Article pubs.acs.org/IECR
Rapid Preparation of Acid-Stable and High Dehydration Performance Mordenite Membranes Mei-Hua Zhu,†,‡ Shui-Lian Xia,† Xue-Mei Hua,† Zi-Jun Feng,† Na Hu,† Fei Zhang,† Izumi Kumakiri,‡ Zhang-Hui Lu,† Xiang-Shu Chen,*,†,‡ and Hidetoshi Kita*,‡ †
Jiangxi Inorganic Membrane Materials Engineering Research Centre, College of Chemistry and Chemical Engineering, Jiangxi Normal University, Nanchang 330022, People’s Republic of China ‡ Department of Environmental Science and Engineering, Graduate School Science and Engineering, Yamaguchi University, Tokiwadai 2-16-1, Ube, Yamaguchi 755-8611, Japan S Supporting Information *
ABSTRACT: Highly intergrown mordenite membranes were rapidly prepared on seeded aluminum supports by microwaveassisted synthesis. Both the thicknesses of the zeolite layer and the sizes of the zeolite crystals of the mordenite membranes were highly dependent on the synthesis time. With a SiO2:0.08Al2O3:0.2Na2O:0.1NaF:35H2O precursor synthesis gel, a compact and 0.75 μm thick mordenite crystal layer was successfully prepared on the aluminum support at 170 °C for 3 h. The as-synthesized mordenite membrane exhibited excellent water perm-selectivity and long-term stability for dehydration of alcohol/water, acetic acid/water, and acetic acid/ethanol/water/ethyl ester mixtures by pervaporation. For dehydration of 90 wt % acetic acid/water solution, the corresponding flux and separation factor (water over acetic acid) of the membrane remained at 0.44 kg·m−2·h−1 and 2300, respectively, at 75 °C even after 59 days of immersion.
1. INTRODUCTION Because of their potential applications in gas separation,1 liquid separation,2 and catalytic reactors,3 zeolite membranes have been attracting great interest over the past few decades. One type of zeolite membrane, LTA-zeolite membrane, has been used in industry to replace the traditional azeotropic distillation process for dehydration of alcohols.4 The LTA-type zeolite membranes have a high water selectivity and flux for dehydration of organic aqueous mixtures, but their poor acidic stability greatly limits their applications. Mallada et al.5 used an LTA-zeolite membrane as an inert membrane reactor to dehydrate the esterification reaction between ethanol (EtOH) and acetic acid (HAc). The separation factors of H2O/EtOH and H2O/HAc for esterification experiments with LTA-zeolite membranes dramatically decreased after 90 wt % HAc.9,11,13 Moreover, mordenite membranes are prepared via hydrothermal synthesis, with synthesis times ranging from 8 © 2014 American Chemical Society
to 96 h. Shortening the synthesis time is an important issue for the preparation of mordenite membranes. Compared with the conventional method, microwave heating can remarkably accelerate the zeolite membrane formation and appropriately synthesize high-purity zeolite crystals with a narrow particle size distribution.14,15 Some zeolite membranes have been successfully prepared by microwave-assisted heating, including ETS-4,8 LTA,16,17 MFI,18−20 TS-1,21 T,22 AFI,23 SOD,24 and FAU.25 However, the literature contains no report of the facile preparation of mordenite membranes by microwave-assisted synthesis. Herein, for the first time, acid-stable mordenite membranes were rapidly prepared by microwave-assisted synthesis. The effects of the synthesis time on the growth and performance of the mordenite membranes were investigated. Furthermore, the mordenite membrane prepared under the optimum synthesis conditions was applied to the dehydration of binary aqueous mixtures of alcohols or acetic acid and of a quaternary acetic acid/ethanol/water/ethyl ester (HAc/EtOH/H2O/AcOOEt) mixture by pervaporation (PV). The long-term stability of the mordenite membrane for the separation of high acetic acid concentration mixtures (80 and 90 wt % HAc/H2O) is also discussed in the current work.
2. EXPERIMENTAL METHODS 2.1. Preparation of Mordenite Membranes. Hydrophilic mordenite membranes were prepared on asymmetric α-Al2O3 Received: Revised: Accepted: Published: 19168
March 25, 2014 November 6, 2014 November 14, 2014 November 14, 2014 dx.doi.org/10.1021/ie501248y | Ind. Eng. Chem. Res. 2014, 53, 19168−19174
Industrial & Engineering Chemistry Research
Article
A = πdl
tubes (Nikaato, outer diameter = 10 mm, inner diameter = 7 mm, pore size = 0.15 and 0.7 μm, length = 100 mm) by microwave-assisted synthesis. Prior to the synthesis, the outer surfaces of the α-Al2O3 supports were rubbed with a water slurry of mordenite crystals (HS-642, Si/Al = 9, Wako) and dried at 80 °C. The synthesis gel had a molar composition of SiO2:0.08Al2O3:0.2Na2O:0.1NaF:35H2O and was prepared as follows. NaOH (sodium hydroxide, 97 wt %, Wako) and NaAlO2 (sodium aluminate, Al/NaOH = 0.79, Wako) were dissolved in deionized water, and colloidal silica (AS-40, 40 wt %, Aldrich) was subsequently added under continuous stirring. Thereafter, an amount of NaF (sodium fluoride, 99 wt %, Wako) was added to the white gel under stirring at room temperature, and the resulting mixture was stirred for 6 h. The precursor synthesis gel was then transferred into a PTFE-lined glass autoclave, into which the two pieces of the seeded support were immersed vertically. The microwave oven (PTFE-lined glass autoclave, 400 mL, Shibaura Mechatronics Corp.) was a computer-controlled Milestone ETHOS 1600 with a fixed frequency of 2.45 GHz. The autoclave was quickly heated to 170 °C under full power of 1.5 kW and was then typically held at this temperature for 2−4 h under low power. Table 1
J = m /(At ) αw/o = (Yw /Yo)/(X w /Xo)
where d, l, t, m, Xw, Xo, Yw, and Yo denote the outside diameter of the support, the length of the membrane immersed in the feed mixture, the test time, the mass of permeate condensed in the cooled trap over a known test time, and the mass fractions of the water and organic components at the feed and permeate sides, respectively. The compositions of the alcohol feed mixtures and permeates were analyzed using a gas chromatograph (Shimadzu, GC-8A, threshold detection level 9999*
*
The asterisk indicates that the concentration of acetic acid in the permeation side was below the threshold detection level of the gas chromatograph (
