Axel Meisen

Research and development issues in CO2 capture

Abstract The principal technologies for CO2 capture (including absorption, adsorption, membrane separation, cryogenic separation) and for producing rich CO2 process streams by CO 2 O 2 combustion cycles are reviewed in summary form and their present limitations are identified. The latter include uncertainties regarding their technical design, short- and long-term operational problems, and economic feasibility. In particular, the current lack of knowledge of physical, chemical and rate data, contact mechanisms, solvent, adsorbent and membrane stability, corrosion, fouling, and by-product generation are considered. These problems together with the need to improve capture rates, raise capture efficiencies and lower capture costs are then used for suggesting directions of future research and development.

CO2 absorption by NaOH, monoethanolamine and 2-amino-2-methyl-1-propanol solutions in a packed column☆

Detailed concentration and temperature measurements are reported for the absorption of CO2 from air into aqueous NaOH, monoethanolamine (MEA) and 2-amino-2-methyl-1-propanol (AMP) solutions. An absorber (0.1 m i.d. packed with 12.7 mm Berl Saddles up to heights of 6.55 m) was used which operated in countercurrent mode and near ambient conditions. The measurements for the CO2NaOH and CO2-MEA systems are compared with predictions from a mathematical model and gave generally good agreement, except at high CO2 loadings of MEA solutions. Compared with MEA, AMP was found to have superior CO2 absorption capacities and inferior mass transfer rates.

Sulfur coating of urea in shallow spouted beds

Abstract Two mathematical models were developed to describe the operation of shallow spouted beds in which droplets of the coating materials (sulfur) are injected coaxially with the spouting gas (air) under steady-state, transient, batchwise and/or continuous conditions. Model I is based on a single zone and perfect mixing whereas model II is based on three zones, detailed hydrodynamics and inertial impaction. Both models predict the distribution of the coating material on the bed particles (urea) and the product quality (expressed in terms of seven day urea dissolution as measured by the TVA test). The results were compared with experimental data obtained from two laboratory coaters (column: 0.24 and 0.45 m dia.; included cone angle: 60; orifice: 3.2–38 nm dia.; sampling ports above cone apex: 0.28−0.56 m). Model II gave better agreement with experimental measurements, but model I is still useful for providing quick approximate estimates provided its inability to give the fraction of uncoated particles can be disregarded. The product quality was found to be primarily dependent on the average sulfur content and it is shown that the quality can also be increased by operating several coaters in series.

Identification of methyl diethanolamine degradation products by gas chromatography and gas chromatography-mass spectrometry

Abstract Partially degraded, aqueous methyl diethanolamine solutions were analyzed by a gas chromatograph equipped with a Tenax column and flame ionization detector; nitrogen was used as the carrier gas. To aid in product identification, the gas chromatograph was coupled to a mass spectrometer operating either in electron impact or chemical ionization mode. The most important degradation products were found to be: methanol, ethylene oxide, trimethylamine, ethylene glycol, 2-(dimethylamino)ethanol, 1,4-dimethylpiperazine, N-(hydroxyethyl)methylpiperazine, triethanolamine; and N,N-bis(hydroxyethyl)piperazine.

Simulation of pilot plant and industrial CO2-MEA absorbers

Abstract A rigorous mathematical model has been used to simulate the performance of a pilot plant absorber (0.1 m internal diameter (ID), 7m high, packed with 1 2 ″ (∼1.27cm) Berl saddles) removing CO2 from air at atmospheric pressure and of an industrial absorber (1.9 m ID, 26.6 m high, packed with 2″ (∼ 5 cm) Pall rings) removing CO2 from natural gas at 5 to 8 atm by means of contact with aqueous monoethanolamine (MEA) solutions. Good agreement was found between the experimental measurements and the model predictions.

Gas chromatographic technique for analysing partially degraded diethanolamine solutions

Abstract A simple and reliable gas chromatographic technique is presented for the quantitative analysis of partially degraded aqueous diethanolamine solutions. The samples are injected, without preparation, into a chromatograph equipped with a 6 ft. × 1/8 in. O.D. stainless-steel column (packed with 60—80-mesh Tenax GC) and a flame-ionization detector. Nitrogen is used as the carrier gas and temperature programming is necessary. Apart from mono-, di- and triethanolamine, eleven degradation compounds could be detected and measured at concentrations as low as 0.5 wt.-% with accuracies of typically ±5 %. The degradation compounds are identified and retention times are given.

Gas chromatographic analysis of alkanolamine solutions using capillary and packed columns

Abstract The detailed analysis of amine solutions used in natural gas treatment is usually based on gas chromatographic (GC) methods which utilize columns packed with Tenax GC or TA, a porous polymer based on 2,6-diphenyl- p -phenylene oxide. This technique has the advantages of the ability to separate the various compounds in solution, minimum sample preparation and short analysis times. Advances in chromatography have shown the general superiority of capillary columns for the analysis of complex solutions. Unfortunately, Tenax is available only in packed columns. This paper presents the results of GC analyses of fresh and partially degraded alkanolamine solutions in which the Tenax column was replaced with a polyethylene glycol-based fused-silica, wide-bore capillary column (15 m × 0.53 mm I.D., 1.0-μm film thickness). It was found that the capillary column provides better peak shape, requires significantly less sample size, maintains higher sensitivity and offers a faster and more efficient separation than the Tenax packed columns.

Degradation of aqueous diethanolamine solutions by carbon disulfide

Abstract The degradation of aqueous diethanolamine (DEA) solutions by carbon disulfide (CS2) was investigated using a batch reactor at temperatures ranging from 120 to 190 °C, DEA concentrations of 2 to 6 M and CS 2 DEA mole ratios of 0.05 to 0.23. Reaction products identified by gas chromatography (GC), gas chromatography/mass spectrometry (GC/MS), melting point determination, elemental analysis and infrared analysis include monoethanolamine, bis(hydroxyethyl)-ethylenediamine, bis(hydroxyethyl)-piperazine, hydroxyethyl-oxazolidone, hydroxyethyl-imidazolidone, tris(hydroxyethyl)-ethylenediamine, bis(hydroxyethyl)-imidazolidone and an insoluble, sulfur-rich, linear, polymeric solid. The formation of the products increased with temperature, DEA concentration and CS 2 DEA mole ratio. A mechanism for the formation of the products is presented, and the experimental data are consistent with a first-order overall reaction with respect to DEA.

Kinetics of CO induced degradation of aqueous diethanolamine

Abstract The kinetics of the reaction between carbon monoxide (CO) and aqueous diethanolamine (DEA) were studied. It was established that CO reacts with aqueous DEA solutions to form formate ions and formyl-diethanolamine (DEAF). A reaction mechanism for this system is proposed and a mathematical model is developed to estimate kinetic and solubility data from absorption experiments conducted in a batch autoclave reactor for 313⩽T⩽413 K , 800⩽p CO ⩽1100 kPa and 5⩽c DEA ⩽50 wt %. To verify the mechanism, experiments were also done with 30 wt % MDEA and 30 wt % DEA plus 20 wt % DEAF solutions. The data are consistent with a mechanism by which DEAF is predominantly formed by direct insertion of CO into DEA. The data also confirm that DEAF formation via the DEA–formate reaction is relatively slow and reversible. Since the Henrys constant of CO in aqueous DEA solutions is one of the key unknown parameters in the reaction model, a novel Nitrogen-Analogy was developed. Values of Henrys constants thus obtained were found to be in fairly good agreement with those estimated directly from the reaction model.

Identification of products resulting from carbonyl sulphide-induced degradation of diethanolamine☆

Abstract The degradation of aqueous diethanolamine (DEA) solutions due to carbonyl sulphide (COS) was studied by contacting the solutions (10–40 wt. %) in a well stirred, 600-ml stainless-steel autoclave with COS-nitrogen mixtures at temperatures ranging from 120 to 180°C. Combined gas chromatography-mass spectrometry, melting point determinations and elemental and infrared analyses were used to identify most of the major reaction products, viz., monoethanolamine, ethylaminoethanol, ethyldiethanolamine, hydroxyethylacetamide, hydroxyethylpiperazine, ethanethioic acid S-hydroxyethylaminomethyl ester, bis(hydroxyethyl)ethylenediamine, bis(hydroxyethyl)piperazine, hydroxyethyloxazolidone, hydroxyethylimidazolidone, tris(hydroxyethyl)ethylenediamine, bis(hydroxyethyl)imidazolidone, acetaldehyde, acetone, butanone, acetic acid, ethanol, diethyl disulphide, dithiane and pyridines. In addition, a solid product containing sulphur was formed. The practical implications of the studies for gas plant operators are discussed.