Study of the liquid activation of CoMo and NiMo catalysts

Transcription

1 Study of the liquid activation of CoMo and NiMo catalysts Silva A. a,b,1, Corre T. b, Lemos F. a a Instituto Superior Técnico, Avenida Rovisco Pais 1, Lisboa, Portugal b IFP Energies nouvelles, Rond-point de l'échangeur de Solaize, BP 3, Solaize, France ABSTRACT In this work, CoMoP and NiMoP catalysts were prepared with similar chemical composition, differing between them just in terms of the nature of the promoter and the final treatment given: drying, calcination and additivation. After the preparation, the liquid sulfidation of the catalysts with SRGO+2%DMDS was followed with time and temperature, through the DMDS decomposition. Finally the catalysts were characterized by elemental analysis and XPS. It was seen that the boosted catalysts are always the ones which present better results when compared with the other catalysts, fact that may be correlated with the presence of an additive that leads to the delay of the DMDS decomposition. In contrast, the calcined catalysts present after the liquid sulfidation, the worst values in terms of global degree of sulfidation and degree of promotion when comparing with the other catalysts. Furthermore, the dried catalysts present, for CoMoP and NiMoP, higher global degree of sulfidation and promotion than the calcined ones. A classification in terms of global degree of sulfidation and degree of promotion was established for both series: CoMoP: boosted=dried>>calcined NiMoP: boosted dried>calcined Finally, the effect of increasing the pressure and time in the sulfidation of the NiMoP catalysts was studied. No change in the sulfidation and dispersion in the catalyst was registered. Keywords: Diesel; liquid sulfidation; CoMoP; NiMoP; DMDS decomposition 1. Introduction Due to the importance of the transportation sector, the global demand of the middle distillates like gasoil is expected to increase in the years to come. Associated to this increase, the reduction of its sulfur content and the tight legislation due to this compound pollutant characteristics, associated with the competition in the refinery market, requires an improvement of the processes and catalysts of hydrotreatment (HDT). The most commonly commercial catalysts used in the HDT are the molybdenum catalysts promoted with cobalt or nickel supported on a gamma alumina. It is possible to give different final treatments to the oxide form of the catalysts: drying, calcination or additivation. When the oxide catalyst is synthetized, its active form must be obtained by sulfidation. In the industry, the sulfidation is usually performed in-situ in the liquid phase, with the feedstock spiked with a sulfiding agent (normally dimethyldisulfide also called DMDS). Many studies report the influence of the sulfidation conditions in the final activities of the catalysts as well as the effect of the addition of the additives to the catalyst. However, a lack of information is found when studying the influence of the final treatment of the catalyst during the liquid sulfidation, and its relation with the HDT activities. Moreover, it is known that, after the liquid sulfidation, the ranking of activities of the CoMo and NiMo catalysts can be described as: boosted> dried calcined The liquid phase activation is the one which is used at the industrial level. In this process, the catalyst is wetted at low temperature by the spiked feedstock, in order to put in contact the sulfur compounds with the oxide phases to be converted. Once the catalyst is completely wetted, the temperature is raised progressively up to the reaction temperature under a stream of H2, and the sulfidation takes place during this heat treatment. However, the increase of temperature must be very slow, in order to facilitate the decomposition of the spiking agent in sulfur compounds such as H2S, and to limit the reduction of the oxides by H2 (since reduced species are more difficult to sulfide) (1). A spiking agent is a sulfur-containing organic compound which releases H2S at a much lower temperature than the sulfur compounds present in the normal feedstock. Among all the spiking agents, the dimethyldisulfide (DMDS) is the one more used industrially due its low vapor pressure and low flammability, its substantial sulfur content and low decomposition temperature, but also due its low cost when compared with polysulfides. In addition, the low temperatures at which the DMDS decomposes in H2S maintains a good concentration of 1 Corresponding author: ana.carolina.silva@tecnico.ulisboa.pt

2 2 sulfur, allowing also, the protection of the catalysts from undergoing reduction by the hydrogen present (2). From the DMDS decomposition it is possible to distinguish different steps (2) (3), as schematized in the Figure 1. results from the contact between the sulfur agents and the oxide precursors, forming gradually in the surface a sulfide phase. This sulfide phase initiate the decomposition of DMDS and methylmercaptan, leading to the appearance of CH4 and H2S in the gas analysis. 2. Experimental part 2.1 Catalysts preparation Figure 1-Mechanism of DMDS decomposition. Adapted from (2). Texier et co-workers (4) studied the decomposition of DMDS during the activation procedure, at 40 bar of total pressure in the presence of a NiMo/Al2O3 catalyst. They saw that the decomposition of that organosulfur compound takes place between 150 C and 350 C. In a first step, below 230 C, the DMDS is completely decomposed in methylmercaptan (CH3SH or MeSH). In a second step, at higher temperatures ( C) the CH3SH decomposes, by hydrogenolysis reactions, into CH4 and H2S. In parallel (T= C), the CH3SH also leads to the formation of dimethylsulfide (C2H6S or DMS) and H2S that subsequently leads to H2S and CH4. In this study CoMoP and NiMoP catalysts were prepared by following the steps described in the Figure 3. All the catalysts were prepared by incipient wetness impregnation using a -alumina support with a trilobe extrude shape, with a length of 2-4 mm and no particular treatment was performed to the support. In terms of chemical composition all the catalysts present the same mass content in molybdenum and the same promoter/molybdenum ratio. The catalysts are doped with phosphorous and were prepared with the same P/Mo molar ratio. After the maturation, the total amount of CoMoP (or NiMoP) catalysts was divided in three parts, in order to proceed to the final treatment: drying, drying and calcination or drying and additivation). Figure 3- Main steps in the preparation of the CoMoP and NiMoP catalysts. Preparation of the impregnation solution Figure 2- Variation in molar fractions of reactant (DMDS) and products (MeSH, DMS, CH4, H2S) (1). From the on-line analysis of this process of decomposition (Figure 2) it is possible to see that the amount of MeSH (CH3SH) reaches a maximum, decreasing after, while the CH4 concentration increases symmetrically (between C). The DMS also reaches a maximum value of concentration around the temperature of 290 C, decreasing after for higher temperatures of activation (due to the appearance of H2S and CH4). A gap between the appearance of the CH4 and H2S is also seen, due to the sulfidation process of the catalyst. It is important to refer that in the liquid phase, the active decomposition of sulfur containing compounds (that include the hydrogen sulfide production) can be considered when the methane starts to appear in the gas analysis. Hydrogen sulfide appears latter in relation with the CH4 since this compound participates in the sulfidation of the catalyst, being only detected when the active metal is mainly saturated with H2S (5). Finally, at 330 C the DMDS is completely decomposed in CH4 and H2S. During the decomposition of the spiking agent, the sulfidation can be divided in two parts: low temperature sulfidation (in which the sulfur agent is mainly the methylmercaptan) and high temperature sulfidation (in which the sulfur agent is the H2S) where the sulfiding reaction competes with reduction. The sulfidation of the catalyst The preparation of the impregnation solution was made by dissolution of the oxide precursors in a water volume equal to 95% of the total amount of water necessary in the solution (leaving some fraction to assure that the washing is well done and to avoid the loss of precursors). The Table 1 summarizes the main characteristics of the products used to prepare both series of catalysts. Table 1- Precursors used in the preparation of the CoMoP and NiMoP catalysts, and their principal properties Oxide Precursor Molar mass (g/mol) Purity (%) MoO MoO3 143, P2O5 H3PO4 98,00 85 CoO Co(OH)2 92,93 95 NiO Ni(OH)2 92,71 95 In a beaker with the distillated water was added the H3PO4, followed by the MoO3 and finally by the promoter precursor (Co(OH)2 or Ni(OH)2). In order to proceed to the total dissolution of the precursors, the solution was left in agitation with heating (around T=90 C) until was translucent. Impregnation To perform the incipient wetness impregnation is used a rotating beaker where the support is placed. The solution is added drop by drop to the support. To improve the impregnation process the operator promotes the support movement by using a spatula. This step lasts around 10 minutes.

3 Maturation Online analysis system 3 The main goal of maturation is to give time to the solution to enter properly in the pores of the support, in other words, to allow the precursors to diffuse in the support, in order to obtain a well dispersed metal phase. This step can have different durations, being in our case of 12 hours, in an atmosphere saturated in water, at T=25 C. Drying The drying process is performed at T=90 C in an oven with air. The aim of this step is to remove the solvent in excess from the support. The dried oxide catalysts are obtained at this point of the preparation. Calcination The calcination step is not a mandatory one, since the catalyst can be directly sulfided after the drying step. The calcination allows the breaking of undesirable ions that may be present on the impregnated and dried support as well as the formation of an oxide phase that differs from the one obtained after drying. This stage in the catalyst preparation was made with a flow of air which varies with the mass of catalyst to be calcined, in a fixed bed. The calcination is performed with an air flow equal to 1,5 L/h/gcatalyst, a temperature of 450ºC during 2 hours, being the heating ramp of 5ºC/min. Additivation The additive is an organic compound added on the catalyst after the drying step by incipient wetness impregnation. After the addition of the appropriate amount of additive, the catalyst is dried in an oven at a temperature close to 100ºC. 2.2 In-situ liquid sulfidation The sulfidation procedure was performed in the unit T58. This procedure allows evaluating the performances of the catalysts during the liquid phase activation step, in a fixed bed up-flow reactor, under hydrogen pressure. The liquid charge is composed by SRGO spiked with DMDS. The general scheme of the unit is presented in Figure 4. The gas phase from is analyzed online by a gas chromatography mass spectrum Balzers Pfeiffer, model TSU065D. This apparatus allow us to follow in time the formation of different products, namely the products that result from the DMDS decomposition (Figure 1): CH3SH, C2H6S, CH4 and H2S. Reactor charge and pressure test The reactor, with an intern diameter of 20 mm and 435 mm of length, is loaded with 20 cm 3 of catalyst. In order to accomplish a good distribution of catalyst and to get a homogeneous dispersion of the heat, the catalytic bed comprises 3 different zones divided by two grids: Zone 1: Glass beads with a diameter of 5 mm (to filtrate little particles and to improve the liquid distribution) and silicon carbide (also known as carbondurum, SiC) with a grain of 1,68 mm to ensure the good thermal diffusion; Zone 2: 20 cm 3 of catalyst; Zone 3: SiC with a grain of 1,68 mm plus glass beads with a diameter of 5 mm. After the charging and installation of the reactor, a pressure test needs to be made, in order to verify that no leaks are remaining in the unit. This test is made at least at 10% above the pressure of the sulfidation test being valid if the pressure drop is lower than 0,5 bar/h. Sulfidation process The two series of catalysts, CoMoP and NiMoP, were sulfided in the liquid phase in the unit T58. The liquid charge consisted in Straight Run Gasoil (SRGO) with 2% in mass of DMDS, being the main characteristics of the gasoil presented in Table 2: Table 2- Important gasoil characteristics. Sulfur (wt. ppm) 4189 Density (g/cm 3 ) 0,8491 The DMDS was used as spiking agent due its chemical characteristics: low vapor pressure, high sulfur content, low decomposition temperature and low cost when compared with polysulfides. The DMDS decomposition (Figure 1) leads to the formation of H2S, compound that sulfides the catalyst. The procedure of the liquid activation used in the unit T58 is described as a temperature profile in the Figure 5. Plateau 8 h Washing with Toluene (3h) + drying (1h, Patm) Figure 4-Schematic description of the T58 unit The unit can be divided in several sections, namely the charge, gas, reaction, separation, pressure and measurement sections. Catalyst wetting at 50 C Sulfidation SRGO+2%DMDS Figure 5- Temperature profile of each test.

4 4 Each test comprises the catalyst wetting at 50 C during 1,5 hours in order to assure a good contact between the solid and the liquid. This step is followed by an increment of temperature at a rate of 8 C/h until 350 C, in which the temperature is maintained constant during 8 hours in a plateau (sulfidation). Then, the catalyst is washed with an organic solvent with low ebullition point (in this case, toluene), in order to remove the charge that is still found in the catalyst bed. The washing is carried out at 200 C during three hours. After that time, the toluene injection is stopped and the drying process takes one hour at 200ºC and atmospheric pressure. Finally, the reactor is unloaded in an inert atmosphere in order to avoid the re-oxidation of the sulfide phase (since X-Ray photoelectron spectroscopy, XPS, analyses are performed to the sulfided catalysts). DMDS decomposition product was analyzed separately. The signal obtained from the GC mass spectrometer was normalized in order to make the comparison easier and more accurate. The evolution of the signal for the CH4 with time and temperature is shown in the Figure 6. 2 h 16 C The sulfidation conditions used in the unit were adapted from other studies performed at IFPEN and are close to the industrial ones. The Table 3 summarizes the operating conditions used in the sulfidation: Table 3- Operational conditions of the sulfidation in the T58 unit. Pressure (bar) 30 or 60 Temperature ( C) Volume of catalyst (cm 3 ) 20 LHSV (h -1 ) 2 H2/Hc (NL/L) 240 Fliquid (g/h) 34 Fgas (NL/h) 9,6 Heating ramp ( C/h) 8 The liquid and gas feeds (F L and F G, respectively) were established from the operational conditions by use of the calculations that follows: F L = V cat LHSV ρ L Eq 1 Being V cat de volume of catalyst (cm 3 ) used during the test, LSHV the liquid hourly space velocity (h 1 ) and ρ L the density of the liquid feed (g/cm 3 ). F G = (H 2 /H c ) F L Eq 2 Where (H 2 /H c ) is the volume ratio of hydrogen and liquid feed (NL/L). During the sulfidation process the DMDS decomposition is followed by mass spectroscopy in line. This apparatus allow us to track the decomposition products (see Figure 1) with the time (and indirectly with the temperature), being possible to compare qualitatively the sulfidation of different catalysts, at the same operational conditions. Concerning the liquid phase analysis, samples were taken from time to time during the increasing in temperature, in order to measure their sulfur content by XRF (X-Ray fluorescence). These samples were taken with 30 minutes (minimum) and 2h (maximum) of interval. It is important to take into account that, once the unit is not completely automatized, the switch from one step to another needs to be made manually. For this reason, in order to complete a test (comprising reactor loading, pressure test, wetting, sulfidation, washing, drying and unloading) four days are necessary, thus meaning it is only possible to make one test per week. 3. Results 3.1 In-situ liquid sulfidation study CoMoP catalysts In order to understand the difference between the CoMoP catalysts dryed, calcined and boosted, concerning the activation procedure, each Figure 6- Online analysis of CH4 for the three catalysts, with time and temperature The moment of appearance of the CH4 corresponds to the beginning of the sulfidation, since the H2S appears simultaneously with the methane, resulting both from the direct decomposition of the CH3SH. From the analysis of the Figure 6 it is possible to see that the dried catalyst present the same trend as the calcined respecting to the evolution of the signal of the methane (CH4). For both catalysts the CH4 appears around 21 h (218ºC). However, for the boosted catalyst, the CH4 curve appears latter, around 23 h (234ºC). It is clear that a gap in the appearance of this product between the curves corresponding to the calcined and boosted catalysts exists. This gap, of about 2 h (16ºC) seems constant until the stabilization of the concentration of CH4. In this way it is possible to conclude that a delay in the DMDS decomposition is seen during the sulfidation of the boosted catalyst. We can, in a first analysis, conclude that the presence of the additive in the catalysts leads to a delay in the DMDS decomposition. A similar analysis can be made for the H2S signal. Figure 7 shows the evolution of the signal with time and temperature for H2S. 2 h 16 C 0 Figure 7- Online analysis of H2S for the three catalysts with time and temperature. The appearance of the H2S for the calcined catalyst takes place at around 25 h (T=250ºC), about 4 hours after the appearance of the CH4. In respect to the presence of H2S (Figure 7), its behavior is similar to the CH4 compound with the difference that the catalyst dried follows the same trend as the boosted catalyst. In this way we can already take

5 5 one conclusion regarding the speed of the sulfidation for the CoMoP dried. Since for this catalyst the CH4 appears earlier than for the boosted, and that the H2S appears at the same time (27 h, T= 266ºC), we may suggest that the dried catalyst is the one that takes more time to sulfide, from the three catalysts. Concerning the sulfidation process of the calcined and boosted catalysts, a careful analysis should be made. On one side, we can notice that it takes around the same time, for both catalysts to be sulfided since the t between the appearance of CH4 and H2S for each catalyst is of around 4 h. This is the analysis that can be made to the so called low temperature sulfidation, and assuming that the rate of sulfidation is the same between catalysts. On the other side, both curves reach the plateau at the same time, which may suggest that the rate of sulfidation at high temperatures is higher for the boosted catalyst: in the beginning of the curves the same gap as for CH4 maintains (2h corresponding to 16ºC), however this gap tends to decrease until disappears completely before the beginning of the temperature plateau. We may conclude that the boosted catalyst sulfides faster than the other catalysts, assumption that can be confirmed if the degree of sulfidation in the catalyst, after the activation step, is at least equal to the calcined one. It is also possible to follow, during the DMDS decomposition the behavior of the signal of the intermediate products, namely, the CH3SH and the C2H6S. Figure 8 presents the variation of the signal of the CH3SH with the time and temperature. Figure 9- Online analysis of C2H6S for the three catalysts, with time and temperature. A similar analysis to the previous one may be made for this compound. The moment at which the C2H6S appears, for the three catalysts, seems to be the same. However, a gap between the maximum concentration of the compounds seems to exist, being the biggest difference registered between the CoMoP calcined and boosted (2h 16ºC). Another conclusion can be taken: the relative concentration of the C2H6S is always lower than the relative concentration of the CH3SH, leading to the conclusion that the most significant part of the H2S is obtain directly by the direct decomposition of the CH3SH. In this way, from the analysis of the Figure 8 and Figure 9, it is possible to confirm that the order of appearance of the species, in the presence of catalyst, is the one described in the literature. Furthermore we can conclude that the DMDS decomposition is complete during the sulfidation procedure since in the end, all the intermediates present signals practically zero, since they decompose completely in order to form CH4 and H2S. In order to have more information about the sulfidation process for each catalyst, liquid samples were taken during the sulfidation process. The content in sulfur was then measured by XRF. This analysis complements the gas-phase analysis, making possible to take more accurate conclusions about the process. Figure 8- Online analysis of CH3SH for the three catalysts, with time and temperature. For all the CoMoP catalysts, it is not very clear due to the noisy signals obtained due to stability problems of the GC mass spectrometer, but in trend, all the curves appear at the same time, meaning that no special effect is seen in the presence of each kind of catalyst. The CH3SH is present in the gas phase starting around 18 h (T=195 C), value that is in accordance with the described in literature in similar conditions. It is also possible to verify that the maximum of the curves (that correspond to the maximum concentration) appears at around 240 C-250 C, temperature at which this compound apparently starts to decompose in other sub-products. In respect to the C2H6S, its evolution with the time and temperature in the presence of the three CoMoP catalysts is depicted in Figure 9. The content in sulfur in the liquid samples for the three catalysts is present in the Figure 10. Gas oil initial sulfur content Figure 10- Sulfur analysis of the liquid effluent from the T58 unit, for the three catalysts. During the sulfidation, as expected, the content of sulfur in the liquid decreases with the time, since the DMDS decomposition leads to the formation of products in the gas phase. It is observed that at low temperatures (T<260 C) the content in sulfur, when the boosted catalyst is present, is always higher than for the others. This data confirms the gas phase analysis, since a delay in the decomposition of

6 6 DMDS by the boosted catalyst leads necessarily to a higher concentration of sulfur in the liquid phase. Additionally, by the end of the 8 hours plateau of temperature at 350ºC, the sulfur concentration in the liquid is the same for all the catalysts around 0,2 %wt. This value confirms that the DMDS is completely decomposed since it is lower than the initial content of sulfur found in the SRGO. In the end of the activation test, the gasoil is slightly desulfurized. However, in order to confirm these conclusions, G.C. analysis should be made to the liquid effluent in order to know the compounds present in the liquid effluent. In this way, from this data, it may be suggested that the decomposition of the DMDS is not complete, since the results obtained are not in accordance with the decomposition mechanism proposed in the literature, for similar conditions. End of the 8 h plateau (T=350 C) NiMoP catalysts A similar study to the one presented before was performed for the NiMoP/Al2O3 catalysts. The Figure 11 represents the evolution with time and temperature of the products that result from the DMDS decomposition for the NiMoP calcined. Figure 13- Online analysis of the CH4 and CH3SH for the NiMo calcined. It is clear, from de comparison between the signals of the CH3SH and CH4 with time and temperature that they present the same trend, stabilizing in the beginning of the temperature plateau, around the same time. Figure 11- Results from the mass spectrum, DMDS decomposition with time, from the start of the heating ramp (8 C/h) until the end of the 8 h plateau, for the NiMoP calcined. Despite the fact that the DMDS decomposition show the same behavior for all the catalysts, the trend of the curves is very different from the one found for the CoMoP. The main differences that it is possible to highlight are the fact that none of the intermediates (CH3SH and C2H6S) exhibit a maximum in their concentration and the H2S does not stabilize even after reaching the temperature plateau. Taking a closer look to each one of the decomposition products, the atypical behavior of the curves (when compared with the ones obtained for the CoMoP series) is confirmed. This information, may suggest an alteration in the mechanism of DMDS decomposition (Figure 14). In accordance with the literature (3), the DMS route represents a minor percentage of the CH4 and H2S formed in the process. In our working conditions in the presence of the NiMoP catalysts, the DMS route is almost negligible, leading to an equilibrium between the formation of CH3SH and the methane and H2S. Figure 14- Modifications proposed in the mechanism of DMDS decomposition, in the presence of NiMoP catalysts, in our working conditions In respect to the sulfidation of the catalysts the behavior of the methane was studied (Figure 15), in order to know at which temperature the H2S would start to be provided to the catalyst, on other words, when the sulfidation process starts. Figure 12- Online analysis for the three catalysts (calcined in blue, boosted in red and dried in green), with time and temperature. Left: CH3SH right: DMS (C2H6S). From Figure 12 (left) the first difference in relation with the CoMoP (see Figure 8) is that when the curve reaches the maximum seems to stabilize, instead of decreasing in benefit of the CH4 and H2S appearance. When following the C2H6S formation with time and temperature (Figure 12, right), no large variation in the signal is seen and no clear maximum exists, despite what is observed for the CoMoP (Figure 9). Figure 15- Online analysis of CH4 for the three catalysts, with time and temperature.

7 7 The effect of delay in the DMDS decomposition caused by the presence of the additive in the boosted catalysts is once again confirmed. In respect to the calcined catalyst, this seems to be the one with the slowest decomposition of the spiking agent, since the CH4 appears before the boosted catalyst and stabilizes in the beginning of the plateau after it. Furthermore, regarding to the temperature of appearance, and like in the CoMoP series, the boosted catalyst present the highest temperature of appearance (T=246 C, 24,5 h ), followed by the calcined (T=211 C, 20 h) and finally by the dried (194 C, 18h). In Figure 16 H2S curve is presented, for the three NiMoP catalysts with the time and temperature. From the liquid analysis one of the conclusions that can be made is the same that the one for the CoMoP catalysts: the content in sulfur is always higher for the boosted catalysts at low temperatures (T<260 C), even though for all the catalysts the trend is the same. In addition, another interesting observation can be drawn: in respect to the DMDS decomposition, in the presence of the NiMoP catalysts, after the 8 hours of plateau, the content in sulfur is lower than the initial one in the gasoil. In this way an important conclusion can be taken: the DMDS is probably completely decomposed, being the effect proposed in its mechanism confirmed. Furthermore, the final content of sulfur found in the gasoil in the end of the test, for the NiMoP and CoMoP is practically the same. This supports the assumption that after 45 hours of sulfidation, the NiMoP catalysts are still changing sulfur with the feed, being the constant increase of the H2S curve due to this fact and not to the HDS of the gasoil. Since in the present working conditions, it seems that the NiMoP catalysts are not completely sulfided, a test in different conditions was made. In this way a test at total pressure equal to 60 bar, remaining the other parameters constants, was performed. The catalyst used was the NiMoP calcined. Figure 16- Online analysis of H2S for the three catalysts, with time and temperature. However it was observed that in the end of the plateau of 8 h at 350ºC, the H2S curve was not stabilized despite the stabilization of the CH4 (indicating that the sulfidation process was still running). In this way, the duration of the plateau at 350ºC was extended 24 h. End of the 8 h plateau (T=350 C) From the study of this figure, we may suggest that the sulfidation process of the NiMoP catalysts, in the end of the 8 hours plateau, seems to be incomplete. This observation is made since no stabilization of the curve is seen, suggesting that, if the CH4 is already stabilized, the difference in H2S concentration in time is due to the fact that sulfur changing is still occurring. This analysis should be made carefully, since the HDS of the gasoil can also lead to an increase of the H2S formed. Furthermore, the appearance of H2S seems to occur at the same time for the three catalysts, thus suggesting that the boosted catalyst sulfides quickly, at least at lower temperatures. However, in a first analysis, no conclusion can be taken for the sulfidation process since the hydrogen disulfide does not reach a plateau (in the end of the test, we cannot assume that the quantity of sulfur incorporated in the catalyst is the same for the three catalysts, being necessary to perform their characterization). In Figure 17 is represented the sulfur content in the liquid effluent, with time and temperature, for the three catalysts. Figure 18- Online analysis of H2S for the three catalysts, with time and temperature. From the H2S curve (Figure 18), we confirm that at 60 bar of total pressure, the catalysts do not seem sulfided in the end of the 8 h, since no stabilization of the signal was detected. In the end of 32 h of plateau, the H2S curve seems to start to stabilize, however this tendency is not very clear. In this way it is concluded that no pressure and time effect on the sulfidation of the NiMoP catalysts seems to exist. Figure 17- Sulfur analysis of the liquid effluent from the T58 unit, for the three catalysts.

8 8 3.2 Catalysts characterization The spent catalysts were analyzed making use of the elemental analysis CHNS and also the XPS surface technique. The Table 4 present the content in carbon, hydrogen and nitrogen present in the active catalysts, from the CHNS for the CoMoP and NiMoP catalysts (dried, calcined and boosted) subject to the liquid sulfidation in the T58. Table 4- CHNS results for the CoMoP and NiMoP catalysts, after the sulfidation in the unit T58. GSDT (%wt) C ±0,4 H ±0,2 N ±0,1 (%) CoMoP NiMoP Dried 3,2 1,2 0,4 88 Calcined 2,4 1,0 0,3 76 Boosted 3,7 1,0 0,3 92 Dried 2,7 1,1 0,3 88 Calcined 2,6 0,9 0,3 88 Boosted 3,5 1,1 0,3 92 The content in nitrogen is equal between catalysts and relatively low, as expected, since the activation was made with SRGO, gasoil poor in this component. Table 4 also reports the value of the global sulfidation degree (GSDT). From the results obtained, two important remarks should be made: Firstly, it is clear that, for both catalyst series, the ones that present a higher global sulfidation degree, thus are probably better sulfided are the boosted ones, with a value of 92%. In a first approach is expected that a catalyst with a better sulfidation lead to better activities. Secondly, these CoMoP and NiMoP boosted catalysts present the highest carbon content, suggesting that they are more susceptible that the other catalysts to coke (we may suggest that some part of the additive still rests in the catalyst, leading to higher C content). In addition, for CoMoP and NiMoP catalysts the same tendency is observed: the calcined catalyst is the one with the lowest carbon content followed by the dried and by the boosted. More important, the CoMoP dried and boosted, as well as all the NiMoP catalysts, achieve higher values of degree of sulfidation when comparing with the CoMoP calcined that presents a value of around 76%. Moreover, despite the fact that, during the liquid sulfidation of the NiMoP catalysts, the H2S did not stabilize (indicating that the sulfidation was not complete), all the catalysts from this step present satisfactory values of global degree of sulfidation. Globally, the results of the content of each species in the catalyst surface obtained by XPS are the ones presents in Table 5. The results are expressed in mass percentage with a maximal relative error of +/- 10%. These values are normalized relatively to the initial theoretical content of metal in the oxide form present in the catalyst. It is important to notice that the normalization was made by dividing the value obtained by a constant, in order to be possible to do the comparisons between catalysts. Since the XPS is a surface technique, higher contents of each compound detected by this method means that a lower stacking degree exists and consequently a better dispersion. Table 5-Results from the XPS analysis for the CoMoP and NiMoP catalysts (+/- 10% maximum of relative error) CoMoP NiMoP Mo Co Ni Dried 0,56 0,71 0 Calcined 0,67 0,72 0 Boosted 0,72 1,06 0 Dried 0,60 0 0,90 Calcined 0,65 0 0,94 Boosted 0,68 0 0,97 For the CoMoP catalysts it is seen that the dried catalyst is the one that presents a worst distribution of the active phase when activated in the presence of the SRGO spiked with DMDS, since is the one with lower content in Mo and Co detected. It can be assumed that the calcined and boosted catalysts present the same Mo degree of dispersion (0,67 and 0,72 for the CoMoP calcined and boosted respectively). In respect to the Co degree of dispersion, the boosted catalyst presents a value of 1,06, higher than the ones found for the calcined (0,72) and dried (0,71). The same analysis can be made for all the NiMoP catalysts with the exception that, concerning the dispersion of the promoter nickel, there are no differences between catalysts, showing that the dried, calcined and boosted catalysts present practically the same promoter dispersion. On the other side, the boosted catalyst has a remarkably good distribution of the active phase: the contents seen with the XPS methods are very close of the global content in the catalyst (values in Table 5 are near the unit), meaning that a good distribution of the species was achieved with success. Table 6 summarizes the results obtained by XPS, being possible to compare the global degree of sulfidation (GDS), Mo degree of sulfidation (MoDS) and degree of promotion (DP), defined by the equations 3, 4 and 5, respectively. From these values it will be possible to take more conclusions respecting the liquid sulfidation procedure for all the catalysts. GDS(%) = C total sulfur ( C 100 total Co OR Ni x + 2 C y total Mo ) Eq 3 MoDS(%) = C MoS 2 C total Mo 100 Eq 4 DP(%) = C CoMoS OR NiMoS phase 100 C total Co OR Ni Eq 5 Where C is the concentration expressed in atomic % and x and y correspond respectively to 8 and 9 for the CoMoP and to 1 and 1 for the NiMoP catalysts.

9 9 Table 6-Global degree of sulfidation, degree of sulfidation of the molybdenum and degree of promotion obtained by XPS for the CoMoP and NiMoP sulfided at 30 bar during 8 hours. CoMoP NiMoP Dried Calcined Boosted Dried Calcined Boosted MoDS(%) GDS (%) DP (%) Co(Ni)/Mo slabs ,30 0,19 0,34 0,43 0,38 0,43 When comparing these results we can see that the boosted catalyst is the one with better results during the sulfidation in the liquid phase, in the present working conditions, since is the one which presents, not only better dispersion of the species, but also presents the higher degrees of sulfidation (with MoDS=78, GDS=84 and DP=46 for the CoMoP series and MoDS=82, GDS=79 and DP=47 for the NiMoP). Despite the first analysis made during the liquid sulfidation of the NiMoP catalysts (where the H2S curve suggested that the sulfidation process was not complete), when examining the degree of sulfidation for these catalysts, the values are satisfactory. However, we may suggest that higher values of degree of sulfidation can be achieved for the NiMoP catalysts. The calcined catalyst present values too different from the ones expected, pointing out a poor sulfidation when comparing with the other catalysts, in both series, being this difference more accentuated for the CoMoP. This result may suggest that the sulfidation conditions are not the optimal for the calcined catalyst, since the GDS does not reach the same values as for the boosted and dried catalysts. A ranking in terms of global degree of sulfidation/degree of promotion can be established, for both series: CoMoP: boosted=dried>>calcined NiMoP: boosted dried>calcined It is important to refer that, even if the dried catalysts have systematically a better degree of sulfidation and promotion, the results also indicate to what seems to be a worst dispersion of the metals in the surface, when compared with the calcined. In this way, it is not possible to affirm that the dry catalyst is more active, since both dispersion and degree of sulfidation contribute to the catalyst activity. Furthermore, activity tests should be made in order to take more conclusions. The results of XPS for both NiMoP calcined sulfided at different pressures and different times on the 350ºC temperature plateau, are summarized in Table 7: Table 7- Global degree of sulfidation, degree of sulfidation of the molybdenum and degree of promotion obtained by XPS. NiMoP Ni/Mo MoDS(%) GDS (%) DP (%) calcined slabs P=30 bar, 8 h P=60 bar, 32 h ,38 0,38 As expected by following the CH4 and H2S curves during the liquid sulfidation with SRGO spiked with DMDS, no difference is seen in the sulfided catalysts, being possible to conclude that no pressure and time effect were seen in the activation of the catalyst. 4. Conclusions The main objective of this work was to study the liquid activation of CoMo and NiMo catalysts in order to understand the differences in activity of boosted, calcined and dried catalysts. Two series of catalysts (CoMoP and NiMoP) were prepared with the same content in molybdenum, the same Co(Ni)/Mo and P/Mo ratios, being then divided in three parts, each one with a different final treatment: drying, calcination and additivation. After the preparation, the liquid sulfidation of the catalysts with SRGO+2%DMDS was followed with time and temperature, through the DMDS decomposition. Finally the catalysts were characterized by elemental analysis CHNS and XPS. From this study, it was possible to conclude that the boosted catalysts is always the one which presents better global degree of sulfidation, better degree of promotion and also better dispersion. Being these parameters all positives we can conclude that probably this catalyst is the most active in HDT, confirming the ranking of activities. Furthermore, it was concluded that the presence of additive leads to the delay of the DMDS decomposition, fact that may be related with the better results for the boosted catalyst. In contrast, the CoMoP/NiMoP calcined catalyst present, after the liquid sulfidation, the worst values in terms of global degree of sulfidation and degree of promotion when comparing with the other catalysts, showing low values in these parameters. This may suggest that higher values (as the ones found for the boosted and dried catalysts) may be achieved in future works, by changing the operational conditions. Moreover, the dried catalyst presents, for CoMoP and NiMoP, higher degree of sulfidation and promotion than the calcined one. However, their dispersion is lower, not being possible to take conclusions concerning the activities of these catalysts in HDT, without catalytic tests. In this way it is not possible to confirm the raking of activities for the dried and calcined catalysts without further studies.

10 10 Finally, the effect of increasing the pressure and time in the sulfidation of the NiMoP catalysts was studied. No change in the sulfidation and dispersion in the catalyst was registered, being possible to conclude that no effect was seen. 5. References 1. Hervé Toulhoat, Ed. e Pascal Raybaud, Ed., Catalysis by transition metal sulphides, I,II et III, Paris, France: TECHNIP, Humblot, Francis e Srinivas, Vijay. Activation of hydroprocessing catalysts: An in depth understanding of dymethyldisulfide (DMDS) decomposition chemistry of hydroprocessing catalysts during activation via sulfiding. 3. Texier, Samuel, et al., Activation of an alumina-supported hydrotreating catalysts by organosulfides or H2S: Effect of the H2S partial pressure used during the activation process, Applied catalysis A: general, 293 (2005) Texier, Samuel, et al., Activation of alumina-supported hydrotreating catalysts by organosulfides: comparison with H2S and effect of different solvents, Journal of catalysis, 223 (2004) Pashigreva, A, et al., Activity and sulfidation behaviour of the CoMo/Al2O3 hydrotreating catalyst: The effect of drying conditions, Catalysis Today, 149 (2010)