Paraxylene or 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.

Paraylene includes several molecular structures; only a few are used commercially. It has a variety of uses. In electronics, it's vapor-deposited at low pressure onto circuit boards as a thin, even conformal coating. Parylene coating has very high electrical resistivity and resists moisture penetration. It's used as a dielectric in certain high-performance capacitors for precision measurement. It has uses in preserving archival paper. Union Carbide is a supplier of materials and coating equipment.

TECHNOLOGY/PROCESS/FEEDSTOCK

Paraxylene is separated out from the mixed xylene stream. In conventional paraxylene technology, isomerisation of mixed xylenes takes place through crystallisation or adsorptive separation. Alternative technologies include toluene disproportionation, which yields paraxylene and benzene co-product. The BP-UOP Cyclar process, in which propane and butane are converted to paraxylene and benzene, has been used in Saudi Arabia. Paraxylene is a colourless, flammable liquid with a sweet odour.
Recovery from mixed xylenes streams is done as follows:

• First, if o-xylene is recovered as a co-product, o-xylene is separated from the other aromatics by distillation with meta and paraxylene going overhead along with the ethylbenzene.
• In the adsorption process, the paraxylene and other constituents are charged to a fixed bed of molecular sieves with paraxylene being selectively absorbed. The molecular sieves are washed with solvent, and paraxylene is recovered by distilling off the recovery solvent. The raffinate is usually isomerized to form more paraxylene, with this stream recycled to the fresh feed. UOP’s Parex and Axen’s Eluxyl processes are the major selective adsorption processes. The selective adsorption process is used in over 90% of the world’s paraxylene plants.

As an alternative to the selective adsorption process:

• Paraxylene is separated from the other components in the overhead stream by crystallization. The first stage yields a slurry of crude paraxylene and a filtrate containing the other isomers. Recrystallization of the other isomers yields a high purity paraxylene. Technologies for paraxylene crystallization include BP, Axens (formerly, the Arco process), GTC Technology’s GT-CrystPX, Sulzer, Raytheon/Niro, and BEFS Prokem. BP is the largest company in the world to employ paraxylene crystallization with six world scale plants.
• After the paraxylene is recovered in either by selective absorption or crystallization processes, the lean para-depleted mixed xylenes are isomerized to reestablish the equilibrium concentration of paraxylene in the mixed xylenes stream. In addition, any ethylbenzene is reacted to form benzene and mixed xylenes. This mixed xylene stream is then recycled as feedstock to the selective adsorption and crystallization processes for additional p-xylene recovery. BP, UOP, Axens, and Engelhard license isomerization catalysts for p-xylene plants.
• Toluene may be disproportionated (in TDP processes) to form equivalent amounts of benzene and xylenes as in UOP’s Tatoray process. This method is not widely practiced in a stand-alone plant because of cost, but it does have the advantages of producing less ethylbenzene (making recovery less expensive) and not requiring any net hydrogen. Toluene TDP processes are typically installed in an integrated paraxylene complex using selective adsorption to produce additional mixed xylenes from toluene for paraxylene recovery. Some TDP catalysts can efficiently react with C9 aromatics together with toluene over a catalyst to form benzene and xylenes. UOP, Axen, Toray, and GTC Technology offer toluene/C9 TDP processes for license.
  

END USE

The market breakdown on propylene use is as follows.

• Terephthalic acid (89%)
• Dimethyl terephthalate (11%)

INDUSTRY STRUCTURE

The top 10 largest producers of paraxylene worldwide account for over 55% of world capacity. The detailed Industry Structure and the Company names with capacity and % Share in the global market is available in the Polyester Chain Report by Yarnsandfibers.com

Price Trends

The current prices and the trends are published weekly in the YnFx PriceWatch Report, which covers 22 textile products, starting from feedstock till yarn, and tracks the international price movement on a weekly basis.

This report is available for online subscription.

AN OVERVIEW

Global capacity of paraxylene stood at 26 million tons in 2005. With capacity utilisation at 88.7% the production touched 21.6 million tons during the year. This was 7% higher than the production of 2004.

The future projections, and country-wise demand for paraxylene is covered in the Polyester Chain Report by Yarnsandfibers.com. You may also get a view of Table of Contents

The report also covers Various aspects in tabular as well as graphical form as shown below -

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