Preparation of cyano-containing compounds

Abstract

In a process for producing a cyano-containing compound, ammonia, an oxygen source, and an organic compound are reacted in an ammoxidation reactor to produce a reaction product comprising a target cyano-containing compound selected from the group consisting of hydrogen cyanide and an organic nitrile compound. The reaction product is fed to a separation section to recover at least a portion of the target compound. A waste stream comprising at least one further organic nitrile compound different from the target compound is combined with at least one organic oxygenate diluent compatible with the ammoxidation reaction to produce a diluted waste stream, and the diluted waste stream is fed to the ammoxidation reactor.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims U.S. Provisional Patent Application Serial No. 63 / 419352, filed on October 26, 2022, entitled “PRODUCTION OF CYANO-CONTAINING COMPOUNDS,” the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0002] The present invention relates to the preparation of cyano-containing compounds, in particular hydrogen cyanide and organic nitriles, and in particular to the preparation of cyano-containing compounds with increased yields and / or reduced nitrogen oxides [NO x ] emission methods for preparing such compounds. Background Art

[0003] A widely practiced method for preparing cyano compounds is "ammoxidation", in which C 1 Hydrocarbon, C 3 Hydrocarbons, alcohols, carboxylic acids, ketones, low molecular weight polyols, tetrahydrofuran and other organic compounds undergo chemical transformations in the presence of ammonia and an oxygen source to form hydrogen cyanide [HCN] and / or other organic nitrile compounds. Well-known examples include the SOHIO ammoxidation process for converting propylene or propane to acrylonitrile and the Andrussow process, in which HCN is formed from methane (natural gas), ammonia and an oxygen source.

[0004] In the process of preparing any given target cyano compound by ammoxidation, several byproduct organic nitriles, referred to as "ON byproducts", are inevitably produced. For example, in addition to acrylonitrile and HCN, the SOHIO ammoxidation process also produces acetonitrile and propionitrile. It is known and observed in the industry that such ON byproducts can cause equipment scaling, plugging, corrosion and foaming due to degradation / polymerization, particularly in the product separation and recovery section. All of these complicate the product recovery / separation process. In addition, unless removed, these ON byproducts can be carried into the final product as undesirable impurities.

[0005] The problem of ON byproduct accumulation in nitrile fractionation equipment is usually solved by allowing ON to accumulate in a determined tray (plate) or section in the fractionation tower. The ON is then periodically removed from the tray (plate) or section and burned as a fuel or processed in a thermal oxidizer. The problem is that this reduces the value of the ON stream to a fuel value. The thermal oxidation of such nitrogen-containing purge streams also results in an increase in nitrogen oxide [NOx] emissions to the environment. Although it is desirable to recycle these purged ON into the process feed, nitrile preparation facilities are not designed for a wide range of changes in process feed composition.

[0006]

[0006] Thus, there remains an industry need to develop improved large-scale nitrile production processes that treat organic nitrile by-product streams in a manner that increases their value while reducing or even eliminating nitrogen oxide [NOx] emissions generated therefrom. Summary of the invention

[0007] According to the present disclosure, it has been discovered that by combining the ON byproduct removed from the separation system of an ammonia oxidation process with an oxygenate diluent, the byproduct can be recycled to the process while maintaining stable operating control, thereby increasing the value of the byproduct stream while reducing NO x emission.

[0008] Therefore, in one aspect, the present application provides a method for preparing a cyano-containing compound, the method comprising the following steps:

[0009] (a) reacting ammonia, an oxygen source, and an organic compound in an ammoxidation reactor to produce a reaction product comprising a target cyano-containing compound selected from hydrogen cyanide and an organic nitrile compound;

[0010] (b) supplying the reaction product to a separation section to recover at least a portion of the target compound;

[0011] (c) providing a waste stream comprising at least one additional organonitrile compound different from the target compound;

[0012] (d) combining at least a portion of the waste stream with at least one organic oxygenate diluent that is compatible with the ammoxidation reaction to produce a diluted waste stream; and

[0013] (e) feeding the diluted waste stream to an ammonia oxidation reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a schematic diagram of a conventional integrated production facility 100 for producing acrylonitrile [acrylonitrile] and HCN.

[0015] Figure 2 is a schematic diagram of a combined production facility 200 for producing acrylonitrile [ACRN] and HCN according to a first embodiment of the present disclosure.

[0016] Figure 3 is a schematic diagram of a combined production facility 300 for producing acrylonitrile [ACRN] and HCN according to a second embodiment of the present disclosure.

[0017] Figure 4 is a schematic diagram of a production facility 400 for producing acrylonitrile [ACRN] according to a third embodiment of the present disclosure.

[0018] It should be noted that in all of the figures herein, there are many details surrounding the various flow lines [process, utility, bypass, vent, purge, sampling], instrumentation, controls, pumps, valves, etc., which are known to those skilled in the art and are therefore not shown. DETAILED DESCRIPTION

[0019] As used herein, the terms "Acrylo" or "ACRN" refer to acrylonitrile and are used interchangeably.

[0020] As used herein, the terms "Aceto" or "ACN" refer to acetonitrile and are used interchangeably.

[0021] As used herein, the term "HCN" refers to hydrogen cyanide.

[0022] As used herein, the term "target compound" refers to a specific cyano compound selected from hydrogen cyanide and an organic nitrile compound that is desired to be prepared by the method described herein. Examples of target compounds for industrial use may include, but are not limited to, hydrogen cyanide and C 1 -C 6 Nitriles and dinitriles, such as acetonitrile, acrylonitrile, succinonitrile, adiponitrile, methylglutaronitrile, pentenenitrile and glutaronitrile.

[0023] As referred to herein, the term "nitrile production process" or "nitrile production facility" refers to a chemical production process or facility that makes useful nitriles. Non-limiting examples of nitrile production processes are the Andrussow HCN process, the BMA (Degussa) HCN process, the Shawinigan HCN process, the methanol ammoxidation to HCN process; the ethanol ammoxidation to acetonitrile process, succinonitrile from heterocyclic materials [e.g., tetrahydrofuran], the ammoxidation of glycerol to nitrile, the ammoxidation of propylene and / or propane acrylonitrile, the ammoxidation of acrylonitrile with a methanol co-feed to produce additional HCN.

[0024] As used herein, the term "ammoxidation" refers to a well-known chemical synthesis step in which C 1 Hydrocarbon, C 3 Hydrocarbons, alcohols, carboxylic acids, ketones, low molecular weight polyols [glycerol], tetrahydrofuran [THF], acetonitrile, etc., undergo chemical transformation in the presence of ammonia and an oxygen source to form nitriles (represented by the functional group "-C≡N" or "-CN").

[0025] As used herein, the term "Andrussow" refers to a well-known chemical synthesis step in which HCN is formed from methane (natural gas), ammonia, and an oxygen source. Depending on the oxygen content, the Andrussow process can be labeled as an air-Andrussow process, an Andrussow of rich air or oxygen-enriched air, or a 100% oxygen feed Andrussow process.

[0026] As used herein, interchangeable terms " containing organic nitrile waste stream " or " organic nitrile by-product stream " or " by-product ON " refer to one or more streams that comprise the nitrile organic component that is different from target compound, and these nitrile organic components are considered to the undesirable impurity that will be removed from nitrile method.In some embodiments, organic nitrile impurity has a molecular weight higher than target cyano compound, such as at least high 10%.Certainly, it should be appreciated that the organic nitrile that may be the target compound of desire in a method may be considered to undesirable by product in another method.

[0027] In one embodiment, an organic nitrile-containing waste stream may be obtained from a dinitrile production facility. Additional ON components present in such waste streams may include, but are not limited to, unsaturated or saturated C 3 -C 4 Nitriles and dinitriles, linear or branched pentenenitriles, 2-methylglutaronitrile (MGN), methyleneglutaronitrile, ethylsuccinonitrile (ESN), and adiponitrile (ADN), to name a few. Such organic nitrile-containing waste streams can be concentrated from the adiponitrile recovery / purification step and used in accordance with the present disclosure.

[0028] In the preparation of acrylonitrile, undesirable by-products ON include hydrogen cyanide, acetonitrile, propionitrile, methacrylonitrile, nitrile dimers, trimers and oligomers, butyronitrile, 6-aminocapronitrile, 4-amino-2-methyl-5,6-trimethylenepyrimidine, cyclic nitriles and polymers of acrylonitrile.

[0029] In the production of HCN, undesirable by-products ON include acetonitrile, propionitrile, acrylonitrile, hemiconitrile, nitrile dimers, trimers and oligomers, and butyronitrile.

[0030] Table 1 provides a list of potentially undesirable by-products ON, depending on the desired target product produced by conventional manufacturing processes.

[0031] Table 1: Undesirable ON generated in various nitrile preparation processes

[0032]

[0033] As shown in the last row of Table 1, the undesirable byproduct ON generated in the process of making polymers from bio-derived C5 diamine [pentamethylene diamine] can be used in the disclosed process.

[0034] In conventional ammoxidation processes, these by-product ON are carried through the product recovery / separation / purification steps and accumulate / concentrate in downstream refining equipment (recovery-separation columns, HCN product refining trains, decanters, etc.). In addition, by-product ON is often unsaturated or otherwise self-polymerizes (forming monomers, dimers, trimers, etc.) and tends to increase in molecular weight under separation conditions.

[0035] The conventional way to manage / control these byproduct ON is to take a purge stream from the appropriate location where these ON are most concentrated and remove them from the process. Usually this purge is discontinuous to minimize the loss of useful products. This practice leads to accumulation of intermediate boiling ON, affecting unit performance.

[0036] The above-mentioned organic nitrile purge stream obtained from the nitrile process is removed via waste gas and / or processed as a concentrated liquid stream. The most common method for processing such organic purge streams is thermal destruction in a thermal oxidizer [TO]. Thermal destruction of such nitrogen-containing purge streams is disadvantageous not only because it reduces the value of the stream, but also potentially leads to increased nitrogen oxides [NOx] emissions to the environment.

[0037] In order to solve this problem, the present disclosure provides a method for preparing a cyano compound selected from hydrogen cyanide and an organic nitrile compound, wherein ammonia, an oxygen source and an organic compound are reacted in an ammoxidation reactor to prepare a reaction product comprising a target cyano compound. The reaction product is then supplied to a separation section, where at least a portion of the target compound is recovered. A waste stream comprising at least one other organic nitrile compound different from the target compound is combined with at least one organic oxygen-containing compound diluent compatible with the ammoxidation reaction to produce a diluted waste stream, and the diluted waste stream is supplied to the ammoxidation reactor. Generally speaking, the waste stream will include a stream containing organic nitrile byproducts removed from a separation system for recovering the target cyano compound. However, in some embodiments, at least a portion of the waste stream may be supplied by a source different from a separation system for recovering the target cyano compound.

[0038] The organic compound fed to the ammoxidation reactor will depend on the target cyano compound to be prepared. For example, when the target compound is HCN, the organic compound fed to the ammoxidation reactor can be methane, and when the target compound is acrylonitrile or acetonitrile, the organic compound can be propylene and / or propane. Other suitable organic compounds are well known to those of ordinary skill in the art. However, for conventional nitrile preparation methods, it is usually important that the organic feed compound has high purity, such as compared with at least chemical grade propylene (92 wt %-95 wt % pure) in the preparation of acrylonitrile with the refining grade propylene (65 wt %-75 wt % pure). This is necessary, because high levels of impurities in the organic feed increase the generation of undesirable organic nitrile by-products, which destroy the acrylonitrile product separation operation, reduce product quality, and produce the NOx level of increase. On the contrary, by recycling the organic nitrile by-product to the ammoxidation reactor, the disclosed method can accept organic feeds or blends of different grades [as available] of lower purity, while realizing the environmental benefits obtained from NOx reduction. Thus, it is not necessary to use expensive and cumbersome feed purification processes to reduce the impurity levels in the organic feed. Similarly, lower purity oxygen and ammonia feeds are also acceptable.

[0039] Non-limiting examples of suitable diluents for use in the process of the present invention include C 1 -C 4 Alcohols (methanol, ethanol, propanol, butanol); C 1 -C 4 Carboxylic acids (formic acid, acetic acid, propionic acid) and their salts (ammonium, amines); C 2 -C 4 Ketones (acetone, methyl isobutyl ketone); low molecular weight polyols (glycerol); certain cyclic ethers (tetrahydrofuran) and mixtures thereof. It is desirable to use a diluent that is chemically compatible with the nitrile purge stream components, has good solubility characteristics for these purge stream components, and is acceptable in the ammoxidation reaction chemistry.

[0040] Pure alcohol, crude alcohol or alcohol mixtures can be used for dilution purposes. Bio-based alcohols, such as biomethanol, bioethanol, biopropanol and biobutanol, alcohols and glycerol from renewable raw materials and sustainable methods, etc. are suitable feeds for dilution of nitrile waste streams. Renewable raw materials suitable for biochemical production may include biomass, lignocellulosic materials, corn, sugar cane, organic municipal waste streams, etc. Sustainable production methods may include aerobic / anaerobic digestion, fermentation, enzymatic conversion, etc.

[0041] The ratio of diluent to waste stream is not critical, but may typically be 0.01:1.0 to ≤80:1.0, such as 0.05:1.0 to 70:1.0, e.g. 0.1:1.0 to 50:1.0, all based on mass. In one embodiment, the diluent is an alcohol and the alcohol stream is 1 kg / hr per kg / hr waste stream, or 5 kg / hr per kg / hr waste stream, or 10 kg / hr per kg / hr waste stream, or 20 kg / hr per kg / hr waste stream.

[0042] Typically, the amount of waste stream recycled back to the ammoxidation reactor does not exceed 10 wt %, such as does not exceed 5 wt %, for example does not exceed 2 wt %, of the total fresh feed to the nitrile synthesis reaction zone.

[0043] Generally, a certain level of scavenging of the byproducts of the ammoxidation process is advantageous in order to avoid excessive accumulation of non-reactive species (potentially including nitrogen-containing species). However, by diluting and recycling a portion of the organonitrile byproduct, the NO produced by the scavenging step can be reduced. x The amount of ammonia can be reduced to at least 50% less, such as at least 75% less, than an equivalent ammonia oxidation process for producing the same target compound but without dilution and recycle.

[0044] With reference to the accompanying drawings, Figure 11 is a schematic diagram of a conventional integrated manufacturing facility 100 for producing acrylonitrile [acrylonitrile] and HCN. Further details of this facility can be found in U.S. Pat. No. 10,647,663, the entire contents of which are incorporated herein by reference. In facility 100, an ammoxidation reactor system 101 converts C 3 Hydrocarbons (stream 1), such as propylene or propane, are catalytically converted to ACRN. The ammoxidation reactor system 101 may include feed delivery / premixing / preheating / distribution, catalytic reaction zones, cyclone separators, and other auxiliary subsystems fully described in the available ammoxidation literature.

[0045] The catalytic reaction zone in the ammoxidation system 101 produces a hot gaseous effluent (stream 4) rich in acrylonitrile and byproducts acetonitrile, HCN, propionitrile, etc. In addition to the ammoxidation reactor system 101, a crude HCN product stream 8 can be produced in a separate HCN synthesis reactor system 201 by a catalytic reaction between methane (stream 5), ammonia (stream 6), and an oxygen-containing source (stream 7). Other examples of HCN synthesis can include methanol ammoxidation and the conversion of acetonitrile to HCN ( Figure 1 Such HCN synthesis can be carried out continuously or intermittently, depending on the demand for HCN product.

[0046] The ammonia feed (stream 2) of the ammonia oxidation reactor system 101 and the ammonia feed (stream 6) of the HCN synthesis reactor system 201 can be supplied by the same ammonia source, or each can have its own dedicated source and impurity control. Similarly, the oxygen-containing feed (stream 3) of the ammonia oxidation reactor system 101 and the oxygen-containing feed (stream 7) of the HCN synthesis reactor system 201 can be supplied by the same oxygen source, or each can have its own dedicated source. For example, in the case of using air, oxygen-enriched air, or a 100% oxygen process in the HCN synthesis reactor system 201, the oxygen-containing source can be different.

[0047] The crude HCN product stream 8 is directed to the quench tower 301 via stream 10 together with the ammoxidation reactor gaseous stream 4. The two streams 4 and 10 can be combined or fed separately to the quench tower 301. Figure 1 As shown, the crude HCN product stream 8 can also be partially directed to the ammoxidation reactor system 101 as stream 11 by adjusting the flow control valve device 501. The use of the directed stream 11 having the inherent components of the ACRN production process supplements and saves the inert gas required for the fluidization of the catalyst in 101. Depending on the relationship between the degree of fluidization in 101 and the throughput load, the flow control valve device 501 can be adjusted to split the crude HCN product stream 8 into its directed partial stream 11 to the system 101, while returning the remaining partial stream 10 to the quenching system 301.

[0048] Both the ammoxidation reactor effluent (stream 4) and the crude HCN product (stream 10) contain unconverted excess ammonia, which is removed before the product is recovered and purified. The ammoxidation reactor effluent (stream 4) is treated with a quench liquid (stream 12) in a countercurrent quench tower system 301 along with the crude HCN product (stream 10) to remove excess ammonia. The quench liquid is acidic (low pH) so that excess ammonia is effectively washed out of the reactor effluent. An organic or inorganic acid (such as sulfuric acid or phosphoric acid) is used to remove ammonia (stream 15) as a soluble ammonium salt at the bottom of the quench tower. The flow rate and acidity of the quench liquid (stream 12) are adjusted so that the combined ammonia enters the quench tower via streams 4 and 10. Excess ammonia is removed from the tower 301 as an ammonium salt via stream 15.

[0049] The ammonia-depleted quench product gas (stream 14) is then passed to a countercurrent absorber system 401, where an absorbent liquid (stream 16) extracts the reactor product (stream 17) at the bottom, while any non-condensable and non-absorbable components are discharged as waste gas (stream 18). No ammonium salt formation is observed, so there is no solid plugging at the bottom of the absorber system 401.

[0050] The crude product stream (17) is further processed in the downstream nitrile recovery and purification section 701 to produce high purity ACRN and byproducts acetonitrile and HCN. The nitrile recovery and purification section 701 includes a continuous distillation and phase separation unit operation equipped with all necessary auxiliary condensers, reboilers, recycles, pump cycles, flow lines, etc. The nitrile recovery and purification section 701 is well described in the available literature for acrylonitrile, acetonitrile and HCN, and is therefore not described in detail herein. The output from section 701, stream 51, is shown together to represent the individual product streams of purified HCN, acetonitrile and acrylonitrile. It should be understood that the product HCN, acetonitrile and acrylonitrile are separated and purified to their desired purity in different subsections (not shown) of the nitrile recovery and purification system 701. For example, dried pure HCN (suppressed) is recovered from the HCN head / drying subsection, while the acetonitrile product is recovered from the acetonitrile refining subsection, and so on.

[0051] During the nitrile recovery and purification section 701 operation of this example, a large amount of undesirable organic nitrile [ON] impurity streams are produced. These mid-boiling and intermediate boiling organic nitrile impurities must be removed from the method, otherwise they may accumulate in the final product. The impurity removal stream or the set of such streams (represented by stream 21) are taken out from several positions where they are most concentrated in the system 701 continuously or intermittently. The removal of this removal stream 21 is needed to maintain stable ON impurity balance and prevent such undesirable impurity from accumulating in the method, and finally accumulate in the final product.

[0052] The undesirable organic nitrile impurity purge stream 21 collected in the above process is removed via an off-gas and / or liquid concentrate stream. The nitrile purge stream 21 is fed to a recovery / processing section 801 where any recoverable products of interest are stripped and returned to the process as stream 43. The residual stream 53 from section 801 then undergoes thermal destruction in a thermal oxidizer [TO] in section 901. Thermal destruction of these highly concentrated nitrogen-containing impurity purge streams results in increased nitrogen oxide [NOx] emissions to the environment and is Figure 1 The exhaust gas flow 57 is represented.

[0053] Figure 2 is a schematic diagram of a combined production facility 200 for producing acrylonitrile [ACRN] and HCN according to a first embodiment of the present disclosure. The construction and operation of the HCN-ACRN combined production facility 200 are similar to Figure 1 The facility described in , except that the treatment sections 801 and 901 are omitted, and the waste stream 23 containing the undesirable organic nitrile impurities is removed from the nitrile recovery and purification section 701 and recycled to the ammoxidation reactor system 101 as a recycle stream 25. A separate stream 55 containing undesirable organic nitrile materials [ON] from another production facility can be introduced and combined in this cycle. For example, an undesirable ON purge stream from an olefin hydrocyanation process for the preparation of adiponitrile and containing butenenitrile, linear or branched pentenenitriles, glutaronitrile, valeronitrile, succinonitrile or other undesirable ON purge streams may be eligible to be combined in the recycle back to the reactor 101.

[0054] The organic nitrile components present in stream 23, mainly trace amounts of HCN, acetonitrile, acrylonitrile, propionitrile, etc., are inherent to the ammoxidation process. It was unexpectedly observed that these components undergo further chemical transformation under the ammoxidation process conditions in 101, thereby reusing the nitrogen contained in stream 25. Therefore, the useful product yield is increased by this redirection of the nitrogen-containing stream 25.

[0055] The organic nitrile waste stream 23 can be fed continuously or can be stored in an intermediate storage vessel ( Figure 2 The feed stream 25 may be mixed with an oxygenate diluent and delivered to the ammonia oxidation reactor system 101. If needed or desired, such as during throughput transitions, load changes, maintenance, etc., a small portion (e.g., less than 5%, less than 10%, or less than 15%) of stream 23 may be diverted to the thermal oxidation system. However, in most cases, no undesirable ON species are fed to the thermal oxidation system [with Figure 1 The opposite is shown].

[0056] Figure 3is a schematic diagram of a combined production facility 300 for producing acrylonitrile [ACRN] and HCN according to a second embodiment of the present disclosure. The construction and operation of the HCN-ACRN combined production facility 300 are similar to Figure 2 The facility described in the above description is different in that the organic nitrile waste stream 23 from the system 701 is partially or completely transferred to the holding / blending system 601 as stream 27. An oxygenate diluent stream 31 comprising an alcohol such as methanol, ethanol, propanol, butanol or a mixture thereof is introduced into the holding / blending system 601 to blend with and dilute the undesirable organic nitrile purge stream 27. The resulting diluted alcohol-organic nitrile stream 29 is fed as stream 25 to the ammoxidation reactor system 101.

[0057] A separate stream 61 containing undesirable organic nitrile materials [ON] from another preparation facility can be introduced and merged in this circulation. For example, an undesirable ON purge stream from an olefin hydrocyanation process for the preparation of adiponitrile and containing butenenitrile, straight or branched pentenenitrile, valeronitrile, glutaronitrile, succinonitrile or other undesirable ON purge streams can be qualified to merge in the recycle back reactor. Similarly, if it is necessary to dilute such waste streams easily for fluidity and handling, a separate stream 71 containing undesirable organic nitrile materials [ON] from another preparation facility can be introduced before dilution.

[0058] Alcohol adds and makes undesirable organic nitrile removal flow homogenization, and helps this flow to flow freely between equipment and not cause pipeline clogging or obstruction.Alcohol will also participate in ammoxidation chemistry usually, for example, methanol helps HCN, and ethanol helps acetonitrile.Although there is no restriction for using how much alcohol to add / dilution, the operating conditions, throughput rate and cost considerations of ammoxidation reactor system 101 determine the ratio of dilution alcohol and waste stream.

[0059] Figure 4 is a schematic diagram of an independent production facility 400 for producing acrylonitrile [ACRN] according to a third embodiment of the present disclosure. The construction and operation of the facility 400 are similar to Figure 3 The facility described in , difference is to omit HCN synthesis reactor system 201 and auxiliary equipment and method stream thereof.Again, nitrile waste stream 23 is directed back to ammoxidation process unit 101, undiluted or using suitable diluent to dilute via keeping / blending system 601.Due to the fact that nitrile removal stream is not damaged by heat, NOx emission is significantly reduced or even eliminated.On the contrary, it is fed back to ammoxidation reactor 101 to improve useful product yield.

[0060] A separate stream 65 containing undesirable organic nitrile materials [ON] from another preparation facility can be introduced and merged in this circulation. For example, an undesirable ON purge stream from an olefin hydrocyanation process for the preparation of adiponitrile and containing butenenitrile, straight or branched pentenenitrile, valeronitrile, glutaronitrile, succinonitrile or other undesirable ON purge streams can be qualified to merge in the recycle back reactor. Similarly, if it is necessary to dilute this type of purge stream easily for fluidity and processing, a separate stream 75 containing undesirable organic nitrile materials [ON] from another preparation facility can be introduced before dilution.

[0061] Methods of the Invention The present invention will now be described in more detail with reference to the following non-limiting examples.

[0062] Comparative Example 1-

[0063] The organic nitrile impurity removal subsystem is shown in U.S. Pat. No. 10,562,782 [hereinafter referred to as '782] Figure 1 In the '782 embodiment, a nitrile purge stream, labeled (8), is removed from the side stream stripper, labeled (5). It is apparent from the '782 composition data for the nitrile purge stream, labeled (8), that this stream is a concentrated organic nitrile impurity purge stream to be processed after the useful contents have been recovered as the stream labeled (6), which is recycled back to the separation vessel, labeled (1), in '782.

[0064] Thermal destruction of each 1.0 kg / hr of '782 stream (8) using a thermal oxidizer having a destruction efficiency of 99.999% produces approximately 0.0024 g / hr of NOx in Example 1; 0.001 g / hr of NOx in Example 2; and 0.0007 g / hr of NOx in Example 3.

[0065] Thus, in the '782 embodiment, about 100 kg / hr of the nitrile purge stream labeled (8) emits about 0.07 g / hr to 0.24 g / hr of NOx.

[0066] Example 1

[0067] The process of Comparative Example 1 was repeated, but part or all of the purge stream was diluted with an organic oxygenate diluent and recycled to the ammoxidation reactor. As a result, for each kg / hr of nitrile purge stream, up to 0.0024 g / hr of NOx emitted to the environment was eliminated.

Claims

1. A method for preparing a cyano compound, the method comprising: The following steps are involved: (a) reacting ammonia, an oxygen source, and an organic compound in an ammoxidation reactor to produce a reaction product comprising a target cyano-containing compound selected from hydrogen cyanide and an organic nitrile compound; (b) supplying the reaction product to a separation section to recover at least part of the target compound; (c) providing a waste stream comprising at least one additional organonitrile compound different from said target compound; (d) combining at least a portion of the waste stream with at least one organic oxygenate diluent compatible with the ammoxidation reaction to produce a diluted waste stream; as well as (e) feeding the diluted waste stream to the ammonia oxidation reactor.

2. The process of claim 1, wherein at least a portion of the waste stream is removed from a separation system used to recover the target cyano-containing compound.

3. The process of claim 2 and further comprising removing a portion of the product stream by a thermal oxidizer, wherein the NO from the removal step is x The yield is at least 50% less than an equivalent ammoxidation process for preparing the target compound but omitting steps (c), (d) and (e).

4. A process according to any preceding claim, wherein the separation section is supplied with reaction products from two or more ammoxidation reactors, the two or more ammoxidation reactors producing different target cyano-containing compounds each selected from hydrogen cyanide and organic nitrile compounds.

5. A process according to any preceding claim, wherein the target cyano-containing compound is selected from the group consisting of hydrogen cyanide, acetonitrile, acrylonitrile, succinonitrile, linear pentenenitriles, branched pentenenitriles and adiponitrile.

6. A method according to any preceding claim, wherein at least part of the waste stream is supplied from a source different from the separation system used to recover the target cyano-containing compound.

7. The method according to any preceding claim, wherein the diluent is selected from the group consisting of: C 1 -C 4 Alcohols and polyols, C 1 -C 4 Carboxylic acids and their salts, C 2 -C 4 Ketone, C 2 -C 6 Ethers and mixtures thereof.

8. The method according to any preceding claim, wherein the diluent comprises C selected from the group consisting of methanol, ethanol, propanol, butanol and mixtures thereof. 1 -C 4 alcohol.

9. The method according to any preceding claim, wherein the diluent comprises C selected from the group consisting of formic acid, acetic acid, propionic acid, ammonium salts, amine salts and mixtures thereof. 1 -C 4 Carboxylic acid or salt.

10. The method according to any preceding claim, wherein the diluent comprises C selected from the group consisting of acetone, methyl isobutyl ketone and mixtures thereof. 2 -C 4 ketone.

11. A process according to any preceding claim, wherein the diluent comprises tetrahydrofuran.

12. A method according to any preceding claim, wherein the diluent comprises glycerol.

13. A method according to any preceding claim, wherein the diluent comprises a bio-based organic oxygenate obtained from a renewable feedstock.

14. The method of claim 13, wherein the diluent comprises biomethanol, bioethanol, biopropanol, biobutanol, bioglycerol or a mixture thereof.

15. A process according to any preceding claim, wherein the weight ratio of diluent to waste stream is from 0.01 :1.0 to 80:1.

0.

16. A process according to any preceding claim, wherein the weight ratio of diluent to waste stream is from 0.05:1.0 to 70:1.

0.

17. A process according to any preceding claim, wherein the weight ratio of diluent to waste stream is from 0.1 :1.0 to 50:1.

0.

18. A process according to any preceding claim, wherein the process is operated without feed pre-treatment to reduce impurity levels.

19. A process according to any preceding claim, wherein the feed is selected from oxygen and ammonia.

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