Erdogan Alper

Gas absorption mechanism in catalytic slurry reactors

Abstract Several aspects of the gas absorption mechanism in catalytic slurry reactors are considered both theoretically and experimentally. The results of Lee and Tsao (1972) - i.e. oxygen absorption into glucose solutions containing platinium deposited on powdered activated carbon - are analysed critically. The experiments which were carried out in stirred cells with unbroken - hence known - interfaces with two different systems (i.e. oxygen absorption into glucose solutions containing Pt/C and carbondioxide absorption into carbonate buffer solutions in the presence of immobilized carbonic anhydrase) showed that the absorption rate can be enhanced because of the catalytic reaction. During the course of this study, it has also been found that finely powdered activated carbon increases, i.e. facilitates the physical absorption of gases significantly.

Measurement and prediction of ozone levels around a heavily industrialized area: a neural network approach

Abstract This paper presents an artificial neural network model that is able to predict ozone concentrations as a function of meteorological conditions and precursor concentrations. The network was trained using data collected during a period of 60 days near an industrial area in Kuwait. A mobile monitoring station was used for data collection. The data were collected at the same site as the ozone measurements. The data fed to the neural network were divided into two sets: a training set and a testing set. Various architectures were tried during the training process. A network of one hidden layer of 25 neurons was found to give good predictions for both the training and testing data set. In addition, the predictions of the network were compared to measurements taken during other times of the year. The inputs to the neural network were meteorological conditions (wind speed and direction, relative humidity, temperature, and solar intensity) and the concentration of primary pollutants (methane, carbon monoxide, carbon dioxide, nitrogen oxide, nitrogen dioxide, sulfur dioxide, non-methane hydrocarbons, and dust). A backpropagation algorithm with momentum was used to prepare the neural network. A partitioning method of the connection weights of the network was used to study the relative % contribution of each of the input variables. It was found that the precursors carbon monoxide, carbon dioxide, nitrogen oxide, nitrogen dioxide, and sulfur dioxide had the most effect on the predicted ozone concentration. In addition, temperature played an important role. The performance of the neural network model was compared against linear and non-linear regression models that were prepared based on the present collected data. It was found that the neural network model consistently gives superior predictions. Based on the results of this study, artificial neural network modeling appears to be a promising technique for the prediction of pollutant concentrations.

Kinetics of reactions of carbon dioxide with diglycolamine and morpholine

Abstract It is reported that in industrial plants, diglycolamine may be dehydrated to morpholine. In this work, the kinetics of reactions of carbon dioxide with aqueous diglycolamine and morpholine solutions were studied at various temperatures and amine concentrations, using a stopped-flow technique. Reaction rates for monoethanolamine were also examined for comparison. Diglycolamine reacts with CO2 according to a second-order mechanism with a rate constant of 4517 m3 kmol−1 s−1 at 298 K and an activation energy of 39.35 kJ mol−1. The reaction between carbon dioxide and aqueous morpholine was faster than that of diglycolamine but it did not follow simple kinetics. The reaction between CO2 and morpholine in methanol was briefly investigated and was found to be third order (second order in amine).

Simulation of an atmospheric residue desulfurization unit by quasi-steady state modeling

The current trend in petroleum refining is to maximize the conversion of the bottom of the barrel to improve the profitability of the refinery. Atmospheric residue desulfurization (ARDS) plays a key role in this, especially, when processing crudes with moderate to high sulfur contents. A deterministic quasi-steady state model has been developed to simulate the long term behavior of the reaction section of an atmospheric residue desulfurization (ARDS) unit, consisting of four co-current catalytic trickle bed reactors in series. The model uses the properties of the feedstock and the catalyst and is capable of simulating profiles of sulfur, coke, and metal depositions and the temperature along the reactors, taking into account also catalyst deactivation. Hydrogen quenching has also been simulated and simulation results predict all the essentials of the long term behavior of both experimental and industrial scale ARDS reactors satisfactorily. Comparing the simulation results with actual commercial data, the model predicted perfectly the middle part of the run. The model is unable to simulate the End-of-Run conditions due to pore mouth plugging phenomenon.

Steady-state rate-based modelling for CO2/amine absorption-desorption systems

Abstract A rigorous rate-based steady-state model of an absorber/desorber unit for the removal of CO 2 by amine solutions was developed. The model, which essentially contains no empirically assigned parameters, is based on a ‘mixing cell’ approach and considers both interphase heat and mass transfer along with simultaneous chemical reaction rates. This deterministic model, which simulates tray and packed columns at steady state, has been validated using the data of two commercial monoethanolamine (MEA) plants. For tray columns, each tray was considered to be a mixing cell, while for packed columns, the required dispersion was provided by choosing a finite number of mixing cells. For a specified CO 2 slippage rate, the effects of certain operating parameters, such as type and total concentration of amine employed, flow rate and composition of entering gas, on solution circulation rate and reboiler duty can be conveniently predicted. The computer program, written in basic language, is designed in a user-friendly form and is a menu-driven interactive simulator. The mathematical model consists of non-linear algebraic equations and can be operated on a PC. A typical running time on an IBM PS/2 with 25 MHz was 4.39 s for the absorber and 1.1 s for the desorber.

EFFECT OF FINE SOLID PARTICLES ON GAS-LIQUID MASS TRANSFER RATE IN A SLURRY REACTOR

The influence of suspended fine particles of differing adsorbing capacity (activated carbon, avicell cellulose, SiO2, and molecular sieves) on the liquid-film mass transfer coefficient κL, was examined experimentally in a stirred cell of well-defined gas-liquid interfacial area by chemical methods. The greatest effect on κL was observed with the activated carbon (about a threefold increase). An addition of glycerine in excess of 2.5 × 10−3 k mol/m3, which was adsorbed on the particles preferentially, removed this increase in κL totally. Amongst other particles, only avicell cellulose showed measureable effects. The increase in κL values was inversely proportional to the temperature and the stirring speed, and the particle loading was found to be immaterial after a certain value. When the reaction rate increased (hence, when the thickness of dissolved gas-rich layer decreased) by gradual addition of a homogeneous catalyst (i.e. Co++ for sulphite oxidation), the effect of particles on κL decreased and event...

Laboratory scale-model of a complete packed column absorber

Abstract A method has been established and tested for simulating in the laboratory the essential features of a complete packed column in which absorption with chemical reaction is occurring. The necessary rules for scaling-down have been established. These are: the same volues of k L , k G , ( aH/L ), ( vH/L ) or ( v/a ) and ( L/ G ) in the model and the packed column which is being simulated. It has been shown that a laboratory-scale string-of-spheres column can simulate a complete packed column as regards both gas-side and liquid-side phenomena and also reactions occurring in the bulk of the liquid.

The kinetics of carbon dioxide capture by solutions of piperazine and N-methyl piperazine

In this paper, kinetics and mechanism of the reaction between CO 2 and piperazine (PZ) or n-methyl piperazine (NMP) in aqueous and alcoholic solutions were investigated using direct stopped-flow technique under a range of temperatures (278, 288 and 298 K). The results show that the reactions follow a single termolecular reaction mechanism and the reaction rate between CO 2 and aqueous PZ (2669(278K), 11335(288K), 18042(298K) m3/kmol⋅s) is significantly higher than that of commonly employed amines, such as monoethanolamine (MEA). Our results strongly suggest that PZ and PZ derivatives can be used as promoters for CO 2 capture by sterically hindered amine solutions.

Modeling of batch catalytic chlorination of toluene in a bubble column

Abstract The chlorination of toluene was studied in a batch bubble column in the presence of ferric chloride. Mass transfer studies (in the absence of dissolved catalyst) showed that Cl 2 absorption into toluene was controlled up to 60% by the gas side mass transfer resistance. In addition, the experimentall obtained liquid side mass transfer coefficients were found to be very low, i.e. more than 10 times lower than the predictions from common correlations. A model was developed which describes the batch chlorination process with striking agreement on the basis of the mass transfer data measured in this study and the solubility and kinetic data reported recently. It was found that the first chlorination step took place in the transition from diffusiona to fast reaction regime. However, due to the dominating gas side resistance, the overall process was only slightly enhanced by the reaction in the liqu

OXIDATION OF GLUCOSE ON SUSPENDED PT/C: REACTION KINETICS AND ABSORPTION STUDIES

In search of a suitable model reaction system for studying hydrodynamic properties of slurry reactors under reactive conditions, the oxidation of glucose on a suspended Pt/C catalyst was investigated. In addition to homogeneous kinetic measurements, gas absorption experiments in a stirred cell with a plane interface were also carried out at 25 to 45°C using finely powdered catalyst particles. It was found that the oxygen consumption rale followed first order kinetics only at the very beginning of the reaction. If the total amount of reacted oxygen was considerably more than that of the initial saturation value (i.e. kinetic runs repeated after some time of aeration under vigorous stirring or lengthy gas absorption experiments), the order with respect to oxygen was ½ Furthermore, the half order rate constant dropped to about ½ to ¼ of its initial value and was constant only after an amount of about 1.5 x 10−2mol O2/g catalyst was reacted. A new plot is also proposed which permits the simultaneous determina...