Progress in Organic Coatings 78 (2015) 5558

Contents lists available at ScienceDirect

Progress in Organic Coatings

j o ur na l ho me pa ge: www.elsev ier .com/ locate /porgcoat

Synthe in rehydr

Guo YanSchool of Chem

a r t i c l

Article history:Received 26 JuReceived in re15 SeptemberAccepted 19 SAvailable onlin

Keywords:Aldol condensCyclohexanonMgAl hydrotaSolid base cata

CFR)rom Mn cate of ho enhe prethe reratin

1. Introdu

Ketone aldehyde resins are one kind of thermoplastic resinsthrough aldol condensation between ketones and aldehydes.Therein, cyclohexanone-formaldehyde resin (CFR) with low molec-ular weight is produced though aldol condensation betweencyclohexanand ink indusolvent. BecCFR is usedresistance aally, aldol cinvolves cothe environ

In recenmuch moreengineeringcompoundstives such abasicity can[36]. The synthesis alike compo

CorresponE-mail add

ondereaction [1215].

In our previous research, LiAl hydrotalcite with strong basicityis synthesized through replacing Mg2+ with Li+ and their corre-sponding double metal oxide is used to catalyze transestericaionbetween ethylene glycol and soybean oil [16]. Herein, MgAl

http://dx.doi.o0300-9440/ ones and formaldehyde and widely applied in coatingstry due to its excellent dissolution in polar and apolarause of unique compatibility with a variety of polymers,

as a multifunctional additive to improve weatheringnd ller dispersion in polymer matrix [1,2]. Tradition-ondensation is catalyzed by aqueous alkaline, whichrrosion of equipment, tedious separation and harm toment.t years, various solid base catalysts have attracted

attention during the development of green chemical. Among various solid base catalysts, hydrotalcite-like

([M2+1xM3+x(OH)2]x+Anx/nmH2O) and their deriva-s double metal oxides have been focused because their

be tuned based on the diversity of cations and anionstuning methods include changing cations during thend post anion exchange [711]. By now, hydrotalcite-unds and their derivatives have been used to catalyze

ding author.ress: zhangyanwu@zzu.edu.cn (Y. Zhang).

hydrotalcite (HT) with stronger basicity are synthesized throughexchanging CO32 with OH and are used to catalyze aldol con-densations in the preparation of CFR. To obtain high crystallinity,MgAl HT was synthesized by a urea method in which pH of thesolution can be kept at a homogeneous level and agglomerationcan be avoided [17,18]. The exchanging CO32 with OH was real-ized through the liquid rehydration of MgAl HT [19]. Consideringliquidliquidsolid multi-phase reaction, the phase transfer cata-lyst CTAB was introduced to enhance the mass transfer. The effectof reaction temperature, reaction time and catalyst loading oncatalytic activity were studied. Furthermore, the reutilization andregeneration of the catalyst were investigated, too.

2. Experimental

2.1. Synthesis of HT

Mg(NO3)26H2O(15.38 g), Al(NO3)39H2O (7.50 g) and urea(21.62 g) (nMg2+ : nAl3+ = 3; nurea : nNO3+ = 2 : 1) was dissolved indeionized water (150 ml) and the solution was fed into a 250 mlask equipped with a condenser and a mechanical stirrer. The solu-tion was agitated at 100 5 C under 400 rpm for 10 h and then aged

rg/10.1016/j.porgcoat.2014.09.0202014 Elsevier B.V. All rights reserved.sis of cyclohexanone-formaldehyde resated MgAl hydrotalcite

g, Junqing Jiang, Yanwu Zhang

ical Engineering and Energy, Zhengzhou University, Zhengzhou 450001, China

e i n f o

ly 2014vised form

2014eptember 2014e 22 October 2014

atione-formaldehyde resinlcitelyst

a b s t r a c t

Cyclohexanone-formaldehyde resin (Therein, MgAl HT was rehydrated fdrated MgAl HT (HT-r) shows certaidramatically improved in the presencas a phase transfer catalyst is helpful tperature and longer reaction time arcatalytic activity of HT-r decreases as regenerated upon calcining and rehyd

ction aldol ccatalyzed by

was synthesized over rehydrated MgAl hydrotalcite (HT).gAl HT of good crystallinity using a liquid method. Rehy-

alytic activity for aldol condensation and catalytic activity isexadecyl trimethyl ammonium bromide (CTAB) because CTABance the mass transfer among three phases. Both higher tem-ferable to increase the molecular weight of CFR. Though theutilization cycle increases, the deactivated HT-r can be easilyg.

2014 Elsevier B.V. All rights reserved.

nsations, etherication reaction and transethericaion

56 G. Yang et al. / Progress in Organic Coatings 78 (2015) 5558

statically without agitation at the same temperature for another20 h. The resulting slurry was ltrated and washed with deionizedwater until the pH value was equal to 7. The solid was dried for 24 hat 90 C and named as HT.

2.2. Rehydration of HT

HT was calcinated at 500 C under N2 for 8 h in the furnace.The obtained MgAl mixed oxide was named as HT-c. Deionizedwater (400 ml) was heated to 40 C in a 500 ml ask equipped witha mechanical stirrer and bubbled with N2 for 30 min. Then HT-c(4.00 g) was dispersed into it and the vigorous stirring continuedfor 8 h under N2. The suspension was ltrated to obtain solid rehy-drated HT. After drying at 40 C in vacuum for 24 h, the product wasnamed as HT-r.

2.3. Synthesis of CFR

Formaldehyde aqueous solution (37%, 10.97 g), cyclohexanone(10 ml), CTAask equipThe mixturcarbonationHT-r was cwith methyproduct wa

2.4. Charac

X-ray pwith a Shim( = 0.1542 microscopyment operato 4000 cmtional viscoviscometer

3. Results

3.1. Synthe

Accordinproved to hof same compattern of smetric charUpon calcincorrespondstructure of

). Ho (Figteriz

in Fitione tha

(Fig struults

dol c

to ded nd crent

incre yie

to inn waphass a pan cacloheB incst enhesized CFR is shown in the Fig. 3. The strong band at aboutm1 is ascribed to C O absorption peak. The band at aroundm1 is the absorption peak of OH. The band at 1448 cm1

) and HT-r (c).B (0.50 g) and HT-r were fed into a three-necked 100 mlped with a reux condenser and a mechanical stirrer.e was stirred at certain temperature under N2 to avoid

of HT-r for a period of time. After the reaction ended,ollected by centrifugation. The product was extractedlbenzene and then precipitated in ligarine. The solids dried overnight in vacuum at 25 C.

terization

owdered diffraction patterns (XRD) were recordedadzu XRD-6000 powder diffractometer using Cu K

nm) radiation (40 kV and 30 mA). Transmission electron (TEM) was performed using JEOL-JEM 1200 equip-ting at 100KV. FT-IR spectra were recorded from 400

1 on a Thermo Nicolet IR 200 spectrometer. The rota-sity of CFR solution was determined by Rotating cylinder

LVDV-2 (Shanghai Jingtian Co.).

and discussion

sis and rehydration of HT

g to Javier, MgAl HT with MgAl molar ratio of 3:1 hasave higher catalytic activity [20]. Therefore, MgAl HTposition was synthesized by a urea method. The XRD

ynthesized HT is shown in Fig. 1a. The sharp and sym-acteristic peaks indicate that HT has good crystallinity.ations, the disappearance of the characteristic peaksing to the layered structure indicates that the layered

HT is destroyed and MgAl double mixed oxide forms

(Fig. 1bdrationcharacshowncalcinaindicatdrationlayeredthe res

3.2. Al

Duewas adhyde ais diffeweightthat thminedreactiothree CTAB aHT-r cand cyof CTAand juof synt1711 c3449 c

Fig. 2. TEM images of HT (a), HT-c (bFig. 1. XRD patterns of HT (a), HT-c (b) and HT-r (c).

wever, the layered structure is recovered after the rehy-. 1c). The microstructure of HT, HT-c and HT-r wased with TEM and their images are shown in Fig. 2. Asg. 2a, HT has a well-developed layered structure. Upon

at 500 C for 8 h, a porous platelet structure forms whicht HT is transformed to MgAl mixed oxide due to dehy-. 2b). When HT-c is rehydrated by a liquid method, thecture is recovered (Fig. 2c). This is in agreement with

of XRD.

ondensation catalyzed by HT-r

easy volatility of formaldehyde, excess formaldehydein the reaction and the mole ratio between formalde-yclohexanone ratio was set as 1.4. Preparation of CFR

from simple aldol condensation because moleculareases as aldol condensation proceeds. Herein, exceptld, CFR viscosity of toluene solution (30 wt%) was deter-directly characterize molecular weight of CFR. When thes catalyzed by HT-r, there existed liquidliquidsolid

es in the reaction system. To enhance mass transfer,hase transfer catalyst was added. As shown in Table 1,talyze the aldol condensation between formaldehydexanone with low yield and the yield of CFR with the aidreases dramatically. CTAB itself has no catalytic activityhance the mass transfer among phases. FT-IR spectrum

G. Yang et al. / Progress in Organic Coatings 78 (2015) 5558 57

Table 1Yields of CFR for different catalysts.a

Run CTAB (g) HT-r (g) Yield (%)

1 0 0.758 7.922 0.5 0 03 0.5 0.758 66.61

a Reaction condition: reaction temperature 75 C, reaction time 20 h, catalystloading 8 wt%.

is the absoabsorption

Accordinelemental rcyclohexanhexanone, 1-hydoxymtion to formimportant rfor differentime is beyoviscosity incyclohexanlongation oyields and vplotted in Fthe yield cabe ascribed75 C. The vwhich indiction.

ffect of reaction time on CFR yield and viscosity (reaction condition: 8 wt%C, 0.5 g CTAB).

ffect of reaction temperature on CFR yield and viscosity (reaction condition:Fig. 3. FT-IR spectrum of synthesized CFR.

rption peak of CH2 and the band at 2933 cm1 is thepeak of CH.g to synthetic mechanism of CFR, there involve twoeactions (Scheme 1). One is the condensation betweenone and formaldehyde to create 1-hydoxymethyl cyclo-and the other is the condensation polymerization ofethyl cyclohexanone through inter-molecule dehydra-

Fig. 4. EHT-r, 75

Fig. 5. E

macromolecules. Reaction time and temperature playoles in synthesis of CFR. The yields and viscosities of CFRt reaction time are plotted in Fig. 4. When the reactionnd 5 h, the yield slightly decreases on the whole and thecreases. This indicates that the condensation betweenone and formaldehyde can be nished in 5 h and pro-f reaction time just increases the molecular weight. Theiscosities of CFR for different reaction temperature areig. 5. When the reaction temperature is beyond 75 C,lculated based on weight decreases slightly. This may

to the decrease of weight caused by dehydration aboveiscosity increases as the reaction temperature increases,ate that higher temperature is preferable to condensa-

Scheme 1. Synthetic mechanism of CFR.

8 wt% HT-r, 10

The effetoo. The yiplotted in Fthe catalyst8 wt%, their

Fig. 6. Yields tion: 75 C, 20 h, 0.5 g CTAB).

ct of catalyst loading on aldol condensation was studiedelds and viscosities for different catalyst loadings areig. 6. Both the yield and viscosity of CFR increase as

loading increases. When the catalyst loading is beyond increments are not obvious.

and viscosities of CFR for different catalyst loadings (reaction condi- h, 0.5 g CTAB).

58 G. Yang et al. / Progress in Organic Coatings 78 (2015) 5558

3.3. Reutiliz

To studydirectly at tfor three timdecreases ato the deacTo study thcycle was cused at thein Fig. 8. Th92.6% of theactivity canto shape me

4. Conclus

MgAl Hmethod. Up

can be recovered and interlayer CO32 was replaced by OH. Rehy-drated HT (HT-r) shows catalytic activity for aldol condensation inthe preparation of CFR. With the help of CTAB, CFR can be synthe-sized over HT-r. Both the yield and viscosity of CFR increase as thecatalyst loading increases. Higher temperature and longer reactiontime are preferable to increase the molecular weight of CFR. Afterthe regeneration, catalytic activity of HT-r can be recovered to ahigh level after the regeneration due to shape memory effect of HT.

wled

s wo Chie Ed

nces

en, Qanoneymer . Hasmaleate. J. PlasGuidaClaiseetone 264. Berb

materothe. Li, J.hFig. 7. Effect of reutilization times on yields.

Ackno

Thition ofChines

Refere

[1] H. RhexPol

[2] S.P(mInt

[3] A. of lac251

[4] M.Rlikehyd

[5] X.hFig. 8. Effect of regeneration times on yields.

ation and Regeneration of HT-r

the reutilization of HT-r, HT-r was collected and reusedhe same condition after one catalysis cycle. The yieldses are plotted in Fig. 7. The catalytic activity gradually

s the reutilization time increases. This can be ascribedtivation of HT-r caused by CO2 during the application.e generation behavior of HT-r, HT-r after one catalysisalcined and rehydrated. Then the regenerated HT-r was

same condition. The yields for three times are plottede yield after three regeneration cycles still reaches to

yield for fresh HT-r. This indicates that their catalytic be recovered to a high level after the regeneration duemory effect of HT.

ions

T with high crystallinity was synthesized by a ureaon calcination and rehydration, layered structure of HT

via esteri(2013) 68

[6] V.V. Ivanosolution

[7] T. Kamedered doulayered dfrom aqu

[8] S.H. Waof hydrsolid ba135141

[9] X.M. Xie,CuFe-hy

[10] S. Britto, layered d119311

[11] C.L. Xu, Yhighly acAdv. 3 (2

[12] K. Winniered dou

[13] C.N. Peremixed oxAppl. Cat

[14] K.R. Kottalcite c115121

[15] K. Piotr, Sthe activiacetone,

[16] J.Q. Jiang,ene glycoTechnol.

[17] H.Y. Zenmethod 122912

[18] P.P. YangReact. Kin

[19] D. Tichit,on hydro

[20] S. Abelloof activa119125gment

rk was supported by National Natural Science Founda-na (50903074) and Key Scientic Research Project ofucation Ministry (212107).

.Y. Zhang, X.W. Chen, A molecular simulation study of a series of cyclo- formaldehyde resins: properties and applications in plastic printing,48 (2007) 887893.ukh, M.N. Amel, Novel unsaturated polyester resins based on

d cyclohexanone-formaldehyde resin)-(epoxy resin) condensation,t. Technol. 13 (2010) 1737., M.H. Lhouty, D. Tichit, Hydrotalcites as base catalysts: kineticsnSchmidt condensation, intramolecular condensation of acetony-and synthesis of chalcone, Appl. Catal. A: Gen. 164 (1997)

.er, I.H. Hafez, K.J. Minagawa, Uniform nanoparticles of hydrotalcite-rials and their textural properties at optimized conditions of urearmal treatment, J. Mol. Strut. 1033 (2013) 104112.. Zhu, Q.L. Liu, The removal of naphthenic acids from dewaxed VGOcation catalyzed by MgAl hydrotalcite, Fuel Process. Technol. 11177.va, S.D. Kirikb, A.A. Shubina, Thermolysis of acidic aluminum chloride

and its products, Ceram. Int. 10 (2012) 226232.a, K. Hoshi, T. Yoshioka, Thermal decomposition behavior of CuAl lay-ble hydroxide, and ethylenediamine tetraacetate-intercalated CuAlouble hydroxide reconstructed from CuAl oxide for uptake of Y3+

eous solution, Mater. Res. Bull. 47 (2012) 42164219.ng, Y.B. Wang, Y.M. Dai, Preparation and characterizationotalcite-like compounds containing transition metal as ase catalyst for the transesterication, Appl. Catal. 439 (2012).

X. An, K. Yan, A new way to synthesize benzoin isopropyl ether ondrotalcite, J. Nat. Gas Chem. 19 (2010) 7780.P.V. Kamath, Thermal, solution and reductive decomposition of CuAlouble hydroxides into oxide products, J. Solid State Chem. 182 (2009)99.. Gao, X.H. Liu, Hydrotalcite reconstructed by in situ rehydration as ative solid base catalyst and its application in aldol condensations, RSC013) 793801.e, J. William, Aldol condensation of acetaldehyde using calcined lay-ble hydroxides, Appl. Clay Sci. 10 (1995) 95102.z, C.A. Perez, C.A. Henriques, Hydrotalcites as precursors for Mg, Al-ides used as catalysts on the aldol condensation of citral with acetone,al. 272 (2004) 229240.tapalli, G. Monique, S.V. Jaime, Activation of MgAl hydro-atalysts for aldol condensation reactions, J. Catal. 173 (1998).. Dominika, C. Lucjan, Inuence of thermal treatment conditions onty of hydrotalcite-derived MgAl oxides in the aldol condensation ofMicroporous Mesoporous Mater. 78 (2005) 1122.

Y.W. Zhang, Y.H. Zheng, Transesterication of soybean oil with ethyl-l catalyzed by modied LiAl layered double hydroxides, Chem. Eng.36 (2013) 13711377.g, X. Deng, Y.J. Wang, Preparation of MgAl hydrotalcite by ureaand its catalytic activity for transesterication, AIChE J. 55 (2009)35., J.F. Yu, Z.L. Wang, Urea method for the synthesis of hydrotalcites,et. Catal. Lett. 83 (2004) 275282.

D. Lutic, B. Coq, The aldol condensation of acetaldehyde and heptanaltalcite-type catalysts, J. Catal. 219 (2003) 167175., D.V. Shankar, J.P. Ramirez, Stability, reutilization, and scalabilityted hydrotalcites in aldol condensation, Appl. Catal. A 342 (2008).

Synthesis of cyclohexanone-formaldehyde resin catalyzed by rehydrated MgAl hydrotalcite1 Introduction2 Experimental2.1 Synthesis of HT2.2 Rehydration of HT2.3 Synthesis of CFR2.4 Characterization

3 Results and discussion3.1 Synthesis and rehydration of HT3.2 Aldol condensation catalyzed by HT-r3.3 Reutilization and Regeneration of HT-r

4 ConclusionsAcknowledgmentReferences