PMMA depolymerization [recycling] reactor

Progress in reaction mechanisms and reactor technologies for thermochemical recycling of poly(methyl methacrylate). The feedstock recycling of poly(methyl methacrylate) (PMMA) through thermal degradation is an important societal challenge enabling the cycle of polymers. The annual global production capacity of PMMA is over 2.4*104tons, but currently only 3.0*103tons are collected and recycled in Europe each year. Despite the rather simple chemical structure of MMA, there is still debate about possible mechanisms of PMMA degradation.

Zamak Mercator reactor for thermal, and therefore non-catalytic, chemical recycling of poly(methyl methacrylate) (PMMA), which uses extrusion technology, is used to heat and initiate thermal degradation of PMMA. The heat necessary to carry out the pyrolysis process is supplied by electric heaters. The advantage of an extruder over a fluidized bed reactor configuration is that the overall process is easier to handle. For example, graphitization is avoided because one of the disadvantages of a fluidized bed reactor with quartz sand as fluidized material is that the liquefied material can be graphitized. Soot can also come off the grains and be drawn into gas stream, thus requiring additional filtration systems that are not needed for the extrusion technology. MMA is discharged via degassing ports and condensed later. from 89 to 97%.
The degradation process can be easily handled on an industrial scale PMMA can be degraded with virtually no residue No residue means that deposits are avoided in the reactor to ensure continuous operation Heating of PMMA is affected by the heat conductivity of the extruder barrel walls As the plant size increases, the ratio of wall area to reactor volume decreases For larger installations, the extruder must be set at a much higher temperature to pyrolyse sufficient amounts of PMMA Careful design of the cylinder and screw layout is a key factor to prevent local overheating causing an increase in by-products Due to this problem, it is important to design the heating system and the simultaneous cylinder zone cooling It is equally important to use professional multi-zone temperature controllers that are able to control the cylinder heating and cooling system in real time.

In the reactor, the polymeric material comes into contact with a hot cylinder and is mechanically mixed and ground by suitably configured segmented screws By-products are continuously discharged through the screws to pressurized waste containers This prevents the agglomeration of by-products inside the reactor Degradation [pyrolysis] is efficient between 400 and 450oC .

The collected gas phase depolymerization products are directly discharged through degassing ports and cooled by cooling product recirculation, then the condensed products are sent to a collection vessel.

The modernized design of the reactor changes the principle of collecting the resulting vapors The novelty of the design consists in extruding the resulting vapors at the end of the extruder, as opposed to direct extraction through multiple venting ports The appropriate design of the screws causes the molten polymer to act as a kind of plug, vapor backflow is impossible Solid and gaseous products are pushed into the pressurized a residue tank, where the MMA vapors are separated from the solid residues formed during the thermal degradation of PMMA. The gaseous products are then condensed in a further cooler.

These processes produce good quality MMA from high quality PMMA waste. This technology has limited recyclability of lower quality PMMA due to the production of more metal contaminated solid residues
It is the most promising reactor technology for the degradation [pyrolysis] of PMMA Low residence time in the depolymerization reactor avoids the production of secondary degradation products Good technical solutions are required for the construction of reactors of this type Contrary to most other vinyl polymers, pure PMMA can be almost completely depolymerized to monomerCurrently there is still limited understanding of the decomposition chemistry of PMMA and its related copolymers, but continuous depolymerization processes are already operating.The key challenge is to achieve adequate heat transfer to facilitate chemical transformations towards fast and high-efficiency MMAW creation. Within the industrial framework, reactor technologies based on twin-screw extruders seem to be the most promising.
Zamak Mercator designed and installed the first extrusion reactor for PMMA depolymerization in 2014. This is an individual project, it is based on a 2 x 90 mm L/D 52 extruder