- Email: [email protected]
An overview of industrial uses of hydrogen
ht. J. Hydrogen Enrvgy, Vol. 23, No. 7, pp. 593-598, 1998 Q 1998 Published by Elsevier Science Ltd on behalf of the International Association for Hydrogen Energy All rights reserved. Printed in Great Britain
Pergamon
PII: SO360-3199(97)00112-2
AN OVERVIEW
OF INDUSTRIAL
RAM RAMACHANDRAN” * BOC Gases, 100 Mountain -t BOC Gases, 575 Mountain
0360-3199/98 $19.00+0.00
USES OF HYDROGEN
and RAGHU
K. MENONt
Avenue, Murray Hill, NJ 07974, U.S.A. Avenue, Murray Hill, NJ 07974, U.S.A.
Abstract-Hydrogen is a very important molecule with an enormous breadth and extent of application and use. It is currently being used in many industries, from chemical and refining to metallurgical, glass and electronics. Hydrogen is primarily used as a reactant. But it is also being used as a fuel in space applications, as an “0, scavenger” in heat treating of metals and for its low viscosity and density. In this paper, current industrial uses of hydrogen in various industries in the industrial world will be summarized. Due to the increased use of heavier crude oils, containing higher amounts of sulfur and nitrogen and to meet stringent emission standards, need for hydrogen is experiencing a very rapid growth in the petroleum refining industry. Hence this application will be discussed in more detail. 0 1998 Published by Elsevier Science Ltd on behalf of the International Association for Hydrogen Energy
INTRODUCTION Hydrogen is one of the oldest known molecules and is used extensively by many industries for a variety of appli-
cations. Most of its use is based on its reactivity rather than its physical properties. Recently its use in petroleum refining has been growing very rapidly due to a combination of factors relating to changes in crude; environmental regulations such as limits of sulfur in diesel, allowable limits of NO, and SO, in off-gas emissions to the atmosphere, aromatic and light hydrocarbon concentrations in the gasoline etc. In this paper, various uses for hydrogen will be outlined and discussed. Following this, its use in petroleum refining industry will be addressed in more detail. Hydrogen’s use can be broadly divided into the following categories: 1. As a reactant in hydrogenation processes-here hydrogen atom is used to produce lower molecular weight compounds or to saturate compounds or to crack hydrocarbons or to remove sulfur and nitrogen compounds. 2. As a 0, scavenger-to chemically remove trace amounts of 0, to prevent oxidation and corrosion. 3. As a fuel in rocket engines. 4. As a coolant in electrical generators, to take advantage of its unique physical properties. HYDROGEN
AS A REACTANT
In majority of applications where hydrogen is used as a reactant, hydrogenation takes place to insert hydrogen
to saturate the molecule or to cleave the molecule to
remove heterogeneous atoms such as sulfur and nitrogen. In most of these applications, the reaction depends on hydrogen partial pressure and hence high purities and high pressures are employed in the process. Majority of hydrogen is used as a reactant in the chemical and petroleum industries. Among the major uses, ammonia production accounts for almost 50%; petroleum processing about 37%; methanol 8% [l]. As mentioned earlier, the usage in petroleum processing is expected to increase rapidly due to various environmental regulations. Hydrogen for these applications is typically produced from an on-site plant by either steam reforming of methane (SMR) over a catalyst or partial oxidation (PO,) of hydrocarbons followed by carbon monoxide/water shift. Petroleum
processing
In the petroleum industry, hydrogen is catalytically reacted with hydrocarbons in many ways. They include hydrocracking and hydroprocessing. In the hydrocracking process, cracking and hydrogenation of hydrocarbons takes place simultaneously to produce refined fuels with smaller molecules and higher H/C ratios. In the hydroprocessing, hydrogen is used to hydrogenate sulfur and nitrogen compounds and to finally remove them as H,S and NH3. The hydrogen demand for hydroprocessing has been steadily increasing. The primary reason for this are the tightening of regulations associated with unit emissions and as well as product specifications, the growing demand for lighter, hydrogen593
R. RAMACHANDRAN
594
rich products, such as gasoline, and the need for refiners to improve profitability margins by processing poorer quality crude. More information regarding this important use of hydrogen is provided later. Petrochemical production Many petrochemicals are produced using hydrogen. The major petrochemical produced using hydrogen is methanol. In methanol production, hydrogen and carbon monoxide are reacted over a catalyst at high pressures and temperatures. Other uses of hydrogen include butyraldehyde from propylene by 0x0 process; acetic acid from syngas, butanediol and tetrahydrofuran from maleic anhydride; hexamethylene diamine from adiponitrile; cyclohexane from benzene etc. In the production of polypropylene, hydrogen is used to control the molecular weight of the polymer. One newer use for hydrogen is in plastics recycling. Here the recycled plastics are melted; molten plastic is hydrogenated to crack it to produce lighter molecules which can again be reused to produce polymers. As the environmental regulations and consciousness of public grow, this may become more popular. Oil and,fat hydrogenation Hydrogen has been used extensively to decrease the degree of unsaturation in fats and oils. During this process, several changes take place and include: an increase in the melting point and enhanced resistance to oxidation that enables preservation for a longer period of time. These are typically carried out in presence of nickel catalysts. Hydrogen is also used as a reducing gas for catalysts such as nickel to convert it from oxide form to the active metal form. Fertilizer production Ammonia is the backbone of the fertilizer industry and is produced by reaction between nitrogen and hydrogen. Ammonia consumes about 50% of all the hydrogen produced in the world. The reaction takes place at high pressures where H, and N, are reacted to produce ammonia. Metallurgical
applications
In the production of nickel by Sherritt Gordon Process, hydrogen is used in the reduction stage. In this stage, nickel present in solution as sulfate in presence of ammonia is converted and precipitated as elemental nickel leaving ammonium sulfate. Electronics industry Hydrogen is used in epitaxial growth of polysilicon. This is done by wafer and circuit manufacturers. Hydrogen is used to reduce silicon tetrachloride to silicon for growth of epitaxial silicon.
and R. K. MENON
HYDROGEN
AS O2 SCAVENGER
In metallurgical processes, hydrogen mixed with N, is used for heat treating applications to remove O2 as Oz scavenger. 0, reacts with H, to form H,O, whose oxidation potential is much lower compared to OZ. This is used in annealing and furnace brazing, powered metal sintering etc. However, for stainless steel wire annealing the trend is towards 100% H,. Use of synthetic gas atmospheres, blended mixture of pure nitrogen and hydrogen stored at customer sites, has grown dramatically over the past few years. Replacement of dissociated ammonia generators by synthetic HZ/N, gas mixture has been one of key elements in the 10 to 15% annual growth in liquid nitrogen demand. In Boiling Water Reactors (BWR) in the nuclear industry, trace amounts of oxygen present in the water is found to cause Inter Granular Stress Corrosion Cracking (IGSCC). It is caused by excess oxygen which results when water dissociates due to the neutron flux in the core of a BWR. Hydrogen is used to scavenge oxygen levels to below 100 ppb. However, downstream of the core, 0, is added to recombine with the excess hydrogen. Left unattended, IGSCC leads to mechanical failure of the fuel elements that can result in higher radiation levels and premature decommissioning. Similar to the application in Boiling Water Reactor, hydrogen is also used in Pressure Water Reactors in the nuclear industry. In float glass manufacture, glass typically floats on a tin bath. A mixture of 4% H, in N, is used to prevent oxidation of molten tin bath. HYDROGEN
AS A FUEL
The primary application of hydrogen as fuel is in the Aerospace Industry. The combination of liquid hydrogen and oxygen has been used as propellants for various applications for a number of years. A mixture of liquid Hz and 0, has been found to release the highest amount of energy per unit weight of propellant which is a key criteria in the space applications. However, the cost of liquefaction, the ability to keep it as a liquid and safe handling aspects have kept liquid hydrogen away from other fuel applications such as automobiles. Since H, is known to burn with a higher efficiency [2] than gasoline and is the cleanest burning fuel, there is a large interest to apply it as a fuel in automobiles. The major issue in the area of storage of hydrogen is the associated cost. Metal hydrides, which reversibly adsorb hydrogen at room temperature and low pressures offer an opportunity in this area. Some of the hydrides under investigation includes LaNi, and TiFe. This offers an opportunity to store hydrogen in density higher than in liquid form and at low pressures and hence offer potential for automobile applications. However, the costs of the metal hydrides are still too high to make it attractive. Research is in progress in this area to address some of these issues. In addition to the use of hydrogen as a fuel for auto-
AN OVERVIEW
OF INDUSTRIAL
mobiles, its use for starting automobiles is being investigated. It has been estimated that most of the pollution from automobiles occur during the first few minutes after start when the catalytic. converter and engine are cold. If the engine can be started with hydrogen and once the engine and catalytic converter warm up, the fuel can be switched back to gasoline. It has been estimated that the pollution by this method will be substantially lower. Fuel cells In addition, extensive research is in progress to use hydrogen as a fuel in fuel cells. Fuel cells are electrochemical power generation devices and are classified based on the electrolyte material used. Electrolytes include alkali, phosphoric acid, proton exchange membrane, molten carbonate and solid oxide. Fuel, H,, at the anode gives up electrons that are transferred through an external load to the cathode where oxygen reacts to form water. Currently several pilot plants (over 100) are in demonstration stage in japan with capacities ranging from a few KW to several KW. The current installations are divided as follows: About 30% of the plants are installed for research, 20% for hotels and hospitals, 15% for industrial sector and 10% in office buildings. The activity in Europe seems to be following Japan with no installations in the US. H, is also considered where clean combustion is required. For example hydrogen is used in flame polishing of glass edges and in the manufacture of optical glass fibers via flame deposition. HYDROGEN USES DUE TO ITS UNIQUE PHYSICAL PROPERTY Viscosity for hydrogen is the lowest among fluids and hence used to reduce friction in rotating armature in electrical power generation systems. This subsequently reduces heat generation and hence the cooling duty. The viscosity of H, and He is about 0.009 and 0.019 cp at atmospheric pressure and 25°C. Even though the amount of hydrogen used for this application is not large, this is one of the few applications that depends on the physical property rather than the chemical reactivity. Even now H, is extensively used in Weather Balloons. Typically for these applications, H, gas in small quantities is produced by cracking of methanol. HYDROGEN
IN PETROLEUM
PROCESSING
Steady utilization of hydrogen in refineries commenced more than 50 years ago with the use of by-product hydrogen from naphtha reformers for the pretreatment of the reformer feed. Hydrogen utilization has subsequently expanded to include the treating of heavier streams, for upgrading processes in fuels and lubes portions of refineries. Although several means have evolved to upgrade and
USES OF HYDROGEN
595
extract hydrogen from refinery and chemical streams, which were previously not utilized or under-utilized, refiners have found it necessary, over the last decade, to steadily increase their availability of large volumes of hydrogen from a dedicated hydrogen plant or supply scheme. This scenario is not expected to change, due to legislative considerations involving both product specifications and plant emissions, and refiners’ profitability considerations. In modern refineries, hydrogen requirement is typically about 1 wt% of crude processed. In broad terms, the principal aspects of hydrogen utilization for upgrading hydrocarbon streams are as follows: l sulfur compound and halides removal, 0 metals removal, l saturation of olefins, diolefins and cycloolefins, 0 aromatics saturation: l isomerization, o removal of nitrogen and oxygen from compounds, l decyclization or ring-opening, and 8 cracking to lighter hydrocarbons.
Depending on the aspect emphasized, by suitably tailoring operating conditions and catalyst, the process is termed as hydrodesulfurization, hydrodemetallation, hydrofining, hydrotreating, hydrocracking, or hydreprocessing. It is important to note, however that several different types of reactions proceed in parallel, in addition to the main upgrading purpose. The utilization of hydrogen might be for process feed upgrading purposes or for upgrading of refined product. Examples of feed upgrading include: pretreating of naphtha reformer feed, hydrotreating of gas oils and other components of Fluid Catalytic Cracking (FCC) feed, and resid desulfurization and hydrotreating prior to Resid Fluid Catalytic Cracking (RFCC). The considerable synergy between feed hydroprocessing and catalytic cracking is the subject of several publications. Examples of product finishing include hydrofinishing of naphtha and distillate principally for sulfur removal. Hydroprocessing can result in upgrading of materials so that feed and product streams are roughly in the same boiling range, such as demetallation, low-severity desulfurization, and aromatics saturation for improving diesel cetane, smoke point for kerosene, and naphthalene saturation for jet fuel. On the other hand, for hydrodewaxing of lube oil stocks for pour point and stability improvement and hydrocracking of various fractions, process products can be significantly lighter than the feed. Typical processing schemes A process schematic for a typical hydrotreating unit is shown in Fig. 1 [3]. Typically the hydrocarbon feed and hydrogen stream are preheated and subsequently enter the top of a down flow fixed bed reactor. The hydrogen and hydrocarbon react in the presence of the metal oxide catalyst, such as CoMo or NiMo. Due to production of H,S in the process, the oxide catalyst actually is converted to metal sulfides. The reaction products are the upgraded
596
R. RAMACHANDRAN
and R. K. MENON
C, and lighter Hydrogen Recycle
Make up H, I
/\ Feed ~
Desulfurized Product Heater
Reactor
Hydrogen Separator
Stripper
Fig. 1. Catalytic hydrotreater.
hydrocarbon stream, hydrogen sulfide, ammonia, water, and coke and free metals which deposit on the catalyst. After cooling the reactor product is flashed to separate the hydrogen, which is typically recompressed and recycled to the reactor, and the hydrocarbon product is stripped of hydrogen sulfide and other lights in a stripper. Due to the solubility of hydrogen in oil, the hydrogen makeup requirements are several-fold compared to the amount required based on stoichiometry. Also the partial pressure of hydrogen required can be as high as 2500 psi for processing of heavier fractions. Hydrocracking was first developed as early as 1927 by I. G. Farben Industrie for converting lignite into gasoline, and subsequently adapted for upgrading petroleum fractions. In a modern refinery it typically supplements the role of catalytic cracking, and is used to process the feed stock which is more difficult to crack. Considerable integration of feed and product streams between hydrocracking, catalytic cracking, and thermal cracking (coking) processes can be expected. Hydrocracking typically involves feed stock preparation by hydrotreating to remove metals, sulfur, nitrogen and oxygen compounds, followed by either one- or two-stage cracking employing hydrogen. A process schematic for a two-stage hydrocracker, very similarto that illustrated for a basic hydrotreating unit, is shown in Fig. 2. Hydroprocessing schemes which afford the flexibility to achieve multimode objectives ranging from gas-oil desulfurization to hydrocracking to gasoline have also been commercialized [41.
In addition to fixed-bed reactors, other schemes employed include ebullated-bed reactors, moving bed
reactors, and slurry reactors. Ebullated bed reactors include the LC-fining process developed by Cities Services and C-E Lummus, and HRI’s H-Oil process. The liquid feed passes upwards through an ebullient catalyst bed, and the principal advantages are temperature control and the ability to withdraw and charge catalyst during operation. The authors know of at least one commercial movingbed bunker reactor. The Veba-combined cracking process (VCC) applies Bergius-Pier technology for conversion of heavies including coal to light products [5]. It combines liquid- and gas-phase hydrogenation and is claimed to be able to handle every type of resid including bitumen. About 5% of the material pass unconverted and this saturated residue can be destroyed by conventional combustion, CFB, or coking. Operating conditions Operating conditions can vary considerably and depend on the feed stock being treated and the conversion and products required. Typical operating ranges for fixed-bed reactor systems for a range of feed stock is summarized in Table 1. More severe conditions, including higher hydrogen partial pressure and lower space velocity, are required for heavier feed stock. Increased feed stock conversion to lighter boiling range material will considerably increase hydrogen requirement as seen by comparing the cases above for gas oil hydrotreating and hydrocracking. Effects on overall hydrogen balance are discussed in a following portion of this section.
AN OVERVIEW OF INDUSTRIAL
USES OF HYDROGEN
Hydrogen Recycle
-
597 C, and lighter
r-
----L-z4
r
Reactor
Heater
Hydrogen Separator Fig. 2. Two-stage hydrocracker.
Table 1. Typical operating ranges for conventional hydroprocessing
Temp, F Pressure,psig Hz Usage, SCF/Bbl LHSV, v/h/v
Naphtha pretreating
Distillate hydrofinishing
550-800 200-800 100-700 1.5-5.0
550-800 300-800 150-700 0.5-5.0
Gas oil hydrotreating 650-800 800-1600 300-800 0.5-1.5
Gas oil hydrocracking
Resid hydrotreating
700-800 2000-2800 1500-2500 0.8-1.5
650-840 2000-3000 500-2000 0.2-1.0
LHSV = Liquid hourly space velocity, volumetric flow per volume of catalyst.
Catalysts employed The active components of hydroprocessing catalysts are principally a hydrogenation component and promoter, and in some cases cracking components. Typical hydrogenation components are sulfides of molybdenum or tungsten, or metals such as palladium, platinum and other rare earths, and promoters include sulfide forms of nickel or cobalt. Cracking components include zeolites, amorphous silica alumina or phosphorous. Catalysts must be loaded into the reactors with care, and is performed by a number of techniques including sock loading. Although the catalysts are developed in the metal oxide forms, they are activated by presulfiding. This operation may be performed with a number of agents including mercaptans, dimethyl sulfide and over the years, several new agents have been developed for this purpose. The process of sulfiding is highly exothermic and is performed with care.
Whereas cobalt-molybdenum hydrotreating catalysts are preferred for desulfurization, nickel-molybdenum catalyst tend to be preferred if denitrogenation is also required. As indicated previously, whereas desulfurization takes place under less severe conditions with lower hydrogen consumption per barrel, greater saturation of aromatics and denitrogenation take place only under more severe conditions. Some key issues associated with the composition and shapes of hydrotreating catalyst are optimization of activity and selectivity and minimization of pressure drop and coking tendency. Catalysts with multi-modal pore size distributions have also been developed for effective demetallation of resid fractions. The catalysts are deactivated by a combination of metals deposition and coking over the process cycle. Regeneration that is accomplished by a number of steps, including coke burn off and fines removal, at the end of the cycle, is being increasingly performed off-site. Catalyst activity and selectivity are restored almost
R. RAMACHANDRAN
598
completely, and the catalyst can be used over several cycles before complete replacement. Overall
re$nery
hydrogen
balance
Typical examples of overall hydrogen balances in refineries are indicated in Table 2. Depending on the
and R. K. MENON refinery configuration and objectives, crude selection and product distribution, there can be considerable variation. In summary, hydroprocessing is one of the important processes within a refinery. Due to the increased processing of heavier, crudes containing hetero atoms and various environmental regulations, its importance is increasing rapidly within a refinery. CONCLUSION
Table 2. Typical refinery hydrogen balance
H2 Producing units Reformer Hz plant Hz Consumers Hydrocracker Gas oil HDT Distillate HDT Naphtha HDT Other
A, %
B, %
C, %
D, %
74 26
22 78
8 92
67
40
0 84 9
80 0 11 6
,68
11
3
0
26
21 2
6 1
33
0
23 9
A, B, C and D shows H, consumption and production for different refinery configurations, crudes and desired products.
A brief review of various uses of hydrogen in the industry is outlined. Hydrogen is being evaluated continuously for a variety of uses by many industries and its use is growing rapidly. REFERENCES I. Czuppon, T. A., Knez, S. A. and Newsome, D. S., KirkOtkmer Encyclopedia of Chemical Technology. New York, 13, 884, 1996. 2. McLaughlin, C. W., U.S. Govt. Res. Develop. Rept., 1966, 41(12), 114. 3. Gary, J. H. and Handwerk, G. E., Petroleum Rejning Tecknology andEconomics. Marcel Dekker, New York, 131,1987. 4. Aalund, L. R., Oil and Gas Journal, 1974,72(April l), 63.
5. Arnold, P., Technologies for disposal of refinery residues. Hydrocarbon Technology International, 1995,59(Autumn).
Pergamon
PII: SO360-3199(97)00112-2
AN OVERVIEW
OF INDUSTRIAL
RAM RAMACHANDRAN” * BOC Gases, 100 Mountain -t BOC Gases, 575 Mountain
0360-3199/98 $19.00+0.00
USES OF HYDROGEN
and RAGHU
K. MENONt
Avenue, Murray Hill, NJ 07974, U.S.A. Avenue, Murray Hill, NJ 07974, U.S.A.
Abstract-Hydrogen is a very important molecule with an enormous breadth and extent of application and use. It is currently being used in many industries, from chemical and refining to metallurgical, glass and electronics. Hydrogen is primarily used as a reactant. But it is also being used as a fuel in space applications, as an “0, scavenger” in heat treating of metals and for its low viscosity and density. In this paper, current industrial uses of hydrogen in various industries in the industrial world will be summarized. Due to the increased use of heavier crude oils, containing higher amounts of sulfur and nitrogen and to meet stringent emission standards, need for hydrogen is experiencing a very rapid growth in the petroleum refining industry. Hence this application will be discussed in more detail. 0 1998 Published by Elsevier Science Ltd on behalf of the International Association for Hydrogen Energy
INTRODUCTION Hydrogen is one of the oldest known molecules and is used extensively by many industries for a variety of appli-
cations. Most of its use is based on its reactivity rather than its physical properties. Recently its use in petroleum refining has been growing very rapidly due to a combination of factors relating to changes in crude; environmental regulations such as limits of sulfur in diesel, allowable limits of NO, and SO, in off-gas emissions to the atmosphere, aromatic and light hydrocarbon concentrations in the gasoline etc. In this paper, various uses for hydrogen will be outlined and discussed. Following this, its use in petroleum refining industry will be addressed in more detail. Hydrogen’s use can be broadly divided into the following categories: 1. As a reactant in hydrogenation processes-here hydrogen atom is used to produce lower molecular weight compounds or to saturate compounds or to crack hydrocarbons or to remove sulfur and nitrogen compounds. 2. As a 0, scavenger-to chemically remove trace amounts of 0, to prevent oxidation and corrosion. 3. As a fuel in rocket engines. 4. As a coolant in electrical generators, to take advantage of its unique physical properties. HYDROGEN
AS A REACTANT
In majority of applications where hydrogen is used as a reactant, hydrogenation takes place to insert hydrogen
to saturate the molecule or to cleave the molecule to
remove heterogeneous atoms such as sulfur and nitrogen. In most of these applications, the reaction depends on hydrogen partial pressure and hence high purities and high pressures are employed in the process. Majority of hydrogen is used as a reactant in the chemical and petroleum industries. Among the major uses, ammonia production accounts for almost 50%; petroleum processing about 37%; methanol 8% [l]. As mentioned earlier, the usage in petroleum processing is expected to increase rapidly due to various environmental regulations. Hydrogen for these applications is typically produced from an on-site plant by either steam reforming of methane (SMR) over a catalyst or partial oxidation (PO,) of hydrocarbons followed by carbon monoxide/water shift. Petroleum
processing
In the petroleum industry, hydrogen is catalytically reacted with hydrocarbons in many ways. They include hydrocracking and hydroprocessing. In the hydrocracking process, cracking and hydrogenation of hydrocarbons takes place simultaneously to produce refined fuels with smaller molecules and higher H/C ratios. In the hydroprocessing, hydrogen is used to hydrogenate sulfur and nitrogen compounds and to finally remove them as H,S and NH3. The hydrogen demand for hydroprocessing has been steadily increasing. The primary reason for this are the tightening of regulations associated with unit emissions and as well as product specifications, the growing demand for lighter, hydrogen593
R. RAMACHANDRAN
594
rich products, such as gasoline, and the need for refiners to improve profitability margins by processing poorer quality crude. More information regarding this important use of hydrogen is provided later. Petrochemical production Many petrochemicals are produced using hydrogen. The major petrochemical produced using hydrogen is methanol. In methanol production, hydrogen and carbon monoxide are reacted over a catalyst at high pressures and temperatures. Other uses of hydrogen include butyraldehyde from propylene by 0x0 process; acetic acid from syngas, butanediol and tetrahydrofuran from maleic anhydride; hexamethylene diamine from adiponitrile; cyclohexane from benzene etc. In the production of polypropylene, hydrogen is used to control the molecular weight of the polymer. One newer use for hydrogen is in plastics recycling. Here the recycled plastics are melted; molten plastic is hydrogenated to crack it to produce lighter molecules which can again be reused to produce polymers. As the environmental regulations and consciousness of public grow, this may become more popular. Oil and,fat hydrogenation Hydrogen has been used extensively to decrease the degree of unsaturation in fats and oils. During this process, several changes take place and include: an increase in the melting point and enhanced resistance to oxidation that enables preservation for a longer period of time. These are typically carried out in presence of nickel catalysts. Hydrogen is also used as a reducing gas for catalysts such as nickel to convert it from oxide form to the active metal form. Fertilizer production Ammonia is the backbone of the fertilizer industry and is produced by reaction between nitrogen and hydrogen. Ammonia consumes about 50% of all the hydrogen produced in the world. The reaction takes place at high pressures where H, and N, are reacted to produce ammonia. Metallurgical
applications
In the production of nickel by Sherritt Gordon Process, hydrogen is used in the reduction stage. In this stage, nickel present in solution as sulfate in presence of ammonia is converted and precipitated as elemental nickel leaving ammonium sulfate. Electronics industry Hydrogen is used in epitaxial growth of polysilicon. This is done by wafer and circuit manufacturers. Hydrogen is used to reduce silicon tetrachloride to silicon for growth of epitaxial silicon.
and R. K. MENON
HYDROGEN
AS O2 SCAVENGER
In metallurgical processes, hydrogen mixed with N, is used for heat treating applications to remove O2 as Oz scavenger. 0, reacts with H, to form H,O, whose oxidation potential is much lower compared to OZ. This is used in annealing and furnace brazing, powered metal sintering etc. However, for stainless steel wire annealing the trend is towards 100% H,. Use of synthetic gas atmospheres, blended mixture of pure nitrogen and hydrogen stored at customer sites, has grown dramatically over the past few years. Replacement of dissociated ammonia generators by synthetic HZ/N, gas mixture has been one of key elements in the 10 to 15% annual growth in liquid nitrogen demand. In Boiling Water Reactors (BWR) in the nuclear industry, trace amounts of oxygen present in the water is found to cause Inter Granular Stress Corrosion Cracking (IGSCC). It is caused by excess oxygen which results when water dissociates due to the neutron flux in the core of a BWR. Hydrogen is used to scavenge oxygen levels to below 100 ppb. However, downstream of the core, 0, is added to recombine with the excess hydrogen. Left unattended, IGSCC leads to mechanical failure of the fuel elements that can result in higher radiation levels and premature decommissioning. Similar to the application in Boiling Water Reactor, hydrogen is also used in Pressure Water Reactors in the nuclear industry. In float glass manufacture, glass typically floats on a tin bath. A mixture of 4% H, in N, is used to prevent oxidation of molten tin bath. HYDROGEN
AS A FUEL
The primary application of hydrogen as fuel is in the Aerospace Industry. The combination of liquid hydrogen and oxygen has been used as propellants for various applications for a number of years. A mixture of liquid Hz and 0, has been found to release the highest amount of energy per unit weight of propellant which is a key criteria in the space applications. However, the cost of liquefaction, the ability to keep it as a liquid and safe handling aspects have kept liquid hydrogen away from other fuel applications such as automobiles. Since H, is known to burn with a higher efficiency [2] than gasoline and is the cleanest burning fuel, there is a large interest to apply it as a fuel in automobiles. The major issue in the area of storage of hydrogen is the associated cost. Metal hydrides, which reversibly adsorb hydrogen at room temperature and low pressures offer an opportunity in this area. Some of the hydrides under investigation includes LaNi, and TiFe. This offers an opportunity to store hydrogen in density higher than in liquid form and at low pressures and hence offer potential for automobile applications. However, the costs of the metal hydrides are still too high to make it attractive. Research is in progress in this area to address some of these issues. In addition to the use of hydrogen as a fuel for auto-
AN OVERVIEW
OF INDUSTRIAL
mobiles, its use for starting automobiles is being investigated. It has been estimated that most of the pollution from automobiles occur during the first few minutes after start when the catalytic. converter and engine are cold. If the engine can be started with hydrogen and once the engine and catalytic converter warm up, the fuel can be switched back to gasoline. It has been estimated that the pollution by this method will be substantially lower. Fuel cells In addition, extensive research is in progress to use hydrogen as a fuel in fuel cells. Fuel cells are electrochemical power generation devices and are classified based on the electrolyte material used. Electrolytes include alkali, phosphoric acid, proton exchange membrane, molten carbonate and solid oxide. Fuel, H,, at the anode gives up electrons that are transferred through an external load to the cathode where oxygen reacts to form water. Currently several pilot plants (over 100) are in demonstration stage in japan with capacities ranging from a few KW to several KW. The current installations are divided as follows: About 30% of the plants are installed for research, 20% for hotels and hospitals, 15% for industrial sector and 10% in office buildings. The activity in Europe seems to be following Japan with no installations in the US. H, is also considered where clean combustion is required. For example hydrogen is used in flame polishing of glass edges and in the manufacture of optical glass fibers via flame deposition. HYDROGEN USES DUE TO ITS UNIQUE PHYSICAL PROPERTY Viscosity for hydrogen is the lowest among fluids and hence used to reduce friction in rotating armature in electrical power generation systems. This subsequently reduces heat generation and hence the cooling duty. The viscosity of H, and He is about 0.009 and 0.019 cp at atmospheric pressure and 25°C. Even though the amount of hydrogen used for this application is not large, this is one of the few applications that depends on the physical property rather than the chemical reactivity. Even now H, is extensively used in Weather Balloons. Typically for these applications, H, gas in small quantities is produced by cracking of methanol. HYDROGEN
IN PETROLEUM
PROCESSING
Steady utilization of hydrogen in refineries commenced more than 50 years ago with the use of by-product hydrogen from naphtha reformers for the pretreatment of the reformer feed. Hydrogen utilization has subsequently expanded to include the treating of heavier streams, for upgrading processes in fuels and lubes portions of refineries. Although several means have evolved to upgrade and
USES OF HYDROGEN
595
extract hydrogen from refinery and chemical streams, which were previously not utilized or under-utilized, refiners have found it necessary, over the last decade, to steadily increase their availability of large volumes of hydrogen from a dedicated hydrogen plant or supply scheme. This scenario is not expected to change, due to legislative considerations involving both product specifications and plant emissions, and refiners’ profitability considerations. In modern refineries, hydrogen requirement is typically about 1 wt% of crude processed. In broad terms, the principal aspects of hydrogen utilization for upgrading hydrocarbon streams are as follows: l sulfur compound and halides removal, 0 metals removal, l saturation of olefins, diolefins and cycloolefins, 0 aromatics saturation: l isomerization, o removal of nitrogen and oxygen from compounds, l decyclization or ring-opening, and 8 cracking to lighter hydrocarbons.
Depending on the aspect emphasized, by suitably tailoring operating conditions and catalyst, the process is termed as hydrodesulfurization, hydrodemetallation, hydrofining, hydrotreating, hydrocracking, or hydreprocessing. It is important to note, however that several different types of reactions proceed in parallel, in addition to the main upgrading purpose. The utilization of hydrogen might be for process feed upgrading purposes or for upgrading of refined product. Examples of feed upgrading include: pretreating of naphtha reformer feed, hydrotreating of gas oils and other components of Fluid Catalytic Cracking (FCC) feed, and resid desulfurization and hydrotreating prior to Resid Fluid Catalytic Cracking (RFCC). The considerable synergy between feed hydroprocessing and catalytic cracking is the subject of several publications. Examples of product finishing include hydrofinishing of naphtha and distillate principally for sulfur removal. Hydroprocessing can result in upgrading of materials so that feed and product streams are roughly in the same boiling range, such as demetallation, low-severity desulfurization, and aromatics saturation for improving diesel cetane, smoke point for kerosene, and naphthalene saturation for jet fuel. On the other hand, for hydrodewaxing of lube oil stocks for pour point and stability improvement and hydrocracking of various fractions, process products can be significantly lighter than the feed. Typical processing schemes A process schematic for a typical hydrotreating unit is shown in Fig. 1 [3]. Typically the hydrocarbon feed and hydrogen stream are preheated and subsequently enter the top of a down flow fixed bed reactor. The hydrogen and hydrocarbon react in the presence of the metal oxide catalyst, such as CoMo or NiMo. Due to production of H,S in the process, the oxide catalyst actually is converted to metal sulfides. The reaction products are the upgraded
596
R. RAMACHANDRAN
and R. K. MENON
C, and lighter Hydrogen Recycle
Make up H, I
/\ Feed ~
Desulfurized Product Heater
Reactor
Hydrogen Separator
Stripper
Fig. 1. Catalytic hydrotreater.
hydrocarbon stream, hydrogen sulfide, ammonia, water, and coke and free metals which deposit on the catalyst. After cooling the reactor product is flashed to separate the hydrogen, which is typically recompressed and recycled to the reactor, and the hydrocarbon product is stripped of hydrogen sulfide and other lights in a stripper. Due to the solubility of hydrogen in oil, the hydrogen makeup requirements are several-fold compared to the amount required based on stoichiometry. Also the partial pressure of hydrogen required can be as high as 2500 psi for processing of heavier fractions. Hydrocracking was first developed as early as 1927 by I. G. Farben Industrie for converting lignite into gasoline, and subsequently adapted for upgrading petroleum fractions. In a modern refinery it typically supplements the role of catalytic cracking, and is used to process the feed stock which is more difficult to crack. Considerable integration of feed and product streams between hydrocracking, catalytic cracking, and thermal cracking (coking) processes can be expected. Hydrocracking typically involves feed stock preparation by hydrotreating to remove metals, sulfur, nitrogen and oxygen compounds, followed by either one- or two-stage cracking employing hydrogen. A process schematic for a two-stage hydrocracker, very similarto that illustrated for a basic hydrotreating unit, is shown in Fig. 2. Hydroprocessing schemes which afford the flexibility to achieve multimode objectives ranging from gas-oil desulfurization to hydrocracking to gasoline have also been commercialized [41.
In addition to fixed-bed reactors, other schemes employed include ebullated-bed reactors, moving bed
reactors, and slurry reactors. Ebullated bed reactors include the LC-fining process developed by Cities Services and C-E Lummus, and HRI’s H-Oil process. The liquid feed passes upwards through an ebullient catalyst bed, and the principal advantages are temperature control and the ability to withdraw and charge catalyst during operation. The authors know of at least one commercial movingbed bunker reactor. The Veba-combined cracking process (VCC) applies Bergius-Pier technology for conversion of heavies including coal to light products [5]. It combines liquid- and gas-phase hydrogenation and is claimed to be able to handle every type of resid including bitumen. About 5% of the material pass unconverted and this saturated residue can be destroyed by conventional combustion, CFB, or coking. Operating conditions Operating conditions can vary considerably and depend on the feed stock being treated and the conversion and products required. Typical operating ranges for fixed-bed reactor systems for a range of feed stock is summarized in Table 1. More severe conditions, including higher hydrogen partial pressure and lower space velocity, are required for heavier feed stock. Increased feed stock conversion to lighter boiling range material will considerably increase hydrogen requirement as seen by comparing the cases above for gas oil hydrotreating and hydrocracking. Effects on overall hydrogen balance are discussed in a following portion of this section.
AN OVERVIEW OF INDUSTRIAL
USES OF HYDROGEN
Hydrogen Recycle
-
597 C, and lighter
r-
----L-z4
r
Reactor
Heater
Hydrogen Separator Fig. 2. Two-stage hydrocracker.
Table 1. Typical operating ranges for conventional hydroprocessing
Temp, F Pressure,psig Hz Usage, SCF/Bbl LHSV, v/h/v
Naphtha pretreating
Distillate hydrofinishing
550-800 200-800 100-700 1.5-5.0
550-800 300-800 150-700 0.5-5.0
Gas oil hydrotreating 650-800 800-1600 300-800 0.5-1.5
Gas oil hydrocracking
Resid hydrotreating
700-800 2000-2800 1500-2500 0.8-1.5
650-840 2000-3000 500-2000 0.2-1.0
LHSV = Liquid hourly space velocity, volumetric flow per volume of catalyst.
Catalysts employed The active components of hydroprocessing catalysts are principally a hydrogenation component and promoter, and in some cases cracking components. Typical hydrogenation components are sulfides of molybdenum or tungsten, or metals such as palladium, platinum and other rare earths, and promoters include sulfide forms of nickel or cobalt. Cracking components include zeolites, amorphous silica alumina or phosphorous. Catalysts must be loaded into the reactors with care, and is performed by a number of techniques including sock loading. Although the catalysts are developed in the metal oxide forms, they are activated by presulfiding. This operation may be performed with a number of agents including mercaptans, dimethyl sulfide and over the years, several new agents have been developed for this purpose. The process of sulfiding is highly exothermic and is performed with care.
Whereas cobalt-molybdenum hydrotreating catalysts are preferred for desulfurization, nickel-molybdenum catalyst tend to be preferred if denitrogenation is also required. As indicated previously, whereas desulfurization takes place under less severe conditions with lower hydrogen consumption per barrel, greater saturation of aromatics and denitrogenation take place only under more severe conditions. Some key issues associated with the composition and shapes of hydrotreating catalyst are optimization of activity and selectivity and minimization of pressure drop and coking tendency. Catalysts with multi-modal pore size distributions have also been developed for effective demetallation of resid fractions. The catalysts are deactivated by a combination of metals deposition and coking over the process cycle. Regeneration that is accomplished by a number of steps, including coke burn off and fines removal, at the end of the cycle, is being increasingly performed off-site. Catalyst activity and selectivity are restored almost
R. RAMACHANDRAN
598
completely, and the catalyst can be used over several cycles before complete replacement. Overall
re$nery
hydrogen
balance
Typical examples of overall hydrogen balances in refineries are indicated in Table 2. Depending on the
and R. K. MENON refinery configuration and objectives, crude selection and product distribution, there can be considerable variation. In summary, hydroprocessing is one of the important processes within a refinery. Due to the increased processing of heavier, crudes containing hetero atoms and various environmental regulations, its importance is increasing rapidly within a refinery. CONCLUSION
Table 2. Typical refinery hydrogen balance
H2 Producing units Reformer Hz plant Hz Consumers Hydrocracker Gas oil HDT Distillate HDT Naphtha HDT Other
A, %
B, %
C, %
D, %
74 26
22 78
8 92
67
40
0 84 9
80 0 11 6
,68
11
3
0
26
21 2
6 1
33
0
23 9
A, B, C and D shows H, consumption and production for different refinery configurations, crudes and desired products.
A brief review of various uses of hydrogen in the industry is outlined. Hydrogen is being evaluated continuously for a variety of uses by many industries and its use is growing rapidly. REFERENCES I. Czuppon, T. A., Knez, S. A. and Newsome, D. S., KirkOtkmer Encyclopedia of Chemical Technology. New York, 13, 884, 1996. 2. McLaughlin, C. W., U.S. Govt. Res. Develop. Rept., 1966, 41(12), 114. 3. Gary, J. H. and Handwerk, G. E., Petroleum Rejning Tecknology andEconomics. Marcel Dekker, New York, 131,1987. 4. Aalund, L. R., Oil and Gas Journal, 1974,72(April l), 63.
5. Arnold, P., Technologies for disposal of refinery residues. Hydrocarbon Technology International, 1995,59(Autumn).