Kinetic Model of Xylose Dehydration for a Wide Range of Sulfuric Acid Concentrations

The main cloud deck within Venus' atmosphere, which covers the entire planet between approx. 50 and 70 km altitude, is believed to consist mostly of liquid sulfuric acid. The temperature below the main clouds is high enough to evaporate the H2SO4 droplets into gaseous sulfuric acid forming a haze layer which extends to altitudes as deep as 35 km. Gaseous sulfuric acid in Venus&#8217; lower atmosphere is responsible for a strong absorption of radio waves as seen in Mariner, Pioneer Venus, Magellan and Venera radio science observations. Radio wave absorption measurements can be used to derive the amount of H2SO4 in Venus&#8217; atmosphere. The radio science experiment VeRa onboard Venus Express probed the atmosphere of Venus between 2006 and 2014 with radio signals at 13 cm (S-band) and 3.6 cm (X-band) wavelengths. The orbit of the Venus Express spacecraft allowed to sound the atmosphere over a wide range of latitudes and local times providing a global picture of the sulfuric acid vapor distribution. We present the global H2SO4(g) distribution derived from the X-band radio signal attenuation for the time of the entire Venus Express mission. The observation is compared with results obtained from a 2-D transport model. The VeRa observations were additionally used to estimate the abundance of SO2 near the cloud bottom. The global distribution of SO2 at these altitudes is presented and compared with results obtained from other experiments. Eight years of VEX observation allow to study the long-term evolution of H2SO4 and SO2. The latter is presented for the northern polar region.

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New particle formation in the sulfuric acid–dimethylamine–water system: reevaluation of CLOUD chamber measurements and comparison to an aerosol nucleation and growth model

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-845-2018 ◽

2018 ◽

Vol 18 (2) ◽

pp. 845-863 ◽

Cited By ~ 31

Author(s):

Andreas Kürten ◽

Chenxi Li ◽

Federico Bianchi ◽

Joachim Curtius ◽

António Dias ◽

...

Keyword(s):

Sulfuric Acid ◽

Detection Threshold ◽

Sulfuric Acid Concentration ◽

Water System ◽

Particle Formation ◽

New Particle Formation ◽

Flow Tube ◽

Aerosol Model ◽

Wide Range ◽

Good Agreement

Abstract. A recent CLOUD (Cosmics Leaving OUtdoor Droplets) chamber study showed that sulfuric acid and dimethylamine produce new aerosols very efficiently and yield particle formation rates that are compatible with boundary layer observations. These previously published new particle formation (NPF) rates are reanalyzed in the present study with an advanced method. The results show that the NPF rates at 1.7 nm are more than a factor of 10 faster than previously published due to earlier approximations in correcting particle measurements made at a larger detection threshold. The revised NPF rates agree almost perfectly with calculated rates from a kinetic aerosol model at different sizes (1.7 and 4.3 nm mobility diameter). In addition, modeled and measured size distributions show good agreement over a wide range of sizes (up to ca. 30 nm). Furthermore, the aerosol model is modified such that evaporation rates for some clusters can be taken into account; these evaporation rates were previously published from a flow tube study. Using this model, the findings from the present study and the flow tube experiment can be brought into good agreement for the high base-to-acid ratios (∼ 100) relevant for this study. This confirms that nucleation proceeds at rates that are compatible with collision-controlled (a.k.a. kinetically controlled) NPF for the conditions during the CLOUD7 experiment (278 K, 38 % relative humidity, sulfuric acid concentration between 1 × 106 and 3 × 107 cm−3, and dimethylamine mixing ratio of ∼ 40 pptv, i.e., 1 × 109 cm−3).

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Sicklepod (Cassia obtusifolia) and Coffee Senna (Cassia occidentalis): Geographic Distribution, Germination, and Emergence

Weed Science ◽

10.1017/s004317450002779x ◽

1980 ◽

Vol 28 (1) ◽

pp. 68-71 ◽

Cited By ~ 59

Author(s):

D. H. Teem ◽

C. S. Hoveland ◽

G. A. Buchanan

Keyword(s):

United States ◽

Sulfuric Acid ◽

Geographic Distribution ◽

Soil Depth ◽

The United States ◽

Cassia Obtusifolia ◽

Cassia Occidentalis ◽

Southern States ◽

Germination Characteristics ◽

Wide Range

The distribution of sicklepod (Cassia obtusifoliaL.) and coffee senna (Cassia occidentalisL.) in the United States is similar and both species are increasing as problems within their range. Sicklepod is a problem in 11 southern states and increasing in 12 while coffee senna is a problem in 7 states and increasing in 8 states. Both species germinated over a wide range of temperature. Germination characteristics were similar in the range of 15 to 36 C. Germination of coffee senna was drastically reduced at 39 C byRhizopussp. Seedling growth was similar for both species and was maximum from 30 to 36 C. Both species have a hard seedcoat. Abrasion for 5, 10, or 15 s, puncturing with a needle, and sulfuric acid were all effective in initiating germination. Both species emerged from a soil depth of 12.5 cm; however, emergence of sicklepod was more rapid than coffee senna with 63% of the sicklepod seedlings emerging from 2.5 cm after only 3 days.

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Modelling casein aggregation and curd firming in goats' milk from backscatter of infrared light

Journal of Dairy Research ◽

10.1017/s0022029903006356 ◽

2003 ◽

Vol 70 (3) ◽

pp. 335-348 ◽

Cited By ~ 17

Author(s):

Manuel Z Castillo ◽

Fred A Payne ◽

Clair L Hicks ◽

José S Laencina ◽

María-Belén M López

Keyword(s):

Kinetic Model ◽

Diffuse Reflectance ◽

Block Design ◽

Reaction Model ◽

Order Reaction ◽

Infrared Light ◽

Wide Range ◽

Data Points ◽

Increasing Temperature ◽

Reflectance Ratio

A kinetic model was proposed for describing the curd assembly of skimmed goats' milk during enzymic coagulation. The enzymic coagulation of milk was monitored using an optical sensor that measured diffuse reflectance (light backscatter) at 880 nm. The appearance of a shoulder, at low temperatures and protein concentrations, in the diffuse reflectance ratio profile after the inflection point of the curve (Tmax) appeared to separate the aggregation and curd firming steps. The diffuse reflectance ratio profile after Tmax was attributed to the overlapping of casein micelles aggregation and curd firming reactions. The developed kinetic model combined a second order reaction model to describe aggregation reactions and a first order reaction model to describe firming processes reactions. A completely randomised block design with three replications was used to determine the effect of protein concentration and temperature on kinetic constants. Milk was adjusted to three levels of protein (30, 50 and 70 g/kg), and coagulated at five temperatures (20, 25, 30, 35 and 40°C) to test a wide range of processing conditions. Data points from each profile after Tmax were fitted to the proposed model using non-linear regression. The average R2 and standard error of prediction (SEP) for 45 tests conducted were in the range of 0·9975±0·0027 and 0·0081±0·0037, respectively. A significant increase in characteristic times for aggregation (τ2) and curd firming processes (τ1) were found when temperature decreased or protein increased. Theoretical asymptotic value of reflectance ratio, R∞, increased with increasing level of protein and temperature (P<0·05). The parameter β1, which represented the fraction of diffuse reflectance ratio attributed to aggregation, decreased with increasing temperature and decreasing protein.

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Kinetic modeling and mechanistic investigations of transesterification of propylene carbonate with methanol over an Fe–Mn double metal cyanide catalyst

Reaction Chemistry & Engineering ◽

10.1039/c9re00372j ◽

2020 ◽

Vol 5 (1) ◽

pp. 101-111

Author(s):

Ziwei Song ◽

Bala Subramaniam ◽

Raghunath V. Chaudhari

Keyword(s):

Experimental Data ◽

Kinetic Model ◽

Propylene Carbonate ◽

Kinetic Modeling ◽

Reaction Parameters ◽

Metal Cyanide ◽

Wide Range ◽

Mechanistic Investigations ◽

Activation Sequence

A kinetic model involving the activation sequence of reactants PC, methanol and an intermediate provides the best description of the experimental data with respect to reaction parameters over a wide range of conditions.

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An Experimental Approach on Industrial Pd-Ag Supported α-Al2O3 Catalyst Used in Acetylene Hydrogenation Process: Mechanism, Kinetic and Catalyst Decay

Processes ◽

10.3390/pr7030136 ◽

2019 ◽

Vol 7 (3) ◽

pp. 136

Author(s):

Ourmazd Dehghani ◽

Mohammad Rahimpour ◽

Alireza Shariati

Keyword(s):

Kinetic Model ◽

Experimental Approach ◽

Catalyst Deactivation ◽

Catalyst Activity ◽

Hydrogenation Process ◽

Support Surface ◽

Acetylene Hydrogenation ◽

Wide Range ◽

Α Al2o3 ◽

Al2o3 Catalyst

The current research presents an experimental approach on the mechanism, kinetic and decay of industrial Pd-Ag supported α-Al2O3 catalyst used in the acetylene hydrogenation process. In the first step, the fresh and deactivated hydrogenation catalysts are characterized by XRD, BET (Brunauer–Emmett–Teller), SEM, TEM, and DTG analyses. The XRD results show that the dispersed palladium particles on the support surface experience an agglomeration during the reaction run time and mean particle size approaches from 6.2 nm to 11.5 nm. In the second step, the performance of Pd-Ag supported α-Al2O3 catalyst is investigated in a differential reactor in a wide range of hydrogen to acetylene ratio, temperature, gas hourly space velocity and pressure. The full factorial design method is used to determine the experiments. Based on the experimental results ethylene, ethane, butene, and 1,3-butadiene are produced through the acetylene hydrogenation. In the third step, a detailed reaction network is proposed based on the measured compounds in the product and the corresponding kinetic model is developed, based on the Langmuir-Hinshelwood-Hougen-Watson approach. The coefficients of the proposed kinetic model are calculated based on experimental data. Finally, based on the developed kinetic model and plant data, a decay model is proposed to predict catalyst activity and the parameters of the activity model are calculated. The results show that the coke build-up and condensation of heavy compounds on the surface cause catalyst deactivation at low temperature.

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An experimental, theoretical and kinetic-modeling study of the gas-phase oxidation of ammonia

Reaction Chemistry & Engineering ◽

10.1039/c9re00429g ◽

2020 ◽

Vol 5 (4) ◽

pp. 696-711 ◽

Cited By ~ 10

Author(s):

Alessandro Stagni ◽

Carlo Cavallotti ◽

Suphaporn Arunthanayothin ◽

Yu Song ◽

Olivier Herbinet ◽

...

Keyword(s):

Kinetic Model ◽

Gas Phase ◽

Theoretical Investigation ◽

Kinetic Modeling ◽

Ammonia Gas ◽

Wide Range ◽

Phase Oxidation ◽

Detailed Kinetic Model ◽

Gas Phase Oxidation ◽

Modeling Study

A wide-range experimental and theoretical investigation of ammonia gas-phase oxidation is performed, and a predictive, detailed kinetic model is developed.

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Growth and nutrient uptake of green alga, Scenedesmus dimorphus, under a wide range of nitrogen/phosphorus ratio—II. Kinetic model

Water Research ◽

10.1016/0043-1354(84)90037-x ◽

1984 ◽

Vol 18 (10) ◽

pp. 1313-1326 ◽

Cited By ~ 10

Author(s):

S. Kunikane ◽

M. Kaneko

Keyword(s):

Kinetic Model ◽

Nutrient Uptake ◽

Green Alga ◽

Wide Range ◽

Scenedesmus Dimorphus ◽

Nitrogen Phosphorus

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Improved identification of evaporation rates and thermodynamic data by Monte-Carlo method

10.5194/egusphere-egu2020-21614 ◽

2020 ◽

Author(s):

Anna Shcherbacheva ◽

Tapio Helin ◽

Heikki Haario ◽

Hanna Vehkamäki

Keyword(s):

Monte Carlo ◽

Sulfuric Acid ◽

Thermodynamic Data ◽

Particle Formation ◽

Forward Problem ◽

Dependent Data ◽

New Particle Formation ◽

Free Energies ◽

Wide Range ◽

Cluster Composition

Atmospheric new particle formation and successive cluster growth to aerosol particles is an important field of research, in particular due to climate change phenomena and air quality monitoring. Recent developments in the instrumentation have enabled quantification of ionic clusters formed in the gas phase at the first steps of particle formation under atmospherically relevant mixing ratios. However, electrically neutral clusters are prevalent in atmospheric conditions, and thus must be charged prior to detection by mass spectrometer. The charging process can lead to cluster fragmentation and thus alter the measured cluster composition.Even when the cluster composition can be measured directly, this does not quantify individual cluster-level properties, such as cluster collision and evaporation rates. Collision rates contain relatively small uncertainties in comparison to evaporation rates, which are computed using detailed balance assumption together with the free energies of cluster formation, which can in turn be obtained from Quantum chemistry (QC) methods. As evaporation rates depend exponentially on the free energies, even difference by several kcal/mol between different QC methods results in orders of magnitude differences in evaporation rates.On the other hand, in spite of the error margins associated with the evaporation rates, simulations of cluster populations, which incorporate collision and evaporation rates as free parameters (such as Becker-D&#246;ring models), have demonstrated good qualitative agreement with experimental data. The Becker-D&#246;ring equations are a system of Ordinary Differential equations (ODE) which account for cluster birth and death processes, as well as external sinks and sources. In mathematical terms, prediction of cluster concentrations using kinetic simulations with given cluster collision and evaporation rates is called a forward problem.In the present study, we focus on the so-called inverse problem of how to derive the evaporation rates and thermodynamic data (enthalpy change and entropy change due to addition or removal of molecule) from available measurements, rather than on the forward problem. We do this by Delayed Rejection Adaptive Monte Carlo (DRAM) method for the system containing sulfuric acid and ammonia with the maximal size of the pentamer. Initially, we tested the method on the synthetic data created from Atmospheric Cluster Dynamic Code (ACDC) simulations. By so doing, we identify the combination of fitted parameters and concentration measurements, which leads to the best identification of the evaporation rates. Additionally, we demonstrated that the temperature-dependent data yield better estimates of the evaporation rates as compared to the time-dependent data measured before the system has reached the steady state.Next, we apply the technique to improve the identification of the evaporation rates from CLOUD chamber data, which contain cluster concentrations and new particle formation rates measured at different temperatures and a wide range of atmospherically relevant sulfuric acid and ammonia concentrations. As a result, we were able to obtain the probability density functions (PDFs) that show small standard variations for thermodynamic data. By using the values from the PDFs as parameters in the ACDC model, we achieve a fair agreement with the measured NPFs and cluster concentrations for a wide range of temperatures.

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Sulfuric acid vapor and sulfur dioxide in the atmosphere of Venus as observed by VeRa

10.5194/epsc2020-139 ◽

2020 ◽

Author(s):

Janusz Oschlisniok ◽

Bernd Häusler ◽

Martin Pätzold ◽

Silvia Tellmann ◽

Michael Bird

Keyword(s):

Sulfuric Acid ◽

Sulfur Dioxide ◽

Local Times ◽

Cloud Base ◽

Acid Vapor ◽

X Band ◽

Upper Limits ◽

Wide Range ◽

Venus Express ◽

Atmosphere Of Venus

The main Venus clouds, covering the entire planet between approx. 50 and 70 km altitude, are believed to consist mostly of liquid sulfuric acid. Below the clouds, the temperature is high enough to evaporate those droplets into gaseous sulfuric acid forming a haze layer which extends to altitudes as deep as 35 km. H2SO4(g) is the main absorber of radio waves as was observed in Mariner, Pioneer Venus, Magellan and Venera radio occultation measurements. Radio wave absorption measurements can be used to derive the amount of H2SO4 as well as to estimate upper limits of SO2 in Venus&#8217; atmosphere. The radio science experiment VeRa onboard Venus Express probed the atmosphere of Venus between 2006 and 2014 with radio signals at 13 cm (S-band) and 3.6 cm (X-band) wavelengths. Thanks to the orbit of VEX, a wide range of latitudes and local times was covered so that a global picture of the H2SO4(g) ditribution was obtained. We present H2SO4(g) profiles as well as upper limits of sulfur dioxide near the cloud base derived from the X-band radio signal from the entire Venus Express mission. More than 600 H2SO4(g) profiles show the global sulfuric acid vapor distribution covering the northern and southern hemisphere on the day- and night side of the planet. A distinct latitudinal&#160;H2SO4(g) and SO2 variation and a southern northern symmetry are clearly visible. Observations over 8 years allow to study also long-term variations. Indications for temporal H2SO4(g) and SO2 variations are found, at least at northern polar latitudes. The results shall be compared with observations retrieved by other experiments onboard Venus Express. Additionally, the observed H2SO4(g) distribution will be compared with results obtained from a mass transport model.

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