Article pubs.acs.org/jced
Adsorption Equilibria of Propylene and Propane on Zeolites and Prediction of Their Binary Adsorption with the Ideal Adsorbed Solution Theory Swapnil Divekar,*,† Anshu Nanoti,† Soumen Dasgupta,† Aarti,† Rekha Chauhan,† Pushpa Gupta,† Madhukar O. Garg,† Surendra P. Singh,‡ and Indra Mani Mishra§ †
CSIR-Indian Institute of Petroleum, Dehradun, 248005, India Indian Institute of Technology, Roorkee, Saharanpur Campus, 247001, India § Department of Chemical Engineering, Indian School of Mines, Dhanbad, Jharkhand, 826004, India ‡
S Supporting Information *
ABSTRACT: Adsorption equilibrium isotherms of propane (C3H8) and propylene (C3H6) on commercial zeolite 5A (UOP), zeolite 13X (Z10-04, Zeochem), and laboratory synthesized titanosilicate Na-ETS-10 were measured using a gravimetric microbalance at 298, 323, 343, 373, and 423 K and over 0 to 300 kPa. The isotherm data were fitted to different isotherm models. A Microsoft Excel based code for solving Ideal Adsorbed Solution Theory (IAST) was validated against literature reported multicomponent isotherm data. The binary adsorption selectivity of propylene over propane was predicted with this IAST solver for two feed compositions, namely, equimolar propane/propylene mixture and 85 mol % propylene with balance propane representing steam cracker and fluid catalytic cracker (FCC) off gas, respectively. High selectivity values in excess of 25 are obtained for Z10-04. Propylene to propane selectivity for Z10-04 and Na-ETS-10 decreases with an increase in temperature, and for zeolite 5A (UOP) the selectivity improves with an increase in temperature. time taken in these measurements.26,27 The available experimental or predicted binary data for commercial zeolites (13X and 5A) from different manufacturers is limited to 100 kPa Pressure.17,28,29 For practical applications isotherm data for higher partial pressures will be required. Tiscornia et al., 200719 have reported propane and propylene isotherm data on a laboratory synthesized Na-ETS-10 adsorbent. The experimental data are reported for a temperature of 311 K and up to 20 kPa only. A comprehensive evaluation of the applicability of these adsorbents as an adsorbent for PSA/VSA process on the basis of such scant data is difficult as the operating pressures of PSA/ VSA process are higher than this pressure range. In the present paper, the equilibrium adsorption data of single-component propane and propylene on commercial zeolite 13X (Z10-04, Zeochem), zeolite 5A (UOP), and Engelhard titanosilicate NaETS-10 (laboratory synthesized) at five temperatures (298, 323, 343, 373, and 423 K) and in the pressure range of 0−300 kPa is reported. Single component adsorption equilibrium isotherm data for propane and propylene for these commercial zeolites, that is, zeolite 5A (UOP) and Z10-04 have not been reported in the open literature. This study also includes the
1. INTRODUCTION Separation of propylene and propane is a very energy intensive process1 in petroleum refineries and petrochemical industries, requiring large cryogenic distillation columns with 75−90 m height and 2−6 m diameter, operating at a temperature of 240 K and a pressure of ∼310 kPa with over 200 theoretical stages and a very high reflux ratio (R ≈ 10) due to low relative volatility of propane with respect to propylene.2−6 This separation becomes challenging because propylene and propane molecules have very similar properties, for example, close boiling point (−42 and −47.6 °C), molecular weight (44 and 42 g/mol, respectively), polarizability (6.29 and 6.26 × 10−24 cm3), and kinetic diameter (4.0 and 4.3 Å), respectively. A number of alternative separation processes have been proposed including membrane separation using highly selective membranes,7 absorption,8 adsorption9 and its variants such as adsorption−distillation hybrid systems,10,11 pressure swing adsorption (PSA) or vacuum swing adsorption (VSA).3,12−16 Many adsorbents have been reported in the literature for propylene−propane separation including metal organic frameworks (MOFs),13 zeolites,6,14−18 Na-ETS-10,19 and π- complexation adsorbents.20,21 The experimental adsorption data for propane−propylene binary adsorption is sparsely available in the open literature22−24 because of the requirements of precise measurement set up,25 analytical facility and the considerable © XXXX American Chemical Society
Received: April 8, 2016 Accepted: June 10, 2016
A
DOI: 10.1021/acs.jced.6b00294 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
isotherm data for these two adsorbates on Na-ETS-10 material at different temperatures and up to 300 kPa pressure. For the optimal design and operation of the industrial PSA plants and also for the evaluation of the selectivity and adsorption capacity of the adsorbents30 for a given adsorbate mixture, data on the pure component and the competitive multicomponent adsorption equilibrium involving constituents of the feed are necessary. As the amount of the binder and the preparation/formulation procedure of commercial adsorbents vary from one manufacturer to the other, considerable differences in physical and surface properties of the adsorbents such as crystal radius, pellet density, active ingredient composition and dispersion, crystal diffusivity, pore size distribution, adsorption capacity, etc can occur.14,15 These properties may affect the performance of the adsorbent bed under PSA/VSA operating conditions in terms of purity, recovery, energy consumption, and productivity of the desired component. Mathematical isotherm models such as the modified or extended forms of single component isotherm equations such as the Langmuir isotherm equation (and its variants, for example, dual-site Langmuir (DSL) and the modified Langmuir−Freundlich isotherm (Sips) etc.), have been reported for predicting multicomponent adsorption equilibria31−36 with an inherent assumption that the saturation capacities of all the adsorbates are the same, irrespective of their size and nature.37 Alternatively, ideal adsorbed solution theory (IAST)38−41 is an effective and versatile tool reported in the literature to predict the adsorption of multi- component mixtures on an adsorbent on the basis of single component adsorption equilibrium isotherms. IAST is a thermodynamically derived model based on the assumption that the adsorbed phase is ideal and is not constrained by the assumption of equal saturation capacities of the adsorbates. The applicability of these adsorbents for PSA/VSA application was tested on the basis of the binary selectivity predicted with the IAST model in conjunction with Dual Site Langmuir (DSL) parameters. The IAST selectivity was predicted for the binary adsorption of the propylene−propane mixture for two compositionsequimolar mixture and 85 mol % propylene and 15 mol % propane mixtures representing steam cracker and FCC off gas, respectively. An algorithm described by Do42 has been employed to perform IAST calculations. For IAST calculations a solver was developed based on Microsoft Excel solver, which is an easily accessible and widely used computational and plotting tool. Most of the literature reports on multicomponent isotherm predictions have employed software like MATLAB and Octave for solving IAST equations, which require skills in program coding.43,44
Table 1. Physical and Surface Properties of Adsorbents adsorbent zeolite 5A (UOP) Z10-04 Na-ETS-10 (lab synthesized) a
size (mm)
BET surface area (m2/g)
pore volume (cm3/g)
bulk density (g/cm3)
pellet
1.6
383
0.24
0.70a
sphere powder
2.0
516 278
0.35 0.18
0.67a 0.89b
form
Data from vendor. bExperimentally measured.
2.2. Adsorption Equilibrium Isotherms Measurements. Single component adsorption equilibrium isotherms of propane and propylene were measured in a Hiden IGA001(Hiden Isochema, UK) gravimetric microbalance at 298, 323, 343, 373, and 423 K up to 300 kPa pressure for the three adsorbents. About 150 mg of adsorbent was loaded in the adsorption cell and the adsorbent was activated in situ at 623 K under vacuum (
