942
Ind. Eng, Chem. Process Des. Dev. 1986, 25, 942-949
Effect of Water on the Catalytic Reaction Network of Quinoline Hydrodenitrogenation Charles N. Satterfleld' and C.
Morris Smith
DepaHment of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02 139
From studies at 375 "C and 6.9 MPa on a presumded NiMo/AI2O3 catalyst, it is shown that water vapor, generated in situ from decanol, moderately increases the hydrodenitrogenation (HDN) rate of quinoline, in either the presence or the absence of H,S. The latter was generated in situ from dodecylmercaptan. At equal partial pressures the enhancing effects of water alone are much less than that exhibited by H2S alone. In the presence of H,S, the presence of H,O or an increase in its concentration had no significant effect on the relative ratios of propylcyclohexene, propylbenzene, and propylcyclohexane in the products, but increasing the water concentration increased the formation of nonane. This is hypothesized to be formed by hydrolsomerization of propylcyclohexene or hydrocracking of propylcyclohexane,on acidic sites caused by the presence of water.
In recent work we have reported that the presence of H2S significantly increases the rate of catalytic hydrodenitrogenation (HDN) of quinoline on a presulfided NiMo/A1203catalyst over that observed in its absence. The overall network consists of a complex of hydrogenation and hydrogenolysis reactions, and the effect of H2S is largely through increasing the rate of hydrogenolysis reactions (Yang and Satterfield, 1984). In a more recent study (Satterfield et al., 1985),we reported that water also increases the rate of quinoline HDN in either the presence or the absence of H2S,although the effect is not as marked as that observed with H2S, at the same partial pressure. The purpose of the present study was to determine how the presence of water affects the product distribution in the overall HDN reaction. Individual rate constants were calculated by a procedure similar to that we used in determining the effects of H2S.
Experimental Section All experiments reported here were performed in a reactor described previously (Satterfield and Yang, 1984). The gas chromatographic system previously used was modified to improve the accuracy of measurement of nitrogen intermediates. Strong nitrogen bases interact with currently available columns so that gas chromatographic peaks tend to tail and response factors vary with concentration. In the present study a calibration curve, which was nonlinear, was determined from time to time using a range of concentrations of the nitrogen compounds of interest. One point on the calibration curve was matched daily with each compound. The system consisted of two 30-m capillary columns installed in a single split/splitless injector. A SPB-1 bonded SE-52 phase column (Supelco) was used with an FID detector to separate hydrocarbon products. Nitrogen compounds were separated on a Supelcowax 10 column, and concentrations were measured on an NPD nitrogen specific detector, an improvement over our earlier method. Separate analyses for the hydrocarbon and nitrogen compounds were l i k e d using dicyclohexylamine as an internal standard. The quinoline was dissolved in an inert paraffin liquid composed mainly of n-hexadecane, described previously. The quinoline concentration was 3.87 X mol/(g of feed), 5 wt % , equivalent to 0.54 wt % nitrogen. All the data were obtained at 375 "C and 6.9 MPa over a commercial HDS catalyst, American Cyanamid Aero HDS-3A,
which we have used in previous studies. During the reaction hydrogen gas was passed into the reactor concurrently with the liquid at a gas-to-liquid ratio of 1600 cm3 of H2 (STP) per cm3 of liquid; this is equivalent to 9000 scf/barrel. Percent HDN is defined as the disappearance of nitrogen in the form of quinoline and other organonitrogen compounds formed as intermediates. Water was generated in situ by adding decanol to the feed. Each of three concentrations of decanol, 18.2, 54.6, and 109.2 X mol/(g of feed), were used. These generate about 14, 42, and 84 kPa of water partial pressure under reaction conditions. When H2Swas desired, it was generated in situ by adding dodecylmercaptan to the feed in a concentration of 8.9 X mol/(g of feed). This generated an H2S partial pressure of 12-14 kPa. The catalyst was crushed and sieved to 150-pm particles; 1.6 g was then diluted in a 1:4 ratio with the same size of silicon carbide, which is inert. In the 0.52-cm-diameter reactor this comprised an active bed about 50 cm long, plus entrance and exit lengths of inert material each about 15 cm long. Once in place the bed was purged under helium flow for 12 h at 100 "C and then at 175 O C for at least 1 additional hour. This catalyst is used industrially in the sulfided form. Presulfiding was accomplished with a 1:9 H2S/H2mixture at 0.24 MPa and 40 cm3 (STP)/min using a temperature program of 12 h at 175 "C, increasing the temperature to 315 "C,holding it for 1 h, and then decreasing the temperature to 150 "C. The catalyst drops in activity significantly upon first being brought on stream. It is essential that the catalyst exhibit a fairly constant activity over a long period during kinetic studies. Therefore, a deactivation procedure was followed to bring the catalyst to this essentially steady-state activity as rapidly as possible. For this purpose quinoline HDN was carried out at a space time of 270 h (g of catalyst)/(mol of feed), 375 OC, and 6.9 MPa of H2 in the absence of H2S. In the absence of H2S,catalyst activity decreases more rapidly than in the presence of H2. Figure 1, for the catalyst sample used in the present studies, is representative. During the first 50 h activity dropped rapidly but subsequently more slowly. Between 100 and 480 h on stream a series of experiments were performed irrelevant to the present report, during which H2S was present about one-half of the time and absent one-half. During this period the percent conversion slowly declined at an average rate of about 3 percentage 0 1986 American Chemlcal Society
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 4, 1986 943 100 1
I
I
I
Conditions
cc VI
70
I
-
I
1
w
7.0 M P a ~ 375 c
LL
0 -0PA
2 7 0 h r s (g-cot)/molo 5 w t % Quinolino w i t h N o HpS A d d e d
w
A
z 1 o
f
-82 TH Q V-DHQ .-0+ P y T H Q
50 40
B a
l o0
L----LJ
0
100
200
300
400
500
W 1
0
I 600
0 100 200 300 400 SPACE T I M E , H R S ( g - c O t ) / M O L E
HOURS ON STREAM
Figure 1. Initial deactivation of catalyst. Table I. Acronyms for Chemical Compounds BzTHQ 5,6,7,8-tetrahydroquinoline DHQ decahydroquinoline ECH ethylcyclohexane methylpropylcyclopentane MPCP OEA o-ethylaniline OPA o-propylaniline PB propylbenzene PCH propylcyclohexane PCHA propylcyclohexylamine PCHE propylcyclohexane PEA p-ethylaniline PPA p-propylaniline 1,2,3,4-tetrahydroquinoline PYTHQ quinoline Q
points/lOO h. The runs reported here were all performed from 480 to 920 h on stream. After 575 h H2Swas always present during reaction, and this has a stabilizing effect on activity. A standard resulfiding procedure was used to maintain the catalyst activity. The reactor was first flushed with a 50/50 mixture of liquid carrier and xylene for ' I 2h at 350 "C and 6.9 MPa of hydrogen. Helium was then passed through the catalyst bed for 30 min at 350 "C to remove any liquid. The catalyst was then resulfided with a 1:9 H,S/H, mixture at 40 cm3 (STP)/min, 0.24 MPa, and 350 "C for 1 h and allowed to cool. Catalyst activity rises significantly after resulfiding and then drops off over the next 10 h or so in either the presence or the absence of H2S in the reactant mixture. If H2S is present, a stable level of activity is reached; in the absence of H2S, activity continues to drift down slowly. This was allowed for when measuring product concentrations in the absence of H2S for kinetic analysis. Isoquinoline. The quinoline used here was Baker Analyzed grade, made synthetically. Its purity exceeded 99%, judging from gas chromatographic analysis. Quinoline derived from a coal tar source, obtained from a second supplier, showed a significantly lower rate of reaction (e.g., about 74% vs. 80% HDN at 375 "C, 6.9 MPa, and 270 space time). Further analysis showed the presence of about 4% isoquinoline. Evidently in a mixture, the I-IDN rate of isoquinoline is relatively low compared to that of quinoline.
Results Eight runs were carried out on one catalyst sample, termed sample 15. In six of these the HDN of quinoline was studied, in the other two, the HDN of o-ethylaniline (OEA) and of decahydroquinoline (DHQ). Table I gives a list of acronyms.
500
QUINOLINE
Figure 2. Distribution of nitrogen compounds in the presence of 14 kPa of H20. H2S absent. Run N.
0
100
200
300
400
500
SPACE T I M E , H R S ( g - c o t ) / M O L E QUINOLINE
Figure 3. Distribution of nitrogen compounds in the absence of both H2S and H20. Run 0. n
0 - OPA A - &THO V - DHQ Q + PyTHQ
.-
W
0
z
2
40
2
20
-
-
-
t
0
-
\
100
200
300
400
500
SPACE TIME, HRS ( g - c o t ) / MOLE QUI NOL INE
Figure 4. Distribution of nitrogen compounds in the presence of 14 kPa of H2S and 14 kPa of H20. Run P.
Figures 2-7 show the mole fraction of various organonitrogen species in the product as a function of space time for the runs with quinoline feed. The mole fraction is based on the total moles of quinoline fed. From a mass balance the moles of feed should correspond to the total moles of N compounds plus hydrocarbons present ex-
944
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 4, 1986
i
0 - OPA
A - EzTHQ V - DHQ
s
- Q + P y THO.
50
LL
w
Table 11. Reaction Rate Constants run Q S N O P figure no. 2 3 4 5 6 reactant Q Q Q Q Q H2S, kPa 0 0 14 14 14 HzO, kPa 14 0 14 0 41.5 5 4 16 16 22 k le 15 12 17 14 34 k2 43 39 50 51 57 k3 54 46 36 43 47 k4 62 52 111 107 128 k5 0 0 0 0 0 k6 43 30 89 80 107 k7
X 7
V
Q
OEA 14
14 83.4 23 38 66 34 169 0
132
10
0 0
97 0 0 0 0 0
U 11
DHQ 14 0 0 0 0 0 379 110 74
'All rate constants have units of moles x 104/[(gramsof cata= 0.70. lyst) hour]. A , = K J K , = 2.0; A2 = K,/K,, 0
200
100
400
300
500
SPACE T I M E , H R S ( g - c a t ) / M O L E QUINOLINE
Figure 6. Distribution of nitrogen compounds with 14 kPa of H2S. H 2 0 absent. Run Q. n w
70
I
/
I
l
iL
w -I
f
a' 8 I-
z
I
I
6o
A- BZTHQ V- DHQ
50
8-
If 0
I
I
I
0 - OPA
a +P Y T H Q
40
30
w
V 12 W
20
a
y
10
0
=
o 0
200
100
300
500
400
SPACE T I M E , HRS ( g - c a t ) / MOLE QUINOLINE
Figure 6. Distribution of nitrogen compounds in the presence of 14 kPa of H2S and 41.5 kPa of HzO. Run S. ,
I
I
I
I
I
,
0 - OPA &THO
V-
DHQ
l
-
.-
A-
I
Q+PyTHQ
-
1
0
100
200
300
400
500
SPACE TIME, HRS ( 9 - c a t ) / MOLE QUINOLINE
Figure 7. Distribution of nitrogen compounds in the presence of 14 kPa of H,S and 83.4 kPa of HzO. Run X.
cluding NH,. Quinoline reacts very rapidly to form an equilibrium mixture with 1,2,3,4-tetrahydroquinoline (PfI'HQ). The figures show the drop in concentration of this equilibrium mixture with increased space time and also the change in concentration of 5,6,7,8-tetrahydroquinoline (BzTHQ), decahydroquinoline (DHQ), and o-
propylaniline (OPA). Space time has units of hours (gram of catalyst)/mole of quinoline or other N compound in the feed; thus a zero-order reaction would appear as a straight line on a plot of conversion vs. space time. The runs fall into three groups. The first group (runs N, 0, P, and Q) shows the effects of adding H2S or H 2 0 or both on the quinoline HDN network. The second group (runs Q, P, S, and X) shows the effect of adding increasing amounts of water on quinoline hydrodenitrogenation in the presence of H2S. Table I1 provides a guide to how variables were changed from run to run within these two groups and also gives the rate constants discussed below. In addition, the HDN kinetics of two reaction intermediates, o-ethylaniline (used to represent OPA) and decahydroquinoline, were investigated by themselves to help develop a kinetic model (runs V and U). General Trends. Quinoline HDN. Figures 2-5 show how the product distribution changes with space time for each of the four possible combinations of the presence or absence of H20 and/or H$, each at about 14 kPa. Figures 5-7 show the effect of increasing concentrations of H 2 0 from 0.0 to 83.4 kPa, all in the presence of 14 kPa of H2S. The first run, N, was started after the catalyst had been on stream 476 h. Figure 2 shows the product distribution as a function of space time in the absence of H2Sand the presence of 14 kPa of H20. The percent HDN at the standard activity conditions dropped from 33% at the beginning of the run to 29% at the end of this run. The catalyst was resulfided and the next run, 0, was performed in the absence of both H2S and H20, with the results shown on Figure 3. The activity during this run was about 26% f 2% HDN. Comparing Figures 2 and 3, it is seen that all nigrogen compounds are present at lower concentrations when H 2 0 is present. An important observation is that the decahydroquinoline (DHQ) peak location is shifted to lower space times with the addition of H20. This implies that the ratio of DHQ formation to DHQ disappearance decreases upon the addition of H20. The next run, P, Figure 4,was carried out in the presence of 14 kPa of both H 2 0 and H,S. After this, the catalyst was resulfided and run Q, Figure 5 , was performed with 14 kPa of H2S and no H 2 0 present. In the presence of H2S, addition of water at the same partial pressure has little effect; it slightly reduces the concentration of DHQ at the lower space times (compare Figures 4 and 5). The other nitrogen intermediates are present at nearly the same concentrations whether or not H 2 0 has been added, and there is no significant effect of H 2 0on the overall HDN. The effect of H,S alone is much greater than the effect of water alone (compare Figure 5 to Figure 3 vs. Figure 2 to Figure 3). In either the presence or the absence of H20, adding H2S reduces the concentration of BzTHQ and DHQ present and increases that of OPA.
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 4, 1986 945
loo
w IL
m
(P0) (0)
(PYIHQ)
(W)
(OPA)
80
(PCH)
a w
P
-gYlnc.ll". PyMP - P Y lor 1 . 2 , ~ , 4 l - t ~ t r ~ h y d m g u ( n o L l n e B z M O -ns lor S . S , l , I I - t c ~ ~ . h y d r o q u l n D l l n c DHO D e w h y d z ~ u l n o l l n e l o l l and t r a m I.o*urml
20
DPA
(MPCP)
PCIII- propyleyclohsrylulne
PB
- propylbcnzene - pmpylcyelohexan.
-
PCllC- propyleyclohcxcn.
-0-propyl.nlline
W C P - rrthylp.Opyl5y51Opnt.n.
PCll
11.1 or 1.1)
Figure 10. Detailed reaction network for quinoline hydrodenitrogenation. 0
100
200
300
400
500
SPACE T I M E , H R S ( 9 - c a t ) / M O L E DEA
Figure 8. HDN of o-ethylaniline (OEA)in the presence of 14 kPa of HzS.
I2I
B z T H QK, . 7 DHQ
90
A BzTHQ V DHQ
n
v2
Y3
HC'NH, Y6
Figure 11. Simplified kinetic model for quinoline HDN.
0
__i -.=-
0
100
200
300
400
500
SPACE T I M E , HRS ( 9 - c a t ) / MOLE DHQ
Figure 9. HDN of decahydroquinoline (DHQ) in the presence of 14 kPa of H2S.
The effect of adding increasing amounts of decanol to the feed to generate higher partial pressures of water in the presence of H2S is shown in Figures 5 (run Q with no H20),4 (run P with 14 kPa of H20),6 (runS with 41 kPa of H20),and 7 (run X with 83 kPa of H,O). As the water partial pressure is increased, the rate of disappearance of the Q-PyTHQ mixture increases. The concentrations of BzTHQ and DHQ also decrease and that of OPA increases. When no water is present the initial rates of DHQ and BzTHQ formation are about equal (Figure 5); as water is added, the initial rate of BzTHQ formation clearly exceeds that of DHQ (Figure 7). This suggests that the formation of DHQ via BzTHQ becomes more important than the formation via PyTHQ as water is added. Another trend is the increase in the rate of reaction of OPA, which is evident from the lower OPA concentrations at high space times. o -Ethyladline. o-Propylaniline (OPA) is not readily available, so some studies were performed with o-ethylaniline (OEA) as a substitute. Figure 8 (run V) shows a representative conversion curve. Decahydroquinoline. To study the HDN of decahydroquinoline, a mixture of about 80% cis and 20% trans DHQ was produced by the hydrogenation of quinoline over a Rh/A1203catalyst (Momose et al., 1977). The reaction was carried out at 80 O C and 0.44MPa of H2 in an ethanol slurry. Selectivity to DHQ was about 98%. Under HDN conditions, cis-trans isomerization was assumed to be very
fast; no cis isomer was detected in the product stream at the lowest space time. A representative conversion curve is shown on Figure 9 (run U). DHQ is converted to hydrocarbon products but to some extent is dehydrogenated to BzTHQ. Kinetic Modeling. The reaction network for quinoline HDN has now been developed in substantial detail (Shih et al., 1978; Satterfield and Cocchetto, 1981; Satterfield and Yang, 1984) and is shown in Figure 10. Figure 11 shows the simplified scheme used for kinetic analysis here. We have developed a Langmuir-Hinshelwood type of kinetic model which involves adsorption constants for the N-containing species present, divided into three groups (see later). A number of simplifying assumptions are also made to reduce its complexity further based on experimental evidence: (1)the reaction between Q and PyTHQ is at thermodynamic equilibrium under typical HDN conditions (Satterfield and Cocchetto, 1981). (2) Dehydrogenation rates are slow relative to hydrogenation rates. (3) Deamination reactions forming hydrocarbons are very fast. The resulting model is similar to that used previously (Satterfield and Gultekin, 1981; Satterfield and Yang, 1984) except that it is further simplified in several respects: we do not attempt to calculate the rate constants k, and k9 for the equilibrium between PyTHQ and quinoline, and terms for reactions corresponding to the reverse of k4 and k3 (these were klo and kll in Satterfield and Yang (1984))) are omitted. Also k, here was set equal to zero, as discussed below. The numerical subscripts here identify the same reactions as they did in our previous publications, but for the above reasons, values of rate constanb reported here cannot be compared quantitatively with those we reported previously. (In Table 111of Satterfield and Yang (1984), there is a decimal point error. The correct values of k2 at 350 "C are 10 times greater than those reported.) The previous method used runs starting with BzTHQ or OPA to determine rate constants for their reactions which were then used in developing the model for the overall series of reactions starting with quinoline. This was not necessary for the present purposes, but reaction studies with DHQ and OEA were made to determine adsorption parameters in the model.
946
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 4, 1986
The mathematical formulation assumes that molecules adsorb and react on one type of site for which they compete. Following the Langmuir-Hinshelwood development by assuming that adsorption equilibrium is always established, we can write the differential rate equations (1)-(6). dY,/dt = (kl'K5Y5 - k&iYi)/+ (1) dYz/dt = (k3'K4Y4 dY,/dt = (kbK,Y,
+ kd(3Y3
- k&zYz)/3/
+ kq'K5Y5 - kGK3Y3 - k,K3Y3)/+
(2)
(3)
+ k4K5Y5 - k3/K4Y4)/+
(4)
dY,/dt = (kgK4Y4 - k9K5Y5 - kl'K5Y5 - k,'K,Ys)/+
(5)
dY4/dt =
+
(-k&4Y4
dYe/dt = (kzKiY1 + k7K3Y3)/+
(6)
Here = 1+ Kl Yl + K zYz + K3Y3 + K4Y4 + K5Y5 + K6Y6, Y, is the mole fraction of component i (based on the total moles of nitrogen in the feed), t is the space time in hours (gram of catalyst)/g-mole of nitrogen in the feed, Ki is the equilibrium adsorption constant of component i, and k, is the rate constant of reaction j as shown in Figure 11. Several approximations are now made to reduce the number of parameters in the mathematical model. First, the rate equations (4) and (5) are added to eliminate the terms containing k8 and k,. Since there is thermodynamic d(Y4 Ys)/dt = (-k3/K4Y4 - ki'K5Y5 - k,'K5Y5)/+ (7)
+
equilibrium between Y4 and Y5, they should always be present in a constant ratio, that is, Keq= k8/k9 = Y5Y4. When this constant is used, the previous equation is transformed to eq 8 where k3 = k i / ( l + ICeq),k, = k;Keq/(l + KeJ, and k4 = k4/Keq/(l+ Keg). d(Y4 + Y5)/dt = + k4)&(Y4 + Y&I/+ (8) I-k3K4(y4 + Y5) The adsorption constants are grouped into three categories according to their basicities or the basicities of like compounds (Satterfield and Yang, 1984). The compounds OPA, BzTHQ, PyTHQ, and Q are treated as aromatic amines, all with'the same adsorption constant K,. DHQ, a secondary amine, has a higher basicity than the aromatic amine and is expected to be more strongly adsorbed; its adsorption constant is termed Ksr Ammonia is treated independently because of its greater volatility under reaction conditions and is assigned an adsorption constant of K,. As in previous developments, the surface is assumed saturated with nitrogen compounds, and thus the 1in the adsorption term (+) is dropped. This results in two adsorption constant ratios in the rate equations, A, = KJK, $' is now defined as Y, + Yz + Y4 + and A2 = K,,/K,. Y5+ A1Y3 + &Ye, and the final mathematical model can then be written (eq 9-13). dYi/dt = [ki(Y4 +
Y5)
- k2Y11/$'
(9)
dYz/dt = [k3(Y4 + Y5) + k6A1Y3 - k5Yz]/$' (10) dYs/dt = [k5Y2 + k4(Y4 + Y5) - AlkaY3 - kTY3]/$' (11)
d(Y4 + Y,)/dt = (-k3 - kl - k4)(Y4 + dY,/dt = (kZY1 + kTAlY4)/$'
Y5)/$'
(12)
(13)
It is desirable to determine the adsorption constants independently before fitting rate constants to the quinoline HDN reaction kinetics. In our earlier work the reactions of p-propylaniline (PPA), p-ethylaniline (PEA), and OEA were each studied separately to determine rate constants and adsorption constants for these reactions using a
Table 111. Effect of Water and Hydrogen Sulfide on Reaction Rate Constants" HzO + H2S (31, rate const H,O (1). % H,S (2). % % Hydrogenation k2 NC 17 42 k3 NC 31 28 k4 NC NC NC k, NC 106 113 ~~
k, k7
Hydrogenolysis NC 300 20 167
~
300 197
"NC, no significant change. HzS and HzO each present at 14 kPa of partial pressure.
Langmuir-Hinshelwood rate expression. From these experiments, it was found that the ratio of the adsorption constant for ammonia to PEA or to PPA was the same, although the reaction rate constant for PEA was about 40% higher. Here eq 9 from the present model was employed to fit the rate constant k2 and the adsorption constant ratio A* The best fit was obtained with A, = 0.7. To determine the adsorption constant ratio Al = K,/ K,, the HDN kinetics of DHQ were modeled by using eq 10 and 11. For this purpose the terms involving k3 and k4 disappear. It is necessary to use eq 10 as well as eq 11 because significant BzTHQ is formed. In modeling the HDN reaction of DHQ, Az was set equal to 0.7, Al was varied, and the rate constants k5, k6, and k, were determined by the HJB method (Himmelblau et al., 1967). The profiles were very sensitive to the value chosen for Al; the best fit to the data was obtained with AI = 2.0 (see Figure 11). For all the kinetic analyses reported here, the above values of Al and A, were used.
Discussion Rate Constants. The curves shown in Figures 2-7 were calculated from rate constants determined by the HJB method using the full reaction scheme from the previous section. The rate constants providing the best fit to the data are shown in Table 11. The reaction of BzTHQ to DHQ is clearly reversible with a foward rate constant K 5 and a reverse rate constant k6,as determined from studying DHQ alone. When we started with quinoline the HJB method did not always produce positive rate constants if the reverse reaction of DHQ back to BzTHQ was allowed. Therefore, the value of k6 was set equal to zero. The value of k5 should therefore be viewed as an approximation of the net rate of reaction of BzTHQ to DHQ. The percentage changes in the rate constants caused by the presence of H2S, H20, or both, each at 14 kPa, are summarized in Table 111. Run 0 in which neither H2S nor HzO was present during reaction is taken as the base case. Rate constants for run N where water was present and H2S was absent were adjusted to match the activity measured in the absence of both H2S and HzO (run 0). Small changes in the rate constants are not regarded as being significant and are designated as NC. The only possibly significant effect of the presence of 14 kPa of water in the absence of H2S (column 1)is a small increase in the hydrogenolysis of DHQ (k,). The addition of 14 kPa of H a in the absence of water (column 2) causes a more marked enhancement of the overall HDN conversion, as showed in previous studies. The effect of higher Hz0 partial pressures on the rate constants is shown on Figures 12 and 13, based on runs Q, P S, and X, for which the H2S partial pressure was constant at 14 kPa. Water vapor increases both hydro-
Ind. Eng. Chem. Process Des. Dev., Vol. 25, No. 4, 1986 I
1801
U
\
m
I
I
0
I
I
I
I
I
I
I
1
1
’“I
A
s
140
60
U
c
2
w
c
VI
$
8
2
0
1
0
l
I
I
I
WATER
I
I
I
90 100
0
I
5 0 60 70 80
2 0 30 4 0
10
PARTIAL
I
1001
I
I
I
I
I
I
I
10
20 30 40 50 6 0 7 0 80 90 100
TOTAL
PRESSURE, kPa
I
._.-: :I---_
1
Figure 12. Effect of partial pressure of water on k4, k5, and k,.
-
8 8 4 kPa Watar
i
8
14 kPa W a t a r
7
2 -
8
40
947
I
HDN CONVERSION,
Yo
Figure 15. Mole percent of nonane increases with quinoline HDN and with water level.
\
i
o l -
VI
700
2
60
i w
z
5
4
z z
0 0
10 2 0 30 4 0 50 WATER
60 70 80 90 100
I
f , , , , , , , , 90 100
0
0
PARTIAL PRESSURE, kPa
10 2 0
30 4 0
50 60 7 0 8 0
WATER PARTIAL PRESSURE, kPa
Figure 13. Effect of partial pressure of water on k,, kO, and k8.
O N 0 W a t a r Addad A 1 4 kPa W a t a r V 4 2 kPo W a t a r 8 8 4 kPa W a t o r
z
Figure 16. Selectivity to nonane increases with water partial pressure.
z
A 1 4 kPa W a t a r 70
I
W
U
t
601
./-V
Y
w
2 0
10 2 0
30 4 0 5 0 60 70 80 90 100
TOTAL HDN CONVERSION, %
Figure 14. Effect of quinoline HDN on concentration of propylcyclohexene.
genation and hydrogenolysis rate constants except for k4 which remains constant within the precision of our analysis. The increase in k3 coupled with no change in k4 expresses mathematically the observed trend in which the concentration of BzTHQ increases relative to DHQ upon water addition. The hydrogenolysis rate constants increase markedly, but the change in k l is from a very low initial value (see table 11). Hydrogenation rate constants increase unevenly, except for k4 which is unchanged. Of the two pathways
8 84 k P a W a t a r
m 4
2 10
o
0
10
2 0 30 40 50
TOTAL
60 70 80 90 100
HDN CONVERSION,
Ye
Figure 17. Selectivity to saturated cyclic compounds plus nonane unaffected by the presence of water.
of DHQ formation, that through the intermediate BzTHQ becomes more important than that through PyTHQ. This shift is not associated in any way with a possible change in equilibrium between quinoline and PyTHQ. This was measured to be at a mole ratio of 15/85 throughout all runs. Product Distribution. The latter stages of the HDN network are shown in Figure 8. Propylcyclohexylamine (PCHA) is formed from either OPA or DHQ and then
948
Ind. Eng. Chem. hocess Des. Ded., Vol. 25, No. 4, 1986
0 No W a t e r Added I
V
0.61
0
G /,
0.41
0
10
1
20 30 40 50 60 7 0 00 90 100
TOTAL HDN CONVERSION, %
Figure 18. Mole ratio of PB to PCH drops markedly with conversion.
undergoes a rapid deamination reaction to form propylcyclohexene. This in turn is hydrogenated to PCH, is isomerized and hydrogenated to methylpropylcyclopentane (MPCP), or is dehydrogenated to PB. Some PCHA may also be deaminated directly to PCH. All the species shown on Figure 8 have been identified in our previous studies by GC/MS methods. Figures 14-18 present information about the distribution of hydrocarbon products from the HDN of quinoline as a function of conversion and water vapor partial pressure. As before HDN conversion is defined as the percent of quinoline and organo-nitrogen intermediates converted to hydrocarbons. Figure 14 shows that the concentration of PCHE in the product goes through a maximum with increased percent HDN, as would be expected for a reaction intermediate. There is no effect of water partial pressure on the PCHE concentration. The two principal hydrocarbon products ultimately formed are P B and PCH, PCH predominating. Within the group of saturated cyclic compounds there is also a small concentration of ethylcyclohexane (ECH). In addition nonane was identified by GC/MS in the product stream when water is present. Its concentration is very minor in the absence of water but increases with increasing water partial pressure and with conversion, as shown on Figure 15 and 16. Nonane could be formed by a hydroisomerization of PCHE or by hydrocracking PCH. Either reaction would presumably be catalyzed by catalyst acidity which logically is increased by increased partial pressure of water vapor. Badilla-Ohlbaum et al. (1979) have shown that hydrocracking is enhanced by increased acidity over a series of NiMo catalybts where acidity was altered by the method of manufacture. In an earlier study of the HDN of quinoline (Yang and Satterfield, 1984),we identified methylpropylcyclopentane (MPCP) in the hydrocarbon products, presumably formed by ring isomerization of propylcyclohexene followed by hydrogenation. I t was present in barely detectable amounts in the absence of H2Sbut increased markedly in concentration as the H2S partial pressure was increased. In both the present and previous studies, at 14 kPa of H2S (no HzO present), the ratio of MPCP to PCH was about 0.02-0.04. However, we could detect no significant effect of the presence of water or ita concentration on this ratio. Contrariwise, no nonane was found in the earlier study at any partial pressure of HzS. Although the adsorptive dissociation of H2S and H 2 0 can be postulated in both
cases to increase catalyst acidity, their effects evidently are not equivalent. Figure 17 gives the mole percent of saturated cyclic compounds plus nonane in the reactor exit stream, as a function of percent HDN. There is no effect of presence or absence of water. Except at very low conversions, saturated hydrocarbons greatly exceed unsaturated hydrocarbons. Figure 18 shows that the mole ratio of PB to PCH, approximately unity at low conversions, drops to about 0.08 at very high conversions. Calculations (Stull et al., 1969) show that at 375 "C and 6.9 MPa, equilibrium would correspond to essentially 100% conversion to PCH. However, when we add n-butylbenzene to the feed during these reaction conditio-is, there is no noticeable hydrogenation. The selectivity pattern displayed in Figure 18 therefore is predominantly a kinetic effect resulting from the reaction scheme in Figure 8 rather than the subsequent hydrogenation of P B to PCH. Effects of H2S and H20. There is some slight conflict here between our present and previous conclusions about the effect of H2S of itself on the individual reactions in the hydrodenitrogenation of quinoline. In agreement with our previous study, it is evident that H2Smarkedly increases hydrogenolysis rates. The present analysis indicates that it also increases hydrogenation rates moderately, whereas previously we concluded that it slightly decreased hydrogenation rates. The present model is slightly different and somewhat simplified from the earlier model but the principal reason for the differing conclusions probably resides in the fact that the calculated hydrogenation rate constants are much more sensitive than hydrogenolysis rate constants to small changes in the observed mole fraction of the nitrogen intermediates. We believe that the improved analytical procedure for N components used here makes the present results more reliable. We have clearly shown that water vapor also increases the rate of HDN but by itself it is much less effective than an equal partial pressure of H2S by itself. Both H2S and H20 are hypothesized to increase catalyst acidity but they seem to affect the reaction network in sowewhat different ways. Thus,methylpropylcyclopentane(MPCP) is formed, but no nonane, when H2S was present but not H20. The amount of MPCP formed increased with the H2S partial pressure. When H 2 0 is added in the presence of H2S, however, MPCP was not identified but nonane formation increased with increased H 2 0 partial pressure. There are also some interaction effects between H20and H2S that can be significant but as yet are somewhat obscure. In the absence of H2S, H 2 0 addition and removal affects the percent HDN in a reversible manner, but in the presence of H2S,the enhancing effect of H,O may persist for some time after it is removed from the feed stream if H2Scontinues to be present (Satterfield et al., 1985). The response of the catalyst to H 2 0 may also be slower or almost unobservable if the catalyst is quite aged or has been highly stressed, as we found with one catalyst after 660 h on stream (Satterfield et al., 1985). Similarly, in a brief earlier study with a different apparatus (Satterfield and Carter, 1981),we observed little net effect on the HDN of quinoline in the presence of 13.3 kPa of H a when water as such was added to constitute 13 kPa of partial pressure. The catalyst there had been on stream for 700 h, during which it had been subjected to a variety of operating conditions.
Summary and Conclusions From our present and previous studies, we come to the following conclusions in studying the hydrodenitrogenation
Ind. Eng. Chem. Process Des. Dev. 1986, 25, 949-957
(HDN) of quinoline on a presulfided NiMo/A1203catalyst at 6.9 MPa and 375 OC: The addition of water vapor alone causes an increase in the percent HDN, but the enhancement is substantially less than that observed upon addition of H2S alone, when comparison is made at equal partial pressure of the two additives. In a mixture of H 2 0 and H2S (each at 14 kPa of partial pressure), the percent HDN is essentially the same as that with 14 kPa of H& by itself. However, higher partial pressures of water, up to 83 kPa in the presence of 14 kPa of H2S, show moderate enhancement. From previous work we have shown that water derived in situ from decanol or m-ethylphenol behaves like water added as such. Similarly H2S derived in situ from CS2 or a mercaptan behaves like H2S added as such. The enhancing effect of water by itself at partial pressures of the order of 10-15 kPa is reversible, but in the presence of H2Sthe effect may persist for some time after water is removed from the system. With aged or highly stressed catalysts, little or no enhancement effect from water may be observed. In the presence of Ha,water vapor moderately increases the rate of formation of benzyltetrahydroquinoline from quinoline. The presence of water or an increase in its concentration had no effect on the relative ratios of propylcyclohexene, propylbenzene, and propylcyclohexane in the hydrocarbon products. It substantially increased the formation of nonane. In the presence of H2S and absence of H20, nonane is insignigicant but methylpropylcyclopentane (MPCP) is found in amounts increasing with the H2S partial pressure. MPCP is not significant when H20 is present and H2S is absent.
949
It is hypothesized that adsorptions of H2S and H20 each increase catalyst acidity but in different ways.
Acknowledgment This work was financially supported by the Office of Fossil Energy, US Department of Energy, under Grant DE-FG22-83PC-60798. Registry No. HzO, 7732-18-5; Ni, 7440-02-0; Mo, 7439-98-7; H,S, 7783-06-4; quinoline, 91-22-5; decanol, 112-30-1;dodecylmercaptan, 112-55-0; 1-propylcyclohexene, 2539-75-5; propylbenzene, 103-651;propylcyclohexane, 1678-92-8nonane, 111-84-2.
Literature Cited Badllla-Ohlbaum. R.; Pratt, K. C.; Trimm, D. L. Fuel 1979, 58, 309. Hlmmelblau, D. M.; Jones, C. R.; Blschoff, K. B. Ind. Eng. Chem. Fundam. 1867. 6. 539. Momose, T.; Uchida, S.; Yamaashi. N.; Imanishi, T. Chem. Pharm. Bull. 1977. 25. 1436. Satterfleld, C. N.; Carter, D. L. Ind. Eng. Chem. Process Des. Dev. 1981, 20, 538. Satterfleld, C. N.; Cocchetto. J. F. Ind. Eng. Chem. Process Des. Dev. 1981,20,53. Satterfleld, C. N.; Giiltekin, S. I n d . Eng. Chem. Process Des. Dev. 1981, 20, 62. Setterfield, C. N.; Modell. M.; Mayer, J. F. AIChE J . 1975, 21, 1100. Satterfleld, C. N.; Smith, C. M.; Ingalls, M. Ind. Eng. Chem. Process Des. Dev. 1985, 24, 100. Setterfield, C. N.; Yang. S. H. Ind. Eng. Chem. Process Des. Dev. 1984, 23, 11. Shih, S. S.; Katzer, J. R.; Kwart, H.; Stiles, A. B. Prepr.-Am. Chem. Soc., Dlv. Pat. Chem. 1978, 22, 919. Stull, D. R.; Westrum, E. F., Jr.; Sinke. G. C. The Chemlcal Thermodynamics of Organlc Compounds:Wiley: New York, 1969. Yang, S. H.; Satterfleld, C. N. Ind. Eng. Chem. Process Des. Dev. 1984, 23, 20.
Received for review March 5, 1985 Revised manuscript received March 5, 1986 Accepted April 21, 1986
Use of Organic Sulfones as the Extractive Distillation Solvent for Aromatics Recovery Fu-Mlng Lee Phillips Research Center, Phillips Petroleum Company, Bartlesvllle, Oklahoma 74004
Di-n-propyl sulfone (DPS) and 3-methylsulfolane (3MSULF) were tested for their applications as the extractive distillation (ED) solvents. The vapor-Uquid equilibrium (VU) data from binary as well as multiimponent hydrocarbon feeds show that both DPS and 3MSULF can be very selecthe for separating aromatics and nonaromatlcs through ED. Up to 10 wt % water can be added to DPS In hydrocarbon mixtures to improve its selectivity without creating a second IlquM phase and to substantially reduce the boiling point of the liquid mixture. Data from a bench-scale continuous ED system shows that the mixture of 50% DPS and 50% sulfolane (SULF) can out perform both SULF and 3MSULF as an ED solvent (as antlcipated from our VLE data). The data also indicates that the water content in the solvent is one of the most sensitive variables for controlling the aromatic product purity and recovery.
In the petroleum industry, aromatics are usually recovered by liquid-liquid extraction using a selective polar solvent. The organic sulfones have long been recognized as the extractive solvents for separations (Kurtz, 1933; Nevitt, 1958). Following a series of process developments since the late 1950s, the extraction of aromatics from catalytic reformates or pyrolysis gasolines by means of sulfolane became an important industrial process (Deal et al., 1959; Papadopoulos et al., 1964; DeGraff and Perga, 0 196-430518611125-O949$O 1.5010
1969; Thompson, 1973). The liquid-liquid phase equilibria of systems composed of aromatic and nonaromatic hydrocarbons and sulfolane were previously studied by Deal et al. (1959) and by DeFre and Verhoeye (1976). Due to the insolubility of sulfolane with nonaromatic hydrocarbons, sulfolane is considered entirely unsuitable for extractive distillation because phase separation of sulfolane and nonaromatics occurs in the rectification section of the extractive distillation column. Nevertheless, a novel 0 1986 American Chemical Society
