petrochemical processes industry
DESCRIPTION
chem processTRANSCRIPT
Chapter 38 – P747
Petrochemical Processes
Dr. Hind Barghash CPI-14
Petrochemical processes are:
1- Lower alkenes
2- Synthesis gases (Syngas)
3- Polymerization
4- Formalin
CRUDE OIL
REFINARY
FEEDSTOCKSGas, Naphtha, Gas Oil, Kerosene
PETROCHEMICAL INDUSTRY
BASIC CHEMICALSEthylene, Propylene, 1.3-Butadiene &
BTX, PETROCHEMICALS
PE,PP,PVC,PS,PBR,MEG,LAB,ACN, AF, PTA, PHA, MA,CPL
Lower Alkenes: Petrochemicals-The OriginPetrochemicals-The Origin
Lower Alkenes: Building block Chemicals
Ethylene Propylene Butadiene (1,3) Benzene Toulene Xylenes
Petrochemicals from EthylenePetrochemicals from Ethylene
Petrochemicals from PropylenePetrochemicals from Propylene
AdiponitrileADN
PolybutadieneRubber
PBR
Styrene-ButadieneRubber SBR
Acrylonitrile-Butadiene
-Styrene ABS
Butadiene
Petrochemicals from ButadienePetrochemicals from ButadienePetrochemicals from BPetrochemicals from B
Specialty Polymers /Chemicals
Petrochemicals from BenzenePetrochemicals from Benzene
Toluene
Specialty/Functionalized
chemicals
XylenesBenzene
Petrochemicals from ToluenePetrochemicals from Toluene
Xylenes
O-Xylenep-Xylenem-Xylene
Phthalic anhydrideTerephthalic acidPTAIso-phthalic acid
PlasticizersPolyestersPET
Petrochemicals from XylenesPetrochemicals from Xylenes
Lower alkenes from oil
Chemical industry uses - 10% of available petroleum and natural gas as feed - 5% as fuel
Produced from steam cracking of various refinery streams. dehydrogenation reactions.
Example: Lower alkenes or olefins an important feed for products such as LDPP or HDPP.
Lower alkenes from oil
C5 olefins
(CH2=CH-CH=CH2)
Steam Cracking: Industrial ProcessA mixture of HC and steam are passed through tubes
inside a furnaceHeating occurs by convection and radiationConsiderable heat input at a high temperature levelLimited HC partial pressureVery short residence times (<1 s)Rapid quench of product to preserve composition
otherwise pyrolysis takes place
Dehydrogenation
Recently, the demand for propenes and butenes has been increasing.
Direct production for these specific alkenes is importantSelectively dehydrogenate the specific alkane (ie propane
to form propylene)Alkane dehyrogenation is highly endothermic
Dehydrogenation
Variables in these processes include:Type of catalyst usedReactor designMethod of heat supplyMethod for catalyst regeneration
Synthesis Gas - Syngas1/2
A mixture of CO and H in varying ratiosUses:
Refinery hydrotreating, hydrocrackingAmmoniaAlkenes Methanol, higher alcoholsAldehydesAcids
Synthesis Gas - Syngas2/2
Produced from coal, natural gas, etc.Major processes:
Steam reforming of NG or light HC in the presence of O2 or CO2
Partial oxidation of heavy HC with steam (H2O) and O2
Partial oxidation of coal with steam (H2O) and O2
Raw materials depend on cost and availability
Production of Syngas
Reactions to form SyngasGeneral reactions(1)C + H2O→ CO + H2 (steam reforming, endothermic)(2)C + ½ O2 → CO (partial oxidation, exothermic)(3)CO + H2O ↔ CO2 + H2 (water gas shift)
NG as a feed:(1) CH4 + H2O→ CO + 3H2 (steam reforming, endothermic)(2) CO + H2O ↔ CO2 + H2 (water gas shift)(3) CH4 + CO2 ↔2CO + 2H2
(4) 2CO ↔C + CO2
(6) CH4 + ½ O2 → CO + H2 (partial oxidation)(7) CH4 + 2O2 → CO2 + 2H2O(8) CO + ½ O2 → CO2
(9) H2 + ½ O2 → H2O
Steam Reforming1/2
High temperaturesNickel catalyst contained in tubes heated by a furnaceA mixture of NG and steam are passed through tubes
inside a furnace. May contain 500-600 tubes that are 7-12 m long with ID of 70-130 mm
Heating occurs by convection and radiationFeed pretreatment required a sulfur removalCoke deposits can form that deactivate the catalyst and
can block the furnace tubes, so excess steam is used to prevent coke deposit
Product is cooled in order to separate the condensed
Steam Reforming2/2
Ammonia synthesis1/2
A major product of the CPIEarly sources were natural, or byproduct of coke ovensMajor use in fertilizers (agricultural) and explosives In 1909 Fritz Haber established the conditions under which nitrogen,
N2(g), and hydrogen, H2(g), would combine using medium temperature (~500oC) very high pressure (~250 atmospheres, ~351kPa) a catalyst such as: 1-a porous iron catalyst prepared by reducing magnetite, Fe3O4).
2-Osmium is a much better catalyst for the reaction but is very expensive.
Requires a H2:N2 ratio of 3:1N2 sources is air, H2 from Syngas 3H2+N2 ↔ 2NH3 H= -91.44 kJ/ml
Ammonia Synthesis2/2
See chapter 2 for process description
Uses of AmmoniaFertiliser ammonium sulfate, (NH4)2SO4
ammonium phosphate, (NH4)3PO4
ammonium nitrate, NH4NO3
urea, (NH2)2CO
Chemicals nitric acid, HNO3, which is used in making explosives such as TNT (2,4,6-trinitrotoluene), nitroglycerine which is also used as a vasodilator (a substance that dilates blood vessels) and PETN (pentaerythritol nitrate). sodium hydrogen carbonate (sodium bicarbonate), NaHCO3
sodium carbonate, Na2CO3
hydrogen cyanide (hydrocyanic acid), HCN hydrazine, N2H4 (used in rocket propulsion systems)
Explosives ammonium nitrate (NH4NO3)
Fibres & Plastics
nylon, -[(CH2)4-CO-NH-(CH2)6-NH-CO]-,and other polyamides
Refrigeration used for making ice, large scale refrigeration plants, air-conditioning units in buildings and plants
Pharmaceutical used in the manufacture of drugs such as sulfonamide which inhibit the growth and multiplication of bacteria that require p-aminobenzoic acid (PABA) for the biosynthesis of folic acids, anti-malarials and vitamins such as the B vitamins nicotinamide (niacinamide) and thiamine
Pulp & Paper ammonium hydrogen sulfite, NH4HSO3, enables some hardwoods to be used
Mining & Metallurgy
used in nitriding (bright annealing) steel,used in zinc and nickel extraction
Cleaning
CO+ 2H2 ↔ CH3OH
CO2+3H2 ↔ CH3OH+H2O
Coupled by: CO+H2O ↔ CO2+H2
Second large scale process involving catalyst and high pressure
Catalyst selectivity is very important, as other products may form.
Cu/ZnO/Al2O3 catalysts are newer catalysts that enable lower pressure
Methanol Synthesis1/3
Methanol Synthesis2/3
Equilibrium data:
Methanol Synthesis3/3
CO, CO2 & H2 from steam reforming,
To distillation
Methanol uses
FormaldehydeOctane booster as Methyl tert-butyl ether
(MTBE)
Sources of PolymersNatural polymers since prehistoric times are:
Wood Rubber Cellulose, rayon
First synthetic polymers: Phenol formaldehyde resins
Used of polymersMain component of food:
Starch, proteinClothes:
Silk, cotton, polyester, nylonBuilding materials
Wood, paints, PVC etc.
Polymers & Polymerization
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What is a “polymer”?
– The terms polymer and monomer are part of our everyday speech.
– Poly = many Mono = one– “Mer” is derived from the Greek meros, meaning “part.” So, a monomer is a “one part” and a polymer is a “many part.”
Polymers
Polymers
Constructed of monomer units connected by a covalent bond:
-R-R-R-R- Or –[R]n-
R: a bi-functional entity not capable of separate existencen: degree of polymerization DPMW: molecular weight, obtained from the MW of the monomer multiplied by n
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Example: PolyethylenePolyethylene is an example of a synthetic
polymer.Ethylene, derived from petroleum: is made to
react with itself to form polyethylene.
H2C CH2 -CH2CH2-CH2CH2-CH2CH2-CH2CH2-
H2C CH2
catalyst-(CH2CH2)-nn
ethylene polyethylene
ethylene unit
Thermoplastic Become flexible solids above a certain Tthen become rigid again upon cooling below this Tflexible/rigid cycle can be repeatedWhen flexible it can be molded into shapesFibers can be drawn into strands, non fibers cannot
Thermoset resinsNetwork co-polymers that do not become flexible until
the T is so high thermal decomposition takes placeSynthetic rubber
Deformed by small stresses but regain original shape
Categories of Polymers1/2
Categories of Polymers2/2
Engineered polymers
High % growthSpecial properties, replacements for metals, chemical
inertness, etc. used in carpet and tirereinforcement.Examples:
Acetal (poly-oxy-methylene POM)Nylons (polyamides)Polyethylene or poly-butylene terephthalate (PET or PBT)Polycarbonate PCPolyphenylene oxide PPO
Polymerization reactions
2 mechanisms: chain growth and step growthChain growth (or additional polymer)
Reaction occurs by successive addition of a monomer to the reactive end
Example, polymerization of a monomers such as ethylene, propylene, styrene, vinyl chloride
nCH2=CHX -(-CH2-CHX)n-Where X can be H, CH3, C5H6 or Cl
Initiator or catalyst is required to start the chain growth reactionHigh MW product is produced right away (during polymerization)Polymerization is generally fast, irreversible and moderately to highly
exothermic.
Step growth (or condensation polymerization)
Formed when monomers combine and split out water or some other simple substance.Essentially a substitution reaction
Nylon is a condensation polymer. High MW product is produced from the end of polymerization
Commodity PolymersPolyethylene (PE)Polypropylene (PP)Polyvinylchloride (PVC)Polystyrene (PS)
Polyethylenes1/2
Classification and properties
linear, unbranched polymers are more densely packed therefore more ordered
Side branches interfere with alignment of polymer chainsDensity can be controlled by operating T, P, catalysts and
co-monomers used Example: LDPE is produced at high T and high P – higher T results in more side reactions and branching,
thus lower density Polymer density is degree of crystallinity
Polyethylenes2/2
Applications
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Production of LDPE1/3
Ethylene fed to reactor at high T, PNo catalystInitiator can be used (oxygen, peroxide)Ethylene behaves like a liquid and a solventCSTR or tubular reactor
Production of LDPE2/3
Using a tubular reactor: a long pipe heat exchanger with 200-1000 m long, and 2.5-7 cm IDReactants heated to 370-470 KHeat of polymerization means cooling is required by outer
jackets, T is raised up to 520-570 KConversions of 15-22%, so recycle stream is employedPressure cycling from 3000 to 2000 bar
Production of LDPE3/3
Production of HDPE1/2
There are many processes for production of HDPE such as:Bulk polymerization
Polymer dissolves in the monomerSolution polymerization
Polymer and monomer dissolve in HC solventSlurry polymerization
Catalyst-polymer particles suspended in HCFluidized bed polymerization
Catalyst-polymer particles fluidized in gaseous monomer
Catalytic processes for HDPE and LLDPE are similar
Fluidized bed polymerization (gas phase polymerization) is the most flexible method
Production of HDPE2/2
Polymer recovery
Unless bulk polymerization, polymer must be separated from the solvent
Typical separation methods such as crystallization, distillation.
Precipitation can’t normally be used (as polymers are highly viscous).
Method for precipitation can be done by non solvent process such as: centrifugation, and removal of solvent by steam stripping can be used.
Exxon Mobile
Formaldehyde ResinsIs used in the production of two different but related classes of thermosets: 1- Phenoplast: is called phenolic resins which is produced by condensation of phenol and formaldehyde.
2- Amenoplast: is prepared from condensation of urea (urea resin) and formaldehyde
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Phenol-Formaldehyde Polymers (Bakelite)
• Each formaldehyde molecule reacts with two phenol molecules to
eliminate water. The polymer is then formed.OH OH
HC
H
O
+ +
OH OHH2C + H2O
• Polymers of this type are used, in electrical equipment, because of the insulating and fire-resistant properties.
Phenolic Resins1/3
Phenolic resins (phenol-formaldehyde polymers), copolymers of phenol and formaldehyde, were the first fully synthetic polymers made. They were discovered in 1910 by Leo Baekeland and given the trade name Bakelite®.
Two processes, both involving step growth polymerization, are used for the manufacture of phenolic resins.
A one-stage resin may be obtained by using an alkaline catalyst and excess formaldehyde to form linear, low-molecular-weight called the resol resins. See next slide
Acidification and further heating causes the curing process to give a highly cross-linked thermoset polymer (ie high molecular weight) called the resite.
The second process (Fig. 1) uses an acid catalyst and excess phenol to give a linear polymer (called novolac as shown next slide) that has no free methylol groups for crosslinking.
In a separate second part of this two-stage process, a cross-linking agent is added and further reaction occurs. In many instances, hexamethylenetetramine is used, which decomposes to formaldehyde and ammonia.
Other modifications in making phenolic polymers are the incorporation of cresols or resorcinol as the phenol (Fig. 1) and acetaldehyde or furfural as the phenol.
Phenolic Resins2/3
Phenolic Resins3/3
Urea Resins1/2
Urea resins (urea formaldehyde polymers) are formed by the reaction of urea with formaldehyde (Fig. 1).
Monomethylolurea (HOH2CNHCONH2) and dimethylolurea ((HOH2CNHCONHCH2OH) are formed first under alkaline conditions. Continued reaction under acidic conditions gives a fairly linear, low-molecular-weight intermediate polymer.
A catalyst and controlled temperature are also needed and, since the amine may not be readily soluble in water or formalin at room temperature, it is necessary to heat it to about 80oC to obtain the methylol compounds for many amine-formaldehyde resins.
Heating for an extended period of time under acidic conditions will give a complex thermoset polymer of poorly defined structure including ring formation.
Urea Resins2/2
Formalin Plant (CH2O)
INTRODUCTION
Formalin is the aqueous form of formaldehyde produced mostly from methanol by an oxidation process.
Recently, the production volume of formaldehyde has grown rapidly thanks to the every-increasing demand in the manufacturing sector for resins including phnolic, urea, melamin, acetal and many additives.
Other additional application areas of formaldehyde include surface coating, leather tanning, bindery applications, laminates, insulation materials, etc.
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Processes
There are two processes known to produce formalin from methanol— methanol excess and air excess.
The basic difference between them is the catalyst applied. 1-The methanol excess process, called the silver process,
employs silver as the catalyst, 2-The air excess process, called molybdenum process, uses
metallic oxides of iron and molybdenum. Second process, is considered a higher investment cost
and more complicated operation than the silver process, the use the silver process is recommended
Process Description1/2
The evaporated methanol, filtrated air and steam are fed into the mixer where theses gases are mixed uniformly, and then sent to reactor.
Most of the methanol is converted into formaldehyde when the mixed gas passes through the catalyst.
The reacted gas is immediately quenched in the waste heat boiler integrated with the reactor. At the same time, the waste heat boiler recovers reaction heat to generate steam, which is effectively used as heat sources for the methanol evaporator and other heaters, and as steam supply for the mixer.
The reacted gas is introduced into the absorber where produced formaldehyde and residual methanol are absorbed by recycling formalin at the lower section of the absorber.
Process Description2/2
The vent gas from the absorber, containing about 20% of hydrogen, can be used as boiler fuel to generate steam and prevent air pollution.
The concentration of formalin produced in the absorber can be adjusted as required by regulating the treated water flow rate. The formic acid content in the raw formalin as produced from the absorber bottom is usually 60~150 ppm, but the lower formic acid content can be obtained by treating it through the ion-exchanger.
The product yield of the reaction is more than 91% (wt) and this process requires small utilities and the cost of catalyst is very low.
Process Flow Diagram
Applications
Phenol Resin and Adhesives / Urea and Melamine Adhesives
Urea Resin / Melamine Resin / Hexamethylenetetramine
Pentaerythritol / ParaformaldehydeMedicines and Agricultural Chemicals as
antiseptic (disinfectant)