Petrochemicals- detailed information

 

Petrochemicals: 

Introduction:

• - In this lecture, we present a brief overview of petrochemical technologies and 
• discuss upon the general topology of the petrochemical process technologies.
• - Petrochemicals refers to all those compounds that can be derived from the 
• petroleum refinery products
• - Typical feedstocks to petrochemical processes include

1. C1 Compounds: Methane & Synthesis gas
2. C2 Compounds: Ethylene and Acetylene 
3. C3 Compounds: Propylene 
4. C4 Compounds: Butanes and ButenesA
5. AromaticCompounds: Benzene

• - It can be seen that petrochemicals are produced from simple compounds such as methane, ethylene and acetylene but not multicomponent products such as naphtha, gas oil etc. https://wwp.hrdtrd.com/redirect-zone/314547ed

  Definition : 

•   chemicals that are made from petroleum and natural gas. Petroleum and natural gas are made up of hydrocarbon molecules, which comprises of one or more carbon atoms, to which hydrogen atoms are attached. 
• About 5 % of the oil and gas consumed each year is needed to make all the petrochemical products. Petrochemicals play an important role on our food, clothing, shelter and leisure. Because of low cost and easy availability, oil and natural gas are considered to be the main sources of raw materials for most petrochemicals.

Classification:  

canbe broadly classified into three categories-

•  Light Petrochemicals: These are mainly used as bottled fuel and raw materials for other organic chemicals. The lightest of these -- methane, ethane and ethylene -- are gaseous at room temperature.The next lightest fractions comprise petroleum ether and light naphtha with boiling points between 80 and 190 degrees Fahrenheit.
•   Medium Petrochemicals: Hydrocarbons with 6 – 12 carbon atoms are called "gasoline", which are mainly used as automobile fuels. Octane, with eight carbons, is a particularly good automobile fuel, and is considered to be of high quality. Kerosene contains 12 to 15 carbons and is used in aviation fuels, and also as solvents for heating and lighting.
•   Heavy Petrochemicals: These can be generally categorized as diesel oil, heating oil and lubricating oil for engines and machinery. They contain around 15 and 18 carbon atoms with boiling points between 570 and 750 degrees Fahrenheit. The heaviest fractions of all are called "bitumens" and are used to surface roads or for waterproofing.
• Bitumens can also be broken down into lighter hydrocarbons using a process called "cracking."

Process Technology:

Reactors: 

• Reactors are the most important units in petrochemical processes. 
• Petrochemicals are manufactured by following simple reactions using relatively purer feedstocks. Therefore, reaction chemistry for petrochemicals manufacture is very well established from significant amount of research in this field. Essentially all petrochemical processes need to heavily depend upon chemical transformation to first product the purification.

Separation: 

• With distillation being the most important unit operation to separate the unreacted feed and generated petrochemical product, the separation processes also play a major role in the process flow sheet. Where multiple series parallel reactions are involved, the separation process assumes adistillation sequence to separate all products from the feed. A characteristic feed recycle will be also existent in the process topology. Apart from this, 
• other separation technologies used inpetrochemical processing units include phase separators, gravity settling units and absorption columns. Therefore, the underlying physical principle behind all these separation technologies is well exploited to achieve the desired separation.

Dependence on Reaction pathway: 

• A petrochemical can be produced in several ways from the same feedstock. This is based on the research conducted in the process chemistry. For instance, phenol can be produced 
• using the following pathways
•  Peroxidation of Cumene followed by hydrolysis of the peroxide
• Two stage oxidation of Toluene
• Chlorination of Benzene and hydrolysis of chloro-benzene

 Direct oxidation of Benzene:

• We can observe that in the above reaction schemes, there are two reaction pathways for phenol from benzene i.e., either chlorination of benzene or 
• oxidation of benzene. Therefore, choosing the most appropriate technology for production is a trivial task.

 Complexity in pathway:

•  In the above Cumeneexample case, it is interesting to note that toluene hydrodealkylation produces benzene which can be used to produce phenol. Therefore, fundamentally toluene is required for the generation of various petrochemicals such as benzene and phenol. In other words, there is no hard and fast rule to say that a petrochemical is 
• manufactured using a suggested route or a suggested intermediate petrochemical. ntermediate petrochemicals play a greater role in consolidating the manufacture of other downstream. petrochemicals

Manufacture of Methanol from Synthesis Gas:

Introduction:

• - Synthesis gas is H2 + CO
• - When synthesis gas is subjected to high pressure and moderate temperature conditions, it converts to methanol.
• - Followed by this, the methanol is separated using a series of phase separators and distillation columns.
• - The process technology is relatively simple

Reactions:

• - Desired: CO + 2H2  CH3OH
• - Side reactions: 
• CO+ 3H2  CH4 + H2O 2CO + 2H2  CH4 + CO2
• - All above reactions are exothermic
• - Undesired reaction: zCO + aH2  alchohols + hydrocarbons
• - Catalyst: Mixed catalyst made of oxides of Zn, Cr, Mn, Al.

Process Technology :

•  Methanol  andCO adjusted to molar ratio of 2.25
• - The mixture is compressed to 200 – 350 atms
• - Recycle gas (Unreacted feed) is also mixed and sent to the compressor
• - Then eventually the mixture is fed to a reactor. Steam is circulated in the heating tubes to maintain a temperature of 300 
• - After reaction, the exit gases are cooled
• - After cooling, phase separation is allowed. In this phase separation operation 
• methanol and other high molecular weight compounds enter the liquid phase 
• and unreacted feed is produced as the gas phase.
• - The gas phase stream is purged to remove inert components and most of the 
• gas stream is sent as a recycle to the reactor.
• - The liquid stream is further depressurized to about 14 atms to enter a second 
• phase separator that produces fuel gas as the gaseous product and the liquid 
• stream bereft of the fuel gas components is rich of the methanol component.
• - The liquid stream then enters a mixer fed with KMNO4 so as to remove traces 
• of impurities such as ketones, aldehydes etc.
• - Eventually, the liquid stream enters a distillation column that separates 
• dimethyl ether as a top product. 
• - The bottom product from the first distillation column enters a fractionator that 
• produces methanol, other high molecular weight alcohols and water as three 
• different products.

Formaldehyde and Chloromethanes:

Introduction:

• - In this lecture, we present the production technology for formaldehyde and 
• chloromethanes.
• - Formaldehyde is produced from methanol
• - Chloromethanes are produced from methane by chlorination route.

Formaldehyde production :

Reactions: 

1. Oxidation: CH3OH + 0.5 O2 HCHO + H2O
2.  Pyrolysis: CH3OH  HCHO + H2
3. Undesired reaction: CH3OH + 1.5 O2 2H2O + CO2

• In the above reactions, the first and third areexothermic reactions but the second reaction is endothermic. The reactions are carried out in vapour phase.
• Catalyst: 
• Silver or zinc oxide catalysts on wire gauge are used.
• Operating temperature and pressure: Near about atmospheric pressure and 500 – 600 oC

Process Technology :

• - Air is sent for pre-heating using reactor outlet product and heat integration concept.
• - Eventually heated air and methanol are fed to a methanol evaporator unit which enables the evaporation of methanol as well as mixing with air. The reactor inlet temperature is 54 oC.
• - The feed ratio is about 30 – 50 % for CH3OH: O2
• - After reaction, the product is a vapour mixture with temperature 450 – 900 oC
• - After reaction, the product gas is cooled with the heat integration concept and then eventually fed to the absorption tower.
• - The absorbent in the absorption tower is water as well as formaldehyde rich water.
• - Since formaldehyde rich water is produced in the absorption, a portion of the rich water absorbent solution from the absorber is partially recycled at a 
• specific section of the absorber.
• - From the absorber, HCHO + methanol rich water stream is obtained as the bottom product.
• - The stream is sent to a light end strippereventually to remove any light end compounds that got absorbed in the stream. The vapors from the light end unit consisting of light end compounds can be fed at the absorption unit atspecific location that matches with the composition of the vapors in the absorption column.
• - Eventually, the light end stripper bottom product is fed to a distillation tower that produces methanol vapour as the top product and the bottom formaldehyde + water product (37 % formaldehyde concentration).

Chloromethanes:

• Chloromethanes namely methyl chloride (CH3Cl),methylene chloride (CH3Cl2), Chloroform (CHCl3) and Carbon Tetrachloride (CCl4) areproduced by direct chlorination of Cl2 in a gas phase reaction without any catalyst.

Reactions:

• CH4 + Cl2 CH3Cl + H2
• CH3Cl + Cl2 CH2Cl2 + H2
• CH2Cl2 + Cl2 CHCl3 + H2
• CHCl3 + H2 CCl4 + H2
• - The reactions are very exothermic.
• - The feed molar ratio affects the product distribution. When CH4/Cl2 is about 1.8, then more CH3Cl is produced. On the other hand, when CH4 is chosen as a limiting reactant, more of CCl4 is produced. Therefore, depending upon the product demand, the feed ratio is adjusted.

Process Technology:

• - Methane and Cl2 are mixed and sent to a furnace
• - The furnace has a jacket or shell and tube system to accommodate feed pre-heating to desired furnace inlet temperature (about 280 – 300 oC).
• - To control temperature, N2 is used as a diluent at times.
• - Depending on the product distribution desired, the CH4/Cl2 ratio is chosen.
• - The product gases enter an integrated heat exchanger that receives separatedCH4 (or a mixture of CH4 + N2) and gets cooled from the furnace exit 
• temperature (about 400 oC).
• - Eventually, the mixture enters an absorber where water is used as an absorbent and water absorbs the HCl to produce 32 % HCl.
• - The trace amounts of HCl in the vapour phase are removed in a neutralizer fed with NaOH  The gas eventually is compressed and sent to a partial condenser followed with a phase separator. The phase separator produces two streams namely a liquid stream consisting of the chlorides and the unreacted CH4/N2.
• - The gaseous product enters a dryer to remove H2O from the vapour stream 
• using 98% H2SO4 as the absorbent for water from the vapour.
• - The chloromethanes enter a distillation sequence. The distillation sequence 
• consists of columns that sequentially separate CH3Cl, CH2Cl2, CHCl3 and CCl4.
• Lecture 16: Vinyl Chloride from Ethylene 
• Introduction
• - In this lecture we study the process technology involved in the production of 
• Vinyl Chloride from Ethylene
• - Vinyl chloride is produced in a two step process from ethylene
• o Ethylene first reacts with Chlorine to produce Ethylene dichloride
• o The purified Ethylene dichloride undergoes selective cracking to form 
• vinyl chloride
• - We first present the process technology associated to Ethylene Chloride

Ethylene dichloride:

Reactions:

• - C2H4 + Cl2 C2H4Cl2
• - Undesired products: Propylene dichloride and Polychloroethanes
• - Reaction occurs in a liquid phase reactor with ethylene dichloride serving as 
• the liquid medium and reactants reacting the liquid phase
• - Catalyst is FeCl3 or Ethylene dibromide

Process Technology :

• C2H4 and Cl2 are mixed and sent to the liquid phase reactor.
• - Here, the feed mixture bubbles through the ethylene dichloride product medium
• - Reactor operating conditions are 50 oC and 1.5 – 2 atms.
• - The reaction is exothermic. Therefore, energy is removed using either cooling jacket or external heat exchanger
• - To facilitate better conversion, circulating reactor designs are used. 
• - FeCl3 traces are also added to serve as catalyst
• - The vapour products are cooled to produce two products namely a vapour product and a liquid product. The liquid product is partially recycled back to the reactor to maintain the liquid medium concentration.
• - The vapour product is sent to a refrigeration unit for further cooling which will further extract ethylene dichloride to liquid phase and makes the vapour phase bereft of the product.
• - The liquid product is crude ethylene dichloride with traces of HCl. Therefore, acid wash is carried out first with dilute NaOH to obtain crude ethylene 
• dichloride. A settling tank is allowed to separate the spent NaOH solution and crude C2H4Cl2 (as well liquid).
• - The crude ethylene dichloride eventually enters a distillation column that separates the ethylene dichloride from the other heavy end products.
• - The vapour phase stream is sent to a dilute NaOH solution to remove HCl and produce the spent NaOH solution. The off gases consist of H2, CH4, C2H4 and C2H6.

Vinyl chloride production:

Reaction:

• - C2H4Cl2 CH2CHCl + HCl
• - Charcoal is used as the catalyst 
• - The reaction is a reversible gas phase reaction

Process Technology :

• Ethylene dichloride is initially vaporized using a heat exchanger fed with process steam
• - Ethylene vapors then enter a dryer that removes traces of water molecules
• - After drying, the vapors enter a pyrolysis furnace operated at 4 atm and 500 oC. The furnace is similar to a shell and tube arrangement with the gases 
• entering the tube side and hot flue gas goes past the tubes in the shell side. 
• - The product vapors eventually enter a quenching tower in which cold ethylene dichloride is used to quench the product gases and cool them
• The gases from the quench tower then enter a partial condenser which produces HCl as a gas and the liquid stream consisting of vinyl chloride, 
• unreacted ethylene dichloride and polychlorides.
• - The liquid stream from the quench tower as well as the condenser is fed to the vinyl still which produces the vinyl chloride product. The product is stabilized using a stabilizer as vinyl chloride is highly reactive without stabilizer.
• - The bottom product from the vinyl still is fed to a distillation column which separates the ethylene dichloride from the polychlorides. The ethylene 
• dichloride vapors are recycled back to the cracking furnace and the ethylene dichloride liquid is sent to the quenching tower to serve as the quenching 
• liquid.

Ethylene oxide and Ethanolamines:

Introduction:

• - In this lecture, we discuss upon the process technology for ethylene oxide and 
• ethanolamines.
• - Ethylene oxide is produced by the oxidation of ethylene using air
• - Ethanolamines are produced using the series reaction scheme of ethylene 
• oxide with ammonia.
• - Ethanolamines are significantly used as absorbents to remove CO2 and H2S 
• from process gas streams.

Ethylene Oxide:

Reactions:

• - C2H4 + 0.5 O2  CH2O.CH2O
• - Ethylene to air ratio: 3 – 10 %
• - Side reaction products: CO2, H2O
• - Catalyst: Silver oxide on alumina
• - Operating temperature and pressure: 250 – 300 oC and 120 – 300 psi
• - Supressing agent for side reactions: Ethylene dichloride
• - Reaction is exothermic

Process technology :

• Air and ethylene are separate compressed and along with recycle stream are sent to the shell and tube reactor
• The reactor is fed on the shell side with Dowtherm fluid that serves to maintain the reaction temperature. A dowtherm fluid is a heat transfer fluid , which is a mixture of two very stable compounds, biphenyl and diphenyl oxide. The fluid is dyed clear to light yellow to aid in leak detection.

• The hot dowtherm fluid from the reactor is sent to a waste heat recovery boiler to generate steam

•  The vapour stream is cooled using a integrated heat exchanger using the unreacted vapour stream generated from an absorber.

• The vapour stream is then sent to the heat integrated exchanger and is then sent back to the reactor and a fraction of that is purged to eliminate the accumulation of inerts such as Nitrogen and Argon.

•  The product vapors are compressed and sent to a water absorber which absorbs ethylene oxide from the feed vapors. Eventually, the ethylene oxide rich water stream is sent to a stripper which desorbs the ethylene oxide + water as vapour and generates the regenerated water as bottom product. The regenerated water reaches the absorber through a heat integrated exchanger.
•  The ethylene oxide + water vapour mixture is compressed (to about 4 - 5 atms) and then sent to a stripper to generate light ends + H2O as a top product and the bottom product is then sent to another fractionators to produce ethylene oxide as top product. The heavy ends are obtained as bottom product.

Ethanolamines:

Reactions:

• - Ethylene Oxide + Ammonia  Monoethanolamine
• - Monoethanolamine + Ammonia  Diethanolamine
• - DIethanolamine + Ammonia  Triethanolamine
• - The above reactions are series reaction scheme
• - Reaction is exothermic
• - Ammonia is in aqueous phase and ethylene oxide is in vapour state. Therefore, 
• the reaction will be gas-liquid reaction
• - Ethylene oxide is the limiting reactant

Process technology 

• Ammonia is mixed with ammonia recycle stream from the process and pumped to the CSTR where liquid phase ammonolysis takes place.

•  Ethylene oxide is compressed and fed to the CSTR.
•  The CSTR operating pressure will be such that the feed (and product) mixtures do not vaporize and good liquid phase reaction can occur.

•  The reactor is cooled using water in the cooling jacket as the reactions are mildly exothermic

• The product stream is then sent to a flash unit that separates NH3 + H2O as a vapour stream and water + ethanolamines as a liquid stream.

•  The ammonia + water stream is recycled to mix with the fresh ammonia and enter the reactor.

•  The bottom product from ammonia flash unit is sent to a water separation tower that again removes dissolved ammonia in the ethanolamine rich solution. Once again ammonia + water are generated and this stream is also recycled to mix with fresh ammonia feed.
• The bottom product consisting of crude mixture of ethanolamines and heavy ends.This mixture is fed to a monoethanolamine tower first to separate the monoethanol amine from the other two and heavy ends.The bottom product from the first distillation tower then enters the second and third distillation towers which are operated under vacuum to produce diethanolamine and triethanolamine as top products. The bottom product from the last distillation tower is the heavy ends product.

 Isopropanol and Acetone from Propylene:

Introduction:

• In this lecture we study the process technology associated to the manufacture 
• of isopropanol and acetone.
• - Isoprpanol is manufactured from hydration of propylene
• - Acetone is produced using the dehydrogenation route of isopropanol
• - We first present the isopropanol process technology

 Isopropanol manufacture:

Reaction:

• - Sulfation: CH3CHCH2 + H2SO4  (CH3)2CH(OSO3H) (Isopropyl acid 
• sulphate)
• - Hydrolysis: Isopropyl sulphate + H2O  Isopropanol + Sulfuric acid
• - Thus sulphuric acid is regenerated in the process
• - Side reaction: Disiopropyl sulphate + H2O  Diisopropyl ether + Sulfuric 
• acid
• - Therefore, the primary reaction is a gas liquid reaction in which propylene is 
• absorbed into a tray tower fed with sulphuric acid.
• - Operating conditions: Room temperature but 20 – 25 atms pressure
• - Reaction is highly exothermic

 Process technology :

• Either pure propylene or a mixture of Propylene and other C2, C3 components can be fed to a reactor.

•  The hydrocarbon feed is compressed and fed to the reactor at about 20 – 25 atms pressure.

•  Sulphuric acid of about 70% acid strength is fed in a countercurrent mode to the tray column where reactive absorption takes place. Here, sulfonation reaction takes place.

•  The reaction is highly exothermic and therefore, refrigerated brine is used to control the temperature in the absorber. Jacketed arrangement will be preferred for the tray absorption column to circulate the refrigerated brine in the cooling jacket. After reaction, the unreacted light ends such as saturated components will leave the unit as the gas stream.

•  The sulfonated product rich stream is then sent to a hydrolyzer cum stripper where isopropanol is produced and is vaporized due to existing stripper temperatures.

•  The hydrolyzer is fed with water to facilitate the conversion of the sulfonate product.

•  The isopropanol rich vapors then enter a caustic wash unit to remove the acidic impurities.

•  The isopropanol rich vapors then enter a partial condenser which separates the unreacted propylene from the alcohol + ether mixture. Here, propylene is separated as the vapour and alcohol + ether is separated as the liquid stream. 

•  The separated propylene gas is once again subjected to water wash to remove soluble impurities (such as ethers and alcohols). Subsequently, pure propylene is sent to mix with the fresh feed stream. Before sending to the unit, the propylene is cooled to room temperature so as to have identification conditions as the fresh feed stock.

•  The alcohol and ether enter a ether column that separates isopropyl ether which is returned to the reactor. The bottom product consisting of isopropyl alcohol and water is sent to a isopropyl alcohol column that produces water + heavy ends as the bottom product and 87 % isoprpanol-water azeotrope mixture as the top product.The azeotrope is sent to an azeotropic distillation column that uses isopropyl ether as a azeotropic agent to obtain 99 % isopropanol as the bottom product. 

• The top product is a mixture of isopropyl ether and water. The top product is a low boiling azeotrope. This stream upon gravity settling will produce the isopropyl ether as the top product which is sent as a reflux stream to the azeotropic column. The bottom product is a mixture of isopropanol and water is recycled back to the isopropyl alcohol column along with the bottom product generated from the ether separating column.

Acetone manufacture from isopropanol:

Reactions:

• Dehydrogenationo Isopropanol
• Isopropanol  Acetone + H2
• Reaction pressure: 3 – 4 atms
• Reaction temperature: 400 – 500 oC
• Copper catalyst on porous carrier is used
• Vapor phase reaction

Process Technology :

• First, Isopropanol is heated using steam to vaporize the same 
• - Then, Isopropanol is compressed to desired reactor pressure i.e., 4 – 5 atms
• - The compressed Isopropanol then enters a catalytic shell and tube reactor in 
• the tube side. The tube is packed with the porous copper catalyst
• - The reactor is operated at 400 – 500 oC using flue gas for heating. The flue gas 
• is passed in the shell side of the shell and tube reactor.
• - After reaction, the gases are condensed using cooling water condenser. The 
• condensed isopropanol and acetone are sent for fractionation.
• - The gases consisting of the remaining quantities of isopropanol and acetone 
• are absorbed into water using a water scrubber.
• - The acetone + isopropanol obtained from the condenser and water + 
• isopropanol +acetone are sent to an acetone fractionator that separates acetone 
• as the top product and isopropanol + water as bottom product.
• - The bottom product isopropanol + water from the acetone fractionators is sent 
• to a isoprpopanol column.
• - This column produces water as the bottom product and isopropanol as the top 
• product.
• - The water is cooled using a water condenser and sent to the water scrubber as 
• fresh water solvent.

Cumene and Acrylonitrile from Propylene:

Introduction:

• - In this lecture, we study the process technology associated to the production of 
• cumene and acrylonitrile from propylene
• - Both Cumene and Acrylonitrile are very important compounds that are 
• required for the manufacture of other downstream petrochemicals
• - We first present the process technology associated to the Cumene

Cumene::

Reactions:

• - C6H6+
• - The reaction is exothermic
• - Side reaction: 
• - C6H6 + C3H6 nC9H12
• - Catalyst: H3PO4 impregnated catalyst on porous carrier
• - Operating conditions: 25 atms pressure and 250 oC temperature.

Process technology :

• NPTEL – Chemical – Chemical Technology II
•  
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• - Propylene obtained from refinery processes as a mixture of propylene and 
• propane
• - The mixture along with benzene is compressed to 25 atms
• - Eventually the mixture enters a heat integrated exchanger to heat the pre-heat 
• the feed mixture.
• - The feed mixture enters a packed bed reactor.
• - The stream distribution in the packed bed reactor corresponds to cold shot 
• arrangement i.e., cold propane from the distillation column in the process is 
• added after every reactor with the product stream so that the temperature of 
• the stream is controlled.
• - Here, propylene is the limiting reactant and therefore, presumably all 
• propylene undergoes conversion.
• - Here, propane does not react but is a diluents or inert in the system. In that 
• way it controls the reaction temperature.
• - The reactor units are maintained at about 250oC
• - The product vapors are cooled using the heat integrated exchanger
• - The vapors then pass to a depropanizer which separates propane from the 
• product mixture.
• - The bottom product consisting of benzene, cumene and polyalkyl benzenes 
• enters another distillation column which separates benzene from the mixture 
• of cumene and polyalkyl benzene. The benzene stream is recycled to enter the 
• compressor.
• - The bottom product from the benzene column is sent to a cumene column 
• which produces cumene as top product and poly alkyl benzene as bottom 
• product.
• - Therefore, the entire process technology is nothing but a simple reactor 
• separator recycle arrangement.

Acrylonitrile:

Reactions:

• - C3H6 + NH3 + O2 C3H3N + H2O
• -
• - The reaction is exothermic
• - Stoichiometric ratio: C3H6 : NH3 : O2 = 1:1:1.5
• - Operating conditions: 1.5 – 3 atms pressure and 400 – 500oC
• - By products: Acetonitrile and Hydrogen cyanide from side reactions
• - Catalyst: Mo-Bi catalyst

Process Technology :

• Propylene + Propane, Air and Ammonia, Steamare compressed to required 
• pressure and are sent to the fluidized catalytic reactor consisting of the Mo-Bi 
• spherical catalyst. The reactor is maintained at 400 – 500oC.
• - Cyclone separator is also kept in the fluidized bed reactor in which catalyst 
• and product gases are separated after fludization. The contact time for 
• fluidization is in the order of seconds.
• - The product vapors then enter a water scrubber that does not absorb propane 
• and nitrogen from the products. The products absorbed in the water include 
• acrylonitrile, acetonitrile and other heavy ends.
• - The very dilute acryolonitrile (about 3 %) solution in water is sent to a 
• fractionator. The fractionators separates acrylonitrile + heavy ends + HCN + 
• light ends as a top product stream and acetonitrile + water + heavy ends as a 
• bottom product.
• - The top product then enters an extractive distillation column with water as 
• extractant. The azeotropic distillation column vapour is partially condensed to 
• obtain a vapour, aqueous and organic layer. The vapour consists of Light ends 
• and HCN and is let out. The organic layer consists of acrylonitrile and heavy 
• ends is sent for further purification. The aqueous layer is sent as a reflux to the 
• azeotropic column. In other words, addition of water enabled the formation of 
• a heterogenousazeotropic mixture at the top.
• - The bottom product from the azeotropic distillation column enters a product 
• purification unit along with oxalic acid where acrylonitrile is further purified 
• from heavy ends (+ oxalic acid) and is obtained as a 99.5 % pure product.
• In similarity to this, the bottom product from the product splitter enters an 
• azeotropic column which produces water as a bottom product. The total 
• condenser in this column generates both aqueous and organic layers. The 
• organic layer is rich in acetonitrile and heavy ends where as the aqueous layer 
• is sent back as a reflux to the azeotropic column.
• - The bottom product from the acetonitrile azeotropic column enters a 
• purification unit where distillation principle enables the separation of 
• acetonitrile from the heavy ends.

Butadiene and Benzene Manufacture:

Introduction:

• - In this lecture, we present the process technologies associated to Butadiene 
• and Toluene.
• - Butadiene manufacture is considered using n-Butane as the feed stock.
• - Benzene process technology refers to the famous hydrodealkylation process 
• that uses toluene as the feed stock.
• - We first present the process technology associated to Butadiene.

Butadiene:

Reactions:

• - Main reaction: n-Butane  Butadiene + Hydrogen.
• - Side reaction: n-Butane n-Butylene + Hydrogen.
• - Catalyst: Chromium oxide on alumina.
• - Coke deposition is a very important issue. Therefore, catalyst regeneration 
• needs to be carried out very frequently.
• - Reaction is exothermic .
• - Operating conditions: 650oC and 120-150 mm Hg (low pressure).
• - Feed stock: n-Butane with some isopentane from refinery processes.

Process Technology : 

• The separation network is extremely complex and involves quenching, 
• absorption, distillation and extractive distillation process.
• - First, the feed stock is pre-heated in a furnace along with unreacted gases that 
• have been recovered in the process using the separator network.
• - After pre-heating in a furnace to desired temperature, the gases enter the 
• catalytic packed bed reactors loaded with the catalyst. 
• - After the specified residence time, the product is withdrawn and the feed to the 
• unit is stopped. The product withdraw and stoppage of the feed flow to the 
• reactor unit is carried out using valves.
• - The coked catalyst is subjected to combustion using pre-heated air. Air pre-
• heating is done using steam in an extended area heat exchanger equipment. 
• Therefore during regeneration, another set of valves operate to allow the pre-
• heated air in and enable the product withdrawal after the combustion.
• - The pre-heated air not only removes the coke as CO2 but increases the reactor 
• temperature to 650 oC.
• - The flue gases are sent to a waste heat recovery boiler so as to generate steam 
• from water.
• - The entire operation of a feed entry, product withdrawal, pre-heated air entry 
• and combustion gases withdrawal from the packed bed reactor corresponds to 
• one single cycle.
• - Since the above operation is a batch operation, to make the operation 
• continuous in accordance to the separation network, two reactors are used and 
• these reactors are operated in cyclic fashion i.e., when the first reactor is 
• subjected to reaction, the second reactor is subjected to catalyst regeneration 
• and vice-versa.
• - The hot reactor outlet gases are sent to a quenching operation where light gas 
• oil is used to quench the gases using a recirculating quenching tower.
• - After product gases from the quenching tower are compressed and cooled to 
• enter an absorber
• - In this absorber, naphtha is used as an absorbent to absorb all hydrocarbons 
• except fuel gas.
• - The absorbent + hydrocarbons enter a stripper that produces fresh naphtha and 
• hydrocarbon mixture. The hydrocarbon mixture consists of unreacted feed 
• stock and butadiene and some heavy ends.
• - This mixture now enters a fractionator to separate the crude butadiene and 
• heavy ends.
• - The crude butadiene consists of butadiene and unreacted feed stock i.e., n-
• butane and isopentane. The separation of n-butane, other hydrocarbons with 
• butadiene is one of the difficult separations and they cannot be separated using 
• ordinary distillation. Therefore, a complicated route of separation is followed 
• next that involves azeotropic distillation using ammonia.
• The crude butadiene is mixed with ammoniated cuprous ammonium acetate 
• solution in a mixer settler. This solution is generated by absorbing ammonia 
• into fresh cuprous ammonium acetate solution.
• - The ammoniated cuprous ammonium acetate is sent to a mixer settler unit 
• where the butadiene dissolves in the ammoniated solution. The gas from the 
• mixer settler unit is recycled to mix with the feed stock and enter the pre-
• heater.
• - The ammoniated cuprous ammonium acetate solution is thereby stripped to 
• separate butadiene + ammonia from the ammonium acetate solution. The 
• regenerated fresh solvent is allowed to absorb NH3 and thereby enter the 
• mixer-settler unit.
• - The ammonia + butadiene mixture enters a fractionator fed with water. Here, 
• water interacts with ammonia and generates the ammonium hydroxide product 
• as the bottom product and butadiene is obtained as the top product.
• - The ammonia solution is subjected to stripping to separate water and 
• ammonia. The water is recycled back to the butadiene purifier and ammonia 
• is allowed to get absorbed into the fresh cuprous ammonium acetate solution.
• This process is not followed in India . In India, it is manufactured from ethanol 
• by catalytic cracking at 400-450 oC over metal oxide catalyst.