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The diverse utilization of pyrolysis liquid is closely related to its chemical compositions. Several factors affect PA compositions during the preparation. In this study, multivariate statistical analysis was conducted to assess PA compositions data obtained from published paper and experimental data. Results showed the chemical constituents were not significantly different in different feedstock materials. Acids and phenolics contents were 31.96% (CI: 25.30−38.62) and 26.50% (CI: 21.43−31.57), respectively, accounting for 58.46% (CI: 46.72−70.19) of the total relative contents. When pyrolysis temperatures range increased to above 350 °C, acids and ketones contents decreased by more than 5.2-fold and 1.53-fold, respectively, whereas phenolics content increased by more than 2.1-fold, and acetic acid content was the highest, reaching 34.16% (CI: 25.55−42.78). Correlation analysis demonstrated a significantly negative correlation between acids and phenolics (r2 = −0.43, p < 0.001) and significantly positive correlation between ketones and alcohols (r2 = 0.26, p < 0.05). The pyrolysis temperatures had a negative linear relationship with acids (slope = −0.07, r2 = 0.16, p < 0.001) and aldehydes (slope = −0.02, r2 = 0.09, p < 0.05) and positive linear relationship with phenolics (slope = 0.04, r2 = 0.07, p < 0.05). This study provides a theoretical reference of PA application.

The complexity of the components in pyrolysis liquid causes serious problems for its downstream utilization. In order to increase the added value and commercialization of pyrolysis liquid, a novel method was developed by combining the sequential multi-step pH adjustment and organic solvent extraction methods to separate the chemical components of crude pyrolysis liquid. The chemical composition of crude pyrolysis liquid was determined by fourier transform infrared spectrometry and gas chromatography–mass spectrometry. The results showed that acids (17.54%) and phenolics (57.44%) were the major constituents. The neutral compounds (e.g. ketones) (38.57%) were enriched at pH 14. Methoxyphenols (e.g., 2,6-dimethoxyphenol) were separated at pH 11, accounting for 63.4%. Phenol and maltol were mainly found at pH 9 and 7, with relative contents of 11.30% and 10.09%, respectively. At pH 6 and 4, acetic acid was the most abundant compound, with contents of 17.23% and 20.72%, respectively. The main compound at pH 2 was 2-methyl-propanoic acid anhydride (35.05%). Principal component analysis (PCA) results showed that the PC1 and PC2 components explained 38.8% and 26.2% of the chemical variance, respectively. The DPPH free radical scavenging rate showed positive correlation with the phenolic component, and was negatively correlated with the acid component. The highest DPPH free radical scavenging rate (88%) was obtained at pH 11. This study provided a theoretical reference for the separation of target components in pyrolysis liquid. [Display omitted] • Sequential multi-step pH adjustment extraction method for chemical components of pyrolysis liquid was developed. • Neutral compounds were separated in the separation fractions at pH value of 14. • Methoxyphenols were separated in the separation fractions at pH value of 11. • Acetic acid was the most abundant in the pH 4 separation fractions. • Antioxidant activities was the highest in the pH 11 separation fractions. [ABSTRACT FROM AUTHOR]