Solids Modelling and Capture Simulation of Piperazine in Potassium Solvents

Abstract

Piperazine is an amine which is used both as an activator or promoter, but also as active component in CO 2 capture solvents. High concentrations are being formulated to draw benefit of the PZ properties. This results in a risk of precipitation of PZ and other solid phases during capture. It could be a benefit to the capture process, but it could also result in unforeseen situations of potential hazardous operation, clogging, equipment failure etc. Security of the PZ process needs to be in focus. Flow assurance requires additional attention, especially due to the precipitation phenomenon. This entails all parts of the streams, but also during formulation and transport of the solvent. In this work the extended UNIQUAC thermodynamic model is presented with the addition of piperazine (PZ or PIPH2) in combination with the potassium ion of mixtures with CO 2 in equilibration with KOH-KHCO 3 -K 2 CO 3 . Phase boundaries are laid out which shows the concentration regions of solid formation. A special focus will be given to the boundary where precipitations occur. The model is a generic. It builds on consistent parameters of the extended UNIQUAC model previously published. It allows for accurate vapor liquid equilibrium (VLE) calculation, heat capacity determination, and similar thermodynamic properties. It especially allows for determination of solid liquid equilibria (SLE) and heat of absorption/heat of desorption which are core variables in the determination of energy requirements for CO 2 capture. In this work the typical phase behavior will be shown for the PZ solvent with potassium (K 2 CO 3 /KHCO 3 ) for CO 2 capture. Conclusions are given on a solvent compositions resulting in low heat requirements using the predictive nature of the extended UNIQUAC model. Concentration of a PZ/K 2 CO 3 solvent is suggested with a heat of absorption/desorption of 40 kJ/mol.

CO2 capture with potassium carbonate solutions: A state-of-the-art review

“…The Extended UNIQUAC thermodynamic model was used for solid-liquid equilibrium representation of the PZ-K 2 CO 3 -KHCO 3 -CO 2 -H 2 O system. The solid formation and the precipitation of PZ and KHCO 3 was studied, and the guideline for mixing the PZ with potassium solvent was given (Fosbøl et al, 2013). Imle et al (2013) carried out the experiments on the effects of borates and vanadates as promoters in the PC solution Some selected modeling studies on the PC solution thermodynamics.…”

“…-The carbon steel corrosion problem which is caused by PC solution, but still is less corrosive than the amines (Smith et al, 2012;Zhang and Martin, 2013). -The precipitation of the solvent in the form of fouling and crystals accumulations in reboilers and pipeline of the process (Fosbøl et al, 2013).…”

A consistent Thermodynamic Model for Solid Liquid Equilibrium (SLE) and Vapor Liquid Equilibrium (VLE) in Aqueous Amine Solutions

“…Fosbøl et al [5] have previously done a similar work in the Piperazine and water system. They demonstrated the ability of the e-UNIQUAC model in representing a co mplex system such Pz-KOH-K2CO3-KHCO3-H2O.…”

“…Such models based on excess Gibbs energy (NRTL [1] and UNIQUAC [2]) have advantages by being able to represent both Solid-Liqu id-Equilibriu m (SLE) and Vapor-liquid-Equilibriu m (VLE) in aqueous amine systems [3], carbonate systems [4] and amine/ carbonate systems [5,6]. Robust and accurate modeling relies on the quality and type of data used to regress the model parameters, and on a robust fitting procedure to obtain the best representation of the data.…”

“…Another method, based on the Gibbs-Helmholt z equation, can be used to derive the equilibriu m constants according to [3][4][5][6] (8) (9) Where is the difference between products and reactants in a reaction. If the heat capacity can be correlated as: (10) Then the change in enthalpy ( ) can be written as:…”