Chemical modification with aldehydes on the reduction of toxic PAHs derived from low temperature coal tar pitch

Abstract Low temperature coal tar pitch (LTCTP) and a model compound of pyrene were modified by formaldehyde (F), benzaldehyde (B) and furfural (K). The effects of the types and amounts of modifiers, the amount of catalyst, the reaction time and reaction temperature on the release of toxic polycyclic aromatic hydrocarbons (TPAHs) during the thermochemical degradation of LTCTP were investigated. The structures of modified LTCTPs were confirmed by FTIR, GPC and Uv-fluorescence, and the escape evaluation of TPAHs was examined by Py-GC/MS and TG-FTIR. The results of the analyses of FTIR, GPC and Uv-fluorescence show that phenols and TPAHs in LTCTP have polymerized with aldehydes to form phenolic resins and polycyclic aromatic hydrocarbon resins, respectively. The reduction rates of TPAHs released from formaldehyde modified LTCTP (MFCTP), benzaldehyde modified LTCTP (MBCTP) and furfural modified LTCTP (MKCTP) under the optimum conditions reach up to 84.01 %, 74.21 % and 81.18 % respectively. The order of carbon residue rates is as follows: MFCTP > MKCTP > MBCTP > LTCTP. Based on the above analysis, TPAHs can polymerize with themselves and phenols in LTCTP to achieve the toxicity inhibition. In addition, TPAHs may be wrapped in the “cage” of phenolic resins and polycyclic aromatic hydrocarbon resins.