Presentation on Petrochemicals: Aromatic Petrochemicals

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A presentation by professor Soltan at the university of saskatchewan. Covers benzenes, xylenes and toluenes as well as their derivatives.

Transcript of Presentation on Petrochemicals: Aromatic Petrochemicals

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Petrochemical EngineeringChE 364.3J. Soltan, Ph.D., P.Eng.Associate Professor of Chemical EngineeringDepartment of Chemical and Biological Engineering

University of Saskatchewan

Term 1 2012-2013

OutlineIntroduction Process considerations Petrochemical Feedstock C2 processes C3+ processesAromaticsPolymers Synthetic fuelsFertilizers Environmental concerns Trends in petrochemical industryAromaticsAromaticsBenzeneEthylbenzeneStyreneCumenePhenolCyclohexaneTolueneBenzoic acidBenzyl aldehydeXylenes

Benzene, Toluene & Xylenes(BTXs)Benzene

BenzeneStructure of BenzeneAll carbons are sp2 hybridizedClouds of electrons are -bonded -bonds make them react by substitution by a different mechanism than paraffins but at mildest conditionsBenzene + nitric acid nitrobenzene + H2OElectrophilic substitution at normal conditionsWill react by addition only under severe conditionsBenzene + hydrogen cyclohexaneHydrogen addition requires a catalyst and high pressures

TolueneC7H8Methyl group(s) activate ring for electrophilic attack, Methyl group Hs are more susceptible to attack because the phenyl group draws electrons in Easy oxidation or chlorination

XyleneC8H10

(1,4 dimethyl benzene)(1,3 dimethylbenzene)(1,2 dimethyl benzene)Benzene, Toluene, XylenesBTXs are refinery streams, particularly catalytic reformate and cracking streams along with steam cracking pyrolysis gasoline and coal liquidsRecovered from these streams by extensive separation processesProducts from BTX

BenzeneMost important aromatic hydrocarbon Does not polymerize stabilized ringProduction of BenzeneCatalytic Reforming (30% of Benzene)Aromatics produced by dehydrogenation of cycloparaffins , dehydroisomerization of alkyl cyclopentanes, and cyclization dehydrogenation of paraffinsToluene hydrodealkylationTransalkylation (or disproportionation)2 toluenes are converted to 1 benzene and 1 molecule of mixed xylene isomersPyrolysis GasolineSteam cracking of heavy naptha

Electrophilic Aromatic SubstitutionBenzene undergoes substitution addition and cleavage reactions, substitution being the most importantA substituent that increases electrophilic substitution relative to benzene is an activating groupan unshared electron group on the atom next to the ring contributes to the electron density of the aromatic ring (stabilization)Common activating groups (in order of decreasing effectiveness:-NR2, -NHR, NH2, -OH, -OR, -NO, -NHCOR, alkyls, -F,-Cl, -Br, -I, aryls, -CH2COOH,

Electrophilic Aromatic SubstitutionDeactivating groups decrease reactivity. No free electrons next to ringOften attached to an electronegative atom by double or triple bondsCommon deactivators (in order of decreasing effectiveness):-N+R3 -NO2, -CN2, -SO3H, -CHO, -COOR, -COOH, -CONH2, -CCl3Alkylation of BenzeneC6H6 can be alkylated using a Lewis or Bronsted-Lowry acid catalystEthylene, propylene and C12 C14 -olefins are important reactants to produce ethylbenzene, propyl benzene and surfactants respectively

C6H6 + C2H4 C2H5-CH2CH3 (ethylbenzene)

Alkylation of BenzeneRate Mechanism:Step 1: Generate CarbocationRHC=CH2 H+ [RC+HCH3]Friedel-Crafts alkylation catalysts can be used with an alkyl hadile as the reagentRCl + AlCl3 [R+AlCl4-]Step 2: Attack by the carbocation on the benzene ring

Step 3: Elimination of a ProtonEthylbenzeneUsed to produce styreneEthylbenzene from benzene:

C6H6 + C2H4

Reaction often catalyzed with AlCl3 HClTypical reaction conditions:AlCl3 Catalyst40-100oC2-8 atmSide products: diethyl benzene, higher alkylated forms

EthylbenzeneTypical vapor-phase reaction (Badger Process):Zeolite heterogeneous catalyst in a fixed bed420oC13-21 atm 98% yield @ 90% conversion of benzeneSide products & unreacted benzene are recycled to reactor

StyreneAka vinylbenzeneEasily polymerizes when initiated by a free radical or when exposed to light

Produced by dehydrogenation of ethylbenzene over a metal oxide catalyst Oxides of Fe, Cr, Si, Co, Zn, etc.

StyreneTypical reaction conditions for vapor phase reaction: 600-700oCAtmospheric pressure90% styrene yield @ 30 - 40% conversionMonsanto/Lummus Crest plantEndothermic rxnHeat provided by superheated steam (also a diluent)Equilibrium-limited reaction Effects of process variables P, T, Steam/EB

StyreneDow chemicals produced styrene from butadiene

Step 1: liquid phase catalytic reaction to produce vinylcyclohexane (VCH)100oC, 18 atmStep 2: catalytic oxidation of VCH in the presence of steam X > 90%, selectivity of 92%

StyrofoamExtruded or expanded polystyrene foam>95% airInsulating propertiesTrademarked by Dow, developed in 1941

CumeneAka isopropyl benzeneB.P. = 152.7oCProduced by alkylation of benzene with propyleneLiquid or gas-phase reaction

CumeneLiquid process50oC, 5 atmH2SO4 or H3PO4 catalystH = -113 kJ/mol

CumeneVapor phase process:250oC, 40 atmSupported phosphoric acid is a common catalystPropane used to dilute propene to limit polyalkylationHigh benzene: propylene ratio to suppress polyalkylation Selectivity of 97% (benzene based)

PhenolCumene is mainly used to produce phenolFigure 10-6 in handoutsStep 1: Oxidize cumene with air to cumene hydroperoxide100-130oC2-3 atmMetal salt catalyst Liquid phaseH = -116 kJ/mol

PhenolStep 2: Decomposition of hydro peroxide in an acidic environment80oC, < 1 atm

Hydrogenation of Benzene H = -266 kJ/molCatalyzed by Ni/Alumina or Ni/Pd)160-220oC25 30 atm Gas phase reaction Large change in volume (gas phase) Highly exothermic reactionSee fig 10-12 for effect of process conds on conversionOlder, liquid phase reaction in Fig. 10-11

TolueneMethyl BenzeneMore active than benzene because of activating CH3 (methyl) group (electron-donating)Less useful than benzene because of its propensity to produce polysubstituted productsPrimary reactions in industry are:Dealkylation to benzeneOxidation of the methyl groupHydrogenation of the phenyl group

Dealkylation of TolueneOccurs over a nickel catalystA cracking reaction favored at high temperatures and pressures (~700oC, 40 atm)Benzene yield is ~96% or more

Dealkylation of TolueneCan also be achieved using steam with a variety of catalysts NiCr2O3 or NiAl2O3320-630oC Yields of ~90%Produces H2 instead of consuming itOxidation of TolueneBenzoic AcidLiquid-phase reaction over a cobalt acetate catalyst165oC, 10 atmYield >90%Used to fix dyes in printing, season tobacco, preserve foods, kill fungus, etc. Precursor to many substances such as phenol

+ 1 O2 + H2OPhenol from Benzoic AcidA reaction with a copper salt catalyst Overall reaction:

Lummus process (Fig. 10-15) is a vapor phase process250oC, yield of 90%Multi-step mechanism

+ O2 + CO2

Benzyl AldehydeSolvent, artificial almond flavor and scentStep 1: Oxidation of Toluene to Benzyl Alcohol

+ O2 Benzyl AldehydeStep 2: Reaction of Benzyl Alcohol to Benzyl Aldehyde

+ O2 + H2O Benzyl AldehydeStep 3: (Side Product)

Each step occurs more readily than the proceeding oneSince introducing O, makes Hs more acidic, facilitating reaction

+ O2

Benzyl AldehydeTo minimize Step 3, a selective catalyst is used UO2 (93%) + MnO2 (7%) at 500oCGives 30-50% yield at conversions of 10-20%Also FeBr-CoBr2 with methanol at 100-140oCAlso, short residence times are neededXylenes (Dimethylbenzene)Para-xylene is the most important isomerUsed to make terephthalic acid (HOOCC6H4COOH)Meta is present in highest quantities at equilibrium compositions from catalytic reforming M-xylene is isomerized to p-xylene 65% of xylenes are used to make chemicalsThe rest are used as solvents or blended with gasolineTeraphthalic AcidFormed from catalytic oxidation of p-xylene Cobalt acetate promoted with NaBr or HBr is the catalyst in an acetic acid medium (liquid-phase)~200oC, ~15 atm Yield is ~95%

Teraphthalic Acid

3/2 O2 + H2OP-toluic acid(side product) dont want the reaction to stop hereTeraphthalic Acid Preferred esterification reaction:

The resultant dimethyl terephthalate (DMT) may be hydrolyzed to terephthalic acidThe DMT process encompasses four major processing steps:Oxidation, esterification, distillation, crystallization

3 O2 + 2CH3OH

+ 4H2O