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Analysis and influence of paraxylene on living environment,Start from here.,About p-Xylene,p-Xylene is an aromatic hydrocarbon based on benzene with two methyl substituents with the chemical formula C8H10 or C6H4(CH3)2. 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. The boiling point of p-xylene is 138.35 C (281 F) and the melting point is 13.2 C (56 F).1 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.,Technology development and process improvement,Paraxylene is currently manufactured by crystallization and adsorption processes. The Pascagoula plant uses the patented hybrid adsorption/crystallization technology to produce paraxylene. This process is characterized by the use of adsorption technology to produce a medium-purity paraxylene feedstock stream that goes into a low-temperature crystallization plant to produce crystals. These crystals are centrifuged and melted to produce high purity paraxylene.,Paraxylene is primarily used as a basic raw material in the manufacture of terephthalic acid (TPA), purified terephthalic acid (PTA) and dimethyl-terephthalate (DMT). TPA, PTA and DMT are used to manufacture polyethylene terephthalate (PET) saturated polyester polymers. Polyesters are used to produce fibers and films. PET bottles are widely used for water because of its non-breakage properties as well as carbonated beverages because of good carbon dioxide barrier properties. In addition, they are light-weight, shatter-resistant and possess high tensile strength. Polyester uses include,Historically, crystallization technology was perceived to suffer from disadvantages of requiring low temperature refrigerants for the freezing process and requiring more rotating mechanical equipment. BP Corporation North America, Inc. (formerly Amoco Chemical Company) has continually improved their para-xylene crystallization process since commissioning their first commercial para-xylene unit in 1967, such that they now claim that their new crystallization technique has lower energy use and unit capital cost than other para-xylene production methods.,para -Xylene separation from mixed xylene feedstocks requires first stage crystallization temperatures as low as -90 F (-68 C). The conventional crystallization processes use cascaded ethylene/propane or ethylene/propylene (C 2/C 3) vapor compression refrigeration systems. The C 3 compressor is an expensive piece of equipment, and a large user of electricity. This report describes a new energy efficient technique that uses waste heat powered ammonia absorption refrigeration (AAR) instead of conventional C 3 refrigeration.,Sources of pollution Pxylene is an important chemical raw materials. The waste water and gas in organic synthesis, synthetic rubber, paints and dyes, synthetic fibers, petroleum processing, pharmaceutical, cellulose production plant and workshop ventilation is the the main source of pxylene into enviroutment.Rollovers,leaks,fires during transportation, storage also cause accidental pollution incidents.,Influence and harmness on local environment,Ecotoxicity Test Data: Para-xylene (p-xylene, or 4-xylene) is toxic to fish and other aquatic life. Published test results of the acute toxicity of of p-xylene for several aquatic species show that concentrations of 2 to 10 mg/L are acutely toxic to most species tested. Acute toxicity endpoints ranged from 2 to 35 mg/L, with a geometric mean of 7 mg/L. The para-isomer appears to be slightly more toxic than the meta- and ortho-isomers. Biodegradation Potential: Xylenes have been shown to be readily biodegradable in water using standard protocols with inocula including sewage, activated sludge, and seawater. Field data indicates biodegradation in several situations. However, reports suggest that p-xylene may persist in some groundwater situations. Rates of degradation are expected to vary with environmental conditions and the extent of adaptation of the microbial population.,Bioconcentration Potential: P-xylene is not expected to bioconcentrate or bioaccumulate. A bioconcentration factor of 138 to 158 is predicted using the estimated octanol-water partition coefficient (log Kow) of 3.12 to 3.2. A bioconcentration factor of 20 was reported for eels. Metabolism and excretion of xylenes has been demonstrated in several organisms, generally via production of toluic acid. Significant bioconcentrations is unlikely if bioconcentration factors are less than 1000 and the chemical is metabolized. Other Ecological Information: P-xylene is expected to volatilize from water and soil with a relatively high Henrys law constant of 0.32, yielding an estimated half-life in water of less than 1 week. Sorption to soil is low to moderate, with the Koc of ortho-xylene being 48-68. Abiotic degradation in air occurs through reaction with photochemically produced hydroxyl radicals, resulting in typical losses of 67-86% per day. Xylenes are likely to move with groundwater from soils and to volatilize from both soil and surface waters. The potential for long-term ecological effects to intermittent environmental releases is expected to be minimal. However, repeated discharges may cause long-term adverse effects in the aquatic environment.,Hazard statement Flammable liquid and vapor. May be fatal if swallowed and enters airways. Causes skin irritation. Causes serious eye irritation. May cause damage to organs (Auditory organs) through prolonged or repeated exposure if inhaled. Toxic to aquatic life. May be harmful if swallowed. May cause respiratory irritation.,Solutions and response measures,In the wake of Xiamen 2007,Dalian2011,Ningbo2012 and Maoming 2014 events,people become more and more aware that the development of paraxylene industry must be banned and expelled from our country.,Some accidents,State media reported that residents of Dalian were recently forced to flee when a storm battering the northeast Chinese coast, whipping up waves that burst through a dyke protecting a local chemical plant. The plant produces paraxylene (PX), a toxic petrochemical used in polyester.On Sunday, some angry residents finally decided that instead of being forced to flee, the chemical plant should be relocated.Tens of thousands of people took to the streets to demonstrate and Dalian, known as one of the most beautiful coastal cities in China, made headlines all over the world.,Blame bad luck or natural disasters, perhaps. Four days ago, an accident at a factory in Shandong province resulted in a deadly chemical gas leak and 125 people, mostly workers and nearby residents, were sent to the hospital, local media reported. About three months ago, poisonous chemical waste was dumped illegally, polluting water sources in Yunnan province. The case was only recently revealed to the public. You can imagine how angry local people must feel.,A BlOODY HISTORY,However,as a matter of fact,what do we know about their situations in so-called developed country?,That is,for example,Houston px project lies about 1.2kms away from the downtown area, also the same as Singapore Exxon mobile, the px factory of which locates merely 0.9km away from its residential area.In a word,there is no such rules like safe interval among all these countries.,Safe interval,When it comes to specific regulations like Globally Harmonized System of Classification and Lablling of Chemicals(known as GHS 全球化学品统一分类和标签制度) ,we find that paraxylene presents as a kind of inflammable liquid, it may lead to water pollution, and beyond that,excessive exposure with its steam may cause you intoxicated or influence your neural centre(神经中枢).But most importantly , it is , lets face the truth, NOT an cancerogan(致癌物) according to International Agency for Research on Cancer (knows as IARC 国际癌症研究所).,Follow these advice:,1.Optimize the distribution of industry(优化产业布局),2.Pay close attention to the requirement of local environment, launch on commissioning of utilizational-facilities.（关注当地环境需求，发展并投产一体化装置）,3.Encourage external capital to enter in multivariant areas.（鼓励外来资本进入多元化领域）,4.Strengthen communication with residents and Motivate PX industry on its long-term development.（加强沟通交流，推动PX工业进行长期发展）,
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