Aromatics Product Profile, Ethylbenzene & Styrene, Cumene & Phenol, (Part - 1) | Chemical Technology - Chemical Engineering PDF Download

Aromatics Product Profile, Ethyl Benzene & Styrene, Cumene and Phenol, Bisphenol, Aniline 

Aromatics are backbone of organic chemical industries. Aromatic hydrocarbons especially benzene, toluene, xylene (BTX), and ethyl benzene are major feedstock for large number of intermediates which are used in the production of synthetic fibers, resins, synthetic rubber, explosives, pesticides, detergent, dyes, intermediates, etc. Styrene, linear alkyl benzene, and cumene are the major consumer of benzene. Product profile of aromatics is shown in Figure MVII 8.1.

Global production and consumption of benzene in 2009 were between 36.4 and 36.6 million metric tons. Average global capacity utilization was 69.2 percent in 2009, lower than in 2008. Global benzene consumption is estimated to have decreased by 3.8 percent in 2009; however, it is expected to average growth of 4.7percent per year from 2009 to 2014, and 2.6percent per year from 2014 to 2019 . Ethyul benzene/styrene monomer and cumene/phenol with demand shares of 52.6percent and 18.3percent respectively of the global benzene market respectively are the leading end-use segments for benzene in 2010. Other uses such as cyclohexane, nitrobenzene and LAB collectively consumed less than 15percent of global benzene demand in 2010.

Global production and consumption of toluene in 2009 were each almost 18.4 million metric tons. Global capacity utilization was 64percent in 2009. Toluene consumption estimated to have decreased by almost 2percent in 2009. Demand is expected to grow on average 3.6percent per year from 2009 to 2014, and 2.2 percent per year from 2014 to 2019.

Global production and consumption of mixed xylenes in 2009 were each approximately 41 million metric tons. Global capacity utilization was around 74percent in 2009. Xylenes consumption in 2009 is estimated to have increased by around 4.6percent from 2008; it is expected to average growth of 5.2percent per year from 2009 to 2014, and 3.3percent per year from 2014 to 2019. Operating rates are expected to drop in 2010 but gradually increase afterward. Product profiles of major aromatics-BTX are given in Table M-VII 8.1. 

Table M-VII 8.1: World Aromatic Petrochemicals Scenario

Figure M-VII 8.1: Product Profile of Aromatics 

Global production and consumption of p-xylene in 2009 were each approximately 27.6 million metric tons. Global capacity utilization was 83percent in 2009, unchanged from 2008. p-Xylene consumption is estimated to have increased by approximately 4.7percent in 2009; it is expected to average growth of 5.5percent per year from 2009 to 2014, and 3.5percent per year from 2014 to 2019.

Global production and consumption of o-xylene in 2009 were approximately 3.7 million metric tons. Global capacity utilization was 66percent in 2009. o-Xylene consumption is estimated to have increased slightly in 2009; it is forecast to average growth of 3.2percent per year from 2009 to 2014, slowing to 2.4percent per year from 2014 to 2019. Average global utilization rates are expected to remain in the 70s range throughout the forecast period . 

Ethyly Benzene and Styrene 

Ethyl benzene and styrene are two important aromatics. Ethyl benzene is mainly used for making styrene. Styrene which finds application in synthetic rubber and polymer industry for the manufacture of SBR and polystyrene, ABS plastic.

Major route for styrene manufacture is dehydrogenation of ethyl benzene which is manufactured by alkylation of benzene. Styrene plant consists of two major units. The process involves:

• Production of ethylene either from molasses route or by naphtha/natural gas cracking
• Production of ethyl benzene by alkylation of benzene
• Dehydrogenation of ethyl benzene to styrene  

Ethyl Benzene

Ethyl benzene is made by alkylation of benzene with ethylene. Ethylene can be produced from either from molasses route or naphtha/gas cracker. The convention alkylation catalysts are metal chlorides (BF₃,AlCl₃, etc) and mineral acids (HF,H₂SO₄). However, with development of zeolite, now the benzene alkylation I is done by using ZSM-5 catalysts using vapor-phase process [Mobil-badger Process] and liquid phase alkylation using MCM-22 azeolite proprietary catalyst based catalyst. 

Vapour Phase Alkylation of Benzene: The process consists of vapor phase alkylation of benzene with ethylene using zeolite catalyst in a fixed bed catalytic distillation technology. Alkylation and distillation takes place in the alkylator. Unreacted ethylene, and benzene vapour are condensed and fed to the finishing reactor where the remaining alkylation is completed in the presence of a catalyst. The product stream goes to fractionating columns where ethyl benzene is separated from the higher ethylated benzene and heavy ends. Higher ethylated alkyl benzene is sent to the trans-alkylator where its trans-alkylated to produce additional ethyl benzene.

Liquid Phase Alkylation Of Benzene With Ethylene Using MCM-22 Catalyst:In this process alkylation of ethylene takes place in a liquid filled alkylator reactor containing multiple fixed beds of MOBIL MCM-22 catalyst. During alkylation Ethyl benzene and small quantity of polyethylbenzene are formed which is converted to ethyl benzene using transalkylation catalyst. The product streams from alkylator and trans-alkylator are sent to various fractionating columns for separation of product ethyl benzene, polyethylbenzene, benzene, gases and heavy ends.

C₆H₆+C₂H₄ →  C₆H₅CH₂CH₃

Styrene 

Styrene is one of the most important monomers for the production of polymers, resins and rubber. The biggest consumer of styrene monomer is polystyrene, other major derivatives are expanded polystyrene, Styrene butadiene(SB) latex, SB rubber, styrene block co-polymers (eg: ABS, MBS, SBS)

Styrene is made by catalytic dehydrogenation of ethyl benzene  

C₆H₅CH₂CH₃ → C₆H₅CH=CH₂ +H₂

Styrene can be also directly recover from raw pyrolysis gasoline derived from cracking of naphtha, gas oils Using GT styrene process 

Lumus/UOP EB One Process: Styrene is made by catalytic dehydrogenation of ethylbenzene in the presence of steam. In Lumus/UOP EB one process involves first alkylating benzene with ethylene followed by dehydrogenating the EB to form styrene. The benzene and recycled benzene are preheated the liquid phase reactor containing zeolite catalyst. The polyethylbenzene formed during alkylkation is fed to another reactor for transalkylating with benzene. Transalkylation reaction is isothermal and reversible in distillation section. The reactor effluent from both reactions is sent to the distillation section for separating ethyl benzene from polyethylbenzene. 

Ethyl benzene and recycled ethyl benzene are then dehydrogenated to styrene in the presence of steam at high temperature (550-68^oC) under vacuum in a multistage reactor 

During dehydrogenation stages air or oxygen is introduced to partly oxidize the hydrogen to reheat the process gas and to remove the equilibrium constrain for dehydrogenation reaction. Reactor effluents are cooled to recover waste heat and condensed, uncondensed gases are used as fuel. The condensed product containing styrene is sent to distillation columns for separating styrene monomer, unconverted ethyl benzene is recycled. 

Toluene is formed during the process which is recovered 

GT Styrene Process: Styrene can be also directly recovered from raw pyrolysis gasoline derived from cracking of naphtha, gas oils Using GT styrene process. Raw pyrolysis gasoline is fractionated into a heart cut C8 stream from which styrene is separated by extractive distillation.

Innovative SNOW Technology: The snow technology has been jointly developed by Snamprogetti and Dow represents a technological and economical breakthrough in styrene production and uses benzene and ethane as raw material which is dehydrogenated in the same reaction for EB dehydrogenation. SNOW reactor is rise type.