Process for reducing excessive chlorination of high selectivity ethylene oxide catalyst during restart

Abstract

Disclosed herein are methods for improving the restart performance of a highly selective ethylene oxide catalyst that has been shut down due to a planned or unplanned interruption. Appropriate selection of process variables at restart is believed to avoid deteriorated catalyst surface over-chlorination that may occur when chloride under the surface diffuses to the catalyst surface. According to the process, the initial restart reaction temperature is no more than five (5) degrees Celsius higher than the initial start-up steady-state reaction temperature on the fresh catalyst and is no more than five (5) degrees Celsius lower than the initial start-up steady-state reaction temperature. The addition of a supplemental organic chloride to the reactor feed gas is delayed until the reactor outlet oxygen concentration is equal to or greater than 0.5 mol% and until the relatively scaled reactor vinyl chloride feed gas concentration is not greater than 110%.

Description

Technical Field

[0001] The present disclosure relates generally to processes for producing ethylene oxide, and more particularly to methods for reducing the degree of overchloriding of a high selectivity ethylene oxide catalyst when restarting the process. Background Art

[0002] The present disclosure relates to a process for making ethylene oxide (EO). Ethylene oxide is used to produce ethylene glycol, which is used as an automotive coolant, antifreeze, and in the preparation of polyester fibers and resins, nonionic surfactants, glycol ethers, ethanolamines, and polyethylene polyether polyols.

[0003] The production of ethylene oxide is usually carried out via the catalytic epoxidation of ethylene in the presence of oxygen. Along with ethylene and oxygen, a gas phase promoter, such as certain organic chloride compounds, is provided in the reactor feed gas and a promoting substance is deposited on the catalyst surface to increase the selectivity and / or activity for the production of ethylene oxide.

[0004] Conventional silver-based catalysts used in such processes provide relatively low efficiency or "selectivity" (i.e., a lower percentage of the reacted ethylene is converted to the desired ethylene oxide). In certain exemplary processes, when conventional catalysts are used in the epoxidation of ethylene, the theoretical maximum selectivity to ethylene oxide (expressed as the fraction of ethylene converted) does not reach values ​​above the 6 / 7 or 85.7% limit. Thus, this limit has long been considered the theoretical maximum selectivity for the reaction based on the stoichiometry of the following reaction equation:

[0005] 7C2H4+6O2→6C2H4O+2CO2+2H2O

[0006] See Kirk-Othmer Encyclopedia of Chemical Technology, 4th edition, Vol. 9, 1994, p. 926.

[0007] Certain "high efficiency" or "high selectivity" silver-based catalysts are highly selective for ethylene oxide production. For example, when certain catalysts are used in the epoxidation of ethylene, the theoretical maximum selectivity for ethylene oxide can reach values ​​higher than the mentioned 6 / 7 or 85.7% limit, such as 88%, or 89%, or more. Highly selective catalysts contain silver, rhenium and at least one additional other metal as their active components. See EP0352850B1 and WO2007 / 123932.

[0008] Conventional catalysts have a relatively flat selectivity curve relative to the concentration of the gas-phase promoter in the feed, that is, the selectivity is almost constant over a wide range of such promoter concentrations (that is, the selectivity changes with respect to changes in the concentration of the gas-phase promoter in the feed are less than about 0.1% / ppmv), and this invariance is substantially unchanged with changes in the reaction temperature during long periods of operation of the catalyst. However, conventional catalysts have an almost linear activity decline curve relative to the concentration of the gas-phase promoter in the feed, that is, as the concentration of the gas-phase promoter in the feed increases, the temperature must be increased or the ethylene oxide production rate will decrease. Therefore, when using conventional catalysts, in order to obtain the best selectivity, the concentration of the gas-phase promoter in the feed can be selected at a level that can maintain the maximum selectivity at a relatively low operating temperature. For conventional catalysts, the reaction temperature can be adjusted to obtain the desired production rate without substantially adjusting the concentration of the gas-phase promoter.

[0009] In contrast, highly selective catalysts tend to exhibit relatively steep selectivity curves as a function of gas-phase promoter concentration as the concentration moves away from the value that provides the highest selectivity (i.e., the change in selectivity relative to a change in gas-phase promoter concentration is at least about 0.2% / ppmv when operating away from the selectivity that maximizes promoter concentration). Thus, small changes in promoter concentration can result in significant changes in selectivity, and when the reactor pressure and feed gas composition remain constant for a given reaction temperature and catalyst age, the selectivity exhibits a significant maximum (i.e., optimum) at certain concentrations (or feed rates) of the gas-phase promoter.

[0010] It has been found that when restarting an ethylene oxide process using a chloride compound as a vapor phase promoter with a high selectivity, rhenium promoted silver catalyst, the performance at restart is often worse than expected, making it difficult to return to stable operation and maximum selectivity for a given target value of the ethylene oxide production parameter.

[0011] For commercial EO method, due to complete gas recycle design, the excessive chloride compounds in the gas phase produced by surface dechlorination during restart can not be removed quickly.Gas phase chloride concentration greater than expected causes greater than expected catalyst surface chlorination.Do not wish to be bound by any theory, at least in some cases, it is believed that when restarting after closing a period of several hours or longer, the efficient ethylene oxide catalyst can desorb and release the chloride compounds under the surface that have migrated to the surface, and these compounds are then redeposited on the surface of the catalyst from the gas phase, usually causing greater than expected catalyst surface chlorination and the extended time period of low selectivity for ethylene oxide production.It is believed that whether to encounter this particular problem during any specific restart depends on the conditions to which the catalyst is exposed during the offline time period.In addition, the selection of process variable values ​​and the mode of adjusting them when restarting strongly affect the degree of surface chlorination in the restart process.

[0012] Therefore, there is a need for a method to improve the restart performance of highly selective rhenium promoted silver ethylene oxide catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a process flow diagram depicting an embodiment of a process for producing ethylene oxide by epoxidation of ethylene over a highly selective rhenium promoted silver catalyst;

[0014] Figure 2A-2C is a flow chart describing a method for restarting a high efficiency ethylene oxide process after an offline period;

[0015] Figure 3A-Figure 3I is a graph of efficiency of a catalyst batch in a first commercial scale high efficiency ethylene oxide process restarted in accordance with the present disclosure, relative scaled vinyl chloride feed gas concentration, reactor inlet carbon dioxide concentration, reactor coolant temperature, relative feed gas ethyl chloride concentration, reactor outlet carbon dioxide concentration, relative ethylene oxide production rate, relative supplemental oxygen feed rate, and relative supplemental ethyl chloride feed rate to supplemental oxygen feed rate ratio versus ethylene oxide (EO) production time;

[0016] Figure 4A-Figure 4I is a graph of efficiency, relative scaled vinyl chloride feed gas concentration, reactor inlet carbon dioxide concentration, reactor coolant temperature, relative feed gas ethyl chloride concentration, reactor outlet carbon dioxide concentration, relative ethylene oxide production rate, relative supplemental oxygen feed rate, and relative supplemental ethyl chloride feed rate to supplemental oxygen feed rate ratio versus ethylene oxide (EO) production time for a first comparative example in which the reactor was not restarted according to the present disclosure Figure 3A-Figure 3I the first commercial-scale batch of a catalyst for a highly efficient ethylene oxide process;

[0017] Figure 5A-Figure 5I is a graph of efficiency, relative scaled vinyl chloride feed gas concentration, reactor inlet carbon dioxide concentration, reactor coolant temperature, relative feed gas ethyl chloride concentration, reactor outlet carbon dioxide concentration, relative ethylene oxide production rate, relative supplemental oxygen feed rate, and relative supplemental ethyl chloride feed rate to supplemental oxygen feed rate ratio versus ethylene oxide (EO) production time for a second comparative example in which a batch of catalyst in a pilot plant high efficiency ethylene oxide process was not restarted in accordance with the present disclosure;

[0018] Figure 6A-Figure 6Iis a graph of efficiency, relative scaled vinyl chloride feed gas concentration, reactor inlet carbon dioxide concentration, reactor coolant temperature, relative feed gas ethyl chloride concentration, reactor outlet carbon dioxide concentration, relative ethylene oxide production rate, relative supplemental oxygen feed rate, and relative supplemental ethyl chloride feed rate to oxygen feed rate ratio versus ethylene oxide (EO) production time for an example in which a batch of catalyst in a pilot plant high efficiency ethylene oxide process of a second comparative example was restarted in accordance with the present disclosure; and

[0019] Figure 7A-Figure 7I is a graph of efficiency, relative scaled vinyl chloride feed gas concentration, reactor inlet carbon dioxide concentration, reactor coolant temperature, relative feed gas ethyl chloride concentration, reactor outlet carbon dioxide concentration, relative ethylene oxide production rate, relative supplemental oxygen feed rate, and relative supplemental ethyl chloride feed rate to supplemental oxygen feed rate ratio versus ethylene oxide (EO) production time for a third comparative example in which a batch of catalyst in a second commercial-scale, high efficiency ethylene oxide process was not restarted in accordance with the present disclosure. DETAILED DESCRIPTION

[0020] The present disclosure provides a method for restarting a process for producing ethylene oxide by reacting ethylene and oxygen in the presence of at least one organic chloride over a highly efficient rhenium-promoted silver catalyst. The method is performed after a certain period of time, during which the process is offline (i.e., shutdown) and no supplementary oxygen is fed to the batch of catalyst. The period of time is preferably at least about two hours, more preferably at least about three hours, and still more preferably at least about 4 hours. Upon restarting, a feed gas comprising a reactor recycle stream is fed to the batch of highly efficient catalyst in combination with a supplementary stream, the supplementary streams comprising at least supplementary ethylene at the initial feed rate of supplementary ethylene and supplementary oxygen at the initial feed rate of supplementary oxygen, and the reaction temperature is adjusted to an initial restart reaction temperature value (i.e., "initial startup steady-state reaction temperature value"), the initial restart reaction temperature value being no more than five (5) degrees Celsius, preferably no more than three (3) degrees Celsius, and more preferably no more than two (2) degrees Celsius, higher than the initial steady-state reaction temperature achieved by the batch when the catalyst batch is fresh. At the same time, the initial restart reaction temperature value is no more than five (5) degrees Celsius, preferably no more than three (3) degrees Celsius, and more preferably no more than two (2) degrees Celsius below the initial steady-state reaction temperature value achieved when the batch of catalyst is fresh. In a preferred example, the initial restart reaction temperature value is no greater than the pre-shutdown steady-state temperature value. It is also preferred that the pre-shutdown steady-state reaction temperature value is higher than the initial startup steady-state reaction temperature value by more than five (5) degrees Celsius, ten (10) degrees Celsius, or fifteen (15) degrees Celsius.

[0021] According to the method, no supplementary organic chloride is fed to the batch of catalyst until the reactor outlet oxygen concentration exceeds a value of 0.5 mol%, preferably 0.7 mol% and more preferably 0.9 mol%. When the reactor outlet oxygen concentration exceeds a value of 0.5 mol%, preferably 0.7 mol% and more preferably 0.9 mol%, supplementary organic chloride selected from ethyl chloride and ethylene dichloride is fed to the batch of high efficiency catalyst at a rate not greater than 30%, preferably not greater than 25% and more preferably not greater than 20% of the last steady-state supplementary organic chloride feed rate value before the period of time when the reactor was offline.

[0022] In an additional preferred example, depending on the selectivity (S) relative to the pre-shutdown steady-state selectivity (S ss ) and the direction in which the selectivity tends, the reaction temperature and the feed rate of supplemental oxygen are slowly ramped up to their pre-shutdown steady-state values ​​(T Rx SS , F O2 MU SS ). In the same or other examples, depending on the selectivity (S) relative to the steady-state pre-shutdown selectivity (S ss ), the direction in which the selectivity tends, and the relative scaled reactor feed gas vinyl chloride (VCl) concentration (C VCl RS ) value and the direction toward which the relatively scaled reactor feed gas vinyl chloride concentration is tending, adjust the feed rate of the make-up organic chloride to achieve and maintain a ratio of the feed gas make-up organic chloride feed rate to the feed gas make-up oxygen feed rate of no more than 115%, preferably no more than 105%, and more preferably no more than 100% of the ratio of the corresponding last steady-state feed rates prior to shutdown.

[0023] This specification provides certain definitions to guide those of ordinary skill in the art in practicing the invention. The provision or non-provision of a definition for a particular term or phrase is not meant to imply any particular importance or lack of importance; rather, unless otherwise noted, the term is to be understood according to conventional usage by those of ordinary skill in the relevant art. Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the invention belongs.

[0024] The "activity" of a catalyst in a fixed bed reactor is generally defined as the rate of reaction of the desired product per unit volume of catalyst in the reactor. The "activity" of a catalyst can be quantified in a variety of ways, one being the mole percentage of ethylene oxide contained in the reactor outlet stream relative to the ethylene oxide in the inlet stream (the mole percentage of ethylene oxide in the inlet stream is typically, but not necessarily, close to zero percent), while the reaction temperature is maintained substantially constant; and another being the temperature required to maintain a given ethylene oxide production rate. In many cases, activity is measured over a period of time in terms of the mole percentage of ethylene oxide produced at a specified constant temperature. Alternatively, activity can be measured as a function of the temperature required to maintain production of a specified constant mole percentage of ethylene oxide.

[0025] Oxidation "efficiency," synonymous with "selectivity," refers to the relative amount (in fraction or percentage) of ethylene converted or reacted to form a particular product. For example, "selectivity to ethylene oxide" refers to the mole percentage of ethylene based on conversion that forms ethylene oxide.

[0026] The term "ethylene oxide production parameter" is used herein to describe variables related to the degree of ethylene oxide production. Examples of ethylene oxide production parameters include ethylene oxide concentration, ethylene oxide yield, ethylene oxide production rate, ethylene oxide production rate / catalyst bed volume, ethylene conversion, oxygen conversion, oxygen feed rate, and ethylene feed rate. Therefore, ethylene oxide concentration is related to ethylene oxide production rate because production rate can be obtained by multiplying ethylene oxide concentration by the net product flow rate from the reactor. Ethylene oxide production rate / catalyst bed volume can be determined by dividing production rate by the volume of catalyst bed. Oxygen and ethylene conversion and oxygen and ethylene feed rate under steady-state conditions are related to the production of ethylene oxide by selectivity. Selectivity and activity are not ethylene oxide production parameters. "Target ethylene oxide production parameters" are ethylene oxide production parameters used as the specification for operating ethylene oxide processes. In one example, the ethylene oxide process is operated to achieve a specified value of ethylene oxide production rate, in which case the ethylene oxide production rate would be considered the target ethylene oxide production parameter.

[0027] "Gas phase promoter" means a compound that increases the selectivity and / or activity of a process for producing ethylene oxide. Preferably, the gas phase promoter comprises an organic chloride. More preferably, the gas phase promoter is at least one gas phase promoter selected from the group consisting of methyl chloride, ethyl chloride, ethylene dichloride, vinyl chloride, and mixtures thereof. Ethyl chloride and ethylene dichloride are most preferred as gas phase promoters fed to the process.

[0028] The terms "high efficiency catalyst" and "high selectivity catalyst" refer to a catalyst capable of producing ethylene oxide from ethylene and oxygen with a selectivity greater than 85.7%. Under certain conditions based on process variables, catalyst life, etc., the actual selectivity observed for a high selectivity catalyst can drop below 85.7%. However, a catalyst is considered to be a high selectivity catalyst if it is able to achieve a selectivity of at least 85.7% at any point during its life (e.g., under any set of reaction conditions), or by extrapolating the lower efficiency observed at two different oxygen conversions obtained by varying the gas hourly space velocity to the limiting case of zero oxygen conversion.

[0029] The term "oxygen flammability concentration" refers to an oxygen concentration based on the oxygen flammability limit, and includes both the oxygen flammability limit itself and an oxygen concentration that deviates from the oxygen flammability limit by a safety margin.

[0030] "Reaction temperature" or "(T Rx )" refers to any selected temperature that directly or indirectly indicates the catalyst bed temperature. In certain embodiments, the reaction temperature may be the catalyst bed temperature at a particular location in the catalyst bed. In other embodiments, the reaction temperature may be the numerical average of several catalyst bed temperature measurements taken along one or more catalyst bed dimensions (e.g., along the length). In additional embodiments, the reaction temperature may be the reactor outlet gas temperature. In further embodiments, the reaction temperature may be a reactor coolant temperature selected from the reactor coolant outlet temperature, the reactor coolant inlet temperature, such as measured in the reactor shell, and the reactor coolant temperature along the tube length between the coolant inlet and outlet (such as at the midpoint of the tube length). In the case of a boiling coolant reactor, the temperature may be determined based on the coolant pressure.

[0031] The term "initial startup steady-state reaction temperature value" (T Rx i SS ) is the first steady state reaction temperature value achieved after a fresh high efficiency ethylene oxide catalyst is subjected to a reactive mixture of ethylene and oxygen.

[0032] The term "initial restart reaction temperature value" refers to the reaction temperature of a high efficiency ethylene oxide process when supplemental oxygen feed is initiated during restart.

[0033] The term "minimum controllable organic chloride feed rate" (F RCl MU min ), “minimum controllable ethyl chloride feed rate” (F ECl MU min ) and the “minimum controllable ethylene dichloride feed rate” (F EDCMU min ) refers to the minimum stable non-zero gas flow rate of all make-up organic chloride streams (collectively), make-up ethyl chloride streams or make-up ethylene dichloride streams, respectively.

[0034] The term "overchloriding", sometimes also referred to in the art as "overmoderating", refers to a process by which the concentration of chloride promoter on the surface of a high selectivity ethylene oxide catalyst is increased to exceed the optimum surface concentration that produces maximum selectivity under a given set of operating conditions. Adjustment of the catalyst surface chloride concentration is typically accomplished by varying the gas phase concentration of one or more organic chlorides in the reactor feed by adjusting the feed rate of the make-up organic chloride into the recycle stream.

[0035] "Shutdown" or "offline" refers to a certain period of time when the high efficiency catalyst is not subjected to the reactive mixture of oxygen and ethylene. "Trip" refers to a shutdown that occurs due to a process upset or some unexpected event, such as pump failure, recycle gas compressor failure, downstream shutdown, feed interruption, failure of a control valve regulating pressure, temperature or flow rate, etc.

[0036] “Ethylene oxide production time,” “ethylene oxide production days,” or “ethylene oxide production hours” means the duration, days, and hours, respectively, of producing ethylene oxide by an ethylene oxide process measured cumulatively from the initial startup of a batch of fresh silver catalyst.

[0037] “Ramp,” “Ramping,” or “Ramp Rate,” when used to refer to a change in the value of a process variable over a period of time, is not limited to the slope of a continuous linear adjustment, but may also include discontinuous and / or non-linear adjustments, such as a step change divided by a period of time over which such adjustment is made.

[0038] "Relative make-up ethylene feed rate" or "relative make-up ethylene feed rate" means the current value of the make-up ethylene feed rate (F Et＝MU ) divided by the pre-shutdown steady-state value of the supplementary ethylene feed rate (F Et＝MU SS ), expressed as a percentage or fraction.

[0039] "Relative feed rate of make-up ethyl chloride" or "relative make-up ethyl chloride feed rate" means the molar or volumetric flow rate of make-up ethyl chloride after restart divided by the pre-shutdown steady-state molar or volumetric flow rate of make-up ethyl chloride.

[0040] "Relative feed rate of make-up ethylene dichloride" or "relative make-up ethylene dichloride feed rate" means the molar or volumetric flow rate of make-up ethylene dichloride after restart divided by the pre-shutdown steady-state molar or volumetric flow rate of make-up ethylene dichloride.

[0041] "Relative feed rate of supplemental oxygen" or "relative supplemental oxygen feed rate" means the current value of the supplemental oxygen feed rate (F O2 MU ) divided by the steady-state supplementary oxygen feed rate before shutdown (F O2MU SS ), expressed as a percentage or fraction.

[0042] "Relative ECl / O2 feed ratio" or "relative ethyl chloride to oxygen feed ratio" means the first current ratio of the supplemental ethyl chloride feed rate value to the supplemental oxygen feed rate value (F ECl MU ) / (F O2MU ) to the second ratio (F ECL MU SS ) / (F O2 MU SS ) ratio, expressed as a percentage or fraction. When the supplemental organic chloride is ethylene dichloride, a similar "relative EDC / O2 feed ratio" or "relative ethylene dichloride to oxygen feed ratio" may be defined.

[0043] "Relative ethylene oxide production parameter value" or "relative EO production parameter value" means the current value of the ethylene oxide production parameter (EO PP ) and the steady-state value of ethylene oxide production parameters before shutdown (EO PP SS ) expressed as a percentage or fraction.

[0044] “Relative EO production rate” means the current value of the EO production rate relative to the steady-state value of the EO production rate before shutdown (EO Prod SS ) ratio.

[0045] "Steady state" when referring to an ethylene oxide process means an ethylene oxide production process wherein (i) the value of at least one ethylene oxide production parameter has reached a daily average value that fluctuates by no more than two (2) percent from a target value for the at least one ethylene oxide production parameter over a period of at least two (2) days, preferably five (5) days, and more preferably seven (7) days, and (ii) the value of efficiency has reached a daily average value that fluctuates by no more than 0.2 percentage points from the average over the same period of time.

[0046] When referring to the value of a process variable, "steady state" means the average value over the corresponding steady state time period for the ethylene oxide process;

[0047] When referring to the value of a particular process variable, "pre-shutdown steady state" means the average value of the variable over the last steady state period prior to the shutdown, prior to restarting the ethylene oxide process.

[0048] Highly selective silver-based catalysts containing rhenium and methods for preparing the same are known to those skilled in the art, see EP0352850B1, WO2007 / 123932, WO2014 / 150669, EP1613428 or CN102133544.

[0049] Reactors suitable for epoxidation reactions include fixed bed reactors, fixed bed tubular reactors, continuous stirred tank reactors (CSTRs), fluidized bed reactors, and a variety of reactors well known to those skilled in the art. Those skilled in the art can also easily determine the desirability of recycling unreacted feed, or using a single-pass system, or using a continuous reaction to increase ethylene conversion by using reactors arranged in series. However, the problems solved by the present disclosure are particularly severe when at least a portion of the reactor outlet stream is recycled to form a portion of the feed gas to the reactor. The epoxidation reaction is carried out at a temperature of preferably at least about 200°C, more preferably at least about 210°C, and most preferably at least about 220°C. A reaction temperature of no more than about 300°C is preferred, more preferably no more than about 290°C, and most preferably no more than about 280°C.

[0050] The reactor pressure is selected based on the desired mass velocity and production rate and is generally in the range of about 5 atm (506 kPa) to about 30 atm (3.0 MPa). The gas hourly space velocity (GHSV) is preferably greater than about 3,000 hr -1 , more preferably greater than about 4,000 hr -1 and most preferably greater than about 5,000 hr -1 .

[0051] Figure 12 is a process flow diagram depicting an embodiment of a process 20 for preparing ethylene oxide by epoxidizing ethylene over a highly selective rhenium-promoted silver catalyst. The process 20 includes a reactor 22 including a plurality of reactor tubes having a highly selective catalyst therein. An ethylene make-up feed stream 36 (which may also include saturated hydrocarbons, such as ethane as an impurity), a ballast gas 32, an oxygen make-up feed 34, and a gas phase promoter make-up feed 33 are each combined with a recycle stream 30 to produce a reactor feed gas inlet stream 24 close to the reactor 22. In addition to by-products (e.g., carbon dioxide, water, and a small amount of saturated hydrocarbons), unreacted ethylene, oxygen, and inert gases, the reactor product stream 26 also includes an ethylene oxide product. The epoxidation reaction is generally exothermic. Therefore, a coolant system 27 (e.g., a cooling jacket or hydraulic circuit with a coolant fluid (such as a heat transfer fluid or boiling water)) is provided to adjust the temperature of the reactor 22. The heat transfer fluid can be any of several well-known heat transfer fluids, such as tetralin (1,2,3,4-Tetrahydronaphthalene).

[0052] The gas phase promoter in the reactor feed 24 is generally used to enhance the process 20 ( Figure 1) of the process 20 for producing ethylene oxide. Preferably, the vapor phase promoter comprises an organic chloride. More preferably, the vapor phase promoter is at least one organic chloride selected from the group consisting of methyl chloride, ethyl chloride, ethylene dichloride, vinyl chloride, and mixtures thereof. Ethyl chloride and ethylene dichloride are most preferably used as the supplemental organic chloride in the vapor phase promoter supplemental feed 33. Using a chlorocarbon vapor phase promoter as an example, it is believed that the ability of the promoter to improve the performance (e.g., efficiency and / or activity) of the process 20 for producing ethylene oxide depends on the extent to which the vapor phase promoter chlorinates the surface of the catalyst in the reactor 22 (e.g., by depositing specific chlorine species, such as atomic chlorine or chloride ions, on the catalyst). However, it is believed that hydrocarbons lacking chlorine atoms strip chlorides from the catalyst and therefore detract from the overall performance improvement provided by the vapor phase promoter. Discussion of this phenomenon can be found in Berty, "Inhibitor Action of Chlorinated Hydrocarbons in the Oxidation of Ethylene to Ethylene Oxide," Chemical Engineering Communications, Vol. 82 (1989) pp. 229-232 and Berty, "Ethylene Oxide Synthesis," Applied Industrial Catalysis, Vol. 1 (1983) pp. 207-238. Paraffinic compounds, such as ethane or propane, are believed to be particularly effective in stripping chlorides from the catalyst. Olefins, such as ethylene and propylene, are also believed to act to remove chlorides from the catalyst. Some of these hydrocarbons may also be introduced as impurities into the ethylene make-up feed 36 and / or the ballast gas feed 32, or may be present for other reasons, such as the use of the recycle stream 30. Typically, when present, the preferred concentration of ethane in reactor feed gas inlet stream 24 is from 0 mole % to about 2 mole %.

[0053] In a preferred example, only a single substance of supplemental organic chloride is supplied in the gas phase promoter supplemental feed 33. Although the gaseous chlorine-containing promoter can be supplied as a single substance, upon contact with the catalyst, other substances may be formed resulting in a gas phase mixture. Therefore, if the reaction gas is recycled, such as via the recycle stream 30, a mixture of substances will be found in the inlet 24 of the reactor 22. Specifically, the recycled reaction gas at the inlet 24 may contain ethyl chloride, vinyl chloride, ethylene dichloride, and methyl chloride, even if only ethyl chloride or ethylene dichloride is supplied to the system.

[0054] As mentioned previously, it is believed that upon restart, a high efficiency ethylene oxide process using an organic chloride vapor phase promoter may experience excessive release of chloride from the surface of the catalyst and migration of subsurface chloride to the surface of the catalyst. It has been found that a useful measure of this phenomenon is the relative scaled VCl feed gas concentration value, which is defined as follows:

[0055] (4) C VCl RS = [C in VCl / F Et＝ MU ][F Et＝ MU SS / C in VCl SS ]

[0056] Among them, C VCl RS = Relative scaled vinyl chloride reactor feed gas concentration (dimensionless);

[0057] C in VCl = actual reactor feed gas inlet concentration of vinyl chloride (ppm molar);

[0058] F Et＝MU = actual supplemental feed rate of ethylene (mol / h);

[0059] F Et＝MU SS = steady-state make-up feed rate of ethylene before shutdown (mol / hour);

[0060] and

[0061] C in VCl SS = Steady-state reactor feed gas concentration of vinyl chloride before shutdown (ppm molar)

[0062] The variables in equation (4) can also be expressed on a mass or volume basis. In a preferred example, C in VCl The F Et＝MU is a real-time measurement of the feed rate of supplemental ethylene, C in VCl SS is the measurement of the last steady-state vinyl chloride concentration in the feed gas prior to the trip or shutdown from which the process was restarted, and preferably is the daily average of the vinyl chloride concentration measured during the last continuous period of steady-state operation prior to the shutdown or trip, and F Et＝MUSS is a measurement of the last steady-state supplemental ethylene feed rate before the trip or shutdown from which the process was restarted, and preferably is a daily average of the supplemental ethylene feed rate measured during the last continuous period of steady-state operation before the shutdown or trip.

[0063] Commercial EO processes are designed to have low single pass conversions and therefore provide for recycle of unreacted ethylene and oxygen. Recycle stream 30 is also used to manage heat of reaction removal and maximize EO selectivity and yield. An example of a suitable recycle system is depicted in Figure 1 As shown in the figure, the ethylene oxide absorber 38 includes a feed stream defined by the reactor product stream 26, and also includes a lean water feed stream 42. The ethylene oxide absorber 38 produces a water-rich stream 44 and an overhead gas stream 35, which is an intermediate stream between the ethylene oxide absorber 38 and the carbon dioxide removal unit 21 and contains unreacted olefins, oxygen, by-product carbon dioxide, ballast gases such as methane or nitrogen, impurities such as ethane and argon. Carbon dioxide is removed in the CO2 removal unit 21 (e.g., a CO2 scrubber coupled to a regenerator) and leaves the CO2 removal unit 21 in a carbon dioxide stream 40. The overhead stream 39 from the CO2 removal unit 21 is combined with a bypass stream 46 of the CO2 removal unit 21 to define a recycle stream 30. A purge line 41 is also provided to remove saturated hydrocarbon impurities (e.g., ethane), inert gases (such as argon) and / or by-products (and carbon dioxide) to prevent them from accumulating in the reactor feed 24. The feed stream 37 to the CO 2 removal unit 21 is defined by the overhead stream 35 of the ethylene oxide absorber 38 after taking into account the bypass stream 46 (if present) and the purge line 41 of the CO 2 removal unit 21 .

[0064] The oxygen supplemental feed 34 may comprise substantially pure oxygen or air. Typically, the oxygen concentration (C in O2 ) is at least about 1 mol %, and preferably at least about 2 mol %. The oxygen reactor feed gas concentration C in O2 Typically no more than about 15 mol % and preferably no more than about twelve (12) mol % will be present. The ballast gas 32 (eg, nitrogen or methane) is typically about 50 mol % to about 80 mol % of the total composition of the reactor feed gas inlet 24 .

[0065] The concentration of ethylene in the reactor feed gas inlet stream 24 (C in Et＝ ) can be at least about 18 mol%, and more preferably at least about 20 mol%. The concentration of ethylene in the reactor feed gas inlet stream 24 is preferably no greater than about 50 mol%, and more preferably no greater than about 40 mol%.

[0066] When present, the carbon dioxide concentration in the reactor feed gas inlet stream 24 has an adverse effect on the selectivity, activity and / or stability of the catalyst used in the reactor 22. Carbon dioxide is produced as a reaction byproduct, and can also be introduced as an impurity with other inlet reaction gases. In commercial ethylene epoxidation processes, at least a portion of the carbon dioxide is continuously removed so that its concentration is controlled to an acceptable level in the cycle. The carbon dioxide concentration in the reactor feed 24 is usually no more than about 8 moles of the total composition of the reactor feed gas stream 24, preferably no more than about 4 moles, and even more preferably no more than about 2 moles. Water can also be present in the reactor feed gas stream 24 at a concentration of up to 2 moles.

[0067] In embodiments, when present, the preferred concentration of ethane in reactor feed gas inlet stream 24 is up to about 2 mole percent, and concentrations of less than 0.1 mole percent or even 0.05 mole percent may be achieved.

[0068] According to a first embodiment of the present disclosure, the process 20 has been shut down or tripped and has been offline for a period of at least about one hour, preferably at least about two hours, and more preferably at least about four hours. PP T ) target value. To start the restart process, the ethylene concentration in the reactor feed gas inlet stream is set to an initial ethylene restart concentration value, which is preferably about equal to the pre-shutdown steady-state feed gas ethylene concentration value, preferably about 20 mol % to about 40 mol %. The reaction temperature (T Rx ) is set to an initial restart reaction temperature value, which is lower than the initial startup steady-state reaction temperature value (T Rx i SS ) does not exceed five (5) degrees Celsius, preferably does not exceed three (3) degrees Celsius, and more preferably does not exceed two (2) degrees Celsius. At lower temperatures, the selectivity variation with temperature may become more severe, and the process generally shows less stable selectivity values. At the same time, the initial restart reaction temperature value is higher than the initial start-up steady-state reaction temperature value (T Rx i SS ) does not exceed five (5) degrees Celsius, preferably does not exceed three (3) degrees Celsius, and more preferably does not exceed two (2) degrees Celsius. T is selected or determined empirically according to any start-up method known in the art for fresh, highly efficient Re-promoted silver catalysts. Rx i SS The initial restart reaction temperature is also preferably not greater than the steady-state reaction temperature (T RxSS ). When T Rx SS Higher than T Rx i SS The methods of the present invention are particularly useful above five (5) degrees Celsius, above ten (10) degrees Celsius, or above fifteen (15) degrees Celsius.

[0069] The oxygen supplement feed rate (F O2 MU ) is set to the pre-shutdown steady-state value of the supplementary oxygen feed rate (F O2 MU SS ) of no more than about forty (40)%, preferably no more than about thirty (30)%, and more preferably no more than about twenty (20)% of the initial restart value. According to a first embodiment, if the selectivity is less than the last steady-state value (S) of the selectivity before the trip and / or shutdown ss ) exceeds three (3) percentage points, preferably exceeds two (2) percentage points and more preferably exceeds 1 (one) percentage point, and if the selectivity also tends to decrease (for example, dS / dt<0, wherein dS / dt is preferably an average value of several time periods, each of which is preferably not longer than one hour, more preferably not longer than 30 minutes, still more preferably not longer than 15 minutes, and each of which is also preferably not less than five (5) minutes and more preferably not less than ten (10) minutes), the reaction temperature (T Rx ) is maintained at its current value. Otherwise, the reaction temperature increases, and when this value is not less than the value of the initial startup steady-state reaction temperature (T Rx i SS ), the reaction temperature increases by no more than about 0.6°C, preferably 0.4°C, and more preferably 0.2°C in any given 15 minute interval. At the same time, the minimum ramp rate is at least about 0.05°C, preferably at least about 0.1°C, and more preferably at least about 0.15°C in any given 15 minute interval.

[0070] If the ethylene oxide production parameters (EO PP ) has not yet reached its target value (EO PP T ) and the reaction temperature has not yet reached a value higher than its steady-state value before shutdown (T Rx SS) at least five (5) degrees Celsius, preferably at least three (3) degrees Celsius above its pre-shutdown steady-state value, and more preferably equal to its pre-shutdown steady-state value, then the ramping of the reaction temperature continues. Otherwise, the temperature ramping is stopped and the method ends. As described below, sequentially or preferably in parallel with the temperature, other selected parameters may also be increased during the restart toward their respective pre-shutdown steady-state values ​​until the ethylene oxide production parameter (EO PP ) reaches its target value (EO PP T ) or other parameters have also reached their respective limits based on their pre-shutdown steady-state values ​​specified below. At this point, the restart is complete, and if necessary, the process can be adjusted using known methods to further increase the ethylene oxide production parameters to EO PP T Or according to various standards in EO PP In one example, the feed gas supplement organic chloride feed rate and the reaction temperature are adjusted to achieve maximum selectivity at the target value of the selected ethylene oxide production parameter. In another example, the feed gas supplement organic chloride feed rate F is adjusted to achieve the best efficiency at the current value of the feed gas supplement organic chloride feed rate F RCl MU At the reaction temperature (T Rx ) to achieve maximum selectivity at the current value of .

[0071] According to a second embodiment, at the time of restart, the process 20 has been shut down or tripped and has been offline for a period of at least one hour, preferably at least two hours, and more preferably at least about four hours. PP T ). To start the restart process, the ethylene concentration in the feed gas is set to an initial ethylene restart concentration value, which is preferably approximately equal to the pre-shutdown steady-state feed gas ethylene concentration value, preferably about 25 mol % to about 35 mol %. The initial restart reaction temperature value is lower than the initial startup steady-state reaction temperature value (T Rx i SS ) does not exceed five (5) degrees Celsius, preferably does not exceed three (3) degrees Celsius, and more preferably does not exceed two (2) degrees Celsius. At the same time, the initial restart reaction temperature value is higher than the initial startup steady-state reaction temperature value (T Rx i SS ) does not exceed five (5) degrees Celsius, preferably does not exceed three (3) degrees Celsius, and more preferably does not exceed two (2) degrees Celsius. In a preferred example, the initial restart reaction temperature value is also no greater than the steady-state reaction temperature (T Rx SS ). When T RxSS Higher than T Rx i SS The methods of the present invention are particularly useful above five (5) degrees Celsius, above ten (10) degrees Celsius, or above fifteen (15) degrees Celsius.

[0072] The oxygen supplement feed rate (F O2 MU ) is set to the supplemental feed rate (F) of oxygen during the last continuous period of steady-state operation prior to shutdown and / or tripping O2 MU SS ) does not exceed about forty (40)%, preferably does not exceed about thirty (30)%, and still more preferably does not exceed about twenty (20)%. No supplemental organic chloride is fed to the process unless and until the reactor outlet gas oxygen concentration (C out O2 ) reaches a value of at least about 0.5 mol %, preferably at least about 0.7 mol %, and still more preferably at least about 0.9 mol %. After the reactor outlet oxygen concentration reaches the desired value, the feed rate of the supplementary organic chloride is started at a selected value that is not less than the minimum controllable feed rate of the supplementary organic chloride and does not exceed the steady-state supplementary organic chloride feed rate (F RCl MU SS ), preferably no more than about 25%, and more preferably no more than 20%. If the ratio of the feed rate of the supplementary organic chloride to the feed rate of the supplementary oxygen (i.e., F RCl MU / F O2 MU ) is less than the steady-state feed rate (F RCl MU SS ) and the steady-state feed rate before shutdown of supplementary oxygen (F O2 MU SS ) is less than 115%, preferably less than 105%, and more preferably less than 100%, the feed rate of the supplementary organic chloride is increased.

[0073] If the relative scaled VCl feed gas concentration (C VCl RS ) exceeds a value of 110%, preferably 105% and more preferably 100%, the feed rate of the supplementary organic chloride is not increased. If (i) the selectivity is less than the last steady-state value (S) of the selectivity before the trip and / or shutdown ss) exceeds three (3) percentage points, preferably exceeds two (2) percentage points and more preferably exceeds 1 (one) percentage point, (ii) the selectivity tends to decrease (for example, using the average of dS / dt over several time periods, dS / dt<0, each of which is preferably no longer than one hour, more preferably no longer than 30 minutes, still more preferably no longer than 15 minutes, and each of which is also preferably no less than five (5) minutes and more preferably no less than ten (10) minutes), (iii) the relatively scaled vinyl chloride feed gas concentration (C VCl RS ) exceeds 110%, preferably exceeds 105%, and more preferably exceeds 100%, and (iv) C VCl RS If it does not tend to decline, the feed rate of the supplemental organic chloride is reduced and preferably stopped.

[0074] Once the ethylene oxide production parameters (EO PP ) has reached its target value (EO PP T ), or the ratio of the feed rate of the supplementary organic chloride to the feed rate of the supplementary oxygen (i.e., F RCl MU / F O2 MU ) reaches the ratio of the pre-shutdown steady-state feed rate of supplementary organic chloride to the pre-shutdown steady-state feed rate of supplementary oxygen (F RCl MU SS / F O2 MU SS ), then the feed rate of the supplementary organic chloride and / or the feed rate of the supplementary oxygen are adjusted in a coordinated manner to maintain the current ratio of the feed rates, and the method ends. In parallel with the ratio of the feed rate of the supplementary organic chloride to the feed rate of the supplementary oxygen, other selected parameters may also be increased during the restart toward their respective pre-shutdown steady-state values ​​until the ethylene oxide production parameter (EO PP ) reaches its target value (EO PP T ) or other parameters have also reached their respective limits based on their pre-shutdown steady-state values ​​as described herein. At this point, the restart is complete, and if necessary, the process can be adjusted using known methods to further increase the ethylene oxide production parameters to EO PP T Or according to various standards in EO PPIn one example, the feed rate of the supplementary organic chloride and the reaction temperature are adjusted to achieve maximum selectivity at a given value of the ethylene oxide production parameter. In another example, the feed rate of the supplementary organic chloride is adjusted to achieve maximum selectivity at a given value of the reaction temperature (T Rx ) to achieve maximum selectivity at the current value of .

[0075] In a third embodiment, process 20 has been shut down or tripped and has been offline for a period of at least about one hour, preferably at least about two hours, and more preferably at least about four hours. PP T ). To start the restart process, the ethylene concentration in the feed gas is set to an initial ethylene restart concentration value, which is preferably approximately equal to the pre-shutdown steady-state feed gas ethylene concentration value, preferably about 25 mol % to about 35 mol %. The initial restart reaction temperature value is lower than the initial startup steady-state reaction temperature value (T Rx i SS ) does not exceed five (5) degrees Celsius, preferably does not exceed three (3) degrees Celsius, and more preferably does not exceed two (2) degrees Celsius. At the same time, the initial restart reaction temperature value is higher than the initial startup steady-state reaction temperature value (T Rx i SS ) does not exceed five (5) degrees Celsius, preferably does not exceed three (3) degrees Celsius, and more preferably does not exceed two (2) degrees Celsius. The initial restart reaction temperature value is also preferably no greater than the pre-shutdown steady-state reaction temperature (T Rx SS ). When T Rx SS Higher than T Rx i SS The methods of the present invention are particularly useful above five (5) degrees Celsius, above ten (10) degrees Celsius, or above fifteen (15) degrees Celsius.

[0076] According to this embodiment, the supplemental feed rate of oxygen is set to the supplemental feed rate of oxygen (F O2 MU SS ) is no more than about forty (40)%, preferably no more than about thirty (30)%, and still more preferably no more than about twenty (20)%. Then, the supplemental oxygen feed rate (F O2 MU ), so that the oxygen concentration of the reactor feed gas inlet flow (C in O2) is increased by no more than 0.5 mol %, preferably no more than 0.3 mol %, and more preferably no more than 0.2 mol %, averaged over any given fifteen (15) minute period. In one example, the supplemental oxygen feed rate is then increased until (i) it reaches its pre-shutdown steady-state value (F O2 MU SS ), (ii) the reactor inlet oxygen concentration (C in O2 ) reaches the flammability limit (C in O2 flamm ), or (iii) the ethylene oxide production parameter reaches its target value, whichever occurs first.

[0077] According to this embodiment, if (i) the selectivity is less than the last steady-state value (S) of the selectivity before the trip and / or shutdown ss ) exceeds three (3) percentage points, preferably exceeds two (2) percentage points and more preferably exceeds 1 (one) percentage point, and (ii) the selectivity also tends to decrease (for example, using an average value of dS / dt over several time periods, dS / dt<0, each of which is preferably no longer than one hour, more preferably no longer than 30 minutes, still more preferably no longer than 15 minutes, and each of which is also preferably no less than five (5) minutes and more preferably no less than ten (10) minutes), the supplemental oxygen feed rate is not increased. Once the ethylene oxide production parameter (EO PP ) has reached its target value (EO PP T ), or the feed rate of supplementary oxygen (F O2 MU ) has reached F O2 MU SS In parallel with the oxygen supplementary feed rate, other selected parameters may also be increased during the restart toward their respective pre-shutdown steady-state values ​​until the ethylene oxide production parameter (EO PP ) reaches its target value (EO PP T ) or other parameters have also reached their respective limits based on their pre-shutdown steady-state values ​​as described herein. At this point, the restart is complete, and if necessary, the process can be adjusted using known methods to further increase the ethylene oxide production parameters to EO PP T Or according to various standards in EO PPIn one example, the feed rate of the supplementary organic chloride and the reaction temperature are adjusted to achieve maximum selectivity at a given value of the ethylene oxide production parameter. In another example, the feed rate of the supplementary organic chloride is adjusted to achieve maximum selectivity at a given value of the reaction temperature (T Rx ) to achieve maximum selectivity at the current value of .

[0078] refer to Figure 2A-2C , describe additional exemplary methods for improving the restart performance of high efficiency rhenium promoted silver catalysts. Figure 2A Involves adjusting the feed rate of the make-up organic chloride to improve restart performance. Figure 2B involves adjusting the feed rate of supplemental oxygen to improve restart performance, and Figure 2C Involving adjustment of the reaction temperature. After reaching or returning to step 1009, Figure 2A-2C The methods can be performed individually or sequentially, but are preferably performed in parallel with each other. Each individual method comprises Figure 2A Steps 1002, 1004, 1006, 1008 and 1009 in , as in an integrated approach, where all three methods are performed simultaneously in parallel.

[0079] In each case, Figure 1 The process is operated during the last period of steady-state operation before the process trip and / or shutdown. In step 1002, a target value for an ethylene oxide production parameter (EO PP T ), which can be compared with the steady-state value of the ethylene oxide production parameter before shutdown (EO PP SS ) are the same or different. The off-line period is at least about one hour, preferably at least two (2) hours, and more preferably at least about four (4) hours. At the start of the process, the reactor inlet concentrations of ethylene, oxygen, and at least one organic chloride (C in Et＝ , C in O2 and C in RCl ) has a corresponding steady-state value C in Et＝SS , C in O2 SS and C in RCl SS Similarly, the make-up feed rates (F Et＝MU 、F O2MU and F RCl MU ) has a corresponding steady-state value F Et＝MU SS 、F O2 MU SS and F RCl MU SS Likewise, the ratio of the supplemental organic chloride feed rate to the supplemental oxygen feed rate (F RCl MU / F O2 MU ) has a corresponding value (F RCl MU SS / F O2 MU SS ). In addition, starting from the last steady-state operation period before the reactor was shut down or tripped, the reaction temperature T Rx and the reactor outlet ethylene oxide concentration C out EtO With a corresponding steady-state value T Rx SS and C out EtO SS It is noted that the reactor feed gas concentration of a compound is the concentration at the reactor feed gas inlet.

[0080] In step 1004, the off-line time period is checked to determine if it has been long enough. If not, the method ends. Otherwise, control transfers to step 1006 and the reaction temperature T is raised to 1004. Rx Adjust to a temperature lower than the initial start-up steady-state reaction temperature (T Rx i SS ) does not exceed five (5) degrees Celsius, preferably does not exceed three (3) degrees Celsius, and more preferably does not exceed two (2) degrees Celsius. At the same time, the initial restart reaction temperature is adjusted to a value higher than T Rx i SS No more than five (5) degrees Celsius, preferably no more than three (3) degrees Celsius, and more preferably no more than two (2) degrees Celsius. In a preferred example, the initial restart reaction temperature is no greater than the pre-shutdown steady-state reaction temperature (T Rx SS ). When T Rx SS Higher than T Rx i SSThe methods of the present invention are particularly useful above five (5) degrees Celsius, above ten (10) degrees Celsius, or above fifteen (15) degrees Celsius.

[0081] In step 1008, the feed rate (F O2 MU ) is initially set to not exceed the average feed rate (F O2 MU SS ), preferably not more than 30%, and more preferably not more than 20 (twenty) %.

[0082] In step 1009, the ethylene oxide production parameter is compared with the target value EO PP T If EO has been reached PP T , the method ends. Otherwise, control is transferred to step 1010 and / or step 1040 ( Figure 2B ) and / or step 1060( Figure 2C ).

[0083] at this time, Figure 2A , Figure 2B and Figure 2C The methods are different, but they can and preferably are performed simultaneously in parallel with each other. Figure 2A In step 1010, it is determined whether the current value of the selectivity S is significantly lower than the selectivity (S ss ).exist Figure 2A In the example, if the selectivity is less than the steady-state selectivity S before shutdown, ss If the value of exceeds three percentage points, preferably exceeds two percentage points, and more preferably exceeds one percentage point, it is considered that the selectivity value is significantly lower than the steady-state value before shutdown.

[0084] If step 1010 returns a value of "yes", control transfers to step 1012 and a determination is made as to whether the selectivity is trending downward over time, i.e., whether dS / dt is less than zero, wherein dS / dt is preferably averaged over several time periods, each of which is preferably no longer than one hour, more preferably no longer than 30 minutes, still more preferably no longer than 15 minutes, and each of which is also preferably no less than five (5) minutes, and more preferably no less than ten (10) minutes. If the selectivity is trending downward, control transfers to step 1014. In step 1014, if the relative scaled vinyl chloride reactor feed gas concentration (C VCl RS) exceeds 110%, preferably 105%, and more preferably 100%, control transfers to step 1030, and the relative scaled vinyl chloride reactor feed gas concentration (C VCl RS ) is flat or tends to rise (d(C VCl RS ) / dt≥0)). If step 1030 returns a value of "No" (C VCl RS If the feed rate of the supplementary organic chloride is high but decreasing), the feed rate of the supplementary organic chloride is maintained at its current value (step 1032). If step 1030 returns a value of "yes", control is transferred to step 1034, and the current feed rate of the supplementary organic chloride is reduced or preferably completely stopped. Then, control is transferred back to step 1009.

[0085] If step 1010 returns a value of "No" (ie, the selectivity is not significantly lower than the previous steady-state value S ss ) or if step 1012 returns a value of no (selectivity is significantly lower but not trending downward), control transfers to step 1015. In step 1015, if the relative scaled reactor feed gas concentration of vinyl chloride (C VCl RS ) exceeds a value of 110%, preferably 105%, and more preferably 100%, control is transferred to step 1032, and the feed rate of the supplementary organic chloride is kept constant. Then, control is transferred back to step 1009. If step 1014 or step 1015 returns a value of "no" (C VCl RS is not too high), control transfers to step 1016 to determine the reactor outlet oxygen concentration (C out O2 ) has reached a value of at least 0.5 mol %, preferably at least 0.7 mol %, and more preferably at least 0.9 mol %. If not, no supplemental organic chloride promoter is fed to process 20 (step 1020), and control transfers back to step 1009. If step 1016 returns a value of "yes", control transfers to step 1018 to determine the feed rate (F of the supplemental organic chloride). RCl MU ) is greater than zero. If step 1018 returns a value of "no", then in step 1026, the feed rate of the supplementary organic chloride is set to be no greater than the steady-state supplementary organic chloride feed rate F before shutdown. RCl MU SS30%, preferably not more than 25%, and more preferably not more than 20%, and control transfers back to step 1009. Otherwise, if step 1018 returns a value of "yes", control transfers to step 1022 to determine the ratio (F) of the supplemental organic chloride feed rate to the supplemental oxygen feed rate, referred to as "ratio" in steps 1022, 1023, 1024, 1053, and 1072. RCl MU / F O2 MU ) is less than the ratio referred to in steps 1022, 1023, 1024, 1053, and 1072 as SS The ratio of the pre-shutdown steady-state value of the supplementary organic chloride feed rate to the pre-shutdown steady-state value of the supplementary oxygen feed rate (F RCl MU SS / F O2 MU SS ), preferably less than 105%, and more preferably less than 100%. If yes (i.e., step 1022 returns a value of "yes"), then the supplemental organic chloride feed rate is increased to increase the ratio F RCl MU / F O2 MU The value of the ratio F before shutdown is close to but not more than RCl MU SS / F O2 MU SS 115%, preferably 105%, and more preferably 100% of F (step 1024), and control transfers back to step 1009. Otherwise, if step 1022 returns a value of "no", the ramping of the supplemental organic chloride feed rate is stopped so that F RCl MU / F O2 MU Can be kept at F RCl MU SS / F O2 MU SS 115%, preferably 105%, and more preferably 100% of the value of (step 1023), and control passes to step 1025, where it is determined whether an increase in the value of other parameters that can be ramped during the restart process can still be made, in particular the feed rate of supplemental oxygen (F O2 MU ) is less than the steady-state feed rate (F O2 MU SS) is 110%, preferably less than 105%, more preferably less than 100%, or the reaction temperature (T Rx ) has not yet reached a temperature higher than the steady-state reaction temperature before shutdown (T Rx SS ) 5 degrees Celsius, preferably 3 degrees Celsius higher than the steady-state reaction temperature before shutdown, and more preferably equal to the value of the steady-state reaction temperature before shutdown. O2 MU and / or T Rx Still rampable), control returns to step 1009, otherwise the restart process is complete and the method terminates.

[0086] Figure 2B An embodiment of a method of adjusting the supplemental oxygen feed rate to improve restart performance is shown. Figure 2A After step 1009 in , control is transferred to Figure 2B In step 1040, it is determined whether the current value of the selectivity S is significantly lower than the selectivity (S) of the last steady-state operation period before the shutdown. ss ).exist Figure 2B In the example, if the selectivity value is less than the steady-state selectivity value S before shutdown, ss If S is significantly lower than S ss , then step 1040 returns a value of "yes" and control is transferred to step 1042. In step 1042, the trend of selectivity with respect to time is evaluated. If the selectivity is trending downward, dS / dt is less than zero. The evaluation of dS / dt is preferably not based on a single instantaneous value, and is preferably an average value taken across several time intervals, each of which is preferably no longer than one hour, more preferably no longer than 30 minutes, still more preferably no longer than 15 minutes, and each of which is also preferably no less than five (5) minutes, and more preferably no less than ten (10) minutes. If the selectivity is trending downward, then step 1042 returns a value of "yes", and the current feed rate (F of the supplemental oxygen) of the supplemental oxygen is calculated. O2 MU ) remains constant. Step 1044. Then, control transfers back to step 1040.

[0087] If step 1040 or step 1042 returns a "no" value, that is, if the selectivity is not significantly below the pre-shutdown steady-state value, or if the selectivity is significantly lower but not trending downward, control transfers to step 1046 and determines whether the ethylene oxide production parameter is below the value from Figure 2A The target value (EO) of step 1002 in PPT If not, the method ends. Otherwise, control transfers to step 1047 and the reactor inlet oxygen concentration is compared with the flammability concentration (C in O2 flamm ), which is preferably the flammability limit concentration minus a safety margin. If the oxygen concentration is not lower than the flammability concentration (step 1047 returns "no") but is determined to be equal to the flammability concentration at step 1048, the feed rate of supplemental oxygen is maintained constant (step 1044) and control is transferred back to step 1040. If step 1048 returns "no", the supplemental oxygen feed rate is reduced (step 1050), and control is transferred back to step 1040 again. If step 1047 returns "yes" (the oxygen concentration is lower than the flammability concentration), control is transferred to step 1049, and the feed rate of supplemental oxygen is compared with the steady-state value before shutdown. If the feed rate F of supplemental oxygen is O2 MU Less than its steady-state value F before shutdown O2 MU SS 110%, preferably less than 105%, and more preferably less than 100%, control transfers to step 1052 and the feed rate of supplemental oxygen is increased to drive the process closer to the target value of the ethylene oxide production parameter so that the reactor inlet oxygen concentration increases at a rate that does not exceed the maximum ramp rate. Step 1052. The maximum ramp rate amount of the reactor inlet O2 concentration does not exceed 0.5 mol%, preferably does not exceed 0.3 mol%, and more preferably does not exceed 0.2 mol% in any 15 minute interval. Therefore, when increasing F O2 MU , while monitoring C in O2 To ensure C in O2 The increase in the income is not greater than the maximum C in O2 After step 1052, control returns to step 1040.

[0088] In step 1049, if the supplemental oxygen feed rate is at least 110%, preferably at least 105%, and more preferably at least 100% of the pre-shutdown steady-state value, control transfers to step 1051 and the supplemental oxygen feed rate is maintained at the pre-shutdown steady-state value (F O2 MU SS), preferably 105%, more preferably 100%. Control then transfers to step 1053, where it is determined whether an increase in the value of other parameters that can be ramped during the restart process can still be performed, in particular the ratio of the supplementary organic chloride feed rate to the supplementary oxygen feed rate (F RCl MU / F O2 MU ) is less than the ratio of the pre-shutdown steady-state value of the supplementary organic chloride feed rate to the pre-shutdown steady-state value of the supplementary oxygen feed rate (F RCl MU SS / F O2 MU SS ), preferably less than 115%, preferably less than 105%, and more preferably less than 100%, or the reaction temperature (T Rx ) has not yet reached a temperature higher than the steady-state reaction temperature before shutdown (T Rx SS )5 degrees Celsius, preferably 3 degrees Celsius higher than the steady-state reaction temperature before shutdown, and more preferably equal to the value of the steady-state reaction temperature before shutdown. RCl MU and / or T Rx can still be ramped), control returns to Figure 2A Step 1009 in , otherwise the restart process is completed and the method terminates.

[0089] Figure 2C An embodiment of a method for adjusting the reaction temperature to improve the restart performance of a high efficiency rhenium promoted silver ethylene oxide catalyst is shown. Figure 2A After step 1009 in , control is transferred to Figure 2C In step 1060, it is determined whether the current value of the selectivity S is significantly lower than the selectivity (S) of the last steady-state operation period before the shutdown. ss ).exist Figure 2C In the example, if the selectivity value is less than the steady-state selectivity value S before shutdown, ss If S is significantly lower than S ss, then step 1060 returns a value of "yes" and control is transferred to step 1062. In step 1062, the trend of selectivity with respect to time is evaluated to determine whether the selectivity is trending downward (i.e., dS / dt is less than zero). The evaluation of dS / dt is preferably not based on a single instantaneous value, and is preferably an average value taken across several time intervals, each of which is preferably no longer than one hour, more preferably no longer than 30 minutes, still more preferably no longer than 15 minutes, and each of which is also preferably no less than five (5) minutes, and more preferably no less than ten (10) minutes. If the selectivity is trending downward, then step 1062 returns a value of "yes", and the reaction temperature T Rx The current value is maintained. Then, control returns to step 1060.

[0090] If the selectivity is not significantly lower than the pre-shutdown steady-state value (i.e., step 1060 returns a "no" value) or the selectivity is significantly lower but not trending downward (i.e., step 1062 returns a "no" value), control transfers to step 1068. In step 1068, it is determined whether the ethylene oxide production parameter is less than the value determined in step 1002 ( Figure 2A ) is equal to the target value set in step 1070. If not, the restart is complete and the method ends. Otherwise, control transfers to step 1070. In step 1070, the reaction temperature is compared with the steady-state reaction temperature before shutdown. If the reaction temperature (T Rx ) has not yet reached a temperature higher than the steady-state reaction temperature before shutdown (T Rx SS ) is at least 5 degrees Celsius above the pre-shutdown steady-state reaction temperature, preferably at least 3 degrees Celsius above the pre-shutdown steady-state reaction temperature, and more preferably equal to the value of the pre-shutdown steady-state reaction temperature, control transfers to step 1074, and during any given fifteen-minute interval, when the reaction temperature is not less than the initial startup steady-state reaction temperature (T Rx i SS ), the reaction temperature is increased at a maximum reaction temperature ramp rate not exceeding 0.6° C., preferably 0.4° C., and more preferably 0.2° C. Then, control is transferred to step 1060 .

[0091] If step 1070 returns a value of "no", the reaction temperature is maintained at 5 degrees Celsius above the steady-state reaction temperature before shutdown, preferably 3 degrees Celsius above the steady-state reaction temperature before shutdown, and more preferably maintained at the value of the steady-state reaction temperature before shutdown (step 1071). Then, control is transferred to step 1072, in which it is determined whether it is still possible to increase the values ​​of other parameters that can be ramped during the restart process, especially the ratio of the supplementary organic chloride feed rate to the supplementary oxygen feed rate (F RCl MU / F O2 MU) is less than the ratio of the pre-shutdown steady-state value of the supplementary organic chloride feed rate to the pre-shutdown steady-state value of the supplementary oxygen feed rate (F RCl MU SS / F O2 MU SS ), preferably less than 105%, and more preferably less than 100%, or the feed rate of supplemental oxygen (F O2 MU ) is less than the steady-state feed rate (F O2 MU SS ), preferably less than 105%, and more preferably less than 100%. If step 1072 returns a value of "yes" (F RCl MU and / or F O2 MU can still be ramped), control returns to Figure 2A Step 1009 in , otherwise the restart process is completed and the method terminates.

[0092] Example

[0093] The following inventive and comparative examples are provided to illustrate the benefits of the restart method described herein. It should be noted that Figure 3A-Figure 7I The data shown in are hourly averaged data and may not represent the instantaneous value of a particular parameter when the parameter changes.

[0094] Example 1

[0095] Example 1 was performed according to the inventive restart method described herein. A commercial ethylene oxide process utilizing a highly efficient rhenium promoted silver ethylene oxide catalyst was subjected to a feed gas formed by combining a reactor product recycle stream with a make-up stream comprising ethylene, oxygen, and ethyl chloride as a gas phase promoter. The pressure and feed gas ethylene concentration were maintained constant. The target values ​​for the ethylene oxide production parameters were 100% of the pre-shutdown steady state value of the ethylene oxide production rate. The process was operated at steady state for four (4) days and was subjected to a process upset for a duration of eleven (11) calendar days beginning on about day 239.2 of EO production online. The pre-shutdown steady state selectivity was about 89.5%-89.7%; the pre-shutdown steady state reaction temperature (measured as the reactor coolant temperature) was about 228.4°C. The pre-shutdown steady state reactor inlet oxygen concentration was about 5.6 mol%-5.8 mol%, and the pre-shutdown steady state reactor outlet oxygen concentration was about 4.0 mol%. Initial startup steady-state reaction temperature (T Rx i SS) is 225℃.

[0096] Then, restart the process, such as Figure 3A-Figure 3I It should be noted that Figure 3A-Figure 7I The x-axis in the graphs is elapsed time in EO production days, i.e., the elapsed time during EO production from the initial start-up of the fresh catalyst batch. Thus, the eleven-day downtime period is not apparent, as it would be if the measured time were not based on production parameters. Because these graphs show elapsed time, the numbered positions represent the number of EO production days completed. For example, the x-axis position identified as 240 marks the completion of day 240, after which day 241 of EO production begins.

[0097] The process was started by setting the reaction temperature (here the reactor coolant outlet temperature) at 220°C ( Figure 3D ), which is lower than the initial steady-state temperature (T Rx i SS ) five (5) degrees Celsius. Supplemental oxygen is initially fed at a first volumetric flow rate that is 10% of the volumetric flow rate before shutdown ( Figure 3H The temperature was slowly ramped up by 5°C to 225°C over a period of about 6 hours, such that the ramp rate never exceeded 0.4°C in any given 15 minute period ( Figure 3D ). During this same time period, the relative supplemental oxygen feed rate was increased to about 70% and the reactor feed gas oxygen concentration at the reactor inlet was increased from 0 to about 3.8 mol%-3.9 mol% such that the ramp rate did not exceed 0.3 mol% during any given 15 minute time period.

[0098] Within about 1-2 hours of restart, the oxygen concentration at the reactor outlet reached 0.5 mol% ( Figure 3F ), at which point make-up ethyl chloride was introduced into the reactor feed at its minimum controllable feed rate and maintained there for approximately 3 hours. Despite the relatively scaled reactor feed gas VCl concentration C VCl RS Up to about 155% ( Figure 3B ), but it decreases in a roughly monotonic manner until reaching 100% shortly before EO production day 240.0. Figure 3E As indicated, the feed rate of make-up ethyl chloride was kept constant while C VCl RS Maintained above approximately 110%. Once C VCl RS To decrease below about 100%, the relative supplemental ethyl chloride feed rate is increased by about 5%. VCl RSThe feed rate of ethyl chloride was rapidly increased to 120%, and the feed rate of supplementary ethyl chloride was kept constant until C VCl RS At the start of restart, the relative make-up ethyl chloride feed rate is ramped to a rate that maintains a constant ratio of the relative make-up ethyl chloride feed rate to the relative make-up oxygen feed rate ( Figure 3E and Fig. 3I After about one day, the relative feed rate of supplemental ethyl chloride is ramped from 30% to 75% and then maintained at about 75% when the ratio of the supplemental ethyl chloride feed rate to the supplemental oxygen feed rate reaches at least 100% of the ratio of the pre-shutdown steady-state value of the supplemental ethyl chloride feed rate to the pre-shutdown steady-state value of the supplemental oxygen feed rate. Fig. 3I After about another day, the relative feed rate of make-up ethyl chloride was slowly increased to 100%, while C VCl RS Approaching a value of about 80%-85% in a generally monotonic manner.

[0099] About three (3) hours after the start of the restart, the selectivity tended to rise monotonically to a value of about 89.8%. The selectivity then reached values ​​that fluctuated between 89.8% and 90.3%, before monotonically reaching 90.0% one (1) EO production day and eight EO production hours after the restart. In the first few hours after the restart, the ethylene oxide production rate increased rapidly to about 70% of the pre-shutdown value and fluctuated slightly from that point until about EO production day 240.4, after which it gradually and monotonically approached its pre-shutdown steady-state value at about EO production day 242.3. It is believed that the initial higher relative scaled VCl feed gas concentration values ​​indicate diffusion and desorption of subsurface chlorides and their subsequent redeposition on the catalyst via recirculation to the reactor inlet feed gas. However, using the inventive method described herein, the process smoothly and steadily returns to its pre-shutdown steady-state selectivity and EO production parameter values.

[0100] Comparative Example 1

[0101] This example illustrates how a poor choice of restart operating conditions can lead to a persistent loss of selectivity after restart. Figure 3A-Figure 3I The process was then operated for a continuous steady state period of at least three (3) days after a period of 15.5 days and then experienced a process upset resulting in a five (5) day shutdown at about day 253.2 of ethylene oxide production, using the same batch of catalyst used in Example 1. The process was restarted as Figure 4A-Figure 4I shown.

[0102] To start the restart process, the reaction temperature was raised to slightly above 220°C, which is lower than the initial steady-state temperature (T Rx i SS ) about five (5) degrees Celsius (FIG. 4D). Supplemental oxygen was introduced at about the same time at a relative supplemental oxygen feed rate of about 14%-16% ( Figure 4H ). Oxygen concentration at reactor outlet (C out O2 ) quickly reached 0.5% ( FIG. 4F ), and at about EO production day 253.3, supplemental ethyl chloride was fed to the reactor at a relative supplemental ethyl chloride feed rate of initially about 14%-16% ( FIG. 4E ). The relative feed rates of both supplemental ethylene and supplemental oxygen were increased over a period of about 3-4 hours, with the relative supplemental oxygen feed rate increasing from about fourteen (14)% to about 53%. Over the same time frame, the reactor inlet oxygen concentration increased from 0 to 3.5% (peak ramp rate of 0.30 mol%-0.35 mol% over 15 minutes). Figure 4C However, within this time frame, the selectivity peaks at a value of about 88.3% and then begins to decline for the remainder of day 253, while the relative scaled feed gas VCl concentration exceeds 135%. Nonetheless, the relative supplemental ethyl chloride feed rate increases approximately linearly until reaching a value close to 90% of its pre-shutdown steady-state value at about day 254.2 of EO production. Figure 4E.

[0103] The selectivity reached a minimum value of about 83% about halfway through EO production day 254, and took about two days to reach 86.5%. About nine (9) days after the start of the restart, the selectivity reached a new steady-state value of about 87.8%, well below the pre-shutdown value of 90.0%. It is believed that the over addition of ethyl chloride due to the continued ramping of the ethyl chloride feed rate, while the relatively scaled VCl feed gas concentration remained high, and especially the ramping of temperature and feed gas makeup oxygen, while the selectivity tended to decline and remained significantly below its pre-shutdown steady-state value, significantly exacerbated the problems of subsurface chloride diffusion, desorption, and surface redeposition, causing the process to remain unstable and the selectivity to continue to remain below the pre-shutdown steady-state value even after the ethylene oxide production rate reached the pre-shutdown steady-state value on about EO production day 262.

[0104] Comparative Example 2

[0105] A pilot plant utilizing a high efficiency ethylene oxide catalyst was subjected to a feed gas formed by combining a recycle stream with a make-up feed stream of oxygen, ethylene, and ethyl chloride (as a gas phase promoter). The target values ​​for the EO production parameters were their pre-shutdown steady state values. The pressure and feed gas ethylene concentration were kept constant.

[0106] The process operated at steady state for three (3) days and, after being online for the first time with fresh catalyst, experienced a process trip after approximately 49.2 days of ethylene oxide production operation. The outage lasted five (5) days.

[0107] Restart the process, such as Figure 5A-Figure 5I The process was restarted with a reaction temperature of about 220.1°C (as measured by the reactor outlet coolant temperature) ( Figure 5D ), which is lower than the initial steady-state reaction temperature (T Rx i SS ) about 4.9 degrees Celsius. The temperature was ramped up to about 226.5°C over the next 3 hours at a peak ramp rate of about one degree Celsius every 15 minutes. However, after a rapid increase to a value of about 88.3% (which is slightly less than 88.5%), the pre-shutdown steady-state selectivity, the selectivity began to tend to decline rapidly, reaching a value of about 82.5% on the 49.5th day of ethylene oxide production. Figure 5A .

[0108] The initial relative supplemental oxygen feed rate at restart was about 15% ( Figure 5H ) and increased to about 80% at the completion of 49.5 days of ethylene oxide production. During this same time period, the average reactor inlet oxygen concentration increased by about 3.8 mol %, with a peak ramp rate of about 0.3 mol % / 15 minutes Figure 5C ). This ramping of oxygen feed rate and concentration occurred even as selectivity tended to drop sharply and remained below the pre-shutdown steady-state value. The reactor outlet oxygen concentration reached 0.8 mole % at about 49.3 days of ethylene oxide production and then supplemental ethyl chloride feed was started at a relative feed rate of about 35%.

[0109] After the restart began, the relative scaled feed gas VCl concentration value rose rapidly to approximately 200% near the end of day 49.8 ( Figure 5B ), and then tended to decline, falling below its pre-shutdown steady-state value at the completion of ethylene oxide production day 49.5. The relatively scaled VCl concentration values ​​showed an opposite trend with respect to selectivity, where the selectivity dropped rapidly when the relatively scaled VCl value increased rapidly to 200% ( Figure 5A), and then selectivity only partially recovered as the relative scaled VCl value decreased. Supplemental ethyl chloride feed was discontinued at the completion of ethylene oxide production day 49.4 when a rapid increase in the relative scaled VCl value was observed, which ultimately helped to restore selectivity to its pre-shutdown steady-state value at the completion of ethylene oxide production day 50.7 because supplemental ethyl chloride feed was not resumed until after the relative scaled VCl value had dropped to well below 100%. However, EO production parameters had not returned to their pre-shutdown steady-state values ​​by the completion of day 53.2. It is believed that the initially poor post-restart selectivity performance was due to the increase in reaction temperature and supplemental oxygen feed rate while the selectivity was below its pre-shutdown steady-state value and tending to decrease, thereby prolonging and deepening the effect of the post-restart excursion in feed gas vinyl chloride concentration.

[0110] Example 2

[0111] The pilot plant and catalyst of Comparative Example 2 continued to operate and then experienced another process upset for about four (4) days starting at the completion of day 56.3 of ethylene oxide production. After restart, the reaction temperature (reactor coolant temperature) was 220°C and ramped up to about 222.3°C in about three (3) hours. The results are shown in Figure 6A-Figure 6I The target values ​​of EO production parameters are the values ​​before shutdown. The pressure and feed gas ethylene concentration are kept constant.

[0112] During this same time period, supplemental oxygen was introduced into the feed gas at an initial relative feed rate of about thirteen (13) percent ( Figure 6H ), reaching a relative supplemental feed rate of about 82% at the completion of ethylene oxide production day 56.5. During the same time period between ethylene oxide production day 56.3 and the completion of ethylene oxide production day 56.5, the reactor inlet oxygen concentration was increased from zero to about 4.8 mol %, with a peak ramp rate of about 0.5 mol % ( Figure 6C Likewise, during this same time period, the relative supplemental ethyl chloride feed rate increased from zero percent to about 42 percent ( Fig. 6E), which was accompanied by an increase in the relative scaled VCl feed gas concentration from zero to 113%. However, in response to observing a relative scaled VCl feed gas concentration exceeding 100%, the relative supplemental ethyl chloride feed rate was reduced back to about 21% and then gradually increased to about 41% at the completion of ethylene oxide production day 57.2, at which time the relative scaled VCl concentration had decreased to about 64% of the pre-shutdown level. Therefore, the ramp rate of the supplemental ethyl chloride feed was increased so that the relative feed rate approached 100% of the pre-shutdown value by the completion of day 57.5, at which time the ramping of the supplemental ethyl chloride feed rate was stopped when the relative ratio of the supplemental ethyl chloride feed rate to the supplemental oxygen feed rate reached 115%. From the completion of ethylene oxide production day 59.3 to the completion of day 60.5, the relative scaled VCl fluctuated between about 100% and about 110%. During the time from completion of ethylene oxide production day 58 to completion of day 60.4, the relative feed rate of supplemental ethyl chloride fluctuated between 93% and 103%, and the relative ratio of supplemental ethyl chloride feed rate to supplemental oxygen feed rate fluctuated between about 105% and 114%.

[0113] The reaction temperature remained essentially constant at about 223.6° C. from completion of ethylene oxide production day 56.7 to completion of day 57.2, and then ramped to about 229° C. over a four hour period with a peak ramp rate of about 0.57° C. every 15 minutes. The reaction temperature remained constant until completion of ethylene oxide production day 58.3, after which the reaction temperature was ramped to about 229.5° C.

[0114] The selectivity increased rapidly to about 89.0% at the end of 56.4 days of ethylene oxide production ( Fig. 6A ), and then dropped sharply to 85.5% at the completion of day 56.6, slowly declining after the relative scaled VCl feed gas concentration reached a peak of about 113%. The selectivity then slowly increased to 89.0% at the completion of day 57.6 of ethylene oxide production, and slowly approached the pre-shutdown steady-state value of 88.7%. After a brief upward rapid increase, the relative ethylene oxide production rate decreased in parallel with the relative feed rate of supplemental oxygen from day 56.3 to day 57.3 of ethylene oxide production ( Figure 6G ), and then gradually increased to the pre-shutdown steady-state value from day 57.3 to day 59.3. It is believed that the actions taken when the relative scaled vinyl chloride concentration exceeded 100% helped the process to recover quickly from the sharp selectivity drop after day 56.4.

[0115] Comparative Example 3

[0116] A commercial ethylene oxide unit was subjected to a reactive mixture of ethylene and oxygen with an ethylene dichloride vapor phase promoter for approximately 126 days of ethylene oxide production and then shut down at the beginning of day 127. The reactor pressure and feed gas ethylene concentration were held constant.

[0117] For the restart, the reaction temperature started at 225.4°C (slightly higher than the initial steady-state temperature after startup on fresh catalyst) and increased rapidly to 236.4°C in about one hour, corresponding to a ramp rate of 2.75°C / 15 minutes ( Fig.7D The relative feed rate of supplemental oxygen was increased from 0% to approximately 60% within the first four hours of restart ( Figure 7H During the same time period, the reactor inlet oxygen concentration rose rapidly to about 5.0 mol % ( Figure 7F ), with a peak rate of increase of 0.6 mol% / 15 minutes during the first hour. The relative feed rate of make-up ethylene dichloride (EDC) increased from 0 to about 176% over the same time period, and then remained constant after the relative scaled VCl concentration reached and exceeded 100%, for about a day, eventually peaking at 123% before the feed rate of make-up EDC was reduced, but not all the way to the minimum controllable feed rate. Throughout the initial portion of this restart, the relative ratio of make-up ethylene dichloride feed rate to make-up oxygen feed rate was typically well in excess of 120% for several hours, and even exceeded 250%.

[0118] The steady state selectivity before shutdown was about 88.7%. At the beginning of the restart at the beginning of ethylene oxide production day 127, the selectivity was initially about 88.0%, and then dropped sharply and continuously to a value of 82.5% at about day 127.5. The selectivity then recovered slowly to reach a value of about 90% at the end of day 132. It is believed that the poor initial selectivity performance can be attributed to the too rapid increase in reaction temperature at the restart, and the excess supplemental ethylene dichloride feed relative to the supplemental oxygen from the start of the restart until day 127.4.

Claims

1. A method for restarting an ethylene oxide production process following a shutdown period lasting at least one hour following a continuous steady-state period, wherein during the continuous steady-state period, the process is operated by: (i) feeding a reactor feed gas to a reactor comprising a batch of a high selectivity rhenium promoted silver catalyst, wherein the reactor feed gas comprises ethylene at a pre-shutdown steady-state ethylene concentration, oxygen at a pre-shutdown steady-state oxygen concentration, and at least one organic chloride at a pre-shutdown steady-state at least one organic chloride concentration, wherein the at least one organic chloride comprises vinyl chloride at a pre-shutdown steady-state vinyl chloride concentration, to produce a reactor product comprising ethylene oxide at a pre-shutdown steady-state value of the selectivity of the process for the production of ethylene oxide, wherein the ethylene oxide An ethane production process characterized by an ethylene oxide production parameter having a pre-shutdown steady-state value, and a reaction temperature having a pre-shutdown steady-state reaction temperature value; (ii) recycling a portion of said reactor product to form a reactor recycle; and (iii) combining said reactor recycle with a make-up stream to form said reactor feed gas, said make-up stream comprising at least make-up ethylene at a pre-shutdown steady-state feed rate of make-up ethylene, make-up oxygen at a pre-shutdown steady-state feed rate of make-up oxygen, and make-up organic chloride selected from ethyl chloride and ethylene dichloride at a pre-shutdown steady-state feed rate of said make-up organic chloride, wherein an off-line period is a period of time during which no make-up oxygen is fed to said batch of said high selectivity rhenium promoted silver catalyst, said method for restarting comprising: re-feeding a reactor feed gas to said batch of said high selectivity rhenium promoted silver catalyst, wherein during said re-feeding reactor feed gas step, said reactor feed gas initially comprises ethylene at an initial ethylene restart concentration and said at least one organic chloride at an initial restart concentration of said at least one organic chloride, and said reactor feed gas is formed by combining said reactor recycle with a make-up stream comprising at least make-up ethylene at an initial restart feed rate of make-up ethylene and make-up oxygen at an initial restart feed rate of make-up oxygen; and The reaction temperature is adjusted to an initial restart reaction temperature value that is no more than five (5) degrees Celsius above the initial start-up steady state reaction temperature value when the high selectivity catalyst is fresh.

2. The method according to claim 1, wherein the initial restart reaction temperature value does not exceed the pre-shutdown steady-state reaction temperature value.

3. A method for restarting an ethylene oxide production process according to any one of the preceding claims, wherein the initial restart reaction temperature value is no more than five (5) degrees Celsius below the initial startup steady state temperature value when the high selectivity catalyst is fresh.

4. A method for restarting an ethylene oxide production process according to claim 2 or claim 3, wherein during an initial startup time period prior to the continuous steady-state time period, the process is operated by: (i) feeding an initial startup reactor feed gas into the reactor, wherein the initial startup reactor feed gas comprises ethylene at an initial startup ethylene concentration, and (ii) adjusting the reaction temperature to the initial startup steady-state reaction temperature value.

5. The method of claim 4, wherein the pre-shutdown steady-state ethylene concentration is equal to the initial ethylene restart concentration.

6. The method for restarting an ethylene oxide production process according to any one of the preceding claims, wherein the method further comprises: selecting a target value for the ethylene oxide production parameter; as well as When the oxygen concentration in the reactor product is equal to or exceeds 0.5 mol % of the reactor product, the supplemental organic chloride is again fed to the batch of the high selectivity rhenium promoted silver catalyst at the initial restart feed rate of the supplemental organic chloride, and when the oxygen concentration in the reactor product is less than 0.5 mol % of the reactor product, the supplemental organic chloride is not fed to the batch of the high selectivity rhenium promoted silver catalyst.

7. The process of claim 6 wherein said initial restart feed rate of said supplemental organic chloride does not exceed 30% of said pre-shutdown steady state feed rate of said supplemental organic chloride on a molar basis.

8. A method for restarting an ethylene oxide production process according to claim 6 or claim 7, wherein the method for restarting further comprises increasing the feed rate of supplemental oxygen until one of the following occurs for the first time: (i) the feed rate of supplemental oxygen reaches at least 110% of the pre-shutdown steady-state feed rate of supplemental oxygen; (ii) the reactor feed gas oxygen concentration reaches an oxygen flammability concentration, and (iii) the ethylene oxide production parameter reaches a value that is not less than a selected target value for the ethylene oxide production parameter.

9. The method of claim 8, wherein during the step of increasing the feed rate of the supplemental oxygen, the reactor feed gas oxygen concentration does not increase by more than 0.5 mole percent during any 15 minute period.

10. A method for restarting an ethylene oxide production process according to claim 8 or claim 9, wherein if the selectivity is less than the pre-shutdown steady-state value of the selectivity by more than three (3) percentage points and the selectivity is trending downward, the step of increasing the feed rate of the supplemental oxygen is not performed.

11. A method for restarting an ethylene oxide production process according to any one of claims 6 to 10, wherein the method for restarting further comprises increasing the feed rate of the supplemental organic chloride if and only if the relative scaled vinyl chloride reactor feed gas concentration is no greater than 110%.

12. The method of claim 11, wherein the step of increasing the feed rate of the supplemental organic chloride is performed until the first of the following occurs: (i) the ratio of the feed rate of the supplemental organic chloride to the feed rate of the supplemental oxygen reaches at least 115% of the ratio of the pre-shutdown steady-state feed rate of the supplemental organic chloride to the pre-shutdown steady-state feed rate of the supplemental oxygen, and (ii) the ethylene oxide production parameter reaches a value that is not less than a selected target value for the ethylene oxide production parameter.

13. A method according to claim 11 or claim 12, wherein the feed rate of the supplemental organic chloride is stopped if the relative scaled vinyl chloride feed gas concentration is greater than 110% and is not tending to decrease, the selectivity is less than the pre-shutdown steady-state value of the selectivity by more than three (3) percentage points, and the selectivity is tending to decrease.

14. A method for restarting an ethylene oxide production process according to any one of claims 11 to 13, wherein the feed rate of the supplemental organic chloride is not increased if the relatively scaled vinyl chloride feed gas concentration is greater than 110% and tends to decrease, the selectivity is less than the pre-shutdown steady-state value of the selectivity by more than three (3) percentage points, and the selectivity tends to decrease.

15. The method for restarting an ethylene oxide production process according to any one of the preceding claims, wherein during the step of re-feeding reactor feed gas, the reactor feed gas initially contains no oxygen.

16. The method for restarting an ethylene oxide production process according to any one of claims 6 to 15, wherein the method for restarting further comprises increasing the reaction temperature until the first of the following occurs: (i) the ethylene oxide production parameter reaches a value that is not less than a selected target value for the ethylene oxide production parameter, and (ii) the reaction temperature reaches a value that is not less than five (5) degrees Celsius above the pre-shutdown steady-state reaction temperature value.

17. The method according to claim 16, wherein during the step of increasing the reaction temperature, during any 15-minute period, when the value of the reaction temperature is not less than the value of the initial startup steady-state reaction temperature, the increase in the reaction temperature does not exceed 0.6°C.

18. A method for restarting an ethylene oxide production process according to claim 16 or claim 17, wherein the step of increasing the reaction temperature is not performed if the selectivity is trending downward and the selectivity is less than the pre-shutdown steady-state value of the selectivity by more than three (3) percentage points.

19. The method for restarting an ethylene oxide production process according to any one of the preceding claims, wherein the pre-shutdown steady state reaction temperature value is more than five (5) degrees Celsius higher than the initial startup steady state reaction temperature value.

20. The method for restarting an ethylene oxide production process according to any one of the preceding claims, wherein the pre-shutdown steady state ethylene concentration is from 23 mol% to 35 mol% of the reactor feed gas.

21. The process according to any one of the preceding claims, wherein the reaction temperature is the reactor coolant temperature.

22. A method according to any preceding claim, wherein the continuous steady-state time period is the last preceding continuous steady-state time period before the shutdown.

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