Highly selective homogeneous ethylene epoxidation in gas (ethylene)‐expanded liquid: Transport and kinetic studies

Abstract

in Wiley Online Library (wileyonlinelibrary.com).Recently a homogeneous liquid-phase ethylene oxide (EO) process with nearly total EO selectivity, catalyzed by methyltrioxorhenium with H 2 O 2 as an oxidant, was reported. Fundamental mass transfer and kinetic studies of this reaction are reported in the present work. Volumetric expansion studies revealed that the liquid reaction phase (methanol þ H 2 O 2 / H 2 O) is expanded by up to 12% by compressed ethylene in the 20-40 C range and up to 50 bars. This represents an increase in ethylene solubility by approximately one-order of magnitude, attributed to the unique exploitation of nearcritical ethylene (P c ¼ 50.76 bar; T c ¼ 9.5 C). Interphase mass-transfer coefficients for ethylene dissolution into the liquid phase were obtained experimentally. Operating at conditions that enhanced the ethylene solubility and eliminated interphase mass-transfer limitations maximized the EO productivity (1.61-4.97 g EO/h/g cat), rendering it comparable to the conventional process. Intrinsic kinetic parameters, estimated from fixed-time semibatch reactor studies, disclosed the moderate activation energy (57 AE 2 kJ/mol). (a) Ethanol þ methanol binary system; (b) (ethylene þ methanol þ 50 wt % H 2 O 2 /H 2 O) ternary system. Initial composition of liquid phase ¼ 0.748 mol methanol þ 0.134 mol H 2 O 2 þ 0.253 mol H 2 O. Initial volume of liquid phase ¼ 15 mL. The size of the plotted data points represents the experimental uncertainty. Ethylene P ¼ 50 bars; T ¼ 40 C; MTO amount ¼ 0.361 mmol; methanol ¼ 0.748 mol; H 2 O 2 ¼ 0.116 mol; H 2 O ¼ 0.220 mol; acetonitrile ¼ 0.0191 mol; pyridine N-oxide ¼ 2.19 mmol; batch time ¼ 5 h; agitation speed (Ä : 1,200 rpm, h: 400 rpm).

Towards highly selective ethylene epoxidation catalysts using hydrogen peroxide and tungsten- or niobium-incorporated mesoporous silicate (KIT-6)

“…1 The oxidant (H 2 O 2 ), operating conditions (20-40°C, 50 bar) and solvent (methanol) are very similar to those employed in the Dow-BASF HPPO technology for making propylene oxide. 8 The main difference is that the HPPO process uses a heterogeneous TS-1 catalyst that does not work for ethylene epoxidation.…”

“…Under these conditions, ethylene (P c = 50.6 ± 0.5 bar, T c = 9.3 ± 0.5°C) is near its critical point and hence exhibits liquid-like density, causing it to substantially dissolve in the liquid phase, expanding its volume by up to 15%. 1 Thus, the reaction occurs in an ethylene-expanded liquid phase. Prior to reaction, the catalyst samples were activated in a stream of flowing air at 500°C for 5 h with a heating rate of 2°C min Tables 2 and 4, the uncertainty in the measured values of the various performance metrics, established through repeated runs, is within 3% of the reported mean values.…”

“…The reactor and the operating procedure have been described previously. 1 Briefly, the catalysts were tested for ethylene epoxidation in a 50 mL Parr reactor operated at 35°C, 50 bar and 1400 rpm (to eliminate gas-liquid mass transfer limitations). Under these conditions, ethylene (P c = 50.6 ± 0.5 bar, T c = 9.3 ± 0.5°C) is near its critical point and hence exhibits liquid-like density, causing it to substantially dissolve in the liquid phase, expanding its volume by up to 15%.…”

“…Recently, we reported a liquid phase ethylene epoxidation process (also referred herein as the CEBC process) that eliminates ethylene burning and produces EO with nearly total selectivity. 1,6,7 Under mild operating conditions of 40°C and 50 bar, the catalyst (methyltrioxorhenium, MTO) shows high activity (1610-4970 mg EO h −1 (g Re)…”

“…During the next decade, the EO demand is projected to grow at an annual rate of 6-7%. 1 Currently, EO is produced through vapor phase ethylene epoxidation over Ag-based catalysts using O 2 as the oxidant. A major challenge in this technology has been to curtail the burning of ethylene as well as EO to CO 2 at typical reaction temperatures (200-240°C).…”