Is maintenance required after replacing the catalyst?
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An article mentions that after replacing the catalyst in vinyl chloride production, it is necessary to allow a curing period of 7 to 20 days. Does this mean that production has to be halted? Is there a problem with this?
Also, how often does the catalyst need to be replaced?
It’s not maintenance; it’s activation. Most catalysts contain water; after replacement, they need to be dried and then activated with hydrogen chloride.
It generally needs to be replaced after 3,000 hours of use; in actual production, the acetylene content in the outlet syngas is the main parameter analyzed.
An article mentioned that after replacing the catalyst in vinyl chloride production, it is necessary to allow a curing period of 7 to 20 days. I’ve heard of nothing like this after all these years! Don’t believe it.
The low-mercury, environmentally friendly catalysts developed now can be used for 7,200 hours – they’re really great!
It mainly involves catalytic dehydration, followed by reduction with hydrogen chloride.
Does that activation time take 7 to 20 days? When I was working at the PVC factory, I heard from the technicians that after replacing the catalyst, it needed to be activated using hydrogen chloride in the converter; but it seems that this process doesn’t take that long
Production does not need to be interrupted; some design processes include a dedicated pipeline for the one-way flow of hydrogen chloride.
May I ask how exactly the catalysts are activated in practice?
First, drying is carried out using hot nitrogen, and it is determined whether to stop the drying process by analyzing the moisture content in the nitrogen at the outlet； After drying, hydrogen chloride is introduced separately for activation, for about 30 minutes.
Today’s catalysts are all treated with acid to reduce the induction period. Activation involves the removal of moisture; generally, the activation process takes no less than 8 hours. When there is no acid emissions and the purity of hydrogen chloride at the inlet and outlet is the same, it is considered that the activation is complete
Nitrogen is used to displace oxygen; the amount of nitrogen required is approximately 4 to 5 times the volume of the converter. Hydrogen chloride is then introduced to drive the nitrogen out of the converter, while maintaining a pressure of 50 kPa. This process lasts for 6 to 8 hours, but it must not exceed 8 hours and should not be less than 6 hours. The inlet valve for hydrogen chloride should be set to the minimum level, sufficient to maintain a pressure of 50 kPa. During the activation process, pay attention to regularly draining acid from the bottom of the converter until crystalline, dry iron chloride crystals are removed. The activation converter must be installed before the mixture is introduced; otherwise, exposure to hydrogen chloride over an extended period can lead to leaks.
In the production of vinyl chloride, it is necessary to carry out curing after replacing the catalyst, which means properly controlling process parameters such as temperature and gas flow rate, in order to extend its lifespan. This is just my personal opinion for reference only. This post was last edited by wang*neng on 2009-4-13 09:42
Most PVC manufacturers still use fixed-bed reactors, which are typically composed of multiple converters. A surplus number of these converters is used; stopping one or two of them and reversing the catalyst does not affect the production capacity, so there is no need to shut down the plant.
May I ask who knows the catalyst activation method? How can hydrogen chloride be used alone for activation and then removed?