HK1151761A - Process for improving adiponitrile quality - Google Patents

Description

Method for improving adiponitrile quality

Technical Field

The present invention relates to a method and apparatus for improving the quality of Adiponitrile (ADN). The invention particularly relates to treating ADN with ozone to react with harmful trace impurities present in the ADN (or to remove such impurities from the ADN) that have an adverse effect on the hydrogenation of ADN to form 6-Aminocapronitrile (ACN) and Hexamethylenediamine (HMD) that are subsequently used in the production of nylon polymers.

Background

It is known in the art that nylons such as nylon 66 can be prepared in a multi-step process. In the first step, Butadiene (BD) is hydrocyanated with Hydrogen Cyanide (HCN) in the presence of a homogeneous nickel catalyst to produce Adiponitrile (ADN). Subsequently, organic impurities are removed from the ADN to produce refined ADN. Suitable methods for removing organic impurities include extraction and distillation. See Ostermaier, U.S. patent 6,331,651, which is incorporated herein by reference. In the next step, the refined ADN is catalytically hydrogenated to produce HMD or a mixture comprising ACN and HMD. Suitable hydrogenation catalysts include iron-based and Raney-type heterogeneous catalysts, such as Raney nickel. In a subsequent step, ACN and HMD are used in the preparation of nylon polymers such as nylon 6 and nylon 66.

ADN produced in this process contains several impurities that may have an adverse effect on the hydrogenation of ADN to form ACN and HMD. The impurities include: phosphorus (III) compounds ("p (III) compounds"); 2-Cyanocyclopentylideneimine (CPI); and tert-butylcatechol (TBC).

The p (iii) compounds are adsorbed on the surface of the heterogeneous catalyst and lead to poisoning and subsequent deactivation of the iron-based catalyst.

During hydrogenation of ADN, CPI is hydrogenated to Aminomethylcyclopentylamine (AMC). AMC is difficult to separate from HMD and results in deterioration of polymer quality when HMD is converted to nylon 66 polymer.

It has been proposed in the past to remove some of these impurities. For example, U.S. patent 6,331,651 ("the' 651 patent") describes ADN containing a p (iii) compound that is treated with air containing greater than 0.1 wt% ozone in a reactor that provides a rapid mass transfer rate, such as a stirred tank equipped with a gas distributor, a tubular reactor equipped with a static mixer, a tank equipped with a jet mixer, or an absorption column. The' 651 patent states that it is believed that the p (iii) compound is converted to a phosphorus compound in the +5 oxidation state by ozone treatment, which is less damaging to the iron-containing hydrogenation catalyst.

Canadian patent 672,712 describes a process for purifying ADN containing impurities that may be produced by several different processes. One of the identified impurities is CPI. The method comprises contacting ADN with gaseous ozone at a temperature between 0 and 110 ℃, preferably 20-50 ℃.

Us patent 6,359,178 discloses a process for the preparation of Hexamethylenediamine (HMD) by hydrogenation of adiponitrile, wherein the ADN recycle stream is purified in a conventional manner, for example by treatment with mineral acids, organic acids, acidic ion exchangers or by treatment with oxidizing agents such as air, ozone or hydrogen peroxide.

USSR patent publication 276033 discusses the purification of ADN by contacting it in a vessel with ozonated air, optionally in the presence of an acid such as phosphoric acid.

Fisher et al, WO 00/03972, discloses the preparation of HMD, wherein the recycling of ADN is cleaned in a known manner, for example by treatment with an inorganic or organic acid, or an oxidizing agent such as air, ozone, hydrogen peroxide or an inorganic or organic peroxide.

Heckle, U.S. patent 4,952,541; yamada et al, U.S. Pat. No. 3,725,459; U.S. patent No. 3,758,545 to pound et al; nishimura et al, U.S. patent 3,803,206, disclose different processes for purifying adiponitrile and acrylonitrile or the reactants used in such processes.

There remains a need for improved methods of using ozone to reduce or eliminate the problems associated with impurities in ADN.

Summary of The Invention

The present invention relates to the use of an efficient, but inexpensive, reactor for storing ozone in a manner that makes the most efficient use of the ozoneA method and apparatus for reacting undesirable trace impurities found in ADN with ozone. This is achieved by the following method: ADN (which is typically refined ADN, as a liquid), which may be referred to hereinafter, and an ozone-containing gas, which may be referred to hereinafter as a PFSMR, are continuously fed to the co-current plug flow static mixer reactor of the present invention, which provides a very rapid and highly selective reaction of ozone with p (iii), CPI, and TBC present in the ADN. It was found that TBC was also adsorbed on the surface of the heterogeneous catalyst, which resulted in catalyst deactivation. It was also found that TBC increases the yield of ADN hydrogenation reaction to the undesirable co-product Hexamethyleneimine (HMI) when an iron catalyst is used in the reaction. Thus, the yield of the desired HMD is significantly reduced. In addition to the above impurities, i.e., P (III), CPI and TBC, a significant amount of the decenedinitrile isomer, referred to herein as DDN (which is C containing a carbon-carbon double bond), is present in the refined ADN₁₀Dinitriles). DDN is hydrogenated to impurities that can be easily separated from HMD and which do not adversely affect hydrogenation catalyst life.

In particular, in one embodiment, the invention relates to a process for reacting at least a portion of the impurities present in purified ADN to less harmful compounds, the process comprising: refined ADN feed and ozone-containing gas are introduced into the PFSMR, and the ADN feed is contacted with the ozone-containing gas in the PFSMR to oxidize at least a portion of the impurities, thereby producing a reactor effluent comprising gas and an ozone-treated ADN liquid comprising unreacted impurities and less harmful impurities. The "less hazardous compound" described herein may also be referred to as a "less hazardous impurity". The reactor effluent is fed to a suitable device, such as a tank, to separate the gas from the liquid. The gas, also referred to as exhaust gas, may be vented to the atmosphere or, if desired, may be vented to a catalytic abatement unit (catalytic abatement unit) to further reduce the ozone content before the exhaust gas is vented to the atmosphere. The degassed liquid containing ozone-treated ADN, unreacted impurities and less harmful impurities is the ozone-treated ADN product, which is then hydrogenated to ACN and HMD. A "less hazardous compound" is a compound that has less of a negative effect on the yield and catalyst life in subsequent ADN hydrogenation process steps than the impurities originally present in the ADN feed. An example of such a less hazardous compound is p (v) formed from p (iii) impurities.

Detailed Description

The PFSMR comprises a static mixer. As known to those skilled in the art, a static mixer, commonly referred to as a static mixer, is an in-line mixing device that includes mixing elements (also referred to as "static mixer elements") inserted over the length of a pipe. There are a variety of component designs available from various manufacturers, but all are stationary in use. The energy for mixing results from the pressure loss caused when the process fluid flows through the mixing element and, in addition to the energy that is usually necessary for pumping, additional pumping energy is necessary. The number of elements required in any application depends on several factors, such as the difficulty of the mixing task. Often, more elements are necessary for difficult tasks. See, Harnby et al, Mixing in the processing industry (Mixing in the Process industries), second edition, Butterworth Heinemann (1992), the entire contents of which are incorporated herein by reference.

The ozone-containing gas comprises ozone and any carrier gas suitable for use in the present invention. Suitable carrier gases are any gas that is substantially inert to the refined ADN at the operating temperatures of the present invention, such as air, air diluted with nitrogen, oxygen-enriched air, nitrogen, carbon dioxide, helium, argon, or a combination of two or more such gases. In one embodiment, the carrier gas is air. The ozone-containing gas can include about 0.1 to about 3.0 wt.% ozone, such as about 1.0 to about 3.0 wt.%, or about 3.0 wt.% ozone.

In one embodiment, the ADN feed may include at least one of the following impurities: 2-Cyanocyclopentylideneimine (CPI), phosphorus (III) compounds (P), (III), decenedinitrile (DDN) or tert-butylcatechol (TBC). The amount of impurities in the ADN feed and in the ozone-treated ADN product can be measured by any suitable method. For example, phosphorus can be determined by inductively coupled plasma mass spectrometry (ICP), and it is believed that all phosphorus present is p (iii). CPI and TBC may be determined by liquid chromatography. DDN can be determined by gas chromatography.

The ADN feed may comprise at least one of: about 0.5 to about 10, such as about 2 to about 10 parts per million (ppm) by weight of P (III), about 10 to about 200, such as about 10 to about 50ppm CPI, about 5 to about 100, such as about 10 to about 50ppm TBC, about 100 to about 600ppm DDN, such as about 200 to about 400ppm DDN, or combinations thereof. In one embodiment, the ADN feed comprises less than 0.1 wt.% of all such impurities: (i.e., P (III), CPI, TBC and DDN).

In one embodiment, the ozone-treated ADN comprises less than 1ppm p (iii), less than 5ppm CPI, and less than 5ppm TBC.

In another embodiment, the amount of ozone supplied to the process is sufficient to react at least about 10 to about 80% of the impurities present in the ADN feed.

In another embodiment, the amount of ozone supplied to the process is sufficient to react at least about 90% of the TBC from the ADN feed. In yet another embodiment, the PFSMR is fed with from about 0.1 to about 4, such as from about 0.1 to about 2 millimoles of ozone per liter of ADN feed.

The ADN feed may be prepared by any suitable method, such as by hydrocyanation of butadiene in the presence of a homogeneous nickel (0) catalyst having a phosphorus-containing ligand. As mentioned above, the ADN used in the process of the invention is typically ADN purified by distillation. The ozone used in the present process can be prepared by any known method. In one embodiment, ozone is produced by passing air through an ozone generator to produce a gas stream containing about 3% by weight ozone.

The process performed in PFSMR utilizes ozone very efficiently. For example, the ozone depletion in the reactor exceeds 99% of the ozone supplied to the reactor. Therefore, the content of unreacted ozone in the exhaust gas is very low. This is very significant and advantageous for environmental reasons. There are severe environmental restrictions on the release of ozone into the atmosphere. The lower the ozone content of the reactor off-gas, the lower the cost of treating the ozone-destroying off-gas prior to discharge into the environment.

Without being bound to any theory, it is believed that ozone reacts very rapidly with all of the impurities listed above that are present in ADN. The reactions are so fast that they are believed to occur substantially entirely in the liquid phase at the gas-liquid interface and can be described as chemically assisted mass transfer control reactions. Although all reactions were fast, some were faster than others. At a certain concentration of impurities, the reaction rate of ozone with the above impurities decreases in the following order: p (III) and CPI > TBC > DDN, where the reaction with DDN is slowest. This means that when all of these components (i.e., impurities) are present at the same time, ozone reacts selectively with these impurities and thus reacts faster with the faster reacting species.

Although ozone reacts slowest with DDN, the concentration of DDN in the feed ADN is typically 4 times higher than the combined concentrations of P (III), CPI and TBC on a molar basis. This means that the amount of ozone that reacts with DDN increases as other impurities are depleted. If it is desired to have the other impurities react completely with the ozone, a significant amount of the ozone may unnecessarily react with the DDN. Any ozone consumed by the DDN is wasted because the DDN is hydrogenated to impurities that are easily separated from the HMD and the DDN has substantially no adverse effect on the hydrogenation catalyst life.

When several different reactions occur in parallel with a single reactant, selectivity to the more reactive species is favored by conducting the reactions in a plug flow configuration. A back-mix configuration, as implemented in a Continuous Stirred Tank (CSTR), or a counter-current configuration, as implemented in an absorption column, results in poor utilization of the ozone reactant, i.e., higher ozone consumption to achieve the same level of conversion of undesirable impurities. Therefore, a co-current plug flow configuration is advantageous for this application.

The reaction that occurs in the PFSMR is very fast and it is believed (without being bound by any feasible theory) that the rate of reaction is controlled by the mass transfer rate of ozone from the gas phase to the liquid phase. High levels of turbulence and large interfacial areas favor high mass transfer. Therefore, a reactor configuration that meets these requirements is needed.

The type of reactor used in the process of the present invention that provides both co-current flow and very high mass transfer rates is a plug flow reactor that includes a static mixer (also referred to herein as a "mixer"). These mixers are sections of pipe that include internal static mixer elements that promote high mass transfer rates. Each segment of pipe may include static mixer elements, or some segments of pipe may not include such static mixer elements. Furthermore, the static mixer elements included in different pipe sections may be the same or different. Other advantages of these static mixer reactors are that they are inexpensive, easy to operate, and require little maintenance. By using such a reactor, the utilization of ozone for the desired reaction is maximized and the reactor cost is low. Example 2 shows the lower ozone depletion obtained with a plug flow reactor relative to a back-mixed tank reactor. For typical impurity levels, ozone depletion is reduced by about 30% compared to a back-mixed reactor.

In addition to providing high reaction rates and ozone selectivity, PFSMR also provides very high ozone conversion compared to back-mixed reactors. The ozone conversion in PFSMR can exceed 99.9% of the ozone in the feed gas. With a properly designed PFSMR, the amount of ozone present in the gas phase exiting the reactor can be reduced to less than 10ppm, which is about 100 times lower than that which can be obtained using a back-mixed reactor. This reduces the size of the environmental abatement equipment (environmental abatement equipment) required to destroy residual ozone in the reactor effluent gas.

In one embodiment, the process of the invention comprises continuously feeding liquid ADN and gaseous air containing about 3 wt.% ozone to the PFSMR. The reactor was run at ambient conditions. The amount of ozone is adjusted to react almost completely with p (iii), CPI and TBC while minimizing the inevitable reaction of ozone with DDN. However, the presence of DDN has the advantage of providing a buffer that consumes any excess ozone fed to the process and eliminates any residual ozone in the exit gas, which alleviates or eliminates the problem of ozone emission into the atmosphere.

The design of a plug flow reactor with static mixer elements, such as the PFSMR of the present invention, involves a number of steps. Step 1 is to determine the amount of ozone required to react with the impurities present; this is determined by the level of impurities present and the reaction stoichiometry. Step 2 is to determine the reactor volume required to produce the appropriate ozone concentration in the exit gas, using appropriate reactor design equations and mass transfer correlations. The book "chemical reaction Engineering, third edition" (incorporated herein by reference) by Octave Levenspiel discusses reactor design equations in chapters 23 and 24. For static mixers that can be used in the present invention, the mass transfer parameter k_La can be derived using proprietary correlations supplied by static mixer suppliers and which are typically between 0.1 and 2 seconds^-1Within (Harnby et al). In step 3, the reactor diameter is selected to provide a suitably high mass transfer rate combined with an acceptable pressure drop across the reactor. Suitably, the pressure drop across the reactor is at least about 1 atmosphere (101.3 kPa). Obtaining a suitable mass transfer rate in the reactor, wherein the mass transfer parameter k_La is about 0.1 second^-1Above, preferably about 0.5 second^-1Above, such as about 0.1 to about 2 seconds^-1. This is done using the vendor correlation of the selected device. Once the reactor volume and diameter are known, the reactor length is determined. Once the reactor length and diameter are determined, a reactor as long as the length of the tube including the internal static mixer elements is purchased from a supplier. Another important parameter is residence time (also referred to as "residence" time). The residence time of the PFSMR used in the present process is from about 2 to about 8 seconds, such as from about 2 to about 4 seconds, for example 2.5 or 3 seconds. The required ozone dosage may be calculated based on the level of impurities in the refined ADN. Adjusting the feed rate of ozone to obtain for a given feedRate and ozone dosage required for impurity levels in the refined ADN liquid. One way to adjust the ozone feed rate is to adjust the concentration of ozone in the ozone-containing gas fed to the PFSMR. The process of the invention is particularly easy to control, since increasing the liquid feed rate simultaneously leads to a reduction in residence time and k_La is increased so that the conversion of ozone remains relatively constant. Decreasing the liquid feed rate while resulting in an increase in residence time and k_La is decreased so that the ozone conversion remains relatively constant. The refined ADN and ozone-containing gas feed to the reactor is operated at a pressure sufficient to overcome the design pressure drop across the reactor as determined in step 3. Typically, the reactor is operated at a temperature of less than 50 ℃, such as ambient temperature. The ozone-containing gas and ADN are fed simultaneously or substantially simultaneously to the reactor inlet, and the reactor effluent is fed to a tank or any other suitable means to separate the gas from the liquid. The gas, including the carrier gas and unreacted ozone, is vented to the atmosphere or, if necessary, to a catalytic abatement unit to further reduce the ozone content prior to venting the exit gas to the atmosphere. The resulting liquid comprising ozone treated ADN, unreacted impurities and less harmful impurities is then reacted with hydrogen to form ACN and HMD.

Example 1

Air was passed through a model SMA 500S Wedeco ozone generator at a rate of 30 standard cubic meters per hour to produce an ozone concentration of 1.0% by weight in the air. The ozone-containing air stream was fed to the PFSMR along with the refined adiponitrile stream. The adiponitrile feed rate was 13.2 metric tons/hour. The static mixer included Sulzer SMV elements. There are a total of six mixing sections, and each section is 6 feet (1.8m) long, providing a total of 36 feet (11m) of static mixer length. Each 6-foot (1.8-m) long section includes six static mixer elements, each of which is 6 inches (15.2cm) long, wherein each of the elements are separated from each other by 6 inches (15.2cm) open pipe, i.e., pipe without static mixer elements. Static mixer diameter 3 inches(7.6 cm). Based on measured performance, mass transfer parameter k_La is calculated to be about 0.7 second^-1. The adiponitrile feed contained 5.7ppm phosphorus in the form of an organic phosphorus containing compound, 31ppm CPI, 2ppm TBC, and 186ppm DDN, where ppm represents parts per million by weight. After ozone treatment, the ozone-treated adiponitrile contained < 1ppm CPI, 2ppm TBC and 130ppm DDN. The concentration of TBC is not significantly reduced because the TBC concentration in the feed is very low and thus its reaction rate is low compared to DDN present in the feed at a much higher (almost 100 times (100X)) concentration in the feed. It is believed that almost all of the CPI is destroyed by ozone and then all of the phosphorus is oxidized from the +3 to +5 oxidation state, as laboratory results show that ozone reacts with CPI and phosphorus at approximately the same rate. The total residence time of the feed in the reactor was 3.7 seconds, while the ozone concentration in the gas leaving the reactor, i.e. air, was 2.5ppm, which corresponds to an ozone conversion of 99.98%.

The ozone-treated ADN was hydrogenated with an iron oxide based catalyst. Based on extensive prior equipment data, ozone treatment was initiated when the ADN hydrogenation catalyst was about half deactivated. After the ozone treatment is started, the catalyst deactivation rate drops to less than half the normal rate, which extends the catalyst life by more than a factor of two.Example 2

This example shows the improved ozone utilization achieved by carrying out the reaction in a Plug Flow Reactor (PFR) relative to a back-mixed reactor (CSTR). This example is a computer simulation of a process based on a conventional reactor selectivity model using experimentally determined relative reaction rate data for various impurities and ozone. In this example, the ADN feed to the two simulated reactors contained the following impurities: 10ppm P (III), 50ppm CPI, 25ppm TBC and 675ppm DDN.

The reaction stoichiometry for the ozone to react with the impurities present is 1 mole of ozone per mole of each of p (iii), CPI, and DDN; for TBC, the stoichiometry is 3 moles of ozone per mole of TBC. Tests were conducted in which refined ADN was reacted with ozone in a CSTR at atmospheric pressure and ambient temperature. MeasuringThe consumption of P (III), CPI, TBC and DDN in the CSTR was measured. These data were fitted to a CSTR reactor design model obtained according to Levenspiel to determine the relative reaction rate constants for the reaction of ozone with p (iii), CPI, TBC and DDN. Phosphorus (III) reacts with CPI substantially completely before ozone attack on TBC and DDN begins. The TBC and DDN then compete for ozone availability. The reaction rate constant for the reaction of ozone with TBC is about 85 times greater than the reaction rate constant for the reaction of ozone with DDN, however, there is significantly more DDN available to compete for the availability of ozone. Using the above data, the amount of ozone consumed at various DDN conversion fractions per liter of ADN feed for both simulated reactor configurations can be calculated. Fig. 1 shows ozone depletion for a Plug Flow Reactor (PFR), while fig. 2 shows depletion for a back-mixed reactor (CSTR) versus transition fraction of TBC (xtbc). These data show the required ozone depletion for 90% reaction of TBC, 1.46 mmoles of ozone per liter of ADN for PFR and 2.11 mmoles of ozone per liter of ADN for CSTR. This corresponds to a 0.65 mmol/l reduction in ozone demand for 90% reaction of the TBC. Figure 3 clearly shows the improved ozone utilization in the PFR relative to the CSTR.Example 3

This example shows the beneficial effect of reducing HMI yield during HMD production achieved by treating the ADN with ozone to destroy TBC prior to hydrogenation.

1 part by weight of ADN was continuously mixed with 6 parts by weight of anhydrous ammonia. This mixture was fed to a bed of heterogeneous iron catalyst together with a stoichiometric excess of hydrogen. The stoichiometric amount of hydrogen is 4 moles of hydrogen per mole of ADN. The reactor was operated at a pressure of about 5000psi (34.5 MPa). The reactor feed temperature was about 100 ℃, and the temperature increased along the length of the bed due to the heat of reaction of ADN with hydrogen.

Initially, ozone treated ADN was fed to the reactor for a period of 250 hours. During this time, when ozone-treated ADN was fed to the reactor, the yield from ADN to HMI averaged 0.10% (moles HMI formed per mole ADN reacted x 100%). The ADN feed was then converted to non-ozonated ADN and run for an additional 150 hours, during which time the average yield from ADN to HMI increased to 0.5%. The amount of TBC in ozone treated ADN was less than 1ppm, while the amount of TBC in untreated ADN was about 25 ppm.

While exemplary compositions, processes, reactors, methods and procedures are described in detail, it is to be understood that various other modifications will be apparent to and can be readily made by those of ordinary skill in the art without departing from the spirit and scope of the present disclosure. Accordingly, it is not the intention of the inventors to limit the scope of the claims of the application to the examples and illustrations described in the application, but rather the claims are to be construed as encompassing all the novel and non-obvious features of the embodiments covered by the claims, including equivalents of such embodiments.

Claims (24)

1. A process for reacting impurities present in Adiponitrile (ADN), the process comprising: introducing an ADN feed and an ozone-containing gas into a co-current Plug Flow Static Mixer Reactor (PFSMR), and contacting the ADN feed and the ozone-containing gas in the PFSMR to oxidize at least a portion of the impurities, thereby producing a reactor effluent.

2. The method of claim 1, wherein the reactor effluent comprises a gas and an ozone-treated ADN liquid comprising unreacted impurities and less harmful impurities.

3. The method of claim 2, wherein the reactor discharge is directed to a device that separates the gas from the ozone-treated ADN liquid to produce an off-gas and a degassed liquid, the degassed liquid being an ozone-treated ADN product.

4. The method of claim 3, wherein the exhaust gas is vented to the atmosphere or to a catalytic abatement unit.

5. A process according to claim 1, wherein the ozone-containing gas comprises ozone and a carrier gas, and wherein the carrier gas is any gas that is substantially inert to the ADN feed at the operating temperature of the process.

6. The method of claim 5, wherein the carrier gas is air, air diluted with nitrogen, oxygen-enriched air, nitrogen, carbon dioxide, helium, argon, or mixtures thereof.

7. The method of claim 5, wherein the ozone-containing gas comprises about 0.1 to about 3 wt.% ozone.

8. The method of claim 5, wherein the ozone-containing gas comprises about 3.0 wt.% ozone.

9. The method of claim 1, wherein the impurities comprise at least one of: 2-Cyanocyclopentylideneimine (CPI), phosphorus (III) compounds (P), (III), or tert-butylcatechol (TBC).

10. A process of claim 9, wherein the ADN feed comprises about 0.5 to about 10ppm p (iii), about 10 to about 200ppm CPI, about 5 to about 100ppm TBC, or a combination thereof.

11. A process of claim 9, wherein the ADN feed comprises about 2 to about 10ppm p (iii), about 10 to about 50ppm CPI, about 10 to about 50ppm TBC, or a combination thereof.

12. A process of claim 3, wherein the ozone-treated ADN product comprises less than 1ppm p (iii), less than 5ppm CPI, and less than 5ppm TBC.

13. A process of claim 1, wherein the amount of ozone supplied to the process is sufficient to react at least about 90% of the TBC present in the ADN feed.

14. A process of claim 1, wherein the process is fed with about 0.1 to about 4 millimoles of ozone per liter of the ADN feed.

15. The process of claim 1, wherein the ADN feed is prepared by hydrocyanation of butadiene using a homogeneous nickel (0) catalyst having a phosphorus-containing ligand.

16. The method of claim 1, wherein the ozone is produced by passing air through an ozone generator to produce a gas stream containing about 3% by weight ozone.

17. A process of claim 1, wherein the ozone consumption in the PFSMR is in excess of 99% of the ozone fed to the PFSMR.

18. The method of claim 1Method, wherein the mass transfer parameter (k)_La) About 0.1 second^-1The above.

19. The method of claim 1, wherein the mass transfer parameter (k)_La) About 0.5 second^-1The above.

20. A process of claim 1, wherein the residence time of the ADN feed and the ozone-containing gas in the PFSMR is from about 2 to about 8 seconds.

21. A process of claim 1, wherein the residence time of the ADN feed and the ozone-containing gas in the PFSMR is from about 2 to about 4 seconds.

22. A process of claim 1, wherein the residence time of the ADN feed and the ozone-containing gas in the PFSMR is about 3 seconds.

23. The method of claim 3, wherein the ozone-treated ADN product is hydrogenated to ACN and HMD.

24. A process of claim 1, wherein the pressure drop across the PFSMR is at least about 1 atmosphere (101.3 kPa).