectric characteristics will consume the microwave energy; the quantity of energy consumed is proportional to dielectric constant. Because borax glass has higher dielectric constant than quartz glass (e.g. 4.6 vs. 3.6 F/M), it causes higher energy loss than quartz glass. Laboratory results reveal that the removal of coke is smaller for the sample placed in the borax glass reactor than in the quartz glass container (17.7 vs. 25.9 %). On the other hand, higher MW output power leads to stronger electrical field to influence the mutual reactions between microwave and dielectric materials (e.g. the absorption of microwave energy), and the overall energy efficiency. The laboratory results also show that when the microwave energy is increased from 250 to 450 W, the carbon removal rate is raised from 25.9 to 38.1% with the sample placed in quartz glass reactor. Using the microwave energy to regenerate high carbon-containing (coke) Pt-catalyst as studied in this research is an innovated technology.

Preparation of extrapure Ga2S3 by reacting GaI3 with sulfur

This paper describes a process for the preparation of extrapure gallium(III) sulfide by reacting gallium(III) iodide with sulfur in an evacuated two-zone quartz glass reactor. The maximum synthesis temperature was 350°C. The residual iodine was removed by calcining the powders at temperatures from 500 to 650°C. The gallium(III) sulfide yield was 93–96% of theoretical yield. The samples were characterized by X-ray microanalysis, X-ray diffraction, and laser mass spectrometry and were shown to contain the following impurities (ppm): silicon, 20–28; iron and calcium, 0.5–0.6; potassium, 0.3–0.7; chromium, 0.2; chlorine, 70–100; aluminum, 0.05–0.1; and phosphorus, 0.1–2. The iodine content varied from 0.04 to 1.8 at %, depending on calcination temperature and time.

Characterisation of CO/NO/SO2 emission and ash-forming elements from the combustion and pyrolysis process

Bioenergy is considered as a sustainable energy which can play a significant role in the future’s energy scenarios to replace fossil fuels, not only in the heat production, but also in the electricity and transportation sectors. Emission formation and release of main ash-forming elements during thermal conversion of biomass fuels at different conditions have been the scope of this study. The experiments were conducted in a quartz glass reactor where the temperature and atmosphere could be controlled. The selected fuels represent a wide range of biomass compositions. They are torrefied softwood, spruce bark, waste wood, miscanthus, and wheat straw. The fuels were first grinded and then pressed with a pellet maker into pellets of the same size and weight. For each fuel, the experiments were carried out under both oxidation and pyrolysis condition, with atmosphere of 3 % O2 + 97 % N2 and 100 % N2, respectively, at four residence times. The selected temperatures under which experiments were performed are 800, 900, and 1,050 °C. The concentration of SO2, NO, CO, and CO2 emissions and O2 were monitored online by three analysers, simultaneously. The residue weight was measured after each process, and the comparison with the ash content of the fresh pellet is made. Additionally, the release of several ash-forming elements (K, Zn, Na, and Mn) from the fuels has been quantified as function of temperature and residence time by inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). Time-dependent formation of NO and SO2 and other emissions is presented and discussed with respect to different temperature and combustion conditions.

Experimental Study of a Single Particle Reactor at Combustion and Pyrolysis Conditions

Emission formation during thermal conversion of biomass fuels at different conditions has been the scope of this study. The experiments were conducted in a quartz glass reactor where the temperature and atmosphere can be adjusted. The fuels were selected accurately in order to cover a wide range of biomass/waste compositions. They are torrefied softwood, spruce bark, waste wood, miscanthus, and wheat straw. The fuels were first grinded and then pressed into pellets of the same size and weight with a pellet maker. Each pellet was about 200 mg.

FT-IR Product Study of the Reactions of NO3Radicals Withortho-,meta-, andpara-Cresol

Product analyses of the NO3 radical-initiated oxidation of ortho-, meta-, and para-cresol have been performed in large-volume chamber systems at the University of Wuppertal (1080 L quartz glass reactor: QUAREC) and the European Photoreactor (EUPHORE), Valencia, Spain. The reaction of O3 with NO2 was used for the in situ generation of NO3 radicals in both QUAREC and EUPHORE. In the QUAREC experiments the gas-phase reaction of ortho-cresol isomer with NO3 yielded (11.5 ± 0.8) % 6-methyl-2-nitrophenol (6M2NP), (4.4 ± 0.3) % methyl-1,4-benzoquinone (MQUIN) and (77.2 ± 6.3) % HNO3. The reaction of NO3 radicals with meta-cresol yielded (21.2 ± 1.4) % 3-methyl-2-nitrophenol (3M2NP), (22.8 ± 1.8) % 3-methyl-4-nitrophenol (3M4NP), (23.5 ± 1.8) % 5-methyl-2-nitrophenol (5M2NP), (4.2 ± 0.7) % MQUIN and (72.3 ± 6.4) % HNO3. In the reaction of NO3 radicals with para-cresol, 4-methyl-2-nitrophenol (4M2NP) and HNO3 were identified as products with yields of (41.3 ± 3.7) % and (85.0 ± 10.2) %, respectively. In the EUPHORE chamber not all products were formed at levels above the detection limit, however, in cases where detection was possible similar product yields were observed. The product formation yields determined in both chambers are compared with available literature data and a gas-phase mechanism is proposed to explain the formation of the products observed from the reaction of NO3 and with cresol isomers.

Using Microwave Radiation to Recover Granular Activated Carbon Exposed to Toluene Vapor

This paper describes laboratory scale experiments examining the impact of microwave irradiation on the Granular Activated Carbon (GAC) exposed to toluene, a common organic vapor frequently released into work environment as well as outdoor. A stream containing 300 ppm toluene was supplied and passed through the granular activated carbon. The saturated adsorbent was placed in a quartz glass reactor and treated by microwave irradiation at heating frequency of 2450 MHz at different power levels. After successive recovery cycles the adsorption capacity was evaluated through breakthrough curves and the residue analyzed by gas chromatography. We found that exposing GAC saturated with toluene under microwave irradiation at 900W for 15 minutes can remove the pollutant from the adsorbent effectively. The recovery efficiency was more than 95% after 10 cycles at high power levels. GAC surface area and porosity values were increased slightly over recovery cycles. Our experiments indicate that GAC could be reused after several cycles of treatment and recovery processes while maintaining its original adsorption capacity and physical properties.

Synergy between surface adsorption and photocatalysis during degradation of humic acid on TiO2/activated carbon composites

A photocatalyst comprising nano-sized TiO2 particles on granular activated carbon (GAC) was prepared by a sol-dipping–gel process. The TiO2/GAC composite was characterized by scanning electron microscopy (SEM), X-ray diffractiometry (XRD) and nitrogen sorptometry, and its photocatalytic activity was studied through the degradation of humic acid (HA) in a quartz glass reactor. The factors influencing photocatalysis were investigated and the GAC was found to be an ideal substrate for nano-sized TiO2 immobilization. A 99.5% removal efficiency for HA from solution was achieved at an initial concentration of 15mg/L in a period of 3h. It was found that degradation of HA on the TiO2/GAC composite was facilitated by the synergistic relationship between surface adsorption characteristics and photocatalytic potential. The fitting of experimental results with the Langmuir–Hinshelwood (L–H) model showed that the reaction rate constant and the adsorption constant values were 0.1124mg/(Lmin) and 0.3402L/mg. The latter is 1.7 times of the calculated value by fitting the adsorption equilibrium data into the Langmuir equation.

Photocatalytic reduction of 6-chloro-3-nitrotoluene-4-sulfonic acid in presence of surfactants

Photocatalytic reduction of 6-chloro-3-nitrotoluene-4-sulfonic acid (CNSA) was studied in UV-irradiated TiO2 suspensions in the presence of methanol and surfactants. A mixture of CNSA, TiO2, water, additives and surfactants was put into a quartz glass reactor with a jacket, which was irradiated with a high pressure Hg lamp in the purging of nitrogen gas. With methanol, the conversion of CNSA increased from 7.7% to 34.6%. Three surfactants significantly promoted the photocatalytic reduction conversion in reduced order of sodium dodecylbenzenesulfonate (DBS), cetyltrimethylammonium bromide (CTAB) and sodium dodecylsulfate (SDS). In suspensions involving DBS and CTAB respectively, CNSA conversion increased in consistence with the adsorption ratio with methanol, but varied inversely with the adsorption ratio without methanol. But no obvious influence on the adsorption ratio was observed with or without methanol added when the SDS concentration was critical micelle concentration (cmc). The photocatalytic reduction of CNSA was enhanced in UV-irradiated TiO2 suspensions in the presence of methanol and surfactants. Methanol inhibited the recombination of photogenerated holes and electrons efficiently. Surfactants around 1 cmc led to the highest reduction conversion.

Catalysts at work: From integral to spatially resolved X-ray absorption spectroscopy

Spectroscopic studies on heterogeneous catalysts have mostly been done in an integral mode. However, in many cases spatial variations in catalyst structure can occur, e.g. during impregnation of pre-shaped particles, during reaction in a catalytic reactor, or in microstructured reactors as the present overview shows. Therefore, spatially resolved molecular information on a microscale is required for a comprehensive understanding of theses systems, partly in ex situ studies, partly under stationary reaction conditions and in some cases even under dynamic reaction conditions. Among the different available techniques, X-ray absorption spectroscopy (XAS) is a well-suited tool for this purpose as the different selected examples highlight. Two different techniques, scanning and full-field X-ray microscopy/tomography, are described and compared. At first, the tomographic structure of impregnated alumina pellets is presented using full-field transmission microtomography and compared to the results obtained with a scanning X-ray microbeam technique to analyse the catalyst bed inside a catalytic quartz glass reactor. On the other hand, by using XAS in scanning microtomography, the structure and the distribution of Cu(0), Cu(I), Cu(II) species in a Cu/ZnO catalyst loaded in a quartz capillary microreactor could be reconstructed quantitatively on a virtual section through the reactor. An illustrating example for spatially resolved XAS under reaction conditions is the partial oxidation of methane over noble metal-based catalysts. In order to obtain spectroscopic information on the spatial variation of the oxidation state of the catalyst inside the reactor XAS spectra were recorded by scanning with a micro-focussed beam along the catalyst bed. Alternatively, full-field transmission imaging was used to efficiently determine the distribution of the oxidation state of a catalyst inside a reactor under reaction conditions. The new technical approaches together with quantitative data analysis and an appropriate in situ catalytic experiment allowed drawing important conclusions on the reaction mechanism, and the analytical strategy might be similarly applied in other case studies. The corresponding temperature profiles and the catalytic performance were measured by means of an IR-camera and mass spectrometric analysis. In a more advanced experiment the ignition process of the partial oxidation of methane was followed in a spatiotemporal manner which demonstrates that spatially resolved spectroscopic information can even be obtained in the subsecond scale.

Pyrolysis of tetrabromobisphenol-A containing paper laminated printed circuit boards

Tetrabromobisphenol-A (TBBA) is the most common brominated fire retardant. In this study, a TBBA containing paper laminated printed circuit board (PCB) prepared from novolac was pyrolysed by both TGA and in a quartz glass reactor between 40 and 1000 °C. The products were online detected by MS. It was found that the PCB degraded in three steps. Step one (<270 °C) consisted of the evolution of water and CO 2 from the paper laminate. In the second step, between 270 and 370 °C, the fire retardant decomposed, releasing HBr and brominated aromatics. In the third step, at temperatures above 370 °C, the phenol resin decomposed and char was formed. Compared to pure TBBA, which mainly produces brominated phenols, the brominated products enclosed in the char released HBr during the last degradation step as well as during the second step. Most of the bromine left the resin in the form of HBr, with about 14% of the bromine being fixed in brominated aromatics and less than 2% remaining in the residue.

Influence of Gas Components on the Formation of Carbonyl Sulfide over Water-Gas Shift Catalyst B303Q

Water-gas shift reaction catalyst at lower temperature (200–400 °C) may improve the conversion of carbon monoxide. But carbonyl sulfide was found to be present over the sulfided cobalt-molybdenum/alumina catalyst for water-gas shift reaction. The influences of temperature, space velocity, and gas components on the formation of carbonyl sulfide over sulfided cobalt-molybdenum/alumina catalyst B303Q at 200–400 °C were studied in a tubular fixed-bed quartz-glass reactor under simulated water-gas shift conditions. The experimental results showed that the yield of carbonyl sulfide over B303Q catalyst reached a maximum at 220 °C with the increase in temperature, sharply decreased with the increase in space velocity and the content of water vapor, increased with the increase in the content of carbon monoxide and carbon dioxide, and its yield increased and then reached a stable value with the increase in the content of hydrogen and hydrogen sulfide. The formation mechanism of carbonyl sulfide over B303Q catalyst at 200–400 °C was discussed on the basis of how these factors influence the formation of COS. The yield of carbonyl sulfide over B303Q catalyst at 200–400 °C was the combined result of two reactions, that is, COS was first produced by the reaction of carbon monoxide with hydrogen sulfide, and then the as-produced COS was converted to hydrogen sulfide and carbon dioxide by hydrolysis. The mechanism of COS formation is assumed as follows: sulfur atoms in the Co 9S 8-MoS 2/Al 2O 3 crystal lattice were easily removed and formed carbonyl sulfide with CO, and then hydrogen sulfide in the water-gas shift gas reacted with the crystal lattice oxygen atoms in CoO-MoO 3/Al 2O 3 to form Co 9S 8-MoS 2/Al 2O 3. This mechanism for the formation of COS over water-gas shift catalyst B303Q is in accordance with the Mars-Van Krevelen's redox mechanism over metal sulfide.

Rate coefficients for the gas‐phase reaction of NO3 radicals with selected dihydroxybenzenes

AbstractUsing a relative kinetic technique, rate coefficients have been determined at (298 ± 2) K and atmospheric pressure for the gas‐phase reactions of the NO3 radical with three vicinal dihydroxy aromatic compounds. The experiments were carried out in a 1080‐l quartz glass reactor at the Bergische Universität Wuppertal and in the European Photoreactor (EUPHORE), Valencia, Spain. The rate coefficients obtained (in units of cm3 molecule−1 s−1) using 2,3‐dimethyl‐2‐butene as the reference hydrocarbon were kNO3(1,2‐dihydroxybenzene) = (9.8 ± 5.0) × 10−11, kNO3(1,2‐dihydroxy‐3‐methylbenzene) = (17.2 ± 5.6) × 10−11, and kNO3 (1,2‐ dihydroxy‐4‐methylbenzene) = (14.7 ± 6.5) × 10−11. This study represents the first kinetic investigation of the reactions of the NO3 radical with dihydroxybenzenes. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 577–583, 2004

MOVPE growth of ZnO using various oxygen precursors

The II–VI compound semiconductor ZnO is already widely used for various applications such as UV resistive coatings, gas sensors and surface acoustic wave devices. Recently, the optoelectronic properties of ZnO are attracting increasing interest, which has been initiated by first reports on p-type doping. ZnO appears especially favorable for such applications because of its large exciton binding energy of about 60 meV, its low-power thresholds for optical pumping at room temperature and the availability of bulk ZnO substrates. Here, we report on the metal-organic vapor phase epitaxy growth of ZnO layers using diethylzinc as the zinc source and iso-propanol or tertiary-butanol as the oxygen precursors. The choice of an appropriate oxygen precursor is of great importance to minimize parasitic prereactions in the gas phase, that have a negative influence on layer quality. Epitaxial growth is conducted in a water-cooled, RF-heated horizontal quartz glass reactor. Growth rates up to 2.6 μm have been accomplished. The influence of the growth parameters as substrate temperature, reactor pressure, gas flow rates, and especially the impact of the II/VI-ratio on growth rates and quality of the epitaxial material will be discussed.

Effective diffusion coefficients in coal chars

Knowledge of effective diffusion coefficients in char particles is important when interpreting experimental reactivity measurements and modeling char combustion or NO and N 2 O reduction. In this work. NO and N 2 O reaction with a bituminous coal char was studied in a fixed-bed quartz glass reactor. Particle sizes in the range 0.05-5 mm were tested, and the effective diffusion coefficients were estimated from measured effectiveness factors using the Thiele modulus. At 1079 K the effective diffusion coefficients were 5.5×10 −6 m 2 /s and 6.8×10 −6 m 2 /s for N 2 O and NO, respectively. The experimental results were compared with theoretical values calculated from the mean pore radius and the cross-linked pore model. The method of mean pore radius underestimated the effective diffusion coefficient more than an order of magnitude. Using the cross-linked pore model, the bimodal pore size distribution, and a tortuosity factor of 5, a complete agreement between the experimental and the theoretical value was found. The conclusion was that for a char with a wide pore size distribution, the cross-linked pore model is a good choice for a theoretical calculation of the effective diffusion coefficient. In the case of strong pore diffusion limitations, the error in the interpretation of experimental results using the mean pore radius could be a factor of 5 on the intrinsic rate constant. For an average coal char reacting with oxygen at 1300 K, this would be the case for particle sizes larger than about 50 μm.

Photochemical Spectrofluorometric Determination of 2,6-Dimethylphenol Based on Monitoring Its Photo-Degradation Intermediate with TiO2 as a Catalyst

A novel spectrofluorometric method for the determination of 2,6-dimethylphenol has been developed. It is based on detecting a fluorophore intermediate produced in the course of 2,6-dimethylphenol photo-degradation with TiO2 as a cata-lyst. A quartz glass reactor containing the required amount of analyte, buffer and TiO2 is irradiated with UV light (<380 nm). The formed intermediate is detectable with fluorescence and UV absorption. What is more, the fluorescence inten-sity of the intermediate is dramatically enhanced when extracted into the CHCl3 phase. A linear calibration graph was obtained over a 2,6-dimethylphenol concentration ranging from 0.002 µg ml–1 to 0.1 µg ml–1 with a detection limit of 0.0008 µg ml–1. Other phenolic compounds as well as those common inorganic ions do not interfere. The kinetics of the photo-degradation reaction, which followed a successive first-order reaction kinetic model, were studied using an error-compensated algorithm.

Morphology analysis of nickel thin films grown by MOCVD

Nickel films on quartz substrates were prepared by metal-organic chemical vapor deposition (MOCVD), from the precursor bis(dimethylglyoximato)Ni(II), [Ni(dmg) 2]. The deposition was carried out at reduced pressure in a horizontal quartz glass reactor. The samples were analysed by profilometry, X-ray diffraction, electron spectroscopy for chemical analysis, atomic force microscopy (AFM) and scanning electron microscopy. Resistances were determined by four-point resistivity measurements. The film microstructure was described by a simplified two-layer model using the data obtained from AFM, profilometry and resistivity measurements. In this model, the films consist of a compact layer (density ≈ 100%) between the substrate and the surface layer and a porous surface layer (density < 100%). Increasing the substrate temperature resulted in an increase in the porous surface layer thickness which can be explained by the growth of separated grains rather than continuous film growth. The grains were thus poorly connected and the resistance increased with an increase in deposition temperature. Metallic films were obtained between 350 and 580°C.

Mechanistic study of the heterogeneous conversion of NO2 into HONO and N2O on acid surfaces

The heterogeneous conversion of NO2 into HONO and N2O on acid surfaces has been investigated in an 11 l Pyrex glass reactor under simulated atmospheric conditions and in a 64 l quartz glass reactor at reduced pressure. NO2, N2O and HONO were monitored with time by long-path tunable IR diode laser absorption spectroscopy using single vibrational rotational lines at 1641.0, 1254.47 and 1254.46 cm–1, respectively.The experimental results show that NO2 is heterogeneously converted on acid surfaces into HONO and then into N2O. HONO formation in the reaction system has been found to occur by the heterogeneous reaction of NO2 with adsorbed water on the surface and does not require NO. The experimental findings indicate that the nitrosyl ion probably plays an important role in converting HONO into N2O and HNO3. A mechanism is proposed which can explain the experimental findings.

Reactor Problems in Modified Chemical Vapour Deposition (II). The Mean Viscosity of Quartz Glass Reactor Tubes

AbstractA new method is developed for deducing viscosity data from collapse experiments with quartz glass reactor tubes. These data involve informations on temperature differences between outer and inner tube surface which are of great importance to the MCVD procedure. The present investigations supported by some deposition experiments yield the surprising result that a considerable temperature gradient exists also at rather low torch speeds. The reason for this effect is discussed.

Atmospheric oxidation of elemental mercury by ozone in the aqueous phase

The aqueous phase oxidation of elemental mercury by ozone has been investigated in the laboratory using a quartz glass reactor with gas phase concentrations of 400–1800ng m −3 and 70–200 ppb for Hg(0) and O 3, respectively. The absorption of Hg in the water phase was increased by three orders of magnitude with O 3 present. If the oxidation were to proceed with the same speed in liquid water in contact with the atmosphere,conversion rales of 1–4% h −1 would be implied. Experiments using ambient urban air with 2–6 ng Hg m −3 confirm the process at elevated O 3 concentrations. At ambient O 3 concentrations competitive reactions become important, e.g. O 3 consumption by SO 2, hydrocarbons etc., and even some reduction of Hg 2+ could occur. The atmospheric oxidation of Hg(0) by O 3 in water is thus considered important at high O 3 levels in regionally polluted or remote areas.

P- T- x phase diagrams of the light lanthanide-hydrogen systems (Ln ≡ La — Nd)

The P- T- x phase diagram of the La-H 2 system has been measured with vapor pressure measurements as a function of composition in the range 868 ⩽ T ⩽ 1111 ° C, using a quartz-glass reactor capable of T ⩽ 1150 ° C and P ⩽ 6 bar. It is shown that the T-x phase diagram does not have a critical point in the two-phase region γ-La(s) + LaH x (s) as mentioned in the literature. Extrapolation of the phase boundaries indicates the existence of a peritectic at T ≈ 1200 ° C. From the Van't Hoff isochore a value of P > 4 bar has been estimated. Just above the peritectic temperature it should be possible to grow crystals of the light lanthanide hydrides. Since these conditions cannot be reached in a quartz-glass reactor with the necessary purity, a steel autoclave is under construction. Measurements of the Pr-H 2 system also indicate the presence of a peritectic. In addition, inflections in the phase boundaries of the β-Pr(s) + PrH x (s) region at ≈ 1060 °C indicate the presence of a transition which has not been reported previously. The existence of peritectic diagrams for the La-H 2 and Pr-H 2 systems is in agreement with that of the Ce-H 2 system; a peritectic diagram is also forecast for the Nd-H 2 system.