Performance of thermochemical conversion of fat, oils, and grease into kerosene-like hydrocarbons in different production scales

Abstract

This work aims to investigate the effect of catalytic cracking of residual fat, oils, and grease (FOG) from grease traps in different production scales (bench, laboratory, and pilot) on the reaction products yields and OLP properties and the feasibility to produce kerosene-like hydrocarbons. The cracking experiments were carried out in batch mode at 450°C and 1.0 atmosphere, with 10% (wt.) Na2CO3 using a laboratory scale cylindrical borosilicate-glass reactor of 143mL, a bench scale stirred tank slurry reactor of 1.5L, and a pilot scale stirred tank slurry reactor of 143L (≈1:10:1000). The reaction liquid products were physical and chemical analyzed for acid and saponification values, density, kinematic viscosity, refractive index, and copper strip corrosion. FT-IR analysis provided the qualitative chemical composition of OLP obtained in bench, laboratory, and pilot scales, as well as kerosene, light and heavy diesel-like hydrocarbons fractions obtained by distillation of OLP produced in pilot scale with 10% (wt.) Na2CO3. The chemical compositions of OLP and kerosene-like hydrocarbons fraction obtained in pilot scale determined by NMR and GC–MS. The results showed an OLP yield ranging from 62.90 to 66.57% (wt.), a coke yield ranging between 7.02 and 9.79% (wt.), and a gas yield ranging from 16.32 to 22.40% (wt.), showing a mean absolute percentage deviation of 2.12%, 11.88%, and 14.91% for OLP, gas, and coke yields respectively, obtained in different production scales (≈10:1000). The OLP acid values varied from 19.08 to 10.45mg KOH/g, the density between 0.820 and 0.835g/cm3, and the kinematic viscosity from 3.28 to 4.21mm2s−1. The yield of kerosene-like hydrocarbons fraction average 14.90% (wt.) with an acid value of 5.43mg KOH/g, density of 0.740g/cm3, and kinematic viscosity of 0.66mm2s−1, while those of light and heavy diesel-like hydrocarbons fractions average 32.01% (wt.) and 19.35% (wt.) respectively. FT-IR and NMR analysis of OLP and kerosene-like hydrocarbons fraction confirms the presence of functional groups characteristic of hydrocarbons (alkenes, alkanes, ring-containing alkenes, and ring-containing alkanes, and cycloalkanes) and oxygenates (carboxylic acids, ketones, fatty alcohols, and dienes). The GC–MS analysis of OLP and kerosene-like hydrocarbons fraction obtained in pilot scale with 10% (wt.) Na2CO3 identified in OLP 76.97% hydrocarbons (39.44% alkenes, 31.91% alkanes, 4.12% ring-containing alkenes, and 1.50% ring-containing alkenes) and 23.03% oxygenates (12.14% carboxylic acids, 6.98% ketones, 1.90% fatty alcohols, and 2.01% dienes). The kerosene-like hydrocarbons fraction is composed by 94.62% (area) hydrocarbon (44.99% alkenes, 29.61% alkanes, 7.58% ring-containing alkenes, 6.15% ring-containing alkanes, 4.31% cycloalkanes, and 1.98% aromatics) and 5.38% (area) oxygenates (5.38% carboxylic acids), showing that catalytic cracking of scum from grease traps with 10% (wt.) Na2CO3 is technically feasible.