30-11-2012, 06:01 PM
Feasibility study on China‘s mercury-free catalyst R&D
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PVC production and mercury management in China
PVC plastic is widely used in industry, agriculture, national defense and chemical construction materials, etc in China.
Chinese PVC production can be divided in two categories: carbide method and ethylene method.
For the carbide route, CaC2 is used as raw material, and activated carbon with HgCl 2 serves as catalyst for the production of VCM which will be further used to make PVC.
Table 1: PVC Data for China 2009 (Source MIIT, 2010)
Mercury in carbide based process
Currently for one ton PVC produced in China:
1.2 kg of HgCl 2 catalyst consumed on average (as 11% of HgCl 2 content).
For 5.8 million tons of PVC produced in 2009, around 7000 tons of mercury catalyst used, comprising:
770 tons of HgCl 2 and 570 tons of mercury were used (MIIT, 2010)
Carbide-based PVC production consumes around 60％ of China’s total annual mercury use.
Catalyst Effectiveness
Sublimation and intoxication causes reduction of catalyst effectiveness.
When it decreases to certain level, catalyst need to be replaced and inactivated catalyst becomes worn catalyst.
Usually waste catalyst contains 3-4.5% mercury.
After Hg remover, part of the sublimated HgCl2 will enter the worn acid and alkali and get emitted.
Necessity of carbide process
Carbide PVC production uses lots of mercury, but it remains necessary：
Chinese energy structure characterized as "lack oil, poor in gas and rich in coal"
Ethylene method can hardly meet the need of PVC industry alone
Carbide PVC industry pays high attention to mercury pollution administration.
Emission reduction measures for carbide PVC production
The industry has adopted the following measures to reduce mercury use and emissions:
low mercury subsititute for high mercury one；
activated carbon in mercury remover to absorb mercury in gas phase；
waste acid recycled by desorption device, a few of which are used to neutralize worn alkali；
waste alkali used to neutralize waste acid, and collected together with other waste liquid for central treatment;
waste catalyst, activated carbon and other waste sludge are sent to certified orgnization for central treatment.
Project background and progress
UNEP has provided funds for China to carry out PVC project through small grants program. The project is now on its second phase.
Phase I “Communication and Deliberation of the Practice of Mercury Use and Emission Reduction during PVC production” agreement was signed in January of 2009.
Phase II “Feasibility study on China‘s mercury-free catalyst R&D ” agreement was signed in April of 2011.
Conclusion
Although the Chinese central government has paid a lot of attention to mercury pollution prevention and control in the VCM sector, it is still facing a lot of difficulties and uncertainties with spreading information on the low-mercury catalyst and the researching & development of free-mercury catalyst.
We hope for more support, including finance and technologies from developed countries!
[attachment=41968]
PVC production and mercury management in China
PVC plastic is widely used in industry, agriculture, national defense and chemical construction materials, etc in China.
Chinese PVC production can be divided in two categories: carbide method and ethylene method.
For the carbide route, CaC2 is used as raw material, and activated carbon with HgCl 2 serves as catalyst for the production of VCM which will be further used to make PVC.
Table 1: PVC Data for China 2009 (Source MIIT, 2010)
Mercury in carbide based process
Currently for one ton PVC produced in China:
1.2 kg of HgCl 2 catalyst consumed on average (as 11% of HgCl 2 content).
For 5.8 million tons of PVC produced in 2009, around 7000 tons of mercury catalyst used, comprising:
770 tons of HgCl 2 and 570 tons of mercury were used (MIIT, 2010)
Carbide-based PVC production consumes around 60％ of China’s total annual mercury use.
Catalyst Effectiveness
Sublimation and intoxication causes reduction of catalyst effectiveness.
When it decreases to certain level, catalyst need to be replaced and inactivated catalyst becomes worn catalyst.
Usually waste catalyst contains 3-4.5% mercury.
After Hg remover, part of the sublimated HgCl2 will enter the worn acid and alkali and get emitted.
Necessity of carbide process
Carbide PVC production uses lots of mercury, but it remains necessary：
Chinese energy structure characterized as "lack oil, poor in gas and rich in coal"
Ethylene method can hardly meet the need of PVC industry alone
Carbide PVC industry pays high attention to mercury pollution administration.
Emission reduction measures for carbide PVC production
The industry has adopted the following measures to reduce mercury use and emissions:
low mercury subsititute for high mercury one；
activated carbon in mercury remover to absorb mercury in gas phase；
waste acid recycled by desorption device, a few of which are used to neutralize worn alkali；
waste alkali used to neutralize waste acid, and collected together with other waste liquid for central treatment;
waste catalyst, activated carbon and other waste sludge are sent to certified orgnization for central treatment.
Project background and progress
UNEP has provided funds for China to carry out PVC project through small grants program. The project is now on its second phase.
Phase I “Communication and Deliberation of the Practice of Mercury Use and Emission Reduction during PVC production” agreement was signed in January of 2009.
Phase II “Feasibility study on China‘s mercury-free catalyst R&D ” agreement was signed in April of 2011.
Conclusion
Although the Chinese central government has paid a lot of attention to mercury pollution prevention and control in the VCM sector, it is still facing a lot of difficulties and uncertainties with spreading information on the low-mercury catalyst and the researching & development of free-mercury catalyst.
We hope for more support, including finance and technologies from developed countries!