6
Journal of Chemical Research 00(0)
monolaurin. The space–time yield of the process in the micro-
Finally, the selectivity was calculated from equation (3).
reactor was 380.91g/h/L, compared with 10.44~47.09g/h/L The selectivity for monolaurin was defined as the ratio of
in batch. This showed that this process has good potential in the formed monolaurin (in moles) with respect to the con-
industrial applications for preparing monolaurin. This new verted starting material (in moles)
method described in this report may serve as an inspiration
for applications to other multiphase and enzymatic reactions.
Selectivityformonolaurin =
(
3)
GCyield
×
100%
Conversion rateof lauricacid
Experimental
Materials and methods
®
Synthetic procedures
Novozym 435, Lipozyme RM-IM, Lipozyme CalB, and
Lipozyme TL-IM were purchased from Novozymes
Batch esterification process in solvent. GL (1.38g) and LA
1.00g) were added to the appropriate solvent (6mL,
.397g/mL) in the 15mL batch and were kept at the
(
Beijing, China). Monolaurin (Analytical Reagent (AR),
9%) was purchased from Sigma-Aldrich. LA (AR, 98%),
(
0
9
tert-butanol (AR, 99.5%), tert-amyl alcohol (AR, 98%),
and methanol (AR, 99.8%) were purchased from Macklin
Shanghai, China. n-hexane, ethyl acetate, acetone, and eth-
anol were purchased from Sinopharm Chemical Reagent
Co., Ltd. GL(98%) was obtained as a gift from Lemonchem
Co., Ltd.
selected temperature using a thermostatic water bath, fol-
lowed by the addition of lipase Novozym 435. The cata-
®
lyst amount (relative to LA+GL) was modified during the
research. The reactions were carried out for the appropriate
period of time (5–6h) in an oil bath under continuous stir-
ring conditions. The stirring rate was 350r/min. For kinetic
research, 200µL aliquots were withdrawn every 1h and
analyzed by GC. For optimization, the reaction was
quenched by adding 0.5mL of acetone/ethanol (1:1) into
the reaction mixture and 200µL aliquots were withdrawn
and analyzed by GC.
Using the standard curve methods, the quantitative deter-
mination of LA and monolaurin was performed via gas chro-
matography (GC, Agilent 7890A) equipped with a flame
ionization detector. The calibration curves for LA and mon-
olaurin were obtained by using LA (AR, 98%) and monolau-
rin (AR, 99%) as standards. The actual content was calculated
by the equation “mass×purity” (mass: the number shown
on the scale). The procedural details for generating the cali-
bration curves are given in the Supporting Information. The
reactant mixture (200µL for LA determination and 50µL for
monolaurin determination) was added into a 20mL volumet-
ric flask and immediately made up to the mark with 1:1 hex-
ane/ethyl acetate solvent mixture. The above solution (1µL)
was injected into an Agilent 7890A GC system (HP-5
Column, 30m×0.320mm×0.25µm), with helium as the
carrier gas at a flow rate of 2mL/min. The detector and injec-
tor temperatures were set at 330°C. First, the column tem-
perature was set at 80°C and kept for 1min, then increased to
The purification of final product. The purification was con-
ducted after the reaction under optimized reaction condi-
tions (15min, 58°C, GL/LA 3:1) kept running for 24h
starting with 47.52g LA. First, saturated sodium bicarbon-
ate and ethylacetate (EtOAc) were added into the reaction
mixture to remove the remained GL and extract the esters.
Vacuum rotating distillation was done after workup, afford-
ing the final product as a white waxy solid (52.80g). The
1
13
H NMR and C NMR were determined and afforded in
the Supporting Information.
Flow esterification process. All experiments under flow con-
ditions were carried out using a Vapourtec fixed-bed reac-
tor and an R-Series machine. As shown in Figure 7, the
solution of GL was pumped through the orange pump
320°C with a rate of 20°C/min and kept for 2min. The con-
centrations of LA and monolaurin in the samples could be
calculated via the standard curve. From GC results, the yield
of monolaurin could be calculated from equation (1). The
(Pump A), and the solution of LA in solvent was pumped
“yield” is also called “GC yield” on assuming no product
through the purple pump (Pump B). The reactant mixture
loss during the purification. The “yield” shown in all tables
and schemes is the “GC yield”
®
passed through the column reactor filled with Novozym
4
35. The inner diameter of the column reactor was 66mm.
The reactor volume was calculated from equation (4). The
reaction details are listed in Table 3. All the reactions in the
microreactor were run for 12h. The sample collection was
performed after 1h, and the collection was continued for 2
to 12h using 10mL tubes. Six of the sample tubes were
Monolaurin calculated
(1)
fromGCin moles
GCyield =
×100%
Producedmonolaurinin theory
Furthermore, the conversion rate of LA can be calcu- detected to obtain the mean values of the conversion and
lated from equation (2). The remaining LA was determined selectivity. In our work, the longest running time was 12h.
by GC using the calibration curve method
The formation of fine particles of the immobilized catalyst
was noted after use. However, we believe the immobilized
catalyst can be used for a longer time without blockage.
The volume of the reactor was according to the manufac-
Conversion rateof lauricacid=
Lauricacidusedin moles −
Remaininglauricacidin moles
(
2) turer settings
×
100%
Lauricacidusedin moles
Volume = 0.3421×scale
(4)