HydroprocessingDr. George Georgiadis Hydroprocessing: Hydrocracking and Hydrotreating The terms hydrotreating, hydroprocessing, hydrocracking, and hydrodesulfurization are used rather loosely in the industry because, they all occur simultaneously and it is relative as to which predominates. Sources of Hydrogen in Refineries Hydrogen became available with the advent of platinum catalyst reforming. In the modern refinery hydrogen is scarce and its use is expected to increase. Hydrogen is used to produce higher yields and upgrade the quality of fuels produced by the refinery in several ways. Catalytic Reformer This is most important source of hydrogen for the refiner. Typically (avg.) 90 vol% from a continuously regenerated reformer and (avg.) 80 vol% from semi regenerated reformer. FCCU Off Gas Typically 5 vol% hydrogen with methane. Several methods for recovery. can be combined (a) Cryogenic (b) Pressure swing adsorption or (c) Membrane separation . ethane and propane. carbon dioxide. and water in a series of three reactions: Methane catalytically reacts to form hydrogen and carbon monoxide in an exothermic reaction Carbon monoxide “shifted” with steam to form additional hydrogen and carbon dioxide in an endothermic reaction Carbon dioxide removed using one of several absorption processes .Steam – methane Reforming Most common method of manufacturing hydrogen Uses methane. ethane. or heavy components reformed to hydrogen. . Process Flowsheet-SMR Process . 5 bar Temperature 950 F Pressure drop 25 psi Pre-reformer Effectiveness The reactor is assumed to achieve equilibrium concentrations.Operating Conditions for Reforming Section Equipment Flowsheet Element Parameter Baseline Temperature Steam feed e 950 F Pressure 30 bar Desulfurized feed to Temperature 950 F pre-reformer Pressure 28. . Pre-reformed feed to Temperature 1200 F primary reformer Pressure 27 bar Temperature 1500 F Pressure drop 25 psi Reformer Effectiveness The reactor is assumed to achieve equilibrium concentrations. Capital & Energy Costs $60 million (1991) including CO2 removal for a 100MMSCFD Fuel Consumption 315MBTU/MSCF Hydrogen . nitrogen. Its is however more expensive than steam reforming but can destroy a variety of polluted streams as well as low quality by product streams . water and sulfur. and other very heavy liquid or coal slurry. Synthesis gas will contain equal volumes of carbon monoxide and hydrogen with about 5 vol% carbon dioxide and smaller volumes of methane.Synthesis Gas Partial oxidation (gasification) of heavy resid feed using the ‘Water gas’ shift technology from asphalts. Hydrogen recovered normally by pressure swing adsorption or membrane separation. resids. oxygen and metals removed Olefinic and aromatic bonds saturated Reduce average molecular weight and produce higher yields of fuel products .Hydrotreating Removal of hetero atoms and saturation of carbon carbon bonds Nitrogen.Hydroprocessing . Hydrodesulfurization Remove sulfur compounds Minimum conversion of feed to lighter products 10% to 20% conversion . Hydrocracking Severe type of hydrotreating Cracking of carbon carbon bonds Drastic reduction of molecular weight 50%+ conversion . Hydrogen Consumption . Hydrogen Consumption The Amount of hydrogen consumed is a function of bonds broken. hydrogen lost with products and chemical consumption due to hydrogenation reactions that are generally exothermic. . This process creates some light ends. .Hydrodesulphurization Sulfur is converted to hydrogen sulfide (H2S) using hydrogen to break the carbon sulfur bonds and to saturate the remaining hydrocarbon chains. Heavier distillates make more light ends from breaking more complex sulfur molecules. more sulfur as disulphides and thiopenes. In heavier feeds. The form of the sulfur bonds in naphtha are generally mercaptans (thiols) and sulfides. As the feeds becomes heavier. such as in heavy distillate and gas oil hydrotreating. This nitrogen is converted to ammonia (NH3) although nitrogen removal is minor in naphtha hydrotreating.Hydrodenitrozation Pyridines and pyrroles are nitrogen containing compounds. Nitrogen removal requires about four times as much hydrogen as the equivalent sulfur removal. denitrogenation becomes more significant. . . Like nitrogen removal. oxygen removal is minor in naphtha hydrotreating but significant in heavy distillate hydrotreating.Hydrodeoxygenation Examples of oxygen containing compounds are phenols and peroxides and the oxygen converted to water (H2O). Oxygen requires about two times as much hydrogen as the equivalent sulfur removal. Other Contaminants Organic chlorides are converted to hydrogen chlorides that are usually present in small amounts and the hydrogen usage per molecule is similar to desulfurization . Olefins are prevalent in cracked streams such as naphtha streams from a coker or visbreaker. catalytic cracker cycle oil. . and catalytic cracker gasoline.Saturation of Hydrocarbons Olefins are saturated to form light hydrocarbons and the consumption is stoichiometric with one hydrogen molecule added for each double bond. and hydrocracking. . Selective catalysts are available for use in hydrotreating and catalytic cracking gasoline for sulfur removal but not to saturate olefins. This is a severe operation and the hydrogen consumption is a strong function of the complexity of the aromatics. Ring saturation arises in heavy distillate hydrotreating. gas oil hydrotreating. thus maintaining high octane ratings Aromatic rings are hydrogenated to cycloparaffins (naphthenes). Hydrogen Losses Hydrogen is lost in equilibrium with light gases. The amount is significant and may double the amount required for sulfur removal. Hydrogen is also absorbed in liquid products however this is usually small compared to hydrogen used for sulfur removal. Hydrogen is also removed with purge gas used to maintain a high purity of hydrogen as the light ends formed dilute the hydrogen concentration . Hydrocracking The Hydrocracker is similar to the FCC in that it is a catalytic process that cracks long chain gas oil molecules into smaller molecules that boil in the gasoline. jet fuel and diesel fuel range. . . First carbon bonds are broken followed by attachment of hydrogen.The fundamental difference is that cracking reactions take place in an extremely hydrogen rich atmosphere. Hydrocracker products are sulfur free and saturated. . High temperature 650-800˚F (345-425˚C) and very high pressures of 1500-3000 psi (105-210 bar) & circulation of large quantities of hydrogen to prevent catalyst fouling and permits long runs.Another difference is operating conditions. . Hydrocracker reactors contain multiple fixed beds of catalyst typically containing palladium. These catalysts are poisoned by sulfur and organic nitrogen. or nickel. so a high-severity HDS/HDN reactor pretreats feedstock prior to the hydrocracking reactors. platinum. . . Hydrocracker units may be configured in single stage or two stage reactor systems that enable a higher conversion of gas oil into lower boiling point material. jet fuel. jet fuel. and/or diesel Vacuum gas oil FCC LCO FCC HCO Coker LCGO Coker HCGO Naphtha. diesel. lube oil Naphtha Naphtha and/or distillates Naphtha and/or distillates Naphtha and/or distillates .Typical Hydrocracker Feedstocks Feed Kerosine Straight run diesel Products Naphtha Naphtha and/or jet fuel Atmospheric gas oil Naphtha. Hydrocracking Reactions Although there are hundreds of simultaneous chemical reactions occurring in hydrocracking. it is the general opinion that the mechanism of hydrocracking is that of catalytic cracking with hydrogenation superimposed . An example of the scission of a carbon–carbon single bond followed by hydrogenation . sometimes. . Careful preparation of the feed is also necessary in order to remove catalyst poisons and to give long catalyst life. Frequently the feedstock is hydrotreated to remove sulfur and nitrogen compounds as well as metals before it is sent to the first hydrocracking stage or. the first reactor in the reactor train can be used for this purpose. Typical Hydrocracker Products Heavy naphtha from the Hydrocracker makes excellent Catalytic Reformer feedstock. Distillates from Hydrocracking make excellent jet fuel blend stocks. . The yield across a Hydrocracker may exhibit volumetric gains as high as 20-25% making it a substantial contributor to refinery profitability. .Light ends are highly saturated and a good source of iso-butane for alkylation. Hydrogen Required for Hydrocracking . Hydrocracking Yields . 8 12.0 .Gas Production mol% wt% C1 C2 20 15 8.4 C3 Total 65 100 78.8 100. Gulf Coast.Catalytic hydrocracking unit investment cost: 1999 U. .S. Catalytic Hydrocracking Unit Cost Data . Hydrocracker Material Balance: 100. Alaska North Slope Crude Oil Basis (10.000 scf H2/bbl) .621 BPCD Fresh Feed. Severity.000 BPCD. 2. 000 scf H2/bbl) . Severity.Hydrocracker Material Balance: 100. 2.621 BPCD Fresh Feed. Alaska North Slope Crude Oil Basis (10.000 BPCD. Mlb/day Power. MMBtu/day 3. $/day 2124 .Hydrocracker Catalyst and Utility Requirements Steam. MkWh/day 797 138 Cooling water.3 138 Catalyst. Mgpn Fuel. 7°.65 bbl of isobutane is needed to produce 1 bbl of alkylate. and contains 1.7 wt% sulfur. and barrels of jet fuel produced per day. For the feed of problem 1. If the hydrocracking hydrogen consumption is 1500 scf/bbl of feed and the feed rate is 7500 BPSD. an API gravity of 23. . barrels of gasoline. Assume the hydrocracking hydrogen consumption is 1750 scf/bbl of feed. determine (a) (b) (c) total hydrogen consumption.A hydrocracker feedstock has a boiling range of 650 to 920°F. and 0. calculate the feed rate in barrels per day needed to produce sufficient isobutane for an alkylation unit producing 3500 BPD of alkylate. Hydrocracking refers to processes whose primary purpose is to reduce the boiling range and in which most of the feed is converted to products with boiling ranges lower than that of the feed. Hydrotreating and hydrocracking set the two ends of the spectrum and those processes with a substantial amount of sulfur and/or nitrogen removal and a significant change in boiling range of the products versus the feed are called hydroprocessing . halides. Objectionable elements removed by hydrotreating include sulfur. oxygen. Hydrotreating is a process to catalytically stabilize petroleum products and/ or remove objectionable elements from products or feedstocks by reacting them with hydrogen. Stabilization usually involves converting unsaturated hydrocarbons such as olefins and gum forming unstable diolefins to paraffins. nitrogen. . and trace metals. When the process is employed specifically for sulfur removal it is usually called hydrodesulfurization. . from naphtha to reduced crude. or HDS. To meet environmental objectives it also may be necessary to hydrogenate aromatic rings to reduce aromatic content by converting aromatics to paraffins. Hydrotreating is applied to a wide range of feedstocks. The cobalt and molybdenum oxides on alumina catalysts are in most general use today because they have proven to be highly selective. and vanadium oxide. and resistant to poisons. nickel thiomolybdate. They must be activated by converting the hydrogenation metals from the oxide to the sulfide form. easy to regenerate. tungsten and nickel sulfides. nickel oxide.Hydrotreating Catalysts Catalysts developed for hydrotreating include cobalt and molybdenum oxides on alumina. . although both catalysts will remove both sulfur and nitrogen. Cobalt–molybdenum catalysts are selective for sulfur removal and nickel– molybdenum catalysts are selective for nitrogen removal. . Reactions The main hydrotreating reaction is that of desulfurization but many others take place to a degree proportional to the severity of the operation. . . and space velocity. Although increasing temperature improves sulfur and nitrogen removal. excessive temperatures must be avoided because of the increased coke formation. hydrogen consumption. Increasing temperature and hydrogen partial pressure increases sulfur and nitrogen removal and hydrogen consumption. Increasing space velocity reduces conversion.Process Variables The principal operating variables are temperature. hydrogen partial pressure. Increasing pressure also increases hydrogen saturation and reduces coke formation. . and coke formation. The sulfur present as mercaptans (RSH).Naphtha Hydrotreating Naphtha is hydrotreated primarily for sulfur removal. disulfides (RSSR). Straight run gasoline may be added to naphtha prior to hydrotreating. and thiophenes (ring structures). sulfides (R2S). Combining offers advantages at the crude unit but calls for a larger hydrotreater and a splitter to separate Pentane/hexane overhead to isomerization as well as bottoms to reformer. . Naphtha Hydrotreating Process . Distillate Hydrotreating Process .