Synthesis of polyaluminum chloride with a membrane reactor: Process characteristics and membrane fou

Available online at www.sciencedirect.comJOURNAL OFENVIRONMENTALSCIENCESScienceDirectISSN 1001-0742CN 1-2629/X =JESJoumal of Environmeotal Sciences 2011, 23(11) 1794-1798www.jesc.ac.cnLELLSynthesis of polyaluminum chloride with a membrane reactor:Process characteristics and membrane foulingZhiqian Jial-2., Fei He2, Zhongzhou Liu21. Colle of Chemistry, Bejing Normal University, Beijing 100875, China2. Research Center. for Eco Environmental Sciences, Chinese Academy of Sciences, Bejing 10085, ChinaReceived 28 Deccember 2010; revised 08 March 201 1; accepted 16 March 2011AbstractPolyaluminum chloride was synthesized with a membrane reactor, in which NaOH was added into AlCl; solution through themembrane's micropores to reduce the NaOH droplets size. The content of the most eficient specics increased to about 80%. Theprocess characteristics in the reaction (i.e., flow velocity, pressure drop), and membrane fouling and cleaning were investigated. Theevolution of both flow velocity and pressure drop during the reaction were related to changes in species distribution and solutionviscosity. The process characteristics were well interpreted in terms of the Bernoulli equation. After reaction, the membranes wererecovered by cleaning with diluted hydrochloride acid. This study is crucial for process design and scale-up of membrane reactors.Key words: polyaluminum chloride; membrane reactor; foculant; Alb; AlsDOI: 10.1016/S1001-0742(10)60614-6Citation: JiaZ Q, He F, Liu Z Z, 2011. Synthesis of polyaluminum chloride with a membrane reactor: Process characteristics andmembrane fouling. Journal of Environmental Sciences, 23(11): 1794-1798Introductionthe process characteristics (i.e., flow velocity and pressuredrop) in the reaction, and membrane fouling and cleaningPolyaluminum chloride (PAC) is an important flocculant were investigated. These studies are important, especiallyin water treatment (Li et al, 2010). It can be divided into for the design and scale-up of membrane processes.three fractions (Bersillon et al, 1980; Parker and Bertsch,1992): Al (mono-nuclear AI), Alb (reactive polynuclear 1 Experimental sectionAI), and Alc (larger polynuclear and solid-phase aluminumtrihydroxides). Generally, Alb is regarded as the mostAll reagents, including Ferron (Sigma Chemical Co.,efficient species. Polyaluminum chloride is usually synthe- USA), NaOH, AlCl3, NaAc, and hydrochloride acid, weresized by partial neutralization of AICl3 solution with base of analytical grade. The membrane module was ftted withsolution (Shen and Dempsey, 1998; Zhaoet al, 2009). Low 10 HFUF membranes (PS/PDC, MWCO 10000, L.D. 1.0adding rate and small droplet size of the base solution favor mm, lengh of 0.13 m, Zhongke Membrane R&D Centerthe increase in Alb content (Bertsch, 1987; Bottero et al, of Bejing, China).1987). Thus, various methods, such as adding base throughThe experimental set-up is schematically shown incapillary with l.D. of 0.1 mm (Vermeulen et al, 1975),Fig.1. In the reaction, NaOH solution (2.0 mol/L) inelectrodialysis (Lu et al., 1999), electrolysis, homogeneousgraduated glass tubes entered the module shell-side andhydrolysis (Vogels et al, 2005), and ulrasounds (Cheng et permeated through the membrane micropores under trans-al, 2008) have been employed to reduce the addition rate membrane pressure (0.0090 MPa). Approximately 100.0and/or droplet size of base solutions.mL of AIClz solution (0.40 mol/L) in the stirred tankIn our previous work (ia et al., 2004; He et al, 2005), aflowed through the membrane lumens with a flow velocitymembrane reactor was employed for the synthesis of PAC,of 1.09 m/sec, reacted with the permeated NaOH, and thenin which NaOH solution was added to AICl3 solution grad-returned to the stired tank. When the basicity (B, molarually through the micropores of hollow fiber utrailtration ratio of NaOH to AlCl3) reached 2.5, the reaction was(HFUF) membranes to reduce the NaOH droplet size. The stopped. The fow rate nf the linuid was measured witheffects of membrane molecular weight cut-of (MWCO) a rotameter. [中国煤化工d in the strredand reactant concentration on species distribution, along tank was sampMHCNMHGwasanalyzedwith the reaction pathways, were studied. In this article,after aging for 24 nr.In the determination of the species distribution, Ferron* Corresponding author. E-mail: zhgjia @ bnu.cdu.cn.No.11Synthesis of polyaluminum chloride with a membrane reactor: Process characteristics and membrane fouling1795brane samples were washed with pure water, dried at roomNaOHtemperature, spurted with carbon, and then observed withSEM (S250MK3, Cambridge Instrument Company, UK).④Flowmetet18 Membrane2 Results and discussionmoduleH8HValve2.1 Process characteristicsWith the addition of NaOH solution, the pH of the团Pressure gaugeAlCl3 solution increased. Figure 2a shows the evolutionof pH values at the reaction temperature of 18, 24, and32°C, respectively. At the same basicity, the pH decreasedAICI, tankPumpwith increasing temperature, which was likely due to theFig1 Experimental set-up.hydrolysis of AICl3, being an endothermic reaction withhigh temperature shifting the hydrolysis balance to thesolution (0.2%), NaAc solution (20%) and dilute hy- right.drochloride acid (VHa:VH2o = 1:9) were mixed with aSpecies distribution changed with the basicity: Ala de-volume ratio of 2.5:2:1. The as-obtained working Ferroncreased linearly; Alb increased apparently when 0< B