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Catalysis Science & Technology
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Scanning electron microscopy (SEM) images were obtained with deionized water. Then the catalyst was dried fVoierw3ArtidclaeyOsnlinine
DOI: 10.1039/D0CY00545B
a Phenom Pro Desktop SEM instrument equipped with EDS a desiccator at 5 °C.
General procedure of the synthesis of alkyl levulinates
detector (15 kV) (Figures S20-S24).
Transmission Electron Microscopy (TEM) images were obtained
using a Tecnai F20 TWIN microscope (FEI Company, USA)
equipped with a field emission gun, operating at an acceleration
voltage of 200 kV. Images were recorded on the Eagle 4k HS
camera (FEI Company, USA) and processed with TIA software
(FEI Company, USA). The samples were prepared on a copper
grid with holey carbon film (Figures S25-S26).
The determination of the contact angle was performed using
GBX Digidrop apparatus. In order to measure the contact angle
hysteresis, 6 μL distilled water droplet was settled on the
surface of the pellet of samples, and next the advancing contact
angle was measured. Then, 2 μL of water was sucked-off and
the receding contact angle was determined. Both temperature
(22 ± 2 °C) and humidity (50%) were kept at constant level. In
order to monitor and record the bubble collisions with the
investigated surfaces, the high-speed camera (SpeedCam 512+)
was mounted horizontally to the pellet of samples.
Nitrogen adsorption/desorption isotherms for carbon materials
were obtained corresponding to the literature.32 The porous
texture of the hybrid MWCNT-PTFE(0.01-20.00 wt.%) supports
as well as CALB/MWCNT-PTFE(0.10 wt.%) biocatalyst was
characterized by nitrogen adsorption at 77 K in ASAP 2020
(Micromeritics) apparatus (p/p0 from 10−7 to 0.98). The
adsorption data were used to determine the total pore
volume VT (at p/p0 = 0.96) and the specific surface area via BET
model (SBET).
The presence of lipase in the filtrate after 7 reaction cycles was
determined via Lowry’s method of protein detection
(application of UV VIS spectroscopy) corresponding to the
literature.17 UV-VIS spectra were recorded on a Jasco V-650
spectrophotometer at 25 °C in aqueous solution and the
absorbance (λ=670 nm) was measured.
A CALB/MWCNT-PTFE(0.01-20.00 wt.%) biocatalyst (10-200 mg
/ 1 mmol of α-angelica lactone) or Novozyme 435 (150 mg
/ 1 mmol of α-angelica lactone) was introduced into the 10-mL
round-bottom flask. Next, n-decane (20 wt. % of α-angelica
lactone, internal standard), solvent (0-1 mL / 1 mmol of
α-angelica lactone), α-angelica lactone (1.0 mmol, 0.098 g) and
alcohol (1.0–16.4 mmol) were added. The reaction mixture was
sealed with septum and mixed using thermostatic shaker
(250 rpm) at 25 °C for 2-6 h. Periodically, during the reaction, 10
µL of samples (diluted with 1.5 mL of acetonitrile) were
collected for monitoring the reaction progress using GC-FID
analysis.
Purification of alkyl levulinates
After the reaction, biocatalyst was filtered off from the post-
reaction mixture. Then, the esters of linear alcohols with boiling
point lower than 113 °C (1 atm) were purified using the rotary
evaporator (ethanol, n-propanol, n-butanol: 40 °C, 8 h,
60 mbar). The post-reaction mixture with iso-propyl levulinate
was concentrated using the rotary evaporator (20 °C, 4 h, 10
mbar) and the crude product was additionally purified via
column chromatography (ethyl acetate: cyclohexane 2:5, Al2O3
as stationary phase). The esters of alcohols with boiling point
higher than 113 °C (1 atm) were purified after removing toluene
using the rotary evaporator via vacuum distillation. The yields
1
and purity of corresponding esters (confirmed via H NMR,
13C NMR and GC-FID analyses):
1
Ethyl levulinate: H NMR (600 MHz, CDCl3, TMS) δ/ppm: 1.26
(t, J=7.1 Hz, 3H), 2.20 (s, 3H), 2.57 (t, J = 6.6 Hz, 2H), 2.75 (t, J =
6.6 Hz, 2H), 4.13 (q, J = 7.1 Hz, 2H); 13C NMR (151 MHz, CDCl3,
TMS) δ/ppm: 14.28, 28.15, 29.99, 38.08, 60.74, 172.86, 206.79
(yield 85%, purity >99%).
n-Propyl levulinate: 1H NMR (600 MHz, CDCl3, TMS) δ/ppm: 0.94
(t, J=7.4 Hz, 3H), 1.65 (dd, J=14.2, 6.9 Hz, 2H), 2.19 (s, 3H), 2.58
(t, J = 6.6 Hz, 2H), 2.75 (t, J = 6.6 Hz, 2H), 4.04 (t, J = 7.6 Hz, 2H);
13C NMR (151 MHz, CDCl3, TMS) δ/ppm: 10.43, 22.05, 28.11,
29.95, 38.08, 66.36, 172.92, 206.78 (yield 96%, purity >99%).
Synthetic procedures
Synthesis of hybrid MWCNT-PTFE(0.01-20.00 wt.%) supports
Into a 300-mL beaker, deionized water (150 mL), industrial
grade MWCNTs (5.00 g), non-ionic triblock copolymer of
polyethylene glycol and polypropylene glycol Pluronic F-127
(0.05 g) as well as PTFE micro-size grains (0.05–1.00 g, 0.01–
20.00 wt.% of MWCNTs) were introduced. The suspension was
mixed using high shear laboratory mixer Silverson L5M-A for
30 min (4500 rpm), filtered off under the vacuum, next washed
with 20 mL of deionized water and dried under reduced
pressure (1 mbar, 30 °C, 24 h).
1
Isopropyl levulinate: H NMR (600 MHz, CDCl3, TMS) δ/ppm:
1.14 (d, J=6.3 Hz, 6H), 2.11 (s, 3H), 2.46 (t, J=6.6 Hz, 2H), 2.65
(t, J=6.7 Hz, 2H), 4.91 (hept, J=6.3 Hz, 1H); 13C NMR (151 MHz,
CDCl3, TMS) δ/ppm: 21.69, 28.30, 29.80, 37.92, 67.91, 172.17,
206.68 (yield 94%, purity >99%).
n-Butyl levulinate: 1H NMR (600 MHz, CDCl3, TMS) δ/ppm: 0.90
(t, J=7.4 Hz, 3H), 1.34 (dd, J= 15.0, 7.5 Hz, 2H), 1.51-1.63 (m, 2H),
2.16 (s, 3H), 2.54 (t, J=6.6 Hz, 2H), 2.71 (t, J=6.6 Hz, 2H), 4.04 (t,
J=6.7 Hz, 2H); 13C NMR (151 MHz, CDCl3, TMS) δ/ppm: 13.80,
19.22, 28.13, 29.98, 30.74, 38.09, 64.67, 172.94, 206.78 (yield
97%, purity >99%).
Isooctyl levulinate: 1H NMR (600 MHz, DMSO, TMS) δ/ppm: 0.84
(dt, J=15.0, 7.1 Hz, 6H), 1.25 (dd, J=26.2, 5.0 Hz, 8H), 1.49 (dt,
J=11.8, 5.9 Hz, 1H), 2.08 (s, 3H), 2.39-2.47 (m, 2H), 2.68 (t, J=6.4
Hz, 2H), 3.89 (dd, J=5.7 Hz, 4.4 Hz, 2H); 13C NMR (151 MHz,
DMSO, TMS) δ/ppm: 10.82, 13.92, 22.43, 23.22, 27.70, 28.35,
29.53, 29.80, 37.46, 38.17, 65.92, 172.29, 206.72 (yield 88%,
purity 99%).
Immobilization of lipase B from Candida antarctica on the hybrid
support MWCNT-PTFE(0.01-20.00 wt.%)
The immobilization step was carried out according to the
literature.16-18 Into a 100-mL round bottom flask the aqueous
solution of lipase B from Candida antarctica (0.1–1.0 g), hybrid
support (MWCNT-PTFE) (0.1 g) and deionized water (3 mL) were
introduced. Immobilization step was carried out for 3 h at 20 °C
in a thermostatic shaker (180 rpm). Next, the mixture was
filtered off under the vacuum and washed with 20 mL of
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