338
Ind. Eng. Chem. Process Des. Dev., Vol. 18, No. 2, 1979
Hydrodealkylation of 2-Ethylnaphthalene. A Study of Reaction Products and Kinetics Paolo Beltrame' and Paolo Carniti Istituto di Chimica Fisica, Universiti, 20 733 Milano, Italy
Bruno Marongiu, Luigi Mura, and Vincenzo Solinas Istituto Chimico, Universiti, 09 100 Cagliari, Italy
Sandro Mori Euteco S.p.A., 20767 Milano, Italy
The thermal hydrodealkylation of 2-ethylnaphthalene (BEN) has been studied in a tubular flow reactor, at effective reaction temperatures in the range from 570 to 710 OC. Total pressure ranged from 2.9 to 44.6 atm, and HJhydrocarbon molar ratio in the feed was varied from 3 to 10. Main products were naphthalene (N), 2methylnaphthalene (BMN) and 2-vinylnaphthalene. The latter is the product of a dehydrogenation which is strongly depressed at pressures larger than 20 atm. Kinetic resutts in the high-pressure region have been interpreted according to a scheme of three parallel-consecutive reactions (BEN BMN; BMN N; BEN N) assuming rate equations of the form r = kCarommCHzn. Arrhenius parameters and partial reaction orders were obtained that reproduce experimental molar conversions f15 % on the average.
- -
-
Studies about reaction products and kinetics of the thermal hydrodealkylation of methylnaphthalenes in a tubular flow reactor have been reported (Beltrame et al., 1975, 1976). Since in industrial applications for naphthalene production feedstocks containing several alkylnaphthalenes are employed (Asselin, 1964;Ballard, 19651, it seemed interesting to extend the study to higher homologues, first of all ethylnaphthalenes. Results for 2ethylnaphthalene (BEN) are presented here. Experimental Section Materials. 2-Ethylnaphthalene was prepared from methyl-2-naphthyl ketone by standard Wolff-Kishner reduction; it was pure by GC. The 1- and 2-vinylnaphthalenes were Fluka technical products. Cylinder 99.99% hydrogen was employed. Apparatus and Procedure. They were as described by Beltrame et al. (1975). However, electric heating was modified in order to reduce the temperature gradient along the reactor, which previously was strongly nonisothermal: the measured axial temperature profile during reactions (thermocouple readings at intervals of ca. 3 cm) showed a large central portion with roughly constant temperature (&lo"C) and lower values in the entrance and exit regions. was defined for An effective reaction temperature (Teff) each run by considering only the length of the reactor (z,R) where temperature was within 40 "C of its maximum value and taking the arithmetic mean of the measured temperatures along it. Reaction Products. Condensed products were examined by GC-MS and quantitatively determined by GC analysis in the conditions previously described (Beltrame et al., 1976). The main condensed products were found *Address correspondence to this author at the Istituto di Chimica Fisica, Universith di Milano, Via C. Saldini 50, 20133 Milano, Italy. 0019-7882/79/1118-0338$01.00/0
Table I. Binaphthyl Derivatives Identified by GC-MS Analysis in the Products (Reaction Conditions: See Runs H in Table IV) ~~
peak no. mol wt mol formula 14 15 16 17 18 19
20 21 22 23
254 268 254 2 68 2 68 2 68 1282
E 282 282
C,,H,, C, ,H,, C2,Hl., C2,Hl, C,,H,, C, H I, C,,Hl, C,,H,, C, H I C,,H,, C,,H,, C,,H,,
~~
~~
assignment 1,l'-binaphthyl methylbinaphthyl 1,2'-binaphthyl methylbinaphthyl methylbinaphthyl methylbinaphthyl ethylbinaphthyl 2,2'-binaphthyl methylbinaphthyl ethylbinaphthyl ethylbinaphthyl unknown methylbinaphthyl
to be naphthalene, 2-methylnaphthalene, and 2-vinylnaphthalene, the latter identified by comparison of both mass spectrum and retention time with those of a sample. Among minor products, a consistent group was that of binaphthyls, as shown in Table I. Benzene and some derivatives (toluene, ethylbenzene, cumene, and indene) were also found. By comparison with literature mass spectral data, diphenylacetylene, 2-methylanthracene, and pyrene were identified. In terms of naphthalene rings (or benzene rings derived from them) the composition of the reaction products was: main products 2 96%; byproducts 5 4%. In the gaseous phase, methane, ethane, and ethylene were recognized (GC analysis) (Beltrame et al., 1975) by comparison with commercial samples, but not exactly determined. The most common abundance order was CH4 > C2H6> C2H4. Results Kinetic runs were carried out at various total pressures from 2.9 to 44.6 atm. The hydr0gen:hydrocarbon molar ratio in the feed (RH) ranged from 3 to 10. Hydrocarbon 0 1979 American Chemical Society
Ind. Eng. Chem. Process Des. Dev., Vol. 18, No. 2 , 1979 339 Table 11. Equilibrium Constants' for Reactions 1-6 from Thermodynamic Data (Stull et al., 1969). Figures in Brackets Refer t o the Corresponding Reactions Involving Benzenic Analogues of the Naphthalenic Compounds reaction
temp, K
1
2
3
4
5
6
800 900 1000
9840 3360 1340
682 297 151
149 74 41
[0.047] [0.38] [2.0]
[ll]
0.675 3.70 14.3
a
[7.6] [5.6]
Pressure in atm.
feed rates were in the range 0.1-0.4 mol/h. Analyses of the condensed reactor effluent always revealed considerable amounts of unreacted BEN, naphthalene (N), and 2-methylnaphthalene (BMN). In the lower pressure runs 2-vinylnaphthalene (BVN) was also an important product, while a t higher pressure it was scarce. Correspondingly, ethylene was found in the low-pressure runs only. For these runs the observed main products are accounted for by the following stoichiometric equations
C10H7CzHS + Hz CloH;CH3 + CH4 CloH&H3 + H2 C10H8 + CH4 CloH:CzHS + Hz CloHs + C2H6 C10H7C2HS F! CloH7CH=CHz + Hz CloH7CH=CH, + Hz C1oH8 + CzH4
-
-+
-+
C10H7CzHS F! C10H8
CzH,
(1) (2) (3) (4)
(5)
(6) The above equations correspond to formation of naphthalene from BEN by successive hydrodemethylations with intermediate production of BMN (eq 1 and 2), by direct
hydrodeethylation (eq 3), by dehydrogenation to BVN (eq 4) followed by its hydrodeethynylation (eq 5), and finally by deethynylation of BEN (eq 6). Only in eq 4 and 6 has the reverse reaction been explicitly indicated. In fact, the available thermodynamic data for the compounds of interest or their benzenic analogues show that in the temperature range of the experimental runs (or in part of it) only reactions 4 and 6 have equilibrium constants K,, 1 or 15 atm). In these cases, therefore, analyses were normalized to three components (N, BMN, BEN) and conversions of BEN to BMN (yM) and to N (yN)were evaluated for each run. Results are shown in Table 111. Molar conversion values in this table (as well as in Table IV) are all given to three decimal places, although only a part of the experiments warrants such precision, for the sake of homogeneity. A t lower pressure ( P C 16 atm; p H o < 12 atm) 2vinylnaphthalene was no longer negligibe and was considered besides BMN and N. In this way one accounts,
Table 111. Kinetic Results of High-pressure Runs molar conversions group of runs
Teff,
"C
feed rate of BEN, mol/h
8.4 8.9 9.0 9.0 9.0 7.4 7.1 7.0 7.0 3.4 3.0 3.0 3.0 2.9
647 646 646 645 647 647 648 646 645 645 647 646 648 648
0.166 0.191 0.254 0.318 0.381 0.191 0.254 0.318 0.381 0.147 0.191 0.254 0.318 0.381
7.8 6.6 6.8 7.1 7.7 7.3 7.4 7.5 6.1
62 1 629 622 62 3 646 646 65 3 649 655
9.2 9.5 9.2 9.8 8.7
57 3 57 5 575 57 6 57 3
RH
YM
exptl
YN
calcd
exptl
calcd
0.123 0.116 0.110 0.102 0.097 0.138 0.140 0.131 0.121 0.253 0.286 0.271 0.260 0.249
0.556 0.524 0.445 0.395 0.391 0.554 0.482 0.428 0.398 0.491 0.442 0.409 0.389 0.360
0.634 0.568 0.456 0.374 0.330 0.596 0.489 0.400 0.339 0.635 0.552 0.443 0.395 0.345
0.108 0.129 0.104 0.098 0.079 0.125 0.133 0.132 0.161
0.420 0.405 0.314 0.314 0.751 0.707 0.693 0.610 0.525
0.516 0.470 0.334 0.310 0.910 0.756 0.707 0.568 0.653
0.052 0.043 0.037 0.030 0.027
0.231 0.192 0.148 0.128 0.081
0.294 0.211 0.160 0.131 0.102
(P = 20.4 atm) E
C
D
L
U
I
M
0.154 0.150 0.127 0.124 0.103 0.138 0.144 0.136 0.138 0.226 0.278 0.257 0.258 0.232 (P= 30.0 atm) 0.191 0.110 0.272 0.140 0.330 0.066 0.381 0.095 0.127 0.117 0.191 0.106 0.254 0.108 0.316 0.094 0.333 0.158 (P = 44.6 atm) 0.124 0.041 0.191 0.048 0.254 0.040 0.318 0.028 0.381 0.017
340
Ind. Eng. Chem. Process
Des. Dev., Vol. 18, No. 2,
1979
Table IV. Measured Conversions in Low-Pressure Runs feed rate group Teff, of BEN, of runs RH "C mol/h
molar conversions
Yv
YM
YN
0.092 0.116 0.141 0.171 0.172 0.128 0.155 0.157 0.170 0.147 0.146 0.198 0.172
0.216 0.193 0.172 0.153 0.134 0.227 0.194 0.207 0.194 0.320 0.333 0.269 0.240
0.504 0.497 0.440 0.356 0.313 0.449 0.357 0.401 0.354 0.354 0.347 0.311 0.321
0.099 0.102 0.084 0.079 0.071 0.062 0.099 0.092 0.056 0.100 0.146 0.133 0.077 0.089 0.099
0.105 0.088 0.074 0.036 0.034 0.138 0.070 0.031 0.205 0.165 0.121 0.116 0.231 0.200 0.142
0.191 0.145 0.156 0.127 0.075 0.172 0.155 0.086 0.479 0.350 0.300 0.281 0.415 0.361 0.263
0.034
0.075
0.158
0.005 0.008 0.020 0.026 0.047
0.230 0.272 0.244 0.236 0.211
0.557 0.398 0.370 0.307 0.280
( P = 2.9 atm)
Q
9.0 9.0 8.9 8.6 9.2 5.1 4.9 5.1 5.0 2.8 2.9 3.1 3.0
703 708 709 708 711 704 694 707 707 697 699 703 700
7.2 7 .O 6.1 7.3 7.8 7.1 6.8 7.0 7.0 6.7 7.4 7.1 5.8 6.5 6.0
648 642 650 649 646 654 643 646 67 2 67 4 68 2 67 8 67 5 67 3 67 0
B
8.3
631
N
3.6 3.6 3.2 3.3 3.8
647 655 65 3 65 2 65 1
P
0
A
R S
H
0.127 0.191 0.254 0.318 0.381 0.191 0.254 0.318 0.381 0.191 0.241 0.318 0.381 ( P = 4.9 atm) 0.166 0.191 0.229 0.334 0.381 0.121 0.181 0.356 0.127 0.203 0.318 0.362 0.139 0.181 0.356 ( P = 8.7 atm) 0.191 ( P =15.5 atm) 0.114 0.181 0.254 0.305 0.381
on the average, for 97% of the reaction products for these runs. Analyses normalized to four components (N, BMN, BVN, BEN) were used to evaluate separate conversions of BEN to BVN (yv), BMN (yM),and N (yN) for each run. Values are given in Table IV. Kinetic computations were performed only for highpressure runs, according to reaction scheme 7. As previously reported and discussed (Beltrame et al., 1975), low Reynolds numbers, typical of laminar flow, characterize the fluid motion in the reactor during kinetic runs. Neglecting radial temperature gradients, the radial velocity profile (8) for laminar flow in annuli (Knudsen and Katz, 1958) was employed 4 = U/U, = 2([RZ2- R2 - (R2' R12)In (Rz/R)/ln ( R Z / R ~ ) I / [ R + Z ~R12 - (Rz' R12)/ln ( R d R J I J (8) where R1 and R2are the inner and outer radii, respectively, urnis the mean velocity, and u is the velocity at a distance R from the annulus axis. Assuming perfect segregation, the actual reactor was considered as the sum of eight concentric annular reactors, characterized by four different average values of 4, equal values being obtained for couples of annuli (the two contacting internal and external walls, the two next to these, etc.) by appropriate sizing. Four virtual reactors, of similar cross section, having 4 values of 0.37,0.94, 1.31, and 1.48 were finally considered (Carniti et al., in press).
Residence time (ti) in the ith virtual reactor was calculated by
u, being equal to FBEN(RH
+ 1).82.Teff/PSR.The rate
equations were taken as
dCN - = k2CH2n2CBMNmz + k3CH?CBENm3 (11) dt In the pseudo-isothermal approximation kl,k2,and 123 are meant as kinetic coefficients a t the effective temperature (Teff)of the reactor. Since hydrogen is an excess reagent, one can take
Assuming that naphthalene is produced in equal amounts through reactions 1-2 and reaction 3, the value of CHpf was approximated by
Under these approximations, hydrogen concentration may
Ind. Eng. Chem. Process Des. Dev., Vol. 18, No. 2, 1979
Table V. Kinetic Parameters for Rate Eq 10 and 11 ( h = Ae-E/1.987T)
reaction 1" 2b A (mol/L)'-m-fl 6.110 x 10" 3.411 'S
X
3" IO8 7.483
X
lo9
I
E (calimol) m n
46634 0.3 0.8
56644 1.0 0
50218 0.3 0.8
be incorporated into kinetic coefficients defined as K , = klCH2flletc. and rate equations (10-11) rewritten as
where CBMN = CBENO - CBEN - CN and dependent variables are CBEN and C N . For the determination of kinetic parameters, we used k2, n2,and m2 values based on previous work (Beltrame e t al., 1975) and selected values of m, and m3. The remaining unknowns ( K , and K3)were obtained by solving
E CNf=
and yNto be compared with the experimental values. This may be done either (a) within the previous approximations ( C H ~z,ff, , and Teffvalues) or (b) removing the approximations. For calculations (b) a further differential equation (18) was added to eq 10 and 11
dCH2 - klCH2n1CBENm1 + k2CH2n2CBMn.m2 + dt ~ ~ C H ~ ~ (18) ~ C B E N ~
" Standard deviations are around 0.5 for log A and 2 kcalimol for E . Parameter values based on previous work (Beltrame et al., 1975).
SR
341
(16)
CN,lfS1dl
(17) SR where CBENf and CNfare experimental values at the reactor outlet, while CBEN,lfand CN,Lf refer to the outlet of the ith segregated annular space and are calculated as functions of K , and K, through integration of differential eq 14 and 15 by the Runge-Kutta method (Carnahan et al., 1969). The following criteria were used for choosing ml and m3 values: (i) (first tentative) ml = m3;in this case eq 14 may be rewritten with a single coefficient K (= K1 + K 3 )and analytically integrated for an approximately isothermal set of runs (groups C, D, E, U, of Table 111); from eq 14 and 16 values of K were calculated for several values m, = m3, and it was found that the best linearity on the plot of log K vs. log C H corresponded ~ to ml = m3 = 0.40, with a slope n (hopefully = nl = n,) of 0.55. Overall reactivity of BEN was fairly well correlated for all runs in Table 111. However, when values of K were split into K1 and K 3 values by using eq 15 and 17 and plots of log K , and log K3 vs. log CH2 drawn for the mentioned groups C, D, E, U of kinetic runs, it was found nl 0 and n3 20.75; this was taken as evidence that reaction 3 was kinetically dissimilar from reaction 1 and similar to reaction 2, since for the latter m2and n2values of 0.35 and 0.75, respectively, had been employed; (ii) (second approximation) m2 = m3 (and moreover, n2 = n3);in this case, starting from the published values (Beltrame et al., 1975) and changing them within their uncertainty limits, it was found that the Arrhenius plot for k3 was optimized by the couple m2 = m3 = 0.30 and n2 = n3 = 0.80; a few values of m, were then tried, and the value 1.0 wasshosen because it linearized best the plot of log K1 vs. log CH2for the usual set of nearly isothermal runs. The slope of the latter plot was n, N 0. . Partial reaction orders are summarized in Table V, where Arrhenius parameters are also reported. By using kinetic coefficients obtained from the Arrhenius equations one can calculate molar conversions yM
and CH2 considered as a dependent variable, besides CBEN and CN;moreover, the actual temperature profiles along the reactor were employed, considering the whole reactor as a sequence of segments of known length and temperature (measured values). Mean square deviations of calculated from experimental conversions were evaluated by both methods, obtaining: for yM,(a) 0.028 and (b) 0.019; for yN, (a) 0.058 and (b) 0.065; for (yM + YN), (a) 0.059 and (b) 0.066. Therefore the kinetic parameters obtained by the shortcut of the pseudo-isothermal approximation are about equally good in the interpretation of experimental results when the approximations are removed. Taking into account the different levels of YM and Y N values in kinetic runs, on the average the relative deviations (method b) are ca. 15% for both YM and Y N , and 12% for overall conversion. Values calculated by method b are presented in Table I11 for comparison with experimental values. Discussion Although it proved possible to handle the kinetics of the hydrodealkylation of methylnaphthalenes in a reactor markedly deviating from isothermal conditions (Beltrame et al., 1975), it was not felt convenient to extend that treatment to the present case, where, even in the simplest approximation (reaction scheme 7) three parallel-consecutive reactions take place. On the other hand, real isothermal conditions would have been very difficult to attain along our reactor (49 cm long) a t temperatures of 600-700 "C. Therefore a compromise was accepted, i.e., to reduce the temperature gradient to a reasonable level and to treat the reactor as pseudo-isothermal by introducing an effective length and an effective temperature. Results show that for reactions at high pressure (the only ones to which reaction scheme 7 could be applied), kinetics are fairly well interpreted using the parameters obtained under the pseudo-isothermal approximation. The presence of little or nil vinylnaphthalene in the high-pressure runs is justified by a shift of equilibrium (4) to the left. Lacking thermodynamic data for BVN, one can consider the analogous reaction CSHjC2Hj F! C,jHSCH=CH2 + Hz (19) for which, a t the reaction temperatures indicated in Table 111, equilibrium constants from 0.1 to 0.5 atm were evaluated. If these values are assumed for reaction 4, the amount of BVN a t equilibrium comes out to be 5 2 % of the aromatic fraction in the conditions of the runs of Table 111. At these low concentrations of BVN, reaction 5 is apparently too slow to give appreciable amounts of ethylene. In the runs of Table IV, pressure was lower and often temperature was higher, both factors favoring the formation of BVN in larger amounts, as observed particularly in runs a t 2.9 and 4.9 atm. In these cases BVN behaved as a reaction intermediate with a concentration (see yv values) typically decreasing with increasing residence time after a maximum; ethylene was found in the gases. This is accounted for by consecutive reactions 4 and 5 while reaction 6, although it cannot be excluded by the present evidence, appears to be of lesser importance.
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Ind. Eng. Chem. Process Des. Dev., Vol. 18, No. 2, 1979
Tables I11 and IV show that the overall trend of YM as a function of residence time is also typical of a reaction intermediate, since often (although not in every case) YM reaches a maximum value, as expected for reactions 1 and 2. The latter point has been quantitatively developed by the kinetic treatment based on reaction scheme 7. The assumption of equal partial orders for reactions 2 and 3 seems justified by its success. Actually these reactions are basically similar, both involving the cleavage of a Calkyl-Caryl bond. It is understandable that reaction 1, where breaking of a C-C bond within an alkyl chain is involved, has a different kinetics. Its reaction order suggests a pyrolysis, kinetically analogous to that of ethylbenzene in the absence of hydrogen (Szwarc, 1949; Esteban et al., 1963; Crowne et al., 1969; Clark and Price, 1970). However, since eq 10 and 11 are empirical equations, meant for practical design purposes, no detailed mechanistic interpretation of the results will be attempted. It may be mentioned that for the kinetics of thermal hydrodealkylation of ethylbenzene (EB), expressed by an equation of the type r = k CEBmCW:, reported results ( m = 0.5, n = 1.0; E = 52 kcal/mol) (Fujii and Kato, 1962) are not too far from those of reaction 3 (Table V). Rates of reactions 2 and 3 may be taken as measures of the different resistance to splitting of the bonds from the naphthalene ring to methyl and to ethyl radicals. At 600 "C, h2 and h3 have values (Table V) of 7.2 x and 20.1 x Lo.1mol4 s-l, respectively. Therefore in the direct reaction to naphthalene, BEN is 2.8 times more reactive than BMN at 600 "C. The same reactivity order and a similar rate ratio were found in a study of the hydrodealkylation of alkylnaphthalenes on a Ni--A1203catalyst (MachgEek et al., 1966; Baiant and Kochloefl, 1970). Therefore, from a practical point of view. reaction conditions apt to give high conversion of BMN would certainly be satisfactory for BEN too. Finally, a comparison can be made between BMN and BEN as to the reaction byproducts. In both cases the presence of benzene derivatives is evidence of a ringcracking secondary reaction. Among heavy byproducts, binaphthyls were obtained from BEN as from BMN; moreover in the high-pressure runs the isomer distribution was, on the average 1,1':1,2':2,2' = 1:6:11, similar to that found, under probable thermodynamic control, in the reaction of methylnaphthalenes (Beltrame et al., 1976). Obvious differences appear in the substituted binaphthyls, with the presence of some ethyl derivatives in the product from BEN (Table I). It should be remembered that secondary products, although numerous, are in small amounts both from 2-methyl- and from 2-ethylnaphthalene hydrodealkylation.
Acknowledgment We thank Dr. L. Cavalli and co-workers for GC-MS analyses. Nomenclature A = Arrhenius frequency factor, (mol/L)'-"-"/s C = molar concentration of j , mol/L E! = Arrhenius activation energy, cal/mol F, = feed rate of j , mol/s k = rate coefficient, (mol/L)'-"-"/s K = rate coefficient, (mol/L)'-m/s m = reaction order with respect to hydrocarbon n = reaction order with respect to H2 P = total pressure, atm pi = partial pressure of j , atm r = reaction rate R = radius R H = (H2/hydrocarbon) feed molar ratio S,= area of the section of the ith annular s ace, cm2 SR = area of the overall reactor section, cm t = residence time, s T = temperature, K Teff= effective reaction temperature, "C u = gas velocity, cm/s u, = mean gas velocity, cm/s yj = molar conversion to product j zeff = effective reactor length, cm = u/u, Superscripts 0 = inlet value of variable f = outlet value of variable Literature Cited
B
Asselin, G. F., Adv. Pet. Cbem. Refin., 9, 47 (1964). Ballard, H. D., Jr., Adv. Pet. Cbem. Refin., I O , 219 (1965). Baiant, V.,Kochloefl, K., Cbim. Ind. (Milan), 5 2 , 870 (1970). Beltrame, P., Marongiu, B., Solinas, V.,Torrazza, S., Forni, L., Mori, S., Ind. f n g . Cbem. Process Des. Dev., 14, 117 (1975). Beltrame, P., Cavalli, L., Landone, A,, Marongiu, B., Solinas, V..Torrazza, S., Cbim. Ind. (Milan), 58, 163 (1976). Carnahan, B., Luther, H. A,, Wilkes, J. O., "Applied Numerical Methods", p 361, Wiley, New York, N.Y., 1969. Carniti, P., Mori, S., Tassara, A,. Forni, L., Ing. Cbim. Ita/., in press, 1979. Clark, W. D., Price, S. J., Can. J . Chem., 48, 1059 (1970). Crowne, C. W. P., Grigulis, V.J., Throssell, J. J., Trans. Faraday SOC.,65, 1051 (1969). Esteban, G. L., Kerr, J. A,, Trotman-Dickenson, A. F., J . Cbem. SOC.,3873 (1963). Fujii, S., Kato, S., Kogyo Kagaku Zassbi, 65, 1396 (1962); Cbem. Abstr.. 58, 6667 (1963). Knudsen, J. G., Katz, D. L., "Fluid Dynamics and Heat Transfer", p 92, Mc3awH11, New York, N.Y., 1958. MachBEek. H., Kochloefl, K., Kraus, M., Collect. Czech. Cbem. Commun., 31, 576 (1966). Stuli, D.R., Westrum, E. F., Jr., Sinke, G. C., "The Chemical Thermodynamics of Organic Compounds", Chapter 9, Wiley, New York, N.Y., 1969. Szwarc, M., J . Cbem. Pbys., 17, 431 (1949).
Receiued for review December 27, 1977 Accepted December 7, 1978
