FIELD OF INVENTION

The present invention generally relates to methods of producing ethylene oxide. More specifically, the present invention relates to ethylene oxide production methods that include directly oxidizing ethylene to produce ethylene oxide and purifying unreacted ethylene by removing carbon dioxide and argon with a membrane separation unit.

BACKGROUND OF THE INVENTION

Ethylene oxide (EO) is used as an intermediate for many organic synthesis processes. For example, ethylene oxide is a raw material used to produce ethylene glycols, including, monoethylene glycol, diethylene glycol, triethylene glycol, and polyethylene glycols. Monoethylene glycol is an antifreeze and coolant for engines and intermediate for producing polyester fibers and plastic bottles. Diethylene glycol can be used to produce polyurethanes, plasticizers, and organic solvents. Triethylene glycols are often used as plasticizers and moisture-retaining agents. Polyethylene glycols are used in perfumes, cosmetics, lubricants, and plasticizers.

In the chemical industry, ethylene oxide is generally produced by direct oxidation of ethylene. By-products of this process include carbon dioxide, which is mixed with unreacted ethylene and other diluent and impurities such as argon. To reduce production cost of ethylene oxide, unreacted ethylene is generally separated from carbon dioxide and argon and then recycled to the reactor. Conventionally, the separation of carbon dioxide from unreacted ethylene is carried out using metal carbonates, such as potassium carbonate in a carbon dioxide scrubber. The potassium carbonate reacts with water and carbon dioxide to form potassium bicarbonate. A large amount of steam is then used to regenerate potassium carbonate from potassium bicarbonate, resulting in high energy consumption. Argon is usually removed from ethylene by bleeding it off, which results in loss of unreacted ethylene.

Overall, while methods of producing ethylene oxide exist, the need for improvements in this field persists in light of at least the aforementioned drawbacks of the conventional methods.

BRIEF SUMMARY OF THE INVENTION

A solution to at least some of the above-mentioned problems associated with the production process for ethylene oxide has been discovered. The solution resides in a method of producing ethylene oxide that uses a membrane separation unit to separate carbon dioxide and argon from unreacted ethylene. Notably, the method is capable of reducing energy consumption for the ethylene oxide production process because the membrane separation unit does not consume a large amount of energy as compared to the CO2absorption process used in the conventional methods. Additionally, the membrane separation unit separates argon along with carbon dioxide from unreacted ethylene. Thus, it avoids loss of ethylene during argon bleeding, which is used in the conventional methods for producing ethylene oxide. Therefore, the method of the present invention provides a technical solution over at least some of the problems associated with the currently available production processes for ethylene oxide mentioned above.

Embodiments of the invention include a method of producing ethylene oxide. The method comprises reacting ethylene with a gas comprising oxygen in a reactor to produce a reactor effluent comprising ethylene oxide, carbon dioxide, unreacted ethylene, oxygen, methane and argon. The method further comprises processing the reactor effluent to produce (a) a product stream comprising 5 to 15 wt. % ethylene oxide, (b) a reabsorber overhead stream comprising 20 to 40 wt. % ethylene and 10 to 30 wt. % methane, 1 to 10 wt. % argon, and 30 to 50 wt. % carbon dioxide and (c) a carbonate flash gas stream comprising 25 to 50 wt. % carbon dioxide, 5 to 15 wt. % ethylene, 5 wt. % to 10 wt. % methane, and 40% to 60% water. The method further comprises combining the reabsorber overhead stream and the carbonate flash gas stream to produce a reclaim gas stream. The method further still comprises removing carbon dioxide and argon from the reclaim gas stream, by a membrane separation unit to form a (1) recycle gas stream comprising ethylene and methane and (2) a gas stream comprising the removed carbon dioxide and the removed argon. The method further still comprises flowing the recycle gas stream to the reactor.

Embodiments of the invention include a method of producing ethylene oxide. The method comprises reacting ethylene with a gas comprising oxygen in a reactor to produce a reactor effluent comprising ethylene oxide, carbon dioxide, unreacted ethylene, oxygen, methane and argon. The method further includes processing the reactor effluent in an ethylene oxide (EO) absorber to produce (A) an aqueous stream comprising 2 to 5 wt. % ethylene oxide and 2 to 5 wt. % monoethylene glycol and (B) an EO absorber overhead stream comprising 2 to 15 wt. % carbon dioxide, 20 to 35 wt. % ethylene, and 30 to 45 wt. % methane. The method further includes processing the aqueous stream to produce (a) a product stream comprising 5 to 15 wt. % ethylene oxide, (b) a reabsorber overhead stream comprising 20 to 40 wt. % ethylene, 10 to 30 wt. % methane, 1 to 10 wt. % argon, and 30 to 50 wt. % carbon dioxide. The method further includes processing the EO absorber overhead stream to produce a carbonate flash gas stream comprising 25 to 50 wt. % carbon dioxide, 5 to 15 wt. % ethylene, 5 to 10 wt. % methane and 40 to 60 wt. % water. The method further includes combining the reabsorber overhead stream and the carbonate flash gas stream to produce a reclaim gas stream. The method further still includes removing carbon dioxide and argon from the reclaim gas stream, by a membrane separation unit to form (1) a recycle gas stream comprising ethylene and methane and (2) a gas stream comprising the removed carbon dioxide and the removed argon. The method further still comprises flowing the recycle gas stream to the reactor.

Embodiments of the invention include a method of producing ethylene oxide. The method comprises reacting ethylene with a gas comprising oxygen in a reactor to produce a reactor effluent comprising ethylene oxide, carbon dioxide, unreacted ethylene, oxygen, methane and argon. The method further includes processing the reactor effluent in an ethylene oxide (EO) absorber to produce (A) an aqueous stream comprising 2 to 5 wt. % ethylene oxide and 2 to 5 wt. % monoethylene glycol and (B) an EO absorber overhead stream comprising 2 to 15 wt. % carbon dioxide, 20 to 35 wt. % ethylene, and 30 to 45 wt. % methane. The method further includes processing the aqueous stream to produce (a) a product stream comprising 5 to 15 wt. % ethylene oxide, (b) a reabsorber overhead stream comprising 20 to 40 wt. % ethylene, 10 to 30 wt. % methane, 1 to 10 wt. % argon, and 30 to 50 wt. % carbon dioxide. The method further includes processing the EO absorber overhead stream to produce a carbonate flash gas stream comprising 25 to 50 wt. % carbon dioxide, 5 to 15 wt. % ethylene, 5 to 10 wt. % methane and 40 to 60 wt. % water. The method further includes combining the reabsorber overhead stream and the carbonate flash gas stream to produce a reclaim gas stream. The method further still includes removing carbon dioxide and argon from the reclaim gas stream, by a membrane separation unit to form (1) a recycle gas stream comprising ethylene and methane and (2) a gas stream comprising the removed carbon dioxide and the removed argon. The membrane separation unit comprises hollow fiber membrane separation unit, spiral-wound membrane separation unit, or combinations thereof. The method further still comprises flowing the recycle gas stream to the reactor.

The following includes definitions of various terms and phrases used throughout this specification.

The terms “about” or “approximately” are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment the terms are defined to be within 10%, preferably, within 5%, more preferably, within 1%, and most preferably, within 0.5%.

The terms “wt. %,” “vol. %” or “mol. %” refers to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume, or the total moles of material that includes the component. In a non-limiting example, 10 moles of component in 100 moles of the material is 10 mol. % of component.

The term “substantially” and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%.

The terms “inhibiting” or “reducing” or “preventing” or “avoiding” or any variation of these terms, when used in the claims and/or the specification, include any measurable decrease or complete inhibition to achieve a desired result.

The term “effective,” as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

The use of the words “a” or “an” when used in conjunction with the term “comprising,” “including,” “containing,” or “having” in the claims or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.”

The words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

The process of the present invention can “comprise,” “consist essentially of,” or “consist of” particular ingredients, components, compositions, etc., disclosed throughout the specification.

The term “primarily,” as that term is used in the specification and/or claims, means greater than any of 50 wt. %, 50 mol. %, and 50 vol. %. For example, “primarily” may include 50.1 wt. % to 100 wt. % and all values and ranges there between, 50.1 mol. % to 100 mol. % and all values and ranges there between, or 50.1 vol. % to 100 vol. % and all values and ranges there between.

Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

