Petrochemical Industry Overview Lecture Notes PDF

Lecture 1: Fundamentals of Petrochemical Content Industry: Overview Petrochemical Value Chain Overview Feedstocks to the Industry Chemical value changes...

Lecture 1: Fundamentals of Petrochemical Content Industry: Overview Petrochemical Value Chain Overview Feedstocks to the Industry Chemical value changes Impact on the region 1 World of chemicals Speciality Petrochemicals chemicals Fertilizers Raw Consumer materials care products Basic inorganic Industrial gases Life sciences Basic +Intermediates 2  Feedstock Monomers\ Derivatives\ Specialties\ Upstream Retail processing Base chem Intermediates conversion Ethylene Oil Olefins Propylene C4s Benzene Gas Toluene Aromatics Coal Xylene Methanol 3 Feedstock Processing – Crude Oil Naphtha Associated Gas Gas Processing Petchem Feedstock Gasoline Crude Diesel Refining Kerosene LPG Fuel Oil Separation Blending Conversion Treatment 4  Dry Gas Wet (Methane) ~ 90% Gas Industry, Oil Residential, separator Electricity Water Sulfur\ separator Co2 Separator Ethane NGL Separator Fractionator Oil/Condensate Water ~ 10% Sulfur/Carbon Dioxide Propane Butane Light Naphtha 5 What's different? Horizontal drilling in low permeability source rock Multi-stage hydraulic fracturing with proppants Multiple wells from one well pad 6  Methanol Ethylene Methanol Propylene Methanol reactor Methanol to Olefins Plant Methanol to propylene Ammonia Urea DME Acrylic acid Vinyl Acetate COKE Calcium carbide Acetylene Polyvinyl chloride 7 Dehydration Ethanol Polymerization is broken into Transform of ethylene & water ethylene to LLDPE 8  Olefins straight chains ‘Unsaturated’ with a double carbon bond Ethylene Propylene Naptha Methane/Hydrogen Crude Oil Refinery H C H Crude C4s H C H Ethane Gas Separation Propane Pygas H Natural Gas Unit Butane BTX H C HeavyAromatics H C Condensates H C H C5/C6 Non Aromatics H Fuel Oil 9 Steam Cracking Product Mix by FeedStock Natural Gas Refinery Feedstocks Feedstocks 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Ethylene Propylene C4s Methane/Hydrogen BTX Other Pygas Fuel Oil 10  Petrochemical value chain Feedstock Monomers/ Derivatives/ Specialites/ Upstream Retail Processing base Chem intermediate Conversion s s Ethylene Polyethylene Ethane Ethylene Oxide Propane/Butane Naphtha EVC/PVC Styrene 11 12 13 14 15 MDI: Methylene diphenyl diisocyanate 16 17   In this lecture, we present a brief overview of petrochemical Lecture 2: technologies and discuss upon the Petrochemicals: general topology of the petrochemical process Overview technologies. 2.1Introduction  Petrochemicals refers to all those compounds that can be derived from the petroleum refinery products. 1 Petrochemicals : Overview 2  Typical feedstocks to petrochemical processes include  C1 Compounds: Methane & Synthesis gas  C2 Compounds: Ethylene and Acetylene  C3 Compounds: Propylene  C4 Compounds: Butanes and Butenes  Aromatic Compounds: Benzene 3  2.1.1 Definition :  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. 4  Classification of petrochemicals:  Petrochemicals can be broadly classified into three categories 1. Light Petrochemicals 2. Medium Petrochemicals 3. Heavy Petrochemicals 5 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. 6  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. 7 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 "bitumen" and are used to surface roads or for waterproofing. 8  2.2 Process Topology  Reactors: Reactors are the most important units in petrochemical processes. Petrochemicals are manufactured by simple reactions using relatively purer feedstocks. Therefore, reaction chemistry for petrochemicals manufacture is very well established from significant amount of research in this field.  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 flowsheet.  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. 9 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 chlorobenzene Direct oxidation of Benzene 10  2.4 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 11 2.4.2 Reactions to methanol production 12  2.4.3 Methanol Process Technology 2.4.3 Process Technology (Figure 2.1) Figure 2.1 Flow sheet of manufacture of Methanol from Synthesis Gas 13 Operating conditions H2 and CO adjusted to molar ratio of 2.25/1 The mixture is compressed to 200 – 350 atm 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 – 375℃ 14  Operating conditions  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 atm to enter a second phase separator that produces fuel gas as the gaseous product and the liquid stream lack of the fuel gas components is rich of the methanol component. 15 Feed and bottom product  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 16  2.4.4 Technical questions 1. Why pressure is not reduced for the first phase separator? Methanol is separated out in the liquid stream by just cooling the reactor product stream. Therefore, since the separation is achieved physically, there is no need to reduce the pressure of the stream. Also, if pressure is reduced, then again so much pressure needs to be provided using the compressor. 2. Why the pressure is reduced to 14 ATMs for the phase separator? The second phase separator is required to remove dissolved fuel gas components in the liquid stream at higher pressure. If this is not done, then methane will remain in the liquid stream and fractionators will produce methane rich ethers which don’t have value. Fuel gas on the other hand has value or it can be used as a fuel to generate steam in a boiler or furnace. 3. Why two compressors are used in the process flowsheet but not one? The main compressor is the feed compressor where feed is compressed to 3000 – 5000 psi. The second compressor is for the recycle stream which is brought to the reactor inlet pressure conditions by taking into account the pressure losses in the reactor, cooler and phase separator. 4. How multiple products are obtained from a single distillation column? Ans: This is an important question. Any distillation column consists of liquid reflux stream. Simulators will define the concentration on each tray. 17 18  References:  Dryden C. E., Outlines of Chemical Technology, East-West Press, 2008 Shreve R. N., Austin G. T.,  Shreve's Chemical process industries, McGraw – Hill, 1984 19  LECTURE 3: FORMALDEHYDE AND CHLOROMETHANES 1 3.1 INTRODUCTION We present the production technology for formaldehyde and chloromethanes. Formaldehyde is produced from methanol Chloromethanes are produced from methane by chlorination route. 2  3.2 FORMALDEHYDE PRODUCTION 3.2.1 Reactions In the above reactions, the first and third are exothermic reactions but the second reaction is endothermic. The reactions are carried out in vapor phase. Catalyst: Silver or zinc oxide catalysts on wire gauge are used. Operating temperature and pressure: Near about atmospheric pressure and 500 – 600℃ 3 Figure 3.1 Flow sheet of Formaldehyde production Figure 3.1 Flow sheet of Formaldehyde production 4  3.2.2PROCESS 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℃ The feed ratio is about 30 – 50 % for CH3OH: O2 After reaction, the product is a vapor mixture with temperature 450 – 900℃ 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. 5 3.2.2PROCESS TECHNOLOGY 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 stripper eventually 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 at specific 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 vapor as the top product and the bottom formaldehyde + water product (37 % formaldehyde concentration). 6 7 3.3TECHNICAL QUESTIONS 1. Why water + HCHO + methanol stream is sent 2. Suggest why pure formaldehyde is not produced in to a specific section of the absorber but not the top the process? section of the absorber? Ans: Pure formaldehyde is not stable and tends to Ans: This is to maximize the removal efficiency of produce a trimer or polymer. Formaldehyde is stable both water and formaldehyde rich solution. If both are in only water and therefore, 37% formaldehyde sent from the top, then formaldehyde rich solution solution with 3 – 15 % methanol (stabilizer) is will be dilute and not effective in extracting more produced as formalin and sold. HCHO + methanol from the gas phase stream. Uses of Formaldehyde: It is used as a preservative in food, paints and cosmetics. Used as an antiseptic in medicine, disinfectant in the funeral home, used in making RDX. To improve the yield of fuels it is used in petroleum and natural gas industries. It is also used in the manufacture of ink. 8  3.4 CHLOROMETHANES Chloromethanes namely methyl chloride (CH3Cl), methylene chloride (CH2Cl2), Chloroform (CHCl3) and Carbon Tetrachloride (CCl4) are produced by direct chlorination of Cl2 in a gas phase reaction without any catalyst. 9 3.4.1 REACTIONS The reactions are highly exothermic. The feed molar ratio affects the product distribution. When CH4/Cl2 is about 1.8, then more CH3Cl is produced. When CH4 is chosen as a limiting reactant, more of CCl4 is produced. Therefore, depending upon the product demand, the feed ratio is adjusted. 10  Figure 3.2 Flowsheet of Chloromethane production 11 3.4.2 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 preheating to desired furnace inlet temperature (about 280 – 300℃). 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 separated CH4 (or a mixture of CH4 + N2) and gets cooled from the furnace exit temperature (about 400℃). 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 vapor phase are removed in a neutralizer fed with NaOH 12  3.4.2 PROCESS TECHNOLOGY 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 vapor stream using 98% H2SO4 as the absorbent for water from the vapor. The chloromethanes enter a distillation sequence. The distillation sequence consists of columns that sequentially separate CH3Cl, CH2Cl2, CHCl3 and CCl4. 13 3.4.3TECHNICAL QUESTIONS  Why water is removed using the dryer?  Ans: Water enters the vapor system due in the absorption column where solvent loss to the vapor will be a common feature. Water molecule can react with the highly active intermediate chloromethanes to form oxychlorides, which are highly undesired.  Will there be any difficulty in separation by increasing boiling points of the chloromethanes in the distillation sequences?  Ans: Definitely yes. This is because the relative volatility of compounds at least slightly increases with reducing pressure and vice versa. But due to cooling water criteria in the distillation sequences also, there is no other way economical than doing distillation at higher pressure. 14  REFERENCES: Dryden C. E., Outlines of Chemical Technology, East-West Press, 2008 Shreve R. N., Austin G. T., Shreve's Chemical process industries, McGraw – Hill, 1984 15  Lecture 4: Hydrocarbon Steam Cracking for Petrochemicals 1 Hydrocarbon Steam Cracking for Petrochemicals 2  4.1 Introduction In industrial processes, hydrocarbons are contacted with H2O, depending upon the desired effect. When hydrocarbon vapors at very high pressures are contacted with water, water which has a very high latent heat of vaporization quenches the hydrocarbon vapors and transforms into steam. In such an operation, chemical transformations would not be dominant, and energy lost from the hydrocarbons would be gained by water to generate steam. 3 4.1 Introduction The quenching process refers to direct contact heat transfer operations and therefore has maximum energy transfer efficiency. This is since no heat transfer medium is used that would accompany heat losses. The steam cracking of hydrocarbons is an anti-quenching operation and will involve the participation of water molecule in reactions. Since steam and the hydrocarbons react in the vapor phase the reaction products can be formed very fast. Therefore cracking of the hydrocarbons on their own as well as by steam in principle is very effective. 4  Cracking of the hydrocarbons 5 4.1 Introduction When steam cracking is carried out, in addition to the energy supplied by the direct contact of steam with the hydrocarbons, steam also takes part in the reaction to produce wider choices of hydrocarbon distribution along with the generation of H2 and CO. Hydrocarbons such as Naphtha and LPG have lighter compounds. When they are subjected to steam pyrolysis, then good number of petrochemicals can be produced. These include primarily ethylene and acetylene along with other compounds such as propylene, butadiene, aromatics (benzene, toluene and xylene) and heavy oil residues. The reaction is of paramount importance to GCC as the petrochemical market is dominated by this single process. 6  4.2 Reaction CxHy + H2O + O2 → C2H4 + C2H6 + C2H2 + H2 + CO + CO2 + CH4 + C3H6 + C3H8 + C4H10 + C4H8 + C6H6 + C+ Heavy oils  The reaction is complex as we produce about 10 to 12 compounds in one go  The flowsheet will be reaction-separation-recycle system only in its topology. But the separation system will be complex.  Almost all basic principles of separation appears to be accommodated from a preliminary look. 7 Important separation tasks: Elimination of CO and CO2, Purification of all products such as ethylene, acetylene etc. The process can be easily understood if we follow the fundamental principles of process technology Typical feed stocks are Naphtha & LPG Reaction temperature is about 700 – 800℃ (Vapor phase reaction). 8  15.3 Process technology 4.3 Process (Figuretechnology 15.1) 1. Naphtha/LPG 4. After pyrolysis reaction, saturates is mixed with the products from the superheated steam furnace are sent to and fed to a furnace another heat recovery fuel gas + fuel oil as steam boiler to cool the fuels to generate heat product streams (from about 700 – 800oC) and 2. The superheated generate steam from steam is generated water. from the furnace itself using heat recovery 5. After this operation, boiler concept. the product vapors 3. The C2-C4 enter a scrubber that saturates are fed to is fed with gas oil as a separate furnace absorbent. The gas oil fed with fuel gas + removes solids and fuel oil as fuels to heavy hydrocarbons. Flow sheet of Hydrocarbon Steam Cracking for Petrochemical generate heat 9 Process description After this operation, the product vapors enter a scrubber The gas oil removes solids and that is fed with gas oil as heavy hydrocarbons. absorbent. Separate set of waste heat recovery boiler and scrubbers After scrubbing, both product are used for the LPG furnace gases from the scrubbers are and Naphtha steam cracking mixed and fed to a compressor. furnaces – 10  The compressed vapor is fed to a phase separation that separates the feed into two stream namely the vapor phase stream and liquid phase stream. Compressed The vapor phase stream consists of H2, CO, CO2 C1-C3+ components in excess. vapor The liquid phase stream consists of C3 and C4 compounds in excess. 11 CO2 in the vapor phase stream is removed using NaOH scrubber. Subsequently gas is dried to consist of only H2, CO, C1-C3 components only. This stream is then sent to a demethanizer which separates tail gas (CO + H2 + CH4) from a mixture of C1-C3 components. Gas stream The C2- C3+ components enter a dethanizerwhich processing separates C2 from C3 components. Here C2 components refer to all kinds of C2s namely ethylene, acetylene etc. Similarly, C3 the excess of propylene, and propane. The C2 components then enter a C2 splitter which separates ethane from ethylene and acetylene. 12  The ethylene and acetylene gas mixture is fed to absorption unit which is fed with an extracting solvent (such as N-methylpyrrolidinone) to extract Acetylene from a mixture of acetylene and ethylene. The extractant then goes to a stripper that generates Ethylene and acetylene by stripping. The regenerated solvent is fed back to the absorber. acetylene gas mixture The ethylene stream is fed to a topping and tailing still to obtain high purity ethylene and a mixture of ethylene and acetylene as the top and bottom products. The mixture of ethylene and acetylene is sent back to the C2 splitter unit as its composition matches to that of the C2 splitter feed. 13 Liquid stream processing The liquid stream consists of C3,C4, aromatics and other heavy oil components is fed to a NaOH scrubber to remove CO2 Eventually it is fed to a pre-fractionator. The pre-fractionator separates lighter components from the heavy components. The lighter components are mixed with the vapor phase stream and sent to the NaOH vapor phase scrubber unit. The pre-fractionator bottom product is mixed with the deethanizer bottom product. Eventually the liquid mixture enters a debutanizer that separates C3, C4 components from aromatics and fuel oil mixture. The bottom product eventually enters a distillation tower that separates aromatics and fuel oil as top and bottom products, respectively. The top product then enters a depropanizer that separates C3s from C4 components. 14  The C4 components then enter an extractive distillation unit that separates butane + butylenes from butadiene. C4 The extractive distillation unit consists of a distillation column coupled to a solvent components stripper. The solvent stripper produces butadiene and pure solvent which is sent to the distillation column. 15 C3 components The C3 components The saturates mixture enter a C3 splitter that is recycled to the separates propylene saturates cracking from propane + furnace as a feed butane mixture. stream. 16  4.4 Technical questions 1. Why two separate furnaces are used for C2-C4 saturates and Naphtha feed stocks? Ans: The purpose of steam cracking is to maximize ethylene and acetylene production. For this purpose if we mix C2-C4 saturates and naphtha and feed them to the same furnace, then we cannot maximize ethylene and acetylene production. The napntha steam cracker has its own operating conditions for maximizing ethylene and acetylene and so is the case for C2C4 saturates. 2. Why specifically the gases are compressed to 35 atm? Ans: The distribution of light and heavy components in vapour and liquid streams is critically dependent on the pressure. Therefore, the pressure of the system plays a critical role in the distribution of these key components. 17 References: Dryden C. E., Outlines of Chemical Technology, East-West Press, 2008 Shreve R. N., Austin G. T., Shreve's Chemical process industries, McGraw – Hill, 1984 18