The apparatus and procedure of
the experiments have been described in detail in an earlier publication,30 (link) with some modifications to the reaction procedure
for propane, as well as the analysis procedure by gas chromatography
(SI Section 1.2) for the complex liquid
product mixture. Briefly, a Parr reactor is used with a Teflon insert
in the reactor along with a shaft and a thermowell coated with Teflon
to prevent ozone decomposition on the metal surfaces.
A dioxygen
stream is used to generate a mixture of ozone and dioxygen with the
desired ozone mole fraction by an Atlas ozone generator and charged
into a reservoir equipped with a pressure transducer.57 (link) Ar is then added into the reservoir to a desired pressure.
Unless otherwise mentioned, the mixture contains about 5% O3 and 45% O2, with the balance being Ar. A Teflon-lined
Parr vessel is evacuated at 80 °C under vacuum. The reactor is
cooled and charged with the desired amounts of liquid alkanes (0.3
mol total alkanes) from an ISCO syringe pump cooled to 10 °C.
An option to direct the liquid alkane stream through a sample loop
containing distilled water is provided to meter in controlled amounts
of water. The reactor stirrer is set at 1000 rpm to allow the reactor
to stabilize at the laboratory temperature of around 24–25
°C. Throughout a semi-batch run, the O2 + O3 + Ar mixture is supplied continuously to the reactor via a pressure
regulator maintained at a constant pressure. The reaction conditions
are provided in figure captions. The alkanes that escape with the
gas phase are partially condensed in a cold trap held around −60
to −50 °C and ambient pressure to concentrate the CO2. The gas from the condenser is collected in Tedlar sample
bags. At the end of a run, the reactor is placed in an ice bath kept
in a freezer at −18 °C. At this temperature, the vapor
pressures of all compounds remaining in the reactor are very low (SI Section 1.1). Then, a weighed amount of cold
methanol is added into the reactor, and the reactor is kept at around
0–4 °C to allow the remaining alkanes to vaporize and
be condensed in the cold trap. The trap is maintained at around −60
to −50 °C for butanes, and around −90 °C when
propane is present. After adding 2-pentanone as an internal standard,
the methanolic liquid sample is injected into an Agilent 7890A GC
equipped with a flame ionization detector (FID) and a HP-PLOT/Q column
to resolve ≥C2 products. The methanolic liquid sample
is also added to D2O with maleic acid as an internal standard
to quantify formic acid by 1H NMR spectroscopy. The gas
samples collected in Tedlar bags were injected into another GC equipped
with a thermal conductivity detector to analyze the CO2 and an FID to analyze the hydrocarbons. More details of the GC/FID
analytical methods, including a sample chromatogram, are provided
inSI Section 1.3.
The details of
estimating alkane conversion (X), molar product selectivity,
and O3 utilization (U), as well as their
confidence intervals, are provided
inSI Section 1.4. The O3 utilization
is characterized by the ratio of utilized oxidizing equivalents from
ozone/theoretical maximum oxidizing equivalents.
the experiments have been described in detail in an earlier publication,30 (link) with some modifications to the reaction procedure
for propane, as well as the analysis procedure by gas chromatography
(
product mixture. Briefly, a Parr reactor is used with a Teflon insert
in the reactor along with a shaft and a thermowell coated with Teflon
to prevent ozone decomposition on the metal surfaces.
A dioxygen
stream is used to generate a mixture of ozone and dioxygen with the
desired ozone mole fraction by an Atlas ozone generator and charged
into a reservoir equipped with a pressure transducer.57 (link) Ar is then added into the reservoir to a desired pressure.
Unless otherwise mentioned, the mixture contains about 5% O3 and 45% O2, with the balance being Ar. A Teflon-lined
Parr vessel is evacuated at 80 °C under vacuum. The reactor is
cooled and charged with the desired amounts of liquid alkanes (0.3
mol total alkanes) from an ISCO syringe pump cooled to 10 °C.
An option to direct the liquid alkane stream through a sample loop
containing distilled water is provided to meter in controlled amounts
of water. The reactor stirrer is set at 1000 rpm to allow the reactor
to stabilize at the laboratory temperature of around 24–25
°C. Throughout a semi-batch run, the O2 + O3 + Ar mixture is supplied continuously to the reactor via a pressure
regulator maintained at a constant pressure. The reaction conditions
are provided in figure captions. The alkanes that escape with the
gas phase are partially condensed in a cold trap held around −60
to −50 °C and ambient pressure to concentrate the CO2. The gas from the condenser is collected in Tedlar sample
bags. At the end of a run, the reactor is placed in an ice bath kept
in a freezer at −18 °C. At this temperature, the vapor
pressures of all compounds remaining in the reactor are very low (
methanol is added into the reactor, and the reactor is kept at around
0–4 °C to allow the remaining alkanes to vaporize and
be condensed in the cold trap. The trap is maintained at around −60
to −50 °C for butanes, and around −90 °C when
propane is present. After adding 2-pentanone as an internal standard,
the methanolic liquid sample is injected into an Agilent 7890A GC
equipped with a flame ionization detector (FID) and a HP-PLOT/Q column
to resolve ≥C2 products. The methanolic liquid sample
is also added to D2O with maleic acid as an internal standard
to quantify formic acid by 1H NMR spectroscopy. The gas
samples collected in Tedlar bags were injected into another GC equipped
with a thermal conductivity detector to analyze the CO2 and an FID to analyze the hydrocarbons. More details of the GC/FID
analytical methods, including a sample chromatogram, are provided
in
The details of
estimating alkane conversion (X), molar product selectivity,
and O3 utilization (U), as well as their
confidence intervals, are provided
in
is characterized by the ratio of utilized oxidizing equivalents from
ozone/theoretical maximum oxidizing equivalents.
