Effect of hydrophobic group on flocculation properties and dewatering efficiency of cationic acrylamide copolymers

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Abstract

Three kinds of hydrophobically modified copolymers of acrylamide with 3-acrylamido-2-hydroxypropyltrialkylammonium chloride were prepared, in which alkyls were ethyl, butyl and octyl, respectively. The conformations of the hydrophobically modified copolymers were studied using TEM micrograph. The flocculation performances and the dewatering efficiencies were investigated. The results showed that the hydrophobic group could enhance the flocculation properties. The longer the hydrophobic alkyl chain was, the better the flocculation result was. Compared with poly-diallyldimethyl ammonium chloride (PDADMAC) and poly-acrylamide (PAM), the hydrophobically modified polymers showed better performances in turbidity removal and were quite more efficient in dewatering examination.

Introduction

Flocculation is one of the most important processes in wastewater treatment to depurate water removing dissolved, colloidal and suspended particles. In this process, flocculant is undoubtedly the most important factor. In recent years, great efforts have been made to study water-soluble polymers, which can be used as flocculant. Research of poly-acrylamide and its copolymers is one of the most popular hot aspects because the reasonable cost, easy polymerization and good-treatment result. Different kinds of derivates of poly-acrylamide have been prepared in order to treat different kinds of wastewater, and improved flocculation performances were demonstrated [1], [2], [3], [4]. In the past few decades, researchers have found hydrophobically modified polymers showed excellent properties in the oily wastewater treatment in oil recovery operations and were effective in cleaning up organic contaminants in wastewater. These polymers include hydrophobically associating polyacrylate [5], [6], vinyl trimethyloxysilane (VTMS) modified PDADMAC [7], hydrophobically modified chitosan [8], hydrophobically modified polycations [9], etc. By introducing hydrophobic group into polymer molecular structure, flocculation performance of the polymer is improved.

Several studies have shown that the polymer structure has a great effect on the flocculation efficiency, such as the COO group in the anionic polyacrylamide-acrylate copolymer [10], which makes the polymer chain expand by reason of negative charge repulsion between molecular chains. Joo [11] found branched polyamines were more efficient than grafted polyamine during the dye wastewater treatment, because the former had higher charge density than the latter. Khalil [12] prepared six types of anionic starch derivatives and found the type of acidic group, the length of the molecular chain and the chemical formula (grafted or etherified) all had effects on the flocculation performance, which was monitored via estimation of the optimal dosage, transmission and weight removal. Pal [13] reported that the starch with longer N-(3-chloro-2-hydroxypropyl) trimethyl ammonium chloride (CHPTAC) chains showed the best flocculation performance among the four prepared cationic starches. Despite the studies noted above, there are few previous reports that study the effect of hydrophobic groups in polymer molecules on the flocculation efficiency.

In our opinion, PAM modified with some hydrophobic group must be efficient in wastewater treatment, and be helpful in solid–liquid separation. In this report, three kinds of cationic copolyacrylamide with different hydrophobic alkyl chains were prepared. They were used in the flocculation test and dewatering experiment. Comparisons of these hydrophobically modified PAMs with non-ionic PAM and high charged mono-poly(diallyldimethyl ammonium chloride) (PDADMAC) were investigated.

Section snippets

Materials

Sodium hydroxide, acetone, methanol, epichlorohydrin, ammonium persulfate and sodium hydrogen sulfite were analytical grade. Acrylamide, triethylamine, tributylamine and trioctylamine were chemical grade. They were obtained from Shanghai Chemical Reagent Co., Ltd. (Shanghai, China). Kaolin clay was purchased from Guangdong Jieshan chemical plant (Guangdong, China) and was chemical grade. Non-ionic polyacrylamide (PAM) was prepared in the laboratory. The intrinsic viscosity ([η]) was 126.7 mL/g.

Effect of the monomer feed ratio on the copolymerization

Three series of copolymers of acrylamide and 3-acrylamido-2-hydroxypropyltrialkylammonium chloride were prepared, in which the alkyl groups were ethyl, butyl and octyl, respectively. Their corresponding English abbreviations are PAAHTE, PAAHTB and PAAHTO. The molecular structures of these three kinds of polymers are listed in Fig. 1. The copolymerization results are summarized in Table 1, Table 2, Table 3. From these tables, we can see the intrinsic viscosity and the yield decreased when the

Conclusions

  • 1.

    Three series of hydrophobically modified copolymers of acrylamide and 3-acrylamido-2-hydroxypropyltrialkylammonium chloride were prepared and their flocculation performances were studied. In the three copolymer families, PAAHTO, which was modified by octyl chain, had the best performances not only in turbidity removal, but also in the settling behavior and dewatering examination.

  • 2.

    TEM micrographs showed the hydrophobic group made the molecule stretching and bulky by the self-forming behavior of

References (18)

  • Tridib Tripathy et al.

    Eur. Polym. J.

    (2001)
  • J.W. Qian et al.

    Eur. Polym. J.

    (2004)
  • A. Ariffin et al.

    Desalination

    (2005)
  • A. McFarlane et al.

    Miner. Eng.

    (2005)
  • H.Z. Zhao et al.

    J. Appl. Polym. Sci.

    (2002)
  • S. Bratskaya et al.

    Colloids Surf. A

    (2006)
  • P. Mpofu et al.

    Miner. Eng.

    (2004)
  • S. Pal et al.

    Carbohyd. Polym.

    (2005)
  • P. Mpofu et al.

    Int. J. Miner. Process.

    (2003)
There are more references available in the full text version of this article.

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