ANILINE PLANT
Technology Supplied by: M/s Dupont of U.S.A. Basic engineering is done by: M/s Chematur Engg. AB of Sweden Detailed Engineering is done by: M/s IBI Chematur, Bombay CAPACITY AT 100% PLANT LOAD: 66.66 MT/DAY
Sr. No.
Raw Materials
Design Sp. Cons. per MT of ANILINE Production.
1
CNA
0.720 MT
2
H2
0.080MT
3
Catalyst (Wet) 1. 2. 3.
0.119 Kg
IN BUILT SAFETY FEATURE OF PLANT: The amines are a possible carcinogen that’s why special design is done in plant to protect personnel. The thickener and the spent catalyst filter are totally enclosed Surrounding Hydrogenation reactor, water sprinkler system is available for handling any emergency caused by hydrogen leakage. PROCESS DESCRIPTION:
1.1 GENERAL Most aniline is produced by reduction of nitrobenzene in various liquid and vapour phase reactions using a variety of catalyst. 1.2 INTRODUCTORY Du Pont has produced aniline from nitrobenzene by a proprietary catalysed liquid phase Hydrogenation process since 1960. The first production unit was situated in New Jersey, But is has now been dismantled. A plant at Beaumont, Texas, was started up in 1972 and is the sole Du Pont aniline production unit. 1.3 GENERAL PROCESS DESCRIPTION In Du Pont’s proprietary process, aniline and water are produced by the liquid phase, Catalytic hydrogenation of nitrobenzene with hydrogen. Nitrobenzene (NB) is fed through two stage of counter-current liquid-liquid extraction, where it is used to recover dissolved aniline from the water of reaction produced in the reaction between NB and hydrogen.
The NB from the extractors, containing small amounts recovered aniline, is preheated and fed to the bottom of the vertical, stage aniline reactor column for conversion to aniline. Aniline slurry of a precious metal on carbon catalyst, recycled water, recycled Aniline, and hydrogen is also fed to the base of the aniline reactor. Hydrogen dissolves in the liquid mixture and reacts with nitrobenzene to form aniline and water. The reactor operates at high-pressure bar g at a temperature which reaches a peak of about 215-225 C near mid-column. The heat of reaction between hydrogen and NB vaporizes most of the aniline and water and the crude products are taken overhead as vapour. A liquid side-stream is drawn from the top tray of the reactor, passes through a gas-liquid separator, and serves to recycle catalyst to the bottom of the reactor and to purge By-product tars from the system. The sidestream is cooled and a portion is passed through a catalyst thickner to remove soluble tars in a filtrate stream. All of the side-stream, except the thickener filtrate, is returned to the base of the aniline reactor. The thickener filtrate is transferred to the purge recovery column feed tank and then to the purge recovery column. This column operates under vacuum to recover aniline overhead and concentrate the tars in the column bottom. Crude aniline, containing non-reactor NB, water, and excess hydrogen, which leave the top of The reactor as vapours or gases, are cooled and condensed through a cooling train. This Cooling train consists of two waste heat boilers, which generates medium pressure steam, a set of boiler feed water pre-heaters and finally water-cooled heat exchangers. The final cooling is critical to reduce the temperature of the stream to <40C to promote gravimetric separation. After cooling, this stream enters a gas-liquid separator and pressure letdown tank where the un-reacted hydrogen is separated from the liquid water/aniline mixture. The un-reacted gases are discharged through a pressure control valve, which controls the pressure at the top of the aniline reactor, and are returned and used as fuel. The crude aniline and water are separated in a gravimetric decanter. The water wet crude aniline is transferred to storage for refining. The water phase, containing dissolved aniline is drawn off and stored in a coarse water tank for recycle as a direct coolant to the aniline reactor or for aniline recovery by extraction. As mentioned earlier, nitrobenzene and the excess water of reaction, which has been separated from crude aniline, is fed to the previously discussed liquid-
liquid extractors. The nitrobenzene extraction reduces the aniline content of the water to ppm levels. The water is then discharged to waste water treatment facilities. The crude aniline, which has been stored for refining, is fed to a dehydration column, which operates under vacuum, where stripping soluble water from the aniline dehydrates it. The overhead distillate is recycled to the crude product decanter for recovery of aniline and gravimetric separation of the water phase. The dehydrated aniline is preheated and fed to a Schiff”s base reactor. This is a large baffled vessel with steam coils, also operated under vacuum. In this reactor, minor quantities of low boiling impurities such as cyclohexyl-amine, cyclohexanone, diphenylamine, and cyclohexylaniline react with aniline, in a dry environment, to form water and a higher boiling Schiff”s base tar. The small amount of water of reaction, generated in this reactor, is stripped from the mass by heat from the steam coils, condensed and returned to the top of the dehydration column. The dry aniline is pumped from the Schiff’s base reactor to the aniline rectifier column, operated under vacuum, where it is refined to product specification material. The higher boiling Schiff”s bases tars are purged from the bottom of the rectifier column and are transferred to the purge recovery column. The thickener filtrate from the catalyst thickener is sent to the purge recovery column feed tank from which it is pumped to the purge recovery column. This column, operated under vacuum, recovers aniline together with water in the column overhead stream, which is sent back via off-decanter and water tank to aniline extractors and aniline reactor. 2.
ANILINE PLANT
INTRODUCTION Nitrobenzene is produced by the catalysed liquid phase reduction of nitrobenzene with Hydrogen in a vertical, tray reactor using a slurryfied precious metal catalyst. The synthesis process consists of several steps outlined as follows: NITROBENZENE FEED SYSTEM Nitrobenzene is pumped to the aniline area by the NB feed pumps (P0703 A/B). These centrifugal pumps transfer to the second stage extractor (S0901) where it is used as a solvent to extract aniline from process water. NB is also sent to the aniline Reactor NB feed tank (T1001) for level control.
PROCESS PARAMETERS Operating pressure Operating temperature
2 bar a 40 °C
EXTRACTOR FEED TANK The extractor feed tank (T0907) receives process water from the separation of crude aniline reactor product. This crude aniline reactor product includes crude aniline and process water of reaction from the hydrogenation of nitrobenzene. The excess process water is fed to the first stage extractor (S0905) for the recovery of aniline values prior to wastewater treatment. PROCESS PARAMETERS Operating pressure Operating temperature
Atmospheric 40 °C
EXTRACTORS This system consist of two stages of counter-counter, liquid-liquid extraction Which utilize static mixers to promote contact between phases. Nitrobenzene Extracts and recovers the dissolved aniline from the water generated in the Aniline synthesis reactor. The nitrobenzene, containing recovered aniline, Discharges from the first stage extractor (S0905) to a reactor NB feed tank (T1001) and is pumped by high – speed centrifugal pumps (P1002 A/B) to the aniline reactor (R1004) for conversion to aniline. The extracted process water, containing < 100 ppm (wt) of aniline, is transferred to waste treatment facilities. The extractors are comprised of two horizontal, cylindrical tanks, each equipped with an internal static mixer. After the intensive mixing the two forming phases are allowed to separate. The water phase overflows a baffle near the end of the vessel into a small component from which it is transferred by a centrifugal pump P0906 (first stage extractor)/P0904 A/B (second stage extractor). Nitrobenzene, the heavy phase, discharges through a nozzle in the bottom of the extractor vessel. Raw process water, containing about 4% (wt) aniline, is mixed with Nitrobenzene from the second stage extractor (S0901), and fed to the static Mixer in the first stage extractor (S0905). The light and heavy phases separate in the extractor vessel. The Nitrobenzene Phase discharges from the first stage extractor by gravity to the reactor NB feed tank (T1001). The water phase from the first stage extractor is transferred and mixed with fresh nitrobenzene as the feed to the second stage
extractor. The light and heavy phases separate in the extractor vessel. The nitrobenzene phase from the second stage Extractor is pumped (P0902 A/B) to the static mixture of the first stage extractor. The water phase from the second phase extractor is pumped to a storage tank (T9410) for Waste treatment. A portion of the heavy liquid from the each extractor can be recycled back to the static mixture feed point of that stage to maintain a high liquid velocity through the mixers. PROCESS PARAMETETRS Operating pressure Operating temperature
Atmospheric 40 C
REACTOR NB FEED TANK The reactor NB feed tank (T1001) receives nitrobenzene by gravity flow from the stage extractor. It serves as a minimum reservoir to prevent cavitations of the reactor NB feed pumps (P1002 A/B). Level in this tank is controlled by the NB feed to the extractors and a make-up stream of fresh nitrobenzene from storage through a separate level control valve. PROCESS PARAMETERS Operating pressure Operating temperature
Atmospheric 40 C
NB PREHEATER Nitrobenzene is preheated with steam in shell and heat exchanger (E1003), to Promote reaction, and is fed to the bottom of the aniline reactor (R1004). PROCESS PARAMETERS Operating pressure Operating temperature
20 bar a 125 C
ANILINE REACTOR The aniline reactor is a multi-stage, trayed, vertical column. Nitrobenzene, recycled process water, catalyst slurry, and aniline, are introduced into the bottom of the column, below the first tray. Hydrogen is fed to the bottom of the reactor through a ring pipe distributor. At operating pressure, hydrogen dissolves in the liquid mixture and reacts with nitrobenzene, in the presence of the catalyst, to form aniline and water. The reaction is highly exothermic and aniline and water are vaporized and removed overhead as vapour. The temperature of the reactor is controlled at a mid-column high temperature of 215-230 C by feeding recycled
process water and aniline. The reactor vapour line is provided with a rupture disc and relief valve in series to protect from vessel over-pressure. PROCESS PARAMETERS Operating pressure Operating temperature
18 bar a 215 C
DEGASIFIER Since catalyst particles tend to migrate to the top of the reactor, a liquid side stream containing aniline, tar, water and catalyst is drawn-off from the top tray of the reactor through a gas-liquid separator or Degasifier (S1005). The gas is returned to the vapour space above the top tray and the liquid side stream is processed through the catalyst recycle system. PROCESS PARAMETERS Operating pressure Operating temperature
17,85 bar a 210 C
SAFETY TANK The over-pressure protection devices on the reactor vapour line discharge to a safety tank (T1006), which contains and separates the gas and liquid discharged from the reactor, should an over-pressure occur. The vent on this tank is equipped with a Steam sparger to prevent light-off of gases by a lightning storm. This tank is also used to receive draining from the reactor when it is emptied for inspections and maintenance. Aniline and catalyst are recovered from the safety tank by filtration. PROCESS PARAMETERS Operating pressure Operating temperature
Atmospheric 40 C
REACTOR COOLING Aniline, water vapour and un-reacted hydrogen in the overheads of the aniline reactor pass through a cooling train, which cools and condenses these vapours. This cooling train consists of two kettle type steam boilers product condensers (E4301/E4302), one shell- and-tube product cooler (E4303), which boiler feed water, and two water cooled shell- and-tube trim coolers (E4304/E4305). The product condensers are a kettle type reboiler with process on the tube side of a U-tube bundle. The shell contains boiler feed water and produces steam at
two different Pressures. The boilers are equipped with two mesh type demisters (S4301.01/S4302.01) To prevent entrainment of boiler water in the stream, a blow-down is also provided to purge solids from the boiler. The product cooler is a shell-and-tube type heat exchanger with process on the tube side. Boiler feed water is on the shell side. The trim coolers are water-cooled, shell and tube type exchangers with process on the tube side and cooling tower water on the shell. They are designed to cool the water/aniline/non-condensable stream to a temperature that minimizes entrainment of liquid in the gas phase during subsequent separation and enhance separation of the aniline and water phases. PROCESS PARAMETERS Operating pressure,
E4301
17.6 bar a
Operating temperature, Operating pressure,
E4301 E4302
215° C 17.4 bar a
Operating temperature, Operating pressure, Operating temperature, Operating pressure, Operating temperature, Operating pressure, Operating temperature,
E4302 E4303 E4303 E4304 E4304 E4305 E4305
194 °C 17.1 bar a 146 °C 16.1 bar a 118 °C 16.1 bar a 55 °C
REACTOR LET - DOWN TANK The cooled reactor product mass, which consists of a gas phase and two Condensed liquid phases, enters a pressure let-down tank (S43060 which serves to separate the gas and liquid phases and control reactor pressure. It contains a Mesh type demister to minimise liquid carry-over with the gas stream. The gas phase, consisting of un-reacted hydrogen, is sent through the reactor pressure control valve to flare. The two liquid phases are transferred through a level control valve to the let - down tank separator (S4307). PROCESS PARAMETERS Operating pressure Operating temperature
11.4 bar a 40° C
LET - DOWN TANK SEPARATOR The two liquid phases enter a let - down tank separator (S4307), which separates any remaining dissolved gases from the liquids and vents them to the safety tank (T1006). PROCESS PARAMETERS Operating pressure Operating temperature
1.2 bar a 40 °C
CRUDE DECANTERS The cooled water and aniline products from the aniline reactor coolers are directed to one of two vertical, cylindrical decanters here the aniline and water phases are allowed to separate by gravity. One of these tanks is called the product decanter (S1101) and the other, the off-spec decanter (S1108). The water phase from these decanters overflow to the coarse water tank (T1114). The aniline phase from the product decanter is pumped (P1102A/B) to one of two crude analysis tanks (T1103/T1104). The aniline phase from the off-spec decanter is pumped (P1109 A/B) to rework aniline storage tank (T1110) PROCESS PARAMETERS Operating pressure
Atmospheric
Operating temperature
40 °C
COARSE WATER TANK Water from the product and off-spec decanters overflows into the coarse water tank (T1114). This tank serves as a reservoir for the cooling water supply to control the aniline reactor temperature. Any entrained aniline, which collects in the bottom of this tank, is pumped (P1117 A/B) back to the off-spec decanter. Excess process water is pumped (P1116 A/B) to the aniline reactor through the aniline extractors before it is transferred to waste treatment facilities. PROCESS PARAMETERS Operating pressure Operating temperature
Atmospheric 40 °C
CRUDE ANALYSIS TANKS The aniline phase from the product decanter (S1101) is pumped to one of two Crude Analysis tanks (T1103/T1104). These tanks are vertical, cylindrical tanks, which serve to provide hold-up time for analysis of the crude aniline being produced. The crude Aniline is analysed for nitrobenzene only to ensure good conversion in the reactor. One tank accumulates
crude aniline while the other is either being analysed or is being transferred to the crude aniline storage tank (T1106) or the rework aniline Storage tank (T1110). PROCESS PARAMETERS Operating pressure Operating temperature
Atmospheric 40 °C
CATALYST RECOVERY SYSTEM The liquid side stream from the degasifier (S1005) is cooled through a jacketed pipe, Trombone cooler (E4501) and enters a mechanically agitated thickener feed tank (T4502). Most of this stream, which contains aniline, catalyst, tar and some water is recycled to the catalyst feed tank (T4504) for return to the aniline reactor (R1004). PROCESS PARAMETERS Operating pressure, Operating temperature, Operating pressure, Operating temperature,
E4501 E4501 T4502 T4502
2 bar a 210 °C Atmospheric 95 °C
THICKENER A portion of the cooled, liquid side stream is processed through a thickener (F4508 A/B). The thickener serves to purge soluble tars from the aniline reactor system by removing a small stream of filtrate, which contains soluble tars generated in the aniline reactor. The bulk of the side stream slurry circulated through the thickener is returned to the thickener feed tank (T4502). The small stream of thickener filtrate is transferred to the purge recovery column feed tank (T1709) for further processing for aniline recovery and tar disposal. PROCESS PARAMETERS Operating pressure Operating temperature
6 bar a 95 °C
CATALYST FILTER A catalyst filter (F4509) is provided to recover catalyst solids for return to a Catalyst manufacturer for precious metals recovery whenever the aniline Reactor is emptied, or when material accumulates in the Safety Tank (T1006). PROCESS PARAMETERS Operating pressure Operating temperature
6 bar a 95 °C
CATALYST MIX TANK The catalyst mix tank (T4506) is a vertical, cylindrical tank equipped with a mechanical agitator. Aniline catalyst received from the catalyst supplier and slurries with aniline in this tank. As needed, this fresh catalyst slurry is transferred to the mechanically agitated reactor catalyst feed tank (T4504). PROCESS PARAMETERS Operating pressure Operating temperature
Atmospheric 40 °C
CATALYST FEED TANK The reactor catalyst feed tank (T4504) is a vertical, cylindrical tank with a conical Bottom head. This vessel is mechanically agitated. Recycled catalyst slurry from the thickener feed tank (T4502) and fresh catalyst from the catalyst mix tank (T4506), as needed, is transferred to the reactor catalyst feed tank. Recycled or rework aniline is also added to control the level in this tank to compensate for the removal of thickener filtrate. The catalyst/aniline slurry is fed by high - pressure centrifugal pumps (P4505 A/B) to the aniline reactor. An overflow line to the safety tank (T1006), is provided to collect material which may overflow the tank during upsets. PROCESS PARAMETERS Operating pressure Operating temperature
Atmospheric 85 °C
CRUDE ANILINE STORAGE TANK If the analysis of material in the analysis tanks (T1103/T1104) is less than two (2) parts Per million by weight of nitrobenzene in the crude aniline, the material is pumped to a vertical cylindrical crude aniline storage tank (T1106) for further processing. PROCESS PARAMETERS Operating pressure Operating temperature
Atmospheric 40 °C
REWORK ANILINE STORAGE TANK If the crude aniline is contaminated with two (2) parts per million by weight or greater of nitrobenzene, the material is pumped to the rework aniline storage tank (T1110) from which it is returned to the catalyst feed tank (T4504) and aniline reactor. Frequently, crude product aniline is transferred to rework storage to provide material make-up for the catalyst feed tank.
PROCESS PARAMETERS Operating pressure Operating temperature
Atmospheric 40 °C
WATER DRAW-OFF TANK Since water phase is lighter than aniline and may accumulate as a top layer in either the rework storage or crude aniline storage tanks, a small draw-off tank (T1112) is provided. Any water that accumulates can be decanted to the draw-off tank and transferred back to the off-specification decanter. PROCESS PARAMETERS Operating pressure Operating temperature
Atmospheric 40 °C
DEHYDRATION COLUMN Crude aniline, which contains about 5.5% (wt) of dissolved water, is pumped (P1107 A/B) From the crude storage tank to the dehydration column (C1201) for water removal. This Column is equipped with structured packing. Vacuum pumps (B1801/B1802) provide the necessary sub-atmospheric pressure for the column operation. A steam heated, forced draft reboiler (calandria) (E1203), and pumps (P1202 A/B) provide the circulated draft, provides boil-up for the column. An overhead condenser (E1204) condenses and cools the water and aniline mixture stripped from the crude material. The overheads stream is returned to the product decanter (S1101) where it is recycled to the process. The dry bottoms stream, containing < 0.05% (wt) of water, is pumped to the Schiff”s base Reactor (R1302) through the base reactor preheater (E1301). PROCESS PARAMETERS Column top pressure Column bottom pressure Column top temperature Column bottom temperature Bottom stream water content Reboiler exit temperature Condenser exit pressure Condenser exit temperature
0.10 bar a 0.11 bar a 73 °C 114 °C < 0,05% (weight) 132 °C 0.09 bar a 40 °C
BASE REACTOR PREHEATER This heater (E1301) is a shell-and-tube exchanger that heats the dry aniline from the bottom of the dehydration column to a higher temperature for processing in the Schiff”s base reactor
PROCESS PARAMETERS Operating pressure Operating temperature
2.2 bar a 150 °C
SCHIFF”S BASE REACTOR Cyclohexanone is a minor, low boiling by-product generated by the aniline reactor. A steam heated and baffled Schiff”s base reactor (R1302) vessel provides residence time to permit reacting of Cyclohexanone with aniline, in a dry environment, to produce a higher boiling Schiff”s Base and water. The base reactor preheater (E1301) and steam coils in the base reactor provide sufficient heat to aid in stripping the water of reaction. The reactor is operated at subatmospheric pressure and water of reaction is stripped as Overhead and condensed (E1304) for return to the dehydration column (C1201). PROCESS PARAMETERS Reactor operating pressure Reactor operating temperature Condenser exit pressure Condenser exit temperature
0.33 bar a 147 °C 0.32 bar a 40 °C
RECTIFIER COLUMN Dry aniline is pumped from the Schiff”s base reactor column (C1501).This column is A trade column. The column operates at sub-atmospheric pressure by the use of vacuum pumps(B1801/B1802). It has also a forced draft, steam heated reboiler (calandria) (E1503). Refined aniline is taken overhead and condensed in a water cooled condenser (E1504) from which it is pumped (P1507 A/B) to finished product analysis tanks (T1671/T1672).A small bottom stream is drawn from the rectifier column to remove tars and Schiff”s base as highboiling impurities. This stream is pumped either to the purge recovery Column (C1701) for recovery of aniline or directly to the tar heels tank (T9420) for disposal by burning in the incinerator (H9424). PROCESS PARAMETERS Column top pressure Column bottom pressure Column top temperature Column bottom temperature Reboiler exit temperature Condenser exit pressure Condenser exit temperature
0.10 bar a 0.15 bar a 111 °C 135.5 °C 155 °C 0.09 bar a 40 °C
PURGE RECOVERY COLUMN FEED TANK This is a vertical cylindrical tank. Thickener filtrate, containing soluble tars, is transferred to the purge recovery column feed tank (T1709), from which it is fed to the purge recovery column (C1701) for recovery of aniline and concentration of tars for disposal. PROCESS PARAMETERS Operating pressure Operating temperature
Atmospheric 80 C
PURGE RECOVERY COLUMN This column (C1701) is a trayed column, which is operated by a steam-heated Reboiler (E1703) at sub-atmospheric pressure. A water - cooled condenser (E1704) Recovers the water and aniline from the column overhead for return to the Process as rework material. The bottoms from this column contain tars, concentrated in a solution with aniline. This tar solution discharges from the Column and is pumped (P1702) to the tar heels tank (T9420) for subsequent disposal. PROCESS PARAMETERS Column top pressure Column bottom pressure Column top temperature Column bottom temperature Reboiler exit temperature Condenser exit pressure Condenser exit temperature
0.10 bar a 0.16 bar a 98 °C 140.1C 148.6 °C 0.09 bar a 40 °C
