Use of the Langmuir-Hinshelwood-Hougen-Watson equation to describe the ethyl esterification of fatty acids catalyzed by a fermented solid with lipase activity

• Published in: Biochemical engineering journal Vol. 168; p. 107936
• Main Authors: Wiederkehr, Bruna, Mitchell, David Alexander, de Lima Luz, Luiz Fernando, Krieger, Nadia
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.04.2021
• Subjects: Biodiesel; Esterification; Fermented solids with lipase activity; Langmuir-Hinshelwood-Hougen-Watson equation; LHHW equation; Solid-state fermentation; Fermented solids with lipase activity; Solid-state fermentation; LHHW equation; Langmuir-Hinshelwood-Hougen-Watson equation; Biodiesel; Esterification
• ISSN: 1369-703X; 1873-295X
• DOI: 10.1016/j.bej.2021.107936

[Display omitted] •Dry fermented solids that contain lipases preferentially sorb polar medium components.•Two-site LHHW model used to simulate ethyl esterification of oleic acid in this system.•LHHW model adjusted well to data for different molar ratios of ethanol to oleic acid.•LHHW model also described a system with a decanting reservoir that removes water.•LHHW model is suitable for describing lipase kinetics in techno-economic analyses. The high cost of lipases is a barrier to producing biodiesel through the enzymatic route. Costs can be reduced by producing the lipases by solid-state fermentation and simply drying the fermented solids to produce the biocatalyst. When dry fermented solids (DFS) are used to catalyze the ethyl esterification of fatty acids, they preferentially sorb hydrophilic components of the reaction medium, thereby complicating description of the reaction kinetics. Here, we use a classical equation from heterogeneous catalysis, the two-site Langmuir-Hinshelwood-Hougen-Watson (LHHW) equation, to describe the ethyl esterification of oleic acid catalyzed by DFS, using Aspen Plus®. The parameters were determined using literature data for the ethyl esterification of bidistilled olein in a closed-loop system with recirculation of reaction medium from a well-mixed reservoir through a packed-bed bioreactor containing DFS. The model was validated with data obtained for ethyl esterification in the same bioreactor, but with the following changes: (1) use of fatty acids from soybean soapstock acid oil as the feedstock and (2) use of bidistilled olein as the feedstock, but with a reservoir with a separation barrier, so that only the organic phase is recirculated through the bed. We conclude that the two-site LHHW equation is suitable for modeling the ethyl esterification of fatty acids in techno-economic analyses of biodiesel production catalyzed by DFS that contain lipases.