Sustainable base oils from non-edible fats: performance of esterified, epoxidized, and hydroxylated brown grease

Abstract

Brown grease (BG), a high free-fatty-acid rendering coproduct, was upgraded to lubricant base stocks via one of four single-step functionalization methods: ethyl esterification, methyl esterification, epoxidation, or hydroxylation to give FAEEc/b, FAMEc/b, Epoxy BGc/b, or Hydro BGc/b, respectively (from crude, c, or bleached, b, BG). Each modification was carried out on crude and degummed/bleached brown grease, and the ten materials were evaluated by thermogravimetric analysis (T _d,5%), dynamic (µ) and kinematic (ν) viscosities at 40 and 100 °C, density, viscosity index (VI), and pour point, then mapped to ISO VG grades. Clear structure-property trends emerge. Esterification lowers ν ₄₀ and improves temperature-thinning (FAEEb: ν ₄₀ = 9.33 mm² s^-1, VI = 199, pour point = 0 °C; ISO VG 10). Hydroxylation raises ν ₄₀ into mid-grade ranges (Hydro BGc: ν ₄₀ = 98.4 mm² s^-1, ν ₁₀₀ = 12.5 mm² s^-1, VI = 121; ISO VG 100) and delivers the highest thermal onset (T _d,5% = 234 °C), but with poor cold-flow (pour point = 28 °C). Epoxidation affords very high viscosities (ν ₄₀ = 1.5-1.7 × 10³ mm² s^-1, VI = 30-40), best suited as thickeners rather than neat base stocks. Parent greases fall near ISO VG 32 (ν ₄₀ = 34-38 mm² s^-1) with pour points of 28-31 °C. These proof-of-concept results delineate application-relevant niches (high-VI light esters; VG 100 hydroxy-oils) and demonstrate a route to valorise non-edible fats into bio-derived lubricants.

Scheme 1. Chemical modification of brown grease by (A) esterification, (B) epoxidation, and (C) hydroxylation. x = c denotes materials made from crude brown grease, while x = b denotes materials made from bleached brown grease. (D) Procedure for bleaching brown grease.

Fig. 1. Pictures of the chemically modified brown grease oil.