Inexperienced synthesis of propylene oxide straight from propane

Supplies and gases

All used supplies are commercially accessible and had been ordered from the next firms: SiO₂ (Quartz) from Supelco (puriss p.a., LOT quantity SZBA0210, inside ID S28035), hexagonal boron nitride (h-BN) from Alfa Aesar (High quality 99.5%, LOT quantity E31M55, inside ID S25618), Aerosil 380 from Evonik (LOT quantity 157012015, inside ID S28106), and silicon carbide (SiC) from ESK-SiC GmbH (LOT quantity 654508, inside ID S32814). The gases propane (purity 99.95%), oxygen (purity 99.999%), helium (purity 99.999%) and nitrogen (purity 99.999%) had been provided by Westfalen firm.

Characterization of filling supplies

Nitrogen adsorption was carried out at −196 °C utilizing the Autosorb-6B analyser (Quantachrome) after outgassing the catalysts in vacuum (SiO₂ and h-BN for two h at 200 °C, Aerosil 380 for 12 h at 200 °C, SiC for two h at 300 °C). All information therapies had been carried out utilizing the Quantachrome Autosorb software program package deal. The particular floor space S_BET was calculated in line with the multipoint Brunauer-Emmett-Teller technique (BET) within the p/p₀ = 0.05–0.15 strain vary assuming the N₂ cross sectional space of 16.2 Ų.

X-ray fluorescence spectroscopy (XRF) was used for elemental evaluation making use of a Bruker S4 Pioneer X-ray spectrometer. For pattern preparation, the combination of 0.1 g of the fabric and eight.9 g of lithium tetraborate (>99.995 %, Aldrich) was fused right into a disk utilizing an automatic fusion machine (Vulcan 2 MA, Fluxana).

Inductively coupled plasma optical emission spectrometry (ICP-OES) was used as a second approach for elemental evaluation. An Optima 8300 from Perkin Elmer with Zyklon nebulizer was utilized in axial mode. Minimal two factors calibration with pressured intercept at zero had been measured with licensed requirements. Peak analysis relies on three factors per peak. Water was used as spectral clean. Dissolution of the samples was performed in a multi-wave Professional autoclave from Anton Paar, outfitted with Teflon liner at 200 °C and 60 bar. Reagents in supra pure high quality and water from an ELGA pure water system (VEOLIA) (conductivity 0.05 µS/cm) had been used.

Section evaluation was carried out by X-ray diffraction (XRD) utilizing a Bruker D8 ADVANCE diffractometer (Cu Kα radiation, secondary graphite monochromator, scintillation counter).

Propane oxidation

The propane oxidation experiments had been carried out in a self-built reactor with plug circulate traits. All measurements had been carried out at atmospheric strain and the strain within the reactor was monitored with strain sensors upstream and downstream of the reactor tube. The next basic response circumstances had been utilized: Mass of fabric from 100 to 1500 mg, temperature from 470 to 510 °C, complete circulate from 6.7 to 25 ml min⁻¹, propane from 10 to 60 vol%, oxygen from 1 to fifteen vol%. Helium was used as steadiness. A specific amount of fabric (sieve fraction from 250 to 355 µm) was crammed into the quartz reactor (interior diameter 7 mm) with out dilution or the empty reactor was used. The gasoline hourly area velocity (GHSV), [h⁻¹] was calculated utilizing the majority quantity of the fabric within the reactor V_materials and the utilized volumetric gasoline circulate at customary circumstances (T = 273.15 Okay and p = 0.1013 MPa) (dot{V}) in line with Eq. (1):

The product gasoline mixtures had been analyzed by on-line gasoline chromatography (Agilent 7890 GC). The next GC column combos had been used for product evaluation: (1) Plot-Q (size 30 m, 0.53 mm inside diameter, 40 μm movie thickness) plus Plot-MoleSieve 5 A (30 m size, 0.53 mm inside diameter, 50 μm movie thickness), linked to a thermal conductivity detector (TCD) for evaluation of the everlasting gases (CO, CO₂, and O₂) and (2) Plot-Q (size 30 m, 0.53 mm inside diameter, 40 μm movie thickness) plus FFAP (size 30 m, 0.53 mm inside diameter, 1 μm movie thickness) linked to a flame ionization detector (FID) for evaluation of hydrocarbons and oxygenates.

The calculation of the propane conversion (X_propane) and selectivity (S_i) of product i in proportion, had been performed primarily based on the carbon quantity and the sum of all merchandise utilizing Eqs. (2) and (3), respectively:

N_i is the variety of carbon atoms in product i, c_i is the focus of product i on the reactor outlet, and (,{c}_{{C}_{3}{H}_{8},{out}}) is the propane focus within the outlet gasoline.

The oxygen conversion was calculated utilizing Eq. (4), the place ({c}_{{O}_{2},{in}}) and ({c}_{{O}_{2},{out}}) are the concentrations of the oxygen within the feed gasoline at inlet and outlet place, respectively, of the reactor.

The yield (Y_i) of product i in proportion was calculated by utilizing Eq. (5):

The carbon steadiness (C_steadiness) was decided in line with Eq. (6):

In all experiments, the carbon steadiness was 100% +/− 5%. The formation of polymerization merchandise was not noticed.

Response charges r_i for propane consumption, propylene formation and propylene oxide formation in mol g⁻¹ h⁻¹ had been calculated utilizing Eq. (7):

The quantity of beginning compound i consumed or product i shaped (n_i) was used within the unit mol ml⁻¹. W is the mass of the fabric in g and F is the entire circulate charge in ml min⁻¹.

Mass switch limitations had been excluded by measuring the propane conversion when utilizing completely different quantities of fabric and completely different gasoline flows (see Supplementary Fig. 5) and checked by calculating the dimensionless Mears and Weisz-Prater standards. SiO₂ has the best Mears modulus of 5.7 × 10⁻⁶ (should be <1.8 × 10⁻²) and Weisz-Prater modulus of two.24 × 10⁻³ (should be <0.07) for measurements at 490 °C of all supplies examined, indicating that mass transport limitations don’t play a task.

Temperature-programmed experiments

The experiments had been carried out in the identical reactor setup, which was described within the earlier part. A web-based mass spectrometer (QMA 400, Pfeiffer Vacuum) was used for recording the reactant and product gasoline streams. 670 mg of SiO₂ and 665 mg of h-BN, respectively, had been loaded into the reactor. A complete circulate of 10 ml/min, which was composed of 30% propane, 15% oxygen and 55% helium, was used. First, the reactor was heated as much as 350 °C with a heating charge of 5 Okay min⁻¹ and maintain at this temperature for minimal 15 min. Then the temperature-programmed experiment was carried out by heating as much as 490 °C with a heating charge of two.5  Okay min⁻¹ or 5 Okay min⁻¹, respectively, holding at 490 °C for 1 h after which cooling down with the identical charge like for heating up.

The response gasoline was withdrawn ~5 cm behind the fabric mattress by utilizing a capillary-vacuum pump mixture and fed into the mass spectrometer (QMA 400, Pfeiffer Vacuum). All m/z from 18 to 60 had been monitored concurrently with a scanning charge of fifty ms per m/z.

Microkinetic simulation

The microkinetic simulations of gas-phase conversion had been applied with the Cantera package deal⁵³, utilizing the “DTU” mannequin of propane oxidation³⁷. The technical settings of those simulations had been analogous to these utilized by Kraus and Lindstedt³¹. Particularly, a continuing strain, preferrred gasoline reactor was used and the time evolution of the gasoline combination was modeled utilizing a dynamic time step, adjusted by the solver. All simulations had been carried out at atmospheric strain and a temperature of 500 °C.

Course of simulation

The direct oxidation of propane has been simulated utilizing Aspen HYSYS. This course of includes the response of propane with oxygen to provide propylene oxide because the goal product. The remainder of the thought-about response merchandise embody a combination of propylene, ethylene, acetaldehyde, hydrogen, water, carbon monoxide and carbon dioxide. The Cubic-Plus-Affiliation (CPA) package deal has been chosen because the fluid package deal for the simulation. The CPA property package deal makes use of the Cubic-Plus Affiliation equation of state mannequin and is appropriate for the simulation of mixtures containing hydrocarbons, non-hydrocarbons similar to carbon dioxide, nitrogen, and polar/associating chemical substances similar to water, alcohols, glycols, esters or natural acids. The method circulate diagram (PFD) comparable to the direct oxidation of propane simulated in Aspen HYSYS is given in Supplementary Fig. 9. Three fundamental elements will be distinguished, i.e., conditioning of the feed gases, response, and separation of the response merchandise and recycling of the unreacted reactants.

The feed gases (propane, oxygen, and helium) are heated as much as the response temperature (490 °C) by warmth exchangers (E-100, E-101, E-102) positioned in every of the reactor inlet gasoline traces. Thereafter, the make-up gasoline enters the reactor CRV-100, the place the response between propane and oxygen takes place at 490 °C and 1 bar. Beneath these circumstances the experimental conversion of propane is 40%. The reactor outlet stream consists of unreacted propane and oxygen, helium, propylene oxide, propylene, ethylene, acetaldehyde, hydrogen, water, carbon monoxide and carbon dioxide. Then, completely different separation levels are carried out to separate the completely different merchandise and unreacted gases. After cooling the response merchandise (E-103), a vapor, liquid and aqueous streams are break up within the separator V-100. The vapor stream is especially composed of ethylene, hydrogen, oxygen, helium, carbon monoxide, and carbon dioxide, whereas most propane, propylene oxide, acetaldehyde, and propylene are recovered within the liquid stream. The vapor stream is additional cooled (E-104) and separated into two streams within the separator V-101. The ensuing streams are a vapor combination consisting of helium and hydrogen, and a liquid shaped by carbon monoxide, oxygen, and minor quantities of different compounds, similar to ethylene, carbon dioxide, propane, and propylene. Helium and hydrogen are separated in V-102 after cooling (E-105). The liquid stream obtained in V-101 is heated (E-106) to get well carbon monoxide and oxygen within the prime stream of the separator V-103. After that, oxygen is separated from carbon monoxide within the distillation column T-104 and fed into the reactor along with a recent oxygen stream. The liquid stream obtained in V-100 is subjected to successive distillation levels to get well propylene, acetaldehyde, propylene oxide and unreacted propane in particular person streams. Within the distillation column T-100, the sunshine elements that might not be separated in V-100 (primarily ethylene, and carbon dioxide) are recovered within the prime stream. Within the backside stream, propane, propylene, acetaldehyde, and propylene oxide are obtained. The underside stream from T-100 enters the distillation column T-101, the place propylene is separated within the prime stream. The underside stream from T-101 is fed to the distillation column T-102. Right here, the unreacted propane is recovered within the prime stream and recirculated to the reactor. Lastly, the underside stream of T-102 is separated into acetaldehyde and propylene oxide within the distillation column T-103.

Supplementary Desk 3 exhibits the restoration of the primary compounds of their corresponding streams in addition to their mole fractions. Greater than ca. 95% of propane, propylene oxide, hydrogen, oxygen, propylene, and helium, respectively, are separated and recovered in particular person streams. They’re excessive purity streams during which the mole fraction of the corresponding compound is ≥0.99, apart from the case of the acetaldehyde stream, which has an acetaldehyde mole fraction of ca. 0.95.

The plant value estimation for the direct oxidation of propane to provide propylene oxide primarily based on the Aspen HYSYS simulation has been carried out utilizing the Aspen Course of Financial Analyzer (APEA) built-in in Aspen HYSYS. The plant prices will be categorized in two main classes, i.e., capital, and working prices. The capital value contains the gear and put in prices. Each prices signify the key fraction of the entire capital value. Alternatively, the prices related to uncooked supplies and utilities like separation account for the primary a part of the working prices. The capital and working prices have been used to calculate the minimal worth at which propylene oxide may very well be offered, assuming that the capital value will probably be fully paid through the first 5 years of the operation of the plant assuming 8000 h of operation per 12 months (Supplementary Desk 4).