Candida rugosa lipase nanoparticles as robust catalyst for biodiesel production in organic solvents

Document Type: Research Paper

Authors

1 Molecular Sciences Research Center, University of Puerto Rico, 1390 Ponce de Leon Avenue, Suite 2, San Juan, Puerto Rico 00926-2614, United States.

2 Department of Environmental Science, University of Puerto Rico, Río Piedras campus, 17 Ave Universidad STE 1701, San Juan, Puerto Rico 00925-2537, United States.

3 Department of Chemistry, University of Puerto Rico, Río Piedras campus, 17 Ave Universidad STE 1701, San Juan, Puerto Rico 00925-2537, United States.

4 Department of Physics, University of Puerto Rico, Río Piedras campus, 17 Ave Universidad STE 1701, San Juan, Puerto Rico 00925-2537, United States.

Abstract

Inexpensive but resourceful sources of lipids, for example, used cooking oil (UCO) and brown grease (BG), which often contain large amounts of free fatty acids (FFA), are difficult to convert into biodiesel economically and in good yield. Candida rugosa lipase nanoparticles (cNP) were formed first and subsequently cross-linked nanoparticles (CLNP) were obtained by crosslinking of them. Alternatively, cNP were conjugated to magnetic nanoparticles (mNP) to achieve a cNP-mNP conjugate. All three formulations were employed in three different organic solvents (n-heptane, 1,4-dioxane, and t-butanol) to produce biodiesel using BG and UCO in the transesterification reaction with ethanol and methanol. The radii of nanoparticles (NP) were 5.5, 75, 100, 85 nm for mNP, cNP, CLNP, and cNP-mNP, respectively, as measured by scanning/transmission electron microscopy and dynamic light scattering. The catalytic efficiency (Kcat/KM) of cNP, CLNP, and cNP-mNP was increased ca. -25, -68, -176 folds in n-heptane and -35, -131, -262 folds in 1,4-dioxane compared to the lyophilized lipase in the model transesterification reaction of p-nitrophenyl palmitate (PNPP) with ethanol. In biodiesel formation, the best performance with 100% conversion of BG was achieved under optimum conditions with cNP-mNP, ethanol at a 1:3 molar ratio of lipid-to-alcohol, NP at a 1:0.1 weight ratio of lipid-to-enzyme, and water at a 1:0.04 weight ratio of enzyme-to-water at 30 oC for 35 h. The operational stability of the CLNP and cNP-mNP was sustained even after five consequent biodiesel batch conversions while 50% and 82% residual activity (storage stability) were retained after 40 d.

Graphical Abstract

Candida rugosa lipase nanoparticles as robust catalyst for biodiesel production in organic solvents

Highlights

  • Formation of the Candida rugosa lipase nanoparticles by nanoprecipitation method.
  • Crosslinking and conjugation of Candida rugosa lipase nanoparticles.
  • Biodiesel production by utilizing brown grease and used cooking oil.
  • Kinetics of the Candida rugosa lipase nanoparticles in n-heptane and 1,4-dioxane.
  • Biodiesel production in organic solvents (n-heptane, 1,4-dioxane, and t-butanol).

Keywords