Aqueous Solubility of Piperazine and 2-Amino-2-methyl-1-propanol plus Their Mixtures Using an Improved Freezing-Point Depression Method

Abstract

In this work the solidÀliquid equilibrium (SLE) and freezing-point depression (FPD) in the electrolytic binary aqueous systems piperazine (PZ, and aqueous 2-amino-2-methyl-1-propanol (AMP, were measured. The FPD and solubility were also determined in the ternary AMPÀPZÀH 2 O system. A method was developed by which solubility can be determined at higher temperatures using the FPD setup. A total of 86 data points are listed in the full concentration range from (À35 to 90)°C. The solid phases piperazine hexahydrate (PZ 3 6H 2 O), piperazine hemihydrate (PZ 3 1/2H 2 O), and anhydrous PZ precipitated during the experiments. The data can be used in the formulation, prevention, or intentional formation of slurries in piperazine solvents for promoting CO 2 capture using absorption and desorption. INTRODUCTIONCO 2 capture is an openly debated topic for carbon emission reduction to reduce pollution by greenhouse gases. Process streams containing carbon dioxide can be cleaned by absorption in aqueous liquid solvents. Amines, strong bases, or combination of the two are typically used as active components. The low heats of absorption and desorption are design criteria that reduce the cost of energy in regeneration of the solvent. This is obtained by using sterically hindered amines. The result is often slow reaction kinetics between the solvent and CO 2 . Consequently piperazine (PZ) is being used in solution formulation to create an enhanced CO 2 capture solvent. PZ can be used with both amine and potash solutions (K 2 CO 3 ) to increase the rate of absorption and thereby promote the CO 2 capture.A lower PZ concentration was typically used in literature. Recently the scope has changed, and PZ is now being used at higher concentrations. On increasing the concentration, the solubility limit of PZ is being reached, especially during winter temperatures and even up to room temperature. The unexpected formation of slurries and solids downstream may create unforeseen process conditions, decrease efficiency, and create clogging which will result in unfortunate hazardous operations. In general it could be interesting to provoke the formation of CO 2 containing solids and thereby facilitate and increase the capacity of the capture solvent. CO 2 deprived solids are rarely preferable in terms of CO 2 capture.The aim of this work is to determine the solidÀliquid phase boundary in the two binary PZÀH 2 O and AMPÀH 2 O systems and also in the ternary AMPÀPZÀH 2 O system. 2-Amino-2-methyl-1-propanol (AMP) is a sterically hindered amine. CO 2 absorption in AMP solutions can be promoted by adding PZ.An additional goal of this work was to enhance the utilization of freezing-point depression (FPD) equipment developing a method for the purpose of studying solidÀliquid equilibrium (SLE) behavior in solutions precipitating solids other than ice.

Solids Modelling and Capture Simulation of Piperazine in Potassium Solvents

“…There is a similar good representation of pressures at other conditions. The precipitation phenomenon in the aqueous PZ system was recently studied in detail by Fosbøl et al [12]. Figure 6 summarizes a section of the findings.…”

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

“…The experimental responses were obtained fro m the reported VLE results [10,11] and the SLE results [7] respectively.…”

“…SLE data could cover the equilib ria with ice, with possible hydrates and with co mplex salt fo rming systems such as in the piperazine water system. In this system, at a specific temperature and concentration, different equilibriu m can occur according to [7]:…”

“…The activity coefficients for water and piperazine can be determined through the gamma-phi method fro m VLE data and such data can be produced fro m an ebullio meter study [10,11]. SLE data are usually gathered fro m freezing point depression measurements [7]. Th is indicates that one set of parameters for the selected thermodynamic model, for water and piperazine, can be implemented to represent the species in all phases.…”

“…Vapor Liquid Equilibrium of Pz + H2O system at different temperatures (Filled Points,[11]; Unfilled Points,[10]; Dash line, NRTL; Solid line, UNIQUAC) Solid Liquid Equilibrium of Pz+H2O system at different temperatures (data,[7]; Blue solid line, NRT L; Red solid line, UNIQUAC)…”