Thermodynamic and mass transfer modeling of carbon dioxide absorption into aqueous 2-piperidineethanol

Abstract

Amine scrubbing is a necessary technology to offset CO 2 emissions from fossil-fuel power plants. Of the many solvents studied, hindered amines are of particular interest for their marriage of the capacity of tertiary amines with rates a hundredfold greater than tertiary amines. The relatively rapid rates of hindered amines have not been adequately explained, despite their extensive use in commercial solvents. This work seeks to explain the rapid rate of mass transfer of 2-piperidineethanol (2PE) and uses this rationale to draw general conclusions on hindered amines.Quantitative 13 C NMR data were collected to determine the equilibrium of carbamate in 30 wt.% 2PE. Using these data along with VLE and pK a data, a rigorous thermodynamic model of 8 molal 2PE was built with electrolyte-NRTL and activity-based kinetics. Wetted-wall column flux data were fit to create the activity-based mass transfer model. Using this comprehensive model, the mass transfer rate was examined through sensitivity studies and Brønsted correlations.This work shows that 2PE forms a more stable carbamate than 2-amino-2-methyl-1-propanol. The carbamate reaction is the most significant component of mass transfer at 40 °C. The Brønsted correlation for carbamate reactions of unhindered amines predicts the rate of carbamate reaction of 2PE, but the Brønsted correlation for bicarbonate underpredicts the regressed rate. The CO 2 solubility is fit with five parameters with an ARD of 0.84%. The kinetics are fit with a carbamate-and a bicarbonateforming reaction with an ARD of 7.03%.The chief conclusions are: 1) that the rapid mass transfer of hindered amines is due to the formation of carbamate and the high pK a of the amine, 2) the carbamate formation rate appears unimpeded by steric hindrance and is predicted by a Brønsted correlation, suggesting that hindered amines react in the same manner as unhindered amines. Keywords: separations; CO 2 capture; eNRTL ; wetted-wall column; hindered amine; carbamate stability Sample preparationAmine solutions were prepared from 2-piperidineethanol (with purity ≥96%) supplied by TCI Europe and were used as received without further purification. Amine solutions were prepared with distilled water, and the resulting solution was 30 wt.% amine. The solutions were loaded with CO 2 (grade 5.0) supplied by AGA Gas (AGA Gas GmbH, Hamburg, Germany). The amine concentration was determined by acid-

Formation Constants and Conformational Analysis of Carbamates in Aqueous Solutions of 2-Methylpiperidine and CO2 from 283 to 313 K by NMR Spectroscopy

“…Several studies on aqueous substituted piperidine + CO 2 mixtures by NMR have been reported. Sherman et al 22 studied 2-piperidineethanol as a candidate for carbon capture purposes and found it to form carbamates. Shin et al 7 reported that 2-MP absorbs CO 2 faster than monoethanolamine (MEA), the gas-processing industry standard, but did not observe the formation of carbamates for 2-MP.…”

A parametric study of CO 2 capture from gas-fired power plants using monoethanolamine (MEA)

“…There have been several efforts to describe the chemical absorption of post combustion CO 2 from the flue gases of both coal-and gas-fired power plants. These models have either been developed on the assumption of equilibrium or rate-based mass transfer with some having been validated on pilot-scale plants Dutta, et al, 2017;(Sherman, et al, 2016;Norouzbahari, et al, 2016;Oko, et al, 2015). Although rate-based process simulation is well-known to provide more insight into the absorption process enabling the engineers to size the equipment and evaluate the process operating conditions more accurately (Sharifzadeh & Shah, 2015;Krishnamurthy & Taylor, 1985b;Krishnamurthy & Taylor, 1985a), equilibrium simulation, owing to its relative simplicity, provides useful insight on the viability of the process if used astutely.…”

Analysis of equilibrium CO2 solubility and thermodynamic models for aqueous 1‐(2‐hydoxyethyl)‐piperidine solution

“…The development of theoretical thermodynamic model for amine‐H 2 O‐CO 2 system, which is crucial in process design, simulation, and optimization, requires VLE data to incorporate chemical reactions and physical transfer . The model is supposed to correlate experimental data and make reasonable predictions for the related studies.…”

“…11 The development of theoretical thermodynamic model for amine-H 2 O-CO 2 system, which is crucial in process design, simulation, and optimization, requires VLE data to incorporate chemical reactions and physical transfer. [12][13][14][15][16] The model is supposed to correlate experimental data and make reasonable predictions for the related studies. Kent and Eisenberg developed a classic semi empirical model for acid gas CO 2 and H 2 S absorption in MEA and DEA aqueous solution.…”

“…The proton concentration [H + ] can be solved out via inputting experimental conditions, that is, temperature, CO 2 partial pressure, and initial amine concentration. Calculated equilibrium CO 2 solubility is obtained using Equation(12) where proton concentration is input as the known parameter. The calculated equilibrium CO 2 solubility data is plotted inFigure 2 with experimental equilibrium CO 2 solubility of 1-(2-HE)PP-H 2 O-CO 2 system.…”