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)