Patent Application
20230347332
The present application claims priority of Mexican patent application number MX/a/2022/003972 filed MARCH 31, 2022.
This invention can be considered within the field of the start-up and activation of catalysts for the deep hydrodesulfurization of middle distillates for producing ultra low sulfur diesel (ULSD).
Based on the new world environmental normativity and legislation, which become stricter every time regarding exhaust emissions, it is necessary that sulfur content in fossil fuels be diminished, and in this case, diesel. Recently, the demand of this fuel has increased and in contrast, the light crude reserves have diminished, which means that there is higher availability of heavy crude oil and the compelling exploitation need.
Heavy crude oil presents a high index of contaminants such as sulfur, nitrogen, asphaltenes, carbon, and metals (Ni and V). This fact has encouraged the joint development of both new and improved deep hydrodesulfurization processes and their corresponding catalysts. In recent studies, the fundamental role played by catalysts to achieve higher activity in the production of diesel with lower sulfur content has been emphasized. At world level, the sulfur content in diesel is found between 10 and 15 wppm and is regulated by the European Union, the United States of America, and several Asian countries.
The catalytic HDS process is employed to reduce the sulfur content in the different oil fractions using hydrogen and a catalyst under specific pressure and temperature conditions. These reaction conditions allow the removal of sulfur from the organic compounds, transforming it into H2S, which is transformed into elemental sulfur in a further process.
The development of new catalysts is intended to increase the removal efficiency of sulfur in diesel. As part of the continuous enhancement of new HDS catalysts, the incorporation of organic additives during their synthesis is found, for organic molecules improve the dispersion of the active phase (active metals) and the metal/support interaction.
In most patents describing HDS catalysts, two main factors have been considered to achieve ultra low sulfur levels: the metal/support interaction and the catalyst activation and start-up stages. As for the deep HDS catalysts for producing diesel, in general, patents have reported on the use of metals from the VIB and VII groups in the periodic table supported on gamma alumina. Other patents have included metals from the IA, IIA, VA, VIIA, IIB, IVB, VB and VIIB groups on supports such as alumina, zeolites, silicon, silicon-alumina, titanium, zirconium and their combinations.
The present invention refers to the activation and start-up stages of deep HDS catalysts for middle distillates, both fresh and regenerated, for producing ultra low sulfur diesel (ULSD) by means of the in situ application of an organic additive (chelating agent) and a sulfhydration agent, employing a hydrocarbon effluent to incorporate them to the catalyst under specific temperature and pressure conditions.
The addition of sulfur compounds to HDS catalysts has been studied for the last four decades; it started with additives or organic molecules containing sulfur in order to activate the catalysts, where an example is the use of alkyl polysulfides. Afterward, free-of-sulfur organic molecules (chelating agents) were studied in the preparation of catalysts as their promoters in their oxidized phase. The application of these organic molecules was divided into two types: chelating additives, which originate the complexation of metallic ions and the non-chelating ones; likewise, the difference between the molecules containing sulfur and those without was established.
Among the additives containing sulfur, thioglycolic acid (TGA) and di-tert-thionylpentasulfide (TNPS) are found and are used in the activation of HDS catalysts by means of hydrogen treatment at temperatures ranging from 100 to 350° C. and within a pressure interval from 20 to 40 kg/cm2. Additionally to TGA and TNPS, there are other chelating agents like the ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA). In this context, the formation of stable complexes featuring TGA and transition metals has been found.
As for the additives containing sulfur, like TGA and TNPS, it is said that they have a double function, combining the effect of organic additives without sulfur with those having a sulfhydration action. The last ones include the role of S-O exchange during the thermal treatment. The chemical effects exerted by these additives are of morphological type.
The formation of stable TGA complexes with transition metals has been the subject matter of various studies, where it has been found that the sulfur carrying molecules are decomposed, producing residual carbon. This residual carbon, present in the active sulfide phase generated from organic sulfur precursors, improves the properties of HDS catalysts through the stabilization of highly dispersed sulfides as a morphological action.
In an activation study of a HDS catalyst, the use of TNPS was compared with ex situ presulfhydration with H2S and it was observed that by using TNPS, higher HDS activity was achieved due to higher dispersion of the presulfhydrated active phase. Additionally, by XPS analysis, a strong interaction between TNPS and the catalyst support was revealed, which was based on the partial reduction of molybdenum ions after the thermal treatment with hydrogen, where TNPS decomposed within the interval ranging from 160 to 220° C., transforming the initial Mo (VI) oxide into MoS2. Likewise, it was also found that the activation of the active phase and its dispersion increased with the hydrogen partial pressure.
In another study, a commercial CoMo/Al2O3 catalyst was presulfhydrated with different agents and its activity was evaluated in the HDS of dibenzothiophene (DBT). The catalyst presulfhydrated with polysulfide showed higher or equal activity to that obtained when dimethyl disulfide (DMDS) and carbon disulfide (CS2) were used as sulfhydration agents. Further studies showed that the effects of additives with organic sulfur and solvents, if identical conditions are used, generate a significant difference in the activity of HDS catalysts. In fact, in the industrial practice, the benefit of employing sulfhydration agents is not only associated with their chemical effect, but also with their “thermal well” effect, where these sulfhydration agents absorb the heat released during the transformation of the oxide to metallic sulfide, with which better dispersion of the active phase is achieved. As a matter of fact, polysulfides are similar in their chemical nature to that of DMDS, although the latter is considered more as a sulfhydration agent than as an organic additive.
To TGA, as chelating agent, the formation of the Mo (V) complex is attributed, from the Mo (VI) ion, where it is considered that it works as a reducing ligand. The chelating properties of TGA set it as a compound that allows the transport of active metallic species, especially with transition metals. TGA is used in the ex situ activation of CoMo/Al2O3 catalysts and its role with different TGA/Mo ratios has been studied in order to make the most of its properties as chelating compound and sulfhydration agent to increase the sulfurization degree of the active metals and the simultaneous sulfurization of Mo and Co, which leads to the shortening of the MoS2 sheets and to the increase in the number of Mo atoms at a given arrangement position.
In the case of the NiMo catalysts, also ex situ TGA treatments have been performed with TGA/Mo molar ratios equal to 4. In tests with 1-benzothiophene and thiophene, higher catalytic activity was observed. Likewise, a Mo supported on alumina catalyst with metallic loading of 14 wt.% of different metal precursors was treated with TGA with a TGA/Mo molar ratio of 1. The different saturated phases were analyzed by XPS and HRTEM-STEM and it was observed that the charge transfer from the ligand to metal (LMCT) between the TGA and Mo atoms led to the formation of reduced Mo5+ species, thus concluding that with the incorporation of TGA, better dispersion of MoO3 crystals was achieved and resulting in metallic sulfide particles with higher stacking of MoS2 sheets. Furthermore, in HDS tests of DBT, high catalytic activity due to the growth of Type II active sites was observed.
Complementarily, the strong effect exerted by TGA on the phases of metallic oxides (Mo, Ni, Co) can be established, which is observed in the formation of active species, chemically different before the thermal activation and in some cases, until their reactivation.
According to the state of the art, organic additives play a major role in the catalytic activity of the HDS catalysts; such role has been referred to as “potentiating effect” and depends on the application stage. The most common case occurs during the catalyst preparation stage, where the main effects are reflected in:
The modification of these properties affects in turn the:
The synergy of these modifications confers the catalyst the most important catalytic property: an increasing number of promoted active sites.
At first, organic additives exerted a strong impact on the synthesis of HDS catalysts, in ex situ treatments with sulfhydration agents for increasing their activity. However, the evaluation of these treatments is currently focused not only on improving the catalytic activity, but also on the rejuvenation of HDS catalysts for their reuse with good performance. The most recent practice consists in activating in situ the HDS catalysts with one or various organic addictives in order to improve their catalytic properties, especially the sulfur removing capacity.
The patent US 6,635,596 B1 (2003) deals with the use of an organic additive in the regeneration of a HDS catalyst with a group VIB metal and other of the VIII group supported on gamma alumina. The catalyst contains, at least, one group component featuring, at least, two hydroxyl groups, from 2 to 10 carbon atoms and polyethers belonging to this group. The regeneration of the HDS catalyst is carried out with an oxygen current, at temperatures from 300 to 500° C., pressure from 5 to 200 kg/cm2, space velocity from 1 to 4 h-1 and hydrogen/hydrocarbon (H2/oil) ratio from 50 to 200 NL/L. The following compounds are included as example additives: citric acid, oxalic acid, malonic acid, maleic acid, butenediol, aldehydes and glycols and aldols. Likewise, these compounds are proposed: ethylenediaminetetraacetic acid (EDTA), hydroxyethylenediamino-triacetic acid (HEDTA) and diethylenetriaminepentaacetic acid (DTPA). The regeneration of the HDS catalysts with the organic additives is carried out within the interval from 0.25 to 24 h. The exhausted catalysts contain between 5 and 20 wt.% of sulfur and the regenerated catalysts have less than 1 wt.% of sulfur. The benefit stems from the fact that the catalysts regenerated by this invention present activity that is higher than that displayed by those with an additive.
The patent US 8,278,234 B2 (2012) describes a regeneration process of catalysts for the HDS of hydrocarbons, where the invention subject matter is based on the fact that these catalysts should possess, at least, a metal from group VIII and at least one from group VIB and deposited on a refractory support. The regeneration consists of at least one thermal treatment of the catalyst in the presence of oxygen at temperatures from 350 to 550° C. and at least, a second stage for adding one or more additives to the catalyst. The regeneration process in this patent is focused on HDS catalysts and the aim of adding organic additives is their rejuvenation to recover their initial activity. For the rejuvenation of the catalysts, an organic molecule from 1 to 30 carbon atoms is proposed, which optionally can feature heteroatoms like oxygen and nitrogen, with saturated or unsaturated molecules. The goal of this invention is that with this additive, the chelating effect of the active metals be generated, i.e. the activation of active sties by means of the transformation of metallic oxides into metallic sulfides.
Patent US 8,377,839 B2 (2013) deals with a regeneration process of catalysts for the HDS of hydrocarbons, where the invention subject is based on the fact that these catalysts should have, at least, one metal from group VIII and at least one from group VIB and be deposited on a refractory support. The regeneration considers, at least, a thermal treatment stage of the catalyst in the presence of oxygen at temperature from 350 to 550° C. and at least, a second stage considering the addition of one or more additives to the catalyst surface. For the rejuvenation of the catalysts, an organic molecule from 1 to 30 carbon atoms, without aromatic rings and that optionally can feature heteroatoms like oxygen and nitrogen, with saturated or unsaturated molecules. The regeneration process proposed by this invention restores a high catalytic activity level with an easy-to-use and non-toxic organic additive.
The Mexican patent 274444 (2005) describes a HDS catalyst for residues and heavy crude, where the current to be treated contains sulfur and nitrogen compounds, metals (nickel and vanadium) and asphaltene material. The employed catalyst is of the NiMo type with percentages from 8 to 12 wt.% of molybdenum and from 2 to 6 wt.% of nickel, supported on mixed oxides based on TiO2/Al2O3 and TiO2-Al2O3. The presulfhydration stage was carried out with reagent grade DMDS (97%), using desulfurated diesel at a temperature of 320° C., pressure of 28 kg/cm2, LHSV of 2.0 h-1 and a H2/oil ratio of 56.6 m3/bbl. The evaluation of the catalytic activity of three catalysts (A3, B1 and C1) in a fixed-bed reactor with ascending flow at pilot plant level was carried out at 400° C., pressure of 70 kg/cm2, LHSV of 1.0 h-1 and H2/oil ratio of 141.6 m3/bbl. The following HDS activities were reported: A3) start-up, 81.6% (6 h) - 47% (36 h) until 120 h; B1) start-up, 63% (6 h) - 47% (36 h) until 120 h; C1) start-up, 82.9% (6 h) - 59% (36 h) until 120 h.
The previous technologies are surpassed by the present invention, for in none of them, the activation and start-up of HDS catalysts with a couple of organic agents with two stages for increasing the catalytic activity under typical industrial plant operating conditions were carried out.
This invention provides an improved process for the in situ activation and start-up of either a fresh or rejuvenated HDS catalyst for the deep hydrodesulfurization of middle distillates, which increases their catalytic activity for the production of ultra low sulfur diesel (ULSD).
This invention offers an activation and start-up through a first stage, where a chelating organic additive is used and a second stage with a sulfur organic agent through a given sequence of times and temperature, pressure, and space velocity conditions in order to increase their catalytic activity for producing ULSD.
This invention provides activation and start-up procedures, combining a first stage with a chelating organic additive and a second stage with a sulfur organic agent with the concentrations of each compound.
Another characteristic that distinguishes this invention is the use of a hydrocarbon current for transporting the chelating and sulfhydration agents, in both stages, with their corresponding concentrations.
Likewise, in the present invention, the addition of the organic additive and sulfhydration agent is carried out in the plant reactor with a sequence given in times and temperature, pressure and space velocity conditions, followed by the feedstock to be hydrotreated by the HDS process.
Finally, this invention is also different from others in the sense that in these activation and start-up procedures with both stages adding an organic additive and a sulfhydration agent with a given sequence of time and temperature, pressure and space velocity conditions not only increase the catalytic activity for the production of ULSD, but also increase the activity of rejuvenated catalysts.
This invention is related to activation and start-up procedures of catalysts for the deep hydrodesulfurization of middle distillates through two stages: the first stage refers to the use of a chelating organic additive consisting of TGA and kerosene or straight run gas oil (SRGO) as transport means and the second stage describes the use of a sulfhydration agent consisting of DMDS and kerosene or SRGO as transport means with a sequence given in times and temperature, pressure and space velocity conditions and feedstock type established for each process run with their corresponding efficiencies in the deep hydrodesulfurization of middle distillates regarding the sulfur content in the produced diesel.
In the present invention, as part of the first stage, the use in situ of an organic additive (TGA), whose main characteristic is its chelating effect or complexation of active metals for the stabilization of highly dispersed metallic sulfides, is proposed. The TGA effect complexing Mo allows the transport of reduced Mo+5 active metallic species.
Another important TGA effect is that the TGA/Mo ratio conditions the chelating effects, which in combination with the organic sulfhydration additive (DMDS) increases the sulfhydration effect of the active metal, i.e. in addition to reduce the length of the MoS2 sheets, higher catalytic activity of the HDS catalysts reducing the content of sulfur in diesel is generated.
Furthermore, TGA produces the in situ redispersion of active metallic sites, which are formed during the start-up thermal treatments, producing a HDS catalyst with higher catalytic activity and then, with higher activity in the deep hydrodesulfurization to obtain ULSD.
In a second stage, DMDS is used as sulfhydration agent, where one of its most important in situ effects is the absorption of heat released during the exothermal transformation of oxides into metallic sulfides, generating higher dispersion of the active species and higher activity in the deep HDS.
In order to better understand the activation and start-up of a deep HDS catalyst and the use in two stages, first of TGA as chelating organic additive and second of DMDS as a sulfhydration agent, it is divided into the following steps for the case of a pilot plant with a reactor loaded with 75 mL of catalyst:
Step 1) It consists in the loading of the catalyst or combined bed of catalysts based on the established loading diagram. This diagram specifies: the catalyst(s) and inert material(s) to be loaded, their location in the reactor, corresponding amounts, heights and estimated value(s) of loaded density/densities.
Step II) It consists in the conditioning of the reactor with the loaded catalyst at ambient temperature for the hermeticity test, which is carried out at a preferred pressure from 70 a 75 kg/cm2 and hydrogen flow preferably from 45 a 75 L/h for a period of time preferably from 2 a 4 h. Once the plant hermeticity has been fully confirmed, the pressure (45 - 60 kg/cm2) and hydrogen flow rate (45 - 75 L/h) are established before starting to increase the reactor temperature to 120° C. at a heating rate of 20 - 30° C./h. Step III) Consists in the drying of the catalyst loaded in the reactor at 120° C. under the same pressure and hydrogen flow rate conditions mentioned in Step II for 2 - 4 h. Once this time is completed, the reactor inlet temperature is increased from 120 to 230° C. at a heating rate of 20 - 30° C./h, keeping constant pressure and hydrogen flow rate.
Step IV) Consists of a first activation stage at which a mixture consisting of TGA with kerosene or diesel is added at a preferable flow rate from 170 to 190 mL/h for a preferable time from 4 to 10 h, at preferable temperature from 200 to 230° C., preferable pressure from 45 to 60 kg/cm2 and a preferable H2/oil ratio from 50 to 60 m3/bbl.
Step V) Consists of a second activation stage at which a mixture consisting of DMDS with kerosene or diesel is added at a preferable flow rate from 170 a 190 mL/h, at preferable temperature from 200 - 230° C., at preferable pressure from 45 - 60 kg/cm2 with preferable H2/oil ratio from 50 - 60 m3/bbl and preferable time from 8 - 16 h. Afterward, the temperature is preferably increased from 240 - 260° C. with a heating rate from 20 - 30° C./h under the same just established flow, pressure, H2/oil ratio and time conditions. During this second stage, the temperature continues being increased preferably from 260 - 280° C. with the same heating rate and same flow rate, pressure, H2/oil ratio and time conditions. The second activation stage continues increasing the temperature, now at preferable temperature from 280 - 300° C. with the same heating rate and same flow, pressure, H2/oil ratio and time conditions. The last part of the second activation stage occurs by increasing the temperature preferably from 300 - 320° C. with the same heating rate and same flow, pressure, H2/oil ratio, and time conditions.
Step VI) Consists in the catalyst stabilization and the treatment is just with kerosene or diesel, with preferable flow rate from 170 to 190 mL/h, under the same pressure and H2/oil ratio conditions mentioned in Step V, at preferable temperature from 300 - 320° C. for a preferable time from 48 to 72 h. During this time period, the feedstock to be processed, whose characteristics should be within the interval of middle distillate mixtures (see Table 1), is made ready. Once the established time has passed, the temperature is increased to the value estimated as start of run temperature preferably from 300 - 320 until 335 - 355° C. with a heating rate from 5 - 10° C./h.
Step VII) Consists in performing the activity tests of the improved process in the deep HDS for producing ULSD with the following sequence:
Table 1 shows the physical and chemical characteristics of the processed feedstocks once the improved activation and run process was applied to the catalysts to be evaluated and that are used in the examples developed and shown in this patent.
Table 2 includes the properties of the catalysts before being loaded in the reactor and that were tested in the pilot plant. Evident differences are observed in the surface area, content, and concentration of the active metals: CATI (LM) and CATII (HM) of NiMo and CATIII of CoMo.
Table 3 shows the sulfur content values after applying the improved activation and start-up procedures as evidence of the activity of the catalysts in the deep HDS for producing ULSD.
What follows is the description of four practical examples to better understand the present invention without this limiting its scope.
Experimental runs were carried out in a pilot plant employing a continuous flow, combined bed reactor with the corresponding hermeticity tests, obtaining the following results:
The average activity of the deep HDS of the CIV feedstock considering 4 balances is in the order of 4.3 wppm of sulfur.
The average activity of the deep HDS of the CII feedstock considering 4 balances is in the order of 2.1 wppm of sulfur.
The average activity of the deep HDS of the CII feedstock considering 4 balances is in the order of 1.1 wppm of sulfur.
| Number | Date | Country | Kind |
|---|---|---|---|
| MX/A/2022/003972 | Mar 2022 | MX | national |
