Study of the pyrolisis of municipal solid waste for the production of renewable fuels and chemicals

Abstract

Pyrolysis experiments of municipal solid waste (MSW) are carried out in a semi-batch reactor under inert nitrogen atmosphere. Slow pyrolysis – characterized by long residence time (2 hours), heating rate of 4°C/min with sand acted as heat transfer medium- is performed at 550°C. Fast pyrolysis - characterized by short residence time (few minutes), high heating rate with sand acted as heat transfer medium- is performed at 450, 480, 510 and 550°C and different input transfer rates (12 or 24g material/min). The pyrolysis products are studied on composition and yield/distribution and investigated for their use as fuel or raw chemical feedstock. Slow pyrolysis liquids can be separated in a water rich and an oil product. For all fast pyrolysis conditions, MSW decomposes to a viscous, brown oil which contains a poly(ethylene-co-propylene) wax. Composition analysis by GC/MS of the oil products (slow/fast) shows that aliphatic hydrocarbons are the major compounds, which can be interesting as a chemical feedstock fraction. The pyrolysis oils have high caloric, low wt% of water and low O/C values. These properties made the oils promising as fuel. The attempt to converse the waxy material by decreasing input transfer rate is only sufficient at fast pyrolysis temperature 510°C. The waxy material can have possibilities for applications as paraffin wax or can be upgraded to lighter (fuel) fractions. The optimal pyrolysis condition, regarding to oil yield, fuel properties, and wax yield is fast pyrolysis at 510°C with 24g material/min input transfer rate. The pyrolysis gasses produced are energetic rich HC gasses. In addition, the main gasses can be valuable within the chemical industry. ICP-AES analysis of pyrolysis products reveals that inorganic compounds present in MSW are mostly distributed in the solid fraction. In view of recycling of metals in industry, elemental metallic compounds present in the solid fraction can be easily removed through sieving. In conclusion it should be stated that municipal solid waste has potential as chemical feedstock as such and certainly after upgrading.