Polymerization Technology Laboratory

Transcription

1 Versuch eacion Calorimery Polymerizaion Technology Laboraory eacion Calorimery 1. Subjec Isohermal and adiabaic emulsion polymerizaion of mehyl mehacrylae in a bach reacor. 2. Theory 2.1 Isohermal and adiabaic calorimery The mos imporan informaion needed for he reacor design for polymerizaion reacions is he hea emission of he reacion over he ime. A good hea dissipaion o he cooling sysem is necessary o avoid accidens. In many cases, lieraure daa are no available for he desired reacion, so ha own measuremens have o be done. For measuremens in he laboraory scale, reacion calorimery is a pracical mehod. This mehod measures he ical hea flow of a reacion which is proporional o he reacion rae. In general, he measuremens are done in a sirred ank reacor wih a hermosa and a compuer. Temperaure sensors are placed in he reacor (in he reacion mass) and in he ouer cooling jacke. The hermosa measures he inner emperaure and regulaes he jacke emperaure in he desired way. eacion Calorimery (SS 2002) Seie 1/6

2 Versuch eacion Calorimery The general hea flow balance of he calorimeer is given as follows [ W ] = + + P accu cond loss = V ( H ) r reacion hea flow accu = V = reacion volume, H = reacion enhalpy, r = reacion rae C p dt C p, hea sorage in he reacion mass [ J / K] = c p imi = hea capaciy of he reacion micure i cond = U A T ( ) conucive hea flow hrough he wall o he cooling jacke U = overall hea ransfer coefficien [W/(K. m 2 )], T = emperaure of he reacor, T J = emperaure of he jacke, A = area of he jacke Q & loss Q & P loss hea flow o he environmen hea flow given in he reacor wih an ecric heaer for calibraion hea flow produced by sirring Now we look a wo special cases o conrol a polymerizaion reacion a) isohermal In he isohermal case he reacion mass is kep a conan emperaure obver he whole reacion ime. For ha reason an occurring hea flow, produced by ical reacion, mus be absorbed o he cooling jacke. Thus he jacke will immediay be cooled down by he hermosa, when he reacion sars. eacion Calorimery (SS 2002) Seie 2/6

3 Versuch eacion Calorimery In he isohermal case he general hea flow balance can be reduced o = P = U A( T T ) cond J P Hea sorage in he reacion mass does no occur, because i is kep a consan emperaure. The loss hea flow is negleced and if he viscosiy of he reacion mass remains low (as i is he case in an emulsion polymerizaion), he hea flow produced by he sirrer can be negleced, oo. In pracice, a sricly consan emperaure in he reacion mass canno be reached. Therefore, he sorage or accumulaion erm canno be negleced. Before an experimen is sared, he produc of he overall hea ransfer coefficien wih he jacke area U. A has o be deermined. The calibraion is done by providing a defined hea flow o he reacor by means of an ecric heaer: U A = ( T, heaing, heaing ) ( T ) T heaing TJ, heaing,, = reacor, jacke emperaure when ecric heaer is on The calibraion is done one ime before and one ime afer he reacion in order o see if any aleraions occur during he reacion. The hea ransfer coefficien migh change due o precipiaed polymer covering he reacor wall. b) adiabaic In his case he jacke emperaure is se o he same emperaure as he reacion mass. If he emperaure in he reacion mass increases by ical reacion he jacke emperaure does also! In an ideal case no hea flow from he reacor o he jacke occurs because boh of hem have he same emperaure. The hea balance is Q & = Q & accu P = C p dt P The deeced emperaure is proporional o he conversion of he reacion if only one reacion occurs. In general, an isohermal conrol of he polymerizaion reacion is desired in he indusrial eacion Calorimery (SS 2002) Seie 3/6

4 Versuch eacion Calorimery scale because no emperaure rise in he reacor influences he reacion. The funcion of adiabaic calorimery is he simulaion of he wors case scenario in a small laboraory scale, i.e., failure of he cooling sysem and unconrolled increase of emperaure in he reacor. The adiabaic emperaure difference Tad is he maximum heaing of he reacor by is own reacion. 2.2 Deerminaion of kineic daa By deerminaion of he hea flow of he reacion, he reacion enhalpy and rae of conversion dx/ can be calculaed: dx = end 0 H ( ) X ( ) = = H 0 end 0 H, he conversion X 0 and end are he imes of he beginning and of he end of he measured hea flow peak (inegraion limis). H () is he reacion enhalpy a ime (parial peak area) and H is he complee enhalpy of he reacion (complee peak area). The ideal case is simple: only one kind of reacion and 100% conversion. In pracice, however, simulaneous reacions occur and 100% conversion is no reached! Therefore, he measured hea flow is he sum of he hea flows of all occurring reacions. 2.3 Wilson plo The Wilson plo is a mehod for deermining hea ransfer daa and geomeric daa of a given reacor. The produc of overall hea ransfer coefficien and jacke surface is measured in dependence on he sirrer speed N U A = ( T, heaing, heaing ) ( T = f ( N ) T ) Please, become familiar wih his mehod by reading he aached lieraure. J 3. Experimenal 1s Day: Isohermal reacion The recipe for he MMA emulsion is given o you by he assisan. MMA (mehyl mehacrylae): _ H 2 O: SDS (sodium dodecylsulfae): AIBA: _ eacion Calorimery (SS 2002) Seie 4/6

5 Versuch eacion Calorimery The emulgaor SDS is dissolved in waer. Then MMA is added and he mixure is filled o he reacor and degassed by nirogen for 30 min. The reacor is heaed a 50 C and he calibraion is done wih he ecric heaer. When he hermical equilibrium is reached again afer swiching off he heaer, he dissolued iniiaor can be injeced ino he reacor by using a syringe. The emperaures of reacor and jacke are displayed on he compuer screen. If he reacion has ended he ecric heaer is swiched on again for he second calibraion. 2nd Day: Wilson plo and adiabaic reacion a) Wilson plo The Wilson plo is done wih waer. A defined hea flow is applied o he reacor by he ecric heaer. Five differen U. A-values should be measured by varying he sirrer speed beween 150 and 500 rpm. b) Adiabaic reacion ecipe for he MMA emulsion: MMA (mehyl mehacrylae): H 2 O: SDS (sodium dodecylsulfae): AIBA: The preparaion is done in he same way as in he isohermal case. Calibraion is no necessary. 4. Analysis and repor Please give a shor heoreical summary of he mehod and he used equaions and a descripion of he experimens. Calculae he conversion rae and he conversion over he ime for he isohermal and he adiabaic case. Deermine he reacion enhalpy from he isohermal experimen and compare wih lieraure daa. Wha are he advanages and he disadvanages of his mehod? Wha simplificaions were made? Please discuss possible errors! Evaluae he Wilson plo as shown in he aached lieraure. Daa: H = kj/mol; c p,mma = 1.5 J/(g. K); c p,waer = 4.18 J/(g. K), M MMA = g/mol eacion Calorimery (SS 2002) Seie 5/6

6 Versuch eacion Calorimery Aachmen: eacion Calorimery (SS 2002) Seie 6/6