Effect of sulfiding temperature on dispersion and chemical states of the

Ind. Eng. Chem. Prod. Res. Dev. 1981, 20, 467-474

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Effect of Sulfiding Temperature on Dispersion and Chemical States of the Components of Co-Mo and Ni-Mo J. Scott Jepsen and Howard F. Rase' Department of Chemical Engineering, The University of Texas, Austin, Texas

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The effect of sulfiding temperature on two types of Ni-Mo and two types of Co-Mo commercial HDS catalysts has been studied using XPS, AES, and SEM with electron probe. Sulfiiing was accomplished with H2S/H2at 232.5, 315,and 371 'C using a microreactor system. Surface studies showed a greater increase for Ni-Mo than for Co-Mo catalysts in the relative amount of Mo(1V)to Mo(V1). Radial scans revealed that relative Mo concentration varied with treat temperature and catalyst type. Some P migration to the surface was observed, and occasional spots of P and Mo of high concentration were noted that were in each case sulfided to a low degree.

Hydrodesulfurization (HDS) catalysts (Co-Mo/Alz03 or Ni-Mo/Alz03) are surely among the most remarkable and fascinating of the commercial catalysts. They remove sulfur and nitrogen from complex hydrocarbons with apparent ease and under the most adverse environments involving large molecules capable of plugging pores and producing deactivating deposits. Innovations in catalyst design continue to improve performance and foster renewed interest in how the catalyst works and, more precisely, the nature of its active components and their optimum form and distribution for maximum activity. One important and commercially significant aspect of this catalytic puzzle involves the sulfiding step that is necessary for maximum activity. The process of presulfiding the catalyst in situ preceding continuous operation is known to be sensitive to the conditions used. If the optimum activity depends upon some particular distribution and state of active components, then the presulfiding step probably has a major role in creating the essential surface changes. By searching for such changes, means for improving catalyst recipes and sulfiding procedures could ultimately arise from the added insights that might be forthcoming for this extremely complex system. The present study was designed to contribute to this goal by observing the effects of sulfiding temperature on surface species of four important types of commercial hydrodesulfurization catalysts, including both Co-Mo and Ni-Mo types. Interesting observations were possible on the effect of sulfiding temperature on the ratio of Mo oxidation states, using X-ray photoelectron spectroscopy (XPS) and the distribution of migrating species, using Auger electron spectroscopy (AES), scanning electron microscopy (SEM)/electron probe, and bulk analyses. Several interesting differences between catalyst types were observed. Previous Work There has been a great deal of interest, and excellent studies have been published on this very important catalyst system. Prior to the early 1970'9, most of the observations, which sought some knowledge of the nature of the active sites, were based on ESR data. Out of these studies, there came some very useful conceptual models of the active surface, which have been augmented, more recently, by other insights and models based on surface-measurement techniques. A recent review by Grange (1980) provides an excellent summary and evaluation of all models of interest. Studies using X-ray photoelectron spectroscopy (XPS) have yielded interesting insights on surface compositions as affected by various treatments. Patterson et al. (19761, 0196-4321/81/1220-046?$01.25/0

for example, conducted studies on Co-Mo/Alz03 catalysts that had been subjected to various treatments. Deconvolution of spectra from catalysts that had been reduced with hydrogen at temperatures between 300 and 500 "C indicated that Mo had not been reduced completely to Mo(IV), but rather consisted of Mo(IV), Mo(V), and Mo(V1). The Mo 3d5 binding energies found by Patterson et al. were 229.d, 231.9, and 233.0 eV, respectively. Analysis of the effect of time upon the relative abundance of the different Mo oxidation states showed that Mo(V) attained a steady-state concentration of 30 atomic % or more of the total Mo concentration depending on the temperature of the reduction treatment. The M O W )and Mo(V1) levels also attained steady-state concentrations with Mo(V1) initially decreasing and Mo(1V) initially increasing with time. Okamoto et al. (1977) reached similar conclusions for a Co-Mo/AlZO3 catalyst treated with thiophene/Hz at 400 "C. Patterson et al. also found that the Mo(V) concentration was higher for the catalysts treated at lower temperatures. The MOW)levels that they reported are much higher than those obtained from ESR bulk measurements for which concentrations in the range of 5-10 atomic % of the total Mo were determined (Seshadri, 1973). Patterson et al. also investigated the effect of thiophene/Hz and HzS/Hz treatments. After exposure to thiophene/Hz or HzS/Hzat temperatures from 420 to 550 "C, a distinct Mo peak at 228.9 eV appeared. This peak was attributed to MoSz based on XPS results giving a value of 228.9 eV for the Mo 3d5/2binding energy from reagent MoSz. Declerck-Grimee et al. (1978a,b)have conducted studies on changes in the Mo XPS spectra for Mo/A120, Catalysts exposed to HzS/Hz at 400 "C. Their results agreed with those of Patterson et al. concerning the Mo peak attributed to MoS% No peaks corresponding to Mo oxides were reported. A shoulder on the high binding energy side of the Mo peak for MoSz was ascribed to the possible formation of Mo(V). Similar results were also found for Co-Mo/ Al2O3catalysts. Okamoto et al. (1977,1979),have reported on the effect of the sulfiding environment on the elemental surface composition of Mo/Alz03 and Co-Mo/A1203 catalysts as determined from XPS measurements. Molybdenumalumina catalysts with Mo concentrations of 5 wt % showed no change in the surface composition upon exposure to thiophene/Hz for 10 min at 400 'C. XPS results for catalysts with concentrations of 10 to 20 wt % and sulfided at the same conditions as before indicated that an enrichment of Mo in the catalyst surface had occurred. 0 1981 American Chemical Society

468

Ind. Eng. Chem. Prod. Res. Dev., Vol. 20, No. 3, 1981


Table I. Bulk Compositions of the Unsulfided Catalysts element, wt %

catalyst

A I

2A 20A 3A 9A

43.13 40.97 41.66 39.88

P

&Io

Co

Ni

S

0.20 0.01 9.90 2.34 -0 . 4 8 10.92 3.74 -- 0.10 2.54 0.23 0.73 10.44 -1.44 11.98 -_ 2.42 0.10

0

Ca

44.36 43.73 44.37 44.17

0.06 0.03 0.03 0.01

The lack of Mo migration in the low weight percent catalyst was attributed to a strong interaction between the A1203support and the Mo. Declerck-Grimee et al. (1978a,b), also investigated the effect of sulfiding environment on Co in Co/A1203and Co-Mo/A1203 catalysts. Exposure of a Co/A1203catalyst (COO4.41 wt %) to a 15% H2S/H2gas at 400 “C led to the reduction of Co to Co metal rather than the formation of a cobalt sulfide. Treatment with H2S/H2resulted in greater Co reduction than with H2alone. The combination of Mo and Co in a Co-Mo/A1203 catalyst led to the formation of a cobalt sulfide. The XPS cobalt sulfide peak was attributed to the formation of Co9Ss. The effect of catalyst composition on the resulting XPS binding energies for unsupported, sulfided Ce-Mo catalysts has been studied by Delvaux et al. (1979). He found that increasing the amount of Co led to a decrease in the Co binding energy. The reported Mo and S binding energies exhibited a rather complicated binding energy-composition curve. The curve assumed a damped sinusoidal shape with increasing Co concentration. Very little work has been reported on the role of temperature on the sulfiding step, particularly in the range of practical interest. There is also a paucity of literature on XPS studies of Ni-Mo catalyst systems. The apparent assumption is that Ni-Mo surface interactions are similar to those for Co-Mo systems (Cimino and DeAngelis, 1975; Farragher and Cossee, 1972; Lo Jacono et al., 1973; Schuit and Gates, 1973). In addition to XPS, Auger electron spectroscopy (AES) is also capable of yielding information on changes in the composition of surfaces. Judging by the literaure, this technique has received little attention in the area of HDS catalysts. Part of the reason for the lack of Auger studies may be the difficulty in getting good quantitative data from surfaces as rough and heterogeneous as supported metal catalysts. Uncontrolled charging can also be a problem. If, however, the correct AES parameters are chosen to minimize charging and the results are viewed in a qualitative or semiquantitative manner, it is thought that useful information on changes in the composition of HDS catalysts can be obtained. A recent paper by Bauwman and Toneman (1980) dealing with radial AES sulfur analyses of a Co-Mo/A1203 catalyst gave good qualitative results. Experimental Equipment and Procedures Catalysts. The catalysts studied were American Cyanamid commercial catalysts-a Ni-Mo/A1203 trilobe (HDS-SA), a Ni-Mo/A1203 cylinder (HDS-3A), a CoMo/Al2O3 trilobe (HDS-20A),and a CeM0/A1203cylinder (HDS-2A). Bulk compositions of the unsulfided catalysts are given in Table I. Sulfiding Technique. Each of the catalysts was treated with an 11.3% HzS-in-H2mixture at temperatures of 232.5, 315, and 371 “C using a microreactor system previously described by Harrison et al. (1965). The catalyst was in each case first calcined in situ under He at the desired test temperature for four hours and then treated with the H2S/H2mixture a sufficient length of time to allow eight theories of sulfur to pass over the sample at

a space velocity of 500 vol. gas/(h) (vol. catalyst). A theory of surfur was defined as the stoichiometric amount of sulfur that would be required to convert the known bulk quantities of Co and Ni or Mo to Cogss, Ni2S3,and MoS% After the catalysts had been sulfided, several different procedures were followed depending on which type of spectroscopic technique was to be applied to the catalyst sample. For the samples that were to be analyzed by AES, electron probe, or for bulk sulfur content, no special precautions were taken to isolate the treated samples from the atmosphere. The samples that were to be analyzed by XPS, however, had to be isolated as much as possible from the atmosphere in order to prevent possible reoxidation of reduced species. After the catalyst sample had been cooled in the microreactor under a flow of helium, the microreactor assembly was quickly removed from the sandbath and placed in a vise. The tubing connections were covered with Parafilm “M” (American Can Company, Marathon Products). One of the connections between the reactor and the tubing was then loosened and also covered with Parafilm “M”. The whole assembly was next transferred to the antichamber of a drybox (He atmosphere). After several evacuations and purgings of the antichamber with He, the microreactor assembly was moved from the antichamber to the drybox proper where the samples were transferred to glass vials and stored. This procedure is somewhat similar in degree of exposure to air as the glovebag technique used by Brinen and Armstrong (1978) which they showed to give similar results to those obtained using in situ treatment at the ESCA unit. Electron Probe A JSM-2 scanning electron microscope manufactured by JEOL equipped with an energy dispersive analyzer (Canberra Industries) was used for the electron probe analyses. X-ray excitation was supplied by electron emission from a tungsten filament. All samples were analyzed for Mo, S, Al, Ni or Co, and P. Oxygen and carbon were not detectable with the analyzer. Net counts for each element were normalized to aluminum. No charging problems were encountered. Surface analyses were done using four catalyst samples of the same type mounted adjacently, an untreated sample and three treated samples, each tested at a different temperature. Each catalyst was examined at five different locations along the longitudinal axis and the results averaged. Radial analysis was also performed by again mounting like catalysts with different treatments. These samples were cemented into holes on a special block and then each sample was broken with a cleaving action perpendicular to the axis of the cylinder. XPS. A Physical Electronics Model No. 548 X-ray photoelectron spectrometer with non-monochromatized Mg Kcu X-radiation was used. Samples for study were mounted inside an He-purged glovebag. Only the exterior surfaces were examined as an indication of an area not affected by intraparticle transport. Sealed sample containers were opened in the glovebag and samples loaded into the carousel located in the previously evacuated out-gassing chamber. Except for the HDS 3A catalyst, which was referenced to the Al2p peak, all other catalyst observations were referenced to the stronger oxygen 1s peak at 531.6 eV which is primarily due to the A1,03 support. Results with the 3A catalyst were found comparable with either reference. AES. Auger spectra were obtained using a Physical Electronics Super SAM 590 unit with primary electron beam set at 5 KeV for this study and a lanthanum, LaBs

Ind. Eng. Chem. Prod. Res. Dev., Vol. 20,No. 3, 1981 409

f v)

I-

Z

g 00

a w -1

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[r

I

DEPTH ( C M )

Figure 1. Radial phosphorus concentration profiles for catalyst 20A as determined by electron probe analysis.

filament. Incident beam currents were between 700 and 1300 nA, and the beam diameter was approximately 2000 A. Both surface analyses and radial analyses of cross sections were performed at five different locations. The catalyst cross sections were made by carefully cleaving the pellets before they were mounted in the holder. The cleaved ends of the catalysts were mounted such that they extended a short distance above the holder surface. The catalyst samples were all analyzed for 0 (KLL), A1 (KLL), Co (LMM) or Ni (LMM), Mo (MNN), P (LMM), and S (LMM) transitions. It was assumed that carbon would affect all the analyses in the same manner. Because of the overlapping of an Mo transition at the 120 eV with that of the P (LMM) transition, the P peak height had to be corrected. The contribution to the P (LMM) peakto-peak height by Mo was taken to be 0.2048 of the Mo (MNN) peak-to-peak height (Davis et al., 1976). Experimental Results Although electron probe analysis and AES have been well established as a technique for doing quantitative analysis on smooth, polished surfaces, their use on unpolished, rough, heterogeneous, semiconducting catalyst samples increases the possibility of error in the results. The experimentally measured changes in the catalyst composition were in all cases viewed with a critical eye relative to reproducibility and error. Useful conclusions are possible, however, even though the observations must be considered as semiquantitative or qualitative. Objectivity was greatly aided by statistical analysis of the results of multiple observations. Electron Probe. Figures 1and 2 show the normalized net counts for P for the 20A and 9A catalysts (Co-Mo and Ni-Mo Trilobe) as a function of depth. As can be seen, phosphorus seems to exhibit surface migration at all temperatures tested. The correlation coefficients for the phosphorus ranged from 0.9 to 0.97 for 20A catalyst and 0.73 to 0.87 to 9A catalyst. The Co and Ni count-ver-

sus-depth correlation had too much scatter to conclude from the electron probe data whether or not these components exhibit migration. Scatter in these and other data may be attributed to the nonuniform metal distribution. XPS. Changes in the chemical state of Mo and S were determined on multiple samples from XPS measurements of the Mo 3d and S 2p orbitals. The Mo 3d envelopes were resolved for Mo(IV), MOW,MOW),and S 2s peaks using a nonlinear least-squares regression computer program written during the course of this study. Parameters held constant were FWHM, peak-to-peak separation of the Mo 3d6,, to 3d3/, (3.1 eV) and height ratio (0.681, and the curve shape. The equation suggested by Siegbahn et al. (1971), was used to describe the ESCA line shapes. A typical resolved curve is shown in Figure 3. Observed binding energies for S and Mo in the sulfided catalysts were within 0.1% of those reported by Wagner et al. (1979) and Patterson et al. (1976). In general, XPS observations showed increasing amounts of Mo(IV) as sulfiding temperature was increased and a decline in Mo(V1) as would be expected. The data for MOW) were less definitive, and in one case (catalyst 9A) exhibited an apparant increase with increasing temperature. These observations agree with trends reported by Patterson et al. (1976) for the Co-Mo catalyst he tested, and specific variations between catalysts may be due to insufficiently long sulfiding times for achieving steady-state distribution of Mo oxidation states as suggested by the work of Declerck-Grim (1978) and Okamoto et al. (1977). The differences observed in relative amounts of Mo(1V) to Mo(V1) oxidation states between the several catalysts may be indicative of a possible optimum time-temperature for presulfiding different catalysts consistent with the economic importance of reducing start-up time in commercial practice. Referfihg to Table 11,the Ni-Mo catalyst exhibits a higher ratio of Mo(1V) to Mo(V1) for equal sulfiding times and gas flow rates. Since these data are for the exterior surface only, differences in pore size and pore-size distribution would not have played a role. Clearly


470


B EDGE

0025

0050

0075

0125

0100

0150

0175

0200

0225

0250

0275

0300

0325

02 0

DEPTH ( C M )

Figure 2. Radial phosphorus concentration profiles for catalyst 9A as determined by electron probe analysis. I

t

,

1

0

I

I

_ _ _ _ S- u-m m o t i o n

of Resolved Envelopes

I

1

i1

Table 11. Oxidation States as a Function of Sulfiding Temperature" catalyst 2A CO-MO ~OACO-MO 3A Ni-Mo 9A Ni-Mo

Figure 3. Resolved XPS envelope for catalyst 9A sulfided at 232.5 "C.

tepp, C 233 316 371 233 316 371 233 316 371 233 316 371

atomic % of total Mo Mo(1V) Mo(V) 36.0 44.0 48.0

33.0 39.0 37.0 48.0

60.0 70.0 46.0 48.0

51.0

26.0 17.0 16.0 29.0 16.0 23.0 21.0 26.0

Mo(V1) 31.0 26.0 26.0 30.0 29.0 22.0 26.0

15.0

4.0 8.0

15.0 22.0 21.0

32.0 19.0 13.0

Treat rate: eight theories at 500 vol. gas/(h)(vol. cat.). Treat gas: 11.3%H,S in H,.

these results confirm once again that the ultimate surface condition for Mo catalysts is dependent not only on sulfiding conditions but also on the nature of catalyst preparation and chemistry. AES. The changes in the relative surface compositions of metal components on the catalysts were compared with changes taking place radially by examining the outer and inner surfaces of the catalysts with Auger spectroscopy. The surface data and radial data were taken in two separate loadings. Multiple spectra for each unsulfided catalyst type were recorded. Sensitivity factors were calculated from the spectra of the unsulfided catalysts by solving a set of five simultaneous equations (one for each compound) of the following form suggested by Davis et al. (1976).

x=l

IJSXMX

where 1, = peak-to-peak height, Sx = sensitivity factor, M ,

= scale factor, and x = element. Each catalyst sample was analyzed for Co or Ni, P, Mo, Al, S, and oxygen. The effect of carbon on the analyses was assumed to be the same for each sample. Since only n - 1of the C, equations were independent, the sensitivity factor for A1 was assumed to be 0.0725. It was assumed for the unsulfided pellets that the composition in the volume of the catalyst being analyzed was the same as the bulk composition. The sensitivity factors used were those calculated from the standard for each catalyst series and loading. For example, the sensitivity factors calculated for the 2A standard from the radical Auger analysis were used in the calculation of the sulfided 2A radial compositions. A similar procedure was followed for the surface analysis so that the calculated compositions would always show changes relative to the standard used for each analysis. Figure 4 shows the change in Mo concentration relative to Mo + Co or Mo + Ni as affected by sulfiding temperature at the surface of the catalyst. The Mo/(Co + Mo)

Ind. Eng. Chem. Prod.

+

Res. Dev., Vol. 20,No. 3, 1981 471

+ SHDS - 2 A

HDS-2A

A =HDS-ZOA

A . HDS -PA 0 = HDS -3A 0 = HDS -9A

OmHDS-3A

0 SHDS-9A

L 0

/+

N

c

I 0

X n * u ! 0

z

0

\

03:

I0


n 0

is 0

a 'STD

232 5

3lb 0

I

c

371'0

0

DEGREES C

Figure 4. Variation of surface Mo/(X + Mo) with sulfiding temperature. X = Ni or Co.

or Mo/(Mo + Ni) ratios for the standards (unsulfided catalysts) are also shown. Figure 4 demonstrates that, in general, treatment a t 232.5 "C causes a decrease in the relative Mo concentration at the surface in comparison to the standard. A statistical analysis (Jepsen, 1980) confirmed that the Mo/(X Mo) ratios are significantly different. Since Co or Ni and Mo are generally thought to be responsible in some kind of combination for the catalytically active centers, changes in ratios as noted could affect ultimate catalytic performance. Treatments at higher temperatures (315 and 371 "C)for three of the four catalysts were accompanied by greater relative amounts of Mo at the surface than for catalysts sulfided at 232.5 "C (Figure 4). The 3A Ni-Mo catalyst, however, showed essentially no change with increasing temperature. Figure 5 reveals the effect of temperature of treatment on the relative amount of Mo in the region within 0.001 cm from the surface of the catalyst. The graph illustrates the same general trends as does Figure 4 for the exterior surface with the exception of the 2A Co-containing catalyst. This catalyst, which contains a negligible amount of P, does not exhibit a sharp decrease at 232.5 "C followed by an increase with temperature as is the case for the other catalysts in this near-surface region. Figures 5-8 summarize the results of the radial analyses. Included in the graphs are the data from the surface analyses. Regions corresponding to plus or minus one standard deviation from the surface measurements have been drawn to give an idea of the actual difference between the surface and radial relative Mo concentrations. Viewing the three graphs as a series, it appears that increasing the H2S/H2 treatment temperature causes changes in the relative amounts of Mo and Co or Ni in the surface and near-surface regions of the catalyst. Figure 6 shows that at 232.5 "C, the relative Mo concentrations seem to be higher in the interior of the catalyst than on the surface and near-surface regions. in Figure 7 equal relative Mo concentrations on the surface and near-surface regions (within 0.001 cm), may be noted for sulfiding at 315 "C,

+

>

ni5.o

252.5

371.6

DEGREES C

Figure 5. Variation of near-surface (0.001 cm from surface) Mol (Mo + X) with sulfiding temperature. (The error bars represent fl standard deviation from the data points of the standard sample. X = Ni or Co.)

and in Figure 8 treatment at 371 "C indicates a consistent pattern of higher relative Mo concentrations at the surface than in the near-surface or inner regions of the catalyst. Apparently the relative gradients of Mo are dependent on temperature of the treatment which suggests the existence of a possible optimum presulfiding temperature if distribution of components is crucial in ultimate catalyst performance. The four catalysts, though indicating similar trends in most instances, are sufficiently unique in behavior that it is quite reasonable to hypothesize that the optimum presulfiding conditions could vary for each type. Auger data also indicated that some phosphorus migration occurred in the 3A, 9A, and 20A catalysts. The phosphorus content of 2A catalyst was negligible. Scatter in the data made the observation less conclusive than that noted in the electron probe scans. No discernible pattern was found between degree of sulfiding and depth by Auger analysis. But on the surface of the catalyst, as shown in Figure 9, the degree of sulfiding increases with increasing sulfiding temperature. It should be noted, however, that the data points were found to be statistically different from each other only for the 2A, 9A, and 3A catalysts (Jepsen, 1980). The sulfur analysis of the catalysts surfaces by Auger spectroscopy is plotted in Figure 10 as a function of temperature. Figure 11 provides the bulk sulfur analysis of the catalysts as a function of temperature. Comparison of these two curves reveals a consistently lower value of sulfur from the AFS analysis than the bulk analysis. Both curves, however, illustrate the trend of increasing sulfur content with temperature. Several anomalous points of high P and/or Mo concentration were noticed for spots near the surface of the 20A and 2A catalysts with concentrations of P, 30 or more times the average. Associated with these areas of high P and/or Mo concentration was a low degree of sulfiding. Based on this low degree of sulfiding, it is plausible that the high P and Mo regions are low in activity. The de-


472


DEPTH ( C M )

Figure 6. Radial variations of Mo/(Mo t X) at 232.5 "C sulfiding temperature. (The error bars represent f l standard deviation from the surface data points. X = Ni or Co.)

t * HDS-2A 315.0 DEG C A . HDS-ZOA 315.0 DEG C 0. HDS-SA 315.0 DEG C 0 HDS-9A 315.0 DEG C

I

DEPTH ( C M )

Figure 7. Radial variations of Mo/(Mo + X) at 315 "C sulfiding temperature. (The error bars represent fl standard deviation from the surface data points. X = Ni or Co.)

posits of Mo and P were probably formed in the manufacture of the catalysts since the deposits were noted in only a very few cases. Work by Dale et al. (1980) indicates that the sulfiding temperatures were not high enough to cause occlusions of Mo. That deposits of abnormal concentrations of P occur in catalyst preparations is not surprising, but the apparent effect of P on degree of sulfiding suggests further paths of study concerning the role of P in catalytic activity or selectivity.

Conclusions The major conclusions possible from the results of the several techniques are as follows. Electron Probe. Phosphorus migrated toward the surface of the catalyst during sulfiding (Figures 1and 2). XPS. The Ni-Mo catalysts exhibit a higher ratio of Mo(IV) to Mo(VI) for equal treat times and gas flow rates. This observation suggests the possible existence of different optimum sulfiding conditions for Ni-Mo catalysts


Ind. Eng. Chem. Prod. Res. Dev., Vol. 20,

SURFACE

EWE

0025

OOCK)

0075

0100

0125

OlSO

0175

0200

0225

0275

0250

NO. 3, 1981 473

OS00

032s

0350

DEPTH ( C M )

Figure 8. Radial variation of Mo/(Mo + X) at 371 "C sulfiding temperature. (The error bars represent fl standard deviation from the surface data points. X = Ni or Co.)

t * HDS-PA A = HDS-2OA 0. HDS-3A 0 HDS-SA

!.so

315.0

371.

DEGREES C

g

- STD

232 s

i

DEGREES C

315 0

371 0

i

Figure 9. Degree of sulfiding at catalyst exterior surface as a function of sulfiding temperature.

Figure 10. Weight percent sulfur at the catalyst exterior surface aa a function of sulfiding temperature as determined by Auger analysis.

than for Co-Mo in commercial practice. AES. Spots of high Mo or Mo-P were sulfide to a low degree compared to other regions. These spots,which are probably formed during the manufacturing process, could provide a hint to some aspects of the effect of phosphorus on activity that is not easily detectable on the major portion of the catalyst where dispersion is uniform. Relative surface composition of Mo is a function of the sulfiding temperature except in the case of 3A Ni-Mo catalyst (Figure 4).

Treatment with H,S/H, causes radial gradients in the Mo/(X + Mo) ratio. At a sulfiding temperature of 232.5 "C, higher relative Mo concentrations are found in the interior of the catalyst than at the surface. At 315 "C,the Mo/(X + Mo) vs. depth curve is relatively flat. Sulfiding at 0371 "C brings about a reversal of the trend seen a t 232.5 "C (Figures 6-8). The radial Auger phosphorus data, when combined with the microprobe results, support the conclusion that phosphorus migrates to the surface.

Ind. Eng. Chem. Prod. Res.

Dev. 1981, 20, 474-481

temperature or one particular catalyst. Any model of the catalyst surface should accout for the temperature dependence of the surface composition, the mode of preparation, and the variations in active components.

~~

+A == HDS-3A HDS-SA

-

0.=-PA 0 HDS-2OA

Literature Cited

_I___ Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on August 25, 2015 | http://pubs.acs.org Publication Date: September 1, 1981 | doi: 10.1021/i300003a009

/ ______r

/ ’D

232 5

315

0

371A

DEGREES C

F i g u r e 11. Bulk weight percent sulfur as a function of sulfiding temperature.

Increasing the sulliding temperature increases the degree of sulfiding at the catalyst surface (Figure 9) as might be expected. Combining the conclusion from the techniques employed in this study, it is apparent that the catalyst surface characteristics cannot be generalized from data at one

Bauwman, R.; Toneman, L. H. J. Catal. 1980, 61, 146. Brinen, J. S.;Armstrong, W. D. J. Catal. 1978, 54, 57. Cimino, A.; DeAngelis, 8 . A. J. Catal. 1975, 36, 11. Dale, J. M.; Huiett, J. D.; Fuller, E. L.; Richards, H. L.; Sherman, R. L. J. Catal. 1980, 61, 66. Davis, L. E.; McDonald, N. C.; Puimburg, P. W.; Rich, G. E.; Weber, R. E. “Handbook of Auger Electron Spectroscopy”; 2nd ed.; Physical Electronics, Inc.: Eden Prairie, Minn., 1976. Declerck-Grimee, R. I.; Canesson, P.; Friedman, R. M.; Fripiat, J. J. J. Phys. Chem. 1978a, 82, 885. Declerck-Grimee, R. I.; Canesson, P.; Friedman, R. M.; Friplat, J. J. J. Phys. Chem. 1978b, 82, 889. Delvaux, G.; Grange, P.; Delmon, B. J. Catal. 1979, 56, 99. Farragher, A. L.; Cossee, P. “Catalytic Chemistry of Molybdenum and Tungsten Sulfides and Related Ternary Compounds”; Preprint 98, Fifth International Congress on Catalysis Palm Beach, 1972. Grange, P. Catal. Rev. 1980, 21, 135. Harrison, D. P.; Hail. J. W.; Rase, H. F. Ind. fng. Chem. 1985, 57, 18. Jepsen, J. Scott M.S. Thesis, The University of Texas at Austin, Aug 1980. Lo Jacono, M.; Verbeek, J. L.; Schuit, G. C. A. J. Catal. 1973, 29, 463. Okamoto, Y.; Nakano, H.; Shimokawa, T.; Imanaka, T.; Teranishi, S. J . Catal. 1977, 50, 447. Patterson, T. A.; Carver, J. C.; Leyden, D. E.; Hercules, D. M. J. Phys. Chem. 1976, 80, 1700. Schuit, G. C. A.; Gates, 8. C. AIChE J. 1973, 19, 414. Seshadri, K. S.;Petrakis, L. J. Catal. 1973, 30, 195. Siegbahn, K.; Nordllng, C.; Fahlman, F.; Nordberg, R.; Hamrin, K.; Hedman, J.; Johansson, G.; Bergmark, T.; Karisson, E. S.;Lindgren, I.; Lindberg. 6. “ESCA. Atomic, Molecular, and Solid State Structure Studied by Means of Electron Spectroscopy”; Aimquist and Wlksells: Uppsela, 1967. Siegbahn, K. ”ESCA Applied to Free Molecules”; North-Holland Publishing Co.: Amsterdam, 1971; p 169. Wagner, C. D.; Rlggs, W. M.; Davis, L. E.; Moulder, J. F.; Muilenberg, G. E., Ed.; “Handbook of X-ray Photoelectron Spectroscopy”; Perkin-Elmer Corp., Physical Electronics Division, Eden Prairie, Minn., 1979. Received for review October 20, 1980 Revised M a n u s c r i p t Received M a r c h 17, 1981 Accepted May 15, 1981

Hydroisomerization/MTBE System Combined with Alkylation To Improve Octane Ronald M. Heck, Ronald G. McClung, Michael P. Wltt,” and Orlando Webb Engelhard Industries, Research & Development, Menlo Park, New Jersey 08817, Engelhard Industries, 429 Delancy Street, Newark, New Jersey 07 105, and Stratford/GrahamEngineering Corporation, 4250 Madison A venue, Kansas City, Missouri 64 1 1 1

The product quality of alkylate produced from sulfuric or hydrofluoric acid cataiyzed alkylation plants can be improved by pretreating the olefin feed using an integrated system consisting of hydroisomerization‘ and MTBE process technologies. The pilot plant studies conducted to develop the hydroisomerization and MTBE technologies are described including figures and a discussion of the effect of key operating variables on each part of the system. A description and the results of a pilot plant study conducted to compare the quality of alkylates produced from normal butene isomers are presented. Proposed mechanisms for sulfuric and hydrofluoric acid catalyzed alkylation processes are discussed along with a comparison of the octane quality of the butene isomer alkylates produced by each process. Integration of the hydrobmeriition/MlBE system with akylation in an existing petroleum refinery is discussed along with the effect on gasoline blend stock quality and quantity.

Introduction As a result of the rapid escalation of petroleum feedstock prices and increased environmental and efficiency standards imposed by the government, petroleum refiners are faced with the task of operating their refineries to eco0196-4321/81/1220-0474$01.25/0

nomically produce higher quality motor fuels. Refiners will also be under pressure to produce higher quantities of motor fuels during periods of excess demand. To help refiners achieve the above goals, Engelhard has developed two process technologies which can be integrated as a @ 1981 American Chemical Society

Effect of sulfiding temperature on dispersion and chemical states of the

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