An Analysis of the Influence of Low Density Polyethylene, Novolac, and Coal Tar Pitch Additives on the Decrease in Content of Impurities Emitted from Densified Pea Husks during the Process of Their Pyrolysis

Abstract

The course of pyrolysis of pea husks was studied. It was stated that the compaction of a sample during its pyrolysis causes an almost two-fold increase in the content of hydrocarbons in the composition of volatile products in the temperature range of 350–470 °C. Low density polyethylene (LDPE), novolac, and coal tar pitch (CTP) wastes were added to feedstocks in the amount of 2 wt% in order to decrease the contribution of saturated and unsaturated hydrocarbons along with oxygen-containing compounds in volatile products. The analysis of the obtained products of pyrolysis was conducted using the techniques of thermogravimetry/Fourier transform infrared spectroscopy (TG/FT-IR), attenuated total reflectance (ATR) and ultraviolet (UV)-spectroscopies, gas chromatography-mass spectrometry (GCMS), X-ray diffractions (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX). It was determined that pitch took the first place in a series of effectiveness in decreasing the content of harmful compounds in pyrolysis products; novolac was the second. A temperature of 370 °C (CTP) lowers the contribution of compounds with carbonyl groups (by approx. 2.7 times) and the contribution of alcohols, phenols, and esters (by approx. 4.4 times). At a temperature of 465 °C, this additive reduces the contribution of saturated and unsaturated hydrocarbons in the composition of volatiles (by approx. 5.8 times) and at a temperature of 520 °C, a more substantial decrease is observed (by approx. 14.3 times). During the pyrolysis in the temperature range of 420–520 °C, LDPE actively emits its own products of decomposition in the form of aliphatic hydrocarbons that negatively affect the environment. The composition of condensed pyrolysis products changes under the influence of additives. In water condensates, the concentration of determined phenols and anhydrosugars increases slightly under the influence of additives. The SEM and XRD investigations proved that inorganics interact with volatile pyrolysis products from the blends of pea husks with additives and change their composition. After the transformation of chemical composition, inorganics catalyse secondary reactions that take place in the pyrolysis products of blends.