The thermodynamic properties of aqueous solutions of physical and chemical solvents are essential in understanding a great variety of problems ranging from the heat of regeneration to corrosion phenomena in the plant. Particularly important is knowledge of the temperature and pressure dependence of the main thermodynamic functions.
Natural gas or flue gases purification requires the removal of acidic impurities, i.e. carbon dioxide and hydrogen sulphide. The removal process of these acid gases requires the knowledge the solubility of the gases in the solvent and the enthalpy of absorption and desorption of the gases in the solvent.
Experimental data can be used to calculate the temperature variation of the solubilities, activity coefficients and reaction constants. In addition, heat transfer and energy balances on the absorption and regeneration units require the measurement of the heat capacity of the solvents and their thermal conductivity.
The calorimeter used for these types of studies is a C 80, a high-performance Calvet type calorimeter. The instrument allows a very large range of applications in various fields to be performed. The instrument can be operated from ambient temperature to 300 °C and up to a pressure of 100 bar. It is equipped with a reversing mechanism and mixing vessels with membranes, liquid heat capacity cells. The calorimeter is equipped a with state-of-the-art software for data collection and processing.
The calorimeter is used to measure the heat of solution of carbon dioxide in physical solvents as well as the heat capacity of aqueous solutions of alkanolamines and mixed solvents. Enthalpy data for mixing of water and other solvents are important to the understanding of the variation in molecular interaction between molecules. It will also be used to measure the heat of reaction of carbon dioxide with various alkanolamines and amine blends. There is a great need for new calorimetric data for a variety of systems of interest.
Corrosion studies are particularly important, given that corrosion problems constitute the major operating difficulty in gas treating plants and have caused unscheduled downtime, production losses, and reduced equipment life. Consequently, corrosion prevention or minimization can be regarded as the cornerstone of any successful CO2 separation technology. It is our goal to perform studies in order to obtain a fundamental understanding of corrosion mechanisms under a variety of operating conditions with a view to formulating an efficient and cost effective control strategy. In general, regenerators, reboilers, and rich-lean exchangers are the areas most susceptible to severe corrosion. Both uniform and localized corrosion take place in the plants, but stress corrosion cracking, pitting, and erosion corrosion are the dominating mechanisms. Although a great deal of work has been conducted to study the corrosion mechanisms for the CO2 environment, the mechanisms are still not well understood. However, it has been observed that the parameters contributing to corrosiveness are dissolved CO2, dissolved O2, type of solvents, degradation products, temperature, and solution velocity.
To tackle the corrosion problem, we study detailed corrosion behaviour in gas treating reactive solutions with and without additives. We focus on a search program for corrosion inhibitors that could be used to lower the corrosion rates in these systems, in addition to our study of the corrosion mechanisms and the effects of factors such as solvent compositions, temperature, flow velocity, and CO2 and O2 partial pressures on corrosion rate. These studies are currently conducted in the laboratory-scale corrosion testing units and also will be conducted in the Technology Development Plant, which has provisions for on-line monitoring of corrosion rates.
Characterization and analysis of catalysts are important in catalyst production, continuous quality control during manufacturing, and fouling and performance investigations. Understanding the composition, physical nanostructure, porosity, and surface properties can all help you improve efficiency or solve a failure problem.
At CETRI, we provide a range of laboratory services to help you to understand your catalyst products including catalyst composition, structure, pore systems, surface area, porosity, material’s thermal stability, response to oxidation, decomposition kinetics, moisture content, and more. These information are generated using our wide range of laboratory testing facilities including:
- Microprocessor-based Infrared Gas Analyzers
- GCs and GC with Mass Spectrometer (GC-MS)
- Capillary Electrophoresis (CE with LC-MSD)
- High Performance Liquid Chromatograph (HPLC-MSD)
- Inductively Coupled Plasma with Mass Spectrometer (ICP-MS)
- Scanning Electron Microscope with Energy Dispersive Spectrometer (SEM-EDS)
- X-Ray Diffractometer (XRD)
- Nuclear Magnetic Resonance coupled with HPLC (LC-NMR)
- Fourier Transform Infrared Spectrometer (FTIR)
- Surface Area, Porosity, and Chemisorption analyzer
- Thermogravimateric Analyzer with Differential Scanning Calorimeter (TGA-DSC)
- Heat of Reactions Calorimeter
- High-speed Digital Data Logging Systems
- 3Flex Surface and Catalyst Characterization Instrument Bench-scale and pilot-scale plants
High Efficiency Column Internals
CO2 separation can be achieved by a number of techniques including absorption, adsorption, cryogenic separation, membrane permeation and others. For removing CO2 from high-volume waste gas streams, absorption into a liquid solvent is considered to be the suitable approach at the moment.
Since CO2 absorption takes place when gas and liquid phases are brought into contact, efficiency of the absorption process is therefore dependent upon the degrees of gas-liquid contact provides by the column. At present, there are various types of column internal devices that have been developed for separation purposes. One of the most sophisticated devices providing favorable characteristics in terms of both mass-transfer and hydrodynamics is structured packing. With its regular geometric structure, structured packing generally offers excellent mass-transfer performance without sacrificing hydrodynamic capacity that will be beneficial to the CO2 absorption application.
To design a CO2 absorption column packed with structured packing, an understanding of mass-transfer characteristics and hydrodynamic behavior of the packing is essential. Therefore, primary focus of our research on high efficiency column internals is given to the following:
Evaluation of CO2 absorption efficiency of various structured packings including Gempak 4A, Mellapak 500Y, Mellapak 500X, Optiflow, etc. The evaluation is conducted by using pilot-scale CO2 absorption unit.
Development of a rigorous mechanistic model based on liquid irrigation pattern inside the absorption column. The model is developed to evaluate the accurate mass-transfer parameters that can be used to rectify the column design approach for CO2 absorption. Determination of the optimum quality of initial liquid distributors and the position of re-distributors to minimize mal-distribution problem, which often occurs in the absorption column.
Laminar Jet Absorber
One of the best apparatus to study the kinetics of reaction between gas and liquid in the field of gas absorption is a Laminar Jet Absorber. This is because the interfacial area is known accurately and the physical absorption rates have been shown to agree with the penetration theory predictions. In this type of experiment, the operating variables, which include temperature, pressure, contact-time and composition, are fixed at a predetermined value. Then the value of the absorption rate of gas into liquid is measured. By repeating the experiments over a range of operating variables, the functional dependency of the absorption rate is determined. By analyzing the dependency of the absorption rate on the operating conditions, the reaction mechanism, reaction-rate constants, and reaction-order can be understood. For example, the laminar jet absorber and our numerical absorption-rate/kinetics model was used to investigate the kinetics of CO2 into highly concentrated and loaded MEA solutions. This study introduced a new termolecular-kinetics model, which proved to be better than the previous published kinetics models for the CO2 reactions with MEA solutions.
Current research activities are as follows:
- Obtaining reliable data on the absorption rate of CO2 into mixed amines under the condition of no interfacial turbulence, and
- Interpreting the experimental data with the aid of numerically solved absorption-rate/kinetics models that take into consideration all the possible reversible reactions of the absorption system.
The actual physical and chemical properties of the system as a function of temperature, concentration, and loading will be used in the interpretation of the absorption data.
Carbon Capture Modelling and Simulation
Modeling and simulation focused on research involving kinetics studies for gas reaction with reactive-liquids require absorption rate data and a mathematical model to interpret these data. The only way to obtain reliable kinetics reaction-rate data is by interpreting the experimental data with the aid of a numerically solved absorption-rate model. In this area of research, a new comprehensive absorption-rate/enhancement-factor model was developed. The model takes into account the coupling between chemical equilibrium, mass transfer, and chemical kinetics of all possible chemical reactions. The mathematical model is capable of predicting gas absorption rates and enhancement factors from the system hydrodynamics and the physico-chemical properties, as well as predicting the kinetics of reaction from experimental absorption data.
Using this absorption-rate/enhancement-factor model, a new kinetics model for CO2 absorption into highly concentrated and loaded MEA solutions was developed. The new kinetics model proved to be better than the previous published kinetics models for this system. Current research activities in this area are as follows:
- Interpreting the experimental data of CO2 absorption into mixed amines with the aid of a numerically solved absorption-rate model, and
- Integrating the enhancement-factor model with the pilot plan simulation program in order to calculate the enhancement factor accurately along the packed column.
Physical and Transport Properties
Knowledge of the density and viscosity of solvents is required for engineering design of equipment involving solvents. In addition, remedy there is interest in using volumetric data for calculation of the effects of pressure and temperature on thermodynamic properties. Excess thermodynamic properties are of great importance to our understanding of the nature and extent of molecular aggregation resulting from intermolecular interactions. Mixtures of water and organic solvents often show strong deviations from ideality as regards to density, viscosity, and refractive index.
In this study, the density, viscosity, and refractive index are measured using a DMA 4500 vibrating tube digital viscometer, Ubbeholde viscometers , and a Leica Mark II plus refractometer. The main objective is to measure the viscosity, density, and refractive index for the aqueous physical solvents, aqueous amines, mixed solvents, and aqueous amine blends. The derived excess volumes, partial molar volumes at infinite dilution, viscosity deviations, and interaction energy constants are used to have a better picture of the solute-water interactions. In some cases, complex formation can occur. The final aim is to be able to use these properties to help in screening the physical solvents for their capacity for CO2 absorption.
Solubility measurements are essential to the design of the absorption process as well as to the measurement of the kinetic rates. The main objective of the present study is to screen a large number of physical solvents from a specific chemical family for their capacity in carbon dioxide removal. The best solvent should have a high solubility for acid gases, low solubility for hydrocarbons, low volatility, moderate viscosity, high boiling point, excellent thermal and chemical stability. Corrosion rates and foaming should be low.
A glass reactor manufactured by Autoclave is used for these solubility studies. The apparatus can be operated up to a pressure of 150 psi and a temperature of 350 °F. Gases of interest are carbon dioxide, methane, ethane, nitrous oxide, hydrogen sulfide and sulfur dioxide. The solvents screened in this study are mainly polyethylene glycol ethers and mixtures of these solvents. The results will be compared to mixtures of other physical solvents recently made available to the industry. The data obtained for pure and aqueous mixtures will be used to test new semi-empirical models for solubility prediction.
Solvent Degradation Studies
Gas treating solvents used in the separation of CO2 break down as a result of long exposure or repeated use because of side reactions with CO2, malady O2, SO2, dissolved metals and other contaminants. This process is called degradation and products formed as a result of degradation are termed degradation products. Formation of degradation products will eventually result in a loss of capacity and give rise to a number of operating problems including corrosion and foaming. In the case of severe degradation, the solvent will need to be replaced and the degraded solvent must be disposed of in an environmentally acceptable manner. This is why it is highly desirable to prevent or at the very least to minimize solvent degradation.
Although it is well known that amines undergo severe degradation in the presence of O2, this gas is usually not present in a typical natural gas stream. As such, there has been no practical incentive to study amine degradation caused by O2. Therefore, although a number of studies have been carried out on degradation of different solvents due to CO2, very limited information is available on solvent degradation with O2. However, since flue gases contain O2 and the desire to separate CO2 from flue gas streams is gaining momentum, there is an urgent need to develop a better understanding of degradation of gas treating solvents with O2. The main objective of conducting this type of study is to develop an understanding of the mechanism of degradation and use this knowledge to formulate a degradation prevention strategy. Degradation prevention becomes important since it implies that any suitable solvent can be used repeatedly without the economic and operational burden imposed by loss of CO2 removal capacity that occurs as a result of severe degradation. The strategy will be as follows:
- Identifying the degradation products.
- Determining the overall rate of degradation of single and mixed solvents in the presence of CO2, O2, SO2 and dissolved metals.
- Postulating reaction mechanisms for degradation of single and mixed solvents in the presence of CO2 and O2.
- Verifying the reaction mechanisms.
- Formulating degradation prevention strategies for single and mixed solvents.
The degradation prevention strategy will likely include the addition of other components aimed at minimizing degradation. It will also look at the role of the operation of the stripping column and other high temperature sections of a typical CO2 extraction plant in causing degradation. All the strategies developed at bench scale will be tested at pilot plant scale.
Possessing an understanding of the working fluid – be that a mixed chemical amine or a physical solvent – is critical in the design, operation, and troubleshooting of carbon capture and acid gas treating processes. In conjunction, understanding how different interacting components (e.g. structured packings) or processes (e.g. amine degradation) will affect overall performance of the system are critical.
CETRI provides both a full complement of laboratory testing and services to evaluate the properties and performance of absorbent solvents for both chemical and physical absorption processes, as well as over 25 years of in-house expertise in the study and development of carbon capture processes. We can assist with a variety of studies, including:
- Calorimetry (for heat capacity and heat of solvation)
- Corrosion Rates, Mechanisms, and Prevention
- Acid Gas Solubility, Kinetics, and Mass Transfer
- Physical Properties (e.g. viscosity, density, refraction, etc.).
- Assessment of Column Packing & Internals
- Solvent Degradation & Prevention
- Computational Modeling & Process Simulation