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Catalytic hydrodesulfurization of a petroleum residue
1810
Shorter Communications
141 Eigenberger G., C/tern. Engng Sci 1978 33 1263.
I51 Takoudis C. G., Schmidt L. D. and Ark R., Chem. Engng Sci 1981 36 377. [6] Chang H. C. and Aluko M., Chem. Engng Sci, 1981 36(10) 1611. I71 Cutlip M. B. and Kenney C. N.. 5th Znz. Symp. Chem. Reaction Engng. 1978 415.
[81 Goodman M. G., Mukesh D., Denney C. N. and Morton w.,
Surface Sci, to he published. M. G. Kenney C. N., Morton W. and Cuthp M. 2nd World Gong. Chem. Engng. B., MOlltrC31, Canada 1981. I101 Morton W., and Goodman M. G., Dons. LChem.E. 1981 59 253.
[91 Goodman
Catalytic hydrodesulfurization of a petroleum residue (Receiued 16 January 1982; accepted Desulfurization of residual oils of high sulfur content has become B subject of considerable investigation in tbe last few years. Direct catalytic hydrodesulfurization is one of the preferred methods employed to lower the sulfur content of resids and to improve the quality of feedstocks. In 1974, a new petroleum deposit was discovered off the island of Thaws, in northern Greece, which has a high sulfur content. Samples of the crude oil were obtained from the Prinos 5 and Prinos 6 wells of this deposit and the atmospheric residue was separated by laboratory distillation. Properties of the r&d feedstocks are given in Table I. A number of investigations have been reported on resid hydrodesulfurization. Beaton[l] has reviewed the subject of hydrodesulfurization of petroleum resids. Cecil et al. [2] discussed fuel oil HDS in terms of plug flow with pseudo-second order kinetics in pilot trickle-bed reactors. Paraskos and bis associates&61 conducted a series of investigations on residuum desulfurization mostly of Kuwait origin reduced crudes, where they took into consideration the effect of liquid holp up, catalyst incomplete wetting and axial backmixing in the trickle bed. They claimed that when these effects are taken into consideration, as suggested by Henry and Gilbert]71 and Mears[%], the data may be interpreted by apparent first-order kinetics[lO]. The nature of sulfur compounds in petroleum residua and the chemistry of hydrogenolysis reactions have been discussed by Schuit and Gates[9]. The refractoriness of asphalterdc sulfur in particular has been demonstrated by Richardson and Alley[ll]. The purpose of this paper is to report on the HDS of a residuum obtained from this new oil deposit in the Aegean sea, which has a high sulfur content, and to interpret the kinetic behaviour of the rate of desulfmization. EXPEEIMRNTAL. The apparatus used included an integral flow-reactor. The trickle-bed reactor had a dieter of 2.54 cm and a total length of 0.50 m. Catalyst bed lengths were 0.16 m, 0.24 m and 0.316 m. The catalyst used was commercial type COMOX 451 donated by Laporte Industries Ltd, Widnes, England, cylindrical exbudates Q 1.5 mm x 3.17 mm, Q 2.5 mm X 4.69 mm, and broken particles of an average diameter 0.34 mm (w Mesh U.S. sieves). The properties of the residuum feedstock used are given in Table 1. The reacctor effluent was analysed by standard methods for sulfur content, nickel and vanadium content, Conradson carbon and asphaltenes. The reactor was operated isothermally, untit steadv-state conditions were attained. Tbe activitv of the catalvst was closely watched by standard experiments and results were corrected to a standard activity. The catalyst was presuhided prior to use in these experiments. Hydrogen gas rate in the exit gas stream was measured at around 80 Nl HJh, sutfcient to keep the I-I&I content of the gas low in the reactor. to minimize inhibition effectsI by HZS DISCUSSION
26 April 1982)
vature indicates that the overall reaction is not apparently first order with respect to total sulfur concentration. Tbis is not necessarily contradictory with the fact that individual sulfur compounds have been observed[l,9] to react accordii to tirstorder kinetics. Figure I shows the same data plotted as (l/Sl/&) vs. space time. Straight lines passing through the origin are obtained. This indicates that the reaction exhibits apparent second-order kinetics in plug flow. This is similar to a conclusion obtained for other types of heavy oils and residues[2,13]. The same result was obtained for bed lengths of 316 mm, 240 mm and 16Omm, which indicates that within this bed-length range axial dispersion (or backmixing of the liquid) was not taking place. The pressure effect is shown in Fig. 2. The data at 350°C are plotted as LHSV (l/S-l/S,) vs. hydrogen pressure. A linear pressure dependence is observed up to one hundred bar pressure. All the above experimental evidence may be described by a plug flow reaction model given in differential form by eqn (1): -FPL dS = kS2pn; Upon integration and substitution velocity, the final form becomes:
(1)
(LHSV) . (l/S - l/So) = 3600 kpu,/pL.
Fig. 1. Second-order
5,. Fig. 2. Effect
space
(2)
kinetics test plot. Catalyst 0.34 mm size at JO bar.
OF RFSULTS
If a typical set of data are plotted as the logarithm of the desulfurization ratio S/So vs space time, for three temperature levels at SObar, a curvature of the plots is exhibited. The cur-
dVR
of the liquid hourly
of hydrogen
pressure on HDS. 0.34nll-n.
bar Catalyst
size
1811
Equation (2) is supported by Figs. 1 and 2. The temperature effect on the specific reaction rate constant k was obtained by an Arrhenius plot. The data are correlated by eqn (3): k= 1.45x 106e~p(-~).gs~‘bar~‘cm~‘.
(3)
The activation energy was 29 kcal/mol, for the small particles of 0.34 mm, indicating that the hydrogenolysis reaction may be the rate limiting step, and that pore-diffusion is not important in the small particle size. Hence, the effectiveness factor may be taken as unity. The effect of catalyst particle size is shown in Fig. 3, for 350°C at 50 bar pressure. It can be see”, that the larger the particle size the lower the catalyst effectiveness. The slopes lead to the following average effectiveness factors: dp = 0.34mm, q=l; d,,=l.Smm, q=O.57; $=2Smm, q=O.32. These values are well correlated by the generalized effectiveness factor chartIl41, for the second-order reaction. It should be noted, that the specific second-order reaction rate constant based on particle volume, %, is related to the rate constant k of eqn (31, by the formula:
feeding at ditTerent velocities. Thus, if the sulfur compounds in the residuum are thought to be composed of two main groups of composition S, and S,, proceeding at HDS rates of klSl and k&, where k, > k2, then the integrated sulfur balance in the reactor, at constant pressure, is given by:
s =(ml
exp [ - -----++Woexp[-$$$&I &$YH!&)
(6)
where (Sl)s and (Ss)s are the initial compositions of “light” and “heavy” key sulfur compounds. If the logarithm of S/S,, is plotted against space time, then kl and k2 may be determined from the initial and tbml slopes of the curves, (52)s can be determined from the y-intercept and (&)a by difference. Thus, at 50 bar pressure for the small particles of 0.34 mm, the data have been satisfactorily correlated by this model, according to eqn (6), with k, and kz given by: k,=6,38x
lO’exp(-+?),
gsm1cmm3
k2=1,13x108exp(-~),gs-1cm“ The effectiveness factor data lead to the determination of an average effective diiusivity 4s = (2.7 f 0.3) x lo-’ cm*/s, at the average sulfur composition of 3.5% w/w. The overalI correlation of all data with T, P, LHSV, or. and n may be given by eqn (5), to a satisfactory degree of confidence.
Model of two parallel first-order reactions It has been known[2,151. that apparent, overall second-order kinetics is manifested by two parallel first-order reactions pro-
‘““C
(LHSV):h Fig. 3. ISBect of catalyst particle size on HDS.
(Sl)s = 0.65 Se
and
(S& = 0.35 So.
In other words, it can be concluded that the two sulfur groups proceed in reaction with a selectivity factor kllkZ=3.55, but essentially with the same activation energy of about 26 kcal/mol, and their initial percentage in the feedstock is 65% and 35% w/w, respectively. Cecilf21 reports similar values for a Middle-eastern residuum, but higher activation energy and lower rates. Sulfur compound analysis Four main groups of hydrocarbon and sulfur compounds have been determined by solid-liquid chromatogmphy[l21: Asphaltenics (insoluble in n-pentane), satnrated (eluted from the cohuuu by n-hexane), aromatics (eluted by benzene) and polar-aromatics (eluted by a methanol-benzene mixture). The weight and the sulfur content of each fraction was determined before and after hydrotreating. Figure 4 presents some data on the contribution of each compound group to total sulfur content. It appears that saturated and aromatics sulfur comnounds are the most diicult to HDS, while polar-aromatics and~asphalteuics proceed faster. In the end, it appears that thiopheulc type sulfur is the one that controls the rate of deep HDS. Asphalteoic hydrocarbons, initially about 25% w/w, nre reduced with the progress of desulfurization to about 15% at 85% HDS. Aromatic hydrocarbons, initially at 22%. show a rise to 25% in the early stages of desuifmization, with a subsequent drop to 19% in deep desulfurization. Polar-aromatics show s similar behaviour. Saturated hydrocarbons. initially at 19% show a continnous increase to 45% in the end. These results suggest that hydrotreating. in addition to HDS, converted the hydrocarbons from one group to the other,
Shorter Communications
1812
NOTATION
external surface area of particle, cm2 C average sulfur concentration, mollcm’ Dee effective diffosivity of sulfur compound in catalyst pores, cm’ls F volumetric flowrate of liquid. m’ls constant, second-order rate k apparent g s-’. bar-’ c,,-~ rateconstant defined by eqn (4) cm3. mol-’ . s-’ pseudo-first order rate constants, g. SC’ . cm-’ k,,: LHSV liquid hourly space velocity, h-’ S total sulfur weight fraction, glgeil initial total sulfur wt fraction sulfur weight fractions for compounds 1,2 S,,Z T temperature, K VR catalyst bed volume, m3 lb‘d catalyst bed void fraction 9 catalyst effectiveness factor PL liquid density, g. cme3
%
Time. h Fig. 4. Distribution of sulfur compounds vs time in HDS. Catalyst size 0.34 mm at 390 “C and 50 bar. x total sulfur. A asphaltenics sulfur, 0 aromatics sulfur, 0 polar aromatics sulfur, 0 saturated sulfur. pcrhaps following the reaction network: aspaltenics
/ T
aromatics p polar aromatics saturated
saturated aromatics
-+
saturated.
CONCLUSIONS
This study has shown that hydrodesulfurization of a high sulfur content atmospheric residuum proceeds with overall secondorder kinetics w.r.t. sulfur and first-order w.r.t. hydrogen, with an intrinsic activation energy of 29 kcal/mol but with small catalyst effectiveness factors for commercial size catalyst particles, indicating strong pore-diffusion limitations. It appeared that plug flow with no backmii prevailed in the trickle bed reactor. A more detailed insight of the reactions is gained when the main groups of sulfur and hydrocarbon compounds are analyzed. Work is now in progress to establish the reaction networks and kinetic performance of the main individual sulfur compounds. Acknowledgement--The authors are thankful to the N.T.U. Athens and the National Research Foundation for partial fmancial support and to the Public Petroleum Corp. of Greece for donation of oil samples. Chemical Process Engineering Laboratory National Technical University Athens, Greece
ALEX SCAMANGASt NICKOS PAPAYANNAKOS JOHN MARANGOZIS*
tPresent address: Petrola Oil Refinery, Elefsis, Greece. ‘Author to whom correspondence should be addressed.
[l] Beaton W. I., Chemical Reactions ns a Means of Sepamtion-Sulfur Removal (Edited by Crynes B. L.), Chap. 1, pp. l-34. Marcel Dekker, New York (1977). [2] Cecil R. R., Mayer F. X. and Cart E. N., Paper 12a presented at the 61st AICh.E. Annual Metting Los Angeles, l-5 Dec. (l%S). [3] Paraskos J. A., Frayer J. A. and Shah Y. T., Jnd. Engng Chem. Proc. Des. Dew. 1975 14 315. [4] Montagna A. A. and Shah Y. T., Ind. Engng Chem., Proc. Des. Dev. 1975 14 479. [5l Shah Y. T. and Paraskos J. A., Ind. Eng. Chrm., Proc. Des. Dev. 1975 14 368. [63 Montagna A. A., Shah Y. T. and Paraskos J. A., lnd. Engng Chem. Proc. Des. Dee. 1977 16 152. [7] Henry H. C. and Gilbert J. B., hd. Engng Chem. Proc. Den 1973 12 328. [S] Mears D. E., ISCRE 3rd Advan. Chem. Ser. 1974 133 218. 191 Schuit G. C. A. and Gates B. C.. k1.Ch.E.J. 1973 19 417. [ioj Marangozis J., Ind. Engttg Ch& Proc. Des. E&U. 1980 19 326. [Ill Richardson R. L. and Alley S. K., Hydrocracking and Hydrotreating (Edited by Ward I. W. and Qader S. A.), pp. 136-149. ACS Symposium Series No. 20, American Chemical Society, Washington 1975. [12] Drushel, H., Analytical Chamctcrization of R&duo and Hydrotreated Products. Am. Chem. Sot., New York Meeting, 27 Aug.-l Sept. 1972. [13] De Bruijn A., Naka I. and Sonnemans J. W. M., Ind. Engng Chem. Proc. Des. Deu. 198120 40. [14] Froment G. F. and Bischoff K. B., Chemical Reactor Analysis and Design, pp. 182-195. Wiley, New York 1979. [IS] Wei 3. and Hung C. W., Ind. Engng Chem. Proc. Des. Dew 1980 19 197.
Effect of desorptfon of air from liquid on gas-side mass transfer coefficient in gas absorption (Received
17 September
1979: accepted
In the absorption of the bubble of carbon dioxide into falling water saturated with air in a column, air was found, though it is slight, to dlfIuse from the water into the bubble and to increase with the rise of contractiong bubble in falling water in the previous experiment[6]. Such an air accumulated in the bubble in process of absorption is thought to cause the decrease of the overall liquid-side mass transfer coefficient, one of the causes of
20 April 1982)
which may probably be an occurrence of gas-side resistance in the bubble. Hatch and Pigford[S], Cairns[4], Onda et aL[9,10], Asano[l,2], Wakao ef al.[lZ], Byers and King[31, and Veilstich[ll] have already been studied on the gas-phase mass transfer coefficient, k. in liquid-jet column, but no evidences have yet been experimentally on the gas-side resistance in the
Shorter Communications
141 Eigenberger G., C/tern. Engng Sci 1978 33 1263.
I51 Takoudis C. G., Schmidt L. D. and Ark R., Chem. Engng Sci 1981 36 377. [6] Chang H. C. and Aluko M., Chem. Engng Sci, 1981 36(10) 1611. I71 Cutlip M. B. and Kenney C. N.. 5th Znz. Symp. Chem. Reaction Engng. 1978 415.
[81 Goodman M. G., Mukesh D., Denney C. N. and Morton w.,
Surface Sci, to he published. M. G. Kenney C. N., Morton W. and Cuthp M. 2nd World Gong. Chem. Engng. B., MOlltrC31, Canada 1981. I101 Morton W., and Goodman M. G., Dons. LChem.E. 1981 59 253.
[91 Goodman
Catalytic hydrodesulfurization of a petroleum residue (Receiued 16 January 1982; accepted Desulfurization of residual oils of high sulfur content has become B subject of considerable investigation in tbe last few years. Direct catalytic hydrodesulfurization is one of the preferred methods employed to lower the sulfur content of resids and to improve the quality of feedstocks. In 1974, a new petroleum deposit was discovered off the island of Thaws, in northern Greece, which has a high sulfur content. Samples of the crude oil were obtained from the Prinos 5 and Prinos 6 wells of this deposit and the atmospheric residue was separated by laboratory distillation. Properties of the r&d feedstocks are given in Table I. A number of investigations have been reported on resid hydrodesulfurization. Beaton[l] has reviewed the subject of hydrodesulfurization of petroleum resids. Cecil et al. [2] discussed fuel oil HDS in terms of plug flow with pseudo-second order kinetics in pilot trickle-bed reactors. Paraskos and bis associates&61 conducted a series of investigations on residuum desulfurization mostly of Kuwait origin reduced crudes, where they took into consideration the effect of liquid holp up, catalyst incomplete wetting and axial backmixing in the trickle bed. They claimed that when these effects are taken into consideration, as suggested by Henry and Gilbert]71 and Mears[%], the data may be interpreted by apparent first-order kinetics[lO]. The nature of sulfur compounds in petroleum residua and the chemistry of hydrogenolysis reactions have been discussed by Schuit and Gates[9]. The refractoriness of asphalterdc sulfur in particular has been demonstrated by Richardson and Alley[ll]. The purpose of this paper is to report on the HDS of a residuum obtained from this new oil deposit in the Aegean sea, which has a high sulfur content, and to interpret the kinetic behaviour of the rate of desulfmization. EXPEEIMRNTAL. The apparatus used included an integral flow-reactor. The trickle-bed reactor had a dieter of 2.54 cm and a total length of 0.50 m. Catalyst bed lengths were 0.16 m, 0.24 m and 0.316 m. The catalyst used was commercial type COMOX 451 donated by Laporte Industries Ltd, Widnes, England, cylindrical exbudates Q 1.5 mm x 3.17 mm, Q 2.5 mm X 4.69 mm, and broken particles of an average diameter 0.34 mm (w Mesh U.S. sieves). The properties of the residuum feedstock used are given in Table 1. The reacctor effluent was analysed by standard methods for sulfur content, nickel and vanadium content, Conradson carbon and asphaltenes. The reactor was operated isothermally, untit steadv-state conditions were attained. Tbe activitv of the catalvst was closely watched by standard experiments and results were corrected to a standard activity. The catalyst was presuhided prior to use in these experiments. Hydrogen gas rate in the exit gas stream was measured at around 80 Nl HJh, sutfcient to keep the I-I&I content of the gas low in the reactor. to minimize inhibition effectsI by HZS DISCUSSION
26 April 1982)
vature indicates that the overall reaction is not apparently first order with respect to total sulfur concentration. Tbis is not necessarily contradictory with the fact that individual sulfur compounds have been observed[l,9] to react accordii to tirstorder kinetics. Figure I shows the same data plotted as (l/Sl/&) vs. space time. Straight lines passing through the origin are obtained. This indicates that the reaction exhibits apparent second-order kinetics in plug flow. This is similar to a conclusion obtained for other types of heavy oils and residues[2,13]. The same result was obtained for bed lengths of 316 mm, 240 mm and 16Omm, which indicates that within this bed-length range axial dispersion (or backmixing of the liquid) was not taking place. The pressure effect is shown in Fig. 2. The data at 350°C are plotted as LHSV (l/S-l/S,) vs. hydrogen pressure. A linear pressure dependence is observed up to one hundred bar pressure. All the above experimental evidence may be described by a plug flow reaction model given in differential form by eqn (1): -FPL dS = kS2pn; Upon integration and substitution velocity, the final form becomes:
(1)
(LHSV) . (l/S - l/So) = 3600 kpu,/pL.
Fig. 1. Second-order
5,. Fig. 2. Effect
space
(2)
kinetics test plot. Catalyst 0.34 mm size at JO bar.
OF RFSULTS
If a typical set of data are plotted as the logarithm of the desulfurization ratio S/So vs space time, for three temperature levels at SObar, a curvature of the plots is exhibited. The cur-
dVR
of the liquid hourly
of hydrogen
pressure on HDS. 0.34nll-n.
bar Catalyst
size
1811
Equation (2) is supported by Figs. 1 and 2. The temperature effect on the specific reaction rate constant k was obtained by an Arrhenius plot. The data are correlated by eqn (3): k= 1.45x 106e~p(-~).gs~‘bar~‘cm~‘.
(3)
The activation energy was 29 kcal/mol, for the small particles of 0.34 mm, indicating that the hydrogenolysis reaction may be the rate limiting step, and that pore-diffusion is not important in the small particle size. Hence, the effectiveness factor may be taken as unity. The effect of catalyst particle size is shown in Fig. 3, for 350°C at 50 bar pressure. It can be see”, that the larger the particle size the lower the catalyst effectiveness. The slopes lead to the following average effectiveness factors: dp = 0.34mm, q=l; d,,=l.Smm, q=O.57; $=2Smm, q=O.32. These values are well correlated by the generalized effectiveness factor chartIl41, for the second-order reaction. It should be noted, that the specific second-order reaction rate constant based on particle volume, %, is related to the rate constant k of eqn (31, by the formula:
feeding at ditTerent velocities. Thus, if the sulfur compounds in the residuum are thought to be composed of two main groups of composition S, and S,, proceeding at HDS rates of klSl and k&, where k, > k2, then the integrated sulfur balance in the reactor, at constant pressure, is given by:
s =(ml
exp [ - -----++Woexp[-$$$&I &$YH!&)
(6)
where (Sl)s and (Ss)s are the initial compositions of “light” and “heavy” key sulfur compounds. If the logarithm of S/S,, is plotted against space time, then kl and k2 may be determined from the initial and tbml slopes of the curves, (52)s can be determined from the y-intercept and (&)a by difference. Thus, at 50 bar pressure for the small particles of 0.34 mm, the data have been satisfactorily correlated by this model, according to eqn (6), with k, and kz given by: k,=6,38x
lO’exp(-+?),
gsm1cmm3
k2=1,13x108exp(-~),gs-1cm“ The effectiveness factor data lead to the determination of an average effective diiusivity 4s = (2.7 f 0.3) x lo-’ cm*/s, at the average sulfur composition of 3.5% w/w. The overalI correlation of all data with T, P, LHSV, or. and n may be given by eqn (5), to a satisfactory degree of confidence.
Model of two parallel first-order reactions It has been known[2,151. that apparent, overall second-order kinetics is manifested by two parallel first-order reactions pro-
‘““C
(LHSV):h Fig. 3. ISBect of catalyst particle size on HDS.
(Sl)s = 0.65 Se
and
(S& = 0.35 So.
In other words, it can be concluded that the two sulfur groups proceed in reaction with a selectivity factor kllkZ=3.55, but essentially with the same activation energy of about 26 kcal/mol, and their initial percentage in the feedstock is 65% and 35% w/w, respectively. Cecilf21 reports similar values for a Middle-eastern residuum, but higher activation energy and lower rates. Sulfur compound analysis Four main groups of hydrocarbon and sulfur compounds have been determined by solid-liquid chromatogmphy[l21: Asphaltenics (insoluble in n-pentane), satnrated (eluted from the cohuuu by n-hexane), aromatics (eluted by benzene) and polar-aromatics (eluted by a methanol-benzene mixture). The weight and the sulfur content of each fraction was determined before and after hydrotreating. Figure 4 presents some data on the contribution of each compound group to total sulfur content. It appears that saturated and aromatics sulfur comnounds are the most diicult to HDS, while polar-aromatics and~asphalteuics proceed faster. In the end, it appears that thiopheulc type sulfur is the one that controls the rate of deep HDS. Asphalteoic hydrocarbons, initially about 25% w/w, nre reduced with the progress of desulfurization to about 15% at 85% HDS. Aromatic hydrocarbons, initially at 22%. show a rise to 25% in the early stages of desuifmization, with a subsequent drop to 19% in deep desulfurization. Polar-aromatics show s similar behaviour. Saturated hydrocarbons. initially at 19% show a continnous increase to 45% in the end. These results suggest that hydrotreating. in addition to HDS, converted the hydrocarbons from one group to the other,
Shorter Communications
1812
NOTATION
external surface area of particle, cm2 C average sulfur concentration, mollcm’ Dee effective diffosivity of sulfur compound in catalyst pores, cm’ls F volumetric flowrate of liquid. m’ls constant, second-order rate k apparent g s-’. bar-’ c,,-~ rateconstant defined by eqn (4) cm3. mol-’ . s-’ pseudo-first order rate constants, g. SC’ . cm-’ k,,: LHSV liquid hourly space velocity, h-’ S total sulfur weight fraction, glgeil initial total sulfur wt fraction sulfur weight fractions for compounds 1,2 S,,Z T temperature, K VR catalyst bed volume, m3 lb‘d catalyst bed void fraction 9 catalyst effectiveness factor PL liquid density, g. cme3
%
Time. h Fig. 4. Distribution of sulfur compounds vs time in HDS. Catalyst size 0.34 mm at 390 “C and 50 bar. x total sulfur. A asphaltenics sulfur, 0 aromatics sulfur, 0 polar aromatics sulfur, 0 saturated sulfur. pcrhaps following the reaction network: aspaltenics
/ T
aromatics p polar aromatics saturated
saturated aromatics
-+
saturated.
CONCLUSIONS
This study has shown that hydrodesulfurization of a high sulfur content atmospheric residuum proceeds with overall secondorder kinetics w.r.t. sulfur and first-order w.r.t. hydrogen, with an intrinsic activation energy of 29 kcal/mol but with small catalyst effectiveness factors for commercial size catalyst particles, indicating strong pore-diffusion limitations. It appeared that plug flow with no backmii prevailed in the trickle bed reactor. A more detailed insight of the reactions is gained when the main groups of sulfur and hydrocarbon compounds are analyzed. Work is now in progress to establish the reaction networks and kinetic performance of the main individual sulfur compounds. Acknowledgement--The authors are thankful to the N.T.U. Athens and the National Research Foundation for partial fmancial support and to the Public Petroleum Corp. of Greece for donation of oil samples. Chemical Process Engineering Laboratory National Technical University Athens, Greece
ALEX SCAMANGASt NICKOS PAPAYANNAKOS JOHN MARANGOZIS*
tPresent address: Petrola Oil Refinery, Elefsis, Greece. ‘Author to whom correspondence should be addressed.
[l] Beaton W. I., Chemical Reactions ns a Means of Sepamtion-Sulfur Removal (Edited by Crynes B. L.), Chap. 1, pp. l-34. Marcel Dekker, New York (1977). [2] Cecil R. R., Mayer F. X. and Cart E. N., Paper 12a presented at the 61st AICh.E. Annual Metting Los Angeles, l-5 Dec. (l%S). [3] Paraskos J. A., Frayer J. A. and Shah Y. T., Jnd. Engng Chem. Proc. Des. Dew. 1975 14 315. [4] Montagna A. A. and Shah Y. T., Ind. Engng Chem., Proc. Des. Dev. 1975 14 479. [5l Shah Y. T. and Paraskos J. A., Ind. Eng. Chrm., Proc. Des. Dev. 1975 14 368. [63 Montagna A. A., Shah Y. T. and Paraskos J. A., lnd. Engng Chem. Proc. Des. Dee. 1977 16 152. [7] Henry H. C. and Gilbert J. B., hd. Engng Chem. Proc. Den 1973 12 328. [S] Mears D. E., ISCRE 3rd Advan. Chem. Ser. 1974 133 218. 191 Schuit G. C. A. and Gates B. C.. k1.Ch.E.J. 1973 19 417. [ioj Marangozis J., Ind. Engttg Ch& Proc. Des. E&U. 1980 19 326. [Ill Richardson R. L. and Alley S. K., Hydrocracking and Hydrotreating (Edited by Ward I. W. and Qader S. A.), pp. 136-149. ACS Symposium Series No. 20, American Chemical Society, Washington 1975. [12] Drushel, H., Analytical Chamctcrization of R&duo and Hydrotreated Products. Am. Chem. Sot., New York Meeting, 27 Aug.-l Sept. 1972. [13] De Bruijn A., Naka I. and Sonnemans J. W. M., Ind. Engng Chem. Proc. Des. Deu. 198120 40. [14] Froment G. F. and Bischoff K. B., Chemical Reactor Analysis and Design, pp. 182-195. Wiley, New York 1979. [IS] Wei 3. and Hung C. W., Ind. Engng Chem. Proc. Des. Dew 1980 19 197.
Effect of desorptfon of air from liquid on gas-side mass transfer coefficient in gas absorption (Received
17 September
1979: accepted
In the absorption of the bubble of carbon dioxide into falling water saturated with air in a column, air was found, though it is slight, to dlfIuse from the water into the bubble and to increase with the rise of contractiong bubble in falling water in the previous experiment[6]. Such an air accumulated in the bubble in process of absorption is thought to cause the decrease of the overall liquid-side mass transfer coefficient, one of the causes of
20 April 1982)
which may probably be an occurrence of gas-side resistance in the bubble. Hatch and Pigford[S], Cairns[4], Onda et aL[9,10], Asano[l,2], Wakao ef al.[lZ], Byers and King[31, and Veilstich[ll] have already been studied on the gas-phase mass transfer coefficient, k. in liquid-jet column, but no evidences have yet been experimentally on the gas-side resistance in the