Chemical Recycling of Phenol Resin by Supercritical Methanol

Abstract

Thermosetting resin is one of the most difficult substances to be recycled, because it includes a highly cross-linked structure which gives the polymer chemical and thermal resistances. A preliminary study on the technique to recycle phenol resin was conducted in the present study, which was intended to be achieved by the use of a supercritical fluid. Supercritical methanol was employed because it has the following advantages over supercritical water: i.e., it allows milder reaction conditions and easier operation for the separation of the products from the solvent. The reaction of phenol resin in supercritical methanol was studied by varying the temperature in the range of 300-420 °C or changing the reaction time 30-150 min to understand the effects of the reaction temperature and of the reaction time. The conversion increased rapidly above 350 °C to give 94% at maximum at 420 °C, and the gas fraction also increased at the same time. When a longer reaction time was employed for the reaction at 400 °C, the conversion increased without giving additional gas product. From the point of view of liquefaction, the longer reaction at lower temperature would give better results. A gas chromatographic study revealed that the liquid product included phenol and its methylated derivatives. The carbon content of the solid product was higher than the initial phenol resin, showing that some carbonization took place during the reaction.

Materials recovery from waste printed circuit boards by supercritical methanol

“…Hence, it is believed that some methylation reactions of phenol took place during the SCM process. In fact, reaction between phenol and methanol under hightemperature and high-pressure conditions is inclined to produce methylation products [21].…”

“…However, the critical temperature and pressure of water (T c = 374 • C, P c = 22.1 MPa) are very high which result in the very serious corrosion of reactor and the higher energy consumption, and require equipment which makes commercial usage of SCW expensive [21,22]. Possible merits of utilizing supercritical methanol (SCM) over SCW are found in the following respects [22].…”

“…Additionally, solvent methanol also can be recycled during the recovery process. Some researchers [21,23] reported the application of SCM for chemical recovery of molding resins such as cross-linked polyethylene and phenol resin.…”

Degradation of brominated flame retardant in computer housing plastic by supercritical fluids

“…Organic solvents such as methanol, acetone, and ethanol are also used as supercritical fluids in chemical recycling of waste plastic. Compared with sc-water, these solvents have not only lower critical temperature and pressure (e.g., the T c and P c of methanol is 239.5 • C and 8.08 MPa, respectively) but also other advantages [19]. Thus far, less report is available on the treatment of BFRs-containing plastics in supercritical organic solvents.…”

Characterization of Cross-linking Structures in UV-cured Acrylic Ester Resin by MALDI-MS Combined with Supercritical Methanolysis

“…On the other hand, supercritical fluids such as supercritical methanol have been utilized to depolymerize intractable polymers such as poly(ethylene terephthalate) (PET) 8 and phenol resin 9 mainly for the purpose of plastic recycling. In the former instance, 8 PET was almost completely decomposed in methanol in 30 min under the supercritical conditions at 300˚C and various pressures over 8.1 MPa.…”