Design, fabrication, and testing of microwave pyrolyzer for polypropylene and low density polyethylene medical plastic waste

• Main Author: Dinh, Chau Van
• Format: text
• Language: English
• Published: Animo Repository 2005
• Subjects: Medical wastes; Polypropylene; Thermoplastics; Health facilities > Waste disposal; Chemical Engineering
• Online Access: https://animorepository.dlsu.edu.ph/etd_masteral/3331; https://animorepository.dlsu.edu.ph/cgi/viewcontent.cgi?article=10169&context=etd_masteral
• Institution: De La Salle University

The enactment of Republic Act 8749, better known as the Clean Air Act, in June 1999, phased out the use of incineration technologies in the Philippines. As a result, alternative non-burn technologies have been used in the treatment of medical plastic wastes, for which pyrolysis has been recommended as a prospect technology. Using microwave energy to pyrolyze is a new technology. It combines the advantages of the pyrolysis technology with the fast heating capacity of microwave heating technology. In this research, a microwave pyrolyzer system was designed and fabricated using a domestic microwave oven with a capacity of 1,000 watts. Distributions of electric field strength (E), dissipated power inside the oven cavity, skin-depth of electromagnetic waves in charcoal media, and mode generation were investigated to determine the dimension of the reactor and the best position for the reactor to be placed inside the cavity in order to get better heating generation. The decomposition temperatures for low-density polyethylene (LDPE) and polypropylene (PP) resins were determined using TGA-50 unit. LDPE and PP resins, and used syringes made of PP were used to test the fabricated microwave pyrolyzer system at 460510 oC. Charcoal powder with particle size of less than 0.01 mm was used in the tests as a microwave absorber. The pyrolysis product was condensed at a temperature of 810 oC. The relationship between the percentage of condensed products and the parameters: residence time (3, 5, and 10 min.) and weight ratio of plastic over charcoal (4/1, 2/1, 1/1, and 0.5/1) were investigated. Biological test was done to determine the population of microorganisms on the used syringes and on the residuals obtained after pyrolysis. It was found that the distributions of E, the dissipated power for the whole cavity was uneven. Skin-depth ranged from 19.20 to 19.657 mm. The reactor, made of the Pyrex or quartz, should be of a diameter less than 19.20 mm and placed in the high-power density regions inside the cavity. The LDPE was thermo-decomposed within 438630 oC while the PP was thermo-decomposed within 448595 oC. On the one hand, the tests showed that the fabricated microwave pyrolyzer system worked well for LDPE and PP resins, and for used syringes. The highest condensed product percentages obtained for the used syringes, LDPE resins, and PP resins were 30.85, 22.81 and 22.37 % at the weight ratio of 2/1, respectively, at residence time of 10 min.; while the lowest condensed product percentages obtained were 6.59, 6.19 and 6.82 % respectively at 3 min. residence time. At longer residence time, 5 and 10 min., the percentage of condensed product depended strongly on the ratio. At 10 min. residence time, no trace of plastic samples in the residual was observed. On the other hand, the results of the biological test showed that no microorganisms were found on the residual obtained after pyrolysis of the used syringes.