Prevention of Acrylic Acid-Induced Fouling
Publication Date: 2016-Jul-20
The IP.com Prior Art Database
Page 01 of 6
*** Prevention of acrylic acid-induced fouling***
In the high pressure polyethylene production process, co-monomers are used to improve the functionality of LDPE. Acrylic acid and acrylates are very reactive and readily polymerize in absence of inhibitor. These polymerization reactions give fouling at various places in the process. The use of activated and non-oxygen activated inhibitors is essential in the fouling prevention. Properbalance between the 2 inhibition systems is a key element for reliable operation.
Case for action
The high pressure polyethylene process is well suited to produce copolymers with polar components like vinyl acetate, acrylic acid, acrylates or methacrylic acid and its esters. Polar components are very reactive and need stabilization for storage, handling and processing. These co monomers are typically injected in the suction of the secondary compressor or directly in the reactor feed. They are very reactive and polymerize in various sub-systems (e.g. purge compressor, condensate handling…), which can create operational upsets. Plugging with "popcorn"-like fouling is one of these possible operational impacts and the use of inhibitors is important to suppress this fouling.
Glacial Acrylic acid and acrylates are mostly stabilized directly by the supplier with methyl hydroquinone that acts in combination with oxygen. For emergencies (e.g. storage tank run away), PTZ (phenothiazine) injection can also be used to stop the polymerization in absence of oxygen.
In the high pressure process oxygen is consumed in the reaction. The unreacted co-monomer is very unstable and reactive. Unreacted co-monomer can be present in the compressor seals, compressor leak gas streams, or in compressor cooling oils, recycle waxes, purge compressor gas and knock out systems, primary compressor gas systems, polymer streams...
Aside of that, also the liquid co-monomer feed and waste streams need effective stabilization for polymerization prevention. For special reactor conditions, oxygen is stripped from the co- monomer, which can be done with an inert gas, like nitrogen. Such oxygen-freed co-monomer is extremely reactive, because the MeHQ inhibitor does not work anymore, which calls for an alternative solution. While PTZ is in principle not desired in the high pressure process, because of discoloration and initiator inhibition, it has been found to be still very effective relatively low concentrations. Such trace quantities can be added to the process either as a trace component of the delivered co-monomer or after addition at the receiving site to the incoming raw material. This can be up to 30 wt ppm PTZ in the co-monomer feed, but even lower quantities (below 1wt ppm) have shown to be are effective, especially in the purge compressor system. In one site, the presence of PTZ helped increasing the interval between cleanings of the 3rd stage purge compressor suction drum from a few we...