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超声场对碳酸钙反应结晶成核影响的研究

2021-03-25 来源:好走旅游网
维普资讯 http://www.cqvip.com №.j ・陕西科技大学学报 joURNAL OF SHAANXI UNIVERsITY OF SCIENCE&TECHN0L0GY Feb.2007 26・ Vo1.25 文章编号:1000--5811(2007)01--0026--06 EFFECT oF ULTRASoUND oN THE NUCLEATIoN oF CALCIUM CARBoNATE DURING REACTIVE CRYSTALLIZATIoN HANG Fang—xue ,LU Qun。,OIU Tai—qiu ,YAO Cheng-can (1.Light and Chemical Industry Institute,South China University of Technology,Guangzhou 510640,China; 2.College of Light Industry and Food Engineering,Guangxi University,Nanning 530004,China;3.Guang- dong College of Pharmacy,Guangzhou 5 10240,China) Abstract:The effect of ultrasound on reactive crystallization is studied by measuring the in— duction time.Calcium carbonate is used as the working substance precipitated by mixing CaC12 and Na2 CO3/NaHCO3 solutions.The experiments were carried with various frequen- cies and insonation time.It is observed that the induction time significantly decreases with increasing insonation time.The mechanism of the ultrasonic effect on nucleation is analyzed. The two effects of ultrasound are discussed.The surfaca tension(y)decreased and the diffu— sion coefficient(DAB)increased in the ultrasound.The induction time reduced after ultra- sound treating. Key words:ultrasound;induction time;crystallization;nucleation CLC Number:TS20 1 Document:A 0 Introduction Uhrasound enhanced crystallization was first observed in 1927 when ultrasound was applied to a su— persaturated thiosulphate solution. In the last decade,sonocrystallization has received much attention. The ultrasonic effect on crystallization has been reported to increase nucleation rate[ ]:change the crys— tal size,size distribution and crystal habits[ ];change the crystal character;depress agglomeration and agglomerate particles[。];accelerate crystal precipitation[4];retard precipitation. In industry,many precipitations of mineral precipitate at undesired location like heat transfer sur— face in heat exchanger and conveyance system.This deteriorates the heat transfer efficiency of heat ex— changer and leads to partial or even total blockage of water flow in the conveyance systems.In most eft— ses,these scales are composed of calcium carbonates,phosphates,and sulfate hydrates Es,6]. In this paper,calcium carbonate,the major scale forming component,is used as the working sub— stance precipitated by mixing aqueous solutions of CaC12 and NaCO3/NaHCO3.The focus of this paper is to work out the effect on induction time.Induction time,”rhich has an inversely proportional relation— ship with nucleation rate,is studied to determine the ultrasoni ̄effect on primary nucleation in lf reactive crystallization process.From this,the mechanism of ultrasonic effect on nucleation is also investigated. 1 Theory When ultrasound propagates through lf liquid medium,its power not only is fl driving force for mass transfer,but also initiates an important phenomenon known as cavitation.Cavitation bubbles form dur— ing the negative-pressure period of the sound wave.When fl cavitation bubble implodes,fl localized hot spot is formed with a high temperature and high pressure with the release of a powerful shock wave. 收稿日期:2006—11—06 作者简介:杭方学(1978一).男,广西自治区南宁市人,在读博士生,研究方向:声化工技术及其应用 基金项目:广东省自然科学基金(980534),广东省重点科技项目(99M02002G) 维普资讯 http://www.cqvip.com 第1期 杭方学等:超声场对碳酸钙反应结晶成核影响的研究 .・ 27 ・ The collapse time of a The reason for the above phenomena is that the collapse process is very rapidcavitation bubble is normally very short compared to its birth time.The power of ultrasound and cavita— tion phenomena influence primary nucleation during crystallization processes[ . Using the classical primary nucleation theory,the rate of homogenous nucleation can be obtained from the number of critical clusters that cross the nucleation barrierTherefore,the nucleation rate(B) .can be expressed as follows E8,93: B0一k'n0exp(一 zSG)z. (1) Where B is homogenous nucleation rate,k is coefficient which cluster cr0ss the barrier,no is the number concentration of molecules in the supersaturated solution,zSG is the free energy of critical clus— ter,k is Boltzman constant,T is absolute temperature,and Z is imbalance factory. The free energy AG can be expressed by following equation: 岳 zXG一 . (2) Where y is the surface tenstionm,V is the molecularvolume,and S is supersaturation ratio. The molecular volume(Vm)is given by Vm ・. . (3) Where NA is Avogadro S number,and Cc is molecular densitv of solid. The coefficient k can be derived from: k 一÷ DABAc. (4) Where DAB is the diffusion coefficient and Ac is the surface area of cluster. The imbalance factory(Z)is given by E83 厶一,7一\/ 一 一亍一^、//z3rcSkGc一 Ti ̄一rcCc ̄l2 AL c24 /y (5) Where Q is quantity of heat,ic is the critical cluster number,and Lc is the lcuster diameter.So inser— irng Eqs.(1)~(5),the homogeneous nucleaetion rate can be obtain from the following equation: Bo—1.5DAB(CN^)i7 1 ex 丽 南 ). (6) Where V is the number of moles of ions that formed from one mole of electrolyte. The induction time is normally found to have an inverse ratio relationship with nucleation rate.It can be expressed by 一 ㈩ Where K is a coeffictent of proportionality.Combining Eq.(6)and(7),the following equation is ob— tained: 砌一l一一1 ̄-5.DAB(CN^); 1 exp(_丽 . (8) Taking the natural logarithm on each side of Eq.(8): lntind—Alln-。S+B1. (9) Where Al= 16u 3v (志T)。(CcN^v) ‘ (10) Bt—ln D邶(CN 7 1 CcN A’ (11) 维普资讯 http://www.cqvip.com ・ 28 ・ 陕西科技大学学报 第25卷 From the slope and intercept of the lines which express the relationship between ln S and ln(tind), the effect of ultrasound on every parameter can be analyzed. 2 Materials and Methods 2.1 Experimental equipment The ultrasonic equipment,used in our experiments,is manufactured by Wuxi Uhrasonic Equipment Factory,China and emits vibration waves and induces cavitation voids throughout a defined volume of liquid.The experiments were performed using the ultrasonic bath assembly(Frequency..16.5 kHz,25 kHz). 2.2 Materials and procedure The induction time experiments were Carried out at 25℃.Calcium carbonate,precipitated by rapid— ly mixing aqueous CaC12 and Na2 CO3/NaHCO3 solutions,was used as the working substance to study the uhrasonic effect on homogenous nucleation during reactive crystallization process.To study the in— duction time,two solutions must be mixed quickly.After the above CaC12 solution was transferred in to vessel,the impeller and the conductivity were switched on.After the signal of conductivity become sta— ble,Na2 CO3/NaHCO3 solution was immediately injected into the vesse1.The power ultrasound was run simultaneously.During the experiments,the temperature was kept at 25 C and the agitation was kept. Two different fr6quency were selected.During insonation,the electrical power to produce the ultra— sound adjusted to 250 W.And the period of application was 5 min,10 min,15 min.The experiments were performed in a water bath vesse1.Mixing was achieved with the use of a pitch blade impeller.The solutions were mixed by CaCO3 and Na2 CO3/NaHCO3,pH 10.0,with a series of the supersaturation ra— tios of solutions.The concentration of CO3_。retained 2.83×10一。mo1.L_。. 2.3 Induction time assay The conductivity method was chosen to determine the induction time.The induction time was detec— ted by a conductivity meter.The change of conductivity,which was record as the change of input volt— age。was collected.The signal remained constant before the solutions mixed.This was followed by a sudden deerease indicating the onset of nucleation.The time between the initial mixing and the first ob— served change of conductivity is defined as the induction time. 3 Result and Discussion 3.1 Effect of ultrasound on induction time The induction time(t nd)is defined as the time interval between the establishment of supersaturation and the formation of critical nuclei.It is expressed as tind=t,+t + ,the slim of three terms,the sub— script t denoting relaxation time,t stable nucleation and tg detectable grown crysta1.In our experi— ment,the two solutions mixed quickly,at high supersaturation,the t,and tg are very short and are vir— tually undistinguishable.Therefore,tind-- ̄t- .The induction period for the material is taken from the in— lfection point of the conductivity as mentioned in the experimental section. The resuIt of induction time experiment with and without ultrasound is shown in Fig.1 Fig.2.The induction time decreased when supersaturation increased with and without ultrasound.However,it was observed that ultrasound had a significant effect in reducing the induction time from the esperiments.At the same supersaturation level。the induction time reduces with,increasing insonation time. The plots of In一 (S)versus ln(tiIld)are shown in Fig.3,Fig.4.The values of slope and intercept of straight line without ultrasound are 10.467 and一2.118 9,respectively.When ultrasound are applied to the system。the corresponding values for straight line with 16.5 kHz,insonation 5 min are 10.215 and 一2.325;16.5 kHz,insonation 10 min:10.077 and一2.402 9;16.5 kHz,insonation 15 min:9.934 8 and一2.429 6;25 kHz,insonation time 5 min:8.858 3 and一1.637 8;25 kHz,insonation time 10 min:8.339 1 and—1.571 2;25 kHz,insonation time 15 min:7.820 9 and~1.410 4.The slopes of straight Iines reduce with increasing the insonation time.The slopes in 25 kHz are lower than those in 维普资讯 http://www.cqvip.com ^,q,)tIH 第1期 杭方学等:超声场对碳酸钙反应结晶成核影响的研究 ・ 29 ・ ; . 450 J 3o0 150 0 3 3.5 4 4.5 5 3 3,5 4 4.5 5 S S Fig.1 Induction time as u function of super- Fig.2 Induction time as a function of super- saturation ratio:(41')without ultrasound. saturation ratio:(◆)without ultrasound. (口)the frequency is 16.5 kHz,insonati- (口)the frequency is 25 kHz,insonati- on time 5 min.(▲)the frequency is 16.5 on time 5 min.(▲)the frequency is 25 kHz,insonation time 10 min.(●)the fre_ kHz,insonation time 10 min.(●)the fre_ quency is 16.5 kHz,insonation time 15 min quency is 25 kHz insonation time 15 min 7.5 })c一 6 5 4 3 7 7 5 6 5 5 5 4 5 3 6.5 6 5.5 5 4.5 4 3.5 3 0.6 o.7 o.8 o.9 0.6 0.7 0.8 0.9 In 5 tf s Fig.3 Induction time as a function of super- Fig.4 Induction time as a function of super- saturation ratio:(◆)without ultrasound. asturation ratio:(◆)without ultrasound. (口)the frequency is 16.5 kHz,insonati- (口)the frequency is 25 kHz,insonati- on time 5 min.(▲)the frequency is 16.5 on time 5 min.(▲)the frequency is 25 kHz,insonation time 10 min.(●)The fre- kHz,insonationtime 10 min.(●)the fre- quency is 16.5 kHz,insonation time 15 min quency is 25 kHz insonation time 15 min 16.5 kHz at 5,10,15 min,respectively.But the intercepts are different. 3.2 Effect of ultrasound on the surface tension The mechanism of ultrasound radiation on homogeneous nucleation can be analyzed from Eq.(9). When ultrasound is applied to the system,the ultrasonic power will influence the surface tension.Ultra— sound may accelerate diffusion and increase as wel1. The straight lines of InS versus In(t nd)with different insonation time have different slopes.From Eq.(10),although the three slopes(16.5 kHz or 25 kHz)are similar,they decreased with increasing insonation time.It can be concluded that ultrasound has little influence on surface tension(),).In super— saturated solution,Ultrasound irradiation will induce cavitation.The cavitation bubbles expand,col— lapse and break quickly,causing the changes of energy.The energy of each point in the system changes due to the nonlinear and alternation vibration of the cavitation bubbles and the pressure caused by the collapse of bubbles,lowering the force between the solute molecules,reducing the surface tension and causing the tiny particles to move and collide with each other more quickly and easily.A large number of nuclei can be produced in a short time,reducing the induction time.The cavitation is induced more with increasing insonation time。and the surface tension becomes lower.Thus,it・is easier for the solute to 维普资讯 http://www.cqvip.com H墨∞ HU ・3O・ 陕西科技大学学报 nucleate,reducing the induction time. ‘ 第25卷 . ▲3.3 Effect of ultrasound on the diffusion coeffi— nt From Eq.(1 1),another influence of ultra一 善sound must be on DAB.The intercepts of straight J lines increased with increasing insonation time and frequency.From the results,it can be inferred that ultrasound can accelerate diffusion and significantly Fig.5 c蚰centration driving forces in crystailiza.shorten induction time・It is shown on Fig・5 about ti蚰f0m solution .two steps in the model of the mass dePos。t。0n process.First is a diffusion process,whereby sol— ute molecu1es are transported from the bulk of the fluid phase through a stagnant film to the solid sur— face.Sec6nd,a reaction process when the solute molecules arrange themselves into the crystal lattice. From the change of intercepts,the magnitude of enhancement of diffusion coefficient with insona— tion time and frequency input can be obtained.When the cavitation bubbles collapse,rapid fluids,such as acoustic streaming and micro streaming,are produced.The thickness of the stagnant film and the ad— sorption layer can be thinned by streaming.It is a significant effect on accelerating the diffusion process, which will increase mass deposition rate and make more solute molecules cross the size barrier and be— come crvstal nuclei.The cavitation is induced more with increasing insonation time,making diffusion co— efficient higher,nucleation easier and the induetion time shorter. , 4 Conclusions The effects of ultrasound on reactive crystallization were investigated by measuring the induction time. Ca1cium carbonate is used as the working substance precipitated.The experiments were carried with uItrasonic frequencies in 16.5 kHz,25 kHz and insonation time at 5,10,15 min.It is observed that uItrasound have significant effects in reducing the induction time.In the experiments,the induction time decreases with increasing insonation time. The mechanism of the ultrasonic effect on nucleation is analyzed. It is found that there are two effects. The surface tension reduces because of the nonlinear and alternation vibration of the cavitation bubbles and the pressure caused by the collapse of bubbles.Thus,it is easier to nucleate.Another effect of uItrasound is to increase diffusion coefficient.The stagnant film and adsorption Iayer must be thinned bv acoustic and micro streaming. Ultrasound has an effect on accelerating the diffusion process.The change of surface tension and diffusion coefficient reduce the induction time. References [1INathalie Lyezko,Fabienne Espitalier,Olivier Louisnard,et a1.Effect of ultrasound on the induction time and mestable zone wodths of potassium sulphate[J].Chemical Engineering Journal,2002,86:233—241- C23Hong Li,Jingkang Wang,Yin Bao,eta1.Rapid sonoerystaflization in the salting-out process[J].Journal of Crystal Growth'2003, 247:192—198. [33Z.Guo,M.Zhang,H.Li,et口z:Effect of ultrasound on anti—solvent crystallization process[J].Journal ofCrystalGrowth,2005, 273:555-563. C43I.Nishida.Precipitation of calcium carbonate by ultrasonic irradiation[J].Ultrasonics Sonochemistry,2004,11I 423。428・ C5]J Lee。N Kim.B Park.Effect of ultrasound on crystallization behavior and ferroeleetrie prope ̄ies of sol。gel-derived Pb(Zr,Ti)Os thin iflm[J].Journal of Crystal Growth,2001,222:289。292. C63Hong Li,Hairong Li,Zhichao Guo,et a1.The application of power ultrasound to reaction crystallization[J].Ultrasonics Sono‘ chemistry,2006,13t359—363. C73Z.Guo,A.G.Jones,N.Li.The effect of ultrasound on the homogeneous nucleation of BaSO4 during reactive crystallization[J]. ChemicaI Engineering Science・2006,61}1 617-1 626. 维普资讯 http://www.cqvip.com 第1期 杭方学等:超声场对碳酸钙反应结晶成核影响的研究 [83Z.Guo,A.G.Jones,N.Li.The effect of uhrasound o n the homogeneous nucleation of BaSO4 during reactive crystallization[J]. Chemica1 Engineering Science,2006,61:1 617-1 626. I [93A.Mersmann.B.Braun.M.Loffelmann.Prediction of crystallization coefficients of the population balance[J].Chemical Engi— neering Science,2002,57。4 267—4 275. 超声场对碳酸钙反应结晶成核影响的研究 杭方学 ,卢 群。, 丘泰球 ,姚成灿 (1.华南理工大学轻工研究所,广东广州 510640;2. 广西大学轻工与食品工程学院,广西南宁530004; 3.广东药学院,广东广州 510224) 摘 要:研究了超声场作用对反应结晶过程中成核诱导期的影响.以碳酸钙为实验对象,在不 同频率和超声作用时间下观察了成核诱导期的变化,结果表明,结晶诱导期随着超声作用时间 的增加而缩短.机理分析认为超声场对成核过程的主要影响有两个方面:溶液表面张力的下降 和扩散系数的上升.超声场作用可降低成核诱导期. 关键词:超声场;诱导期;结晶;成核 中图分类号:T¥201 文献标识码:A (上接第25页) [123 Germana B,Luciana B,Giovanni P,et a1.Flavor compounds of dry-cured ham EJ3.J.Agric.Food Chem.,1992,40:2 389—2 394. [133 Grosch。W.Lipid degradation products and flavours.In food flavours[M3.Amsterdam:Elsevier,1982. C143 Lillard D A,Day E A.Degradation of monocarbonyls from autoxidizing lipids[J3.J.Am.Oil Chem.Soc.,1964,41:549—552. [1 53 Vernin G,Parkanyi I .Mechanisms of formation of heterocyclic compounds in Maillard and pyrolysis reactions.In chemistry of heterocyclic compounds in flavors and aromas I-M].Chichester,U.K.:Ellis Horwood.1982. [163 MacLeod G,Coppock B M.A comparison of the chemical composition of boiled and roast aromas of heated beef[J3.J.Agric. Food Chem.,1977,29:834—836. [173 Bell L N.Peptide stability in solids and solutions[J3.Biotechno1.Prog.,1997,13:342—346. [183 Cambero M I,Pereira—Lima C I,Ordohez J A,et a1.Beef broth flavor:relation of components with the flavor developed at differ- ent cooking temperatures[J3.J.Sci.Food Agric..2000,80。1 519—1 528. 加热灭酶对鸡骨酶解产物风味影响的研究 曾晓房,赵谋明,王金水,崔 春,赵强忠 (华南理工大学轻工与食品学院,广东广州 510640) 摘 要:采用差别成对比较和评分法评价了灭酶前后鸡骨风味的变化,采用GC-MS联用仪鉴 定了灭酶前后鸡骨风味成分的差异,分析研究了鸡骨酶解过程中加热灭酶对产物风味的影响. 感观检验结果表明,加热灭酶有利于鸡骨酶解产物整体风味的改善,有助于消除不良风味,增 强鸡脂风味和鸡肉风味.GC-MS分析结果表明,加热灭酶能增加酶解产物总体风味物质数量 以及相对风味强度,产生新的风味物质,如二烯醛和含氮杂环物质;加热灭酶过程中,油脂氧化 是造成酶解产物风味差异的主要原因,其次还可能与蛋白质和肽的降解产物与还原糖之间的 Maillard反应有关. 关键词:鸡骨酶解产物;风味特征;加热灭酶;GC-MS分析 中图分类号:TS201 文献标识码:A 

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