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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-xylene, di-p-xylene (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-xylene 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 31.5 MMT and it is expected to reach 49 MMT in 2016 and demand is expected to touch 38 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. In India the projected capacity for 2016-17 is around 3660 KTA against the estimated demand of 3571 KTA.

Reliance Industries Ltd (RIL) has commissioned the first phase of its 2.2 million mt/year para-xylene (PX) plant at Jamnagar in Gujarat in Dec’16. The 2.2 million metric tonnes per annum plant is built with technology from BP, its partner in the D6 block of the Krishna Godavari basin on the east coast. With the commissioning of this plant, RIL’s PX capacity will more than double from 2.0 MMTPA to 4.2 MMTPA. On commissioning of entire PX capacity, Reliance will be the world’s second largest PX producer with 9% of global PX capacity and 11% share of global production.

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 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.

Para-Xylene production via crystallization technology

Capacity (kt) Actual Actual Actual Actual Actual Projected
2011-12 2012-13 2013-14 2014-15 2015-16 2016-17
BRPL 0 0 0 0 0 0
IOC 360 360 360 360 360 360
MRPL 0 0 0 537 920 920
RIL 2088 2112 2112 2112 2112 2382
Total 2448 2472 2472 3009 3392 3662
Source: Industry
  PX: India Demand Supply
Actual Actual Actual Actual Actual Projected
2011-12 2012-13 2013-14 2014-15 2015-16 2016-17
Capacity 2448 2472 2472 3009 3392 3662
Production 2328 2326 2259 2813 3338 3573
Dom Sales 1700 1713 1619 1743 2420 2057
Imports 454 550 679 699 799 1514
Exports 671 595 640 1066 837 775
Consumption 2154 2263 2298 2442 3219 3571
  5.1% 1.5% 6.3% 31.8% 10.9%
Source: Industry

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

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