Issues regarding the recycling of polypropylene films
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Process: The gas from the compression gas tank of compressor i is compressed and fed into a buffer tank (at around 2 MPa). The non-condensable gases at the top (without heating) are sent to the membrane recovery system, where the inlet pressure for membrane recovery is set at 1.95 MPa. Question: After operating the membrane recovery system for a while, it was found that the vent line of the membrane recovery system was severely frosted. What I want to ask is whether this situation indicates that the membranes have been flooded How exactly was this situation caused, and how should it be dealt with? 1. It could be that the inlet pipeline for membrane recovery is not equipped with heating; 2. it might also be that the load on the membrane recovery system is too low, resulting in insufficient recovery. However, even after reducing the amount of fluid in the inlet buffer tank by opening part of the compressor return flow, this issue persists. After this problem occurred in the membrane recovery system, new membranes were installed, but it still happens! The components of the non-condensable gas at the top include propylene (60–80%), nitrogen, hydrogen, etc
It is estimated that frosting occurs due to the high-pressure gas inside, particularly the endothermic vaporization of propylene, which causes frosting in the pipelines. I’m not quite familiar with your detailed process; you can contact me at QQ84568088
The key is to add heat tracing to prevent the saturated propylene mixture in the membrane module from forming liquid propylene due to temperature drop caused by flow obstruction. :lol
This issue has been perfectly resolved; the P-membrane recovery system operates stably, with no occurrence of membrane flooding. With one set of membranes in use, the propylene content in the exhaust gases has been reduced to below 5%. On this basis, several key factors in membrane recovery operation were identified for analysis: 1. An increase in the temperature of the chilled water leads to poor condensation, resulting in a smaller decrease in the purity of the propylene gas entering the membrane; at an absolute pressure of 1.6 MPA, about 70% of it is propylene, with a saturated vapor pressure of 22 degrees. If the temperature in the membrane system or in the pipes beforehand is below 22 degrees, a liquid phase can precipitate. 2. The refrigeration unit has a high capacity, resulting in a large amount of liquid propylene being formed within the cryocooler. This liquid cannot be collected in tanks in time and is carried away by the gas phase; it may also enter the membrane system. This possibility cannot be refuted either; further observation is needed. 3. The ice machine is operating normally; the gas coming out of the precooler is saturated propylene gas, and if the temperature drops, a liquid phase will precipitate. 4. If the separation efficiency of the membrane system declines for unknown reasons, the propylene content in the exhaust gas will be high, resulting in a higher saturated vapor pressure and making liquid phase precipitation very likely. The key to solving the problem is still adding heat tracing.
In membrane separation systems, the membrane allows gases to pass through; electric heating is required to convert propylene into a gaseous state. Membrane separation technology is a new generation of gas separation technique that was developed in the 1970s. Its principle involves separation under pressure, taking advantage of the differences in the adsorption capacity of various components in the gas on the surface of the polymer membrane, as well as differences in their dissolution and diffusion within the membrane – that is, differences in permeation rates. It has now become a relatively mature process technology and is widely used in the separation and concentration of many gases. In industrially developed countries, this is referred to as \"creative technology for resources.\" Currently, there are mainly two processing methods: the positive pressure method and the negative pressure method. The former is suitable for situations where both oxygen and nitrogen are used, or where a high oxygen concentration is required. As early as the early 1980s, many developed countries invested substantial human and financial resources in researching membrane-based oxygen enrichment technology. Japan, in particular, had its Ministry of International Trade and Industry fund 7 companies and research institutions, including Asahi Glass, to participate in the \"Research Group on Membrane-Based Oxygen-Enriched Combustion Technology.\" Due to energy shortages, nearly 20 companies in Japan have successively introduced membrane-based oxygen enrichment systems. The main advantages of membrane technology include the absence of phase changes, low energy consumption; the scale of the equipment can be adjusted according to the required treatment capacity; it features simple design, easy and safe operation, fast startup, high operational reliability, no environmental pollution, low investment costs, and a wide range of applications. The scale, cost-effectiveness, technical maturity, energy consumption, and applications of various gas separation methods are as follows: Polymer separation membranes are semipermeable thin films made of polymer materials that possess selective permeability. The main ones include polyamides, polyimides, polysulfones, polyvinic acids, acrylic derivative polymers, and celluloses. However, most polymer materials suffer from the interdependent relationship between PO2 and αO2/N2, as well as drawbacks such as poor heat resistance and susceptibility to corrosion. Polysulfone is a membrane material with excellent mechanical properties, good heat resistance, resistance to microbial degradation, and is inexpensive and readily available. Membranes made of polysulfone are often used as the basic material for gas separation membranes, owing to their thin structure, high pore volume in the inner layer, and regular micropores