Patent Description:
Hydroprocessing includes processes which convert hydrocarbons in the presence of hydroprocessing catalyst and hydrogen to more valuable products. Hydrotreating is a process in which hydrogen is contacted with a hydrocarbon stream in the presence of hydrotreating catalysts which are primarily active for the removal of heteroatoms, such as sulfur, nitrogen and metals, such as iron, nickel, and vanadium from the hydrocarbon feedstock.

Residue or resid streams are produced from the bottom of a fractionation column. Resid hydrotreating is a hydrotreating process to remove metals, sulfur and nitrogen from an atmospheric residue (AR) or a vacuum residue (VR) feed, so that it can be cracked to valuable fuel products.

Hydrotreating of resid streams requires high severity. Resid desulfurization units typically have hydrodemetallization (HDM) catalyst up front, followed by hydrodesulfurization (HDS) catalyst. Frequently, a resid hydrotreating unit is metal limited so the HDM catalyst is not fully utilized relative to its residual ability to hydrotreat more resid feed at the time of unit shutdown or turnaround. At the reactor inlet, HDM catalyst is fully adsorbed of metals where the feed metals are most concentrated. However, in downstream HDM catalyst beds, the lower concentration of metals in the feed operates to avoid full adsorption onto the HDM catalyst. Metal laying down on HDM catalyst causes the chemical reaction rate to decrease, which primarily occurs on the HDM catalyst surface. In practice, the reactor temperature is increased to compensate for the reaction rate decrease. Thus, when a portion of HDM catalyst in a demetallation reactor is saturated with metal, metals in the feed migrate to downstream HDS catalyst beds which affects HDS activity. In addition, coke buildup also affects reaction rate negatively across all catalyst beds. At a later stage of operation, metal breakthrough into downstream HDM catalyst starts to occur when temperature adjustment cannot compensate for the desulfurization reaction rate decrease. Consequently, the unit is shut down and the cycle is ended for replacement with fresh catalyst.

Refiners frequently desire a constant product quality in hydrotreated product below a certain sulfur specification. When a higher desulfurization reaction rate can be obtained and maintained throughout operation of a fixed unit cycle period, manifested as a consistent temperature profile along the unit cycle period, better product quality is achieved across the cycle for the same volume of catalyst.

It would be highly desirable to have a hydrotreating process that can efficiently demetallize and desulfurize a resid stream.

<CIT> discloses a resid hydrotreating process.

The subject process enhances catalytic activity for demetallization and desulfurization of a residue feed stream by injecting water into the feed and hydro treating in two stages with interstage separation. Water injection improves the desulfurization activity of the HDM catalyst and separating vapor comprising hydrogen sulfide from the demetallized effluent before entering the desulfurization reactor improves the activity of the HDS catalyst. We have discovered that the water injection and hydrogen sulfide removal together provide a profound synergetic effect.

<FIG> is a schematic drawing of a two-stage hydrocracking unit.

The term "communication" means that material flow is operatively permitted between enumerated components.

The term "downstream communication" means that at least a portion of material flowing to the subject in downstream communication may operatively flow from the object with which it communicates.

The term "upstream communication" means that at least a portion of the material flowing from the subject in upstream communication may operatively flow to the object with which it communicates.

The term "direct communication" means that flow from the upstream component enters the downstream component without undergoing a compositional change due to physical fractionation or chemical conversion.

The term "column" means a distillation column or columns for separating one or more components of different volatilities. Unless otherwise indicated, each column includes a condenser on an overhead of the column to condense and reflux a portion of an overhead stream back to the top of the column and a reboiler at a bottom of the column to vaporize and send a portion of a bottoms stream back to the bottom of the column. Absorber and scrubbing columns do not include a condenser on an overhead of the column to condense and reflux a portion of an overhead stream back to the top of the column and a reboiler at a bottom of the column to vaporize and send a portion of a bottoms stream back to the bottom of the column. Feeds to the columns may be preheated. The overhead pressure is the pressure of the overhead vapor at the vapor outlet of the column. The bottom temperature is the liquid bottom outlet temperature. Overhead lines and bottoms lines refer to the net lines from the column downstream of any reflux or reboil to the column unless otherwise indicated. Stripping columns omit a reboiler at a bottom of the column and instead provide heating requirements and separation impetus from a fluidized inert vaporous media such as steam.

As used herein, the term "True Boiling Point" (TBP) means a test method for determining the boiling point of a material which corresponds to ASTM D-<NUM> for the production of a liquefied gas, distillate fractions, and residuum of standardized quality on which analytical data can be obtained, and the determination of yields of the above fractions by both mass and volume from which a graph of temperature versus mass % distilled is produced using fifteen theoretical plates in a column with a <NUM>:<NUM> reflux ratio.

As used herein, the term "initial boiling point" (IBP) means the temperature at which the sample begins to boil using ASTM D-<NUM>.

As used herein, the term "T5", "T70" or "T95" means the temperature at which <NUM> mass percent, <NUM> mass percent or <NUM> mass percent, as the case may be, respectively, of the sample boils using ASTM D-<NUM>.

As used herein, the term "separator" means a vessel which has an inlet and at least an overhead vapor outlet and a bottoms liquid outlet and may also have an aqueous stream outlet from a boot. A flash drum is a type of separator which may be in downstream communication with a separator which latter may be operated at higher pressure.

The subject process and apparatus enhances catalytic activity for demetallization and desulfurization of a residue feed stream by injecting water into the feed and hydrotreating in two stages with interstage separation between demetallation and desulfurization stages. The apparatus and process <NUM> for hydrotreating a hydrocarbon resid stream comprises a first stage hydrotreating unit <NUM>, a first stage separation section <NUM>, a second stage hydrotreating unit <NUM> and a second stage separation section <NUM>.

A hydrocarbon resid stream in resid line <NUM> and a first stage hydrogen stream in a first hydrogen line <NUM> are fed to the first stage hydrotreating unit <NUM>. A stream of water in water feed line <NUM> is also delivered to the first stage hydrotreating unit <NUM>. The stream of water may comprise <NUM> to <NUM> wt% and preferably <NUM> to <NUM> wt% water based on the weight of the resid hydrocarbon stream in resid line <NUM>. In an aspect, the water stream may be added or pumped into the first stage hydrogen stream in the first stage hydrogen line <NUM> to mix the streams. Mixing makes the hydrogen stream include <NUM> to <NUM> wt% water based on the weight of the resid hydrocarbon stream in resid line <NUM>. The stream of water may be provided from boiler feed water which is condensed from steam and therefore comprises little or no salts.

In one aspect, the process and apparatus described herein are particularly useful for hydrotreating a hydrocarbon feed stream comprising a resid hydrocarbonaceous feedstock. A resid feedstock may be taken from a bottom of an atmospheric fractionation column or a vacuum fractionation column. A suitable resid feed is AR having an T5 between <NUM> (<NUM>°F) and <NUM> (<NUM>°F) and a T70 between <NUM><NUM> (<NUM>°F) and <NUM> (<NUM>°F). VR having a T5 in the range between <NUM> (<NUM>°F) and <NUM> (<NUM>°F) may also be a suitable feed. VR, atmospheric gas oils having T5 between <NUM> (<NUM>°F) and <NUM> (<NUM>°F) and vacuum gas oils (VGO) having T5 between <NUM> (<NUM>°F) and <NUM> (<NUM>°F) may also be blended with the AR to make a suitable resid feed. Deasphalted oil, visbreaker bottoms, clarified slurry oils, and shale oils may also be suitable resid feeds alone or by blending with AR or VR.

Typically these resid feeds contain a significant concentration of metals which have to be removed before catalytic desulfurization can occur because the metals will adsorb on the HDS catalyst making it inactive. Typically, suitable resid feeds include <NUM> to <NUM> wppm metals but resid feeds with less than <NUM> wppm metals may be preferred. Nickel, vanadium and iron are some of the typical metals in resid feeds. Resid feeds may comprise <NUM> to <NUM> wppm nickel, <NUM> to <NUM> wppm vanadium, <NUM> to <NUM> wppm iron and/or <NUM> to <NUM> wt% Conradson carbon residue. Resid feeds may comprise <NUM>,<NUM> wppm to <NUM>,<NUM> wppm sulfur. Frequently refiners have a targeted product specification depending on downstream application of hydrotreated products, primarily on sulfur and metal content.

The first stage hydrogen stream in the first hydrogen line <NUM> may join the resid stream in the resid line <NUM> to provide a resid feed stream in a resid feed line <NUM>. The resid feed stream in the resid feed line <NUM> may be heated in a fired heater. The heated resid feed stream in the resid feed line <NUM> may be fed to a first resid hydrotreating unit <NUM>. With the water stream from line <NUM> added to the first stage hydrogen stream in line <NUM>, the first stage hydrogen stream, the water stream and the resid feed stream in line <NUM> may all be heated together in the fired heater in resid feed line <NUM>.

Hydrotreating is a process wherein hydrogen is contacted with hydrocarbon in the presence of hydro treating catalysts which are primarily active for the removal of heteroatoms, such as sulfur, nitrogen and metals from the hydrocarbon feedstock. The first hydrotreating unit <NUM> may comprise three demetallizing reactors comprising a first demetallizing reactor <NUM>, a second demetallizing reactor <NUM> and a third demetallizing reactor <NUM>. More or less demetallizing reactors may be used, and each demetallizing reactor <NUM>, <NUM> and <NUM> may comprise a part of a demetallizing reactor or comprise one or more demetallizing reactors. Each demetallizing reactor <NUM>, <NUM> and <NUM> may comprise part of a catalyst bed or one or more catalyst beds in one or more demetallizing reactor vessels. In <FIG>, the first hydrotreating unit <NUM> comprises three demetallizing reactors <NUM>, <NUM> and <NUM> each comprising a single bed of HDM catalyst.

Multiple demetallizing reactors <NUM>, <NUM>, <NUM> may also include demetallizing reactors operating in swing bed mode and/or in lead-lag mode. In one aspect, the first demetallizing reactor <NUM> and the second demetallizing reactor <NUM> may operate in swing bed and/or in lead lag mode. In an embodiment, the first demetallizing reactor <NUM> and the second demetallizing reactor <NUM> are in series with the first demetallizing reactor <NUM> in the lead and the second demetallizing reactor <NUM> in the lag, downstream of the first demetallizing reactor <NUM>. The second demetallizing reactor <NUM> may be switched to the lead when the first demetallizing reactor <NUM> is shut down for catalyst replacement or regeneration. In this embodiment, the second demetallizing reactor <NUM> may stay in the lead even after the first demetallizing reactor <NUM> is brought back on stream in the lag, downstream of the second demetallizing reactor <NUM>. The second demetallizing reactor <NUM> may stay in the lead until it is shut down for catalyst replacement or regeneration, in which case the first demetallizing reactor <NUM> is returned to the lead as the cycle resumes. The third demetallizing reactor <NUM> may also be operated in the lead-lag cycle with the first demetallizing reactor <NUM> and the second demetallizing reactor <NUM> or not.

Suitable HDM catalysts for use in the first resid hydrotreating unit <NUM> are any conventional resid hydrotreating catalysts and include those which are comprised of at least one Group VIII metal, preferably iron, cobalt and nickel, more preferably nickel and/or cobalt and at least one Group VI metal, preferably molybdenum and tungsten, on a high surface area support material, preferably alumina. It is within the scope of the present invention that more than one type of hydrotreating catalyst be used in the same reaction vessel or catalyst bed. The Group VIII metal is typically present on the HDM catalyst in an amount ranging from <NUM> to <NUM> wt%, preferably from <NUM> to <NUM> wt%. The Group VI metal will typically be present on the HDM catalyst in an amount ranging from <NUM> to <NUM> wt%, preferably from <NUM> to <NUM> wt%.

In an embodiment, the first demetallation reactor <NUM>, the second demetallation reactor <NUM> and the third demetallation reactor <NUM> may comprise a HDM catalyst comprising cobalt and molybdenum on gamma alumina. The HDM catalyst in the first demetallation reactor <NUM>, the second demetallation reactor <NUM> and the third demetallation reactor <NUM> may have a bimodal pore size distribution with at least <NUM>% of the pores on the catalyst particle being characterized as small pores, in the micropore or mesopore range of <NUM> to no more than <NUM> and at least <NUM>% of the pores being characterized as large pores, in the mesopore or macropore range of greater than <NUM> to <NUM>. The large pores are more suited for demetallation and the small pores are more suited for desulfurization. The ratio of large pores to small pores may decrease from upstream to downstream in the first demetallation reactor <NUM>, the second demetallation reactor <NUM> and the third demetallation reactor <NUM>. In an aspect, the first demetallation reaction <NUM> will have a larger ratio of large pores to small pores than the second demetallation reactor <NUM>. In a further aspect, the second demetallation reaction <NUM> will have a larger ratio of large pores to small pores than the third demetallation reactor <NUM>.

The resid feed stream in line <NUM> may be fed to the first demetallation reactor <NUM>, the second demetallation reactor <NUM> and the third demetallation reactor <NUM>. The first demetallation reactor <NUM>, the second demetallation reactor <NUM> and the third demetallation reactor <NUM> may be arranged in series such that the effluent from one cascades into the inlet of the other. It is contemplated that more or less demetallation reactors may be provided in the first stage hydrotreating unit <NUM>. The first demetallation reactor <NUM>, the second demetallation reactor <NUM> and the third demetallation reactor <NUM> are intended to demetallize the heated resid stream, so to reduce the metals concentration in the fresh feed stream by <NUM> to <NUM> wt% and typically <NUM> to <NUM> wt% to produce a demetallized effluent stream exiting one, some or all of the first demetallation reactor <NUM>, the second demetallation reactor <NUM> and the third demetallation reactor <NUM>. The metal content of the demetallized resid stream may be less than <NUM> wppm and preferably between <NUM> and <NUM> wppm. The first demetallation reactor <NUM>, the second demetallation reactor <NUM> and the third demetallation reactor <NUM> may also desulfurize and denitrogenate the resid stream. A demetallized resid stream reduced in metals and sulfur concentration relative to the resid feed stream fed to the reactor may exit first demetallation reactor <NUM>, the second demetallation reactor <NUM> and the third demetallation reactor <NUM>.

Preferred reaction conditions in each of the first demetallation reactor <NUM>, the second demetallation reactor <NUM> and the third demetallation reactor <NUM> include a temperature from <NUM> (<NUM>°F) to <NUM> (<NUM>°F), suitably <NUM> (<NUM>°F) to <NUM> (<NUM>°F) and preferably <NUM> (<NUM>°F) to <NUM> (<NUM>°F), a pressure from <NUM> MPa (gauge) (<NUM> psig) to <NUM> MPa (gauge) (<NUM> psig), preferably <NUM> MPa (gauge) (<NUM> psig) to <NUM> MPa (gauge) (<NUM> psig), a liquid hourly space velocity of the fresh resid feed from <NUM> hr-<NUM> to <NUM> hr-<NUM>, preferably from <NUM> to <NUM> hr-<NUM>, and a hydrogen rate of <NUM><NUM>/m<NUM> (<NUM>,<NUM> scf/bbl) to <NUM>,<NUM><NUM>/m<NUM> oil (<NUM>,<NUM> scf/bbl), preferably <NUM><NUM>/m<NUM> oil (<NUM>,<NUM> scf/bbl) to <NUM>,<NUM><NUM>/m<NUM> oil (<NUM>,<NUM> scf/bbl).

The first stage demetallized resid stream may exit the third demetallation reactor <NUM> or whichever demetallation reactor <NUM>, <NUM>, <NUM> is the last on stream in the first demetallized effluent line <NUM>, be cooled by heat exchange with the first stage hydrogen stream in line <NUM> and enter the first stage separation section <NUM> comprising a first stage hot separator <NUM>. The first stage separation section <NUM> comprises one or more separators in downstream communication with the first hydrotreating unit <NUM> including the first stage hot separator <NUM>. The first demetallized effluent line <NUM> delivers a cooled demetallized effluent stream to the first stage hot separator <NUM>. Accordingly, the first stage hot separator <NUM> is in downstream communication with the first demetallation reactor <NUM>, the second demetallation reactor <NUM> and the third demetallation reactor <NUM>.

The first stage hot separator <NUM> separates the demetallized resid stream to provide a hydrocarbonaceous, first stage vapor stream in a first hot overhead line <NUM> and a hydrocarbonaceous, first stage hot liquid stream in a first hot bottoms line <NUM>. The first stage vapor stream comprises the bulk of the hydrogen sulfide from the demetallized resid stream. The first stage liquid stream has a smaller concentration of hydrogen sulfide than the desulfurized resid stream. A second stage hydrogen stream may be taken from the first stage vapor stream in line <NUM>.

The first stage hot separator <NUM> may operate at <NUM> (<NUM>°F) to <NUM> (<NUM>°F) and preferably operates at <NUM> (<NUM>°F) to <NUM> (<NUM>°F). The first stage hot separator <NUM> may be operated at a slightly lower pressure than the first desulfurization reactor <NUM> accounting for pressure drop through intervening equipment. The first stage hot separator <NUM> may be operated at pressures between <NUM> MPa (gauge) (<NUM> psig) and <NUM> MPa (gauge) (<NUM> psig). The hydrocarbonaceous, first stage vapor stream in the hot overhead line <NUM> may have a temperature of the operating temperature of the first stage hot separator <NUM>. The first stage hot liquid stream in the first hot bottoms line <NUM> may be mixed with a second stage hydrogen stream in a second hydrogen line <NUM> and be fed to the second hydrotreating unit <NUM>.

The first stage hot vapor stream in the first hot overhead line <NUM> may be cooled by heat exchange with the first stage hydrogen stream in line <NUM> before entering a first stage cold separator <NUM>. The first stage cold separator <NUM> may be in downstream communication with the hot overhead line <NUM>.

As a consequence of the reactions taking place in the first stage hydrotreating unit <NUM> wherein nitrogen, chlorine and sulfur are reacted from the feed, ammonia and hydrogen sulfide are formed. The first stage hot separator <NUM> removes the hydrogen sulfide and ammonia from the first stage liquid stream in the first hot bottoms line <NUM> into the first stage vapor stream in the hot overhead line <NUM> to provide a sweetened, demetallized resid stream for desulfurization in the second hydrotreating unit <NUM>.

At a characteristic sublimation temperature, ammonia and hydrogen sulfide will combine to form ammonium bisulfide and ammonia, and chlorine will combine to form ammonium chloride. Each compound has a characteristic sublimation temperature that may allow the compound to coat equipment, particularly heat exchange equipment, impairing its performance. To prevent such deposition of ammonium bisulfide or ammonium chloride salts in the first hot overhead line <NUM> transporting the first stage vapor stream, a suitable amount of wash water may be introduced into the first hot overhead line <NUM> by a first water wash line <NUM>.

The cooled first stage vapor stream may be separated in the cold separator <NUM> to provide a first stage cold vapor stream comprising a hydrogen-rich gas stream including ammonia and hydrogen sulfide in a first cold overhead line <NUM> and a first stage cold liquid stream in a first cold bottoms line <NUM>. The cold separator <NUM> serves to separate hydrogen rich gas from hydrocarbon liquid in the first stage hot vapor stream for recycle to the second stage hydrotreating unit <NUM>. The first stage cold separator <NUM>, therefore, is in downstream communication with the first hot overhead line <NUM> of the first stage hot separator <NUM>.

The cold separator <NUM> may be operated at <NUM>°F (<NUM>) to <NUM>°F (<NUM>), suitably <NUM>°F (<NUM>) to <NUM>°F (<NUM>), and just below the pressure of the last demetallation reactor <NUM>, <NUM>, <NUM> and the first stage hot separator <NUM> accounting for pressure drop through intervening equipment to keep hydrogen and light gases in the overhead and normally liquid hydrocarbons in the bottoms. The first stage cold separator <NUM> may be operated at pressures between <NUM> MPa (gauge) (<NUM> psig) and <NUM> MPa (gauge) (<NUM>,<NUM> psig). The first stage cold separator <NUM> may also have a boot for collecting an aqueous phase. The first stage cold liquid stream in the first cold bottoms line <NUM> may have a temperature of the operating temperature of the cold separator <NUM>. The first stage cold liquid stream in the first cold bottoms line <NUM> may be delivered to a cold flash drum <NUM>, in an embodiment after mixing with a second stage cold liquid stream in a second cold bottoms line <NUM>. The cold flash drum <NUM> may be in downstream communication with the first cold bottoms line <NUM> of the first cold separator <NUM>.

The first stage cold vapor stream in the first cold overhead line <NUM> is rich in hydrogen. Thus, hydrogen can be recovered from the first stage cold vapor stream. However, this stream comprises much of the hydrogen sulfide and ammonia separated from the demetallized resid stream. The cold vapor stream in the cold overhead line <NUM> may be passed through a trayed or packed recycle scrubbing column <NUM> where it is scrubbed by means of a scrubbing extraction liquid such as an aqueous solution fed by line <NUM> to remove and acid gases including hydrogen sulfide and carbon dioxide by extracting them into the aqueous solution. Preferred aqueous solutions include lean amines such as alkanolamines DEA, MEA, and MDEA. Other amines can be used in place of or in addition to the preferred amines. The lean amine contacts the first stage cold vapor stream and absorbs acid gas contaminants such as hydrogen sulfide and carbon dioxide. The resultant "sweetened" first stage cold vapor stream is taken out from an overhead outlet of the recycle scrubber column <NUM> in a recycle scrubber overhead line <NUM>, and a rich amine is taken out from the bottoms at a bottom outlet of the recycle scrubber column in a recycle scrubber bottoms line <NUM>. The spent scrubbing liquid from the bottoms may be regenerated and recycled back to the recycle scrubbing column <NUM> in line <NUM>. The scrubbed hydrogen-rich stream emerges from the scrubber via the recycle scrubber overhead line <NUM> and a recycle portion in recycle line <NUM> may be added to the make-up hydrogen stream in make-up line <NUM> for supplying a second stage hydrogen stream in second hydrogen line <NUM> to the second stage hydrotreating unit <NUM>. Accordingly, the second stage hydrogen stream in second hydrogen line <NUM> may be taken from the first stage vapor stream in the hot overhead line <NUM> and the first stage cold vapor stream in the first stage cold overhead line <NUM>. Another portion of the scrubbed hydrogen-rich stream in the recycle scrubber overhead line <NUM> may be purged in line <NUM> and/or forwarded to a hydrogen recovery unit <NUM>. The recycle scrubbing column <NUM> may be operated with a gas inlet temperature between <NUM> (<NUM>°F) and <NUM> (<NUM>°F) and an overhead pressure of <NUM> MPa (gauge) (<NUM> psig) to <NUM> MPa (gauge) (<NUM> psig).

A demetallized first stage liquid stream exits the first hydrotreating unit <NUM> and the first stage separation section <NUM> in the first stage liquid stream transported in the first hot liquid line <NUM> with a reduced concentration of metals, sulfur and nitrogen relative to the resid stream in line <NUM>. The second stage hydrogen stream in second hydrogen line <NUM> is heated in a fired heater and mixed with the demetallized resid stream in the first hot separator bottoms line <NUM> and fed to the second hydrotreating unit <NUM>. The first stage liquid stream is still at elevated temperature and may not need further heating before entering the second stage hydrotreating unit <NUM>. In an embodiment, the second hydrotreating unit <NUM> comprises a first desulfurization reactor <NUM> and a second desulfurization reactor <NUM> which may include a hydrodesulfurization (HDS) catalyst. More or less desulfurization reactors may be used. The HDS catalyst may comprise nickel or cobalt and molybdenum on gamma alumina to convert organic sulfur to hydrogen sulfide. The HDS catalyst may have a monomodal distribution of mesoporous pore sizes with at least <NUM>% of the pores on the catalyst particle being in the range of <NUM>-<NUM>. The first desulfurization reactor <NUM> and the second desulfurization reactor <NUM> may be operated in series with the effluent from the first desulfurization reactor <NUM> cascading into an inlet of the second desulfurization reactor <NUM>. The first desulfurization reactor <NUM> and the second desulfurization reactor <NUM> desulfurizes the demetallized resid feed to reduce the sulfur concentration in the demetallized resid stream by <NUM> to <NUM> wt% and typically <NUM> to <NUM> wt% to produce a desulfurized effluent stream exiting the second desulfurization reactor <NUM> in a desulfurized effluent line <NUM>. The bulk of the desulfurization, however, does occur in the first stage hydrotreating unit <NUM>.

Preferred reaction conditions in each of the first desulfurization reactor <NUM> and the second desulfurization reactor <NUM> include a temperature from <NUM> (<NUM>°F) to <NUM> (<NUM>°F), suitably <NUM> (<NUM>°F) to <NUM> (<NUM>°F) and preferably <NUM> (<NUM>°F) to <NUM> (<NUM>°F), a pressure from <NUM> MPa (gauge) (<NUM> psig) to <NUM> MPa (gauge) (<NUM> psig), preferably <NUM> MPa (gauge) (<NUM> psig) to <NUM> MPa (gauge) (<NUM> psig), a liquid hourly space velocity of the fresh resid feed from <NUM> hr-<NUM> to <NUM> hr-<NUM>, preferably from <NUM> to <NUM> hr-<NUM>, and a hydrogen rate of <NUM><NUM>/m<NUM> (<NUM>,<NUM> scf/bbl) to <NUM>,<NUM><NUM>/m<NUM> oil (<NUM>,<NUM> scf/bbl), preferably <NUM><NUM>/m<NUM> oil (<NUM>,<NUM> scf/bbl) to <NUM>,<NUM><NUM>/m<NUM> oil (<NUM>,<NUM> scf/bbl).

The second stage desulfurized resid stream may exit the second desulfurization reactor <NUM> in the desulfurized effluent line <NUM>, be cooled by heat exchange perhaps with the first stage hydrogen stream in line <NUM> (not shown) and enter the second stage separation section <NUM> comprising a second stage hot separator <NUM>. The second stage separation section <NUM> comprises one or more separators in downstream communication with the second hydrotreating unit <NUM> including the second stage hot separator <NUM>. The first desulfurized effluent line <NUM> delivers a cooled desulfurized effluent stream to the second stage hot separator <NUM>. Accordingly, the second stage hot separator <NUM> is in downstream communication with the first desulfurization reactor <NUM> and the second desulfurization reactor <NUM>.

The second stage hot separator <NUM> separates the desulfurized effluent stream to provide a hydrocarbonaceous, second stage vapor stream in a second hot overhead line <NUM> and a hydrocarbonaceous, second stage hot liquid stream in a second hot bottoms line <NUM>. The second stage hot separator <NUM> may operate at <NUM> (<NUM>°F) to <NUM> (<NUM>°F) and preferably operates at <NUM> (<NUM>°F) to <NUM> (<NUM>°F). The second stage hot separator <NUM> may be operated at a slightly lower pressure than the second desulfurization reactor <NUM> accounting for pressure drop through intervening equipment. The second stage hot separator <NUM> may be operated at pressures between <NUM> MPa (gauge) (<NUM> psig) and <NUM> MPa (gauge) (<NUM> psig). The hydrocarbonaceous, the second stage vapor stream in the second hot overhead line <NUM> may have a temperature of the operating temperature of the second stage hot separator <NUM>. The second stage hot liquid stream in the second hot bottoms line <NUM> may be fed to a hot flash drum <NUM>.

The second stage hot vapor stream in the second hot overhead line <NUM> may be cooled by heat exchange before entering a second stage cold separator <NUM>. The second stage cold separator <NUM> is in downstream communication with the hot overhead line <NUM> of the second stage hot separator <NUM>. At a characteristic sublimation temperature, ammonia and hydrogen sulfide in the second hot overhead line <NUM> will combine to form ammonium bisulfide and ammonia, and chlorine will combine to form ammonium chloride. To prevent deposition of ammonium bisulfide or ammonium chloride salts in the second hot overhead line <NUM> transporting the second hot vapor stream, a suitable amount of wash water may be introduced into the second hot overhead line <NUM> by a second water wash line <NUM>.

The second stage hot vapor stream may be separated in the second stage cold separator <NUM> to provide a second stage cold vapor stream which becomes the first stage hydrogen stream comprising a hydrogen-rich gas stream including ammonia and hydrogen sulfide in a second cold overhead line <NUM> and a second stage cold liquid stream in a second cold bottoms line <NUM>. The second stage cold separator <NUM> serves to separate hydrogen rich gas from hydrocarbon liquid in the second stage hot vapor stream into the second stage cold vapor stream for recycle to the first stage hydrotreating unit <NUM> in second cold overhead line <NUM>. The second stage cold vapor stream rich in hydrogen can be compressed in a compressor <NUM> for recycle as the first stage hydrogen stream in the first hydrogen line <NUM>. Accordingly, the first stage hydrogen stream in the first hydrogen lien <NUM> may be taken from the second stage vapor stream in second stage hot overhead line <NUM> and the second stage cold vapor stream in the second stage cold overhead line <NUM>. In an aspect, the water stream is pumped into the first stage hydrogen stream in line <NUM> from the water feed line <NUM>, mixed therewith and heated with the first stage hydrogen stream in one or more heat exchangers before it is mixed with the resid feed stream <NUM>.

The second stage cold separator <NUM> may be operated at <NUM>°F (<NUM>) to <NUM>°F (<NUM>), suitably <NUM>°F (<NUM>) to <NUM>°F (<NUM>), and just below the pressure of the second desulfurization reactor <NUM> and the second stage hot separator <NUM> accounting for pressure drop through intervening equipment to keep hydrogen and light gases in the overhead and normally liquid hydrocarbons in the bottoms. The second stage cold separator <NUM> may be operated at pressures between <NUM> MPa (gauge) (<NUM> psig) and <NUM> MPa (gauge) (<NUM>,<NUM> psig). The second stage cold separator <NUM> may also have a boot for collecting an aqueous phase. The second stage cold liquid stream in the second cold bottoms line <NUM> may have a temperature of the operating temperature of the cold separator <NUM>. The second stage cold liquid stream in the second cold bottoms line <NUM> may be delivered to the cold flash drum <NUM> and be separated together in the cold flash drum <NUM>. In an embodiment the second stage cold liquid stream in the second cold liquid bottoms line <NUM> may be mixed with the first stage cold liquid stream in the first cold bottoms line <NUM> and be separated together in the cold flash drum <NUM>.

The hydrocarbonaceous second hot liquid stream in the second hot bottoms line <NUM> may be sent to fractionation. In an aspect, the second hot liquid stream in the second hot bottoms line <NUM> may be let down in pressure and flashed in a hot flash drum <NUM> to provide a hot flash vapor stream of light ends in a hot flash overhead line <NUM> and a hot flash liquid stream in a hot flash bottoms line <NUM>. The hot flash drum <NUM> may be in direct, downstream communication with the second hot bottoms line <NUM> and in downstream communication with the second hydrotreating unit <NUM>. In an aspect, the hot flash liquid stream in the flash hot bottoms line <NUM> may be forwarded to product fractionation which may be preceded by stripping to remove hydrogen sulfide from product streams including a desulfurized resid stream. Accordingly, a stripping column and a fractionation column may be in downstream communication with the hot flash drum <NUM> and the hot flash bottoms line <NUM>.

The hot flash drum <NUM> may be operated at the same temperature as the second hot separator <NUM> but at a lower pressure of between <NUM> MPa (gauge) (<NUM> psig) and <NUM> MPa (gauge) (<NUM> psig), suitably no more than <NUM> MPa (gauge) (<NUM> psig). The flash hot liquid stream in the flash hot bottoms line <NUM> may have a temperature of the operating temperature of the hot flash drum <NUM>.

In an aspect, the second cold liquid stream in the second cold bottoms line <NUM> may be sent to fractionation. In a further aspect, the second cold liquid stream may be let down in pressure and flashed in a cold flash drum <NUM> to separate fuel gas from the second cold liquid stream in the second cold bottoms line <NUM> and provide a cold flash liquid stream in a cold flash bottoms line <NUM>. The cold flash drum <NUM> may be in direct downstream communication with the second cold bottoms line <NUM> of the cold separator <NUM>. In a further aspect, the cold flash drum <NUM> may separate the first cold liquid stream in the first cold bottoms line <NUM> to provide a fuel gas stream in a cold flash overhead line <NUM> and a cold flash liquid stream in a cold flash bottoms line <NUM>. In an aspect, the second cold liquid stream in the second cold bottoms line <NUM> and the first cold liquid stream in the first cold bottoms line <NUM> may be flash separated in the cold flash drum <NUM> together. The cold flash liquid stream in the cold flash bottoms line <NUM> may be sent to product fractionation which may be preceded by stripping to remove hydrogen sulfide from product streams including a desulfurized resid stream. Accordingly, a stripping column and a fractionation column may be in downstream communication with the cold flash drum <NUM> and the cold flash bottoms line <NUM>.

The first cold liquid stream in the first cold bottoms line <NUM> and the second cold liquid stream in the second cold bottoms line <NUM> may enter into the cold flash drum <NUM> either together or separately. In an aspect, the first cold bottoms line <NUM> joins the second cold bottoms line <NUM> and feeds the cold flash drum <NUM> together.

The cold flash drum <NUM> may be operated at the same temperature as the second cold separator <NUM> but typically at a lower pressure of between <NUM> MPa (gauge) (<NUM> psig) and <NUM> MPa (gauge) (<NUM> psig) and preferably between <NUM> MPa (gauge) (<NUM> psig) and <NUM> MPa (gauge) (<NUM> psig). A flashed aqueous stream may be removed from a boot of the cold flash drum <NUM>. The flash cold liquid stream in the flash cold bottoms line <NUM> may have the same temperature as the operating temperature of the cold flash drum <NUM>.

Experimentation was conducted to determine the improving effect of the subject process on desulfurization of a resid stream with steps of demetallation in Example <NUM> and desulfurization in Example <NUM>. The feedstock was Arabian medium atmospheric resid having <NUM>,<NUM> wppm sulfur, <NUM> wppm nickel, <NUM> wppm vanadium and <NUM> wt% Conradson carbon residue. The apparatus involved three tubular down flow reactors. Reactor <NUM> was loaded with KFR-<NUM> catalyst available from Albemarle designed for hydrodemetallation reaction. Reactor <NUM> was loaded with <NUM> wt% KFR-<NUM> catalyst and <NUM> wt% <NUM> KFR-<NUM> catalyst available from Albemarle also designed for hydrodemetallation reactions. Reactor <NUM> was loaded with KFR-<NUM> catalyst available from Albemarle designed for hydrodesulphurization reactions. All reactors were also loaded with inert quartz in the catalyst bed as diluent to ensure uniform flow distribution.

Example <NUM> consists of one pair of experiments conducted to determine effect of water injection. The same configuration was applied with hydrodemetallation and hydrodesulfurization catalysts using Reactor <NUM>, Reactor <NUM> and Reactor <NUM> in series at the same temperature and weight hourly space velocity and with no interstage separation. The only difference was the feed to the demetallation reactor in Experiment 1B was injected with water while Experiment 1A had no water injection into the feed.

Table <NUM> shows the experimental conditions for the single stage example for Reactors <NUM>, <NUM> and <NUM> using both HDM and HDS catalyst. Water rate is based on fresh feed weight. The temperature was the catalyst weight averaged temperature. The weight hourly space velocity was based on the weight of the hydrocarbon resid feed only.

Example <NUM> consisted of one pair of experiments conducted to determine a baseline hydrodemetallation performance using Reactor <NUM> and Reactor <NUM> only at the same temperature with and without water injection to exemplify the first demetallation stage. Products were collected to be used as demetallized feed for the second desulfurization stage.

Table <NUM> shows the experimental conditions for the first stage example for Reactors <NUM> and <NUM> using HDM catalyst only. The water rate was based on fresh feed weight. The temperature was the catalyst weight averaged temperature. The weight hourly space velocity was based on the weight of the hydrocarbon resid feed only.

Example <NUM> consisted of one pair of experiments conducted to determine a baseline hydrodemetallation performance using Reactor <NUM> and Reactor <NUM> only at a same temperature with and without water injection to exemplify the first demetallation stage. Products were collected to be used as demetallized feed for the second desulfurization stage. The key difference of Example <NUM> from Example <NUM> lies in the reactor temperatures.

Demetallized resid products from Example <NUM> were used as feed to the desulfurization stage of Example <NUM> to exemplify a process with and without interstage separation to remove hydrogen sulfide. To represent the two stage concept having a separation step, hydrogen sulfide concentration was reduced to <NUM> and the flow rate was reduced by <NUM> wt% to represent removal of the first stage vapor stream from the demetallized resid feed stream. Because the apparatus could not retain the vapor from the first stage, we added <NUM> vol% hydrogen sulfide to the feed to the second desulfurization stage to represent the base case without interstage vapor removal. Unisim simulation software was used to determine hydrogen sulfide concentrations and overall flow rates with and without interstage separation. To keep comparisons equivalent, we reduced the flow rate of feed in the water injection case with interstage separation to maintain space velocities equivalent. For the water injection with interstage separation case, the flow rate was reduced by <NUM> wt% similar to the interstage case.

Table <NUM> shows the conditions and results for the second desulfurization stage. The weight hourly space velocity was based on the liquid hydrocarbon fed to the second desulfurization stage only. The temperature was the catalyst weight averaged temperature. The sulfur concentration was in the liquid product.

Similar to Example <NUM>, demetallized resid products from Example <NUM> were used as feed to the desulfurization stage of Example <NUM> to exemplify a process with and without interstage separation to remove hydrogen sulfide. To represent the two stage concept having a separation step, hydrogen sulfide concentration was reduced to <NUM> and the flow rate was reduced by <NUM> wt% to represent removal of the first stage vapor stream from the demetallized resid feed stream. Because the apparatus could not retain the vapor from the first stage, we added <NUM> vol% hydrogen sulfide to the feed to the second desulfurization stage to represent the base case without interstage vapor removal. Unisim simulation software was used to determine hydrogen sulfide concentration and overall flow rates with and without interstage separation. To keep comparisons equivalent, we reduced the flow rate of feed in the water injection case with interstage separation to maintain space velocities equivalent. For the water injection with interstage separation case, the flow rate was reduced by <NUM> wt% similar to the interstage case.

Tables <NUM>, <NUM> and <NUM> summarize desulphurization rate constant calculations using Formula <NUM> for the results from Tables <NUM>, <NUM> and <NUM>: <MAT>.

In Formula <NUM>, "k" is the rate constant. "WHSV" is weight hourly space velocity based on the liquid hydrocarbon fed to the first demetallation stage and the second desulfurization stage. "Temp" is averaged reactor temperature in °F taken over both stages. Sulfur content is applied as <NUM>/1x10<NUM> when in terms of wppm. "E/R" is an activation term equaling the activation energy for hydrodesulfurization over the gas constant. We have taken E/R as <NUM>,<NUM> with <NUM>°F as a reference temperature.

Table <NUM> calculates the reaction rate constant from the data of Example <NUM>.

The rate constant, k, indicates how fast organic sulfur is converted to hydrogen sulfide and hydrocarbon. The improvement in the rate constant for water injected into the demetallation stage is shown as <NUM><NUM>/hr.

Table <NUM> calculates the reaction rate constant for the data from related Examples <NUM> and <NUM>.

The rate constant, k, indicates how fast organic sulfur is converted to hydrogen sulfide and hydrocarbon. The improvement in the rate constant for water injected into the demetallation stage followed by removal of hydrogen sulfide before the desulfurization stage is greater than the improvement in the individual rate constant for each of water injection and hydrogen sulfide removal by <NUM>% for Examples <NUM> and <NUM>. Therefore, water injection into the demetallation stage followed by removal of hydrogen sulfide before the desulfurization stage provides an unexpected synergetic effect.

Table <NUM> calculates the reaction rate constant from the data from related Examples <NUM> and <NUM>.

The improvement in the rate constant for water injected into the demetallation stage followed by removal of hydrogen sulfide before the desulfurization stage is greater than the improvement in the individual rate constant for each of water injection and hydrogen sulfide removal by <NUM>% for Examples <NUM> and <NUM>. Therefore, water injection into the demetallation stage followed by removal of hydrogen sulfide before the desulfurization stage provides an unexpected synergetic effect in both data from pairs of Examples <NUM> and <NUM>, and Examples <NUM> and <NUM>.

Claim 1:
A process for hydrotreating a hydrocarbon resid stream comprising:
adding a water stream and a first stage hydrogen stream to a resid stream;
hydrotreating said resid stream over a demetallation catalyst to demetallize said resid stream in the presence of the first stage hydrogen stream to provide a demetallized resid stream reduced in metals and sulfur concentration;
separating said demetallized resid stream into a first stage vapor stream comprising hydrogen sulfide and a first stage liquid stream with a smaller concentration of hydrogen sulfide than in the demetallized resid stream;
adding a second stage hydrogen stream to said first stage liquid stream; hydrotreating said first stage liquid stream over a desulfurization catalyst and the second stage hydrogen stream to provide a desulfurized resid stream; and
separating said desulfurized resid stream to provide a second stage vapor stream and a second stage liquid stream and taking said first stage hydrogen stream from said second stage vapor stream.