The Study on Mercury Processing in PVC Production

Abstract. Mercury is highly toxic heavy metal pollution attracted the attention of the world. This paper analyzes the situation the main industry in mercury use PVC production. Manufacture of battery， electric light， medical equipment in China. Furthermore， it discusses the details of the best technology the use of mercury emissions reduction and mercury control in that industry. The result is that certain technologies such as low mercury. In PVC industry catalyst， as mercury battery， amalgam substituted Mercury and LED light in the electric light source industry， electronics the thermometer and blood pressure in the medical device industry and so on， reduce mercury able to make full use of and emission reduction in risk mercury pollution to the environment.

Key words： Mercury Processing； PVC Production； control technology

1. Introduction

Calcium carbide method of vinyl chloride synthesis reactions to the activated carbon as the carrier chlorinated mercury accelerant， due to high temperature in chlorinated mercury sublimation， in high temperature reaction process always have a certain amount of chlorinated mercury into reaction generated into gas， refined syn gas technology different， produce the level of pollution and party type are different. Add catalyst micro activity poisoning， stopped the factors. The deactivation， chlorinated mercury catalyst must produce certain consumption. Because mercury is a scarce resource， and polluted， has caused the height of the international concern， in calcium carbide method of vinyl chloride mercury-free catalyst development. Before success reduces the consumption and production process mercury pollution， has become Calcium carbide method for polyvinyl chloride （PVC） enterprise and chlorinated mercury catalyst industry must face problems. Yunnan salinization Co.， LTD is located in kunming， yunnan chlor-alkali device An NingShi， for ChongHuaGong concentration areas of yunnan province， is located in the upper reaches of Yangtze river， belong to environmental sensitive river basin. As early as in 2008， the people's government is of Kunming Ming. It required， area of drainage of waste water treatment by all water quality must reach to the urban sewage treatment plant emissions standards （GB18918- 2002） level 1 A standard. To this， the company actively response， made ensure that the "standards"， and finally achieve the wastewater "zero emissions overall orders mark， around mercury pollution reduction and did a lot of work and study， obtain some progress.

2.The flow of mercury will check

2.1 Analysis methods of optimization， improvement and search for the implementation of the programmed

Although 100000 t/a PVC device supporting a more complete test Means， basic can complete the daily production organization of raw materials， intermediate control， Ann all， environment and health requirements of analysis， but to complete the flow of mercury will check work also need to be studied further the process of different material form analysis method. Combined with calcium carbide method of vinyl chloride material characteristics， increased the cold. Atomic absorption analyzer and microwave digestion device. In order to ensure the accuracy of the data analysis， the different forms of contain Mercury samples method research and analysis， acquired the production data of the system and make check set the options laid a foundation. Considering the 100000 t/a PVC device has been put into production more than 2 years， in the short term to find PVC device mercury balance， get a complete and credible data have great difficulty. So the mercury will focus on touch check as soon as possible clear the flow of mercury and losing rule， especially to find out as early as possible sources of pollution， press according to the material flow， the mixed dehydration to dry tail exhaust for a whole party a system analysis.

A distillation tail exhaust gas samples， and the storm dry， to smoke exhaust catalyst true exhaust air pump， production device inside the atmospheric environment differences concentration， in and out activated carbon is mercury in addition to syn gas； Liquid sample have mixed dehydration condensing acid and waste. Hydrochloric acid， alkali， waste soda-wash tower before the machine， finished product， the condensed water drainage from the mother liquor， calcium carbide slag heart on clear liquid， vacuum pump cycle fluid， edible and total row wastewater， etc.； Solid sample have catalysts， and waste activated carbon， sawdust， sludge and so on. At present already complete test method of optimization and improvement， PVC production work. In the process of the flow of mercury art investigation and inspection， contain mercury wastewater treatment of device check， operation data detection， a total of 12 has more than 700 data. Prison the data show that the production environment atmosphere within the device testing results is low， far lower than the harmful factors workplace occupational exposure limits part 1 chemical harmful factors "（GBZ 2.1） limit. Solid phase samples by test results representative samples and data analysis method， means and limit， its fruit is not support the establishment of mercury device balances， as long as the strict implementation of the crisis risks waste management relevant provision， solid waste pollution can be to control.

2.2 Shall check

In the preliminary check for process， according to the monitoring data of continuous adjustable the whole scheme， respectively， aiming to take common key monitoring， sustained attention and so on way. According to the testing results， conditional， and immediately the improvement is the discharge of waste water containing mercury scattered for the collection， after cyclical multiplexing， to contain Mercury wastewater treatment plant. Along with the rack cleaner tap， the rain the sewerage and other measures implementation， vinyl chloride device for trench and total drainage mercury in content gradually declined， realize the stable standards. Check the system will work contract half a year， the monitoring data can reflect the basic production load， operation now shape， corrective actions， and the difference of the device， through reading monitoring data， that， take off the mercury device activated carbon efficiency， remove the syn gas mercury； vice the mercury in content with hydrochloric acid in off the mercury in the use time of activated carbon， a very slowly rising， can be used as the basis for the judge to take off the mercury effect； Alkali washing tower waste alkali contain mercury quantity is low， the mercury in syn gas that get the effective intercept； Transformation workshop pit wastewater contain mercury quantity change is great， mercury pollution mainly comes from the change of when splashed Isaac， necessary height attention， once the plant area drainage system produce pollution， it is difficult to short-term snap after， also easy to accident emissions.

3.The establishment and implementation of measures

Facing local higher environmental protection requirements， the company set in cut mercury pollution scheme to satisfy （GB18918-2002） level 1 A standard at the same time， positive research and formulated a finally realize wastewater zero emission the overall scheme of the， implement the mature technology of centrifugal biochemical mother liquor （depth） processing， acetylene clean waste time sodium circulation reusing， project.

At present， most in the industry mercury wastewater treatment commonly the method of sulfide， treated can satisfy the reuse and emissions requirements. And the company always Haikou to achieve discharge standards is < 0.001 mg/L， according to this a standard must be to evaluate current of production device every step of the way. According to the characteristics of the mercury wastewater treatment， waste water to get the economy， have the efficiency of the management must be sharply reduce the discharge of sewage low contain mercury， therefore， formulated the "rack cleaner tap， rain water and the sewerage， collect high.

（1） Set up the new wastewater collection pit. Will alkali washing tower to monomer lay aside between the gas holder slot and all drainage collect into gas holder cofferdam newly established within in the pit， used as a base， to take off the acid washing tower of the tower of process water， and turn the factory building area of the floor or equipment flush water.

（2） The sewerage implementation of the rain. Device construction considered the south the rain； the effects of the converter are arranged in the workshop， according to the ground pollution situation， and will lead to the further roofing rain storm sewer contaminated area the nets， in the area of mercury homework early collect rainwater reuse.

（3） Set up special assignments section in mercury. Adding new catalyst warehouse library， to meet new and old catalyst and other contain mercury solid waste management， regulating the catalyst in the factory in transportation line， eliminate spilled and. In the transformation workshop， a especially the door system flushing area concentrated wastewater treatment to avoid the overhaul of the cause time pollution.

（4） Strengthen the water management. In converter and related production area， cancelled most production point， only a few points left to meet emergency requirements， and the valve and seal.

（5） Strengthen site process control and no leakage management. Through the above measures to take， contain mercury wastewater quantity effectively control. Transformation workshop original wastewater pit （including discharge waste alkali washing tower base） as the only source of waste water containing mercury， contain mercury wastewater quantity reduced greatly Less， 100000 t/aPVC full load operation of the device when mercury wastewater quantity. Only 20 to 30 m3 / d， wastewater treatment and cost are the difficulty of innovation former has greatly reduced.

Facing the current environmental protection department higher request， the first priority is to contain mercury wastewater treatment technology promotion. The company has formed a characteristic calcium carbide method of vinyl chloride contain mercury wastewater treatment techniques， concrete process. Treatment of wastewater containing mercury meets the caustic soda， PVC industrial water pollution emissions standards （GB 15581） table 6 requirements， mercury content < 0.005 mg/L.

And part of the process in the industry compared， this technology has the following characteristics.

（1） When the mercury in waste water content in a certain range change， can use fixed elixir formula， improve the treatment efficiency， vary considerably， according to treatment results adjusted formulation， rework can.

（2） The clear separation， not adding filter aid agent and auxiliary filter Water， reduce the quantity of the sludge， and a small amount of sludge through the air basks in can bagging.

（3） Reaction tank effective volume for 30 m3， and set before and after bigger Volume pool， is helpful for adjusting water quality and production organization.

（4） Processing cost is low， regardless of the adjusting the pH of the acid and consumption Alkali， contain mercury wastewater treatment costs for 3 ～ 5 yuan/t

Although the syn gas activated carbon to take off the mercury， but byproduct hydrochloric acid still contain a certain amount of mercury， cannot satisfy the byproduct hydrochloric acid "（HG/T 3783） heavy Metal （to lead plan） 0.005% or requirements. Therefore， only completely disappear

In addition to produce byproduct hydrochloric acid to put an end to the transfer of mercury， and byproduct hydrochloric acid quantity and vinyl chloride device technology and operation control has close cut relationship. Vinyl chloride synthesis， chlorinated hydrogen control excessive， generally for acetylene the gas by 5% ～ 10%， if not more than control index cap， into the take off acid the tower of accurate operation of hydrogen of 2 times. In order to reduce the part of the byproduct hydrochloric acid amount， usually adopts the technology of the conventional to take off the post-mortem hydrochloric acid， this kind， too much about two-thirds of the hydrogen can be recycled.

In addition to byproduct hydrochloric acid， must use depth to take off the post-mortem process， further recovery chlorine of hydrogen， dilute acid HCl （< 1%） back to take off acid tower recycling. Efficient gas phase mercury recovery technology can remove most of the syn gas point’s mercury， leaving a small bit of mercury into the byproduct hydrochloric acid， using hydrochloric acid. To take off the post-mortem process， circulation hydrochloric acid or calcium chloride mercury in will enrichment， use the following method in addition to mercury.

（1） Using waste alkali neutralization. Because of the syn gas contains carbon dioxide carbon， alkali washing tower of the utilization rate of caustic soda is not high. Use the waste alkali not in the product of the reaction of NaOH Na2CO3 to counteract byproduct hydrochloric acid， take out the part of the water and acid mercury， the generation of wastewater containing mercury in wastewater send Richard device.

（2） Cycle in acid liquid to take off the mercury. Part of the cycle hydrochloric acid bypass into the mercury device equipped with adsorbent off sorbents constantly absorbing the circulation acid mercury so as to realize the balance of mercury. The company was choose 3 kinds of different absorption agents do byproduct hydrochloric acid removal from the mercury in test， of different test conditions， no with the removal rate of mercury adsorbent differences， the first time use of absorbent .Mercury removal rate is 79.59% ～ 97.52%， considering the subsequent recovery of mercury and contain mercury waste disposal， absorbent choose activated carbon particles.

High mercury of catalysts， and the mercury levels low mercury catalyst respectively by 11.5%， 6.5% plan， use the deactivation catalyst mercury levels after with 3.5% plan， tons of PVC the products in both consumption， low efficiency in the use of mercury catalyst for high Mercury catalyst 2.67 times. Therefore， low development and use of mercury catalyst for calcium carbide method reducing the consumption of polyvinyl chloride （PVC） industry mercury and reduce the pollution of mercury meaning Major righteousness， and no mercury catalyst development， to become the industry mercury pollution prevention and control are the most important. Chlorinated mercury in the loss from the syn gas into， the mercury device， take off hydrochloric acid washing mercury in gas phase is effectively intercepted. Since the last century the 70 s began， calcium carbide method PVC industry by active in addition to the mercury removal from the carbon mercury in syn gas， removing the obvious effect. The company through to the byproduct hydrochloric acid mercury concentrations in the analysis and change in time to take off the mercury lives carbon， preliminary accounting also support its views， but active carbon adsorption capacity quantity， adsorption rules， use cost to be groping to continue. In fact， through the use of low mercury accelerant， mercury sharply reduce the loss， the syn gas to take off the mercury activated carbon consumption will also will be reduced correspondingly， which is beneficial to the recovery of mercury use and reduce production cost.

Vinyl chloride in syn gas off mercury， should be actively looking for adsorption efficiency and capacity are better adsorbent， through the chlorinated mercury sorbents recovery recycling， may reduce the calcium carbide method of polyvinyl chloride （PVC） industry mercury apparent disappear fee quantity. Adsorbent regeneration and recycling may reduce the take off of activated carbon mercury running cost. Therefore， a real sense of efficient mercury recovery technology is included from the production， use mercury chloride， recovery and to take off the mercury adsorbent processing the whole process of the integration of technology.

With mercury catalyst for its source in the flow of the mercury will check and process effect evaluation process， test object involves gas， liquid and solid phase. The company the current analysis methods have extraction， heat cracking method， microwave digestion cold the original. The analysis method exist to varying degrees sample processing capacity， poor little representative， dilute levels number， error control has the certain difficulty， can't solve element mercury and chlorinated mercury problems such as identification.

In order to give mercury pollution prevention and control work and providing comprehensive support， build more effective analysis system is necessary. Preliminary planning adopting micro wave digestion + icp-ms Ed， complementary with automatic measuring instrument for solid sample mercury the core of the system solutions.

Microwave digestion + icp-ms Ed method， with the icp-ms mention rose method detection limit； To microwave digestion to form detection， and exactly grasp the mercury existing form； Through the ICP， can effectively eliminate the showering cheated produce of the testing error； Testing ability to extend a space is big， the appropriate sample processing method can process of polyvinyl chloride （PVC）. The gas phase， liquid and solid materials heavy metals are in the total content and form of implementation.

Automatic measurement instrument solid sample mercury is the advantage of samples and the amount quantity are bigger， sample quality for 500 mg， volume is 500 mL； 70 sample a sample of the automatic system to ensure a sample flux； Need not kind product processing， the samples have high representative； Has the ideal of the detection limit.

Through the appropriate sample is processing methods but the production process of polyvinyl chloride （PVC）. The gas phase， liquid， and solid materials in the content of total hg implementation accurate inspection

To measure， is currently contain mercury materials total content detection method of the relatively optimal scheme. Defect is the only materials total mercury content detection. This method "microwave digestion + icp-ms even usage" is to contain mercury materials detection. Strong complementarily， will contain mercury is highly completion and system test materials.

4.Conclusions

Through the operation of the management， contain mercury wastewater treatment， hydrochloric acid to take off the post-mortem process renovation， low in mercury catalyst use and take off the mercury and other projects the step by step， this company mercury pollution prevention has obtained the certain into exhibition. The cycle of mercury recycling is the guide to industry and the policy support， calcium carbide method mercury pollution comprehensive prevention and control work polyvinyl chloride （PVC）.

References

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