Modeling Complex Chemical Reaction Systems Gary C . April* Chemical and Metaiiurglcal Engineering Department, Univers/ty of Alabama. University, Alabama 35486
and Ralph W . Pike Chemical Engineering Department Louisiana State University, Baton Rouge, Louisiana 70803
A method for determining the energy absorbed by gases undergoing complex chemical reactions is presented. The conditions of the study are typical of those encountered during thermal degradation of nylon-phenolic resin heat shield materials with subsequent flow of pyrolysis gases through the ablated char layer. Results are reported for a temperature range 700-1300" and pyrolysis gas fluxes between 0.001-0.01 g/cm2 voids sec. Radioactive labeled methane and phenol are used to determine product distribution and location of carbon deposition within the porous char. Comparison of these experimental results with those of the model is also presented.
Introduction The objective of this research is to determine accurately the energy absorbed by a complex mixture of gases undergoing chemical reaction. The specific example is a reacting gas flow through the char zone of a charring ablator. By its very nature this system involves a very complex mixture of gases evolved during thermal degradation of a nylon-phenolic resin heat shield. Because of this inherent complexity. application of mathematical modeling methods founded on the laws of conservation of mass and energy are used. Subsequent verification of the model by experimental simulation of the charring ablator is achieved by passing reacting gas mixtures through heated char sections. Chemical analyses of the pyrolysis products of methane and phenol over the char, both by gas chromatographic and radioactive tracer methods, lead to specific reactions used to describe the system. Experimental rate law data from the literature for each reaction are then used to predict the composition of the reaction products as they exit the char zone. Direct comparison of model and experimental results are presented as carbon deposition and pyrolysis product composition profiles as a function of temperature within the char. Energy transfer, reflected as a surface heating potential and a reacting gas heat capacity, is calculated using the verified model as a means of relating the various system variables to the improvement in energy absorption resulting from the predominantly endothermic chemical reactions ofthe gases within the char layer. Mass and Energy Transfer in the C h a r Zone
To compute the composition of the pyrolysis gas stream leaving the char zone, it is necessary to solve the species continuity equation for each gas component. The equation for one-dimensional, steady flow of gases through the char zone, neglecting diffusion, is
c h a n g e in m a s s by convective t r a n s p o r t
mass generation by chemical reaction
T o compute the energy transferred in the char zone, It is necessary to solve the energy equation with appropriate boundary conditions. For steady flow of reacting gases in a char zone of constant thickness, the energy equation has the following form according to April (1971) - dT U',C,t -
dz convective heat transfer
conductive h e a t transfer
heat absorbed by c h e m i c a l reactions The energy absorbed in the char zone is equal to the difference between the heat flux at the high-temperature surface and the heat flux at the low-temperature surface. Thus the energy absorbed for reacting gas flow in the char is given by
h e a t absorbed due t o c h a n g e in g a s e n t h a l p y
h e a t a b s o r b e d by chemical reaction I :i,
In order t o solve the above equations. the calculation of the reaction rate, R,, for an arbitrary number of simultaneous chemical reactions involving an arbitrary number of chemical species must be made. A chemical reaction can be written in general as
For this ith chemical reaction. the r,, and p l , represent the stoichiometric coefficients of the reactants and products. respectively, for species A , . The forward and reverse reaction rate constants are k f , and k r L .There are K chemical species. For the rate of reaction of the j t h species. K,, this is given by the following equation for n chemical reactions
Deposition or depletion of species by chemical reaction is considered to be insignificant such that the gas mass flux remains constant. Ind. Eng. Chem., Process Des. Develop., Vol. 13, No. 1 , 1974
1
Table I. List of Reactions and Associated Kinetic Data for Predicting the Stoichiometric Conversion of Pyrolysis Product Species in the Char Zone between 200 and 1300' (April, 1969)
+
+
+
+
+
+
General Form of the Reactions aA bB = rR SS General Rate Constant Equation h = PT-9 expi - E R T ) Reaction no.d
Reaction
+ + + +
~~
1 2
3 4
5 6 7 8 9 10
Rate law
CHI = ','zH?':'zC2H6 C?Hs = CzH, Hz C,H, = C?Hz H, CZH: = 2C H? C 2H2 = CHd CGH60 H, = H,O CsH6 C6H6 = 3C2H2 C H?O = CO H: CO HzO = Hz CO? c cor = 2 c o
+
+
+ + +
+
+ +
Activation energy, E , kcal'g mol
k iA k iA k iA hiA2 k iA k iA
ktAB hiAB hiA - kxR2
a First order, sec-l. * Second order, cm3 'g mol sec. c Zero order, g mol/cm3 sec. considered negligible.
where cJ is the concentration of component j in appropriate units. This equation has the powers on the composition terms the same as the stoichiometric coefficients. However, it is not necessary to do this. If this is not the case for some of the reactions being used, it is only necessary to include two additional matrices besides rLJand pi, in the computer implementation. The species continuity and energy equations are solved simultaneously using a fourth-order Runge-Kutta analysis programmed in Fortran IV on an IBM 360 computer. However, before the calculations can be performed, two additional pieces of information must be known. These are the specific stoichiometric conversion of the pyrolysis products in the char as predicted from chemical kinetic data in the literature, and the initial composition of the pyrolysis gases entering the char zone. The ten specific chemical reactions and the kinetic data that predict chemical conversion of the gases within the char are listed in Table I. These data were critically selected and are representative of the best available information in the literature (April, 1969). Criteria for Reaction Selection
In a study by Pike (1966) the literature was surveyed for the kinetics of the chemical reactions that could possibly occur in the char zone during ablation. However, it can be shown that not all of these possible reactions are important in the temperature range of interest. To determine the chemical reactions that would occur with a significant conversion in the char, two procedures were used. One procedure consists of computing the conversion of one reaction of an equal molal mixture of reactants flowing isothermally through the char. The other procedure consists of estimating the species and the composition that entered the char zone from thermogravimetric analysis, pyrolysis gas chromatographic analysis, and thermodynamic equilibrium calculations. A comparison of the initial composition from this latter approach is given in Table 11. These two procedures combined with subsequent experimental verification using carbon-14 tracer studies determine the important reactions that describe reacting gas flow in the char. Experimental Simulation of the C h a r Zone during Ablation Experiments were conducted to establish the accuracy of the kinetic model with an experimental system that 2
Ind. Eng. Chem., Process Des. Develop., Vol. 13, No. 1, 1974
d
S
7.6 X
95.0 70.0 40.0 10.0 17.0 45.0 35.0 82.0 30.0 50.0 61.0
hi
Frequency factor
x 1014~ 2 . 6 x 108U 2 . 1 x 10'0b 2 . 0 x 10gc 2 . 0 x 1013a 1 . 4 x 109a 1 . 2 x 1012b 1 . 0 x 10'2b 1 . 0 x 106" 1 . 0x 10-9b 3.1
0 0 0 0 0 0 0 -1 0 -1 0
I n reactions 1-9, the reverse reactions are
p k 3 . L RECORDERS
qsg \
1
"IN1
CHAI UNIT
AIR
HEbTlNG
;j
MANOMEIER
Figure 1. Schematic diagram of the char zone thermal environment simulator. simulates the char zone during ablation. A schematic diagram of the char zone thermal environment simulator is shown in Figure 1. In this simulator actual chars formed in arc jets are utilized. Gas compositions typical of the degradation products are passed through the heated chars. Important variables are monitored with exit gas samples taken a t specific time intervals. These samples are then analyzed using a Packard Model 7800 gas chromatograph equipped with a Model 871 proportional temperature controller and a Model 836 power supply. A 9 ft by 0.25 in. diameter column packed with Hewlett-Packard BPL-20 activated charcoal is used to determine Hz, CO, and CH4 while a 6 ft by 0.25 in. diameter Porapak S coiumn is used t o determine CHI, CO, C2H4, CzH2, and &He. In the cases where carbon-14 tagged methane and phenol are used, a Packard Model 2002 liquid scintillation spectrometer with a Model 280A ratemeter is available for determining product distribution from the labeled compounds. A Model 325 Tri-Cab combustion furnace is used to combust the separated gas components as they exit the gas chromatograph prior to entry into the spectrometer. Radioactive methane and phenol are used in separate experiments to determine the specific products of decomposition from each labeled species. Also, the amount and location of carbon deposition in the char due to the thermal cracking of each species is determined. Typical results for carbon-14 labeled methane are shown in Figure 2a, in which the gas chromatogram(s)
Table 11. Composition of the Pyrolysis Gases from Phenolic Resin, Nylon, and a 50% Phenolic Resin-50 W t yoNylon Mixture in Mol c/o
Thermogravimetric and pyrolysis gas chromatographic analyses ___ __ __ Phenolic resin Nylon-6 only only" iSykes and Nelson, ilkladorski,
Equilibrium composition calculated for the phenolic-nylon mixture (del Valle, 1967) 300 500'
Component
1.45 32.47 8.06 0.02 10 --11 10 -:J 1.52 56.48 10 --20 10 - 2 0 10 - 20 b b b 0 100.00
H2 HZO N2 NH, HCN CO CO, CH, C,Hy CrH: CaH, CiHa CFHSOH Methyl phenols Others Total
1967)
~~-_______
500' 15.1 34.8
43.25 19.01 6.28 0.02 10 -5 1.85 3.42 26.15 10 -10 10 - j 10 - I 3 b b b 0 100.00
0
0 0
4.5 0.9 7.8 0 0
0.2 0.8 28.1 7.8 0 100.00
~
-.
100 -1000" 50.0 23.4 0 0 0
5.5 1.6 10.0 0 0 0.2 0 .3 7.1 1.8 0 100.00
.-
1964) -
400
0 35.4 0 0 0 0 55.8 0
Nylonphenolic {Sykes, -
1967)
800--900' 32.2 23.3 0 0,4 0 3 6 6.8 4.0
0 0 ,4
0
0 0 .4
5.8
0 .3
0 0
0 2.6 100.00
7.6 9.9
11.5 100.00
Liquid products obtained during pyrolysis were not identified (about 95% of the total pyrolysis products). sidered. due to the lack of necessary free-energy data. 'j
I
I L
. I
CARBON I4
PORAPAK I
L
[
1\
CARBON 14
PORAPAK f
I
I A
Figure 2. Gas chromatograms and radioactivity curves for carbon-14 labeled phmol ( a ) and methane ( b ) . and corresponding radioactivity curve are presented. The particular results are for a front surface temperature of 1060" and a gas mass flux of 0.005 g/cm2 voids sec. By comparing the two curves, the products of methane decomposition are found to be unreacted methane, carbon monoxide, carbon dioxide, ethylene, and acetylene. These results for methane are very important in the light of predicting the manner in which energy can be absorbed by chemical reaction. Ethylene and acetylene, for example, are indirect products of methane decomposition predicted by reactions 1-4 in Table I, while carbon monoxide and dioxide are formed by the reaction of steam with deposited carbon in reactions 8-10. This information establishes that the chemical reactions used to predict the stoichiometric conversion of species in the pyrolysis gas system and corresponding heats of reaction are adequate. A similar discussion is presented for labeled phenol. These results are likewise shown in Figure 2b. Conditions for the presented data are a front surface temperature of 1070" and a mass flux rate of 0.001 g/cm2 voids sec. The exit gas products for phenol degradation are methane, carbon monoxide, carbon dioxide, ethylene, and acetylene, as well as unreacted phenol analyzed in the liquid phase. Once again insight into the kind of reactions necessary to produce the products is obtained. The formation of
Not con-
hydrogen and carbon by reactions 6 and 7 is probable by the observed carbon deposition within the char. Hydrogenation of carbon by reaction 5 to form methane, followed by the steam-gas reactions 8-10 and the hydrocarboncracking reactions 1-4 accounts for each radioactive species observed. In both methane and phenol degradation. thermal decomposition of the major species in the simulated pyrolysis product stream is described and accounted for by the reactions considered important between 200-1300". In addition to the product distribution resulting from the thermal degradation of methane and phenol, deposited carbon is also observed to occur. The location of the carbon deposition within the char layer is important in defining the temperature at which reactions become significant. Carbon Deposition Studies by Radioactive Tracer Methods The location and extent of carbon deposition resulting from methane and phenol decomposition is determined using carbon-14 labeled methane and phenol. In the specific cases studied, labeled methane and phenol are fed separately as components in the simulated pyrolysis product stream entering the char. The char is removed after each experiment and sectioned by removing thin layers. These layers vary between 1 and 10% (by weight) of the total char and are combusted separately with collection of the carbon dioxide in 1 M hydroxide hyamine (in methanol) solution. The radioactivity of each thin layer is determined and plotted as a lunction of char depth. In Figure 3 curves for the thermal degradation of phenol and methane are shown. These curves represent the per cent radioactivity per unit thickness a t a particular char depth. The results are for phenol decomposition at a mass flux rate of 0.0015 g/cm2 voids sec and a front surface temperature of 1070". Deposition of carbon appears to start at a temperature of 700", and continues uniformly to 1050". At this point a rapid decrease is noted indicating either no further carbon deposition or disappearance of carbon by chemical reaction. Ind. Eng. Chern., Process Des.
Develop.,Vol. 13, No. 1 , 1974 3
1
d
I -
1 -
I
I
I
"t 0
I
I
I
TEMPERATURE.
1
1000
800
600
400
1200
OC
Figure 3. Carbon deposition profiles resulting from carbon-14 la-
beled methane and phenol degradation. Methane W , g / cm2 voids sec 0.001 L , cm 0.61 c (porosity) 0.5 T b a c k surface,
"c
Tfront s u r f m , "C Feed composition, mol % CsHsOH CHI CO,
Phenol 0.0015 0.61 0.5 500 1060
600
1070
co
H? H?O
6.2 6.7 1.1 3.7 33.4 48.9
100.0 Similar results are observed for carbon deposition by methane decomposition in Figure 3. Since carbon deposition by methane and/or phenol degradation is an increasing function of temperature, and, since a substantial amount of phenol and methane is present in the exit gas stream, it is unlikely that carbon deposition reactions have terminated. Instead, the reaction of the deposited carbon (and char) with water vapor, carbon dioxide, or hydrogen is a more probable explanation of the decline noted in Figure 3. This is also substantiated by the rapid decrease in water concentration and a net increase in carbon content as measured by the exit gas analysis a t the same temperature where carbon deposition declines. Additionally, carbon is observed on the quartz cover plate and inside surfaces of the outer char holder section which indicates that the carbon deposition reactions are continuing after the gases have left the char surface. Therefore, a very comprehensive picture of carbon deposition with regard to its location, the possible causes for its appearance and disappearance, and its effect on the exit gas product distribution is obtained. This is one additional, important tool in developing an accurate mathematical model for predicting phenomena very difficult and often impossible to determine using theoretical considerations.
Verification of the Model Equations The method used to test the accuracy of the model in describing the behavior of reacting gas flow within the char layer of an ablator is one of direct comparison of experimental and model exit gas compositions. The data collected using the char zone thermal environment simulator are shown in Figure 4. Excellent agreement between the experimental and model values are indicated for wide variations in exit gas compositions resulting from variations in the gas mass flux and front surface temperature. Of particular significance is the curve for carbon depletion us. temperature within the char. Although carbon deposition is observed in the tracer studies there seems to be significant reaction of the carbon (or char) to produce a net decrease in carbon within the porous medium. To 4
Ind. Eng. Chem., Process Des. Develop., Vol. 13, No. 1, 1974
t
r-
700
I
9W
I
o+
Il
1100 TEMPERATURE, g:
Figure 4. Comparison of experimental (dots) and model (lines) exit gas compositions: W = 0.001 g/cm2 voids sec; I, = 0.61 cm; c = 0.5; composition (same as Figure 3).
some extent, the carbon depletion curve follows the steam depletion curve indicating significant production of CO by eq 8. Similarly, the rate of methane production is never exceeded by the rate of methane depletion, although there is evidence from the tracer studies that methane does in fact degrade. Hydrogen likewise follows an unusual path first decreasing then increasing to a relatively stable value indicating nearly equal rates of depletion and generation. The fate of other gas species are predicted well by the model results, but follow less dramatic paths. In all cases the predicted values of the gas composition were within experimental accuracy. Results of a Parametric Study of the Flow of Reacting Gases in the C h a r Zone A comparison of the model results with the experimental data is important in determining the accuracy of the flow model. However, very little quantitative information, beyond the discrete sets of data for each experiment, are assembled regarding the effect of changing mass flux and/ or temperature. As a result, a parametric analysis is presented to accurately relate the changes in these variables with variations in energy absorption within the char. To do this the back surface temperature and temperature gradient are specified as boundary conditions in eq 2 and 3 for various values of the mass flux. The results of the calculation are in the form of the net heat transfer a t the surface, called the approximate aerodynamic heating, which is the sum of the surface heat flux and radiant heat flux resulting from the calculated front surface temperature q, = -he
dT1 6
l:=i
+COT,~
(6)
where a value of 0.95 was used for the emissivity. This information is shown in Figure 5 in which the mass flux is plotted against the approximate aerodynamic heating for various heats of pyrolysis, q p (function of the temperature and gradient at the back surface)
where q p is the sum of the energy absorbed by the decomposition of the polymer and the energy conducted through
the virgin plastic. Results for a nonreacting and a reacting flow model are presented. This form of presenting the results is a very convenient and informative method as will be seen. In a reentry problem one of the important questions asked is what is the required heat shield weight for protection for a certain mission. Specification of the type of heat shield material to be used ( e . g . , nylon-phenolic resin) brackets the heat of pyrolysis value, while the trajectory calculations determine the amount of surface heating that can be expected. For example, an approximate aerodynamic heating rate of 135 cal/cm2 sec and a heat of pyrolysis of 220 cal/g locates two points on Figure 5; one for each of the nonreacting and reacting flow cases. This corresponds to two distinctive values of the mass flux; 0.008 g/cm2 sec for the nonreacting case and 0.0045 g/cm2 sec for the reacting case. The reacting flow model accurately predicts the behavior and specifies more exactly the heat shield weight (function of the mass flux) required while the nonreacting case shows an over-prediction because important endothermic reactions are omitted. The results presented in Figure 5 also provide a way of determining a t what point the reacting flow model changes from a nonreacting to a reacting flow condition governed by finite reaction rates (13.5 cal/cm2 sec).
t
d
Calculation of t h e Reacting Gas Heat Capacity In addition to the above information, the reacting gas heat capacity for the reacting flow of pyrolysis products through the char can be determined. This term is very useful in the calculation of the one-dimensional, transient response of an ablative composite. The energy equation for the transient case can be put in the following form as described by April and Pike (1971)
Figure 5 . Parametric analysis relating variations in energy absorption with system variables for reacting and nonreacting flow models: heat of pyrolysis, cal/g: curves a, 220; curves b, 330, curves c, 440; curves d, 550; composition (same as Figure 3 ) .
K+,
P NONREACTING
where W is the mass flux of pyrolysis products a t z and Wo is the mass flux of pyrolysis products entering the char. The term in brackets is referred to as the effective reacting gas heat capacity. Hence, the flow within the char zone can be considered nonreacting (ZHJ?, = 0) by introducing the reacting gas heat capacity estimated from experimental data or from the reacting flow model as an input function to the transient calculations. In Figure 6 a plot of the reacting gas heat capacity as a function of temperature is shown for nonreacting and reacting flow within the char layer u p t o 1300".These curves are calculated for a mass flux of 0.02 g/cm2 sec, a back surface temperature of 250", and char porosity and thickness of 0.8 and 0.61 cm, respectively. Again the separation in the curves is attributed to the increased energy absorption due to endothermic chemical reaction of the gases. Conclusions A method for describing complex reacting gas flow within porous media has been demonstrated for the particular case of pyrolysis gas flow in the char layer of an ablator. This method includes a mathematical model based on the principles of conservation of mass and energy with emphasis on a method for including experimental reaction rate parameters of the various species present in the gas system. Extension of the method to other complex systems is suggested when a detailed chemical kinetics analysis is untractable.
I 900
I
I
1100 TEMPERATURE OC
I
I
I
1300
1500
Figure 6. Reacting gas heat capacity as a function of temperature for the reacting and nonreacting flow models: W = 0.025 g/cm2 sec; L = 0.61 cm; 6 = 0.8; composition (qame as Figure 3).
Verification of the model results is made by direct comparison of experimental results obtained in a char zone thermal environment simulator using gas chromatographic and carbon-14 tracer analyses of the exit gas and solid medium. In all cases studied, the predicted compositions of the model were within the experimental accuracy of the measured values. Application of the model in predicting energy absorbed by chemical reaction of pyrolysis gases within the char layer of an ablator is illustrated by comparison of surface heating curves and reacting gas heat capacities for reacting and nonreacting flow cases. In both cases, the reacting flow model predicts a significant improvement in energy absorption by including the effect of endothermic reactions of the pyrolysis gases within the char. Ind. Eng. Chern., Process Des. Develop., Vol. 13,No. 1, 1974
5
Acknowledgment This research was sponsored by the National Aeronautics and Space Administration under Grant No. NGR 19001-016 a t Louisiana State University, and continued under RGC Grant No. 726, The University of Alabama. There support is gratefully acknowledged. Nomenclature
A = cross-sectional area ofthe char zone, cm2 = species identification code = concentration, cm3/g mol = heat capacity ofthe gas mixture, cal/g "C k,, = effective thermal conductivity of the gas mixture, cal/cm2 sec "C/cm H,,= enthalpy per unit mass of component;, cal/g K = number of gaseous species n = number of chemical reactions pi, = stoichiometric coefficients of the products y = heat flux, cal/cm2 sec q,, = heat ofpyrolysis, cal/g R, = reaction rate of component;, g mol/cm3 sec r,, = stoichiometric coefficients of the reactants T = temperature ofthe gases within the char, "C t = time, sec I ) = velocity of gases within the pores, cm/sec W , = mass flux of gases within the pores, g/cm2 sec
c,) c b
c
= porosity gas density, g/cm3 = Stephan-Boltzmann constant
p = CT
Subscripts
cz = refers to char zone i = refers to chemical reactions j = refers to chemical species 0 = refers to initial value L = refers to final value Literature Cited April, G . C.. Ph.D. Dissertation, Louisiana State University, Baton Rouge, La., 1969. April, G. C., Pike, R . W.. del Valie, E. G . . National Aeronautics and Space Administration, Report No. NASA-CR-1903, 1971. April, G. C.. Pike, R. W.. A l A A J . , 9 (e), 11 13 (1971). del Valle, E. G . , April, G. C., Pike, R. W., Paper 13e. 62nd Annual Meeting of the AIChE. Salt Lake City, Utah, May 1967. Madorski, S. L., "Thermal Degradation of Organic Polymers," Wiley-lnterscience, New York, N. Y . . 1964. Pike, R. W., National Aeronautics and Space Administration, Working Paper No. 181, 1966. Sykes. G. F.. National Aeronautics and Space Administration, Report No. NASA TN-D-3819, 1967. Sykes, G. F., Nelson, J. B., Preprint 7b, 61st National Meeting of the AIChE, Houston, Tex., Feb 1967.
Receiued for reuieu' J u n e 19, 1972 Accepted August 2, 1973
Modeling of a Thin-Film Sulfur Trioxide Sulfonation Reactor Gary R . Johnson Chemicals Research Division. Conffnental Of1 Company. Ponca Cfry, Oklahoma 74601
and Billy L. Crynes* Scbool of Chemfcal Engineering. Oklahoma State University Sfillwater Oklahoma 74074
Thin-film sulfonation reactors are becoming more widely used in the detergent industry as a means of directly combining sulfur trioxide with organic materials. The reaction however is highly exothermic and can under certain conditions produce degradation of the product. Presented is an engineering model for predicting the longitudinal temperature and conversion profiles of the organic liquid film during its travel along the reactor tube. The model then predicts product quality under various operating conditions. Results show that a large portion of the total conversion occurs in the first few inches of the reactor length producing a maximum liquid film temperature in that region. Reactor outlet temperatures do not give a clear indication of the magnitude of the front end temperature peak. Variables such as loading, inert gas rate, cooling water temperature, and reactor diameter substantially affected the liquid film temperature profile.
Introduction The manufacture of detergents is a n interesting and highly specialized industry in the United States. At the present time the most common raw material for formulation of household detergents is linear alkylbenzene. The alkylbenzene is sulfonated with sulfur trioxide to make the sulfonic acid.
Following this, the sulfonic acid is then neutralized and mixed with other ingredients to make the final detergent. 6
Ind. Eng. Chern., Process Des. Develop., Vol. 13, No. 1 , 1974
Sulfur trioxide is a n extremely reactive compound, being a n oxidizing as well as a sulfonating agent. The sulfonation reaction rate is instantaneous and exothermic; the heat of reaction is about 900 Btu/lb of SO3 reacted. As a result liquid SO3 cannot be added directly to the organic material to be sulfonated because of safety and product degradation problems. Instead SO3 is commonly vaporized and diluted with dry air. One of the most widely used systems for reacting sulfur trioxide with organic materials is a tubular thin-film sulfonation reactor. Figure 1 illustrates a typical reactor. It consists of a vertical tube into which the organic liquid and the SO3-inert gas mixture are continuously fed. The organic liquid forms a thin-film on the inside of the tube wall, while the SOZ-inert gas mixture travels down the
