Ind. Eng. Chem. process Des. Dev. 1983, 22, 594-598
594
Registry No. H20, 7732-18-5; stannous chloride, 7772-99-8; molybdenum trisulfide, 12033-29-3.
Literature Cited Barton, P.; Fenske, M. R. Ind. €4. Chem. Process Des. Dev. 1970, 9 , 18. Barton, P.; Hajnlk, D. F. In "Adeorptlon and Ion Exchange with Synthetlc Zeolites", ACS Symposlum Serles 135; Flank, W. F.; Ed.; American Chemlcal Socbty: Washington, DC. 1980; Chapter 12. Chrastll, J. J . U?ys. Chem. 1982, 86, 3016. Ferguson, D. E., et al. Chem. Technol. Div. Annu. Prog. Rep. March 1978, ORNL-5383, Oak R@o National Laboratory, Oak Rldge, TN, 1978; p 11. Furman, N. H., Ed. "Scott Standard Methods of Chemlcal Analysis". Vol. 11, 5th ed.;D. Van Nostrand Co. 8 Gorp.: Prhceton, NJ, 1939 pp 1539-50. Gangoll, N.; Thodos, G. Ind. Eng. Chem. Prod. Res. D e v . 1977, 16, 208. Johnston, K. P.; Zlger, D. H.; Eckert, C. A. Ind. f n g . Chem. Fundam. 1962, 27, 191. ModeH, M.; ReM, R. C.; Amln, S. I. U.S. Patent 4113446, Sept 12, 1978. Panzer, F.;Ellls, S. R. M.; Bott, T. R. Can. Inst. Mln. Metall. 1977, 21, 685.
Ross. D. S.; Blessing, J. E.; Nguyen, Q. C. "uqulfaotbn of Bituminous coal in Aqueous Systems", AIChE 88th National Meetlng, Philadelphla, June 8-12. 1980. Ross, 0.' S.; Nguyen, Q. C. "Coal Conversion In Aqueous Systems", AIChE 92nd Natlonal Meetlng, Orlando, FL, Feb 28-Mar 3, 1982. SchneMer. G. M.; Stahl, E.; Wllke, (3, Ed. "Extraction wlth Supercrltlcal Gases", Verlag Chemle: Deerfiekl Reach, FL, 1980. Stewart, T. A., Jr.; Dyer, G. H. US. Patent 3 850 738, Nov 28. 1974. Studlengesselschaft Kohle, m.b.H., MuthelmRuhr, Brlsh Patent 1 057 91 1, 1967. Weller. S. W. In "Catalysls, Vol. IV, Hydrocarbon Synthesis, Hydrogenation and Cyclization"; Emmet, P. H.,Ed.; Reinhold Publishing Co.: New York, 1956. Zhuze, T. P.; Yushkevlch, G. N. Izv. Akad. Nauk S . S . S . R . . -1. Tekh. Nauk 1957, 1 1 , 63.
Received for review April 20, 1982 Revised manuscript received January 5, 1983 Accepted January 29, 1983
Performance of a Pilot Trickle-Bed Reactor for Hydrotreating of Petroleum Fractions: Dynamic Analysis Antonkt Iannlbello, Serglo Marengo, and Alessandro Guercl Stazione Sperimentale per i Combustlbbwl. S. Donato Milanese. Italy
Glancarlo Baldl' and Sllvlo Slcardl Dlpartimento di Scienza del Materiali e Ingegnerte Chimica, Politecnico, Torino, Italy
The total liquid holdup and the intraparticle apparent dlffusivlty have been measured in a pilot trickle-bed reactor by a dynamic method. Different liquids and catalyst particles were tested. The total holdup results show that pore fwling of the catalyst may be considered as total even at very low IiiuM Row rate and at a relatively high temperature. The apparent intraparHcle diffusMty is In line with that measured in bench scale reactors and with other liquid phases.
Introduction The conversion rate of the hydrotreating reactions of petroleum fractions in pilot trickle-bed reactors may be appreciably affected by their hydrodynamics. According to the literature (Satterfield, 1975; Gianetto et al., 1978), this influence is largely due to uneven distribution of the liquid around the catalyst particles. At the low liquid flow rates adopted in some pilot plant units, in fact, there may be zones where the catalyst external surface is scarcely in contact with the liquid, and others where the catalyst is in contact with stagnant pockets. As a result, the apparent conversion rate of hydrotreating reactions in pilot reactors can increase when the liquid flow rate increases (Satterfield, 1975; Paraskos et al., 1975; Montagna and Shah, 1975) at the same space velocity. Solid-liquid contacting effectiveness was first introduced by Satterfield (1975) to explain the influence of uneven contacting on the conversion rate. Colombo et al. (1976) established a connection between contacting effectiveness and the apparent intraparticle diffusivity of a tracer (DJaPp.in trickle conditions: the poorer the contacting effectiveness, due to poorer external wetting of the catalyst, the smaller the (DJapp.Baldi (1980) defined the contacting effectiveness VCE as 112
(1) 0196-4305/83/1122-0594$01.50/0
where Di is the intraparticle diffusivity for a totally wetted particle. Mills and Dudukovic (1981) have proposed a correlation of 7CE as given by eq 1from their own data and those of other workers (Colombo et al., 1976; Herskowitz et al., 1979). Connected with the contacting effectiveness (or external effective wetting) is the issue of internal wetting, Le., the amount of pore volume occupied by the liquid. The results obtained in laboratory reactors with model liquids (Colombo et al., 1976; Mills and Dudukovic, 1981) show a complete pore filling, whereas those obtained with a heavy oil show a poor pore filling that increases considerably (from 30% to 70%) by increasing the liquid holdup (Van Klinken, 1978). Knowledge of both internal and external effective wetting is of the utmost importance in scale-up of trickle-bed reactors. Research work on this topic has mostly been done with bench scale reactors; in this paper we describe the results obtained by applying a dynamic method already used by other (Colombo et al., 1976; Mills and Dudukovic, 1981; Van Klinken, 1978), namely generation of a tracer disturbance in the liquid at the reactor inlet and analysis of the response curve at the reactor outlet. The experimental procedure required a minor modification of the apparatus. Ethyl alcohol at room temperature and a paraffinic oil at 150 "C were used as test liquids. Heptane and decalin were used as the respective nonadsorbing tracers. Nitrogen was employed as gas phase. @ 1983 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 22, No. 4, 1983 595
Table I. Series of Runs
I
I1
I11
IV
test liquid tracer temperature, "C catalyst type bed height, m nominal particle diameter, m bed porosity, e o catalyst porosity, e l
ethyl alcohol
paraffinic oil
paraffinic oil
paraffinic oil
n-heptane 25 Ketjenfine 124-1.5 E extrudate 1.36 2 x lo-' 0.446 0.65
decalin 150 Ketjenfine 124-1.5 E extrudate 1.36 2 x 10-3 0.446 0.65
decalin 150 Ketjenfine 124-1.5 E crushed part. 0.50 8.5 x 10-4 0.40 0.65
decalin 150 Bauxite crushed part. 0.50 8.5 x 10-4 0.40 0.42
Table 11. Physical Properties of the Test Liquids a t the Test Temperature test liquid
viscosity, P a s
surface tension, N/m
density, kg/m3
boiling temp, "C
ethyl alcohol paraffinic oil
1.2 x 10-3 2.78 x 10-3a
2.2 x 1 0 3.3 x 10-b
790 880
> 201
78.5
Extrapolated value from experimental data (from 20 t o 100 "C) according ASTM D 341-74. Calculated from the relationship by Johnson e t al. (as quoted by Chem. Eng. Handbook, 1963). From the distillation curve: initial boiling point, 201 "C; 5% distillate, 370 "C; 30% distillate, 389 "C; 50% distillate, 397 "C. 1
1 -Test liquid tank
2 - Tracer solution tank 3 - Metering pumps 4 - Main pipeline
12
6 - Three - way valves for loop filling and discharge 7 - Three-way valves
8 - Check vaives 9 - Preheater
13 - Liquid sampling
Figure 1. Scheme of apparatus.
Experimental Apparatus and Procedure The schematic drawing of the experimental apparatus is shown in Figure 1. The reactor is designed to attain temperatures and pressures of up to 600 "C and 6 X lo6 Pa. The upper section, 0.4 m long, is the preheating section, in which the liquid and gas phases flow through a double helical path, to improve heat transfer with the hot external wall. The catalytic section is 1.4 m long, with an internal diameter of 2.8 X m; inside, there is a thermocouple m. well with a diameter of 6 X The liquid feed was held in tank 1and pumped to the reactor by a metering pump. A small volume (36 cm3) of a tracer solution in the test liquid was held in a loop connected to the main pipe by the two three-way valves (7). The loop was filled with the tracer solution by a pump. After 20-30 min at the steady state, the valves (7) were suddenly and simultaneously switched to inject the solution into the reactor. The inlet disturbance obtained in this way was similar to a square wave. The response curve was determined by analyzing samples of the outlet liquid with a Carlo Erba gas-chromatograph equipped with a thermal conductivity detector and a 1-m column containing Porapak QS and connected with a Model 3388 Hewlett-Packard integrator. The liquid samples were taken at the outlet of the reactor in the low-temperature tests, otherwise after the heat exchanger ( l l ) , when the paraffinic oil was used. The ratio between the maximum and minimum measured values of the tracer concentration was about 100 in all runs. As a check on the accuracy of the procedure, the total amount of tracer injected into the reactor (calculated from the solution con-
centration and the loop volume) was compared with the amount determined from the response curve. The two values generally agreed within i 3 % . Other details of the experimental and analytical procedure can be found elsewhere (Guerci, 1981). Four sets of experiments with different test liquids, catalyst shapes and type, and bed heights (see Table I) were conducted. The bed porosity was measured in a glass cylinder of the same diameter as the reactor. The physical properties of the test liquids are listed in Table 11. The liquid flow rate was from 1.6 X lo-' kg/(m2 s) to 1.51 kg/(m2 e); the concurrent gas flow rate between 0.037 and 0.067 kg/(m2 s). Under these operating conditions, the reactor was in the trickling flow regime, according to the flow map of Gianetto et al. (1978). Data Analysis The response curves were analyzed by the method of moments. The nth moment and the variance are defined by
J m t n C dt Pn
=
JmC dt
and
2 = P2 - PI 2
(3)
Using the piston-dispersion model for the bed, and the diffusivity model for the particle, the first moment and the variance of the response curve obtained from a perfect Dirac disturbance are (Colombo et al., 1976) PI =
htZ0
(4)
The total holdup ht is given by the sum of interparticle and intraparticle holdup h, = he + hi (6) hi is the liquid volume (per unit reactor volume) internal to the catalyst. For total pore filling, it is given by hi = ti(1 - €0) (7)
BW
-
i
!PJI
isI 600 -
1
I
hr
I series
( ~ , ) ~ 14 = i1 0 - 4 ~ - ‘
I
I
o
0 7r
‘
a
0
Ethyl alcohol runs
A
Paraffinic oil runs
2 4 6 8 L-T 1 0 - 5 1 ~ / ~ 3 ;
i
I
Figure 2. First moment of the resppqae curve from inlet and outlet sections of the reactor vs. L-’.
I
I
a
I
I
0.5 GL r k g / d . SJ
1.0
b)
I
I
1s nd 381y
Figure 4. Total holdup h, vs. GLfor 1.36 m bed height: (a) I series; (b) I1 series; (0) experimental values; (--) calculated from Mills and Dudukovic (1981); calculated from Specchia and Baldi (1977); (-) calculated from Satori and Nishiraki (1971). (-e.-)
id
0.3
os 0 03 0.6 4CbW.SI Figure 5. Total holdup h, vs. GL for 0.50 m bed height: (a) I11 series; (b) IV series; (0) experimental values; (--I calculated from calculated from Specchia and Mills and Dudukovic (1981); Baldi (1977); (-) calculated from Satori and Nishiraki (1971). 0
03
(-e.-)
‘“‘*-e
L 0-7
0-6
LCWsl
Figure 3. Variance of the response curve from inlet and outlet sections of the reactor vs. L.
Equations 4 and 5 are also valid for imperfect pulse disturbance, provided that (8) P1 = (Pdo - G 1 ) I 6 2 = (a2)o - (U2)I (9) where the subscripts 0 and I stand for the curves a t the outlet and inlet of the packed bed (Bishoff and Levenspiel, 1962). The whole apparatus can be regarded as consisting of three sections: an inlet section (l),the packed bed (2), and an outlet section (3). By assuming linear systems, (pl)I and ( u ~can ) ~ be calculated from the response curve of sections (1)and (3) together. The dynamic characterization of these sections was done by taking the packing out of the reactor. It was supposed that the liquid falling into the empty reactor did not affect the response curve. Tailing was taken into consideration by extrapolating the response curves to infinite time, using an exponential function. Experimental Results Analysis of Section 1 and 3. The results of the dynamic analysis of the apparatus without any packing are
shown in Figures 2 and 3. The same volumetric ratio between gas and liquid flow rate was adopted as that employed in the analysis of the packed bed. The first moments for both the tested liquids were straight lines as a function of L-I, showing a constant volume of the liquid in the two sections: 46.7 cm3for ethyl alcohol and 114 cm3 for the paraffinic oil (for which the final heat exchanger was used). These values are reasonable compared with the geometric volumes; they correspond to the volume of the loop plus about 50% of that of the preheater and heat exchanger (where a two-phase flow exists). The ( 2 ) I values were well correlated as a function of L-”, where a was close to 2. For a turbulent system, in fact, u2 may be thought of as u2 0: i.t12/Pe
If Pe = constant on changing the liquid flow rate, u2 is proportional to p12. As this is proportional to L-l, u2 becomes approximately proportional to L-2. Total Liquid Holdup. The results of total holdup are shown in Figures 4 and 5 as a function of L. Theoretical curves, derived from eq 6, assuming a total pore filling and adopting for he some correlations available in the literature (Mills and Dudukovic, 1981; Specchia and Baldi, 1977; Satori and Nishiraki, 1971) are also plotted. The calculated values of hewere always much lower than the measured ht values. For the 1.36-m bed, the total holdup ranged roughly between 0.45 and 0.55; the he values calculated from the Specchia and Baldi correlation ranged from 0.09 to 0.16 approximately. Therefore, he has a minor
Ind. Eng. Chem. Process Des. Dev., Vol. 22, No. 4, 1983
597
Table 111. Values of the Apparent Intraparticle Diffusivity for 1.36-mBed
(Di)appx 1O'O m z / s
GT..
test liquid
kg/Gi s
a
b
C
ethyl alcohol
0.162 0.372 0.761 1.51 0.208 0.447 0.859
3.17 4.03 4.89 6.47 1.58 2.02 1.90
14.0 7.1 5.9 7.1 4.35 6.38 2.20
131.0 8.61 6.23 7.26 8.20 7.17 2.33
paraffinic oil
a
D L = 0.
(1969).
D L from Hochman and Effron correlation D L from Turek and Lange correlation (1981).
importance on ht, which is instead mainly determined from the hi values. In this connection, the generally good agreement between the experimental h, values and the calculated curves for the 1.36-m bed shows that the total pore filling is a reasonable hypothesis, even at a very low liquid flow rate. The results from a 0.5-m high bed are less accurate, since the influence of the inlet and outlet sections on the total response curve is considerable. Even so, total pore filling remains a reasonable assumption. It is interesting to note that the intraparticle holdup for total pore filling in the two cases of Figures 5a and b was significantly different (0.36 and 0.25), due to the difference in porosity of the particles. Notice that for the small crushed particles used in I1 and IV series of runs, the external holdup correlation proposed by Satori and Nishiraki seems much less accurate that the other two examined. Analysis of the Variance. Equation 5 shows that the variance is a function of intraparticle (apparent) diffusivity and axial dispersion. The literature data and correlations for dispersion, however, are not consistent. From the results of van Swaaij et al. (1969), the minimum value of the particle Pecl6t number uLd /DL in our operating conditions is of the order of 0.05. %his would enable the axial dispersion effect to be ignored for the runs carried out in the 1.36-m bed. By contrast, when the correlations given by Hochman and Effron (1969) and Turek and Lange (1981) are used, axial dispersion must be taken into consideration, at least for low liquid flow rates. Table I11 compares the values of (DJappwhen DL = 0 with those obtained when DL is calculated from these correlations. The latter behave irregularly as the liquid flow rate increases, while the former increase, in agreement with the findings of other workers (Colombo et al., 1976; Mills and Dudukovic, 1981; Sicardi et al., 1981). The (Di)appvalues for the 0.5-m bed are very inaccurate: sections 1and 3 have a much greater influence on the variance than on the first moment. According to eq 1, the contacting effectiveness TCE is given by the square root of the ratio between the apparent diffusivity and the true intraparticle diffusivity Di; this latter is a property of the tracer and the pore structure and should be unaffected by the hydrodynamics. By determining qCE with the correlation proposed by Mills and Dudukovic (1981),Di was calculated from
The values of (DJWpresulting from DL = 0 were used. The Di values are plotted in Figure 6 vs. the liquid flow rate; it can be observed that they are not significantly affected by GL, as they are supposed to be.
0.5
1.0
1.5
G~[kg/d.*]
Figure 6. Calculated intraparticle diffusivity of the tracers vs. GL.
The tortuosity factor y of the pores can now be obtained from Dti y=-
Di where D is the diffusivity of the tracer in the liquid. According to the Wilke and Chang (1955) equation, for nm2/s and for heptane in alcohol, 25 OC: D = 1.27 X decalin in paraffinic oil, 150 OC: D = 6.40 X 10-lo m2/s. Combination with eq 11gave for n-heptane, y = 1.04 and for decalin, y = 1.18. One would expect y to be much higher than unity. It is important to note, however, that it is virtually the same for both tracers and for different operating conditions. This may be considered as a satisfying result, since the dynamic analysis of a pilot reactor is inevitably less accurate than that of a bench reactor. Furthermore, it appears to substantiate the hypothesis of a lower value of axial dispersion than that calculable from the literature correlations. Conclusions Some conclusions can be drawn from these findings. Pore filling of the catalyst may be considered as total, even at very low liquid flow rates (and hence very low interparticle liquid holdup) and at a relatively high temperature. Notice that no particular care was taken to ensure a good distribution of the liquid in the bed. This means that the catalyst internal active area is, potentially, totally available for the liquid reactants. The partial catalyst utilization as observed by Koros (1976) and Van Klinken and Van Dongen (1980) is probably more due to intraparticle diffusivity phenomena than to a partial pore filling. The behavior of (DJappvs. the liquid flow rate is the same as in laboratory reactors with other test liquids and tracers, and in line with the correlation of contacting effectiveness proposed by Mills and Dudukovic (1981). This conclusion may be interesting for scale-up purposes. It is well known, in fact, that the apparent first-order kinetic constant for desulfurization and demetallation reactions of heavy oils decreases as the liquid flow rate decreases. Bearing in mind the very low intraparticle diffusivity of the large molecules containing sulfur and metals, it may be hypothesized that the rate of these reactions is strongly affected by intraparticle mass transport phenomena. Catalyst effectiveness factors as low as 0.2 were in fact observed for devanadation reactions (Newson, 1970). Therefore, the decrease of the apparent kinetic constant may be ascribed to the decrease of the apparent
598
Ind. Eng. Chem. Process Des. Dev. 1983, 22, 598-604
intraparticle diffusivity of the reactants. The correlation of (Di!app/Diproposed by Mills and Dudukovic (1981) which is, to a certain extent, validated by this work, may be useful to evaluate the hydrodynamic conditions where the kinetic rate constant may be independent from hydrodynamics. Nomenclature
C = tracer concentration, kg-mol/m3
D = molecular diffusivity, m2/s Di = intraparticle diffusivity, m2/s (DJWp= apparent intraparticle diffusivity for partially wetted particles, m2/s DL = axial dispersion, m2/s D, = particle diameter, m GL,G, = mass velocity of liquid and gas respectively, kg/m2 S
he,hi, h, = interparticle, intraparticle, and total liquid holdup L = volumetic liquid flow rate, m3/s P, = ULZO/DL,axial P&l& number rp = radius of the pellet, m t = time, s uL = liquid superficial velocity, m/s 2, = bed height, m Greek Letters y = turtuosity factor ci = particle porosity to
= bed void fraction
qCE =
contacting effectiveness
pL = liquid viscosity, kg/m p,, = nth moment, s"
s
liquid density, kg/m3 Ek - variance of the response curve,
UL
= surface tension, N/m
Registry No. Ethyl alcohol, 64-17-5; Ketjenfine 124-1.5 E, 86422-55-1; bauxite, 1318-16-7.
L i t e r a t u r e Cited Bakli, G. I n "Muhiphase Chemical Reactors", Rodrigues, A. E. et ai., Ed.; SlJthoffand Nmrdhoff Int. Aiphen aan den Rijn, The Netherlands, lS6l; Voi. 11, p 323. Blshoff, K. B.; Levenspiel, 0. Chem. Eng. Sci. 1962, 17, 247. "Chemical Engineers Handbook", 4th ed.;Perry, J. H., Ed.; McGraw-Hili: New Y d , 1963. Colombo, A. J.; BaMi, G.; Sicardi, S. Chem. Eng. Sci. 1976,3 1 , 1101. Gianetto, A.; &Mi, 0.; Specchia, V.; Sicardi, S. A I C E J. 1976,24, 1087. Guerci, A. Chemical Eng. Thesis, Poihecnico of Twln, Oct 1981. Herskowltz, M.; Carbonell, R. D.; Smlth, J. M. A I C E J . 1979,25, 272. Hochman, J. M.; Effron, E. lnd. Eng. Chem. Fundem. 1969,8 . 63. Koros, R. "hoceedings", 4th International Symposium on Chemical Reaction Engineering, Hebiberg, West Germany, Apr 4-6, 1976. MiHs, P. L.; Dudukovic, M. P. AIChE J. 1961,2 7 , 693. Montagna, A. A.; Shah, Y. T. Ind. Eng. Chem. Process D e s . D e v . 1975, 14, 479. Newson, E. I."Preprints A", 160th National Meeting of the American Chemical Society, Chicaga, Sept 1970;American Chemlcel Society: Washington, DC, 1970. Paraskos, J. A.; Frayer, J. A.; Shah, Y. T. Ind. Eng. Chem. Process Des. Dev. 1975, 14. 315. Satori, H.; Nishiraki, S. Int. Chem. Eng. 1971, 1 7 , 339. satterfleld, C. N. AICM J. 1975,21,209. Sicardi. S.;BaMi, G.; Speccha, V.; Gianetto, A,; Mazzarino, I.Chem. Eng. Sci. 1961,3 6 , 226. Specchia, V.; BaMi, G. Chem. Eng. Sci. 1077,3 2 , 515. Twek, F.; Lange, R. Chem. Eng. Scl. 1961,3 6 , 569. Van Kiinken, J. "Proceedings International Symposium on Chemical Engineering-Gas-Liquid-Solid Catalyst Reaction"; Li6ge. Belgium Mar 1-3, 1978. Van Kiinken. I.; Van Dongen, R. H. Chem. Eng. Sci. 1060,35,59. Van Swaaij, W. P. M.; Charpentier, J. C.; Viiiermaux, J. Chem. Eng. Sci. 1969,24, 1083. Wiike, C. R.; Chang, P. AIChE J. 1955, 1, 264.
Received for review May 10, 1982 Accepted February 8, 1983
s2
Sulfation of Calcium Hydroxide and Simulation of Sulfur Dioxide Remowal in a Transport-Line Reactor with Recirculation Mlloslav Hartman, Karel Svoboda, Otakar Trnka, and Robert W. Coughlln' Institute of Chemical Process Fundamentals, Czechoslovak Academy of Science, 165 02 Prague-Suchdo/, Czechoslovakia
The rates of sulfation of calcium oxide formed in situ by thermal decomposition of calcium hydroxide were measured at 800 'C. A kinetic equation based on Jerofeev's theory of random nucleation and growth fits the data with gocd accuracy. This rate law equation is used as the basis for a simple model of a transport-line reactor for contacting flue gas with solid sorbent, including recycle of the soli phase. The model predicts that under specified conditions the transport-line reactor is capable of removing a large portion of SO2 present in flue gas. Even at large recirculation ratios the volume fraction of solids in the reactor remains less than 0.03.
Introduction
Experimental findings and theoretical consideration (Potter, 1969; Borgwardt and Harvey, 1972; Hartman and Coughlin, 1976; Hartman et al., 1978; Bhatia and Perlmutter, 1981) indicate that both the rates of sulfation and the attainable conversions of calcareous sorbents are strongly influenced by the porosity and grain size of the *Addresscorrespondence to this author at the Department of Chemical Engineering, University of Connecticut, Storrs, CT 06268. 0196-43051831 1122-0598$01.50/0
solid particles. According to these results calcareous sorbents for sulfur dioxide should be fine-grained and highly porous for maximum efficiency. Unfortunately, the large majority of commercial limestones and dolomites do not meet such requirements. In previous work (Hartman et al., 1982), we compared the reactivity of a high grade commercial limestone with that of hydrated lime made from the same limestone. Calcium hydroxide reacted with sulfur dioxide much more rapidly and extensively than did the carbonate. While the attainable conversion of the carbonate was only about 25%, the hydroxide was almost completely converted to 0 1983 American Chemical Society
