Studies on a Cationically Modified Quaternary Ammonium Salt of Lignin*

CHEM. RES. CHINESE U.

Available online at w.sciencedirect.com

2007, 23 ( 4 ) , 4 7 9 4 8 2 Article ID 1005-9M0(2007)-04479434

ScienceDirect

Studies on a Cationically Modified Quaternary Ammonium Salt of Lignin* YANG Ai-li * * and JIANG Wen-ju College of Architecture and Environment , Sichuan University, Chengdu 610065 , P. R. China Received Dec. 18, 2006

A new quaternary ammonium salt monomer was synthesized and a quaternary amination of lignin( noted as QL) , with the monomer was carried out by grafting copolymerization. The products were characterized by Fourier Transform Infrared spectroscopy( ETIR) . The experimental results indicate that the yield of the monomer was 99.06% , and the conversion of the monomer and the grafting yield of QL were 93.69% and 185.78% , respectively. The feasibility of QL as the flocculant to be applied in color removal of five artificial dyes, eriochrome black T( dye A) , gongo red ( dye B) , direct fast black G ( dye C ) , cuprofix blue green B ( dye D) , and acid black A l T ( dye E ) was examined. Results show that QL exhibits the favorable flocculation performance and high stability. Keywords Quaternary ammonium salt of lignin( QL) ; Cationic monomer; Grafting copolymerization; Flocculation

Introduction Lignin is the second most abundant renewable biomass resource, the first being cellulose. The pulp and paper industry produces very large quantities of lignin by kraft and sulfite processes; most of the lignin is burnt to recover energy and pulping chemicals"]. This method brings with it not only a waste of resource, but also high pollution. Therefore , the development of lignin and its derivatives are receiving growing attention in view of economic benefit and environmental protection12-91. A number of modification methods of lignin , such as , sulfonation" I , polymerization"01 , epoxy modification'" I , oxidation' '*I , and hydroxylmethylation[13], have been reported. However, most of them require rigorous reaction conditions or high cost. To enhance the flocculation property of lignin, the most widespread method is to introduce a cationic group such as the quaternary ammonium group, into l i g~i n[~-". The quaternary ammonium salt of lignin is a wellknown , nontoxic, biodegradable polymer, with high positive charges hence it will not bring secondary H3C h-CH=CH2 / H3C

+C

Anhydrous I H I C ~ ~

contamination when it is used to treat wastewater, as a flocculant. Another benefit of lignin application is a possibility of using lignin containing sludge , formed during the wastewater treatment in the production of fertilizers or additives , to animal feeding mixtures"41 . To improve the properties of lignin and reduce cost, in this study, a new quaternary ammonium salt monomer was prepared from N, N-dimethylallylamine , with reaction temperature at 50 'T . It has an advantage of low cost in industrial practical application compared to the reaction temperature at - 3 to - 6 'T in the synthesis of the monomer from tri-methylamine , proposed by the other researcher^'^^]. The high active epoxy group on the monomer is easily grafted into lignin, producing a viscous lignin-based polymer, which has not been reported yet. The synthesis route is shown in Scheme 1. The products are characterized by FTIR. The synthetic QL , with a high stability, has a favorable flocculation performance and can effectively remove the colored group of wastewater from dyes.

-

L-O-CH2CH(OH)H2C-N

(QL)

/!CH3)2 C1F 'CH=CH2

,

2,3-Epoxypropyldimethylallylammonium chloride

L-OH represents lignin

Scheme 1 Synthesis route of quaternary ammonium salt monomer and QL

Experimental 1 Apparatus A centrifugal machine ( Shanghai Shoushu Appli-

ance Co. , China) , a PH S3C pH meter ( Shanghai Leici Appliance Co. , China), a JJ4six-shaft electric stirrer with stainless steel paddles( Guohua Electric Ap-

* Supported by the National Nature Science Technology Item of of China( No. 2005DC105005-01) . * * To whom correspondence should be addressed. E-mail: yangaili-770117@ yahoo. corn. cn

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480

pliance Co. , China), and a 721 model spectrophotometer( Shanghai, China) were used. The FTIR spectra were determined on a Nicolet 170SX FTIR spectrometer ( USA) .

2 Reagents Alkaline lignin with lilac group( high grade) was purchased from Keyi Chemical Industry Co. ( Shandong, China) , and used without further purification. N ,N-dimethylallylamine ( DMAA , analytical grade ) was purchased from Luyue Chemical Industry Co. (Shandong , China). Eriochrome black T ( dye A ) , gongo red ( dye B ) , direct fast black G ( dye C ) , cuprofix blue green B (dye D ) , and acid black A l T (dye E ) were commercial dyes and used without further purification. All the other reagents were of analytical reagent grade. Distilled water was used for preparing all the solutions.

3 Preparation of Monomer 2,3-Epoxypropyldimethylallyl Ammonium Chloride Under agitation, 18.50 g of epoxy chloropropane was added dropwise to a mixture of 18.70 g of DMAA and 74.40 g of anhydrous ethanol at about 31 “c. After completion of dropwise addition, the reaction solution was agitated at 50 “c for 4 h and cooled to mom temperature. The monomer, refined by vacuum distillation, was a viscous yellow liquid.

4 Preparation of CationicaUy Modified Lignin (QL) In nitrogen atmosphere, a mixture of 23.43 g of lignin and 35 mL of distilled water was adjusted to pH 10-11 with 40% NaOH solution, under agitation. The resulting solution was heated to 50 “c and trickled with 2.5 x lo-*moVL K2S,0,/Na,S,03 5 H 2 0 solution as the initiator. After activation for 1 min, a monomeric mixture of 11.72 g of the monomer mentioned earlier and 20 mL of distilled water was added dropwise

-

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5 Jar Tests The initial concentration of the dyes was 0. 1 g/L. The target pH was adjusted by adding dilute HCl or NaOH solution into the dye solutions. A water sample of 200 mL was poured into a 500 mL beaker, to which a required dose of the flocculant was added, and was mixed rapidly at 250 r/min for 1 min , followed by slow mixing at 60 d m i n for 5 min. The flocs were allowed to settle down and were undisturbed for 30 min. The color removal was measured on a 721 model spectrophotometer at the maximal absorbance wavelength (Am). The Amas of dye A , dye B , dye C , dye D, and dye E were 534, 490, 660, 600 and 620 nm, respectively.

Results and Disccusion 1 Synthesis and Characterization of the Monomer and QL To determine the optimum conditions, reaction time, reaction temperature, and molar ratio of DMAA to epoxy chloropropane, the three main effecting factors, were investigated. The optimal conditions for the synthesis of the monomer were a reaction temperature of 50 “c , a reaction time of 4 h , and the molar ratio of DMAA to epoxy chloropropane of 1. 1 : 1 , with the yield of the monomer being 99.06%. The monomer was freshly prepared to avoid any possible degradation and dissolved in distilled water for the next reaction. In grafting copolymerization, initially, the effects of different initiators on the grafting reactions and the flocculation efficiency were studied ( see Table 1 ) . The results show that K,S,0,/Na,S203 * 5 H 2 0 was determined as the optimal initiator. Next, the reaction time, reaction temperature, the mass ratio of lignin to the monomer, and the initiator concentration, as the four main effecting factors were investigated. The optimal conditions of QL were reaction temperature 60 “c , reaction time 4 h , the mass ratio of lignin to the monomer 1 : 0.5, and the initiator concentration 2.5 x moVL, with the conversion of monomer and the grafting yield being 93.69% and 185.78% respectively.

to the reaction solution. After completion of dropwise addition, the reaction mixture was agitated at 50 “c for 5 h and cooled to room temperature. The obtained grafted copolymer was then adjusted to pH 2 with dilute HCl. By centrifugation, the viscous puce precipitant (QL) was collected and vacuum-dried. Table 1 Effects of different initiators on synthesis and flocculation performance of QL Initiator

Color removal ( % )

Grafting yield( % ) Monomer conversion( % )

Ce4

+

96.95 140.42 88.92

Fez /H2 0, +

96.95 142.46 94.22

The FTIR spectra of DMAA, the monomer, QL, and lignin are shown in Fig. 1. Compared with that of DMAA( Fig. 1 curve u ) , the IR spectrum of the qua-

K2 S, 0,

96.57 114.49 94.57

K, S, O,/NaHSO, 96.76 96.13 91.20

K2S,O,/N%S,O,

5H20

96.38 185.78 93.69

ternary ammonium salt monomer( Fig. I curve b) shows the appearance of a new intensive peak at 1475 cm ascribed to the characteristic peak of the quaternary

-’

No. 4

YANG Ai-li et al.

ammonium group[61, and the disappearance of the NR,-associate bands at 1360-1310 cm and 27002330 cm-' , is ascribed to the characteristic peak of

-'

1475

I

I

4000

3200

I

2400 1600 u1crn-l

800

48 1

the ternary amine N-H vibration deformation. Results indicate that the substitution reaction has occurred successfully.

I

I

I

0

4000

3200

I

I

I

800

0

I

2400 1600 Plcm-I

Fig. 1 FTIR spectra of DMAA(a) , the monomer(b) , QL(c) and lignin(d)

In the IR spectrum of lignin( Fig. 1 curve d) , the peak at 1514 cm-' is attributed to the characteristic peak of the benzene rings of lignin. The IR spectrum of QL( Fig. 1 curve c ) shows the appearance of a new strong, ,middle peak at 1470 cm-' , attributed to the characteristic peak of the N-H bend vibration of the quaternary ammonium group, which indicates that there are quaternary ammonium ions in the product. The peak at 1470 cm-' covers the characteristic peak of the benzene rings of lignin at 1514 cm-' , which can still be seen. On the other hand, QL is precipitated by the addition of HCl and centrifugation, whereas, the quaternary ammonium salt monomer cannot be precipitatedL6I. Therefore, it can be concluded that quatemary ammonium ions are grafted on lignin and the grafting copolymerization occurs successfully.

2 Flocculation Property of QL The flocculation performance of QL used to treat five artificial dyes was investigated. The effect of the flocculant dose on color removal at pH 2 is shown in Fig. 2. During grafting copolymerization, the cationic flocculant QL with a positive charge quaternary ammonium group was found to be very effective for the color removal of dyes with negative surface charges. It is observed from Fig. 2 that the optimum doses of QL are 0.5, 0.5, 1 . 0 , 1 . 0 , and 1.0 g/L, respectively, when the decolorizing rates of dye A , dye B , dye C , dye D , and dye E are up to 95.86% , 99.04% , 98.70% , 100.00%, and 89.64% , respectively. The reason for this is that adsorption occurs because of the formation of electrical interaction or chemical bond between the dyes and QL. It is well known that the most widespread flocculation mechanism may be the result of the bridging adsorption and charge patch between the

negative charges on the particulate surfaces and the cationic groups of the interacting polymer.

1 -

120

,(,,)

0 1 I I , I , , -20 0.1 0.3 0.5 1.0 2.0 3.0 4.0 5.0 Flocculant dose/(g.L-')

I

Fig. 2 Effect of the flocculant QL and lignin dose on color removal

-*-*-

-.-

- -0-- Dye A( lignin) ; dye A( QL) ; - -A- - dye B( lignin) ; -Adye B( QL) ; - -0- - dye C( lignin) ; dye C( QL) ; - - dye D( lignin) ; dye D( QL) ; - - + - - dye E( Iignin) ; - +- dye E( QL).

-*-

Results in Fig. 2 also indicate that the flocculation performance of QL is more effective on the five dyes than that of lignin, which proves further that the quaternary ammonium salt monomer is grafted onto lignin, and electrostatic interactions probably play an important role in controlling the adsorption of dye molecules on the cationic polymer surfaces. Anionic lignin is almost ineffective in the flocculation process, as still no flocs can be observed. These results show that the flocculation efficiency is markedly improved as lignin is quaternized.

3 Effect of Storage Time To study the QL storing stability, the flocculation performance of QL stored for different periods at room temperature has been investigated. The results are shown in Fig. 3. It is observed that the flocculation

CHEM. RES. CHINESE U.

482

efficiency of QL stored for several months is not markedly different from that of freshly prepared QL. Therefore, it can be concluded that storage time has little effect on the flocculation property of QL, hence, there are no obvious changes in the physical stability or the flocculation property when QL has been stored for six months.

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of five artificial dyes. It was found that the optimum dose of QL is up to 1.0 g/L when the decolorizing rate is from 89. 64% to 100.00% at pH 2. QL possesses a favorable flocculation performance and physical stability in the dye wastewater treatment process.

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102

82 0

1

2 3 4 5 Storage timehonth

6

Fig.3 Effect of storage time on the flocculation property of QL Dye A; -.-dye B; -Adye C;

-*-x-

dye D; -#-dye

E.

Conclusions In the synthesis of the monomer, the optimum conditions are a reaction temperature of 50 “c , a reaction time of 4 h , and the molar ratio of DMAA to epoxy chloropropane of 1. 1 : 1. The yield of the monomer is 99.06%. In the synthesis of QL, the optimum conditions are, reaction temperature of 60 “c , reaction time of 4 h , and mass ratio of lignin to monomer, 1: 0.5. The conversion of monomer and the grafting yield of QL are 93.69% and 185.78% , respectively. The cationic QL is very effective to color removal of the wastewater

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