The Development of Stirred-Tank Heat Flow Calorimetry As a Tool For

SAFETY AND ENVIRONMENTAL PROTECTION IN CHEMISTRY 189 CHIMIA 5/ (1997) Nr. 5 (Mail

Chimia 51 (1997) 189-200 drugs, crop-protection agents, coat-pro- © Neue SchlVeizerische Chemische Gesellschaft tecting additives, dyes or pigments) in a ISSN 0009-4293 form (or formulation) which the consumer needs or particularly likes. It must be eco- nomic but also safe and ecologically ac- The Development of Stirred- ceptable. The task of chemical process develop- Tank Heat Flow Calorimetry as ment is to elaborate such processes effec- tively and efficiently. Fast implementa- a Tool for Process Optimization tion of new processes is becoming in- creasingly important. Ideally, in a well- and Process Safetya) developed process, we have a basic understanding of all reaction steps (kinetics, influence of process parameters on selec- Willy Regenass* tivity, potential of thermally hazardous conditions) and a quantitative, model- based understanding of separation stages. Abstract. Calorimetry based on the measurement of heat release rates has found The tools of process development have widespread use in chemical process work, particularly for aspects of thermal process improved in recent decades to an impres- hazards. However, it has not yet found the breadth of application it deserves. This sive extent. The most important of these contribution discusses the tasks and problems of chemical process development and the tools are: role of heat flow calorimetry in this context. It reviews the historical development of - methods of analysis to follow the com- heat flow calorimetry and analyzes the prerequisites for a successful development of the position of reaction mixtures and method in the future. streams in separation processes, - methods for physical property estimation, 1. Stirred- Tank Heat Flow Calorimetry - temperature may be held constant, or methods of steady state and dynamic may be increased or decreased at con- process simulation. Heat flow calorimeters measure the in- stant rate, or follow any imposed vari- Consequently, we might expect a sim- stantaneous rate of heat release (or heat ation over time, ilarly impressive improvement in process consumption) at specified temperatures. - pressure may be varied within limits development effectiveness. Unfortunate- Fig. ], a shows the general scheme, Fig. ], restricted by the strength of the vessel, ly, this has largely not happened. The state b the type where heat flow is controlled - components may be added during of the art is widely different between var- and measured by adjusting the tempera- measurement, in portions, at constant ious process development groups. Some ture of a fluid in ajacket around the sample rate, or following a time program, are indeed much faster and produce far vessel. - stirring and mixing conditions may be better results than what was standard in- Fig. 2 compares heat flow calorimetry varied. with the better known heat accumulation calorimetry, where heat release causes temperature changes which are used to meas- 2. Process Development and Its a) ha.t t'ansfe, and ure heat effects. Problems helt flow m••• urlng device Stirred-tank heat flow calorimeters have all essential features of a laboratory When we want to asses the role of heat reactor (and a few more). They are ideally flow calorimetry, we must have a look at suited to do experiments under the condi- chemical process development as a disci- q tions of an industrial process and to deter- pline, at its tasks, and at trends with respect mine in the course of such runs: to requirements and tools. he I Ink rates of transformation (kinetics of re- In the life cycle of a chemical product, sampl v •• I actions, crystallizations, etc.), the quality of process development affects - heats of transformation. the resource consumption to provide Modern instruments provide a wide manufacturing facilities, b) T cemperllturw control variety of operating conditions: - the resources (raw materials, utilities, f"od oncalorimeter; a) a) Extended version of a lecture given at the 8th elaboration of the final application form) general scheme; b) with control ofjacket temper- Mettler RC User Forum in October 1996. designed to produce chemicals (such as ature SAFETY AND ENVIRONMENTAL PROTECTION IN CHEMISTRY 190

CHIMIA 5/ (1997) Nr. 5 (Mai) dustry practice 20 years ago. Others have neering'), process developmentre- 3. Range of Applications made little progress. The latter is particu- mains a second-class activity, be- larly true for the interface of process engi- cause short term tasks of high pri- Stirred-tank heat flow calorimeters (the neering and project engineering (i.e., the ority absorb most of the available Mettler RCI [1] being the best-known preparation ofinvestment projects for new management attention. example) provide the following types of manufacturing facilities). With the present trend to short term information: Likely causes of this situation are: 'business focus', there is a lot of pressure - by direct measurement, the instanta- - The fact that sophisticated methods to outsource the process engineering end neous rate of heat release (or con- require highly skilled people who ex- of process development, making the com- sumption) q(t); pect to work as creative and relatively munication problems even more serious - by integrating q over time, we obtain independent partners in a team, com- than they were in the recent past. Conse- Q(t), the total heat removed from bined with the fact that human commu- quently, in the real world, results of pro- (or absorbed by) the sample up to time nication skills have evolved much slow- cess development are often mere recipes t; er than technical skills. and equipment specifications, which de- - if we can attribute this heat to a specific - The appreciation and organizational fine operating procedures and process reaction, we obtain its heat of reaction attachment of process development as plants which work (in most cases), but (-Mf) = Q(t)ln a discipline in the triangle research! miss the opportunity to provide the basic (n = moles converted at time t) and the eng ineeri ng/manufacturing: understanding required to assess the con- instantaneous reaction rate ret) = q(t)1 - sometimes claimed as their domain sequence of deviations from specified con- Qe (Qe = heat released for total conver- by R+D directors with little affinity ditions, or to assure that the chosen condi- sion); for process technology, tions are really the best. Heat flow calor- - the temperature difference between - sometimes considered plainly su- imetry is a tool which can help to narrow sample and wall to create a specified perfluous by research chemists, the gap between chemical research and heat flux provides information about - even with the organizationally most process engineering. It could become even the heat transfer properties of the sam- appropriate attachment (to 'manu- more important in this function in the ple; facturing' or 'production and engi- future. - the heat input (or removal) rate required to create a specified temperature ramp in the sample allows the calculation of the heat capacity of the The limiting cases of calorimetry: a) ideal accumulation b) ideal heat flow sample and its specific heat cp. qf= 0 qf= qs Such information has many applications, not confined to reactions. Heat release may mean very different things: - a hazard, - a chemical engineering problem (like design of heat transfer equipment, of TOt=:Tob matching heat release with available o time 0 time heat transfer capacity), - an opportunity of tracing physicochemical transformations (reactions or phase transitions). TEnvironment Applications dealing with the three mentioned aspects are now discussed. r, : rates of conversion qs: heat release within sample time time qf : heat flow from sample o o 3.1. Thermal Process Safety Exothermic reactions may lead to run- Fig. 2. Comparison of heat flow calorimetry with heat accumulation calorimetry away and thermal explosion, when the potential temperature rise is high and heat removal is insufficient, because reaction rate (and consequently heat release rate) increases very rapidly with increasing tem- recycling of perature, according to theArrhenius equa- excess rectants additives tion k(T) = k(To) . exp«EIR)· (lITo-liT») (with E = activation energy; R = gas con- rectants stant) reaction separation finishing The reason for high potential tempera- auxiliary products materials ture rise may be: - too high concentration of reactants of a highly exothermic desired reaction (this recycling of waste may happen in the batch, in the fed solvents, etc. n stages batch, or in the continuous mode); - potential highly exothermic decomposition (mostly of reaction masses). Fig. 3. The chemical process Moderate temperature excursions of SAFETY AND ENVIRONMENTAL PROTECTION IN CHEMISTRY 191

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a) b) 80 140 140% 120

Q" (t), heat released when no accumulation 70 120 120% 100 G> 60 ;;? III • 100 . 100% 'i: CD I ~ G> •• G> I: 80 III •. :> 50 G> == ••G> iT ~ .. 80 '" •• 80% •.... ~ ~ > 60 &..!:.. '" 10 40 ~ .,. G> G>•• '= 60% e- J: 60 J: ..!. S 8 .•. '0 0 30 40 -.. .." ~ 40% !l 40 lD ~!G> •• E 20 0 20 Q. 20% 10 20

0% 0 0 0 0 4 8 10 0 0.5 1.5 2 2.5 3.5 4 hours time (hours)

Fig. 4. Determination of reactant accumulation in a fed batch reaction; a) heat flow and heat released; b) effect offeed rate on accumulation

a) b) various times of cooling failure 250 175 failure of cooling 225 when 0.5 equivalent fed

200 150 E 175 ~ ~ :> ~ 150 l!! 125 G> .a Q. E 125 G> e Q. !l e 100 s 100 t failure of cooling 1 hour after 1.0 equivalent was fed 1 hour after 100 equivalent % fed 75

50 75 0 5 10 15 20 0 2 3 4 hours hours

Fig. 5. Cooling failure causing runaway; a) desired reaction as cause qf runaway; b) desired synthesis reaction triggering decomposition

desired reactions may trigger a decompo- - heat transfer properties of the mixture reactor (mostly diluted in a solvent). Its sition runaway. under consideration; temperature is adjusted to the desired start- The analysis of the thermal safety of a - data on reactant accumulation; ing temperature of the process. Subse- process requires experimental confirmation of the ini- quently, B is fed at constant rate and the knowledge of the energies involved tial phase of calculated runaway sce- heat flow q(t) is measured over time. At (heats of desired reactions and decom- narios, the end of the experiment, we have the position reactions) as well as specific It is not suited for the investigation of following information: heats to calculate the potential temper- slow, highly exothermic decomposition - Q(t), the amount of heat released in the ature rise; reactions. Here, micromethods (differen- experiment up to time t. an assessment of the heat transfer ca- tial thermal analysis, differential scanning - Qtotab the amount of heat con'espond- pability of the industrial equipment; calorimetry) should be chosen. However, ing to the conversion of all A charged. enough knowledge of kinetics to as- be aware: The necessary warnings on how Qna(t), the amount of heat which would sess the extent of reactant accumula- not to evaluate kinetics of decomposition be released up to time t, if the reaction tion; reactions would exceed the scope of this would be very fast (no accumulation); the assessment of runaway scenarios text! it is proportional to the amount ofB fed (preferably by simulation). Determination of reactant accumula- up to the equivalence point, and then This approach of analysis was devel- tion and adjustment of reactant addition, equal to Qtotal' oped by many authors in recent years, in such a way that the 'maximum temper- Qacc(t) = Qna(1) - Q(t), the amount of particularly by Gygax [2], Stoessel [3], ature of the synthesis reaction' (MTSR) heat which can be released by the reac- and Steinbach [4 ]. (attained by adiabatic conversion of accu- tion mass when feeding is stopped at Stirred-tank heat flow calorimetry pro- mulated reactants after a cooling failure) time t. For constant feed rate ofB, Qacc vides in this context does not exceed a critical limit Tmax, are has its maximum at the equivalence - heats of highly exothermic desired re- the most important safety applications of point (nA,fed = nB.charged)· actions (which are difficult to measure stirred-tank heat flow calorimetry. Fig. 4 - Dividing Qacc by the heat capacity by heat accumulation calorimetry) and shows how this is done for a fed batch (which increases with t as the batch specific heats; reaction A + B ~ P; A is charged to the mass increases), we obtain a worst- SAFETY AND ENVIRONMENTAL PROTECTION IN CHEMISTRY 192

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case estimate of the temperature rise trial scale. This is a feasible way to avoid property estimation packages. For viscous which will occur when heat removal the worst. Early consideration of thermal slurries, this is not the case. Here, an fails. effects and appropriate analysis of the experimental determination based on Eqn. From Fig. 4, b, we see that (not surpris- situation would be more effective. 1is advisable. By rearranging it, we obtain ingly) for a second-order reaction, the feed duration must be increased by a factor 3.2. Heat Transfer Issues 4 to halve accumulation. Heat transfer is obviously an important

Fig. 5, a shows calculated runaway function in chemical processes. We need englneenng datil phys I propertIeS scenarios, where the heat of the desired data and understanding for of the reactor of reactor con enlS reaction causes the total temperature rise - safety analysis, WIth 11~ graVItatIOnal accele bon [mI"] (cooling failure and stop of feed, after 0.5 - optimization of process procedures, and 1.0 equiv. of B are fed). Fig. 5, b - design of new equipment and assess- shows the case, where the temperature rise ment of existing equipment. Here, h is the product of two factors, caused by near adiabatic conversion of There is excellent literature on heat one of the depending only on equipment accumulated reactants of the desired reac- transfer mechanisms and heat transfer data. geometry and operation (the stirrer speed), tion triggers an exothermic decomposi- In most cases, no measurements are need- the other onlyon physical properties of the tion. Here, the heat from the desired reac- ed for solving heat transfer problems in sample. tion drives the temperature of the mass process development. The fact is that we In a stirred-tank heat flow calorimeter i'fltoa range where the decomposition re- often ignore or neglect heat transfer is- with heat flow control by wall-tempera- action is fast enough to become danger- sues. Thus, the main virtue of applying ture adjustment (see Sect. 4.1), we deter- ous. The main heat comes from the de- heat flow calorimetry is the fact that it mine the overall heat transfer coefficient composition reaction. creates awareness of heat transfer prob- (or its inverse, the overall heat transfer For simulation, the following parame- lems. resistance) by measuring the temperature ters were assumed (SR = synthesis reac- difference required to remove a known tion, D = decomposition): 3.2.1. Film Heat Transfer Coefficients of imposed heat release (electric heating) - rate constants [h-I] at 1000 (process Process Fluids (Fig. 6). Since the heat transfer resistance temperature): SR: k'CAO = 1; D: k = The film heat transfer coefficient at the of inner film, wall and outer film add 2.5·10-4. boundary of a turbulent liquid is correlat- I , d. I 1 - Temperature rise for adiabatic conver- ed by the Nusselt relation: +-+-= +- sion: SR: 200 K (80 K for Fig. 5, b); D: u'" •....•h. ~ It. VI u = II ·dJ?.) = n t.. Re2J3. Pr1f3 (I) depends on depends (3 500 K. reaction mass on reactor - Activation energy [kJ/mole]: SR: 60; II = II self numb r D: 100. Re = Reynolds numb r = . d,2 . p/,., When we detect unacceptable accu- Pr = PralldtL numb r = ,.,. c,!?. we can easily determine the sample film mulation, we have to modify the process II = film h at trail, fer efficient coefficient. This is preferably done by procedure, be it by elongation of the feed /(m2. K ] means of the Wilson plot [5 ][6] (Fig. 7): duration or by increasing the reaction tem- 1J = t1ynami vi c . ity [Pa .. J We vary the stirrer speed N and plot the perature, or both. This often affects selec- A = thermal condu ti it IV 1(01 . K)] inverse of the overall heat transfer coeffi- tivity and, worse, product quality. This p = den ity [kg/mll cient U over N-213, first with a liquid of may lead to a whole new development = .tirrer spe d [!i-I] known r to determine the heat transfer effort. It is therefore advisable to consider d, = diameter of e ellm] data of wall and outer film, ]/cp, and the the safety aspect mentioned above early in d, = diameter of tirrer [m] geometric factor z of the calorimeter ves- a process development project. cp = p ifi heat [J/(kg . K)] sel, then with the sample to determine its It has become a (questionable) custom y-value. The same procedure can be ap- to request a run in a heat flow calorimeter For pure liquids, reliable estimates of plied to determine cp and z of industrial at the end oflaboratory work before a new the film heat transfer coefficient are possi- vessels, if they are equipped with a varia- process procedure is introduced on indus- ble, based on data obtained from physical ble speed stirrer drive.

jacket wall sample 0.01 1/U

0.009 -I slope =(z.y)=O.00192

0.008 -1 (jJ = 0.00802 q 0.007 Tj -213 (NINo) jacket side -l h 0.006 film heat transfer j o 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 coefficient '

Fig. 6. Heat transfer through wall of stirred vessel Fig. 7. Wilson plot (Courtesy of F. Stoessel) SAFETY AND ENVIRONMENTAL PROTECTION IN CHEMISTRY 193

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3.2.2. Design of New and Assessment of Existing Equipment 140% 120 The use of heat transfer data in the durallon from feed start to 98% conversion: •..CIl 1: 8.9 hours I 2: 3.2 hours I 3: 2.3 hours ::l design of new equipment is straightfor- 120% - 100 :! ward: Know the heat duty and the availa- .!:Cl '0 ble (or allowable) temperature of the heat _ 100%- 1 constant feedrate 0 '

3.2.3. Scale-Down for Scaleup On laboratory scale, heat effects cause - reaction to the desired degree of con- k(T)' or: rarely problems; mostly they are not no- verSIOn, ((Tmax- T) . k=· exp(-E/RT). By differ- ticed; consequently most laboratory pro- - heat transfer (heating, cooling, heat entiation of this rate term with respect to T, cedures are elaborated as if heat effects transfer for physicochemical transfor- we obtain would not exist. The problems start with mations like reaction, vaporization, scaleup: Feed rates prescribed cannot be etc.). maintained, because heat cannot be remov- Very often, heat transfer is the most 4) ed fast enough or because they would lead time-consuming among these activities, to unacceptable reactant accu mulation. and when we know the heat to be trans- There is no need of solving the quad-

Therefore, as mentioned before, heat re- ferred and the (correct) heat transfer ca- ratic equation for Topt, as Top! = Tl11ax- R . moval considerations should start early in pacities of the equipment, we are well- T ~aJ E is a good conserv ative approxi ma- process development work, and the timing supported in finding ways to improve. tion. The rate optimum is flat (the gain in of the elaborated process steps should be If in reaction steps heat removal is cycle time by increased temperature is feasible on an industrial scale. limiting (this is the case for fast and highly modest) and, for the sake of safety, tem- The correct sequence of actions is: exothermic reactions), constant addition peratures below Top! should be chosen determine heats of reaction, heats of rate of reactants (a standard procedure in anyway. For curve 3 in Fig. 8, Twas vaporization, heat capacities, etc.; batch processing) is correct. If, however, chosen according to this optimization. - estimate the heat transfer capacity of the need to limit accumulation restricts the industrial equipment intended to be allowable feed rate, addition programs 3.3. Heat Effects as an Event Tracer used; providing constant accumulation should This is the most valuable and probably - estimate therequired heat transfer times be applied. From Fig. 8 (simulated with the most neglected use of heat flow calor- for heating, cooling, evaporation, re- the same reaction parameters as Fig. 4, b), imetry. When we trace heat release (or actions, etc.; we see that feed duration can be about absorption), we get immediate informa- do the laboratory experiments (at least halved by this measure (left side part of tion of what is going on in a reactor. Some the final ones) with a duration of the curve 2). If we allow the process temper- examples: process steps which is in line with the ature to rise as accumulation decreases - Catalysis and inhibition (Fig. 9,a, left): industrial process. (due to the completion of the reaction after The effect of added components is the end of the feed period), the time to immediately seen. 3.2.4. Cycle Time Optimization achieve a desired extent of reaction (e.g. - Reaction progress affecting kinetics 'Debottlenecking' (capacity increase 98%) can be considerably reduced (right due to polarity changes (Fig. 9, a, of existing plants without major invest- side part of curve 2). right): The reaction shown is a first- ment) has become an important process Iftemperature excursion considerations order isomerization. As conversion pro- development activity in recent years. In a are the only restriction on process temper- ceeds, polarity of the medium increas- batch plant, capacity is determined by the ature, cycle time can be further reduced by es, enhancing the rate constant by a expression (plant availability (also called optimization of the process temperature factor of ca. 30. on-stream efficiency) . batch yield/cycle during the feed phase: - Initiation of reactions with a tendency time). The component which can be most The higher we choose the temperature, to hazardous reactant accumulation easily improved is cycle time. There are the less accumulation we can tolerate. On (Fig. 9, b): Ifwe can immediately see, three main types of process activity re- the other hand, higher temperature will whether the formation of a Grignard quiring time: increase the reaction rate constant. Reac- reagent 'starts' (left part of Fig. 9, b), - macro mass transfer (charging/dis- tion rate is proportional to the product itis easy to elaborate a procedure which charging), 'concentration of the fed reactant times safely avoids accumulation. SAFETY AND ENVIRONMENTAL PROTECTION IN CHEMISTRY 194

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Sudden changes in reaction rates (Fig. ysis much more selectively and conse- Even for simple reactions, there are 9, c): In the liquid-phase oxidation of quently save cost and move faster. problems (e.g. the determination of the aromatic methyl groups with molecu- exact reaction order). Be aware of the lar oxygen, catalyzed by Co and Br, 3.4. Limitations of the Method fact that the rate of a stoichiometric rate changes by orders of magnitude Heat flow calorimetry is, of course, not second-order batch reaction at 90% can be observed. 'a cure to all evils'. Many failures experi- conversion is I% of its initial rate. Although it is rarely possible to estab- enced with the method are due to attempts Consequently, it is impossible to get lish accurate and reliable kinetics from to apply it where it is inappropriate. A few any meaningful information from heat heat flow experiments alone, heat flow examples: release at high conversion. information considerably accelerates the - Kinetics of complex reactions, without - Investigation of slow, very exothermic acquisition of kinetic understanding. Also, the support of supplementary meth- decomposition reactions (as mentioned we will take samples for component anal- ods. above). - Working under reflux conditions. It is possible to include a reflux con- a) densor in the overall heat balance. Appropriate equipment is available. Watt/mole WaWmole reaction However, the loss of accuracy and, C = addition of CH3J addition of CH J rate (h·1) II I = addition of amine 3 worse, reliability is considerable. 3D + (inhibitor) Working under reflux is a standard mode oflaboratory operation, because 20 10 0.2 it is an easy way of maintaining a temperature accurately. Doing the same 10 r 5 0.1 on an industrial scale is in most cases a waste of energy. Very few processes o o require reflux (e.g. for the stripping of o .1 .2 .3.4 hours o 2 4 6 8 hours a reaction product in an equilibrium reaction to obtain high conversion, or for the stripping of components which b) c) are detrimental for the reaction or for

160 Watt the desired product). Therefore, reflux ~ on plant scale should be confined to 140 o 600 such cases and to process steps where £i•• heat has to be removed from the reactor 120 '0 /--- ~ 40 (because reflux is a very effective and c 400 / / 100 .2 reliable way of heat removal). On a /-- Rei added-,l I 50 / /. ~ 60 ::I laboratory scale, heat should be re- / / I 80 Ul o I ---1 C 200 moved through the wall. It will then be tempera!~~_.J 60 rS* 80 measured much more accurately (pro- 0.5 1.0 vided evaporation is suppressed by o o 0.5 1.0 hours 2 hour.; applying pressure). Fig. 9. Heat release as a tracer: a) The highly exothermic isomerization of trimethyl phosphite [7]. Catalysis and inhibition (catalyst: CH}I; inhibitor: amine). Acceleration of reaction rate, caused by increasing polarity of the reaction mixture. b) The check of the reaction initiation in an industrial 4. Instrumentation manufacture ofGrignard Reagent (RCI + Mg --7 RMgCl); c) The oxidation of chlorotoluene in solution with molecular Ob catalyzed by Co2+and Br [8] (R-CH3 --7 R-CHO --7 R-COOH) 4.1. Available Calorimetric Principles, Classification of Calorimetric Instru- ments a) passive b) active There is no generally satisfactory clas- heat sink sification of calorimeters, because there heat transfer are so many characteristic features. With resistance focus on heat flow calorimetry, the following classification (Figs. 2 and ]0) has sample been proposed [9], distinguishing mainly thermal insulation between: "heat pump" - heat accumulation methods (adiabatic and most isoperibol instruments), T - heat flow methods. temperature Heat flow methods may be further cl as- sified with respect to their various ways heat flow of: a) Heat flow control: start of reaction - passive (heat flow driven by partial heat accumulation, Fig. 10, a), Fig. 10. Passive and active heat flow calorimeters - active (heat flow forced by a control SAFETY AND ENVIRONMENTAL PROTECTION IN CHEMISTRY 195

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system, Figs. 10, band 11), e.g. - compensation heating, a) Peltier b) Compensation c) Heat-Transfer d) Heat-Balance Peltier heat transfer, Heating * - temperature adjustmentin the 'heat mecp sink'. b) Heat flow measurement: electric current (Peltier or Joule effect), heat balance in the heat sink, - temperature difference over heat transfer resistance. 3 Some Comments: * - Passive heat flow calorimeters are qs=UeAe(Ts·Tf) qs= meCpe(Tfo·Tfi) useful only for small samples and good heat transfer between reactor and heat o variable affected by controller C: I p = Peltier current, sink. If this condition is not fulfilled, qc = heater power, Tf = temp. of heat transfer fluid dynamics will be poor and deviations variable sensed by primary measuring device M: Ip,qc,Tf see above of the reactor temperature from the D temperature: Ts = sample; Tfj, Tfo = inlet I outlet of heat transfer fluid desired value will be large. 1 heat source, 2 heat sink, 3 thermal insulation, Peltier heat transfer (Fig. 11, a) is = = = 4 heat transfer resistance (area A, transfer coefficient U) based on a principle which might be = called the inverse of the effect on which the thermocouple is based: When we Fig. 11. Combinations of heat flow control and measurement used in active heat flow calorimeters impose a current on a thermocouple, (from [38]) heat will be transferred from junction to junction. Peltier cells are batteries Table 1. Heat Flow Calorimetry of large numbers of semiconductor 'thermocouples'. Heat flow is strictly 1923 TiallIIO] thermopile calorimeter proportional to current; thus, Peltier cells can be used simultaneously as 194 alvet [II] twin-celltherm pile cal rimeter heat pumps and heat flow measuring devices. (A complication comes from 1965 Becker and Wulisch 112] Peltier-contr lied heal now cal rim t'r the fact that a Peltier battery has its 1960-83 various author' in indu try own heat generation, caused by Ohm- heatllO\ cal rimeler f r safety and proce.\. d ign type losses which are proportional to 19 _ if ~'onand i/l'egrell [I model-supponed Peltier-c ntr lied heat 11 w the square of the imposed current.) al rimeter Peltier-type heat flow calorimeters have excellent dynamics. However, 19 I Eigenherger and worker. [I I, ratory fermenter alorim 'ter until recently, there were serious re- strictions in their application range 1992 Moritz and coworker [17 J model-supponed c mpen ation-h 31 r heat no calorimeter (temperature range, materials, and geometry of reactor). I 93 Reichert and coworkers [I ] calorimetry with a model-supported standard For compensation heating (Fig. 11, In rat rca t r b), a constant temperature difference is maintained between the sample and 19 2197 1'011 tockar and cow rkers B -811R I-bas d fermenrulion calorimeter the heat sink. This causes a constant [19]l20] heat flow out of the sample (constant as long as the heat transfer resistance is constant). The temperature of the sam- temperature of the heat sink (jacket fluid within the heat balance limits ple is maintained by means of an elec- around or coil within the sample) for cannot be kept very small. tric heater with measured power input. heat flow control (Fig. 11, c and d) are Both subtypes are calibrated by means Heat release rates in the sample cause presently most commonly used for of an electric heater immersed in the sam- corresponding changes of the power process work. Heat flow is measured ple. input to the heater. Among active heat by one of two methods: flow calorimeters, compensation heat- - by sensing the temperature differ- 4.2. Short History of Heat Flow Calor- er types are by far the easiest to build. ence over the heat transfer resist- imetry and Overview of Past and They also have excellent dynamics. ance (Fig. 11, c). Here, variation of Present Designs Their problem is the fact, that changes the heat transfer resistance affects Heat flow calorimetry (TabLe 1) has its of the heat transfer resistance (which sensitivity (with other words: the roots in differential thermal analysis. It are unfortunately quite common when calibration factor). was systematically developed in the sec- reactions take place) cause serious - Via a heat balance on the heat trans- ond quarter of this century by Tian [10] baseline drift. fer fluid (Fig. 11,d). Here, dynamics and Calvet [11], who designed highly sen- Heat flow calorimeters adjusting the are poor, if the mass of heat transfer sitive unstirred instruments which are still SAFETY AND ENVIRONMENTAL PROTECTION IN CHEMISTRY 196 C'HIMIA 51 (1997) Nr. 5 (Mai) in use. Important systematic work towards - Model-based designs by Moritz and signed for industrial needs were built in modern active heat flow calorimetry was coworkers [17] and Reichert and cow- almost every major chemical company done in the sixties by Becker and cowork- orkers [18]. They will be discussed in (Table 2). ers [12] in Germany (Universities of the section on future development. The first design to be mentioned here is Saarbri.icken and Frankfurt). - Adaptations ofBSC-8 1(Ciba)andRCl not an instrument but an analogue compu- Other stilTed-tank heat flow calorime- (Mettler) instruments for the use in ter (with vacuum tubes). Its purpose was ters developed at universities are; fermentation by von Stockar and co- the control of feed rate and cooling of an - The Peltier-type instrument by Silve- workers [19]. The most recent designs olefin polymerization reactor at Phillips gren and coworkers [13] (now availa- are sensitive enough « 50mW/l) to Petroleum based on the use of heat release ble commercially by Chemisens [14]). trace oscillations of heat release rate to calculate the instantaneous reaction rate - A fermenter calorimeter from the Uni- which are caused by synchronization and the degree of polymerization (Mor- versity of Stuttgart [15], also available of cell growth [20]. gan [21]). This was a very progressive commercially (by Berghof[16]). Stirred-tank heat flow calorimeters de- approach. Nothing on its implementation, not even recently, was found in the literature search. Table 2. Heat Flow Calorimeters from the Chemical Industry The first instrument from industry found in this search came from the Institut Year ulh r Affiliarion Frans;ais du Petrole [22]. It was a passive heat flow calorimeter which was available 1957 h 'al 10"' calorimcl lor 'all I_II Phillip.\' Pe/mlt'lIl11 (In an induslrial reaclor commercially in the early sixties, but seems to have disappeared soon thereafter.

19611 p3. SIVC 'Th'rmokinegraph' BIlIIIIIl(lIrlller and In I. rJJ1 ai The most frequently used method of Oil/Will 1_2J du Petr Ie heat flow control is compensation heating (used by authors from Monsanto (Andersen 1966 aClivc compensalion h'aler Alldu\VI[231 MOllsuI/to [23]), BASF (Kohler [29]), Ciba UK (Chandler [32]), Roche (Schildknecht 19 6/ I ;jcli\.' .djtl. (menl ofjackellCmp. Rel(e/l{ls.\' and oworkel'5 Ciba H 12 27J [33]), Hiils (Hentschel [34]), and Bayer (Litz [35]), sometimes with sophisticated 19 9 l1\C 'ldjtl Imenl Ofj3Ckcllcmp. Het'/.;\·I_ Doll' features to cope with the inherent flaws of this method. 197~ aCl1\c mpensal1 n h al'r KilhleJ (,t (/1. [291 B F Adjustment of the temperature of a heat exchanger coi I(and heat balance over 1975 aCli\c adjustment of jackett 'l11p. Huh [.0][311 alldo: this coil) was used at Dow (Meeks [28]).

I 76 a \In: campen ati n heater 'wlldler [321 Cibll K Jacket temperature adjustment was used at Ciba Basel (Regenass [24-26], 1977 aClive wall mp.;n mi 11 healcr ,hildkm'dll [3. I Giger [27]) (deriving heat flow from the temperature difference over the reactor 1979 aClive t; mpcnsalion heater Hiils wall) and at Sandoz (Hub [30][31]) (determining heat flow by a heat balance on the 19 O/IL a 'til' 'ompensali n hCaler Lil: [351 Baw'r + hcal balance n ja'k I jacket). The Sandoz design was commer- cialized by Contraves, the Ciba design by Mettler [1]. The list is necessarily incomplete. Many successful efforts were probably never published. That is the reason of the 1965 1966 1967 mention of the work by Dr. Chandler who built with essentially no money acompen- sation heater calorimeter which worked ~T I , I perfectly in its range of application. , . , Reviews on heat flow calorimetry were , given by Becker [36], Regenass [37][38], Karlsen and Villadsen [39], and Moritz [40].

electric heater 4.3. The Development within Ciba Calorimetric work in the Chemical Engineering Section of Ciba started 1965 with the task to keep a Skraup reaction (the highly exothermic formation of a quino- line by condensing an aniline with glycerol in sulfuric acid) under control. There had q = U* A * L\T q=U*A*L\T been a runaway in the plant, and process safety had to be improved [41]. Atthattime Fig. 12, Early Izeatflow calorimeters at Ciba (Fig. 12), temperature control on industrial SAFETY AND ENVIRONMENTAL PROTECTION IN CHEMISTRY 197

C'HIMIA 5/11997) Nr. 5 (Mai) stirred tanks was improved by 'cascaded Ciba heat flow calorimeters (Martin [7], control': The heat flow from or to the Gautschi [45], Kanert [46], BUrli [47], reactor (steam/cooling water) is controlled Beyrich [8]). not only by the temperature of the reactor In the early seventies, we came to the contents, but the temperature of the jacket conclusion that we should have 'Bench is also sensed and adjusted according to the Scale Calorimeters' (BSC's) (Fig. 13) in deviation of the reactor temperature from the various process development depart- its set point: e.g., when TR is 1° too high, ments, for two reasons: the jacket is set 5° below the reactor tem- - After a few serious thermal runaways perature set point. This greatly improves in the plants, there was a long queue of temperature control stability. work orders. A little box built at Ciba's electronic We had noticed that is was very diffi- shop [42] made this type of temperature cult to convey insight on process im- control available for the laboratory. Plot- provement opportunities to those re- ting the temperatures of reactor and jacket sponsible for the processes. vs. time (on an automatic recorder), we After a failed attempt to convince an obtained heat release data which immedi- established supplier ofthennal instruments ately led us to a kinetic model of the to provide calorimeters for us, we started reaction, from which we could predict a redesign. It was fortunate that W. Kanert, safe and time-efficient temperature pro- a chemist with a professional education as grams for the industrial reactor. This fas- a draftsman, had just obtained his chemis- cinated us and gave us recognition and try diploma and was looking for a Ph.D. freedom to do some method developments. thesis opportunity. He implemented the When we want to measure heat release 'BSC-75' [26][46], a design which was rates by transferring the involved heat to a much more compact than its predecessor Fig. 13. BSC-75 heat transfer fluid, the temperature of this (Fig. 13). 18 units were built; some are fluid must be adjusted very fast (at least, still in use. A wide range of options were 5. Future Developments we thought so at the time). available: Our first attempt (Fig. 12, left) was a - pressure reactors up to 150 bar, 5.1. How Well is Heat Flow Calorime- jacket circuit with cooler and a gas heater - heaters, coolers, and heat transfer flu- try Developed? switched on and off by a controller. Heat ids for a temperature range of -70 to At present, heat flow calorimetry is release rate was determined from the tem- 250°, generally accepted as a tool for optimizing perature difference between reactor and - various construction materials for re- processes and assuring process safety. jacket. It worked, but it was an energy- actors (glass, glass-lined steel, titani- Several designs are available commer- wasting machine, and the big fire was not um). cially. Many users build their own instru- exactly what we needed in the lab. In 1979, we were faced with problems ments from components now easily avail- Next (1966), we tried a fast tempera- of instrument supply again. We improved able (fast, closed thermostatic baths, con- ture-controlled electric heater on a coil the mechanical design (based on studies trol hardware and software). Thus, one circuit in a Dewar type of reactor (Fig. 12, done jointly with Mettler) and used acom- might call heat flow calorimetry a suc- middle). We used constant fluid flow and puter-based control system supplied by cessful method. However, if we compare measured the temperature between the the same manufacturer [48] who had sup- heat flow calori metry with other scientific inlet and outlet of the reactor. The result plied the electronic equipment of the methods and measure its success by the was a typical lab calorimeter, useful for BSC-75. percentage of the area of its potential ap- data, but awkward to operate. This 'BSC-81' [27] could be accom- plication it occupies and by the speed of its Third (1967), we went back to jacket modated in a standard fume cupboard and development, then heat flow calorimetry temperature control (Fig. 12, right), now could do automatic experiments, data ac- is at the low end of the success ladder. with temperature adjustment by mixing quisition, and evaluation. However, it was Some methods found general accept- (injection of precooled or preheated fluid far less successful than the BSC-75 as it ance immediately after their detection. [43]), required 'experts' to operate it, and there The most stunning example is X-rays (more With this design, we could solve many were more computer failures than accept- than 1000 publications in the first year process problems. By 1970, this type of able for a safety calorimeter. [49]). Methods introduced extremely suc- instrument was used on a service basis for In 1981, the project of a Mettler Bench cessfully in the recent past are Atomic customers in various areas of Ciba. The Reaction Calorimeter was started. The Force Microscopy [50] and the Polymer- key players in the early period were H. 'RC I' became commercially available in ase Chain Reaction [51]. Other methods Martin, who developed the method as a ] 985, first mechanically identical with the fully developed within a few decades (e.g. service, and l.R. Randegger, who man- later version of the BSC-81, but with an GLC and NMR). aged the group for some years and then appropriate and reliable control and eval- On the other hand, Liquid Chromato- introduced the method to US sites of Ciba uation system; however, with quite re- graphy (Table 3) developed extremely [441. Three application examples from stricted application accessories. Only re- slowly. It became widely used as an ana- this time period were shown in Fig. 9. cently, important features of our BSC-75 lytical tool only recently in the form of Besides applications, we could also (pressure, temperature range) were added HPLC (High-Pressure or 'High-Perform- look into the basics. Several colleagues to the RCI. ance' Liquid Chromatography). did their Ph.D. thesis work on perform- Fig. 14, a-c, shows photographs of In stirred-tank heat flow calorimetry, a ance evaluation and on applications of the Ciba instruments from various periods. few hundred instruments are in use in SAFETY AND ENVIRONMENTAL PROTECTION IN CHEMISTRY 198 CHIMIA 5/ (1997) Nr, 5 (Mai)

a) b) c)

Fig, 14. Photographic documentation of the effortfor more compact design: a) the voluminous setup in the late sixties, b) the 8SC-75, c) the 'heart' of the BSC-8]

Table 3. Liquid Chromatography [52] time requirement for preparation, for the calorimetric run and for the 1906 T. '1I'e/l lbolamsll scparali n f c mponem' by ad orplion chr mal graphy evaluation,

I 1 ~ i/hliiuer cann I reproduc TSlI'et( s r 'uhs and c ndemn. Ih meLhod space requirement in the laboratory, 1931 R. Kllh" fCC mmends the meLhod - availability to user (cost of acquisition 1939 'c1mliber disc vcr lhin-Illyer eh malography and cost operation), hi w rk remain' unn Liced we see that the problem of presently avail- 1941 A.l.P Marti" and introduc partilion chromalOgmphy able calorimeters is not with sensitivity or R.LM 'llge clevel p pial lheory ancl elution the ry with accuracy, but with handling proper- (bi I gi, IS) ugge I high-pre. sure L (HPL ) suggesl gas chromal graph ties and with cost. The handling and cost specifications Kirchller redlsc vc Lhin-layer hrom I graph 1 5\ are set by conventional laboratory reactor ]96 J.l. KII'k/muf deteclor for LC systems (i.e., vessels for samples (reac- \970, HP becomes an eSlablished analylical melhod tion mass), heat transfer equipment, con- 1990 HP n or the m t used anal}Lical method trol equipment, etc.). Such systems are of course not calorimeters, but they have many components in common with calo- quite restricted areas of application. The the development of a more sui table instru- rimeters, including computers for data extent of use is summarized and com- ment. acquisition and/or automatic running pro- mented in TabLe 4. cedures. The development of a method is dri ven 5.2. Needs and Open Opportunities This leads to the question, whether it is by needs and its capabilities to serve the Heat flow calorimetry could be as much feasible to turn conventional laboratory needs, and by human fascination and en- a standard method of monitoring reactions equipment into a simple calorimeter by thusiasm (TabLe 5). as all the forms of spectrometry and modeling and data treatment, and if so, Heat flow calorimetry has the problem chromatography presently in use. It is not what accuracy and sensitivity of heat re- that it has no glamour and is not in the as specific as the methods mentioned, but lease should one aim for? mainstream interest of potential users, not much more convenient. An accuracy of ± 10% of the released among physical chemists, much less When we try to translate the needs of heat is probably sufficient and easily among chemists. The interest of chemical the users into instrument specifications achievable. engineers is also low, although increas- such as: - Sensitivity requirements are more strin- ing. Further constraint results from the - measuring qualities (sensitive, accu- gent and much more difficult to achieve. fact that present instruments are either too rate, representative of process under Probably, the detection of a change in costly and require too much space, or they question), heat release rate (in a 5-min mean), are not easy enough to use to be a real help - handling qualities, which corresponds to 5% of the maxi- in problem solving. Consequently, there variety of standard operations (stir- mum heat release rate of the investigat- is not much demand, and no instrument ring, adding components, ramping ed reaction, would be quite helpful. maker will dare to put much resources into temperatures, etc.), But if the maximum is 20 WIl, this SAFETY AND ENVIRONMENTAL PROTECTION IN CHEMISTRY 199

CHIMIA 5/(1997) Nr. 5 (Mail

means that a change in heat release of Table 4. Development Status of Heat Flow Calorimetry 1 Wil should produce a meaningful signal. This is not an easy task. pplicuti n rea .lenl f e - Good dynamics are also of interest. We often want to know, whether a reaction thermlLl process 'afet high: probably lOOhigh. starts immediately when the reactants Then: i~ a 101 f ilClivilY guided b the ohligallon 10 a. ~U01e responsibility, rsimpl b fear. get together, or whether there is a de- 1u h of lhe data now elabor,llcd in R I-t) pc equipment lay. might be obtained on a muchm.lIlcr, Ic~~ stl> s 01 . In the past, much effort was made to match heat release with heat flow as accu- seal up /10 ale-d wn low rately and as fast as possible by means of (general PI' cess devel pmcnl) Probably 1 s. Ihan 20% of the pI' ess development sophisticated control hardware. The ad- laboratories use heotl1o~ colorimelCrs. allh ugh th'rc I a vent of fast and inexpensive computers sCl'i us n ed ~ I' bcut:r insight int th' proce:~ asi's and for provides opportunities to reconstruct true more and betiCI' data. heat release rates from signals which are badly distorted. This greatly reduces per- monil ring synthcsi war" er 10\ Heal now calorim try I bare I u ed 1Il~l1lhesis labonHories formancerequirements on instrument hard- (heat as a tracer) ~ here reactions and proce s PI' edurcs are lIliu:lted and ware: heat flow calorimeters can be made where the 'pI' e~~ vi v.' PI' vid d hy heat 11 \\ calonmctry simpler and cheaper. would lead to betiCI' laborat procedure. and faster Two attempts in this direction have implementation. been published in recent years: A model-based isoperibol calorimeter developed by Moritz and coworkers Table 5. Key Success Factors for the Development of Methods [17], which operates similar to a tradi- tional combustion calorimeter (using a fI:ature -Ray •.• toml Free LiqUid Heal 11,')\\ large liquid mass as thermal ballast to Microsc p hr mutography alorimcll)' keep temperature changes in the sample small) and calculates instantaneous heat release rates. Published per- as ina\J n (Glamour) ++ ++ formance data are impressive. The approach relates to earlier work by Kiiss- Main_trcam inlere_l ++ ++ ner [53]. '? Reichert and coworkers [IS] attached Obvious usefulness ++ ++ ? a fast commercial thermostat to a com- rrordability mercial autoclave and modulated the - C lot of a quisiti n + '! + ? set temperature of the reactor within - cost of operation + + + narrow limits. They obtained (for a slow polymerization reaction with very large changes of viscosity as conversion proceeded) heat release data and and by mechanical heat dissipation in the heat transfer data simultaneously. sample, caused by stirring. Possibly one can get the desired results To focus on the most difficult prob- from even simpler equipment. The objec- lem, the dynamics of temperature in the - The next step of sophistication (to al- tives are: vessel wall, we simplify by neglecting: low for time lag in the temperature - measure the instantaneous heat release - secondary heat flows (loss through the adjustment of the jacket) is or heat absorption rate of a sample; lid of the vessel, etc.); qs = qr + ts • (m.cp)s , assuming still qr= - estimate heat transfer properties of the - local variations of the fluid tempera- (7) U • A. (Ts - T ) sample to the extent needed to adjust tures of the jacket and of the sample (as i calibration; far as heat balance is concerned, not To obtain a decent qs-signal, Tj must be - use the most simple and inexpensive the gradients in the heat transfer resist- adjusted smoothly and fast. equipment available to achieve this ance); When we want to allow considerable goal. - the dynamics of the temperature sen- deviations of 1j from the value making qf The following discussion assumes that sors. = qs and use temperature transients in the a jacketed vessel is used and heat flow is The heat balance over the sample re- sample caused by such deviations to deter- controlled by adjustment of the jacket sults in mine the heat transfer resistance (which is temperature. Two temperatures are meas- affected by the sample side film heat trans- ured by sensors placed into the jacket fluid (5) fer coefficient, varying with time), we and into the sample. . must take into account the dynamics of the The real system is extremely difficult with qs = heat evolved in the sample (in- temperature distribution in the wall. Fig. to describe mathematically. There are time- cluding heat dissipation by stirring), 15 sketches the dynamics of the local dependent local temperature gradients in qf = heat flow from the sample to the temperature profiles. Heat flow out of the the jacket, within wall, and at the interface jacket, sample equals heat flow into the wall on of the sample. Additional problems are (m . cp)s = heat capacity of the sample. the sample side (qr = qw.s) and is only caused by secondary heat flows ('losses') - The simplistic approach is dependent of instantaneous local temper- SAFETY AND ENVIRONMENTAL PROTECTION IN CHEMISTRY 200

CHIMIA 5/ (1997) Nr. 5 (Mai) ature distribution (and not dependent of Received: March II, 1997 Party on Chemical Reaction Engineering qs)' We can calculate the temperature dis- (body of EFCE), PontaMousson (F), ]966 tribution in the wall (including the sam- [I] Mettler Toledo, CH-8603 Schwerzenbach. (first public presentation, no printed pro- ceedings). ple-side wall surface temperature which [2] R. Gygax, Chem. Eng. Sci. 1988, 43, 1759; (ISCRE 10 plenary lectures). [25] W. Regenass, W. Gautschi, H. Martin, M. determines qf, the variable we are looking [3] F. Stoessel, Chem. Eng. Progr. 1993, 89 Brenner, Thermal Analysis, ICTA 1974, for) from the past history of the tempera- (10),68-75. Vol. 3, 823. tures on both sides of the wall. [4] J. Steinbach, 'Chemische Sicherheitstech- [26] W. Regenass, ACS Symp. Ser. 1978,37. Karlsen, Sr/Jberg, and Villadsen [54] nik', Verlag Chemie, 1995, p. 198-208. [27] G. Giger, A. Aichert,W. Regenass, Swiss [55] did this with a BSC-8l in 1984 by [5] E.E. Wilson, Trans. Am. Soc. Mech. Eng. Chem. 1982/3a, 4, 33. 1995,37,47. [28] M.R. Meeks, Polym. Eng. Sci. 1969,9, 141. heating and cooling the reactor contents [29] W. Kohler, O. Riedel, H. Scherer, Chen/.- from the jacket. The heat release calculat- [6] J .R. Bourne, M. Burli, W. Regenass, Chem. Eng. Sci. 1981,36, 1153. Ing.-Techn.1972,44,1216;ibid.1973,45, ed by the estimator (true value = 0) was [7] H. Martin, Ph.D. Thesis, University of 1289. within 0.2% of the heat transferred and the Basel, 1975. [30] L. Hub, Ph.D. Thesis, No. 5577, ETH- estimated heat release rates (true value = [8] 1. Beyrich, Ph.D. Thesis, No. 6578, ETH- Zurich, ]975. 0) were (as a 3-min mean) less than 4% of Zurich, ]980. [31] L. Hub, Chem.-lng.-Techn. 1982,54, MS 978/82. the mean heat transfer rates during the [9] W. Regenass, Thermochim. Acta 1977 20 65. ' , [32] 1.F. Chandler, Duxford (UK), personal com- experiment (see [55], pp. 1170 and I 171). [10] M. Tian,Bull. Soc. Chim. Fr. 1923,33,427. munication. The results mentioned were obtained with [II] E. Cal vet, H. Prat, 'Microcalorimetrie', [33] J. Schildknecht, Thermochim. Acta 1981, a computer which was a hundred times Masson, Paris, 1956. 49,87. 'weaker' than present laptop computers. [12] F. Becker, W. Walisch, Z. Phys. Chem. [34] B. Hentschel, Chem.-lng.-Teclm.1979, MS Thus, there is reason for hope that heat N.F. 1965,46,279. 725. [35] W. Litz, J. Therm. Anal. 1983,27,215. flow calorimeters can be built without [13] H. Nilsson, C. Silvegren, B. TomeI!, Chi- [36] F. Becker, 'ThennokinetischeMessmetho- very fast and highly accurate jacket tem- mia Scripta 1983, 19, 164. [14] Chemisens AB, Lund, Sweden. den', Chem.-lng.-Techn. 1968,40,933. perature control. The only accessories [15] Ott, Meyer, Eigenberger, 'Development of [37] W. Regenass, Chimia 1983, 37, 430. needed to convert a conventional auto- a laboratory fennenter-calorimeter' , in 'Bio- [38] W. Regenass, Thermochim. Acta. 1985, 95, mated laboratory reactor into a calorime- chemical Engineering', G. Fischer, Stutt- 351. ter would be: gart, 1991, p. 352-356. [39] L.G. Karlsen, 1. Villadsen, Chen/. Eng. Sci. 1987,42, 1153. - a temperature sensor in the jacket, [16] Berghof GmbH, D-72800 Eningen, Ger- [40] H.-U. Moritz, in 'Praxis der Sicherheits- - a high resolution of the reactor temper- many. [17] T. Stockhausen, J. Pruss, H.-U. Moritz, in technik', Dechema, Frankfurt, 1995, Vol. ature, 'Polymer Reaction Engineering', Deche- 3, p. 149. - a calibration heater, ma Monographie 1992, 127, 341. [41] W. Regenass, Chimia 1971, 25,154. and, of course, algorithms for control, [18] A. Tietze, A. Pross, K.H. Reichert, Chem.- [42] Designed by A. Mauerhofer. self-tuning, and evaluation. 1ng.-Techn. 1996,68,97. [43] Based on a suggestion of H.-P. Gfrorer. [44] G.A. Marano, J.R. Randegger, D. Weir, The development effort will be high. [19] I. Marison, U. von Stockar, Proc. Biotech. Am. Lab. (Fairfield ConT!.) 1979/1 0, 11, And commercial success is achievable 1983,83,947. [20] U. von Stockar (Inst. Genie Chim., EPF III. only if the resulting instrument Lausanne), Lecture March 5, ]997. [45] W.Gautschi,Ph.D. Thesis, No. 5652,ETH- - is as easy or easier to use than a con- [21] L.W. Morgan, US Pat.697' 997, filed 1957. Zurich, 1976. ventional laboratory reactor, [22] P. Baumgartner, P. Duhaut, Bull. Soc. Chim. [46] W. Kanert, Ph.D. Thesis, University of - has modest space requirements, Fr. 1960, 1178. Basel, 1977. - has additional costs which are clearly [23] H.M. Andersen,l. Polym. Sci.A-1, 1966,4, [47] M. Burli, Ph.D. Thesis, No. 6479, ETH- Zurich, 1979. outweighed by the value of additional 783; ibid. 1969, 7,2889. [24] W. Regenass, Colloquium of the Working [48] Systag System Technik AG, CH-8803 information. Ruschlikon. [49] O. Glasser, 'Dr. W.C. Roentgen', Charles C. Thomas, Springfield/Illinois, 1958. [50] A. Newman, Anal. Chem. 1996, April 1, jacket wall sample 267A. [51] K.B. Mullis, Sci. Am. 1990/4,262,36. [52] R.P.W. Scott, 'Techniques and Practice of T-sensor for jacket T-sensor for sample Chromatography', Marcel Decker, 1995. [53] A. Kussner, Chem.-lng.-Teclm. 1989,61, Tj (to) '-,. • MS ]778/89. --. [54] L.G. Karlsen, H. Sj~berg, J. Vil!adsen, J. h· J Thermochim. Acta. 1984, 72, 83. jacket side film ~ I J [55] L.G. Karlsen, J. Villadsen, Chem. Eng. Sci. * * qf = A hs (1 s - Tw) 1987,42, 1]65. heat transfer properties I I (known by calibration) [56] A calibration heater is indispensable for I I-- inside wall temperature calibrating specific calorimeter vessels I determines heat transfer I (once and for all) and for determining the I from or to sample I heat capacity of the vessel contents (from transients, only the ratio of heat transfer I I qs = qf + (m*cpk;-s capacity to heat capacity UA/m'c can be Tw (tn) I obtai ned). As a cal ibration heater is an alien h _ sample side film w . element in synthesis equipment, it is prob- heat transfer properties ably preferable to use the heater forcalibra- (estimated on-line) tion only, and to calculate the heat capacity of the contents from the batch recipe by Fig. 15. Change of local temperature profiles after a temperature change in the jacket fluid means of a physical property estimator.