Kinetics and modeling of carbon dioxide absorption into aqueous solutions of piperazine

In this work, the kinetics of the reaction between CO₂ and aqueous piperazine (PZ) have been estimated over the temperature range of 298-313 K from the absorption data obtained in a wetted wall contactor. The absorption data are obtained for the PZ concentrations of 0.2- and for CO₂ partial pressures up to 5 kPa. A coupled mass transfer-kinetics-equilibrium mathematical model based on Higbie's penetration theory has been developed with the assumption that all reactions are reversible. The model is used to estimate the rate constants from the experimental data for absorption of CO₂ in aqueous PZ. The estimated rate constants of this study are in good agreement with those reported in the literature.     

煤燃烧烟气中CO2的吸收控制技术研究进展

阐述了燃煤烟气中二氧化碳脱除的各种方法。研究了各种CO2的吸收方法,包括物理吸收法中的膜吸收法、吸附剂等,物化吸附法,还有化学吸收剂中的氨水、有机氨等吸收方法,并分析各种方法的特点及优缺点。     

EFFECT OF HETEROCYCLIC AMINE ADDITIVES ON THE ABSORPTION RATES OF CARBONYL SULFIDE AND CARBON DIOXIDE IN AQUEOUS METHYLDIETHANOLAMINE SOLUTIONS

Absorption rates of carbonyl sulfide and carbon dioxide into aqueous methyldiethanolamine solutions with and without heterocyclic amine additives were measured in a stirred cell apparatus. All of the heterocyclic amine additives catalyzed COS absorption more strongly than that for CO₂. In instances in which absorption rates were improved by the additives, those with the lowest pK_b's were the most effective, although steric factors also apparently influence reaction kinetics.     

Experimental validation of a rate-based model for CO2 capture using an AMP solution

Detailed experimental data, including temperature profiles over the absorber, for a carbon dioxide (CO₂) absorber with structured packing in an integrated laboratory pilot plant using an aqueous 2-amino-2-methyl-1-propanol (AMP) solution are presented. The experimental gas-liquid material balance was within an average of 3.5% for the experimental conditions presented. A predictive rate-based steady-state model for CO₂ absorption into an AMP solution, using an implicit expression for the enhancement factor, has been validated against the presented pilot plant data. Furthermore, a parameter sensitivity analysis for the proposed model has been carried out.     

Simultaneous absorption of carbon dioxide and hydrogen sulfide into aqueous blends of 2-amino-2-methyl-1-propanol and diethanolamine

This work presents an experimental and theoretical investigation of the simultaneous absorption of CO₂ and H₂S into aqueous blends of 2-amino-2-methyl-1-propanol (AMP) and diethanolamine (DEA). The effect of contact time, temperature and amine concentration on the rate of absorption and the selectivity were studied by absorption experiments in a wetted wall column at atmospheric pressure and constant feed gas ratio. The diffusion-reaction processes for CO₂ and H₂S mass transfer in blended amines are modeled according to Higbie's penetration theory with the assumption that all reactions are reversible. The blended amine solvent (AMP+DEA+H₂O) has been found to be an efficient mixed solvent for simultaneous absorption of CO₂ and H₂S. By varying the relative amounts of AMP and DEA the blended amine solvent can be used as an H₂S-selective solvent or an efficient solvent for total removal of CO₂ and H₂S from the gas streams. Predicted results, based on the kinetics-equilibrium-mass transfer coupled model developed in this work, are found to be in good agreement with the experimental results of rates of absorption of CO₂ and H₂S into (AMP+DEA+H₂O) of this work.     

CO2 Absorption into Aqueous Solutions of Monoethanolamine,Methyldiethanolamine, Piperazine and their Blends

The removal of carbon dioxide from industrial gases, e.g. in thermal power stations to meet the discharge limits for CO₂ in flue gases, is usually achieved with a reactive absorption technique using aqueous solutions of alkanolamines. From the absorption performance point of view, primary and secondary amines are preferred. However, in case the costs of the solvent regeneration are also taken into account, tertiary amines are much more attractive. In order to combine the specific advantages of tertiary and primary/secondary alkanolamines, both types of solvents are mixed. In this paper, mixtures of monoethanolamine and methyldiethanolamine with piperazine as absorption activator are experimentally compared with respect to CO₂ removal performances at 25 °C. The absorption process in a special packed column has also been simulated with the use of published data on reaction kinetics, physicochemical properties (densities, viscosities, diffusivities, Henry coefficients) of the CO₂‐amines systems, including experimentally determined hydrodynamic and mass transfer characteristics of the CO₂ scrubber.     

Aqueous mixtures of AMP,HMDA-N,N′-dimethyl and TEG for CO2 separation: a study on equilibrium and reaction kinetics

Abstract

The hindered amine 2-amino-2-methyl-1-propanol (AMP) is a capable CO₂ separation solvent. HMDA-N,N′-Dimethyl (or HMDA-N,N′), which is the dimethyl derivative of 1,6-hexamethyl diamine, is a prospective activator of the absorption rate in AMP/H₂O mixtures. If a less volatile co-solvent such as triethylene glycol (TEG) is used in AMP-based solutions, the regeneration energy constraint will be lowered. In this work, a formulated blend of AMP (2-3?M), HMDA-N,N′ (0.1–0.5 M), TEG (0.7–2?M) and water was suggested for improved CO₂ capture from flue gas in thermal power stations. Kinetics of the CO₂ reaction with the suggested blend was studied in a stirred cell at 35, 40, and 45?°C. The pathway was elucidated using the renowned zwitterion mechanism. Overall, it was envisaged that both AMP and HMDA-N,N′ react with CO₂ in parallel. The values of the pseudo-first order rate constant were determined. It was found that HMDA-N,N′ reacts with CO₂ according to a second-order reaction (rate constant k_2,HMDA-N,N^′ = 79,525?M^?1 s^?1 at 35?°C), whose energy of activation is 38?kJ mol^?1. Lastly, the loading capacity of the suggested blend was measured in an ambient-pressure equilibrium setup. Its highest value was 1.4?mol CO₂/mol amine, when equilibrium CO₂ pressure was 4?kPa.     

现代二氧化碳吸收工艺研究

综述了现代二氧化碳吸收工艺研究进展,介绍了目前国内外现有的二氧化碳吸收方法,包括物理吸收法、膜吸收法、化学吸收法、离子液体法、电化学法和O2/CO2燃烧法,简要介绍了各种吸收方法的特点及所做研究,重点讨论了工业应用较广的化学吸收法,分析了离子液体法与其他有机溶剂比较的优缺点,并对新工艺方法进行了展望.     

Optimization of supercritical extraction of nimbin from neem seeds in presence of methanol as co-solvent

Mathematical modeling and optimization of the extraction of nimbin from neem seeds using supercritical carbon dioxide with methanol as co-solvent is the subject of this study. At first a correlation for Sherwood number (Sh) as a function of Reynolds number (Re) and Schmidt number (Sc) was proposed using a Genetic Algorithm (GA) technique. This correlation was compared to previous correlations and was found to give the most accurate results. Moreover, optimum conditions (temperature, pressure, solvent flow rate and particle diameter) which maximizes the extraction yield have been determined using GA. At the next step, methanol was used as a co-solvent and the dynamic equilibrium constant of solute between the solid phase and the solvent was estimated. By applying the new determined equilibrium constant, good agreement between the model and experimental data was observed.     

Interfacial area and mass transfer in carbon dioxide absorption in TEA aqueous solutions in a bubble column reactor

The hydrodynamic behaviour and mass transfer of carbon dioxide removal process by aqueous solutions of triethanolamine (TEA) are analysed. The experiments were made in a bubble column reactor (BCR) as gas–liquid contactor. The interfacial area and mass transfer coefficient were calculated by using a photographic method based on the bubble diameter determination. The influence of operation conditions, liquid phase nature and chemical reaction on the mass transfer coefficient and gas–liquid interfacial area has been also analysed.     

Absorption of carbon dioxide into aqueous solutions of piperazine activated 2-amino-2-methyl-1-propanol

In this work, new experimental data on the rate of absorption of CO₂ into piperazine (PZ) activated aqueous solutions of 2-amino-2-methyl-1-propanol (AMP) are reported. The absorption experiments using a wetted wall contactor have been carried out over the temperature range of 298-313 K and CO₂ partial pressure range of 2-14 kPa. PZ is used as a rate activator with a concentration ranging from 2 to 8 wt%, keeping the total amine concentration in the solution at 30 wt%. The CO₂ absorption into the aqueous amine solutions is described by a combined mass transfer-reaction kinetics-equilibrium model, developed according to Higbie's penetration theory. Parametric sensitivity analysis is done to determine the effects of possible errors in the model parameters on the accuracy of the calculated CO₂ absorption rates from the model. The model predictions have been found to be in good agreement with the experimental results of rates of absorption of CO₂ into aqueous (PZ+AMP). The good agreement between the model predicted rates and enhancement factors and the experimental results indicates that the combined mass transfer-reaction kinetics-equilibrium model with the appropriate use of model parameters can effectively represent CO₂ mass transfer in PZ activated aqueous AMP solutions.     

Process design and energy requirements for the capture of carbon dioxide from air

A process to capture carbon dioxide from air to reduce its atmospheric concentration and to mitigate climate change is studied. It is based on the absorption of carbon dioxide in a sodium hydroxide solution, its precipitation as calcium carbonate, and its release as pure gas stream through oxy-fuel calcination. The process utilizes existing commercial technologies wherever possible, particularly in the case of the absorber, whose design is carried out in detail. The analysis allows deriving material and energy balances for the whole process and determining energy demands that can be used for a technical, economical, and environmental feasibility evaluation of the technology. In particular, it indicates that the real specific energy demand is larger than the heat released to emit the same amount of CO₂ by the combustion of coal, and smaller than that of methane.     

Absorption of carbon dioxide into aqueous PAA solution containing diethanolamine

Carbon dioxide was absorbed into aqueous polyacrylamide (PAA) solution containing diethanolamine (DEA) of 0–2 kmol/m³ in a flat-stirred vessel with the impeller of 0.034 m and agitation speed of 50 rpm at 25 °C and 0.101 MPa to measure the absorption rate of CO₂. The volumetric liquid-side mass transfer coefficient (k_La) was obtained from the dimensionless empirical correlation formula presenting the rheological behavior of aqueous PAA solution. PAA with elastic property of non-Newtonian liquid made the rate of chemical absorption of CO₂ accelerate compared with Newtonian liquid based on the same viscosity of the solution. The estimated value of the absorption rate of CO₂ was obtained from the model based on the film theory accompanied by chemical reaction and compared with the measured value.