Xylene

C₈H₁₀ (C₆H₄(CH₃)₂) · 106.16 g/mol

C₈H₁₀ (C₆H₄(CH₃)₂)

Aromatic mixture (ortho, meta, para isomers) for PET and phthalates

Molecular Weight

106.16 g/mol

State

Liquid

Catalyst

Zeolite mordenite or ZSM

Reactor

Fixed bed transalkylatio

Xylene molecular structure — 2D structure

Olefinverbund Integration

Inputs

Toluene

→

Product

Xylene

→

Outputs

Terephthalic Acid, Phthalic Anhydride

Chemistry & Engineering

Reaction	`2 Toluene ⇄ Benzene + Xylene (Disproportionation)`
Thermodynamics	Close to thermoneutral
Catalyst	Zeolite mordenite or ZSM-5
Reactor class	Fixed bed transalkylation unit
Note	Mixture of isomers (ortho, meta, para). Para-xylene is crucial for PET; Ortho for phthalic anhydride.

Applications

p-Xylene → terephthalic acid → PET polyester
o-Xylene → phthalic anhydride
Solvent applications
Isophthalic acid production

Extraterrestrial Production Pattern

Catalytic reforming of naphtha produces mixed xylenes
Toluene disproportionation over zeolite catalyst
Isomerization to shift equilibrium toward p-xylene
Adsorptive separation (Parex process) for pure p-xylene

Reaction Diagram

Naphtha reforming -> C8H10 isomers

Unit Operations

Process steps following chemical engineering unit operation principles

#	Operation	Description
1	Reformate C8 Cut	Fractionate C8 aromatics from reformate
2	Xylene Isomerization	Isomerize to equilibrium mixture
3	p-Xylene Recovery	Adsorption (Parex) or crystallization
4	o-Xylene Recovery	Distillation of o-xylene
5	m-Xylene Recycle	Return m-xylene to isomerization
6	Product Finishing	Final distillation to specs

S88 Batch Control Model

ISA-88 BatchML schema — simplified for educational purposes

<?xml version="1.0" encoding="UTF-8"?>
<!-- ISA-88 Batch Control Model for Xylene -->
<!-- Educational schema - simplified for demonstration -->
<BatchML xmlns="http://www.wbf.org/xml/B2MML-V0600">
  
  <ProcessCell ID="XYLENE_COMPLEX_CELL">
    <Description>Process cell for Xylene production</Description>
    
    <Unit ID="XYLENE_COMPLEX">
      <Description>Main synthesis unit</Description>
      
      <!-- Equipment Modules -->
      <EquipmentModule ID="SPLITTER">
        <Description>Splitter</Description>
      </EquipmentModule>
      <EquipmentModule ID="ISOMERIZER">
        <Description>Isomerizer</Description>
      </EquipmentModule>
      <EquipmentModule ID="PAREX_UNIT">
        <Description>Parex Unit</Description>
      </EquipmentModule>
      <EquipmentModule ID="OX_COLUMN">
        <Description>Ox Column</Description>
      </EquipmentModule>
      <EquipmentModule ID="RECYCLE_SYSTEM">
        <Description>Recycle System</Description>
      </EquipmentModule>
      <EquipmentModule ID="PRODUCT_COLUMN">
        <Description>Product Column</Description>
      </EquipmentModule>
    </Unit>
  </ProcessCell>
  
  <MasterRecipe ID="XYLENE_COMPLEX_RECIPE">
    <Description>Master recipe for Xylene</Description>
    <ProductID>XYLENE</ProductID>
    
    <UnitProcedure ID="XYLENE_COMPLEX_UP">
      <Description>Unit procedure for synthesis</Description>
      
      <Operation ID="OP_01">
        <Description>Operation 1</Description>
        <Phase ID="FRACTIONATE">
          <Description>Fractionate phase</Description>
          <PhaseLogic>
            <Step ID="STEP_1"><Action>Initialize</Action></Step>
            <Step ID="STEP_2"><Action>Execute</Action></Step>
            <Step ID="STEP_3"><Action>Complete</Action></Step>
          </PhaseLogic>
        </Phase>
      </Operation>
      
      <Operation ID="OP_02">
        <Description>Operation 2</Description>
        <Phase ID="ISOMERIZE">
          <Description>Isomerize phase</Description>
          <PhaseLogic>
            <Step ID="STEP_1"><Action>Initialize</Action></Step>
            <Step ID="STEP_2"><Action>Execute</Action></Step>
            <Step ID="STEP_3"><Action>Complete</Action></Step>
          </PhaseLogic>
        </Phase>
      </Operation>
      
      <Operation ID="OP_03">
        <Description>Operation 3</Description>
        <Phase ID="RECOVER_PX">
          <Description>Recover Px phase</Description>
          <PhaseLogic>
            <Step ID="STEP_1"><Action>Initialize</Action></Step>
            <Step ID="STEP_2"><Action>Execute</Action></Step>
            <Step ID="STEP_3"><Action>Complete</Action></Step>
          </PhaseLogic>
        </Phase>
      </Operation>
      
      <Operation ID="OP_04">
        <Description>Operation 4</Description>
        <Phase ID="RECOVER_OX">
          <Description>Recover Ox phase</Description>
          <PhaseLogic>
            <Step ID="STEP_1"><Action>Initialize</Action></Step>
            <Step ID="STEP_2"><Action>Execute</Action></Step>
            <Step ID="STEP_3"><Action>Complete</Action></Step>
          </PhaseLogic>
        </Phase>
      </Operation>
      
      <Operation ID="OP_05">
        <Description>Operation 5</Description>
        <Phase ID="RECYCLE_MX">
          <Description>Recycle Mx phase</Description>
          <PhaseLogic>
            <Step ID="STEP_1"><Action>Initialize</Action></Step>
            <Step ID="STEP_2"><Action>Execute</Action></Step>
            <Step ID="STEP_3"><Action>Complete</Action></Step>
          </PhaseLogic>
        </Phase>
      </Operation>
      
      <Operation ID="OP_06">
        <Description>Operation 6</Description>
        <Phase ID="FINISH">
          <Description>Finish phase</Description>
          <PhaseLogic>
            <Step ID="STEP_1"><Action>Initialize</Action></Step>
            <Step ID="STEP_2"><Action>Execute</Action></Step>
            <Step ID="STEP_3"><Action>Complete</Action></Step>
          </PhaseLogic>
        </Phase>
      </Operation>
    </UnitProcedure>
  </MasterRecipe>
  
</BatchML>

Process CellPhysical grouping of all production equipment

UnitMajor equipment performing the synthesis

Equipment ModulesIndividual devices: reactors, columns, absorbers

PhasesLowest control level: REACT, SEPARATE, PURIFY

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