Research On Microwave-Assisted Pyrolysis Of Hazardous Waste And Products

This paper studied the microwave-assisted pyrolysis of waste printed circuit board(WPCB)and polymer-containing oily sludge(OS).The microwave-assisted pyrolysis tube furnace was used to pyrolyze WPCB,and solid,liquid and gas products were collected.The effects of different pyrolysis conditions(temperature,time,additives)on product distribution and characteristics were explored.The possible pyrolysis mechanism and Br fixation in WPCB pyrolysis were studied.The main research results were as follows:(1)At 550 0C and 15 min,the yield of WPCB pyrolysis oil reached the maximum value(27.8 wt%),and the pyrolysis conversion reached 89.95%.WPCB pyrolysis oil contained a large amount of aromatics,of which phenols were the main components.With the increase of pyrolysis temperature,the types of organic matter in pyrolysis oil and the relative percentage of C11-C20 was increased.Na2CO3 and NaOH promoted the production of C6-C 10 and monocyclic aromatic hydrocarbons(except phenols),while K2CO3 had a high selectivity for phenols in pyrolysis oil.Kaolin and ZSM-5 increased the relative percentages of C11-C20 and?C21 compounds and monocyclic aromatic hydrocarbons(except phenols)in pyrolysis oil by promoting the recombination reaction of pyrolysis products,and reduced the content of small molecular gases(CO2,CO,CH4 and H2)in pyrolysis gas.The increase of pyrolysis temperature and time promoted the transfer of Br element from pyrolysis residue(WPCB-PR)to pyrolysis liquid and gas,and a small amount of Br remained in WPCB-PR in the form of C-Br.The addition of Na2CO3,NaOH and K2CO3 improved the Br fixation efficiency in WPCB-PR from 29.11%to 86.69%?99.8%,and most of Br was fixed in WPCB-PR in the form of NaBr and KBr.In addition,a small amount of C-Br remained in WPCB-PR.(2)According to the results of kinetic fitting,thermogravimetric-infrared and thermogravimetric-mass spectrometry analysis,the WPCB pyrolysis process at 30?900? was divided into five stages.In the first stage(30?305?),the raw material was dried and the adsorbed gas was removed.In the second stage(305?340?),the brominated flame retardant cracked and generated HBr.In the third stage(340?380?),the polymer in WPCB cracked and generated phenols,alkylene oxides and polycyclic aromatic hydrocarbons.In the fourth stage(380?600?),the small molecule free radicals and macromolecular benzene rings released by WPCB pyrolysis were combined into many new compounds(such as naphthol,biphenyl,fluorene and other polycyclic aromatic hydrocarbons)through random breaking and recombination.In the fifth stage(600?900?),WPCB-PR was continuously coked.(3)The addition of KOH,CaO and ? molecular sieve reduced the yield of OS pyrolysis liquid from 85.93wt%to 64.45?71.44 wt%.At 500? and 15 min,the aqueous phase yield of OS pyrolysis was 56.25 wt%.The addition of CaO,KOH and ? molecular sieve reduced the aqueous phase yield to the range of 29.56?50.33%.Among them,the effect of 10%KOH was the most significant,reducing the aqueous phase yield from 56.25 wt%to 29.56 wt%.The pyrolysis oil of OS contained naphthenes,benzene,naphthalene,and biphenyl.At low temperature(<650?),the?C21 components in pyrolysis oil accounted for more than 90%.However,high temperature promoted the decomposition of macromolecular organic matter.Both of CaO,KOH and P molecular sieve catalyzed the cracking of macromolecular organic matter,in which the increase of ? molecular sieve addition ratio(from 5wt%to 100wt%)had higher selectivity for C1?C10 components in pyrolysis oil(from 53.18%increased to 67.74%).