Plastics pyrolysis gas ultracleaning
Gangotena Palacios, Pablo Andres (2023)
Diplomityö
2023
School of Engineering Science, Kemiantekniikka
Kaikki oikeudet pidätetään.
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi-fe2023030930739
https://urn.fi/URN:NBN:fi-fe2023030930739
Tiivistelmä
Pyrolysis of plastic waste is suggested to produce value-added products such as olefins that can be converted to polymers. However, the gaseous mixture produced from the pyrolysis of plastic waste contains several impurities. Tars are an undesired liquid impurities comprised of hydrocarbons and free carbon that can be removed by oil scrubbing. After tars, the main impurities are the acid gasses, including carbon dioxide and hydrogen sulphide, and alkaline gasses like ammonia. Different absorption technologies for gas removal such as adsorbents, membranes and various scrubbing solvents already reported in the literature are compared and discussed. This master’s thesis is focused mainly on carbon dioxide and methane absorption using caustic scrubbers. For low carbon dioxide concentrations in the gas inlet, caustic solvents were found to be more efficient, cost effective and readily available compared to amines and organic solvents. Related aspects of the scrubbing process, including the absorber column type, caustic scrubbing concept and gas-liquid mass transfer theory are also presented.
During the experimental part, a set of two glass bottles was used with a simulated gas comprised of CO₂/N₂ to study the effects of different sodium hydroxide concentrations ranging from 0.12 to 12.77 g/L. High caustic concentrations at room temperature and pressure, proved to be the most effective conditions to reach low carbon dioxide concentrations at the outlet. For the following experiments the caustic concentration was kept constant along with the experiment conditions like gas feed composition, gas flow, temperature and pressure. However, the reaction times that are directly related with the number of bottles were variated from one to six bottles. The best performance was achieved by the six-bottle system, meaning longer residence times and lower ppm concentration of CO₂ at the outlet. With a functional six bottle system it was time to test if organic gasses were absorbed along with CO₂. While the operation parameters remained unchanged, the new inlet gas mixture was composed by CO₂/N₂/CH₄. The experiment was brief, lasting less than an hour, where no absorption of methane was observed. The experimental results will aid in the process design of industrial-sized scrubbing columns.
During the experimental part, a set of two glass bottles was used with a simulated gas comprised of CO₂/N₂ to study the effects of different sodium hydroxide concentrations ranging from 0.12 to 12.77 g/L. High caustic concentrations at room temperature and pressure, proved to be the most effective conditions to reach low carbon dioxide concentrations at the outlet. For the following experiments the caustic concentration was kept constant along with the experiment conditions like gas feed composition, gas flow, temperature and pressure. However, the reaction times that are directly related with the number of bottles were variated from one to six bottles. The best performance was achieved by the six-bottle system, meaning longer residence times and lower ppm concentration of CO₂ at the outlet. With a functional six bottle system it was time to test if organic gasses were absorbed along with CO₂. While the operation parameters remained unchanged, the new inlet gas mixture was composed by CO₂/N₂/CH₄. The experiment was brief, lasting less than an hour, where no absorption of methane was observed. The experimental results will aid in the process design of industrial-sized scrubbing columns.