JPS6247867B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel gas phase production method for nitrite esters. More particularly, the invention relates to the production of nitrite esters of methanol or ethanol produced in gas phase synthesis from the reaction of a critical proportion of methanol or ethanol with a nitrogen oxide composition under relatively mild operating conditions. Regarding. Nitrite esters, or esters of nitrous acid, are generally colorless liquids and have applications in areas such as additives to motor fuels, stabilizers for vinyl compounds, antispasmodics, as diazotizing agents, and as reagents for chemical synthesis. has been found. The classical method for making nitrite esters involves the liquid phase reaction of sodium nitrite and sulfuric acid with the desired alcohol. This reaction is usually carried out at freezing temperatures due to the extremely exothermic nature of the reaction and produces the nitrite ester as follows: 2NaNO ₂ +H ₂ SO ₄ +2ROH → 2RONO + Na ₂ SO ₄ +2H ₂ O . The nitrite ester produced is insoluble in water (approximately 1% or less in water, or approximately 1% water in nitrite).
% or less), the nitrite ester can be easily separated from the reaction product. The production of nitrite esters in the liquid phase is disclosed in U.S. Pat. The aliphatic compound and nitrous acid are reacted in an aqueous medium, and then the nitrite ester is extracted from the reaction system.
The nitrite is produced by withdrawing it essentially as soon as it forms in the reaction system. The nitrite ester produced therein reacts quickly with an alcohol, such as ethyl alcohol, by transesterification to produce an alkyl nitrite, such as ethyl nitrite. US Pat. No. 2,739,166 describes the production of alkyl nitrites in a liquid phase process by bubbling nitrogen dioxide gas into a cooled liquid-hydric aliphatic alcohol. British Patent Specification No. 586022 discloses a liquid phase process for the production of nitrate esters, which consists of reacting an alcohol with nitrogen tetroxide in the liquid phase. German Patent No. 1156775 discloses that by using a molar excess of alcohol over dinitrogen trioxide at a temperature below the boiling point of the alcohol,
A method for producing a nitrite ester in a liquid phase is disclosed by continuously taking out the produced ester and simultaneously distilling off the produced ester. Furthermore, the document recognizes that gas phase decomposition of alcohols with nitrogen dioxide/nitrogen monoxide mixtures at temperatures between 100° and 420° is known. Japanese Patent Application No. 8268/1987 describes the production of nitrite esters by a conventional liquid phase process as part of a continuous process for the production of oxalate diesters using nitrite esters as starting materials. .
The nitrite ester in this method is produced by combining nitrogen oxides and alcohol using an ordinary gas-liquid contacting device.
It is produced by reacting at a temperature below the boiling point of the alcohol. The above-mentioned methods are difficult to separate from the nitrite ester product in the liquid phase method, and the alcohol in the liquid phase may be oxidized during production and separation, producing undesirable by-products. It differs from the vapor phase method in that Additionally, the separation of highly flammable and toxic nitrites from the liquid phase may represent a significant safety and health issue. A gas phase method is disclosed in US Pat. No. 2,831,822. This patent specifies vaporized alcohol and 0.4 to 0.6 moles of nitrogen dioxide and 0.4 to 2.0 moles of nitrogen oxide per mole of alcohol in the presence of 2 to 25 moles of a diluent which may be water, nitrogen or carbon dioxide. Below, a process for the production of nitrite esters is disclosed which consists of reacting at temperatures between 100°C and 420°C with contact times of 1 to 10 seconds. 4 in the table of U.S. Patent No. 2831882
Two examples are described, in which the NO vs.
The molar ratio of NO ₂ is greater than 1, but the molar ratio of the sum of NO and NO ₂ that needs to react with as much as possible of the alcohol to N ₂ O ₃ is less than 1. In each case a relatively high 80
In order to achieve conversions of more than %, it is necessary to employ temperatures above about 130°C. In addition to the increased rate of decomposition of the nitrite ester (product) at this temperature, the document raises other problems due to the need to use significant amounts of water in each example. By using water in the process, nitric acid will be produced, at least some of which will appear in the ester product. Examples are given in the table of said US Pat. No. 2,831,882, which employ various molar ratios of nitric acid, nitrogen dioxide, nitric oxide and nitrogen dioxide or nitric acid to alcohol (n-butanol). ing. In each example the molar ratio of alcohol to total nitrogen oxides is less than 1. Furthermore, in each example, temperatures in excess of 170°C were required to obtain conversions to nitrite esters greater than 70%. Furthermore, the third part of the patent specification
In columns 55-64: When nitrogen dioxide reacts with alcohol in the presence of water at temperatures below 250°C, equimolar proportions of nitrite and nitric acid are produced. By increasing the reaction temperature to 350°C, the production of nitric acid is almost eliminated and the conversion to nitrite ester is increased. These results are consistent with the reaction mechanism described above. This is because increasing temperature increases the decomposition of both nitric acid and nitrogen dioxide. It has said. Thus, not only does the process require relatively high temperatures, but it also results in the production of nitric acid, which can decompose at high temperatures. In Example 1 of the above-mentioned US Pat. No. 2,831,882, a nitrite ester of isopropyl alcohol is prepared. This example in U.S. Pat. No. 2,831,882 is
The molar ratio of NO ₂ and the molar ratio of isopropanol to the sum of NO and NO ₂ is determined to be greater than 1. This process is performed at a pressure of 90 psi with only 58% conversion to product (the literature probably suggests an 89% yield based on nitrite converted from consumed alcohol). (which is actually about 39% conversion based on available nitrogen oxide and nitrogen dioxide). Furthermore, the method results in incomplete reaction of nitrogen dioxide. This unreacted nitrogen dioxide can be quite detrimental to some subsequent operations using nitrite esters. In US Pat. No. 4,229,591, the production of nitrite esters is utilized as an intermediate step in the process of producing oxalate diesters. The patent specification is the second
In column, lines 21-35: The nitrogen compound used in the present method does not necessarily have to be in the form of an ester of nitrous acid; compounds that produce esters of nitrous acid in the reaction system can also be used. In addition, when nitrogen monoxide is used, by introducing a gas containing molecular oxygen into the reaction system, nitrogen monoxide, nitrogen dioxide, dinitrogen trioxide, and tetroxide can be substituted for the ester of nitrous acid. It may be advantageous to use alcohols with nitrogen compounds selected from the group consisting of dinitrogen and hydrates of nitrogen oxides. As the hydrate of nitrogen oxides, nitric acid, nitrous acid, etc. can be effectively used. The alcohol used in the above case is selected from alcohols constituting esters of nitrous acid, which will be described later. This is disclosed. In order to overcome the problems associated with known nitrite ester production methods, it is necessary to
Moreover, methods must be found that can be carried out in the gas phase while minimizing the formation of by-products. The above-mentioned processes are performed at relatively low temperatures and pressures, and the ratio of nitrogen oxide (NO) to nitrogen dioxide (NO ₂ ) is reduced to provide an effective process that minimizes the formation of by-products. There is no recognition of the need to provide a gas phase process in which the molar ratio and the molar ratio of alcohol to the total molar amounts of nitrogen oxide and nitrogen dioxide are each greater than 1. The present invention relates to a process for producing methyl nitrite or ethyl nitrite from methanol or ethanol, respectively, comprising: (i) 1
and (ii) moles of vaporized methanol or ethanol having a molar ratio of methanol or ethanol to nitrogen oxide composition greater than 1. amount, and reacting in the vapor state. The reaction is carried out using methyl nitrite or nitrous acid at a temperature of at least about 10°C to about 300°C, preferably at atmospheric pressure or superatmospheric pressure, in the presence of a gaseous diluent inert to the reaction. It is carried out for a sufficient period of time to produce ethyl. The production of nitrite esters, in particular methyl nitrite and/or ethyl nitrite, will now be described. This method can be explained using the following equation: (1) 2NO+O ₂ → 2NO ₂ (2) NO ₂ +NO N ₂ O ₃ (3) 2ROH+N ₂ O ₃ →2RONO+H ₂ O (4) ROH+N ₂ O ₃ →RONO+HONO (5) ROH+HONO→ RONO+H ₂ O (6) 2NO ₂ N ₂ O ₄ (7) ROH+N ₂ O ₄ →RONO+HNO ₃ (in each of the above formulas, R is methyl or ethyl) to explain more fully. Since the objective of the process is to maximize the production of methyl nitrite or ethyl nitrite while minimizing, preferably substantially eliminating, the production of nitric acid and other by-products, the reaction is carried out by the equation ( 1), (2),
(3) is characterized in that it is integrated into reaction (4) that supplies nitrite to equation (5). Although the above reaction sequence is preferred, the reactions characterized by equations (6) and (7) should be minimized because they produce nitric acid. It has been found that by supplying NO, _NO2 , and ROH in specific molar ratios, alkyl nitrites can be produced in high yields with minimal production of nitric acid. To achieve these results, the molar ratio of nitric oxide to nitrogen dioxide is such that it is greater than 1, and the molar ratio of alcohol to the total molar amount of nitric oxide and nitrogen dioxide is greater than 1. There must be. The interrelationship of these two molar ratios defines the method of the invention. In carrying out the method of the present invention, the reactant materials are not magnetically applied. Nitric oxide can be provided by decomposition of nitric acid and/or nitrogen dioxide, or can be introduced from a source such as an ammonia oxidizer. The process will generally be carried out by introducing nitrogen oxide and oxygen to produce the required amount of nitrogen dioxide (see equation (1)). In this case, the molar ratio of nitrogen oxide to nitrogen dioxide is made greater than 1 by supplying nitrogen oxide and oxygen in a molar ratio greater than 4:1 so that the molar ratio of nitrogen oxide to nitrogen dioxide is greater than 1. keep. Higher nitrogen oxides (N ₂ O ₃ ,
(N ₂ O ₄ , N ₂ O ₅ etc.) it is possible to obtain a gaseous medium with the desired ratio of nitrogen oxide to nitrogen dioxide, in which case higher oxides such as those mentioned above are used, Said higher oxides can be used to the extent that they can provide a gaseous medium with a molar ratio of NO to NO ₂ greater than 1, with or without the addition of molecular oxygen.
Additionally, it is also possible to use compounds such as nitrous acid, which can be decomposed and reacted to provide a gaseous medium with a molar ratio of NO to NO ₂ greater than 1. As mentioned above, the method preferably uses molecular oxygen.
This is done by forming the desired NO to NO ₂ molar ratio by reacting with NO in a molar ratio of 4 to 1 or more. Although the process can be carried out by mixing together nitric oxide, oxygen and alcohol (methanol or ethanol) in the desired molar ratio, such mixing may be undesirable. because,
Oxygen oxidizes alcohol (methanol or ethanol) to various undesirable reaction products,
This results in the loss of valuable starting materials and can produce flammable compositions that may be hazardous to safety. Such undesirable reaction products, as impurities in the nitrite esters, can be used in subsequent reactions of the alkyl nitrites, such as the production of alkyl oxalates by the process of the aforementioned U.S. Pat. No. 4,229,591. may be shown to be harmful to Therefore, the present method combines nitrogen oxide and molecular oxygen into the reaction (the above equation
(1)) for a sufficient period of time to obtain a nitrogen oxide mixture (larger than 1).
Preferably, oxygen is consumed before mixing the mixture (having a molar ratio of NO to NO ₂ ) with the alcohol. The process is carried out in the presence of an inert gas diluent to moderate the reaction, eliminate the formation of explosive mixtures, and prevent the formation of excessive amounts of undesirable by-products. When carrying out the method, the inert gas diluent is added simultaneously with nitrogen oxide or molecular oxygen, or both. Additionally, an inert gas diluent can be added to support and vaporize the alcohol. Preferably, nitrogen, carbon dioxide or other gaseous compounds are used as the inert gas diluent. With the use of carbon dioxide,
Higher heat capacity is obtained compared to nitrogen. Carbon monoxide can be present and used as a diluent, but its concentration in the reaction system must be carefully controlled to prevent the formation of flammable mixtures. The inert gas diluent is used in an amount sufficient to achieve the above objectives. Generally, the inert gas diluent is about 1 mole % in the present method.
and about 99 mol%, preferably about 30 mol% and about
70 mol%, most preferably between about 30 mol% and about
Between 70 mole percent and inert gas diluents are used. The exact amount of inert gas diluent is
It is determined in part by the ester of nitrous acid selected and the process parameters selected, such as temperature and pressure. According to the invention, the process is carried out at between about 10°C and about 300°C, preferably between about 20°C and about 130°C, and most preferably between about 50°C and about 110°C or less. The minimum temperature at which the process is carried out is generally determined by the dew point of the alcohol used and the concentration of the reactants. The pressure at which the method is carried out is not strictly critical. Preferably atmospheric pressure or above atmospheric pressure is used, more preferably about atmospheric pressure (14.7 psia).
between 100psia, most preferably about 20psia and about
60 psia is used. Pressures up to 14.7 psia can be used if desired. Preferably, the process is carried out using reactants that are substantially anhydrous. This is because the presence of water in the reactants promotes the formation of undesirable by-products which must ultimately be separated off if the ester of nitrous acid is to be used subsequently in further operations. The process is preferably carried out in such a way that the amount of water provided by the reactants is minimized. It should be remembered that this reaction produces water and the water thus produced must be tolerated. As mentioned above, the molar ratio of nitrogen oxide to nitrogen dioxide is greater than 1. Typically the molar ratio (NO to
NO ₂ ) is from 1 to about 10, preferably from 1 to about 2, and most preferably from 1 to about 1.5. The molar ratio of alcohol (methanol or ethanol) to the total molar amount of nitrogen oxide and nitrogen dioxide is greater than 1. The term "total molar amount" refers to the amount of NO that reacts according to the above reaction formula (2).
It means the quantitative sum of the molar amounts with NO ₂ . Typically the molar ratio of ROH to (NO+ _NO2 ) is from 1 to about 10, preferably from 1 to about 2, and most preferably from 1 to about 1.5. The process of the invention can be carried out in almost any commercially available reactor and is generally carried out on a continuous basis by using tubular reactors. The contact time (or residence time in the reactor) during which the gaseous materials react to form methyl nitrite or ethyl nitrite generally ranges from about 0.1 to about 30
seconds, preferably about 0.1 to about 2 seconds. The temperature employed, as long as sufficient reaction time is allowed;
Shorter or longer times can be used depending on pressure, molar ratio, diluent and feed rate. Additionally, the choice of reactor geometry for the nitrite production reaction zone will also affect the actual residence time employed. When the process is carried out in a continuous manner, the feed rate is not strictly critical and is selected to satisfy the particular design of the continuous system. The present invention will be explained by the following drawings and description of examples, but they are not intended to limit the scope of the present invention in any way. FIG. 1 schematically shows the design and operation of an apparatus using a tubular reactor for carrying out the process of the invention. FIG. 2 schematically depicts a particular reactor design for the production of alkyl nitrites. In FIG. 1, methanol or ethanol (labeled alcohol) is introduced into conduit 10 as a liquid or vapor and is mixed at point 12 with an inert diluent, shown here as nitrogen. The flow in conduit 10 passes to preheater 14;
It exits the preheater 14 via conduit 16 in vapor form. Nitrogen oxide (preferably NO) is introduced into conduit 20 and an inert diluent, shown here as nitrogen, is added at point 22 within conduit 20. This order of addition is not critical. If nitrogen oxide is used as the nitrogen oxide, a conduit 26 for the addition of molecular oxygen is provided. If the nitrogen oxide selected is nitrogen oxide, the gas streams in conduits 20 and 26 are fed to an oxidizer 28 for the production of higher nitrogen oxides. The gaseous stream exiting the oxidizer 28 via conduit 30 mixes with the contents of gaseous stream 16 and the combined stream is fed through conduit 32 to the nitrite reactor 34 where the reaction product nitrous oxide is Methyl nitrate or ethyl nitrite is formed. The reaction products and any other stream components (such as nitrogen oxide alcohol and produced water) exit the nitrite reactor 34 through conduit 36, leaving a substantial portion of unreacted alcohol and produced water. This leads to a heat exchanger (condenser) 40 which is kept at a temperature at which the quantity or desired quantity is condensed. The condensed gaseous alkyl nitrite-containing mixture is then fed to a gas-liquid separator 42 where water, excess alcohol, etc. are separated and collected via conduit 44. The flow of gaseous alkyl nitrite exits the gas-liquid separator 42 via conduit 46 and passes through a pressure regulator 48 (which controls process pressure). If condensed alkyl nitrite is to be obtained, the flow of gaseous alkyl nitrite is carried through conduit 50.
to a product condenser 54 (optional). The condensed alkyl nitrite product is transferred to conduit 56.
It is collected after The uncondensed gaseous product is transferred to conduit 6
It exits the product condenser 54 via 0 (discharge line) and is treated to remove harmful components contained therein or recycled to conduit 20. Figure 2 schematically shows a nitrite ester reactor;
In the figure, nitrogen oxides are introduced into a nitrite reactor 76 through conduit 74. If the nitrogen oxide is nitrogen oxide, a feed conduit is provided for introducing molecular oxygen (not shown) into conduit 74 before reactor 76 . Alcohol mixed with nitrogen is introduced through conduit 70 and evaporated through evaporator 72 (fine aerosol decomposition). Methyl nitrite or ethyl nitrite produced in nitrite reactor 76, as well as other gaseous components, exit through conduit 80 to a condenser (such as heat exchanger 40 in FIG. 1). Some alcohol and water condenses in reactor 76 and flows through conduit 78
Sometimes I leave. Nitrite ester reactor 7
6 may or may not be filled as desired, but is preferably filled with an inert material, particularly in the space above the evaporator 72. The condensed product is then processed in the same manner as the condensed product of FIG. 1 was done. Additionally, it has been observed that in carrying out the method it may be preferable to carry out the method in such a manner that the reactions characterized by equations (4) and (5) discussed above are taken into account. Ta.
In such cases the process is carried out in two reaction zones. The first reaction zone is generally a tubular reaction zone, as shown for nitrite reactor 34 in FIG. 1, as the reaction characterized by equation (4) proceeds. Designed to minimize back-mixing in the first reaction zone.
Such tubular reactors or other similar reactors may be filled or unfilled as desired. The second reaction zone is designed taking into account the ionic nature of the reaction characterized by equation (5). The nitrite reactor shown in Figure 2 is suitable for the second reaction zone as described above, and it preferably controls the temperature and pressure in the second reaction zone to the alcohol ( It is filled with an inert material, such as glass beads, placed so as to provide a wetted surface by maintaining it slightly above the dew point of methanol or ethanol). It has been observed that by employing such two reaction zones, the formation of by-products can be greatly minimized. Minimizing the formation of by-products in this way means that
This is very important if the alkyl nitrite is desired to be used in a subsequent step, and reduces the degree of purification of the alkyl nitrite that is required (if at all). Experimental Procedures Examples were carried out using an apparatus as illustrated in FIG. 1, using the reactor of FIG. 2 in place of the single tube reactor shown in FIG. When using the apparatus as illustrated in FIG. 1, the oxidizer (NO oxidizer) was a 6-foot No. 304 stainless steel tube with an outside diameter of 3/8 inch (0.31 inch inside diameter). The alcohol preheater was a 6-foot No. 304 stainless steel tube with a 1/2 inch outside diameter (0.435 inch inside diameter) filled entirely with stainless steel sponge. The nitrite reactor was a 17 foot length of No. 304 stainless steel tubing with a 3/8 inch outside diameter (0.31 inch inside diameter). The three types of stainless steel tubes mentioned above were heated in a common ethylene glycol heating bath. The reactor in Figure 2 is a Hoke (304 stainless steel, 400 psig 4LS500) with an internal volume of approximately 530 ^cm3 .
It was made from a cylinder. The reactor was equipped with a side tube 3 1/4 inches from the bottom. 1/8 inch outer diameter tube [Cat. No. 9402
An All TECH™ low pressure solvent filter (with All TECH attached) having Hasteloy™ stainless steel is installed through the side tube with a fritted opening at its end. Established. A gas inlet tube was attached to the bottom of the reactor. This is the evaporator and take-off for discharging all reaction liquid.
It was located directly below the valve. The reactor was electrically heated by heating wires wrapped around the reactor cylinder. An alcohol feed, with or without nitrogen as a gaseous diluent, is fed through the side tube and forced through the frit to form a fine aerosol dispersion of alcohol, while nitrogen oxidation is introduced through the gas inlet tube. A nitrogen/nitrogen mixture was fed. The gas stream from the nitrite ester reactor (one of those mentioned above) was cooled in an ice-water bath,
The partially condensed stream was then fed to a gas-liquid separator (ice-water temperature) and then to a 5-in. Shedule 10SNo.304 Stainless Steel Piping (Length 1.1
Inch) product condenser (ice water temperature). The various conduits of the device were formed by 1/4" outside diameter (0.185" inside diameter) stainless steel tubing. Pressure differential control was provided by stainless steel capillary orifice nipples.
nitrogen oxides, oxygen, and carbon monoxide were introduced using Pressure was controlled by a Grove pressure regulator (Model No. SD91LW (35254-315)) using a Teflon seal. The pressure on the globe adjustment device bleed from Moor 4300-35353-299.
It was controlled by a mold regulator. Alcohol was metered into the process using a Fluid Metering Inc. metering pump (Model RP-650-OSSY). Condensate from the gas-liquid separator and product condenser was analyzed by gas phase chromatography. Examples 1 and 2 The process of the invention was carried out using the setup shown in FIG. 1, with the exception that in Example 1 the reactor of FIG. 2 was used instead of the tubular reactor 34 of FIG. . The results of each example are shown in the table. The molar ratio of nitrogen oxide to nitrogen dioxide (produced from a mixture of nitrogen oxide and molecular oxygen) is greater than 1, and the molar ratio of alcohol to the total molar amount of nitrogen oxide and nitrogen dioxide is 1.
It was bigger than that. Comparative Example 3 Comparative Example 3 was conducted as shown in Example 3 of the table.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the design and operation of an apparatus using a tubular reactor for carrying out the process of the invention. FIG. 2 is a schematic diagram showing a particular reactor design for producing alkyl nitrites.

Claims (1)

Claims: 1. In the reaction zone, a molar amount of a nitrogen oxide composition having a molar ratio of nitrogen oxide to nitrogen dioxide greater than 1 is defined as a molar amount of vaporized methanol or ethanol, in this case methanol or said molar ratio of ethanol to the total molar amounts of nitrogen oxide and nitrogen dioxide is greater than 1, and in the vapor state, in the presence of an inert gas diluent for the reaction, at about 10° C. and about 300° C. A process for producing methyl nitrite or ethyl nitrite from methanol or ethanol, respectively, characterized in that the reaction is carried out at a temperature between methanol and ethanol for a time sufficient to produce methyl nitrite or ethyl nitrite. 2. The method of claim 1, wherein the inert gas diluent is nitrogen. 3. The method of claim 1, wherein the inert gas diluent is carbon dioxide. 4 Approximately 1% by volume and approximately 99% by volume of inert gas diluent
Claim 2 existing in an amount between
The method described in Section 3 or Section 3. 5 Approximately 30% by volume and approximately 90% by volume of inert gas diluent
Claim 4 exists in an amount between
The method described in section. 6. The method of claim 1, wherein the nitrogen oxide comprises nitrogen oxide and molecular oxygen in a molar ratio of nitrogen oxide to molecular oxygen greater than 4 to 1. 7. The method according to claim 1, wherein the method is carried out under substantially anhydrous conditions. 8. The method according to claim 1, wherein the method is for producing methyl nitrite from methanol. 9. The method according to claim 1, wherein the method is for producing ethyl nitrite from ethanol. 10. The method of claim 1, wherein the temperature is between about 20°C and about 130°C. 11. The method of claim 10, wherein the temperature is between about 70°C and 110°C or less. 12. The method of claim 1, wherein the method is carried out at atmospheric pressure (14.7 psia) or at a pressure above atmospheric pressure. 13 Pressure is approximately atmospheric pressure (14.7psia)
13. The method of claim 12, wherein the pressure is between 100 psia. 14. The method of claim 13, wherein the pressure is between about 20 psia and about 60 psia. 15. The method of claim 1, wherein the molar ratio of nitrogen oxide to nitrogen dioxide and the molar ratio of methanol or ethanol to the total molar amount of nitrogen oxide and nitrogen dioxide are each between 1 or more and about 10. Method. 16. The method of claim 15, wherein each molar ratio is between 1 or more and about 2. 17. The method of claim 16, wherein each molar ratio is between 1 or more and about 1.5. 18. The method of claim 1, wherein at least a portion of the inert gas diluent is carbon monoxide.