Production of biofuels by thermal catalytic cracking of scum from grease traps in pilot scale

• Catalytic cracking of Scum from grease traps investigated in pilot scale at 450 °C and 1.0 atm.
• Activated Red Mud used as catalyst produced OLP yields between 62.34 and 75.92%.
• OLP physical-chemistry properties dependent on catalyst content.
• Light diesel with 15% (wt.) activated Red Mud presents 73.86% hydrocarbons and 26.14% oxygenates.

In this work, the residual fat material (scum) from grease traps were submitted to catalytic cracking in order to systematically investigate the feasibility to produce light and heavy diesel-like fractions. The cracking reactions were carried out in a stirred tank slurry reactor of 143 L, operating in batch mode at 450 °C and 1.0 atmosphere; using 5, 10, and 15% (wt.) activated Red Mud obtained by calcination at 1000 °C as catalyst. The catalyst was prepared and characterized by FT-IR, XRF, XRD, SEM, EDX, and BET. The organic liquid products (OLP) were physical chemistry analyzed for acid and saponification values, specific gravity, refractive index, kinematic viscosity, flash point, and copper strip corrosion using AOCS and ASTM methods. The chemical composition of OLP, light and heavy diesel-like fractions were determined by FT-IR and GC–MS. The results showed an average OLP yield ranging from 62.34 to 75.92% (wt.) with acid values between 84.65 and 109.55 mg KOH/g, saponification values between 104.93 and 132.52 mg KOH/g, and kinematic viscosity between 10.96 and 14.08 mm2 s−1. For OLP obtained with 5% (wt.) activated Red Mud, the yield of light diesel-like fraction average 6.39% (wt.) with an acid value of 126.24 mg KOH/g, while that of heavy diesel-like fraction average 41.33% (wt.) with an acid value of 94.18 mg KOH/g. FT-IR analysis of OLP and diesel-like fractions confirms the presence of functional groups characteristic of hydrocarbons (alkenes, alkanes, ring-containing alkanes, and aromatics) and oxygenates (carboxylic acids, ketones, and esters). The GC-MS analysis of OLP and light diesel-like fraction obtained with 15% (wt.) activated Red Mud confirms that OLP is composed by 37.49% of hydrocarbons (10.83% alkenes, 14.16% alkanes, and 12.50 ring-containing alkanes) and 62.51% of oxygenates (59.49% carboxylic acids, 1.14% ketones, and 1.88 allyl esters). The light diesel-like fraction is composed by 73.86% of hydrocarbons (29.98% alkenes, 29.38% alkanes, 11.75% ring-containing alkanes, and 2.78% aromatics), and 26.14% of oxygenates compounds (23.48% carboxylic acids and 2.66% ketones), showing that thermal-catalytic cracking of scum from grease traps using activated red mud as catalyst is technically feasible.