Intraparticle Diffusion Limitations in the Hydrogenation of Monounsaturated Edible Oils and Their Fatty Acid Methyl Esters

Abstract

Intraparticle diffusion limitation in the hydrogenation and isomerization of fatty acid methyl esters (FAMEs) and edible oils (triacylglycerol, TAG) in porous nickel catalyst was investigated both under reactive and under inert conditions. Under reactive conditions, the diffusion coefficients were determined from the best fits of the model simulations applying the intrinsic reacting kinetics of monounsaturated FAME hydrogenation to experiments under diffusion limited conditions. For 0.02 < P H 2 < 0.50 MPa, an effective hydrogen diffusion coefficient of D e,H 2 = (1.6 ± 0.7) × 10-10 m2/s (T = 443 K) was obtained in Pricat 9910 (sample 1992). TAG hydrogenations, at 373 < T < 443 K and 0.30 < P H 2 < 0.50 MPa, appear to be limited by diffusion limitation of TAG, yielding D e,TAG = (4.5 ± 2.2) × 10-13 (T = 373 K), (2.0 ± 0.9) × 10-12 (T = 403 K), and D e,TAG = (3.3 ± 1.1) × 10-12 m2/s (T = 443 K). The temperature dependency of D e follows the relation D eη/T = 2 × 10-7 (m2 Pa)/K (η is the fluid viscosity, Pa s) for 373 < T < 443 K. Independent determination of D e in porous nickel catalyst (Pricat 9933, sample 1992: average particle diameter, d p = 10 μm) was performed with tracer pulse column experiments using the HPLC (high-performance liquid chromatography) technique, in the absence of reaction. The packed columns (length 0.05 and 0.10 m; diameter 4.6 × 10-3 m) were eluted with n-octane, 3 × 10-10 < Φv < 80 × 10-10 m3/s (η = 0.5 mPa s), and MCT oil (medium C10−C12 chain triglyceride, η = 17 mPa s) in the temperature range 313 < T < 353 K. The response curves indicated a regular packing of the column. Intraparticle effective diffusivities were measured with more viscous MCT oil as an eluent: 1.4 × 10-11 < D e < 2.7 × 10-11 m2/s for methyl palmitate and 4 × 10-12 < D e < 7 × 10-12 m2/s for trioleate and triacyl octadecenoic ester (95% confidence limit, T = 313 K). Due to the absence of reaction (hydrogenation of double bonds), the obtained D e with the HPLC technique is volume averaged and thereby determined by the larger intercrystalline pores (<30% of the total pore volume) only. Moreover, D e measured under reaction conditions reflected the influence of the micropores, resulting in a 10-fold lower value.

How nitric oxide affects the decomposition of supported nickel nitrate to arrive at highly dispersed catalysts

“…Based on literature we conclude that the monomodal pore system of our catalyst with pores around 7 nm will lead to severe diffusion limitation for the soybean hydrogenation. This limitation likely masked the intrinsic differences in catalytic activity between the air calcined and NO treated catalysts G/D-C air and G/D-C NO/He [63,64]. This explains that the improvement of catalytic activity going form air to NO calcination appeared more modest than previously observed for CO hydrogenation [31].…”

Hydrogenation of Vegetable Oils with Minimum trans and Saturated Fatty Acid Formation Over a New Generation of Pd-catalyst

“…Transport limitations on hydrogen and triglycerides to the active sites of the catalyst, have a strong influence on both selectivity [10] and TFA production [11,12]. The effect of operating parameters such as temperature, H 2 pressure, catalyst loading, and agitation on selectivity and TFA production are reported in the literature [13,14].…”

Intraparticle diffusion mechanisms in SC sunflower oil hydrogenation on Pd

“…Jonker et al49 investigated the intraparticle diffusion limitation in the hydrogenation and isomerization of fatty acid methyl esters (FAMEs) and soybean edible oil [triacylglycerol (TAG)] in porous nickel catalyst under reactive and inert conditions. They found that FAME hydrogenation reaction at 443 K appears to be controlled by intraparticle diffusion of hydrogen ( D = 1.6 × 10 −10 m 2 /s).…”