1792
I n d . Eng. Chem. Res. 1988,27, 1792-1797
temperature was increased. The midboiling point values showed only a very small decrease with increasing temperatures. The aniline point values for all these runs were within 44-47 "C, which was lower than for the original oil (52.7 "C). It appears from these observations that mostly the long-chain paraffinic components are cracked, giving lower viscosity values and lower aniline points. The resulting increased aromaticity could thus explain the negligible change in density and midboiling points. It can be concluded from a comparison of these results with those obtained with the catalyst that most of the sulfur and nitrogen removal was mainly due to the catalytic activity and not the thermal effects. Also the catalyst was able to successfully break the condensed aromatic molecule to yield more paraffinic product oil. Conclusions The hydrotreatment of heavy oil was investigated over a highly efficient catalyst containing 2.24 wt % NiO and 5.37 wt % Mooz supported on a support (10 w t % silica, 25 w t % rare earth exchanged Y-zeolite, and 65 wt % alumina) in a trickle bed reactor at 623-698 K (350-425 "C), LHSV of 1-4, and 6.99 MPa. At 698 K (425 "C) and a LHSV of 2, it removed 99% S and 80% N present in the heavy oil as compared to 86% S and 61.4% N removed by a commercial Ni-Mo on alumina catalyst at 723 K (450 "C)and at the same pressure and LHSV. A maximum gas formation of about 0.7 wt % of feed oil was observed at 698 K (425 " C ) and LHSV of 1. The kinetic study suggested orders of 1.5 and 2.0 in the power law model for S and N removal, respectively. Activation energies for the
HDS and HDN were found to be 20.8 and 25.1 kcal/mol, respectively.
Acknowledgment We are grateful to the Natural Science and Engineering Research Council of Canada for financial aid (A-1125)and to CANMET. Registry No. Ni, 7440-02-0;Mo, 7439-98-7. Literature Cited Benesi, H. A.; Bounar, R. V.; Lu,C. F. Anal. Chem. 1955,27,1963. Bolton, A. P.Experimental Methods i n Catalyst Research; Anderson, R. B., Ed.; Academic: New York, 1976;p 33. Box, G. E. P.; Hunter, J. S. An. Math. Statis. 1957,28, 195. Box, G.E. P.; Wilson, K. B. J . R. Stat. SOC.1951,13, 1. Faeth, P.A.; Willingham, C. B. "The Assembly, Calibration, and Operation of Gas Adsorption". Technical Bulletin of Physical Chemistry, Carnegie Mellon Institute of Research, Pittsburg, Sept 1955. Heinemann, M. CataE. Rev. Sci. Eng. 1981,23(1982),315-328. Mann, R.S.;Sambi, I. S.; Khulbe, K. C. Ind. Eng. Chem. Prod. Res. Deu. 1982,21 (4),575. Mann. R. S.: Sambi., I. S.:. Khulbe. K. C. Ind. Enp. - Chem. Res. 1987, 26,'410.
'
Sambi, I. S. Ph.D. Thesis, University of Ottawa, Ottawa, Canada, 1986. Smith, J. M. Chemical Engineering Kinetics, 3rd ed.; McGraw-Hill: New York, 1981. Vogel, A. Textbook of Quantitative Inorganic Analysis, 4th ed.; Longman: London, 1978.
Received for review September 30, 1987 Revised manuscript received April 12, 1988 Accepted May 23, 1988
Measurement of Brernsted Acid and Lewis Acid Strength Distributions of Solid Acid Catalysts Using Chemisorption Isotherms of Hammett Indicators Kenji Hashimoto,* T a k a o Masuda, and Hideki Sasaki Department of Chemical Engineering, Kyoto University, Kyoto 606, Japan
A new method was developed that discriminates Brernsted acid and Lewis acid sites and measures the distributions of both kinds of sites. It uses the chemisorption isotherms of Hammett indicators. Three different samples were prepared: an unpoisoned sample and two poisoned samples. In one of the poisoned samples, only the Brernsted acid sites were poisoned with 2,6-dimethylpyridine, whereas in the other poisoned sample both types of acid sites were completely poisoned with ammonia. The amount of indicator chemisorbed on each kind of acid site was calculated from differences in the amounts of indicators adsorbed on the three samples. Using the two kinds of chemisorption isotherms obtained, we calculated the acid strength distribution curves of the Brernsted acid and Lewis acid sites for the range of acid strengths (Ho)from -3 to the strongest strength using our recently reported indicator adsorption method. The acidic properties of six silica-alumina catalysts were measured in the range of acid strength from -3 to about -15 by use of the proposed method. The Brernsted acid sites on the silica-alumina catalysts had a relatively wide distribution of strengths, whereas most of the Lewis acid sites were distributed in the narrow range of acid strength from -10 to -13. Acid sites of different strengths are distributed over the surfaces of such solid acid catalysts as silica-alumina and zeolite. These acid sites are classified as Brernsted acid sites which donate protons to the reactants and as Lewis acid sites which accept a lone pair of electrons from the reactants. The functions of these sites differ. Therefore, it is necessary to discriminate between them and to 0888-5885/88/2627-1792$01.50/0
evaluate the distribution curves of the two kinds of acids. Methods have been presented for measuring the acidic properties of the Brernsted acid and Lewis acid sites (Benesi and Winquist, 1978; Tanabe, 1970). The infrared absorption spectra of pyridine on silica-alumina and on zeolite have been studied (Parry, 1963; Ward, 1967). Pyridine chemisorbed on Brernsted acid sites can be dis0 1988 American Chemical Society
Ind. Eng. Chem. Res., Vol. 27, No. 10, 1988 1793 cerned from that coordinately bonded on Lewis acid sites by its different respective frequencies of 1545 and 1450 cm-I. But, the intensity of the infrared absorption band is influenced strongly by several factors, including the thickness of the pelleted sample. The reactions of cumene cracking (Jacobs et al., 1974) and propylene polymerization (Shephard et al., 1962) are enhanced by Brernsted acid sites, and the rates of these reactions often are used as an index of the number of Brernsted acid sites present. The methods briefly reviewed above are unsatisfactory, because the distribution curves of the two types of acids cannot be measured by these methods. Recently we reported a new, "indicator adsorption" method for continuously measuring acid strength distribution that uses the chemisorption isotherms of Hammett indicators on acid sites (Hashimoto et al., 1986). In the research reported here, we have extended this method to the measuring of the acid strength distributions of Brernsted acid and Lewis acid sites over a wide range of acid strengths. Three different samples were prepared an unpoisoned sample and two poisoned samples. In one of the poisoned samples, only the Brernsted acid sites were poisoned with 2,6-dimethylpyridine, both types of sites being completely poisoned with ammonia in the other sample. The amounts of indicator chemisorbed on each type of acid site were calculated from differences in the amounts of adsorption on these three samples. Using these two chemisorption isotherms, we obtained the acid strength distributions of the Br~lnstedacid and Lewis acid sites over a wide range of acid strengths. The acid strength distributions of the Brernsted acid and Lewis acid sites of silica-alumina catalysts that have different acidic properties could be measured by this method.
Method for Measuring Brernsted Acid and Lewis Acid Strength Distributions The indicator adsorption method is reviewed briefly (Hashimoto et al., 1986), and its extension to measuring Brernsted (abbreviated B) acid and Lewis (L) acid strength distributions is described. A. Indicator Adsorption Method. This method assumes that a linear free-energy relation (Laidler, 1978) holds for the adsorption of an indicator on a series of acid sites of different acid strengths in a nonpolar solvent such as benzene or cyclohexane. Therefore, the acid strength, Ho, that corresponds to an equilibrium concentration, C, of an indicator can be expressed by eq 1, and the amount of chemisorbed indicator, q(C),at a concentration of C is equal to the cumulative number of the acid sites, G(Ho), in the range of acid strength from the strongest acid strength, Ho,mh,to Ho (Ho,,i, < Ho) (eq 2). In eq 1 and
Ho = (l/@)(lnC + In KO) q(C)
JHo HO,,
(1)
g(Ho) m o = G(Ho) HO5 pKa (2)
2, K, represents the dissociation constant of the conjugate acid of the indicator, pK, is equal to -(log K,)g(Ho) is the density distribution function of acid strength such that g(Ho) dHo represents the number of acid sites of acid strength between Ho and Ho dHoper unit surface area of the catalyst, and @ and KOare parameters whose values can be estimated easily by the method presented by Hashimoto et al. (1986). From eq 1 and 2, the cumulative distribution of acid strength can be obtained continuously over a wide range of acid strengths (Ho) from to the acid strength corresponding to the pK, value of the Hammett indicator
+
( B-si te)
Figure 1. Structures of Bransted (B) acid and Lewis (L) acid sites.
""'0
Qmmonia
h
c=]:adsorption -----_-__---_---_J
B P -sample) Br@nstedacid sites poisoned
:desorption by heating
Figure 2. Adsorption states of ammonia and 2,6-dimethylpyridine on Bransted acid and Lewis acid sites.
from its chemisorption isotherm. B. Extension of the Indicator Adsorption Method To Measure Brernsted Acid and Lewis Acid Strength Distributions. The center of the B site on silica-alumina and zeolite corresponds to the silanol groups adjacent to the aluminum atom. The oxygen atom of the silanol group is bound also with the aluminum atom, as shown by the broken line in Figure 1. The acid strength increases with the strength of this binding. The B site has a structure that protrudes from the oxygen atoms on the catalyst's surface, whereas, the center of the L site is the tricoordinated aluminum atom that has a hollow structure, as shown in Figure 1 (Benesi and Winquist, 1978; Tanabe, 1970). The structures of the B and L sites are shown schematically for the unpoisoned sample (UP sample, Figure 2). Ammonia has the smallest molecular size of the bases and is chemically adsorbed on both the B and L sites (BLP sample, Figure 2). 2,6-Dimethylpyridine (DMP) contains methyl groups at its second and sixth positions which inhibit the nitrogen atom of DMP from coordinating with the L sites because of steric hindrance between the methyl groups and the oxygen atoms adjacent to the L site (Benesi, 1973; Jacobs and Heylen, 1974). Therefore, DMP is adsorbed preferentially on the B sites (Matsubara et al., 1978). When the catalyst is exposed to DMP vapor, DMP is adsorbed strongly on the B sites and weakly on the L sites. The DMP adsorbed on the L sites can be removed by heating, yielding a catalyst in which the B sites are selectively poisoned (BP sample, Figure 2). Consider the adsorption of Hammett indicator on the UP, BP, and BLP samples in Figure 2. The strongest base of the Hammett indicators used was dicinnamalacetone (pK, = -3). Because the basic strengths of ammonia (pK, = 10.2) and DMP (pK, = 6.4) are much greater than the strength of dicinnamalacetone, none of the ammonia and DMP adsorbed on the acid sites could be displaced by the indicators used in our experiments. The amounts of indicator adsorbed on the three types of samples (UP, BP, and BLP) are the amounts adsorbed
1794 Ind. Eng. Chem. Res., Vol. 27, No. 10, 1988 Table I. Samples Used in the Proposed Chemisorption Method sample amount of indicator adsorbed on sample
1 1 on B sites (qB), L sites (qL),and the nonacidic surface UP BP
qL
BLP
QP
QT ( = q B
+
+ q~
-t QP)
600.2 K
Region I
difference:
*
653.2 K
i
II
111
qB
QP
difference: q L (Qp).
The relations of these amounts are summarized in Table I. The q B value is calculated by subtracting the amount of indicator adsorbed on the BP sample from that adsorbed on the UP sample, and the qL value is the difference between the amounts on indicator adsorbed on the BP and BLP samples. The two kinds of chemisorption isotherms obtained can be converted to acid strength distributions of the B and L sites by eq 1 and 2.
Experimental Section A. Materials. (1) Catalysts. The six silica-alumina catalysts used previously (Hashimoto et al., 1986), SA, S3, S10, S20, JRC-SAH1, and -SAL2, were used in the experiments reported here. SA is a commercial silica-alumina catalyst (N631-L; Nikki Chem.) that has an AlzO, content of 13 wt 90. Samples S3, S10, and S20 were prepared by sintering SA for different periods (the numerals in the symbols refer to the sintering period (hour)) at 923.2 K and a partial pressure of steam of 101.3 kPa (Hashimoto and Masuda, 1985). JRC-SAH1 and -SAL2, standard silica-alumina catalysts that have respective Alz03 contents of 14 and 29 wt % , were supplied by the Catalysis Society of Japan. Preliminary treatment of these samples has been described by Hashimoto et al. (1986). (2) Hammett Indicators. Five Hammett indicators were used: dicinnamalacetone (pK, = -3), benzalacetophenone (-5.6), anthraquinone (-8.2), p-nitrotoluene (-10.5), and nitrobenzene (-11.4). B. Procedures. (1) Preparation of Catalysts in Which Only Br~rnstedAcid Sites Are Selectively Poisoned with DMP (BP Sample). The catalyst is exposed to DMP vapor, and DMP adsorbed on its surface except the B sites is desorbed by heating the catalyst to obtain the BP sample (Figure 2). The desorption temperature of DMP was determined from the following two experiments: reaction of isomerization of 1-butene over the catalyst in which acid sites are partially covered with DMP, and measurement of desorption spectrum of DMP from the catalyst. (1-a) Reaction of Isomerization of 1-Butene. The catalyst SA was placed in a microreactor; then its B and L sites were completely masked by DMP to render them inactive. The catalyst was heated under a stream of nitrogen to a temperature at which DMP was partially removed, after which it was cooled to 393.2 K and 1-butene was isomerized to cis- and trans-2-butenes. This experiment was repeated by varying the desorption temperature; the results are shown in Figure 3. The solid (e)and open (0) circles in Figure 3 represent the initial consumption rate of 1-butene, u, and the ratio, K , of the rate that produces cis-2-butene to that which produces trans-2-butene. The selectivity of this catalytic reaction is reported to depend on the kind of acid sites. The K value of the reaction for the B sites is very close to 1 and that for the L sites is 2 (Hightower and Hall, 1967). Therefore, the change in the K value of the catalyst samples prepared by varying the desorption temperature is an indicator of the kind of acid site from which DMP is desorbed. (1-b) Measurement of Desorption Spectrum of DMP from the Catalyst. A thermobalance reactor was used in this experiment. The sample SA was placed on
T
CKI
Figure 3. Changes in activity and selectivity of SA catalyst by varying the desorption temperature and desorption spectrum of 2,6-dimethylpyridine. Reaction conditions for the isomerization of and 1-butene: molar flow rates of nitrogen and 1-butene, 5.4 X mol/s; reaction temperature, 393.2 K. Unpoisoned cata6.7 X lyst: u = 0.301 mol/(kg s), K = 1.42.
the basket of 80-mesh platinum net which was suspended by a fine quartz rod connected with one arm of a thermobalance. The catalyst was exposed to DMP vapor at 307.2 K to cover completely acid sites with DMP. The catalyst was held in a nitrogen stream and heated stepwise by 10-20 K. When the prolonged desorption of DMP at a certain temperature produces no further decrease in the weight of the catalyst, the amount q D w of DMP retained on the catalyst at the temperature was measured. The repetition of this procedure gave the amount of DMP retained on the catalyst at various desorption temperature, T. By differentiating graphically a smooth curve passing through these points, the desorption spectrum (-dqDw/ d T ) of DMP was obtained, as shown by the broken curve in Figure 3. The area beneath the -dqDw/dT curve in the range of temperatures from TI to Tz is equal to the amount of DMP desorbed in the temperature range. Thus, the -dqDw/dT curve shows whether DMP molecules are desorbed or not at a certain temperature. Desorption temperatures can be categorized as three regions: region I (T < 600.2 K), region I1 ( T = 600.2-653.2 K), and region I11 (T > 653.2 K). In region I, both the B and L sites are completely masked by DMP; no catalytic activity is present. The -dqD,p/dT curve exhibits two peaks in this region. By taking into account the boiling point of DMP (416.2 K), the peak in the lower temperature range is corresponding to the desorption of DMP condensed within the catalyst particles. The other one represents the desorption of DMP adsorbed on the nonacidic surface. In region 11, only the desorption of the DMP adsorbed on L sites proceeds as the desorption temperature increases, the DMP being removed from most of the L sites at 653.2 K. Therefore, the K value is almost constant at 1.85, the value of which is very close to the value of 2.01 for the activated alumina (JRC-AL05 supplied by the Catalysis Society of Japan) which has only the L sites (James, 1975). Jacobs and Heylen (1974) studied the infrared absorption spectra of the DMP adsorbed on HYtype zeolites at different desorption temperatures and found that no DMP molecules are adsorbed on L sites above a temperature of 673.2 K. Our results reported here agree well with their results. In region 111, desorption of the DMP adsorbed on the B sites proceeds and produces unpoisoned B sites, over which, as well as the L sites, isomerization of 1-butene
Ind. Eng. Chem. Res., Vol. 27, No. 10, 1988 1795 10“
1
1
I
1
1
1
1
I
Table 11. Parameters, B and Kn, of Dicinnamalacetone Brornsted acid Lewis acid B KO,m3/moi P KO,m3/mol 1.02 1.11 x 10-3 0.574 5.17 X lo-*
,
Catalyst :SA 1ndicator:nitrobenzene
L
/
7,
I
I
I
I
1o - ~
1o - ~
102
6’
1
,
I
1
,
I
10
, ,
I
I
I
,JRC-SAL2
I
1o2
c Cmollm33 Figure 4. Adsorption isotherms of nitrobenzene on catalyst SA at 303.2 K.
takes place. The K value decreases rapidly as the desorption temperature increases and reaches a value of 1.42 for the unpoisoned catalyst at temperatures of more than 803.2 K. The KB value (1.18) for silica gel modified with chloride, at only the B sites, is shown in Figure 3. All the results described above show that a sample in which only the B sites are covered by DMP can be obtained by desorbing the DMP adsorbed on the catalyst at 653.2 K. To prepare a catalyst sample that has only its B sites selectively poisoned, it is necessary to ascertain that no molecules of DMP are decomposed near 653.2 K. Jacobs and Heylen (1974) reported that no species produced by the decomposition of DMP were detectable at 673.2 K, when infrared spectra were checked. To examine in detail the stability of the DMP adsorbed on the catalyst, we measured the contents of the carbon, hydrogen, and nitrogen of the DMP retained between 430.2 and 730.2 K with an element-analyzing CHN Corder (MT-3, Yanagimoto). The composition of the materials retained on the catalyst is represented by the formula CH,N,. The obtained values of m and n, 1.40 i 0.25 and 0.142 f 0.002, are very close to those for DMP, 1.29 and 0.143. This indicates that none of the DMP molecules retained on the catalyst are decomposed during repeated adsorption and desorption. We prepared catalyst samples with selectively poisoned B sites (BP sample) as follows: The catalyst was calcined at 723.2 K for 3.5 h under a nitrogen stream and then exposed to DMP vapor with a partial pressure of more than 0.263 kPa at 308.2 K for 1h, after which it was heated at 653.2 K under a nitrogen stream for 1 h to remove the DMP molecules adsorbed on the nonacidic surface and the L sites. This procedure gave the BP sample. (2) Preparation of Catalysts Poisoned with Ammonia (BLP Sample). BLP samples (Figure 2) were prepared as described elsewhere (Hashimoto et al., 1986). Catalysts were held in a vacuum overnight at 573.2 K and then exposed overnight at 303.2 K to an ammonia atmosphere with a pressure higher than 3 kPa and again held in a vacuum overnight at 303.2 K to remove ammonia molecules adsorbed physically on the nonacidic surface. This gave the BLP sample. (3) Adsorption of Indicators on Samples. Solutions of Hammett indicators were prepared in such nonpolar solvents as benzene and cyclohexane, and the catalyst particles added to them. The equilibrium adsorption of the indicator on a sample was reached after shaking at
I 0
520’
2
4
6
8
1 0 1 2 1 4
-tio C-I
Figure 5. Cumulative distributions of B r ~ n s t e dacid strengths of silica-alumina catalysts.
303.2 K for 20 h. The amounts of indicator adsorbed on the catalysts were calculated from the differences between the initial and equilibrium concentrations of the indicator in solution. The concentration of the indicator was measured by ultraviolet spectroscopy (UV-240,Shimazu). The amounts adsorbed were measured for three kinds of catalysts, the UP, BP, and BLP samples listed in Table I. Experimental conditions and procedures of adsorption of indicators on samples were described in details by Hashimoto et al. (1986).
Results and Discussion A. Adsorption Isotherms of Indicators. The typical adsorption isotherms of nitrobenzene on catalyst SA are shown in Figure 4. The open circles ( O ) ,the solid circles ( O ) , and the triangles (A),respectively, represent the amounts of indicator adsorbed on the UP sample ( Q T = q B qL Qp), the BLP sample (Qp), and the BP sample (qL + Qp). The dashed curve shows the amount chemisorbed on the B sites, q B , which was calculated by subtracting qL + QP from QT. The chain curve shows the amount chemisorbed on the L sites, qL, obtained by plotting the difference between Qp and qL + QP. Both q B and qL have definite values, indicating that the B and L sites are distributed over the entire surfaces of the silicaalumina catalysts. B. Acid Strength Distributions. Cumulative distributions of the acid strength of the B and L sites can be obtained continuously over a wide range of acid strengths (Ho)from Ho,min to -3 corresponding to the pK, value of dicinnamalacetone from its chemisorption isotherm on each acid site. The values of the parameters p and KOin eq 1 must be estimated for each type of acid site. These values can be obtained easily from the maximum values, qm, of the chemisorbed amounts of benzalacetophenone and nitrobenzene as described by Hashimoto et al. (1986). The results are listed in Table 11. When these values are substituted in eq 1, the cumulative distributions of acid strength of the B and L sites can be obtained from eq 1 and 2 by use of the chemisorption isotherm of dicinnam-
+ +
1796 Ind. Eng. Chem. Res., Vol. 27, No. 10, 1988 61
I
I
I
I
I
I
I
I
51 n
NE
I
k
0
2
-
4
x
y
6
,
8
,JRC-SAL2
1 0 1 2 1 4
- H o C-3
Figure 6. Cumulative distributions of Lewis acid strengths of silica-alumina catalysts.
alacetone for each kind of acid site. The curves in Figure 5 and 6 show the cumulative distributions of the acid strengths of the B and L sites, GB(H,,) and GL(H0). The data points in these figures, which represent the qm values of the chemisorbed amounts of a series of indicators, were closely approximated by the curves obtained by our proposed method. For JRC-SAH1 and -SAL2, no qm values of the indicators, except dicinnamalacetone, were measured; therefore, the values of /3 and KOwere not estimated. Hashimoto et al. (1986) measured the acid strength distributions (GB+L(H~)) of the sum of B and L sites by the indicator adsorption method. The differences in the values of the parameters /3 and KOwere found to be less than 12% among six kinds of silica-alumina catalysts. Hence, the values listed in Table I1 are approximately constant, as far as similar catalysts (silica-alumina) are concerned. Therefore, the acid strength distributions of JRC-SAH1 and -SAL2 were calculated from the /3 and KOvalues given in Table 11. The strongest acid strength of the silica-alumina catalysts (catalyst SA) is about -13 for both the B and L sites. The density distributions of the acid strengths of the B and L sites on several catalysts, gB(Ho) (Figure 7) and gL(Ho)(Figure 8), were obtained by graphically differentiating the cumulative distribution curves in Figures 5 and 6. B sites have a relatively wide distribution of strengths (Ho= -5 to -13), whereas most of the L sites are distributed in a narrow range of strengths from -9 to -13 (catalyst SA). In actual reactions catalyzed by solid acid catalysts, coked catalysts are regenerated by burning off the coke, at which time catalysts sinter rapidly, resulting in a decrease in catalytic activity. Thus, sintering as well as coking is a cause of deactivation (Hashimoto et al., 1988). Changes in physicochemical properties of the catalyst during sintering have not, however, been established. Hence, it is interesting to measure the changes in acidic properties during sintering, as shown by samples SA to S20 in Figures 7 and 8. The amount of acid on both the B and L sites decreases as sintering progresses (from SA to S20). Interestingly, the distribution of the L sites shifts to the weaker acid region. The L site represents the tricoordinated aluminum atom (Figure 1). During sintering, steam reacts with the catalyst surface, producing stable species such as the hexacoordinated aluminum atom, the strength of which is considered to be very weak (Seiyama, 1978; Tanabe et al., 1974). These changes result in deactivation of the catalyst during sintering.
2
4
6
8
-H,
10
12
14
I-I
Figure 7. Density distributions of Brmsted acid strengths on silica-alumina catalysts.
n
JRC-SAH1
SA
E 6
Y
a
0
% 01
2 0
L 2
4
6
8 -H,
10
12
14
C-3
Figure 8. Density distributions of Lewis acid strengths of silicaalumina catalysts.
Conclusions (1)2,6-Dimethylpyridine was adsorbed on Brransted acid sites more strongly than on Lewis acid sites. The 2,6-dimethylpyridine adsorbed on the catalyst's surface, except the Bransted acid sites, could be desorbed by heating at 653.2 K. Thus, we obtained samples in which Brransted acid sites were selectively poisoned. (2) The amounts of Hammett indicator chemisorbed on the Brransted acid and Lewis acid sites were calculated from differences in the amounts of indicator adsorbed on three different samples; unpoisoned catalyst, catalyst with only its Bransted acid sites poisoned with 2,6-dimethylpyridine, and catalyst with both acid sites poisoned with ammonia. We measured the acid strength distributions of Brransted and Lewis acid sites on six silica-alumina catalysts from these two kinds of chemisorption isotherms for acid strengths (Ho)from -3 to about -15 by our indicator adsorption method. (3) Bransted acid sites on a silica-alumina catalyst have = -5 to -13), a relatively wide distribution of strengths (Ho whereas, most of the Lewis acid sites are distributed in the
Ind. Eng. Chem. Res. 1988,27, 1797-1802 narrow range of acid strength from -9 to -13. Nomenclature G(Ho) = cumulative amount of acid sites from Ho,~i, to Ho, mol/m2 g(Ho) = density distribution function of acid strength, mol/m2 Ho= Hammett acidity function = strongest acid strength K , = dissociation constant of conjugate acid of indicator KO = constant in eq 1, m3/mol pKa = -(log Ka) QP = amount of indicator adsorbed on nonacidic surface of catalyst, mol/m2 QT = amount of indicator adsorbed on acid sites and nonacidic surface of catalyst, mol/m2 q(C) = amount of indicator chemisorbed on acid sites at equilibrium concentration C, mol/m2 q m = maximum value of q(C), mol/m2 T = absolute temperature, K u = initial reaction rate of isomerization of 1-butene,mol/(kg 9)
Greek Symbols /3 = constant in eq 1 K = ratio of reaction rate producing cis-2-butene to that
producing trans-%butene Subscripts B = Brcansted acid site L = Lewis acid site
1797
Registry No. AZO3,1344-281;SiOz,7631-86-9;NH3,7664-41-7; 2,6-dimethylpyridine,108-48-5.
Literature Cited Benesi, H. A. J. Catal. 1973, 28, 176. Benesi, H. A.; Winquist, B. H. C. Adv. Catal. 1978, 27, 97. Hashimoto, K.; Masuda, T. J . Chem. Eng. Jpn. 1985, 18, 71. Hashimoto, K.; Masuda, T.; Isobe, K. J. Chem. Eng. Jpn. 1988,21, 249. Hashimoto, K.; Masuda, T.; Motoyama, H.; Yakushiji, H.; Ono, M. Ind. Eng. Chem. Prod. Res. Deu. 1986, 25, 243. Hightower, J. W.; Hall, W. K. J. Am. Chem. SOC.1967, 89, 778. Jacobs, P. A.; Heylen, C. P. J. Catal. 1974, 34, 267. James, A. S. J. Vac. Sci. Technol. 1975, 12, 321. Laidler, K. J. Chemical Kinetics, 2nd ed.; McGraw-Hill: New Delhi, 1978, pp 246-249. Matsubara, T.; Imokawa, T.; Take, J.; Yoneda, Y. Shokubai 1978, 20, 202. Parry, E. P. J. Catal. 1963,2, 371. Seiyama, T. Kinzoku Sankabutsu to sono Shokubai Sayou; Kodansha: Tokyo, 1978. Shephard, F. E.; Rooney, J. J.; Kemball, C. J. Catal. 1962, 1, 379. Tanabe, K. Solid Acids and Bases; Kodansha Academic: Tokyo, 1970; pp 5-33, 58-66, 73-80. Tanabe, K.; Sumiyoshi, T.; Kiyoura, T.; Kitagawa, J. Bull. Chem. SOC. Jpn. 1974, 47, 1064. Ward, J. W. J. Catal. 1967, 6, 225.
Received for reuiew September 16, 1987 Accepted June 6, 1988
MATERIALS AND INTERFACES Polymers for Removal of Free and Combined Active Chlorine and Active Bromine from Water. Sulfonamides Derived from Styrene-Divinylbenzene Copolymers. Polymer Supported Reagents. 4 David W. Emerson Department of Chemistry, The University of Nevada, Las Vegas, Las Vegas, Nevada 89154 Sulfonamides and N-alkylsulfonamides derived from styrene-divinylbenzene copolymers were prepared by reaction of sulfochlorinated styrene-divinylbenzene copolymers with ammonia or aminoalkanes and alkanediamines such as methylamine, ethylamine, isobutylamine, 1,2-ethanediamine, 1,3-propanediamine, and 1,6-hexanediamine. When solutions containing sodium hypochlorite, hypochlorous acid, chloramine, dichloramine, trichloramine, or hypobomous acid or sodium hypobromite were pumped through a column containing one of the polymeric sulfonamides, the active halogen content of the water was greatly reduced, often by 99% or more. After saturation of the resins with chlorine or bromine is approached, their ability to remove active halogen compounds diminishes. The ability of the resins to react with active halogen can be restored by removing the active halogen with suitable reducing agents such as hydrazine or sodium sulfite. This enables use of the resins for cycles of halogen loading followed by regeneration. Active chlorine compounds, such as hypochlorites, hypochlorous acid, chloramine, dichloramine, and trichloramine, have found widespread use in water disinfection (White, 1972,1978). It is sometimes undesirable, however, to have these disinfectants present when the water is put to its end use or discharged into a natural waterway (Brungs, 1973). Dechlorination may be accomplished by
the use of sulfites, thiosulfate, or activated carbon (White, 1972),but the sulfites and thiosulfates add to the mineral burden of the water and are toxic (Shaw and Snodgrass, 1983). Activated carbon is consumed. The classical studies of Chattaway (1905) and Dakin et al. (1916) reported methods for chlorinating primary arenesulfonamides (11)to N-chloroarenesulfonamides(111)and
0888-5885/88/2627-1797$01.50/0 0 1988 American Chemical Society
