Valorization of tannery fleshing waste into high energy biofuel through pyrolysis: process optimization and fuel properties analysis

Abstract

Fleshing waste (FW) is an unavoidable solid waste generated during the fleshing operation of the leather tanning process. FW is hazardous because it contains significant amounts of sulfides and harms the environment by polluting soil and water, and emits greenhouse gases. This study examined the pyrolysis process for producing biofuel from FW and optimized the process parameters using response surface methodology. FW contains 3.77% moisture, 15.68% ash, 71.24% volatile matter, and 9.31% fixed carbon based on dry mass, according to proximate analysis. Ultimate analysis determined 50.41% C, 9.79% H, 4.02% N, 0.24% S, and 19.85% O in FW by dry mass, yielding a higher heating value of 27.62 MJ kg⁻¹ and a lower heating value of 25.48 MJ kg⁻¹. Under optimized conditions (555 °C, 60 minutes, and 1 L h⁻¹ N₂ flow rate), the pyrolysis process yielded 55% biofuel from FW. FTIR analysis of biofuel identified absorption bands at 3350, 2920, 2855, 1660, and 1455 cm⁻¹ corresponding to –OH and –NH stretching, –CH stretching, –CO stretching, and –CH bending groups. The biofuel exhibits enhanced energy density and ease of handling, with a calorific value of 40.24 MJ kg⁻¹, a kinematic viscosity of 2.12 cSt, and a density of 860 kg m⁻³. Chemical stability of the biofuel is ensured by an acid value of 16 mg KOH per g. Fuel safety is ensured by a flash point of 60 °C and a fire point of 78 °C. GC-MS analysis of biofuel detected significant compounds like decahydro-8a-ethyl-1,1,4a,6-tetramethylnaphthalene and 1-methyl-2-propylpyrazolium bromide along with other active components. Therefore, the produced biofuel offers practical application potential, promotes sustainable waste management in the leather industry, and creates opportunities for a renewable energy source.