阅读说明：本技术 控制来自odh方法的二氧化碳输出 (Controlling carbon dioxide output from an ODH process ) 是由 V.西曼真科夫 S.谷达尔兹尼亚 于 2018-10-09 设计创作，主要内容包括：本文提供了控制来自氧化脱氢(ODH)方法的二氧化碳输出水平的方法。来自ODH方法的二氧化碳输出包括在ODH反应中产生的二氧化碳输出,以及当二氧化碳用作惰性稀释剂时的携带。在某些情况下,二氧化碳也可以通过用作氧化剂在ODH方法中被消耗。通过改变引入ODH方法的蒸汽的量,操作者可改变二氧化碳用作氧化剂的程度,这反过来允许一定程度地控制在该方法中消耗二氧化碳的程度,影响总的二氧化碳输出。使二氧化碳输出最小化提供机会来限制或消除将二氧化碳释放到大气中的需要。(Provided herein are methods of controlling carbon dioxide output levels from Oxidative Dehydrogenation (ODH) processes. The carbon dioxide output from the ODH process includes the carbon dioxide output produced in the ODH reaction, as well as carryover when carbon dioxide is used as an inert diluent. In some cases, carbon dioxide can also be consumed in ODH processes by acting as an oxidant. By varying the amount of steam introduced into the ODH process, the operator can vary the extent to which carbon dioxide is used as the oxidant, which in turn allows some degree of control over the extent to which carbon dioxide is consumed in the process, affecting the overall carbon dioxide output. Minimizing carbon dioxide output provides the opportunity to limit or eliminate the need to release carbon dioxide into the atmosphere.)

1. A method of controlling carbon dioxide output from an oxidative dehydrogenation process comprising the steps of:

i) introducing a gas mixture comprising a lower alkane and oxygen, and optionally one or more of steam and an inert diluent, into at least one ODH reactor containing the same or different ODH catalysts, under conditions to produce a product stream comprising the corresponding alkene, and possibly one or more of unreacted lower alkane, unreacted oxygen, carbon dioxide, carbon monoxide, inert diluent, and acetic acid from each of the at least one ODH reactor, with the proviso that the at least one ODH catalyst is capable of utilizing carbon dioxide as an oxidant;

ii) measuring the level of carbon dioxide in one or more of the product streams; and one of the following:

a. introducing steam into the at least one ODH reactor or increasing the amount of steam introduced into the at least one ODH reactor in an amount sufficient to reduce the carbon dioxide output level when the measured carbon dioxide level is above a predetermined target carbon dioxide level;

b. decreasing the flow rate of steam introduced into the at least one ODH reactor to increase the carbon dioxide output level when steam is introduced in step i) and the measured carbon dioxide level is below the predetermined target carbon dioxide level;

c. increasing the volume ratio of oxygen to ethane in the gas mixture introduced into the at least one ODH reactor to a degree sufficient to reduce the carbon dioxide level when the measured carbon dioxide level is above a predetermined target carbon dioxide level; or

d. When the measured carbon dioxide level is below a predetermined target carbon dioxide level, the volumetric ratio of oxygen to ethane in the gas mixture introduced into the at least one ODH reactor is reduced to a degree sufficient to increase the carbon dioxide level.

2. The process of claim 1, wherein the lower alkane is ethane and the corresponding alkene is ethylene.

3. The process of claim 1 or 2, wherein at least one ODH reactor is a fixed bed reactor.

4. The method of claim 3, wherein at least one fixed bed ODH reactor comprises heat dissipating particles having a thermal conductivity greater than the catalyst.

5. The process of claim 1 or 2, wherein at least one ODH reactor is a fluidized bed reactor.

6. The process of any of the preceding claims, wherein at least one ODH catalyst is a mixed metal oxide.

7. The process of any one of the preceding claims, wherein at least one ODH catalyst comprises a mixed metal oxide of the formula:

Mo _a V _b Te _c Nb _d Pd _e O _f

wherein a, b, c, d, e and f are the relative atomic numbers of the elements Mo, V, Te, Nb, Pd and O, respectively; and when a = 1, b = 0.01 to 1.0, c = 0.01 to 1.0, d = 0.01 to 1.0, 0.00. ltoreq. e.ltoreq.0.10, and f is a number satisfying the valence of the catalyst.

8. The method of any one of the preceding claims, wherein the inert diluent is carbon dioxide.

9. The method of any of the preceding claims, wherein steam comprises up to 40wt% of the gas mixture.

10. The process of any of the preceding claims, wherein the conditions in at least one ODH reactor are a temperature from 300 ℃ to 450 ℃, a pressure from 0.5 to 150 psig (3.447 kPag to 689.47 kPag), and a residence time of the lower alkane in the reactor from 0.002 to 30 seconds.

11. The method of any one of the preceding claims, wherein the gas mixture has a gas hourly space velocity of from 500 to 30000 h^-1。

12. The process of any of the preceding claims, wherein the weight hourly space velocity of the gas mixture is from 0.5 h^-1To 50 h^-1。

13. The method of any of the preceding claims, wherein the linear velocity of the gas mixture is from 5 cm/sec to 1500 cm/sec.

14. The method of any of the preceding claims, wherein the temperature in the reactor is maintained at a temperature of less than about 340 ℃.

15. The method of claim 14, wherein the steam added to the at least one ODH reactor is at least about 10wt%, and the steam is increased by at least 20 wt% and results in a change in carbon dioxide output of at least 1 wt%, as measured by normalized product selectivity.

16. The method of claim 14, wherein the steam added to the at least one ODH reactor increases by at least 30wt% and results in a change in carbon dioxide output of at least 2.5 wt%, as measured by normalized product selectivity.

17. The method of claim 14, wherein the steam added to the at least one ODH reactor increases by at least 40wt% and results in a change in carbon dioxide output of at least 7.5 wt%, as measured by normalized product selectivity.

18. The process of any one of claims 1 to 13, wherein the temperature in the reactor is maintained at a temperature above about 340 ℃.

19. The method of claim 18, wherein the steam added to the at least one ODH reactor increases by at least 40wt% and results in a change in carbon dioxide output of at least 0.5 wt%, as measured by normalized product selectivity.

20. The method of any one of claims 1 to 13, wherein the vol% of oxygen in the gas mixture is about 20%, and the oxygen in the gas mixture: the volume ratio of ethane was about 0.4, and changed to oxygen: the volume ratio of ethane is about 0.6 and results in a change in carbon dioxide output of at least 2.5 wt%, measured as normalized product selectivity.

21. The process of any one of claims 1 to 13, wherein the vol% of oxygen in the gas mixture is such that the feed mixture stays outside the combustible enclosure of the hydrocarbon feed mixture, and the oxygen in the gas mixture: the volume ratio of ethane is about 0.1 and is changed to the maximum ratio allowed before the feed mixture enters the combustible containment zone of the hydrocarbon feed mixture and results in a change in carbon dioxide output of at least 0.5 wt%, measured as normalized product selectivity.

Technical Field

The present invention relates generally to the Oxidative Dehydrogenation (ODH) of lower alkanes to the corresponding alkenes. More particularly, the present invention relates to controlling the level of carbon dioxide output from an ODH process.

Background

Olefins such as ethylene, propylene and butylene are the basic building blocks for a variety of commercially valuable polymers. Since naturally occurring olefin sources are not present in commercial quantities, polymer producers rely on processes for converting more abundant lower alkanes to olefins. The process currently selected by commercial scale producers is steam cracking, a highly endothermic process in which the steam diluted alkanes are very briefly subjected to a temperature of at least 700 ℃. The fuel requirements to produce the required temperature and the requirements for equipment that can withstand this temperature add significantly to the overall cost. In addition, the high temperatures promote coke formation, which accumulates in the system, resulting in the need for expensive periodic reactor shutdowns for maintenance and coke removal.

Oxidative Dehydrogenation (ODH) is an alternative to steam cracking, which is exothermic and produces little or no coke. In ODH, a lower alkane (such as ethane) is mixed with oxygen in the presence of a catalyst and optionally an inert diluent (such as carbon dioxide or nitrogen) at temperatures as low as 300 ℃ to produce the corresponding alkene and unfortunately various other oxidation products, most notably carbon dioxide and acetic acid. Furthermore, ODH has a lower conversion rate compared to steam cracking, which fact, when combined with lower selectivity and risk of thermal explosion due to hydrocarbon mixing with oxygen, has hindered the widespread commercial implementation of ODH.

The concept of ODH is known at least since the late 60 s of the 20 th century. Since then, considerable effort has been spent on improving the process, including improving catalyst efficiency and selectivity. This has led to numerous patents for various catalyst types including carbon molecular sieves, metal phosphates and most notably mixed metal oxides. Early catalyst U.S. patents assigned to Petro-texchemics, including U.S. patent nos. 3,420,911 and 3,420,912 in the name of Woskow et al, teach the use of ferrites in the oxidative dehydrogenation of organic compounds. The ferrite is introduced for a short period of time into a dehydrogenation zone containing organic compounds and an oxidant, then into a regeneration zone for reoxidation, and then fed back into the dehydrogenation zone for another cycle.

The preparation of supported catalysts for the low temperature oxidative dehydrogenation of ethane to ethylene is disclosed in U.S. patent No. 4,596,787 issued to Manyik et al 24.6.1986, assigned to Union Carbide Corporation. The catalyst was prepared by: (a) preparing a precursor solution having soluble and insoluble fractions of metal compounds, (b) separating the soluble fraction, (c) impregnating the catalyst support with the soluble fraction and (d) activating the impregnated support to obtain the catalyst. The calcined catalyst had the following composition

Mo_aV_bNb_cSb_dX_e

Wherein X is absent or Li, Sc, Na, Be, Mg, Ca, Sr, Ba, Ti, Zr, Hf, Y, Ta, Cr, Fe, Co, Ni, Ce, La, Zn, Cd, Hg, Al, Tl, Pb, As, Bi, Te, U, Mn and/or W; a is 0.5 to 0.9; b is 0.1 to 0.4; c is 0.001-0.2; d is 0.001-0.1; and when X is an element, e is 0.001 to 0.1.

U.S. patent No. 6,891,075 issued to Liu on 10.5.2005, assigned to symyx technologies, inc, teaches a catalyst for the oxidative dehydrogenation of paraffins (alkanes), such as ethane. The gaseous feed comprises at least alkanes and oxygen, but may also include diluents (e.g., argon, nitrogen, etc.) or other components (e.g., steam or carbon dioxide). The dehydrogenation catalyst contains at least about 2 weight percent NiO and a wide range of other elements, preferably Nb, Ta, and Co. The claims require that the selectivity to ethylene is at least 70% at conversions in excess of 10%.

U.S. patent No. 7,319,179 issued to Lopez-Nieto et al, 15.1.2008, assigned to concejo Superior de investigitions cis and universal polarimeter de valencia, discloses Mo-V-Te-Nb-O oxide catalysts that provide 50-70% conversion of ethane and up to 95% (at 38% conversion) selectivity to ethylene at 360 to 400 ℃. Of catalystsEmpirical formula of MoTe_hV_iNb_jA_kO_xWherein A is a fifth modifying element. The catalyst is a calcined mixed oxide (mixed oxide of at least Mo, Te, V and Nb), optionally supported on: (i) silica, alumina and/or titania, preferably silica, which comprises 20 to 70 wt% of the total supported catalyst, or (ii) silicon carbide. The supported catalysts are prepared by conventional methods of precipitation from solution, drying the precipitate and subsequent calcination.

The oxidant in the ODH process is typically oxygen added with the lower alkane. However, carbon dioxide is also known as an oxidizing agent. Liu et al, New and Future Developments in Catalysis, Elsevier,189-₂in Several Typical Processes "review CO₂As an oxidant in the oxidative dehydrogenation of alkanes. Studies have shown that CO₂Can be used as a mild oxidant in ODH reaction, can inhibit deep oxidation of reaction products, and also provides for using CO₂As a mechanism of origin. For ethane ODH ethylene, the catalyst type includes SiO supported₂、ZrO₂、Al₂O₃Or TiO₂The above active metals and oxides, which in combination show different conversions and selectivities to ethylene.

U.S. patent No. 2,604,495 issued to Erkko on 21/7/1948, assigned to Hercules powder company, teaches a process for the dehydrogenation of ethane to produce ethylene by mixing carbon dioxide and ethane in the presence of an iron oxide catalyst at a temperature between 750 ℃ and 950 ℃. The examples show that the conversion of ethane to ethylene is between 34% and 68.7%, depending on the molar ratio of carbon dioxide to ethane added to the reactor and the catalyst composition.

U.S. patent No. 7,767,770 issued to Han et al on 3.8.2010, assigned to Rohm and haas company, teaches a process for producing a mixture of ethylene and carbon monoxide by contacting ethane and carbon dioxide with a mixed-valence catalyst. The reaction is carried out in the absence of elemental oxygen at a temperature of at least 550 ℃ and produces a mixture of ethylene and carbon monoxide which can be used as a feedstock for other processes, for example processes for producing methacrylates.

We have found that the extent to which carbon dioxide produced during an ODH process or added as a diluent acts as an oxidant can be manipulated in order to control the output of carbon dioxide from the process to a desired level. Using the methods described herein, a user may choose to operate under carbon dioxide neutral conditions so that the remaining carbon dioxide does not need to be burned or released into the atmosphere.

Disclosure of Invention

The present invention provides a method of controlling carbon dioxide output from an ODH process, consisting of: a gaseous mixture of lower alkane, oxygen and carbon dioxide is introduced into at least one ODH reactor under conditions that allow production of the corresponding alkene and lesser amounts of various by-products. For a plurality of ODH reactors, each reactor contains the same or different ODH catalyst, provided that at least one ODH catalyst is capable of using carbon dioxide as an oxidant. Steam or other inert diluent may also be introduced into the reactor as part of the gas mixture. The amount of carbon dioxide exiting the reactor is then monitored, and if the amount of carbon dioxide output is below a desired level, the amount of steam introduced into the reactor may be increased, and if the amount of carbon dioxide output is above the desired level, the amount of steam introduced into the reactor may be decreased. Alternatively, the oxygen added to the at least one ODH reactor may be increased: the lower alkane volume ratio to reduce carbon dioxide output, or the oxygen added to the at least one ODH reactor: lower alkanes to increase carbon dioxide output.

In an embodiment of the invention, the lower alkane is ethane and the corresponding alkene is ethylene.

In a further embodiment, at least one ODH reactor is a fixed bed reactor. In another embodiment, the at least one ODH reactor is a fixed bed reactor comprising heat dissipating particles in a fixed bed. The heat dissipating particles have a thermal conductivity greater than the catalyst. In an alternative embodiment, at least one ODH reactor is a fluidized bed reactor.

In an embodiment of the invention, the at least one ODH catalyst is a mixed metal oxide catalyst. In a further embodiment, the at least one ODH catalyst is a mixed metal oxide of the formula: mo _a V _b Te _c Nb _d Pd _e O _f Wherein a, b, c, d, e and f are the relative atomic numbers of the elements Mo, V, Te, Nb, Pd and O, respectively; and when a = 1, b = 0.01 to 1.0, c = 0.01 to 1.0, d = 0.01 to 1.0, 0.00. ltoreq. e.ltoreq.0.10, and f is a number satisfying the valence of the catalyst.

Description of the embodiments

Other than in the operating examples, or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, and the like, used in the specification and claims are to be understood as modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

The present invention relates to the Oxidative Dehydrogenation (ODH) of lower alkanes to the corresponding alkenes. Lower alkanes are intended to include saturated hydrocarbons having from 2 to 4 carbons, and the corresponding alkenes include hydrocarbons having the same number of carbons but having a single carbon-carbon double bond. The present invention is most ideally suited for ODH of ethane to produce its corresponding olefin, ethylene.

ODH method

ODH of a lower alkane comprises contacting a mixture of the lower alkane and oxygen with an ODH catalyst in an ODH reactor under conditions that promote oxidation of the lower alkane to its corresponding alkene. The conditions in the reactor are controlled by an operator and include, but are not limited to, parameters such as temperature, pressure, and flow rate. The conditions will vary and may be optimized for a particular lower alkane, or for a particular catalyst, or whether an inert diluent is used in the mixing of the reactants.

It is within the knowledge of one skilled in the art to carry out the ODH process according to the present invention using an ODH reactor. For best results, oxidative dehydrogenation of the lower alkane may be carried out at a temperature of from 300 ℃ to 450 ℃, typically from 300 ℃ to 425 ℃, preferably from 330 ℃ to 400 ℃, at a pressure of from 0.5 to 100 psi (3.447 to 689.47 kPa), preferably from 15 to 50 psi (103.4 to 344.73 kPa), and the residence time of the lower alkane in the reactor is typically from 0.002 to 30 seconds, preferably from 1 to 10 seconds.

Preferably, the process has a selectivity to the corresponding olefin (ethylene in the case of ethane ODH) of greater than 85%, preferably greater than 90%. The flow rates of the reactants and inert diluent may be described in a variety of ways known in the art. Generally, the flow rates are described and measured relative to the volume of all feed gases (reactants and diluent) or Gas Hourly Space Velocity (GHSV) through the volume of the active catalyst bed in one hour. GHSV can be from 500 to 30000 h^-1Preferably greater than 1000h^-1. The flow rate can also be measured as Weight Hourly Space Velocity (WHSV), which describes the flow in terms of the weight of gas flowing through the weight of active catalyst per hour, rather than volume. In calculating WHSV, the weight of the gas may include only the reactants, but may also include a diluent added to the gas mixture. When the weight of diluent is included, when used, the WHSV may be from 0.5 h^-1To 50 h^-1Preferably from 1.0 to 25.0 h^-1The range of (1).

The gas flow through the reactor can also be described as the linear velocity of the gas stream (m/s), which is defined in the art as the flow rate of the gas stream/cross-sectional surface area of the reactor/void fraction of the catalyst bed. The flow rate generally refers to the total flow rate of all gases entering the reactor and is measured at the point where oxygen and alkane first contact the catalyst and at the temperature and pressure at that point. The cross-section of the reactor is also measured at the inlet of the catalyst bed. The void fraction of a catalyst bed is defined as the volume of voids in the catalyst bed per the total volume of the catalyst bed. The volume of the voids refers to the voids between the catalyst particles and does not include the volume of the pores inside the catalyst particles. The linear velocity can range from 5 cm/sec to 1500 cm/sec, preferably from 10 cm/sec to 500 cm/sec.

The space-time yield (productivity) of the corresponding olefin in g/hour/kg catalyst should be not less than 900, preferably greater than 1500, most preferably greater than 3000, most desirably greater than 3500 at from 350 to 400 ℃. It should be noted that the productivity of the catalyst will increase with increasing temperature until selectivity is sacrificed.

ODH catalyst

Any ODH catalyst known in the art is suitable for use in the present invention. When selecting a catalyst, the skilled user will appreciate that the catalyst may vary with selectivity and activity. For ODH of ethane, mixed metal oxides are preferred as the catalyst of choice because they can provide high selectivity to ethylene without significant activity loss. Particular preference is given to catalysts of the formula:

Mo _a V _b Te _c Nb _d Pd _e O _f

wherein a, b, c, d, e and f are the relative atomic numbers of the elements Mo, V, Te, Nb, Pd and O, respectively; and when a = 1, b = 0.01 to 1.0, c = 0.01 to 1.0, d = 0.01 to 1.0, 0.00. ltoreq. e.ltoreq.0.10, and f is a number satisfying the valence of the catalyst.

ODH reactor

The present invention contemplates the use of any known reactor type that can be applied to lower alkane ODH. Particularly suitable for use in the present invention are conventional fixed bed reactors. In a typical fixed bed reactor, reactants are introduced into the reactor at one end, flow over the immobilized catalyst, form product and exit at the other end of the reactor. Designing a fixed bed reactor suitable for the present invention may follow techniques known for this type of reactor. Those skilled in the art will know which features are required with respect to shape and size, input of reactants, output of products, temperature and pressure control, and the manner in which the catalyst is immobilized.

The present invention also contemplates the use of inert, non-catalytic heat dissipating particles in one or more ODH reactors. Heat dissipating particles are present in the bed and comprise one or more non-catalytically inert particles having a melting point at least 30 ℃, in some embodiments at least 250 ℃, in further embodiments at least 500 ℃ above the upper temperature control limit of the reaction, a particle size in the range of 0.5 to 75 mm, in some embodiments 0.5 to 15 mm, in further embodiments 0.5 to 8mm, desirably 0.5 to 5 mm, and a thermal conductivity greater than 30W/mK (watts/meter kelvin) within the reaction temperature control limit. In some embodiments, the particles are metal alloys and compounds having a thermal conductivity greater than 50W/mK (watts/meter kelvin) within the reaction temperature control limits. Some suitable metals include silver, copper, gold, aluminum, steel, stainless steel, molybdenum, and tungsten.

The heat dissipating particles may typically have a particle size of from about 1 to 15 mm. In some embodiments, the particle size may be from about 1 mm to about 8 mm. The heat dissipating particles may be added to the fixed bed in an amount of from 5 to 95 wt.%, in some embodiments 30 to 70wt.%, and in other embodiments 45 to 60 wt.%, based on the total weight of the fixed bed. The use of particles potentially improves cooling uniformity and reduces hot spots in the fixed bed by transferring heat directly to the reactor walls.

The present invention also contemplates the use of a fluidized bed reactor. These types of reactors are also well known. Typically, the catalyst is supported by a porous structure or distribution plate located near the bottom end of the reactor, and the reactants flow through at a velocity sufficient to fluidize the bed (e.g., the catalyst rises and begins to rotate about in a fluidized manner). The reactants are converted to products upon contact with the fluidized catalyst and are subsequently removed from the upper end of the reactor. Design considerations include the shape of the reactor and distributor plate, input and output, and temperature and pressure control, all of which will fall within the knowledge of one skilled in the art.

The invention also includes the use of a combination of both fixed bed and fluidized bed reactors, each reactor having the same or different catalyst. The multiple reactors may be in series or parallel configurations and the design thereof is within the knowledge of one skilled in the art.

Limit of flammability

The security of this approach is a major concern. For this reason, the mixture of lower alkane and oxygen should preferably comprise a proportion falling outside the flammability envelope. The present invention contemplates that the alkane to oxygen ratio can fall outside of the upper flammability envelope. In this case, the percentage of oxygen in the mixture is no more than 30%, preferably no more than 25%, most preferably no more than 20%.

For higher oxygen percentages, it is preferable to select the percentage of alkane that keeps the mixture outside the flammability envelope. Although the person skilled in the art will be able to determine appropriate levels, it is recommended that the percentage of alkanes does not exceed 40%. For example, in the case where the gas mixture prior to ODH comprises 20% oxygen and 40% alkane, the balance must be supplemented by an inert diluent such as one or more of nitrogen, carbon dioxide and steam. The inert diluent should be present in the gaseous state under the conditions in the reactor and should not increase the flammability of the hydrocarbon added to the reactor, the characteristics of which will be understood by those skilled in the art when deciding which inert diluent to use. The inert diluent may be added to the lower alkane-containing gas or the oxygen-containing gas prior to entering the ODH reactor, or may be added directly to the ODH reactor.

Mixtures that fall within the flammable envelope are not ideal, but may be used where the mixture is present under conditions that prevent the propagation of an explosive event. That is, a combustible mixture is produced in the medium where the fire is immediately extinguished. For example, the user may design a reactor in which oxygen and lower alkane are mixed at the point where they are surrounded by the flame retardant material. Any fire will be extinguished by the surrounding material. Flame retardant materials include, but are not limited to, metal or ceramic components, such as stainless steel walls or ceramic supports. Another possibility is to mix oxygen and lower alkanes at low temperatures, where a fire event would not lead to an explosion, and then introduce them into the reactor before the temperature is raised. There are no flammable conditions until the mixture is surrounded by the flame arrestor material inside the reactor.

Carbon dioxide output

Carbon dioxide may be produced as a by-product of the oxidation of lower alkanes in the ODH reaction. When used as an inert diluent, carbon dioxide may also be added to the ODH reactor. Conversely, when carbon dioxide is used as the oxidant for the dehydrogenation reaction, it may be consumed. Thus, carbon dioxide output is a function of the amount of carbon dioxide added and produced minus the amount consumed in the oxidation process. The present invention is directed to controlling the extent to which carbon dioxide acts as an oxidant to affect the overall carbon dioxide output from the ODH reactor.

The amount of carbon dioxide exiting the ODH reactor can be measured using any means known in the art. Preferably, one or more detectors such as GC, IR or raman detectors are located directly downstream of the reactor to measure carbon dioxide output. Although not required by the present invention, the output of other components can be, and typically is, measured. These include, but are not limited to, the amount of ethylene, unreacted ethane and oxygen, and by-products such as acetic acid. Furthermore, it should be noted that depending on the measure of carbon dioxide output chosen, the output level of other components (most notably ethane) may actually be required.

Carbon dioxide output may be expressed using any metric commonly used in the art. For example, carbon dioxide output can be based on mass flow rate (g/min) or volumetric flow rate (cm)³/min). In addition, the normalized selectivity can be used to assess the degree of carbon dioxide production or consumption. In this case, CO₂Net mass flow rate-CO entering and leaving the ODH reactor₂Is normalized to the conversion of ethane, which essentially describes how much of the ethane is converted to carbon dioxide rather than ethylene, or other by-products such as acetic acid. A carbon selectivity of 0 means that the amount of carbon dioxide entering the reactor is the same as the carbon dioxide output. In other words, the process is carbon dioxide neutral. Positive carbon dioxide selectively alerts the user that carbon dioxide is being produced and any oxidation of carbon dioxide that is occurring is insufficient to counteract the production, resulting in the process being carbon dioxide positive.

When the output of carbon dioxide or other components produced (e.g., acetic acid and carbon monoxide) is described in terms of normalized product selectivity, the calculation is made according to the following equation:

where X is the product to be evaluated, the net mass flow rate refers to the flow of X or ethane entering the reactor minus the flow rate leaving the reactor in g/min, and the molar equivalent (mol. Equiv.) refers to the amount of X that is fully reacted with one mole of ethane in moles. Selectivity is mentioned in wt% despite the fact that the calculation results in wt% being converted to mole percent, since the gravimetric flow rate is the measure used in the calculation.

A potential advantage of the present invention is the possibility of a negative carbon dioxide process. In this case, carbon dioxide is oxidized at a higher rate than it is produced, and shows negative carbon selectivity. The ODH process can produce carbon dioxide, but the extent to which carbon dioxide is consumed as an oxidant offsets any production that is occurring. In addition to ODH, many industrial processes produce carbon dioxide, which must be captured or burned in the event that it contributes to the emission of greenhouse gases. Using the negative carbon dioxide process, excess carbon dioxide from other processes can be captured and used as an inert diluent in ODH processes in the presence of negative carbon selectivity. Then there is an advantage in that the amount of carbon dioxide produced in the ODH process can be reduced in combination with other processes, such as thermal cracking. Furthermore, the oxidation of carbon dioxide is endothermic, and by increasing the extent to which carbon dioxide acts as an oxidant, the heat generated by the ODH of ethane is partially offset by the oxidation of carbon dioxide, thereby reducing the extent to which heat must be removed from the reactor. Finally, when carbon dioxide is used as the oxidant, it can produce carbon monoxide, which can be captured and used as an intermediate in the production of other chemical products (such as methanol or formic acid).

Addition of steam

The amount of steam added to the ODH process affects the extent to which carbon dioxide acts as an oxidant. The steam may be added directly to the ODH reactor, or the steam may be added to individual reactant components-lower alkanes, oxygen, or inert diluents-or combinations thereof-and subsequently introduced into the ODH reactor with one or more of the reactant components. Alternatively, steam may be added indirectly as water mixed with a lower alkane, oxygen, or an inert diluent, or a combination thereof, wherein the resulting mixture is preheated prior to entering the reactor. When steam is added indirectly as water, it is important that the preheating increases the temperature so that the water is completely converted to steam before entering the reactor.

Increasing the amount of steam added to the reactor increases the extent to which carbon dioxide acts as an oxidant. Reducing the amount of steam added to the reactor reduces the extent of carbon dioxide as an oxidant. In the present invention, the user monitors the carbon dioxide output and compares it to a predetermined target carbon dioxide output. If the carbon dioxide output is above the target, the user may increase the amount of steam added to the ODH process. If the carbon dioxide output is below the target, the user may decrease the amount of steam added to the ODH process, if steam has already been added. The target carbon dioxide output level is set depending on the user's requirements. Increasing the added steam will have the additional effect of increasing the amount of acetic acid and other by-products produced in the process. Users equipped with processes that cannot separate larger amounts of acetic acid from the output of the ODH may prefer to minimize steam levels, while users desiring methods that consume carbon dioxide may prefer to maximize the amount of steam that can be added. In some embodiments, the amount of steam added to the one or more reactors is up to 60 wt%, preferably about 40 wt%. It should be noted that wt% is used to describe that the amount of steam or other component added as part of the feed is true wt%, meaning that it is the mass flow rate of that component divided by the total mass flow of all feed components multiplied by 100. This is different from using wt% to describe product selectivity.

The effect of steam addition on carbon dioxide output is more pronounced at lower temperatures. The carbon dioxide selectivity can vary from 1 wt% to 20 wt% at temperatures ranging from 300 ℃ to 340 ℃, depending on the variation of the steam added to the reaction. At higher temperatures ranging from 350 ℃ to 425 ℃, the carbon dioxide selectivity varied from 0.25 wt% to 1.5%.

In some embodiments, when the reaction temperature is less than 340 ℃, varying the amount of steam added to the reactor by at least 20 wt% results in a change in carbon dioxide output of at least 1 wt%, as measured by normalized product selectivity.

In some embodiments, when the reaction temperature is less than 340 ℃, changing the amount of steam added to the reactor by at least 30wt% results in a change in carbon dioxide selectivity of at least 2.5 wt%.

In some embodiments, when the reaction temperature is less than 340 ℃, changing the amount of steam added to the reactor by at least 40wt% results in a change in carbon dioxide selectivity of at least 7.5 wt%.

In some embodiments, when the reaction temperature is greater than 350 ℃, changing the amount of steam added to the reactor by at least 20 wt% results in a change in carbon dioxide selectivity of at least 0.25 wt%.

In some embodiments, when the reaction temperature is greater than 350 ℃, changing the amount of steam added to the reactor by at least 40wt% results in a change in carbon dioxide selectivity of at least 0.5 wt%.

When two or more reactors are used, the present invention contemplates that the user may choose to control the carbon dioxide output of only one or less than all of the reactors. For example, a user may choose to maximize the carbon dioxide output of an upstream reactor so that higher levels of carbon dioxide may constitute part of the inert diluent for a subsequent reactor. In this case, the addition of steam to the first reactor will be minimized, while in the second reactor, the addition of steam may be maximized to facilitate the use of carbon dioxide as an oxidant. The carbon dioxide produced in the first reactor may act as both an inert diluent and an oxidant in the second reactor. Maximizing upstream carbon dioxide output minimizes the amount of inert diluent that needs to be added to the stream before the next reactor.

No steam need be added to the ODH process as it is only one of many alternatives to an inert diluent. For processes without steam addition, carbon dioxide output is maximized under the conditions used with respect to ethane, oxygen, and inert diluent inputs. Then reducing the carbon dioxide output is the source of the steam addition to the reaction until the carbon dioxide output drops to the desired level. In embodiments of the invention where oxidative dehydrogenation conditions do not include the addition of steam, and the carbon dioxide output is above a desired target level of carbon dioxide, steam can be introduced into the reactor while keeping constant the relative amounts of the primary reactants and inert diluents-lower alkanes, oxygen, and inert diluents-added to the reactor, and the carbon dioxide output monitored, increasing the amount of steam until the carbon dioxide is reduced to the target level.

In the case where carbon dioxide is not added as a diluent, it is not possible to produce a negative carbon dioxide process. However, the carbon dioxide neutral process can be achieved by increasing the added steam so that any carbon dioxide produced in the oxidative dehydrogenation process can subsequently be used as an oxidant so that there is no net production of carbon dioxide. Conversely, if the user desires a net positive carbon dioxide output, the amount of steam added to the process can be reduced or eliminated to maximize carbon dioxide production. As carbon dioxide levels increase, there is a potential to reduce oxygen consumption as carbon dioxide competes as an oxidant. The skilled person will appreciate that the use of steam to increase the extent of carbon dioxide as an oxidant may affect oxygen consumption. This means that the user can optimize the reaction conditions with a lower oxygen contribution, which can help to keep the mixture outside the flammability limit.

Oxygen/ethane relative volume ratio

Addition of oxygen in ODH process: the relative volume ratio of ethane can also affect the extent to which carbon dioxide acts as an oxidant. Increasing the amount of oxygen added relative to the amount of ethane added reduces the carbon dioxide selectivity. The degree to which the carbon dioxide selectivity changes depends on the oxygen added to the reactor: a change in the relative volume ratio of ethane, and whether an inert diluent is included in the input stream. In the absence of inert diluents, the effect is more pronounced, in order to makeFor all reasons, this will limit the amount of oxygen added to not more than 30 vol%, preferably not more than 20 vol%, in the absence of diluent. It is conceivable to use higher vol% O₂However, in order to remain outside the flammability limit, the amount of ethane would be limited to a level below about 3 vol%.

Oxygen: the ethane relative volume ratio is determined by dividing the volume% of oxygen fed to the ODH process by the volume% of ethane added. For example, a gas mixture consisting of 20 vol% oxygen, 40 vol% inert diluent and 40 vol% carbon dioxide has an oxygen: ethane relative volume ratio was 0.5. In embodiments where no inert diluent is present, the ratio of oxygen: the ethane relative volume ratio preferably falls between 0.1 and 0.45. In embodiments where an inert diluent is present, the ratio of oxygen: the ethane ratio may range from 0.1 to 2.0.

Changing oxygen: the ethane ratio can be achieved by keeping the vol% of oxygen or ethane constant, then decreasing or increasing the vol% of oxygen or ethane, then increasing or decreasing the vol% of inert diluent added to the process in equal amounts. In some embodiments, vol% of the added oxygen is kept constant while adjusting the vol% of ethane, correspondingly adjusting the vol% of the added inert diluent. When air is used as the oxygen source, vol% is adjusted to reflect an air composition where oxygen is-21 vol% and nitrogen is about-78%. The contribution of nitrogen will be used to calculate the vol% of inert diluent added to the reaction.

In some embodiments, the oxygen: the ethane relative volume ratio can be performed by decreasing the vol% of oxygen or ethane and increasing one of the unreduced oxygen and ethane by a similar vol% while keeping the vol% of the added inert diluent constant.

In some embodiments, the amount of oxygen added is about 20 vol% while the amount of ethane added ranges from 80vol% to 15vol%, and the corresponding range of inert diluent added to the ODH process ranges from 0 to 65 vol%. Within these ranges, oxygen: the ethane relative volume ratio ranges from 0.25 to about 1.33.

In some embodiments, the amount of inert diluent added to the ODH process is from about 40 vol% to about 55vol%, and the ratio of oxygen: the ethane ratio was about 0.30.

Varying the oxygen added to the ODH process: the effect of ethane relative volume ratio on carbon dioxide output, measured as carbon dioxide selectivity, can be a change in carbon dioxide selectivity of up to 5 wt%. In some embodiments, the change in carbon dioxide selectivity is about 2.5 wt%. In other embodiments, the change in carbon dioxide selectivity is about 1.0 wt%.

Negative carbon dioxide

One aspect of the invention is the ability of the operator to adjust the conditions to promote carbon dioxide oxidation so that the overall process is carbon dioxide neutral or even carbon dioxide negative. By including carbon dioxide as or as part of the inert diluent, a net negative carbon dioxide process can follow. This will allow the use of carbon dioxide captured from a process for producing carbon dioxide, thereby minimizing the need to burn or convert the captured carbon dioxide. For example, an ODH process for ethane produces a product stream comprising unreacted ethane, ethylene, water, and one or more of carbon dioxide, acetic acid, and carbon monoxide. A wide variety of products need to be separated downstream of the reactor. Acetic acid and water are removed using a quench tower, while carbon dioxide may be removed by a combination of an amine wash tower and an alkaline treatment tower. The remaining ethane and ethylene can be separated using a separator so that ethane can be recycled to the ODH reactor and relatively pure ethylene can be used for downstream applications, most notably polymerizations using any known catalyst to make polyethylene. For example, the ethylene produced can be used to prepare Low Density Polyethylene (LDPE), Linear Low Density Polyethylene (LLDPE), High Density Polyethylene (HDPE), and minimum density products, elastomers and plastomers using methods known in the art.

The carbon dioxide removed by the amine scrubber is typically burned off, resulting in the emission of greenhouse gases. In the present invention, carbon dioxide may be used as an inert diluent in the ODH process, with the amount of steam added and the oxygen added being adjusted accordingly: ethane to volume ratio to promote oxidation of the added carbon dioxide. In some embodiments, captured carbon dioxide from an ODH process separation sequence is used as an inert diluent, and the amount of steam added to the ODH process is adjusted such that the carbon dioxide output is neutral or negative. Those skilled in the art will appreciate that operation under negative carbon dioxide conditions cannot continue indefinitely without an external supply of carbon dioxide. When the supply of captured carbon dioxide is near zero, the operator may reduce the amount of steam added if the ODH method is carbon dioxide neutral.

In some embodiments, the present invention contemplates a continuous negative carbon dioxide process, wherein the carbon dioxide is supplied by an industrial process such as thermal cracking. In this case, there is an opportunity to reduce the amount of carbon dioxide that must be burned under normal operating conditions of the industrial process. In this embodiment, the operator varies the amount of steam added to the reaction and the oxygen added to the reactor: ethane relative volume ratio is maximized to reduce carbon dioxide selectivity so that the added carbon dioxide added from the industrial process is almost completely consumed.