WO2015051028A1

WO2015051028A1 - Methods and systems for preparation of 1,3-butadiene

Info

Publication number: WO2015051028A1
Application number: PCT/US2014/058678
Authority: WO
Inventors: Jr. William M. Cross
Original assignee: Invista Technologies S.A.R.L.
Priority date: 2013-10-02
Filing date: 2014-10-01
Publication date: 2015-04-09

Abstract

The present disclosure is directed to 1,3-butadiene processes and systems. Such methods and systems can include dimerization of ethylene to produce a first product stream, including n-butene. The first product stream can be converted to a second product stream, including 1,3-butadiene, via oxidative dehydrogenation. The second product stream can be distilled via at least a first extractive distillation step to produce a 1,3-butadiene fraction and a raffinate product. At least a portion of the raffinate product can be recycled and/or fed to additional partitioning steps.

Description

METHODS AND SYSTEMS FOR PREPARATION OF 1 ,3-BUTADIENE

BACKGROUND Methods for the oxidative dehydrogenation of butenes can be used for the production of 1 ,3-butadiene. Typical feedstocks have traditionally involved either steam cracker C4 Raffinate II or refinery based feedstock, produced via the extraction of the n- butenes from a Refinery Fluid Catalytic Cracking (FCC) methyl fe/f-butyl ether (MTBE) Raffinate. One process for the oxidative dehydrogenation of n-butenes is known and reported in SRI Report 2011-5 (commercialized by both Phillips Petroleum and by Texas Petrochemicals).

Overall, oxidative dehydrogenation utilizes feedstocks of n-butenes (typically mixtures of 1-butene, cis-2-butene, and trans-2-butene) with relatively high n-butene purities. The remaining C4's (ranging from 5 to 20%) are primarily composed of C4 paraffins, such as isobutane, n-butane, and/or mixtures thereof.

C4 paraffins are often considered to be essentially nonreactive under typical oxidative dehydrogenation conditions for n-butenes. To keep these constituents in the feed from building up in the overall process, many known processes traditionally employ a once-through operation of the oxidative dehydrogenation unit (ODU) where the resulting ODU raffinate, a mixture of unconverted n-butenes and C4 paraffins, is sold as a separate stream and consumed in downstream units-outside the scope of oxidative dehydrogenation.

In contrast to a once-through operation, when the pricing of desired 1 ,3- butadiene product is significantly above that of the n-butene feed, it may be beneficial to recycle the ODU raffinate and blend material back with the main n-butene feed going

l into the ODU in order to increase overall process 1 ,3-butadiene yield. Unfortunately, the presence of n-butane and/or isobutane make this particularly difficult.

SUMMARY

The disclosures herein relate to methods and systems for producing 1 ,3- butadiene. In one embodiment, a method of manufacturing 1 ,3-butadiene is described. This method can include dimerizing ethylene via a dimerization step to produce a first product stream including n-butene. The n-butene can be converted via an oxidative dehydrogenation step to produce a second product stream including 1 ,3-butadiene. The second product stream, which includes 1 ,3-butadiene, can be distilled via a first extractive distillation step to produce a 1 ,3-butadiene fraction and a first feed. The first feed obtained from the first extractive distillation step can be partitioned to produce an n-butene raffinate A stream and an n-butene raffinate B stream. The n-butene raffinate A stream can be recycled to the oxidative dehydrogenation step.

In another embodiment, another method of manufacturing 1 ,3-butadiene is described. This method can include dimerizing ethylene via a dimerization step to produce a first product stream including n-butene. The n-butene can be converted via an oxidative dehydrogenation step to produce a second product stream including 1 ,3- butadiene. The second product stream, which includes 1 ,3-butadiene, can be distilled via a first extractive distillation step to produce a 1 ,3-butadiene fraction and a raffinate A stream. The raffinate A stream can include n-butane and butene, where butene can include -butene, cis/trans 2-butene, or mixtures thereof. A feed from the raffinate A stream, which can include n-butane and butane, can be recycled to the oxidative dehydrogenation step. Additionally, the n-butane in the feed can be present at a first concentration less than or equal to about 2 weight percent before recycling and can be allowed to build-up in the recycled feed to an extent greater than the first concentration and less than about 40 weight percent. Such build-up can occur by cyclic recycling of the feed from the first extractive distillation step to the oxidative dehydrogenation process step.

In yet another embodiment, a system for manufacturing 1 ,3-butadiene is described. This system can include a dimerization unit configured to dimerize ethylene into a first product stream including n-butene. The system can also include an oxidative dehydrogenation unit configured to receive the first product stream including n-butene and to convert the n-butene into a second product stream including 1 ,3-butadiene. Further, the system can include a first extractive distillation unit configured to receive the second product stream including 1 ,3-butadiene and to produce a 1 ,3-butadiene fraction and a first feed. Additionally, a partition module can be included, which is configured to receive the first feed and to produce an n-butene raffinate A stream and an n-butene raffinate B stream. A recycle line can also be included that is configured to recycle at least a portion of the raffinate A stream from the partition module to the oxidative dehydrogenation unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart of a 1,3-butadiene manufacturing process.

FIG. 2 is a flow chart of another 1 ,3-butadiene manufacturing process.

FIG. 3 is a flow chart of a 1,3-butadiene manufacturing process in accordance with one embodiment of the present disclosure.

FIG. 4 is a flow chart of a 1 ,3-butadiene manufacturing process in accordance with one embodiment of the present disclosure.

FIG. 5 is a flow chart of a 1 ,3-butadiene manufacturing process in accordance with one embodiment of the present disclosure.

FIG. 6 is a flow chart of a 1 ,3-butadiene manufacturing process in accordance with one embodiment of the present disclosure.

FIG. 7 is a flow chart of a 1 ,3-butadiene manufacturing process in accordance with one embodiment of the present disclosure.

FIG. 8 is an extractive distillation tower section used in a 1 ,3-butadiene manufacturing process in accordance with one embodiment of the present disclosure.

FIG. 9 is an extractive distillation tower section used in a 1 ,3-butadiene manufacturing process in accordance with one embodiment of the present disclosure. It should be noted that the figures are merely exemplary of several embodiments of the present disclosure and no limitations on the scope of the present invention are intended thereby. DETAILED DESCRIPTION

Although the following detailed description contains many specifics for the purpose of illustration, a person of ordinary skill in the art will appreciate that many variations and alterations to the following details are within the scope of the herein disclosed embodiments.

Accordingly, the following embodiments are set forth without any loss of generality to, and without imposing limitations upon any claimed invention. Before the present disclosure is described in greater detail, it is to be understood that this disclosure is not limited to particular embodiments described, as this may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present disclosure will be limited only by the appended claims. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

As used in this specification and the appended claims, the singular forms "a,"

"an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a butane" includes a plurality of butanes.

In this disclosure, "comprises," "comprising," "containing" and "having" and the like can have the meaning ascribed to them in U.S. Patent law and can mean

"includes," "including," and the like, and are generally interpreted to be open ended terms. The term "consisting of" is a closed term, and includes only the components, structures, steps, or the like specifically listed, and that which is in accordance with U.S. Patent law. "Consisting essentially of or "consists essentially" or the like, when applied to methods and compositions encompassed by the present disclosure refers to compositions like those disclosed herein, but which may contain additional structural groups, composition components or method steps. Such additional structural groups, composition components or method steps, etc., however, do not materially affect the basic and novel characteristic(s) of the compositions or methods, compared to those of the corresponding compositions or methods disclosed herein. In further detail,

"consisting essentially of" or "consists essentially" or the like, when applied to methods and compositions encompassed by the present disclosure have the meaning ascribed in U.S. Patent law and the term is open-ended, allowing for the presence of more than that which is recited (e.g., trace contaminants, components not reactive with the polymer or components reacted to form the polymer, and the like) so long as basic or novel characteristics of that which is recited is not changed by the presence of more than that which is recited, but excludes prior art embodiments. When using an open ended term, like "comprising" or "including," it is understood that direct support should be afforded also to "consisting essentially of" language as well as "consisting of" language as if stated explicitly.

It should be noted that ratios, concentrations, amounts, and other numerical data may be expressed herein in a range format. It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges

encompassed within that range as if each numerical value and sub-range includes "about 'x' to about 'y'". To illustrate, a concentration range of "about 0.1 % to about 5%" should be interpreted to include not only the explicitly recited concentration of about 0.1 wt% to about 5 wt%, but also include individual concentrations (e.g., 1 %, 2%, 3%, and 4%) and the sub-ranges (e.g., 0.5%, 1.1 %, 2.2%, 3.3%, and 4.4%) within the indicated range. In an embodiment, the term "about" can include traditional rounding according to significant figures of the numerical value. In addition, the phrase "about 'x' to 'y'" includes "about 'x' to about 'y'".

The term "about" as used herein, when referring to a numerical value or range, allows for a degree of variability in the value or range, for example, within 10%, or, in one aspect within 5%, of a stated value or of a stated limit of a range.

In the methods described herein, the steps can be carried out in any order without departing from the principles of the invention, except when a temporal or operational sequence is explicitly recited. Furthermore, specified steps can be carried out concurrently unless explicit claim language recites that they be carried out separately. For example, a claimed step of doing X and a claimed step of doing Y can be conducted simultaneously within a single operation, and the resulting process will fall within the literal scope of the claimed process.

As used herein, the term "fractionation" refers to a distillation step whereby a feed stream is separated into a light and heavy boiling fraction.

As used herein, the term "extractive distillation" refers to a distillation step whereby a solvent is added to a fractionation step, for the purpose of changing the relative volatility of the constituent components within the feed, which is to be

fractionated.

In addition, where features or aspects of the disclosure are described in terms of a list or a Markush group, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group. For example, if X is described as selected from the group consisting of bromine, chlorine, and iodine, claims for X being bromine and claims for X being bromine and chlorine are fully described as if listed individually. For example, where features or aspects of the disclosure are described in terms of such lists, those skilled in the art will recognize that the disclosure is also thereby described in terms of any combination of individual members or subgroups of members of list or Markush group. Thus, if X is described as selected from the group consisting of bromine, chlorine, and iodine, and Y is described as selected from the group consisting of methyl, ethyl, and propyl, claims for X being bromine and Y being methyl are fully described and

supported.

As used herein, all percent compositions are given as weight percentages, unless otherwise stated. When solutions of components are referred to, percentages refer to weight percentages of the composition including solvent (e.g., water) unless otherwise indicated.

As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features that may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure. Any recited method can be carried out in the order of events recited or in any other order that is logically possible.

Embodiments of the present disclosure employ, unless otherwise indicated, techniques of chemistry, and the like, which are within the skill of the art. Typically, such techniques are explained fully in the literature.

The disclosures herein relate to a method for the production of 1 ,3-butadiene (BD) and to the independent extractive distillation of n-butenes from paraffins. One method of manufacturing 1 ,3-butadiene is illustrated in FIG. 1. This method can use a fluid catalytic cracking (FCC) raffinate, wherein the raffinate is passed through an n- butene extractive distillation unit to remove n-butanes from the system or process prior to the oxidative dehydrogenation step. Thus the n-butene-rich first product stream 101 can be fed to an oxidative dehydrogenation unit to produce a second product stream 102 of crude C4s that includes 1 ,3-butadiene. This product stream can be purified via a 1 ,3-butadiene extractive distillation unit, where the 1 ,3-butadiene fraction is removed and collected and the raffinate stream 103 can be discarded. However, without incorporating the n-butene extractive distillation unit before the oxidative

dehydrogenation unit, the process would include a significant concentration of n-butane, making the oxidative dehydrogenation step more challenging, n-butane build-up can require an increase in the overall oxidative dehydrogenation equipment size, particularly in the recovery section, which increases utilities usage for its processing. Hence, good control of n-butane is of significant interest, particularly where feed n-butenes are intended to be recycled, rather than wasted by straight purging.

For processes that utilize FCC C4 methyl fert-butyl ether (MTBE) Raffinate, such as that shown in FIG. 1 , a subsequent recycle step can also be employed. Because this configuration uses a separate n-butene extractive distillation column to purify the n- butenes from the dilute FCC C4 Raffinate feed, it can inherently provide an internal process means for the separation of the C4 paraffins from C4 olefins. This process is illustrated in FIG. 2. Similar to FIG. 1 , the n-butene-rich first product stream 201 can be fed to an oxidative dehydrogenation unit to produce a second product stream 202 of crude C4s that includes 1 ,3-butadiene. This product stream can be purified via a 1 ,3- butadiene extractive distillation unit, where the 1 ,3-butadiene fraction is removed and collected and a recycle raffinate stream 203 can be recycled back to the n-butene extractive distillation step. The raffinate purge 204 can be discarded.

One alternative to this process is to utilize higher purity n-butene feedstocks. High purity n-butenes can be produced via ethylene dimerization technologies. In a dimerization configuration for n-butene feed production, two isomers are possible, 1- butene and cis/trans 2-butene. Unfortunately, due to the upstream nature of these conversions, similar to the cracker and refinery C4 streams, dimerization processes can also produce an n-butene stream which contains minor portions of C4 paraffin components that must be dealt with. These paraffins, particularly n-butane, can build-up in a process configuration intended to obtain high overall n-butene conversion, such that an appropriate and economic process solution should be developed to handle these constituents.

Of concern to both options for feeding an oxidative dehydrogenation unit with a recycle raffinate is the build-up of smaller quantities of n-butane. The present disclosure provides embodiments overcoming the limitations associated with the build-up of n- butane.

In accordance with this, methods and systems for producing ,3-butadiene are provided. In one embodiment, a method of manufacturing 1 ,3-butadiene is described. This method can include dimerizing ethylene via a dimerization step to produce a first product stream including n-butene. The n-butene can be converted via an oxidative dehydrogenation step to produce a second product stream including 1 ,3-butadiene. The second product stream, which includes 1 ,3-butadiene, can be distilled via a first extractive distillation step to produce a 1 ,3-butadiene fraction and a first feed. The first feed obtained from the first extractive distillation step can be partitioned to produce an n-butene raffinate A stream and an n-butene raffinate B stream. The n-butene raffinate A stream can be recycled from the partitioning step to the oxidative dehydrogenation step.

Dimerizing ethylene to produce a product stream that includes n-butene is generally known in the art. Any suitable method of dimerizing ethylene to produce a product stream that includes n-butene is contemplated as useful in the present technology. In one such method, ethylene can be passed over a supported catalyst including a metal or combinations of metals from Group VIII of the Periodic Table and an oxide of a metal or combination of metals from group VIIB of the Periodic Table. In one example, palladium and molybdenum oxide can be included in the supported catalyst. Optimal flow rates can depend on temperature, pressure, catalyst particle size and surface area, and other process considerations. All of these parameters can be optimized to achieve desirable yields. Such optimization parameters are known in the art. Other methods of dimerizing ethylene are known in the art and can likewise be used in the present technology.

Oxidative dehydrogenation is also generally known in the art. Any suitable oxidative dehydrogenation method to convert n-butene to a second product stream that includes 1 ,3-butadiene is contemplated as part of the current technology. Oxidative dehydrogenation can use a variety of catalysts, such as mixed oxides including ferrites and bismuth molybdate. Additionally, a variety of temperatures, pressures, and flow rates can be used to optimize the oxidative dehydrogenation reaction. Such conditions are known in the art and are contemplated as part of the current technology.

Extractive distillation and fractionation are also generally known in the art. Any suitable extractive distillation or fractionation method is contemplated as part of the current technology. One such method can use solvents such as acetonitrile, methyl ethyl ketone, dimethylformamide, furfural, N-methyl-2-pyrrolidone, acetone, sulfalone, dimethylacetamide, water, other suitable solvents, and combinations thereof to facilitate the separation of 1 ,3-butadiene from the other components of the second product stream. Additionally, flow rates, temperatures, pressures, column type and

configuration, and other process parameters can be optimized to increase the separation of 1 ,3-butadiene from the other components of the second product stream and are generally known in the art.

In addition to the first extractive distillation step, the current technology can employ a variety of additional partition steps and subsequent recycling steps. The partition step can be used to partition the first feed obtained from the first extractive distillation step to produce an n-butene raffinate A stream and an n-butene raffinate B stream. Specific embodiments illustrating a variety of these partition steps are described in greater detail below, but an initial overview is provided here. In one aspect, the partition step can include a second extractive distillation step. In another aspect, the partition step can include a fractionation step. The fractionation step can also include purging the n-butene raffinate B stream. In each of these aspects, the n-butene raffinate A stream can be recycled from the partitioning step to the oxidative dehydrogenation step via any suitable recycling step.

In another aspect, the partition step can include distilling the first feed from the first extractive distillation step via a second extractive distillation step to produce a second feed and a n-butene raffinate A stream. Additionally, the second feed from the second extractive distillation step can be fractionated via a fractionation step to produce an n-butene raffinate B stream. In this case, both the raffinate A stream and the raffinate B stream can be recycled to the oxidative dehydrogenation step.

Turning now to the more detailed embodiments, one such embodiment can include dimerizing ethylene via a dimerization step to produce a first product stream including n-butene. The n-butene can be converted via an oxidative dehydrogenation step to produce a second product stream including 1 ,3-butadiene. The second product stream, including 1 ,3-butadiene, can be distilled via a first extractive distillation step to produce a 1 ,3-butadiene fraction and a first feed. The first feed from the first extractive distillation step can be further distilled via a second extractive distillation step to produce an n-butene raffinate A stream and an n-butene raffinate B stream. The n-butene raffinate A stream from the second extractive distillation step can be recycled to the oxidative dehydrogenation step. This embodiment is illustrated in FIG. 3.

As shown in FIG. 3, dimerization of ethylene can produce a first product stream 301 , including n-butene, which can be transferred to an oxidative dehydrogenation step. The oxidative dehydrogenation process can produce a second product stream 302 of crude C4s, including 1 ,3-butadiene. The second product stream 302 can be passed to a first extractive distillation step to produce a 1 ,3-butadiene fraction and a first feed. The 1.3-butadiene fraction can be collected and the first feed can be further partitioned using a second extractive distillation step to produce an n-butene-rich raffinate A stream 304 and an n-butene-lean raffinate B stream 303. The raffinate A stream 304 can be recycled back to the oxidative dehydrogenation step and cycle through the subsequent steps again. The raffinate B stream 303 can be purged to eliminate butanes from the process.

Further, regardless of the n-butene isomer, a configuration using an additional extractive distillation zone residing above the traditional 1 ,3 butadiene extraction zone can be useful to increase the overall n-butene conversion in the overall process. FIG. 3 illustrates one example of such a configuration. As can be seen in FIG. 3, there are two n-butene raffinate streams produced from the 1 ,3 butadiene extractive distillation column. The first can be produced using a vapor side draw and the second is produced as an overhead stream.

Not shown in FIG. 3, but also relevant to the present disclosure, is the injection of

"lean" extractive solvent above the n-butene extraction zone. "Lean" solvent refers to a regenerated solvent containing little absorbed material. In this case, 1 ,3 butadiene is the primary absorbed material, which is "lean" or at a substantially reduced concentration in the regenerated solvent.

This "lean" solvent is prepared, in addition to the solvent injection made for that of the 1 ,3 butadiene extractive distillation column. In some aspect, a lean extractive solvent can include fufurol, acetone, methyl ethyl ketone, dimethyl acetamide, dimethylformamide (DMF), acetonitrile (ACN), n-methyl pyrrolidone (NMP), morpholine, sulfolane, water, and mixtures thereof.

This provides an extractive column with a minimum of two extractive solvent injections, one above the new additional n-butene zone, and one above the traditional lean solvent injection from 1 ,3 butadiene recovery. To provide additional boil-up between the zones, an additional side heater may be placed between the new top extraction zone and above the traditional 1 ,3 butadiene zone to aid stripping of the butenes above or within the 1 ,3 butadiene zone.

Besides the additional n-butene extraction zone, one difference with this configuration is the production of two different n-butene raffinate products. The upper raffinate (Raffinate B) can be produced substantially solvent free, using a traditional fractionation zone placed above the new n-butene extraction zone. For the lower vapor draw (Raffinate A), a side rectifier unit may be used for solvent removal. Water washes, typically associated with extractive distillation units, may then be used for both raffinates to provide solvent free product raffinates.

In another embodiment, a method of manufacturing 1 ,3-butadiene can include dimerizing ethylene via a dimerization step to produce a first product stream including n- butene. n-butene can be converted via an oxidative dehydrogenation step to produce a second product stream including 1 ,3-butadiene. Additional steps can include distilling the 1 ,3-butadiene via a first extractive distillation step to produce a 1 ,3-butadiene fraction and a Raffinate A stream. The Raffinate A stream can include n-butane and butene, where butene can be 1 -butene, cis/trans 2-butene, or mixtures thereof. Further, the Raffinate A stream can be recycled via a recycling step from the first extractive distillation step to the oxidative dehydrogenation step, the feed comprising n-butane and butene. The n-butane in the feed can be present at a first concentration less than or equal to about 2 weight percent before recycling, and the n-butane can be allowed to build-up in the recycled feed to an extent greater than the first concentration and less than about 40 weight percent. In one aspect, the first concentration can be less than or equal to about 3 weight percent, and the n-butane can be allowed to build-up in the recycled feed to an extent greater than the first concentration and less than about 40 weight percent. In another aspect, the first concentration can be less than or equal to about 3 weight percent, and the n-butane can be allowed to build-up in the recycled feed to an extent greater than the first concentration and less than about 20 weight percent. In still another aspect, the first concentration can be less than or equal to about 5 weight percent, and the n-butane can be allowed to build-up in the recycled feed to an extent greater than the first concentration and less than about 15 weight percent. The build-up occurs by cyclic recycling of the feed from the first extractive distillation step to the oxidative dehydrogenation process step. In one example, the Raffinate A stream can be purged in an amount of about 0.2% to 20% by mass, or from 0.5% to 5% by mass in another example. In another aspect, the feed can include at least about 80 weight percent of the raffinate A stream. In another aspect, the feed can include at least about 90 weight percent of the raffinate A stream. This embodiment is illustrated in FIG. 4. As shown in FIG. 4, dimerization of ethylene can produce a first product stream 401 , including n-butene, which can be transferred to an oxidative dehydrogenation step. The oxidative dehydrogenation process can produce a second product stream 402, including 1 ,3-butadiene. The second product stream 402 can be passed to a distillation step utilizing a first extractive distillation step to produce a 1 ,3-butadiene fraction and a raffinate A stream 403. The raffinate A stream 403 can include n-butane and butene, where the butene can include -butene, cis/trans 2-butene, or mixtures thereof. A feed 404 of the rafinate A stream 403 can be recycled back to the oxidative dehydrogenation step and residual raffinate product 405 can be purged.

This embodiment can be used as an alternative to the production of 1 ,3 butadiene using the configuration illustrated in FIG. 3. In this embodiment, the production of 1 ,3 butadiene, using a dimerization process, may utilize a direct recycle. A minor impurity in the feed, n-butane, is allowed to build-up allowing high overall conversion. It has been found that building up n-butane in the raffinate recycle to from 1% to 20% can be effective in the methods and systems of the present disclosure, and more typically from 3% to 10% can be desirable. Such a direct recycle configuration is provided in FIG. 4. Thus, in one example, in FIG. 4, the n-butane is purged from the process by recycling up to 97% of the produced raffinate from the butadiene extractive distillation column and purging as low as 3% of the raffinate.

In another embodiment, the method can include dimerizing ethylene via a dimerization step to produce a first product stream including n-butene. The n-butene can be converted via an oxidative dehydrogenation step to produce a second product stream including 1 ,3-butadiene. The second product stream, including 1 ,3-butadiene, can be distilled via a first extractive distillation step to produce a 1 ,3-butadiene fraction and a first feed. The first feed from the first extractive distillation step can be

fractionated to produce an n-butene raffinate A stream and an n-butene raffinate B stream. The n-butene raffinate A stream from the fractionation step can be recycled to the oxidative dehydrogenation step and the n-butene raffinate B stream can be purged. This embodiment is illustrated in FIG. 5.

As shown in FIG. 5, dimerization of ethylene can produce a first product stream

501 , including n-butene, which can be transferred to an oxidative dehydrogenation step. The oxidative dehydrogenation process can produce a second product stream 502 of crude C4s, including 1 ,3-butadiene. The second product stream 502 can be passed to a first extractive distillation step to produce a 1 ,3-butadiene fraction and a first feed 503 that includes the raffinate A from the extractive distillation step. The 1.3-butadiene fraction can be collected and the first feed 503 is split into a recycled raffinate 504, which is recycled back to the oxidative dehydrogenation step, and a raffinate feed 505, which is transferred to the subsequent distillation or fractionation step. The raffinate feed 505 is further partitioned via fractionation into an n-butene-rich raffinate A stream 506 and an n-butene-lean raffinate B stream 507. The raffinate A stream 506 is recycled back to the oxidative distillation step and the raffinate B stream 507 is purged from the process.

In another embodiment, the method can include dimerizing ethylene via a dimerization step to produce a first product stream including n-butene. The n-butene can be converted via an oxidative dehydrogenation step to produce a second product stream including 1 ,3-butadiene. The second product stream, including 1 ,3-butadiene, can be distilled via an extractive distillation step to produce a 1 ,3-butadiene fraction and a first feed. The first feed from the first extractive distillation step can be fractionated to produce an n-butene raffinate A stream and an n-butene raffinate B stream.The n- butene raffinate A stream from the fractionation step can be recycled to the oxidative dehydrogenation step. This embodiment is illustrated in FIG. 6.

As shown in FIG. 6, dimerization of ethylene can produce a first product stream 601 , including n-butene, which can be transferred to an oxidative dehydrogenation step. The oxidative dehydrogenation process can produce a second product stream 602 of crude C4s, including 1 ,3-butadiene. The second product stream 602 can be passed to a first extractive distillation step to produce a 1 ,3-butadiene fraction and a first feed. The 1 ,3-butadiene fraction can be collected and the first feed can be transferred to a fractionation section where the first feed is further partitioned into a 1-butene-rich raffinate A stream 603, which is recycled back to the oxidative dehydrogenation step, and a n-butene-lean raffinate B stream 604, which can be removed from the process.

The embodiments illustrated in FIGS. 5 and 6 represent other desirable and economic methods for using similarly rich n-butene feed streams, but with even higher utilization. These figures show the use of 1-butene vs. 2-butene, although this feed may include either n-butene isomer or mixtures thereof. As used herein, "rich 1-butene feed stream" generally refers to a stream or portion thereof containing 1-butene in an amount ranging from 60% to 100% by weight. In one aspect, the rich 1-butene feed stream can contain 1-butene in an amount ranging from 60% to 98% by weight. In another aspect, the rich 1-butene feed stream can contain 1-butene in an amount ranging from 80% to 95% by weight. In still another aspect, the rich 1-butene feed stream can contain 1- butene in an amount ranging from 80% to 99% by weight. Additionally, FIG. 6 provides the use of a lean feed from a vapor side draw.

As used herein, "lean feed" generally refers to a stream or portion thereof containing n-butene in an amount ranging from 20% to 95% by weight. In one aspect, the n-butene can be present in an amount ranging from 50% to 95% by weight. Herein, an additional fractionation unit (FIG. 5) or zone (FIG. 6) is added to split a rich 1-butene product from the n-butane to be purged. Compared to running the full raffinate stream through the fractionator, these methods allow a portion of the n-butane to build-up via a direct raffinate recycle, providing an n-butane content in the raffinate which is higher than that of the overall feed going into the oxidative dehydrogenation unit. In some embodiments using a fractionator, the n-butane can be present in a bottom stream from the fractionator in an amount ranging from 15% to 99% by weight. Typically, there is a bias to only send between 3% to 35% of the raffinate produced from the 1 ,3 butadiene extractive distillation to the new fractionation zone, and directly recycle the remainder. More particularly in one example, from 10% to 25% is sent to fractionization and the new fractionation zone would utilize a minimum reflux ratio of at least 2.

As the amount going to the fractionator increases, heat integrating this new 1- butene fractionator with an existing distillation column is directionally used to enable an energy efficient process. One heat integration option is the integrating of this distillation column's [C1] reboiler with another C4 fraction [C2] columns overhead condenser, whereby the operational pressure on C2 is greater than that of C1. Heat integration refers to the use of a hot process stream to handle some energy duty, required by the distillation column reboiler. This stream could be obtained from a pump around, vapor side draw or a process condenser load. Of course other heat integration schemes with this new column can be constructed by those skilled in the art.

Beyond heat-integration, several other possible configurations exist as well, such as those shown in FIGS. 5 and 6, wherein the 1 ,3 butadiene extractive distillation section and 1-butene fractionation zone are integrated using a single column with divided walls or separate rectifying and/or stripping sections. What is unique for these configurations shown is (1) either the use of at least two raffinate streams, which are produced through the integration of an additional extraction zone located above a 1 ,3 butadiene extraction zone, where the rich n-butene raffinate stream is recycled to an oxidative dehydrogenation process, or (2) the use of a composite recycle for the oxidative dehydrogenation unit, which is composed of two streams, where the first is a directly produced raffinate stream from the 1 ,3 butadiene extractive distillation unit and the second is produced using a separate distillation step.

In another embodiment, the method can include dimerizing ethylene via a dimerization step to produce a first product stream including n-butene. The n-butene can be converted via an oxidative dehydrogenation step to produce a second product stream including 1 ,3-butadiene. The second product stream, including 1 ,3-butadiene, can be distilled via a first extractive distillation step to produce a 1 ,3-butadiene fraction and a first feed. The first feed from the first extractive distillation step can be distilled via a second extractive distillation step to produce a second feed and an n-butene raffinate A stream. The second feed from the second extractive distillation step can be

fractionated to produce an n-butene raffinate B stream. The n-butene raffinate A stream and the n-butene raffinate B stream from the second extractive distillation step and the fractionation step can be recycled to the oxidative dehydrogenation step. This

embodiment is illustrated by FIG. 7.

As shown in FIG 7, dimerization of ethylene can produce a first product stream 701 , including n-butene, which can be transferred to an oxidative dehydrogenation step. The oxidative dehydrogenation process can produce a second product stream 702 of crude C4s, including 1 ,3-butadiene. The second product stream 702 can be passed to a first extractive distillation step to produce a 1 ,3-butadiene fraction and a first feed. 1 ,3- butadiene can be collected and the first feed can be passed to a second extractive distillation step to produce a second feed 703 and an n-butene raffinate A stream 704. The second feed 703 is further partitioned via fractionation to produce bottoms 705 rich in butanes, which are removed from the process, and overhead 706 rich in 1-butene, to produce a 1-butene-rich raffinate B stream 707 being recycled back to the oxidative dehydrogenation step.

In another embodiment, a system for manufacturing 1 ,3-butadiene is described. This system can include a dimerization unit configured to dimerize ethylene into a first product stream including n-butene. The system can also include an oxidative

dehydrogenation unit configured to receive the first product stream including n-butene and to convert the n-butene into a second product stream including 1 ,3-butadiene. Further, the system can include a first extractive distillation unit configured to receive the second product stream including 1 ,3-butadiene and to produce a 1 ,3-butadiene fraction and a first feed. Additionally, a partition module can be included, which is configured to receive the first feed and to produce an n-butene raffinate A stream and an n-butene raffinate B stream. A recycle line can also be included that is configured to recycle at least a portion of the raffinate A stream from the partition module to the oxidative dehydrogenation unit.

A variety of dimerization units are known in the art and any suitable dimerization unit can be used with the present technology. A suitable dimerization unit can be designed to house a variety of catalysts, such as supported catalysts including a metal or combinations of metals from Group VIII of the Periodic Table and an oxide of a metal or combination of metals from group VI IB of the Periodic Table. One example of such catalysts can include palladium and molybdenum oxide. The catalysts can be adapted to have varying surface areas and particle sizes based on preference of the user.

Further, the dimerization unit can be adapted to accommodate a variety of

temperatures, pressures, flow rates, ratios of catalyst to reactants, and other

parameters that can be optimized according to desired outcome, and are known in the art. Dimerization units using a variety of such parameters to optimize desired outcomes are contemplated as useful in the present technology.

Any suitable oxidative dehydrogenation unit can be used with the present technology. Oxidative dehydrogenation units are known in the art and can be adapted to house a variety of catalysts known in the art, such as metal oxides, including ferrites and bismuth-molybdate. Oxidative dehydrogenation units can be adapted to

accommodate a variety of optimization parameters such as suitable temperatures, pressures, flow rates, concentrations of catalysts, and other suitable parameters.

Oxidative dehydrogenation units using a variety of such parameters to optimize desired outcomes are contemplated as useful in the present technology.

A first extractive distillation unit can include any suitable extractive distillation unit. Such units are known in the art and are contemplated as useful in the present technology. In one aspect, an extractive distillation unit can be adapted to use a variety of separation solvents such as acetonitrile, methyl ethyl ketone, dimethylformamide, furfural, N-methyl-2-pyrrolidone, acetone, sulfalone, dimethylacetamide, water, other suitable solvents, and combinations thereof. Additionally, the extractive distillation unit can be adapted to accommodate a variety of flow rates, temperatures, pressures, columns, column configurations, and other suitable parameters based on desired separation outcomes.

A variety of partition modules can also be used in the current system. A general overview of such partition modules will be given here and more detailed descriptions of embodiments using these partition modules will be given below. In one aspect, a partition module can include a second extractive distillation unit. In one aspect, a partition module can include a fractionation unit. Such a fractionation unit can be positioned relative to the first extractive distillation unit such that a solvent can cascade from the fractionation unit to the first extractive distillation unit. Fractionation units are generally known in the art. Any suitable fractionation unit can be used in the current technology and can employ any suitable optimization parameters such as temperatures, pressures, flow rates, columns, separation solvents, and other suitable parameters. In each of these aspects, a recycle line can be configured to recycle at least a portion of the raffinate A stream from the partition module to the oxidative dehydrogenation unit.

In another aspect, the partition module can include both a second extractive distillation unit and a fractionation unit. The second extractive distillation unit can be configured to receive the first feed and to produce a second feed and the n-butene raffinate A stream. The fractionation unit can be configured to receive the second feed and to produce the n-butene raffinate B stream. In this aspect the recycle line can be configured to recycle at least a portion of both the raffinate A stream and raffinate B stream to the oxidative dehydrogenation unit.

Turning now to the more detailed embodiments. In one embodiment, a system for manufacturing 1 ,3-butadiene can include a dimerization unit configured to dimerize ethylene into a first product stream including n-butene. Additionally, the system can include an oxidative dehydrogenation unit configured to receive the first product stream including n-butene and to convert the n-butene into a second product stream including 1 ,3-butadiene. The system can also include a first extractive distillation unit configured to receive the second product stream including 1 ,3-butadiene and to produce a 1,3- butadiene fraction and a first feed. Further, the system can include a second extractive distillation unit configured to receive the first feed and to produce an n-butene raffinate A stream. Moreover, the system can include a fractionation unit configured to receive the second feed and to produce an n-butene raffinate B stream. The system can also include a recycle line configured to recycle at least a portion of the raffinate A stream and at least a portion of the raffinate B stream from the second extractive distillation unit and the fractionation unit to the oxidative dehydrogenation unit.

In still another embodiment, a system for manufacturing 1 ,3-butadiene can include a dimerization unit configured to dimerize ethylene into a first product stream including n-butene. In addition, the system can include an oxidative dehydrogenation unit configured to receive the first product stream including n-butene and to convert the n-butene into a second product stream including 1 ,3-butadiene. The system can also include a first extractive distillation unit configured to receive the second product stream including 1 ,3-butadiene and to produce a 1 ,3-butadiene fraction and a first feed.

Further, the system can include a fractionation unit configured to receive the first feed and to produce an n-butene raffinate A stream and an n-butene raffinate B stream. The system can also inlcude a recycle line configured to recycle at least a portion of the raffinate A stream from the fractionation unit to the oxidative dehydrogenation unit.

In yet another embodiment, a system for manufacturing 1 ,3-butadiene can include a dimerization unit configured to dimerize ethylene into a first product stream including n-butene. In addition, the system can include an oxidative dehydrogenation unit configured to receive the first product stream including n-butene and to convert the n-butene into a second product stream including 1 ,3-butadiene. The system can also include a first extractive distillation unit configured to receive the second product stream including 1 ,3-butadiene and to produce a 1 ,3-butadiene fraction and a first feed.

Further, the system can include a second extractive distillation unit configured to receive the first feed and to produce an n-butene raffinate A stream and an n-butene raffinate B stream. The system can also include a recycle line configured to recycle at least a portion of the raffinate A stream from the second extractive distillation unit to the oxidative dehydrogenation unit.

In still another embodiment, a system for manufacturing 1 ,3-butadiene can include a dimenzation unit configured to dimerize ethylene into a first product stream including n-butene. In addition, the system can include an oxidative dehydrogenation unit configured to receive the first product stream including n-butene and to convert the n-butene into a second product stream including 1 ,3-butadiene. The system can also include a first extractive distillation unit configured to receive the second product stream including 1 ,3-butadiene and to produce a 1 ,3-butadiene fraction and a first feed.

Further, the system can include a fractionation unit configured to receive the first feed and to produce an n-butene raffinate A stream and an n-butene raffinate B stream. The system can also include a recycle line configured to recycle at least a portion of the raffinate A stream from the fractionation unit to the oxidative dehydrogenation unit. The fractionation unit can be positioned above or otherwise relative to the extractive distillation unit such that a solvent can cascade from the fractionation unit down to the extractive distillation unit.

In one embodiment, a system for manufacturing 1 ,3-butadiene can include a dimerization unit configured to dimerize ethylene into a first product stream including n- butene. Further, the system can include an oxidative dehydrogenation unit configured to convert the n-butene into a second product stream including 1 ,3-butadiene. The system can also include a first extractive distillation unit configured to produce a 1 ,3-butadiene fraction and a Raffinate A stream comprising n-butane and butene, the butene comprising 1 -butene, cis/trans 2-butene, or mixtures thereof. A feed line can also be present and configured to recycle a feed from the Raffinate A stream from the first extractive distillation unit to the oxidative dehydrogenation unit. In this embodiment, the feed can comprise n-butane and butene. The system can be adapted such that the n- butane in the feed before recycling can be present at a first concentration less than or equal to about 2 weight percent and n-butane can be allowed to build-up in the recycled feed to an extent greater than the first concentration and less than about 40 weight percent. The build-up occurs by cyclic recycling of the feed from the first extractive distillation unit to the oxidative dehydrogenation unit.

EXAMPLES

Example 1

A simulation representative of the configuration illustrated in FIG. 5 is provided below. In this example, a mixed 1 -butene recycle stream is recycled back to the oxidative dehydrogenation section, n-butane is purged from the overall system as bottoms from a fractionator, and the mixed recycle is produced through both the direct recycle of a produced raffinate (after BD extraction) and recycle of a butene rich fraction produced (as overheads via fractionation).

The oxidative dehydrogenation effluent, going into extraction, was carried out using techniques generally known to those in the art. The feed used for oxidative dehydrogenation was chosen as 1 -butene. No isomerization of 1 -butene to 2-butenes was considered in the oxidative dehydrogenation section.

The resulting feed, crude C4 stream, Raffinate, & distillation Overhead stream, is provided in Table 1.

Table 1

Table 1. Recycle with partial distillation; 3% Raffinate A Fed to Distillation; Distillation using 60 Stages at 10 Reflux Ratio; 100% Feed Utilization

It is noted that the current price of 1 ,3 butadiene compared to 1-butene feed was such that high utilization of 1-butene would be more cost effective. Thus, n-butane, present in the 1-butene feed, is allowed to buildup in the overall system. The quantity of direct recycle stream was set to be 97% of the raffinate produced from BD extraction. 3% was sent to the fractionation section, and a column using 60 stages and a reflux ratio of 10 was utilized.

In this case, the quantity of n-butane is allowed to build up to 8.9% of the total C4's [Net Butene Feed + Recycle], which is introduced into the oxidative

dehydrogenation section. This equates to approximately 43 times the amount of n- butane present in the net Butene Feed. The resulting recycle design provides 100% utilization of the net butenes, without the use of a butene extractive distillation unit, where feed Utilization is defined as: ([n-butene Feed] - [n- butene Purged]) / [n-butene Feed] . In Figure 5, the means for purging n-butane (Purge) is represented by Line 507, distillation bottoms.

Tables 2 and 3 provide two additional cases, whereby the price of 1-butene to

1 ,3 butadiene provides for slightly lower Feed Utilization with less total recycle. Table 2 provides for a feed utilization of 99.99% and Table 3 provides a case with approximately 97% Feed utilization.

The main variable changes between the 3 cases (Tables 1-3) in Example 1 occur through adjustments in (1) the quantity of Raffinate sent to fractionation and (2) the distillation overhead design specification. Table 2 is based on 20% of the Raffinate sent to distillation, using 60 trays at a 5 reflux ratio. Table 3 is based on 30% of the Raffinate sent to distillation, using 60 tray and a 3 reflux ratio.

For these cases, the feed flow and reflux were adjusted such that the approximate column diameter is approximately the same (providing similar distillation equipment and cost).

Table 2

Table 2. Recycle with partial distillation; 20% Raffinate A Fed to Distillation; Distillation using 60 Stages at 5 Reflux Ratio; 99.99% Feed Utilization

Table 3

Table 3. Recycle with partial distillation; 30% Raff A Fed to Distillation, at Reflux Ratio = 3 & 60 Stages; 97% Feed Utilization Example 1 shows how an oxidative dehydrogenation unit, using a rich 1-butene feedstock, can be integrated into an existing ethylene complex, containing a Raffinate II superfractionator, for separation of 1-butene and 2-butenes. Given the small quantity of purge required, it can be seen that this design would require minimal modification and/or change to a fractionator's hydraulic capacity, while increasing the overall 1- butene utilization and corresponding butadiene yield.

Table 1 represents a valuation between 1 ,3 butadiene to 1-butene where the added utilities cost associated with recycling the feed is justified. For smaller price spreads, the specification on the fractionation can be reduced and/or the total quantity of feed sent to fractionation can be modified, as provided in Tables 2 & 3.

Example 2

Using the configuration provided in FIG. 4, without the fraction step, a similar price driver for recycling of 1-butene is used. Setting the purge to 1.5% of the raffinate produced from extraction, an overall design with 99.7% utilization of the net butenes is provided without fractionation. The overall n-butane in the total C4's [Butene Feed + Recycle], sent to the oxidative dehydrogenation unit, is increased to 10.2% or approximately 53 times the quantity present in the net butene feed.

Table 4 provides the compositional and flowrate information for the feed, recycle, and purge streams.

Table 4

Table 4. Direct recycle to Oxidative Dehydrogenation; 99.7% 1-butene Utilization.

A trade off from Example 1 to Example 2 is the increased hydraulic sizing of the all the equipment used in the oxidative dehydrogenation section as well as the use of heat recovery equipment. A good comparison of cases to illustrate this comes from Table 2 vs. Table 4, whereby the feed utilization is higher (99.99% vs. 99.7%) and the quantity of n-butane in the recycle raffinate is approximately 3 times lower. As such, addition of fractionation is often justified when high feed utilization of butenes is needed.

In one aspect, an extractive distillation tower as depicted in FIG. 8 can be used with this and other system configurations. As can be seen in FIG. 8, Stream 802 is introduced along the vertical tower between the two raffinate products. A first solvent injection (Traditional), Stream 801 , is used to impart the butadiene recovery from the extractive distillation unit. The crude C4 feed Stream 803 toward the bottom of the vertical tower. Generally, only trace quantities of butenes will reside in the bottoms solvent stream sent to recovery [807, so essentially 100% of the butenes are recovered as draws, either as raff i nates A 805 and B 804 or as minor impurities within the butadiene stream 806.

Example 3

Example 3 provides an additional option for reducing the recycle described in

Example 2. With the addition of a second raffinate purge (Raffinate B) and a solvent injection to a conventional butadiene extractive distillation unit, some additional separation of the butenes from the n-butane can be set up, without substantial equipment modification. By producing two raffinate streams (Raffinate A & Raffinate B), both with relatively high butene concentrations, but disproportionate n-butane contents, high utilization of the butene feed can be accomplished while allowing for an n-butane purge. FIG. 9 provides a simplified view of such an extractive distillation tower section and FIG. 3 provides the overall oxidative dehydrogenation process flow utilized for this example.

The reduction of n-butane content, through the use of two Raffinate draws, is illustrated in Table 5. Raffinate A represents a side draw of approximately 89% of the total Raffinate produced through the use of the extractive distillation process provided in Figure 9. Raffinate B represents 11% of this material, which is taken as an n-butane purge for the system.

Table 5

Table 5. Reduction of n-butane by use of two Raffinate streams In this case, Raffinate A (containing a lower relative n-butane content than Raffinate B) is recycled back to the oxidative dehydrogenation process and Raffinate B is purged from the system to remove n-butane.

It has been found that the more successful overall designs herein (a) provide a Raffinate B n-butane content significantly higher than the Raffinate A n-butane content, (2) have a Raffinate A draw with very low butadiene content, and (3) maintain a high recovery of the 1 ,3 butadiene via a separate (traditional) BD draw.

To help impart a significant difference in the n-butane content between the two raffinate products, an additional solvent injection is utilized. From FIG. 7, that injection is labeled as Stream 902. Along the vertical tower height, Stream 902 is introduced between the two raffinate products. A first solvent injection (Traditional), Stream 901 , is used to impart the butadiene recovery from the extractive distillation unit. The relative solvent mass flow rates, Streams 901 and 902, to the crude C4 feed Stream 903 were set as follows:

Stream 901 = 3.5 x Crude C4 Feed

Stream 902 = 10.4 x Crude C4 Feed

The 1 ,3 Butadiene purity was set to be 99 wt%, and a solvent of NMP and water was utilized. Table 5 illustrates the second injection benefit, showing a 50% increase in the relative n-butane content in the Raffinate B draw.

Only trace quantities of butenes reside in the bottoms solvent stream sent to recovery 907, so essentially 100% of the butenes are recovered as draws, either as raffinates A 905 and B 904 or as minor impurities within the butadiene, Stream 906. The mass quantity of Raffinates A and B draws (mass flow), relative to the crude C4 feed, were:

Raffinate A = 49.2% x Crude C4

Raffinate B = 5.2% x Crude C4

Relative to one another, Raffinate B was approximately 11 % of the total raffinate produced. The relative quantity of n-butane found in Raffinate B, however, is

approximately 14% of the total n-butane present in the total raffinate. For design purposes, both solvent injections could represent the same solvent composition and varying flow rates. Information provided in Table 5 utilized varying water contents for the two injections, whereby more relative water to solvent ratio was utilized for the top injection. Thus, it is within the scope of the disclosure that solvent injections with varying aqueous concentrations and/or varying solvent compositions may be utilized to further aid the relative volatility between the desired recycle component (butenes) and the purge component (n-butane). Additionally, varying flow rates and added equipment for reducing solvent carryover or recovering heat may be used, as would be appreciated by one skilled in the art.

To further illustrate the usefulness of an extractive distillation side draw for the overall process, depicted in Figure 3, two additional simulations were performed. These results are provided in Tables 6 & 7. Table 6 represents a process with 98.7% Feed Utilization, and Table 7 represents a slightly higher Feed Utilization of 99.7%.

Table 6

Table 6. Use of 2^nd Raffinate Draw for n-butane Purge; 98.7% Feed Utilization

Table 7

Table 7. Use of 2^nd Raffinate Draw for n-butane Purge; 99.7% Feed Utilization

To show the additional usefulness of incorporating a 2^nd Raffinate Draw, one can compare the results in Table 7 with those of the direct recycle approach provided in Table 4. Looking at the Recycle Raffinate n-butane content, a reduction from 41.5% to 26.9% is achieved at the same Feed Utilization of 99.7%. This allow for some reduction in equipment size within the oxidative dehydrogenation section, which is associated with the higher n-butane content found in Table 4

Example 4

In addition to the application of an extractive distillation column design using two raffinate products, it is within the scope of the invention that a produced Raffinate B be further distilled for higher n-butene utilization. This distillation would be similar to that of Example 1. Combining these two recycle options together (a Raffinate Draw plus a distillation step) for 1-butene would produce a total recycle composed of a Raffinate A (extractive distillation draw) along with a rich n-butene stream produced from a fractionation unit. Such a configuration is represented in FIG. 7. Using this option, the results provided in Table 8 were achieved. Table 8

Table 8. Combined use of Raffinate Draw with Distillation; 10% Raffinate to Distillation; 60 Stages & Reflux Ratio = 5; 99.7% Feed Utilization

Several benefits of the process provided in Figure 7 process are shown by the data listed in Table 8, including : (1) High feed utilization, (2) Low n-butane content in the Recycle (-12.7%), (3) Low quantity of required feed sent to distillation.

For FIG. 7, in one aspect, the n-butene Raffinate A stream can be a vapor side draw comprising n-butene in an amount ranging from 60% to 99% by weight. In another aspect, the n-butene raffinate B stream can be an overhead comprising n-butene in an amount ranging from 40% to 96% by weight

Although the subject matter has been described in language specific to compositional features, structural features and/or operations, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features and operations described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. Numerous modifications and alternative arrangements can be devised without departing from the spirit and scope of the described technology.

Claims

CLAIMS What is claimed is:

1. A method of manufacturing 1 ,3-butadiene, comprising:

dimerizing ethylene via a dimerization step to produce a first product stream including n-butene;

converting the n-butene via an oxidative dehydrogenation step to produce a second product stream including 1 ,3-butadiene;

distilling the second product stream including 1 ,3-butadiene via a first extractive distillation step to produce a 1 ,3-butadiene fraction and a first feed;

partitioning the first feed via a partition step to produce an n-butene raffinate A stream and an n-butene raffinate B stream; and

recycling the n-butene raffinate A stream via a recycling step to the oxidative dehydrogenation step.

2. The method of claim 1 , wherein the partition step includes a second extractive distillation step.

3. The method of claim 1 , wherein the partition step includes a fractionation step.

4. The method of claim 3, further comprising purging the n-butene raffinate B stream.

5. The method of claim 1 , wherein the partition step includes:

distilling the first feed from the first extractive distillation step via a second extractive distillation step to produce a second feed and the n-butene raffinate A stream; and

fractionating the second feed from the second extractive distillation step via a fractionation step to produce the n-butene raffinate B stream.

6. The method of claim 5, wherein recycling further includes recycling the n- butene raffinate B stream to the oxidative dehydrogenation step.

7. A method of manufacturing 1 ,3-butadiene, comprising:

distilling the second product stream including 1 ,3-butadiene via a first extractive distillation step to produce a 1 ,3-butadiene fraction and a raffinate A stream, the raffinate A stream comprising n-butane and butene, the butene comprising 1-butene, cis/trans 2-butene, or mixtures thereof; and

recycling a feed from the raffinate A stream via a recycling step from the first extractive distillation step to the oxidative dehydrogenation step, the feed comprising n- butane and butene,

wherein the n-butane in the feed before recycling is present at a first

concentration less than or equal to about 2 weight percent and wherein n-butane is allowed to build-up in the recycled feed to an extent greater than the first concentration and less than about 40 weight percent, and wherein the build-up occurs by cyclic recycling of the feed from the first extractive distillation step to the oxidative

dehydrogenation process step.

8. The method of claim 7, further comprising purging the raffinate A stream in an amount from about 0.2% to about 20% by mass.

9. The method of claim 7, wherein the feed comprises at least 80 wt% of the raffinate A stream.

10. A system for manufacturing 1 ,3-butadiene, comprising:

a dimerization unit configured to dimerize ethylene into a first product stream including n-butene; an oxidative dehydrogenation unit configured to receive the first product stream including n-butene and to convert the n-butene into a second product stream including 1 ,3-butadiene;

a first extractive distillation unit configured to receive the second product stream 5 including 1 ,3-butadiene and to produce a 1 ,3-butadiene fraction and a first feed;

a partition module configured to receive the first feed and to produce an n-butene raffinate A stream and an n-butene raffinate B stream; and

a recycle line configured to recycle at least a portion of the raffinate A stream from the partition module to the oxidative dehydrogenation unit.

o

11. The system of claim 10, wherein the partition module includes a second extractive distillation unit.

12, The system of claim 10, wherein the partition module includes a5 fractionation unit.

13. The system of claim 12, wherein the fractionation unit is positioned relative to the first extractive distillation unit such that a solvent can cascade from the

fractionation unit to the first extractive distillation unit.

0

14. The system of claim 10, wherein the partition module includes: a second extractive distillation unit configured to receive the first feed and to produce a second feed and the n-butene raffinate A stream; and

a fractionation unit configured to receive the second feed and to produce the n-5 butene raffinate B stream.

15. The system of claim 14, wherein the recycle line is further configured to recycle at least a portion of the n-butene raffinate B stream to the oxidative

dehydrogenation unit.

0