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化学品失控反应危害与防范-失控聚合-苯乙烯

Styrene is one of the most important monomers produced by the chemical industry today.  Styrene monomer is a basic building block of the plastics industry. The conventional method of producing styrene involves the alkylation of benzene with ethylene to produce ethylbenzene, followed by dehydrogenation of ethylbenzene to styrene.

苯乙烯是当今化学工业生产的最重要的单体之一。 苯乙烯单体是塑料工业的基本构件。 生产苯乙烯的常规方法包括用乙烯烷基化苯以制备乙苯,然后将乙苯脱氢成苯乙烯。

Styrene undergoes polymerization by all the common methods used in plastics technology to produce a wide variety of polymers and copolymers.  Styrene is readily polymerized and copolymerized by both batch and continuous mass polymerization, emulsion, suspension, and solution processes.  The most important products are polystyrene (PS), rubber-modified high impact polystyrene (HIPS), styrene butadiene latex (SBL), styrene-acrylonitrile copolymer (SAN), acrylonitrile-butadiene-styrene/ terpolymer (ABS), and styrene-butadiene copolymer (SBR, synthetic rubber).  An approximate breakdown of styrene’s markets are polystyrene 54%, expandable polystyrene 12%, ABS 10%, SBR 7%, SBL 6%, and other 11%.  Other important uses of styrene are in styrene-polyester resins, latexes, and styrenated oils and alkyls.

苯乙烯可经由塑料加工技术中使用的各种常用方法进行聚合,从而生成多种聚合物和共聚物。 苯乙烯容易通过间歇和连续本体聚合,乳液,悬浮液和溶液方法聚合和共聚。 其最重要的产品是聚苯乙烯(PS),橡胶改性的高抗冲聚苯乙烯(HIPS),丁苯胶乳(SBL),苯乙烯 - 丙烯腈共聚物(SAN),丙烯腈 - 丁二烯 - 苯乙烯/三元共聚物(ABS塑料)以及苯乙烯-丁二烯共聚物(SBR,合成橡胶) 苯乙烯市场的近似分解是聚苯乙烯54%,可发性聚苯乙烯12%,ABS 10%,SBR 7%,SBL 6%,其它类11%。苯乙烯的其它重要用途包括苯乙烯 - 聚酯树脂,胶乳和苯乙烯化油和烷基化物。

Polystyrene is primarily used in packaging, disposables, and low cost consumer products.  Expandable polystyrene beads (EPS) are primarily used in food and beverage packaging, insulation and cushion packaging.  Improved grades of resins are used in higher performance applications, such as home electronics and appliances.  ABS and SAN have many uses in the consumer durables market.  Styrene-based polyesters have lifetimes of over thirty years in both indoor and outdoor applications, e.g., polyester boats typically last longer than boats made from conventional materials.  Thermoplastic elastomers are directly replacing natural and traditional synthetic rubbers in many established applications and entering new markets.  Other applications include carpet backing (SB Latex), production of tires (SB Rubber) and castings for textiles and paper.

聚苯乙烯主要用于包装,一次性用品和低值消费品。发泡聚苯乙烯粒子(EPS)主要用于食品和饮料包装,绝缘和衬垫包装。高等级树脂用于更高性能的场合,例如家用电子产品和电器。 ABSSAN在耐用消费品市场有许多用途。苯乙烯基聚酯在室内和室外使用寿命超过三十年,例如聚酯船通常比由常规材料制成的船使用更为长久。热塑性弹性体在许多成熟应用中直接替代天然和传统的合成橡胶并还进入新的领域。其他应用包括地毯背衬(SB胶乳),轮胎生产(SB橡胶)和用于纺织和造纸的铸件。

 

POLYMERIZATION IN STORAGE 储罐中的聚合

Styrene polymerizes slowly at normal ambient temperatures but very rapidly at elevated temperatures. Styrene polymerization is initiated by heat, lack of inhibitor and dissolved oxygen, and contact with peroxides and other free-radical initiators, ionic initiators, and redox initiators.  Polymerization can take place in storage as well as under more controlled conditions. The polymerization process is exothermic, evolving 288 btu/lb (17.8 kcal/gm-mole). If this evolved heat cannot be dissipated rapidly enough, the temperature of the monomer will rise, increasing the rate of polymerization and, with it, the rate of evolution of heat.  The temperature may rise to the point where the reaction becomes very rapid and self-sustaining (a runaway polymerization). Normally temperatures above 65°C (149°F) are needed to initiate runaway polymerizations.  During a runaway polymerization, the temperature will reach and exceed the boiling point of styrene.  The vapor may erupt violently from the tank vents or, if the vents are plugged or too small, it can create enough pressure to rupture the tank.  As the liquid polymerizes and becomes more viscous, vapor bubbles may become trapped, expanding the liquid and causing spills or rupture of the tank.  The important point is that polymerization may occur spontaneously in storage tanks. Depending on the quantity of material being stored, serious consequences may result.

苯乙烯在正常环境温度下缓慢聚合,但在温度升高下快速聚合。苯乙烯聚合在下列因素下引发,加热,缺乏阻聚剂和溶解氧、以及接触过氧化物和其它自由基引发剂,离子引发剂和氧化还原引发剂等。聚合可以在储存以及更受控的条件下发生。聚合过程是放热的,产生288btu / lb17.8kcal / gm-mole)。如果释放热不能尽快消散,单体温度将升高,从而加快聚合速率,并且随之增加热释放速率。 温度可以升高到反应变得非常快速和自我维持的点(失控聚合) 失控聚合通常需要高于65(149) 而引发。在失控聚合过程中,温度将达到并超过苯乙烯的沸点。 蒸汽可能会从储罐排气口剧烈爆发,或者如果排气口堵塞或太小,则会产生足够的压力造成储罐爆破。当液体聚合并变得更粘稠时,可能裹挟大量蒸气泡,使液体膨胀并导致储罐溢漏或破裂。重要的是聚合可以在储罐内自动发生。根据原料储量程度,可能会导致严重的后果。

 

PREVENTION OF POLYMERIZATION 防止聚合

Polymerization during storage may be prevented by close attention to monomer temperature, inhibitor level, polymer content and oxygen content. Determinations of inhibitor content, oxygen level in the vapor space, polymer content, and monomer temperature should be made on a routine basis (details are provided in Part 4). Styrene-containing vessels should be protected from external sources of heat. Running pumps against closed valves (dead-heading) should be avoided.  Care should be taken that vents, valves, pressure-relief devices, gauges, and controls do not become plugged with polymer.  (Requirements for the preceding are discussed in detail in the Styrene Monomer Storage Section of this publication). 

可以通过密切注意单体温度,抑制剂水平,聚合物含量和氧含量来防止储存期间的聚合。 应定期进行抑制剂含量,蒸气空间中的氧含量,聚合物含量和单体温度的测定。苯乙烯容器应免受外部热源的影响。应避免运行的输送泵出口阀错误关闭(憋泵) 应注意,排气口,阀门,减压装置,压力表和控制器不被聚合物堵塞。

HANDLING RUNAWAY POLYMERIZATIONS 处置失控聚合

The action to take will depend on how far the runaway has proceeded. The beginning of a runaway polymerization may be identified by an increase in monomer temperature (particularly if monomer temperature exceeds ambient or rises more than 3°F in one day)  The higher the temperature the further the runaway has progressed and the more difficult to stop.  Decisions concerning what actions to take must be made on-site. The following suggestions are listed approximately in the order recommended for halting a runaway polymerization and dealing with an advanced runaway:

应对措施将取决于失控进展程度。失控聚合的征兆可以通过单体温度的升高来识别(特别是如果单体温度超过环境温度或在一天内升高超过摄氏1.6℃或华氏3)。温度越高,失控程度越严重并且越难以停止。 必须在现场决定相关应对措施。以下大致按顺序列出用于阻止失控聚合和处理严重失控聚合各项建议的措施:

1. Add up to 0.5 % TBC and aerate.  Aeration can be accomplished by bubbling in air, or stirring the product while exposed to air.  Facilities storing and handling styrene monomer should have TBC inhibitor on hand in case of emergency.

加入0.5TBC阻聚剂并充气。 充气可以通过在空气中鼓泡或在暴露于空气的情况下搅拌物料来完成。 储存和处理苯乙烯单体的设备在紧急情况下应常备TBC阻聚剂。TBC溶液可通过专业渠道获得。

2. Reduce temperature of tank with water spray.  If the tank is insulated, the insulation should be removed as quickly as possible and prior to spraying with water.  Use ice, if feasible, but not in the product directly, as it will tend to remove the TBC.  If placed in the product, ice should be in a sealed metal container.

水雾降低储罐温度。 如果储罐是绝热的,应尽可能快地去除绝热层,然后再用水喷雾。如果可行,使用冰,但不直接放入产品中,因为冰会倾向于去除TBC。用冰放入产品中时,应放在密封的金属容器中。

3.  Keep vessel vented. 
保持储罐排气。

4. Dilute with ethylbenzene or toluene if tank is not venting and product temperature is below 231°F (110°C) to retard polymerization and reduce viscosity. 

如果罐内尚未排出气体且产品温度低于231(110),用乙苯或甲苯稀释以延缓聚合反应并降低粘度。

5. If possible remove product from tank before it solidifies, to save the tank. Use drums, diked area, or float on water.

如果可能,在物料固化前从储罐中转出产品,以挽救储罐。 使用桶,围堰或浮于水上。

 

INHIBITION 阻聚

TBC (4-tert-butylcatechol) is customarily added to styrene to prevent polymer formation and oxidative degradation during shipment and subsequent storage. 

通常在苯乙烯中加入TBC (4-tert-butylcatechol 4-叔丁基儿茶酚) 以防止在装运和随后的储存期间发生聚合以及氧化降解。


Inhibitors prevent polymerization in two ways.
阻聚剂从两方面阻止聚合过程:

(1)  They can react with and deactivate the free radical in a growing chain.

其可在聚合链增长过程中与自由基反应并使其失活。

(2)  They can act as an antioxidant and prevent polymerization by reacting with oxidation products in the monomer. It should be noted that sufficient oxygen must be present for inhibition. In the absence of oxygen polymerization will proceed as if no inhibitor were present.

其可作为抗氧化剂,通过与单体中的氧化物反应来防止聚合。应当注意,为了抑制必须存在足够的氧。 在不存在氧的情况下,聚合将如同不存在阻聚剂一样地发生。


The TBC level should be checked at regular intervals. Additional inhibitor should be added to maintain a safe level.

应定期检查TBC水平。必要时应加入额外的阻聚剂以保持其安全水平。


The time required for TBC concentrations to fall to a dangerously low level varies greatly because of different storage and handling conditions. The depletion rates in actual storage may be appreciably faster or slower depending on the set of environmental conditions. Factors which affect depletion of TBC are heat, water and air, with heat being the most important.

由于不同的储存和处置条件,TBC浓度下降到危险性低水平所需的时间差别很大。 实际存储中的耗率可以明显偏快或偏慢,其取决于一组环境条件。影响TBC消耗的因素是热,水和空气,热是最重要的。


If the inhibitor has been depleted and polymerization has begun, inhibitor should be added immediately. If unstable monomer is not treated promptly, it may become unsalvageable.

如果阻聚剂已经耗尽并且聚合已经发生,应立即添加阻聚剂。如果不稳定的单体不能得到迅速处理,情况会变得无可救药。


Additional inhibitor should be added when inhibitor levels drops below 10 ppm to maintain adequate inhibition.  Normal levels are 10-15 ppm, but some customers require up to 60 ppm because of unique storage conditions or process requirements. After addition, the storage tank should be recirculated until inhibitor is uniformly mixed and testing shows that target levels have been achieved. The tank should also be aerated to provide the proper amount of dissolved oxygen. Refer to Table 3A or 3B to determine proper amount of inhibitor to add.

当阻聚剂水平低于10ppm时,应加入额外剂量以保持足够的抑制力。 正常水平为10-15ppm,但是由于特殊的储存条件或工艺要求,一些客户需要高达60ppm 阻聚剂添加后,储罐应进行再循环,直到其均匀混合,测试显示达到了目标水平。储罐也应充气以提供适量的溶解氧。


The relatively small quantities of TBC required to raise the inhibitor level in stored monomer can most easily be added by using an 85% TBC/15% Methanol blend or a concentrated stock solution in the monomer or other solvent. Concentrated stock solution has an indefinite storage life when stored in the dark at normal ambient temperatures.

在储存的单体中提高阻聚剂水平所需的相对少量的TBC可以通过使用85TBC / 15%甲醇共混物或溶于单体或其它溶剂中的浓缩备份溶液最便捷地加入。浓缩备份溶液在正常环境温度下不透光储存时,其储存寿命几近无限。


A TBC concentrate for use in increasing the inhibitor level in styrene monomer can be prepared by dissolving 704 grams of pure TBC in 1 gal of styrene monomer (186 gram/liter).  At this concentration, 1 cc of the concentrate will raise the level of inhibitor 1 ppm in a drum of styrene having a net weight of 410 pounds. Table 3A lists the amount of concentrate required to increase the inhibitor level of bulk quantities by 10 ppm.

用于提高苯乙烯单体中阻聚剂水平的TBC浓缩液可通过将704克纯TBC溶解在1加仑苯乙烯单体(186/升)中来制备。在该浓度下,1cc浓缩物将在净重量为410磅的苯乙烯桶中将抑制剂的水平提高1ppm


Styrene vapors in storage tanks are not inhibited and can polymerize on roofs of storage tanks and around vents. Vapor space inhibitors are available but are not viewed as being adequately effective.

储罐中的苯乙烯挥发气并未被阻聚,可能在储罐顶部和排气口周围聚合。挥发气阻聚剂是有的,但并不被认为足够有效。

 

OXYGEN REQUIREMENTS 氧气需求

The problem presented by air is complex.  TBC is not an effective inhibitor for styrene monomer in the complete absence of dissolved oxygen. Excessive amounts of oxygen in the storage tank, on the other hand, may lead to other serious storage and handling problems.

空气带来的问题比较复杂。 TBC在完全不存在溶解氧的情况下不是苯乙烯单体的有效阻聚剂。另一方面,储存罐中过量的氧气可能导致其他严重的储存和处置问题。


Monomer vapors above the liquid level in the tank are uninhibited. These uninhibited vapors and condensed monomer droplets are readily oxidized on contact with air. These droplets containing oxidation products will polymerize quite rapidly and adhere to the rusted, porous surfaces of unlined steel tanks. They form stalactites on the roof and coat the sidewalls above the liquid level.

储罐中液面上方的单体挥发气并未被阻聚。未受阻聚的挥发气和冷凝的单体液滴在与空气接触时容易氧化。这些含有氧化产物的液滴将相当快地聚合并且粘附到无衬里钢罐锈蚀的多孔表面。其在罐顶形成钟乳石状结晶,并覆盖液面上方的侧壁。


Complete elimination of oxygen from the vapor space will lead to depletion of dissolved oxygen from the liquid monomer.  If this dissolved oxygen is greatly reduced, the TBC inhibitor becomes ineffective and rapid polymerization of the stored monomer will take place.  If an inert gas blanket such as nitrogen is used, provisions should be made to aerate the monomer once a week for approximately 30 minutes, or until the oxygen level again reaches saturation.  An alternative is to recirculate product and inject air at a rate approximately 1-2 ft3 /hr/million pounds of styrene monomer.  (Orbisphere Laboratories Oxygen Analyzer is suitable for measuring dissolved oxygen content.)

从气相空间完全消除氧气将导致来自液相单体中溶解氧损耗。如果溶解氧大大减少,则TBC阻聚剂会变得无效并且将使所储存的单体发生快速聚合。如果采用惰性气体保护层如氮气,则应该规定每周一次通气约30分钟,或直到氧气水平再次达到饱和。变通方案是循环物料并以约0.08-0.16立方/小时/千吨 (1-2 ft 3 / 小时 /百万磅) 苯乙烯单体的速率注入空气。(Orbisphere Laboratories氧分析仪可适用于测量溶解氧含量。)

 

POLYMER BUILDING IN STORAGE 储灌中累积的聚合物

The polymer deposited under storage conditions will be discolored, cross-linked, and high in peroxides, aldehydes, and other oxidation products. Deposits of contaminated polymer could eventually produce serious color and polymer problems in monomer stored under air in unlined steel tanks. Internal reflux, (the vaporization and condensation due to normal temperature differentials) will dissolve small amounts of this polymer and carry it back into the tank, thereby increasing both the polymer content and the color of the stored monomer.

在储存条件下沉积的聚合物将变色,交联,并有高含量的过氧化物,醛和其它氧化物。受污染聚合物的沉积最终可能在无内衬钢质储罐中含空气储存的单体中产生严重的色泽和聚合物问题。内部回流(由于温差而汽化和冷凝)也会溶解少量的这种聚合物并将其带回储罐液相中,从而增加聚合物含量和加深所存单体的颜色。


Polymer deposits in tanks also create difficult removal and cleaning problems. If stalactites are allowed to grow, their weight may damage the roof or roof-supporting structure of large vertical storage tanks.

储罐中聚合物沉积也产生除污和清洁的难题。如果任由钟乳石状结晶生长,其重量可能损坏大型直立储罐的罐顶或罐顶支撑结构。


Styrene monomer should not be allowed to remain in any hose after use because the monomer will polymerize and form undesirable reaction products.  Promptly drain and clean these lines after usage. Toluene or ethylbenzene may be used to clean lines.

苯乙烯单体在使用后不应留在任何软管中,因为单体会聚合并形成不希望的反应产物。使用后立即排干并清洁这些管线。甲苯或乙苯可用于清洁管线。

 

4-TERT-BUTYLCATECHOL (TBC):

TBC is typically added to styrene monomer to inhibit polymer formation and oxidative degradation during storage and shipment.  Typically, product is inhibited when TBC levels are between 10-15 ppm, but if long storage times or high temperatures are anticipated, product is inhibited up to 100 ppm. Many customers store limited quantities of TBC concentrate or solid TBC for emergency use.

TBC通常添加到苯乙烯单体中以抑制聚合物形成以及储存和运输过程中的氧化降解。通常,当TBC水平在10-15ppm之间时,物料受到阻聚,但是如果预期储存时间较长或温度较高,则物料有效阻聚剂量可达100ppm。许多用户存储有限数量的TBC浓缩物或固体TBC用于紧急使用。


TBC is severely injurious (extremely corrosive) to the skin and eyes, and may be absorbed through the skin in toxic amounts.  TBC is a known skin sensitizer and may cause depigmentation of the skin.  Once an individual has become sensitive, even exposure to very small amounts can cause a response. Concentrated solutions in styrene can be expected to cause greater irritation than would be expected from just the monomer.  Slight damage to the liver has been reported in a rat feeding study.

TBC对皮肤和眼睛具有严重伤害性(极高腐蚀性),并且可以通过皮肤吸收致害剂量。TBC是已知的皮肤致敏剂,并可引起皮肤褪色。一旦个体致敏,即使暴露于非常小的剂量也可引起反应。可以预期苯乙烯中的浓缩溶液比纯单体更具刺激性。在大鼠喂养研究中已经报道了其对肝脏具有轻微损害。


Personnel should wear goggles and/or full face shield and protective clothing including gloves and apron made of Viton while working with TBC or its concentrated solutions. It should not be pipetted by mouth. In case an accidental contact with TBC or its strong solutions should occur, it should be removed immediately from the skin by washing with soap and plenty of water; for eyes, flush them with plenty of water; for at least 30 minutes and get medical attention immediately.

使用TBC或其浓缩溶液时,人员应戴护目镜和/或全面罩和防护服,包括Viton氟橡胶制手套和围裙。切勿用嘴移液。如果发生意外接触TBC或其浓溶液,应立即用肥皂和大量的水冲洗皮肤加以清除;  对眼睛,也用大量的水冲洗,至少30分钟,并立即就医。

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