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PX - Paraxylene

P-Xylene is an aromatic hydrocarbon, based on benzene with two methyl substituents. The “p” stands for para, identifying the location of the methyl groups as across from one another.

It is an isomer of xylene. Other isomers include o-xylene and m-xylene. P-Xylene is used on a large scale for the manufacture of terephthalic acid for polyester. Its polymer is known as Parylene. P-Xylene is produced by catalytic reforming of petroleum naphtha as part of the BTX aromatics (benzene, toluene and the xylene isomers) extracted from the catalytic reformate. The P-Xylene is then separated out in a series of distillation, adsorption or crystallization and reaction processes from the m-xylene, o-xylene and ethylbenzene. Its melting point is the highest among this series of isomers, but simple crystallization does not allow easy purification due to the formation of eutectic mixtures. It is also highly flammable.

Paraxylene is one of the three Dimethyl Benzene isomers and therefore belongs to the Aromatics family, so called BTX where X stands for Xylene. Paraxylene is also called P-Xylene or even PX. Paraxylene is a colorless liquid. Paraxylene is obtained by the distillation of camphor with zincchloride. Then Paraxylene can be oxidized to form PTA. Paraxylene is the principal precursor to PTA and Dimethyl Terephthalate, the two monomers used in the production of PET.

At the time of Michael Mojzesz Szwarc's discovery in the late 1940s, the young and growing plastics industry was in search of better thermal stability in prospective new polymers. Michael's observations inspired vigorous research in many industrial laboratories, including I.C.I. in the U.K. and DuPont, Kellogg and Polaroid in the U.S. A few years later, William Franklin Gorham at Union Carbide proposed using the very stable dimer of the reactive p-xylylene, di-p-xylylene (DPX), or paracyclophane, as the feedstock for an industrial Vapor Deposition Polymerization (VDP) process to produce PPX. Gorham demonstrated that the necessary reactive intermediate could be produced quantitatively in pure form from DPX under milder conditions than those required for its production from p-xylene. A further advantage of the Gorham proposal was the absence of gaseous by-products, a feature of the production of p-xylylene by all other means presently known.

Technology used to produce paraxylene is Parex (UOP) Process Description and IFP's Eluxyl (Adsorption) Process. Major technology providers are Chevron Phillips, ExxonMobil, IFP (Axes), and UOP. Global capacity of PX in 2011 was 37 MMT as against a demand of 30 MMT and it is expected to reach 52 MMT in 2016 and demand is expected to touch 40 MMT. GS Caltex, BP, Chevron Phillips Chemical Co, Chevron Phillips Chemical, ExxonMobil, Mitsubishi Chemical, Polimeri Europa, Reliance Industries, Shanghai Petrochemical, Teijin Ltd are some of the leading producers of paraxylene in the world.

The global paraxylene (PX) market has undergone dramatic expansion over the past few years. Despite massive capacity additions during 2009-2010, PX prices and margins remained strong, driven by demand growth in China, a severe shortage of cotton and production issues in the Middle East and Asia. From 2012, purified terephthalic acid (PTA) and polyester capacity development has created a serious concern over PX supply. The PX market is expected to remain tight on rising polyester demand, while PTA and polyester operating rates will be severely depressed. PX operating rates are likely to decline over 2013-2015 as a result of several new PX production plants in the Middle East and Asia. With the current aggressive development in downstream polyester by companies such as India's Reliance Industries and Thailand's Indorama Ventures, rapid growth of PX consumption is expected. This will, however, come together with new PX capacity by Reliance, Oil and Natural Gas Corp. The recent strong PX price premium over naphtha has been driven not only by robust demand, but also by a number of production issues in the Middle East and Asia, particularly in Iran and China.

From 2013 onwards, new PX capacity in Asia and the Middle East includes Luoyang Petrochemical and Hainan Refinery in China; HC Petrochem, Samsung Total and the joint venture between Japan's JX Nippon Oil & Energy and SK Global Chemical in South Korea; Jurong Aromatics Corporation in Singapore; Reliance and ONGC in India; Byco Oil Pakistan Ltd. in Pakistan; and Saudi Aramco Total Refinery and Petrochemical Company and Ibn Rushd in Saudi Arabia. Saudi Aramco is studying a major investment in aromatics, potentially adding a few million tonnes of PX. Zhejiang Hengyi is also looking to secure PX supply through a joint venture with Brunei Shell Petroleum. The project detail is still unclear, as it will produce refined products along with PX. In India the total capacity is expected to touch 4576 KTA in 2016 from 2306 KTA in 2011. Reliance Industries Ltd has capacity expansion plans for PX from 2088 KTA in 2011 to 3912 KTA in 2016.

PX trade from the Middle East to Asia is forecast to expand further, despite substantial expected PTA developments in the Middle East. PX profitability will face the opposing effects of relatively strong demand growth and weak benzene co-product returns from reforming and toluene disproportionation. The additional supply from 2013 onwards could provide some relief to the currently tight market, with margins easing modestly in the medium term.

Paraxylene is one of the isomers of xylene. It is a colorless, volatile liquid. Paraxylene is a very important raw material in the preparation of PET (polyethylene terephthalate) chips, which are extensively used in packing industries, for example, for mineral water and carbonated soft drink bottles. Paraxylene is also used in the manufacture of PTA (purified terephthalic acid), which is a basic petrochemical used in the textile industry for making polyester. The PET is one of the main source of raw materials to produce plastic bottles and polyester clothing. 98% of the Paraxylene production, and half of all xylene, is consumed in this way.

The PxMax process flow (shown) is typical for a vapor-phase reaction in a fixed-bed reactor. Toluene feed, combined with hydrogen-rich recycle gas, is preheated and passed through the EM-2300 catalyst bed. Disproportionation occurs here, at moderate temperature and pressure, to produce a paraxylene-rich xylene product along with co-product benzene. Byproduct yields are small.


Para-Xylene production via crystallization technology


Para-Xylene Production via UOP Parex/Isomar Process

The Parex Process, the key to the production of high purity para-xylene, uses a selective and proprietary solid adsorbent developed by UOP to separate para-xylene from a mixed C8 aromatic stream. Commercial Parex Process units typically are able to produce 99.9 wt% para-xylene purity at greater than 97% recovery.



       

Capacity (kt) Actual Projected
2011-12 2012-13 2013-14 2014-15 2015-16 2016-17
BRPL 29 29 29 29 29 29
IOC 360 360 360 360 360 360
MRPL 0 0 0 900 900 900
RIL 2088 2112 2555 3912 3912 3912
Total 2477 2501 2944 5201 5201 5201

Producer PX: India Demand Supply
Actual Projected
2011-12 2012-13 2013-14 2014-15 2015-16 2016-17
(kt)  
Capacity 2477 2501 2944 5201 5201 5201
Prod/Cons 2352 2370 2814 4959 4959 4959
Imports 648 770 770 770 770 770
Exports 656 672 664 1153 1153 1153
Consumption 2306 2468 2920 4576 4576 4576
             
Cons Growth (%)   7% 18% 57% 0% 0%


PX has only one end use consumption in India, i.e. it goes into production of PTA.

 
 
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