JPS5814364B2 - Method for producing compound of formula N↓2H↓4CO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a process for the catalytic production of urea or its equivalents such as ammonium isocyanate.

Urea or its equivalent, ammonium incyanate, is used in many economically important applications.

For example, urea is used as a major component in fertilizers, as a heptamer in plastic manufacturing, and as an ingredient in animal feed.

Large quantities of urea, more than 4,000,000 tons per year in the United States alone, are produced under high pressure, typically between 200 and 400 atmospheres, and at temperatures between 140 and 210 degrees Celsius, producing CO2 and NH3.
It is synthesized industrially by contacting the ammonium carbamate with urea and forming an ammonium carbamate, which is then decomposed into urea and water.

This high pressure requires the use of expensive and complex equipment.

Furthermore, the conversion rates normally obtained with this industrial process are low, e.g., about 50%, so that unreacted NH3 and C02
recirculation (lagoon cycle) is necessary.

Therefore, it is not cost-effective to produce smaller quantities using this high-pressure method.

Even when large quantities are desired, initial capital investment is an obstacle.

The industrial production of the reactant NH3 of this process is also about 50
The cost and quantity constraints inherent in industrial urea production processes are further created by the inclusion of high pressure processes that are economical only on a scale of 0,000 cm/year.

In certain situations, however, low-volume, low-investment methods are most appropriate.

For example, the need for significantly less capital investment would facilitate the production of fertilizer-based urea in low-technology agricultural countries.

Similarly, on-site production of urea from waste by-products of other processes is a desirable process which usually involves much smaller scale.

Such recovery methods are often economically advantageous if sufficiently high conversions of reactant by-products to marketable products can be obtained.

These two special circumstances and many equivalents illustrate two important factors.

First, techniques involving relatively low pressure conditions are important to reduce the initial investment and technical complexity involved.

Second, the potential for increased efficiency of raw material utilization afforded by a high-yield process for making urea from by-products is significant.

Thus, a method for producing urea with relatively low pressure and high efficiency would be beneficial in many situations.

When a gas mixture of NOX, carbon monoxide, where X is 1 or 2, and a hydrogen source such as H20 or H2 is passed over a hydrogenation catalyst such as platinum or rhodium, if the product is It has been found that upon condensation to temperatures urea is obtained and upon condensation below 60 DEG C. ammonium cyanate, NH40CN, is obtained.

Yields of up to 100% (based on conversion of NOx to urea or NH40CN) are possible.

Other catalysts such as Monel give lower yields, such as about 30%, but are still useful.

Such yields are obtained at atmospheric pressure and at temperatures of 200-600°C.

This process provides advantageous conversion to urea or NH, OCN when the concentration of NOx is as low as 200 ppm or as high as 5%.

Therefore, this method reduces NOx by-products of other manufacturing operations.
suitable for use.

This is particularly important because low concentrations of conventional nitrogen oxides have negative manufacturing costs, such as converting NOx to other relatively worthless, non-polluting substances to meet federal environmental law requirements. There are significant expenses involved in converting.

The method of this invention inherently has the ability to convert manufacturing costs into manufacturing assets.

This change is combined with a reasonably low capital investment resulting from relatively mild reaction conditions.

The interest of this process is further enhanced by the high conversion rates that can be achieved.

FIG. 1 is an explanatory diagram of an apparatus suitable for carrying out the present invention.

Figures 2-7 show the conversion under various reaction conditions.

A preferred embodiment of the invention is shown in FIG.
, can best be described by detailing each step of the synthetic method individually.

The reactant gas cylinders (1, 2 and 3 in FIG. 1) and the inert carrier gas cylinder 4 are connected to the manifold 9 via individual flow regulators 5, 6, 7 and 8.

The reactant gas is nitrogen oxide, i.e. NO or NO2 or NO2
0 combination, carbon monoxide, and a third substance that is a source of hydrogen.

Molecular hydrogen and water are examples of substances suitable as hydrogen sources.

In the latter case, since the process involves a gas phase reaction, water is added by such a method as passing the reaction gas through a water bubbler.

Indeed, if the other reactants have a sufficiently high water impurity content, further additions are not necessary.

The particular substance used as the inert gas is not limited.

Laboratory-prepared helium is usually used because of its ready availability and because it facilitates analysis of the reaction products.

However, other inert gases such as N2 are also acceptable.

A catalyst 10 is inserted into a reaction vessel 11 and a thermocouple 1
2 or other temperature monitoring means are placed near the catalyst.

The catalyst used is a hydrogenation catalyst.

For example, catalysts such as rhodium, platinum and palladium are suitable.

Other hydrogenation catalysts such as Monel (trade name for a natural alloy of nickel, copper, and other elements) are also useful.

The physical form of this catalyst is not limiting.

Common shapes such as small metal particles or entrained catalysts are useful.

The yield of urea or urea equivalent, NH40CN, depends on the reaction conditions and the particular catalyst used.

In many applications, 30% or more NOx to urea or NH
, it is desirable to select conditions and catalysts to obtain conversion to OCN.

For small-scale industrial applications, a conversion of preferably 70% or more is advantageous.

After placing the reactants and catalyst, the apparatus is sealed and the entire system is purged with inert gas.

If desired, the catalyst is then heated to 200-60°C, preferably 300-500°C, for 1-24 hours and purified by passing H2 over the catalyst.

For this purpose, H2 is introduced into the system in pure form or diluted with inert gas to an inert gas to H ratio of between 0 and 50. This purification process removes oxygen from the catalyst surface. , and generally makes the catalyst more active.

Upon initiation of the reaction process, NOx, CO1 hydrogen sources such as H2 and inert gases are flushed through their respective flow controllers into manifold 9 and routed to mixing coil 14 to ensure uniformity. can be attached.

A typical example of the concentration of reactants in this gas stream is 2X10-'
Atmosphere to 0.05 atm, preferably 2X10-3 atm to 0.05 atm.
Partial pressure of NOx of 02 atm, 0.5-10 preferably 1-
A CO/NOx ratio of 4 and a H2/NOx ratio of 1 to 10, preferably 1 to 2.

The remainder of this gas stream is made up of inert gases, ie, gases that do not interfere with the desired reaction.

A suitable pressure for the total gas flow is about 1 to 5 atmospheres, preferably 3/3 atmospheres.
The pressure is 4 to 11 atmospheres.

Within these limits on reactant concentration, total gas flow and pressure, the situation is included where no inert gas is used and the system operates under partial vacuum.

Such situations are within the scope of this invention.

However, it is generally most convenient to operate at pressures in the range of 1 atmosphere, which usually requires the addition of some inert gas.

The gas mixture has a temperature of about 200-600°C, preferably 300-600°C.
The flow rate of the gas passed over the catalyst, which is heated to a temperature of 500° C., is adjusted to give a substantial portion of the reactants sufficient time to react and also provide an industrially viable processing time.

Generally, standard catalysts have about 1,000 to 1
A flow rate of 00.000 rl/h is desirable.

(This 2 refers to the total surface area of the catalyst that can react with the reactant gas stream.

) The reacted gas is passed from the reactor into tube 15 and the NH40CN is frozen out of the gas stream by passing through trap 17, which is maintained at a temperature between 0<0>C and 120<0>C.

Ammonium cyanate is stable in the gas phase.

However, upon condensation, it spontaneously converts to urea at temperatures above 60°C.

Urea decomposes in the solid state at 120°C.

Therefore, when the reacted gas is frozen below 60°C, NH40CN is obtained as a solid.

If the gas is condensed to 60°C to 120°C, urea is obtained.

Condensation above 120°C is not recommended.

The remaining gas is then discharged via pipe 25. The final yield obtained depends on the particular reaction conditions used.

In certain situations, control samples are used to fix the desired optimal conditions.

The following examples illustrate the effects and results of various parameters obtained by practicing the invention.

Examples 1-4 demonstrate the effect of temperature on the yield of various catalysts.

Each example was made at a total gas pressure of 1 atmosphere.

Some of the embodiments use NOx to CO ratios outside the suggested ranges.

Although these examples were done with large CO excess,
The purpose was to evaluate the present invention in order to confirm the reaction of nitrogen oxide.

However, the suggested range is around stoichiometric ratios, where the CO to No in the reaction mixture is very close to equivalent.

In this way, CO is efficiently utilized and uneconomical waste of reactant gases is avoided.

Example 1 Gas chromatograph 20 and NH40CN for measuring the concentration of NOx and N2 in exhaust gas for analysis
The apparatus shown in FIG. 1 was used, which included a modified Technicon force-mouth remetric autoanalyzer 22 for the determination of the concentration of .

Modifications to the analyzer were necessary to prevent clogging of the device with urea or NH40CN.

This modification consists of installing an absorber that forces hot gas through a silver nozzle and then condensing and dissolving the incyanate component onto a surface that is continuously flushed with an alcohol solution.

This solution was heated at 60-90% to achieve total conversion to urea.
heated to ℃.

The urea solution is then analyzed using the carbamide diacetyl reaction.

(J. Biochemistry (Bioche-mistr.
y) 33.902 (1939).

) Approximately 5 g of platinum sponge with an active surface area (area available for contact with reactants) of 0.12i2/r was placed in the reaction vessel.

0.3% NO, 0.5% H2, 5
．． A gas mixture of 0 percent CO and balance He1 was flowed over the catalyst at 115 CC/min (1 atm total pressure).
.

Measurements of the production of urea (NH40CN) were made for various temperatures of the catalyst in the range 300-500 DEG C. (the catalyst was heated by a bed of fluidized sand with heating coils 27).

) A sample of the reactor effluent was dried and the CO removed in an ascarite trap 13.

The exhaust of this askarite trap is N2, NO, NO
It was analyzed by gas chromatography for components such as 2 and CO.

Another effluent sample was analyzed in autoanalyzer 22 for NH40CN and/or urea content, the results of which are shown graphically in FIG.

Example 2 The catalyst of Example 1 was heated at 480°C for 8 hours and then at 500°C for 3 hours.
A mixture of 2 percent H2 was passed through the depths over the spongy alloy for a period of time to decompose (purify).

Data obtained under the same reaction conditions as in Example 1 are shown in FIG.

A comparison of these two figures shows the improved effectiveness generally associated with catalyst floatation.

Example 3 Approximately 1.5 I of rhodium sponge with an active surface area of 1.69 d2/f was placed in the reaction chamber.

Pure H2 was flowed over the catalyst at 100 CC/min.

The catalyst was heated to 500°C and maintained at this temperature for 1-3/4 hours.

The temperature of the catalyst was then lowered to room temperature and the gas stream was changed from pure H2 to pure He for overnight storage.

0.31% NO, 0.5% H2,
Analysis of the product was then made at various catalyst temperatures as a mixture of 5.0 percent CO and balance He (1 atm total pressure) was heated to 360° C. over the rhodium at a rate of 230 cC/min. The results are shown in FIG.

Example 4 Approximately 41 metal Monel filings (
An active surface area of 0.12 d2/r) was placed in the reactor and heated to 450° C. under a 2% H2/He flow of IOOCC/min.

The purification process continued throughout the night.

The temperature of the catalyst was then lowered to 200° C. and the gas flow was changed to Zoo (1/min) pure H2.

The temperature was then increased to 450°C for 4-1 hours.

Various runs were made and the system was kept under He for several days.

Then 0.3 percent No. O. A gas flow of 5 percent H2, 5.0 percent CO, and balance He1 was introduced at a flow rate of 125 CC/min (total pressure 1 atm).
.

Yields were measured over time and at various catalyst temperatures.

The catalyst was kept under pure He when no measurements were taken.

The results are shown in FIG. As can be seen in Figures 2 to 5, almost 100% NO to NH40CN
It was possible to convert to

The following examples represent typical flow effects on yield at various temperatures.

Example 5 The catalyst used in Example 1 was again heated to 2% H at 500°C.
Digested under 2/Heo (2 hours).

0.3% 17) NO, 0.5% H2
360 and 410 for various flow rates of a mixture of 5.0 percent CO and balance H2 (1 atm total gas pressure).
The yield in °C was determined.

Line 30 in FIG. 6 shows the results at low temperature and line 31 shows the results at high temperature.

Approximately 5 grams of spongy platinum (active surface area o. 12 m2)
/g) was exposed to 2% H2 overnight at 50°C.
/Ie flow.

The catalyst temperature was adjusted to 430°C and a gas mixture of 0.33% NO, 0.5% H2, 5.0% CO and balance H2 (total pressure 1 atm) was
A flow rate of 00 rl/min was introduced.

This flow rate was varied by partially leaking the gas flow before the gas mixture reached the reactor.

The yield of NH40CN at 430° C. for different flow rates is represented by line 32 in FIG.

(The flow rate is shown as F/S, where F is Il
/hour, and S is the surface area of the catalyst sample that reacts with the reactant gas stream.

) The following example illustrates the effect of reactant ratio on reaction yield.

Example 6 Approximately 51 spongy platinum (active surface area 0.12 2/1
) was placed in the reactor.

The catalyst temperature was increased to 450°C and 2% H2
/}{ was flowed through the system overnight at a rate of 60 CC/min.

The temperature was then lowered to 404°C and 0.3% NO, 5.0% CO, 0.3% H2 and balance H.

(1 atm total gas pressure) was flowed through the system at a rate of 400 CC/min.

The Co concentration was varied (the He concentration was also varied to compensate) and the yield of NH40CN was measured.

The following results were obtained. This stream was then converted to a 2 percent H2/Ho mixture (flow rate 60 cC/min) and the catalyst was decomposed overnight at 450C.

The catalyst temperature was lowered to 420° C. and the various reaction mixtures were flowed (400 CC/min) through the system (total pressure of any given mixture was 1 atm).

The yields of the condensate of the reaction gas mixture (the remainder is H2 not shown) and NH40CN are shown in the following table.

The above table shows that the conversion rate is quite insensitive to H2/NO close to the stoichiometric ratio, but this rate is significantly reduced when the H2/NO ratio is increased above about 1.5. It shows.

This table further shows that H20 was effectively used as a hydrogen source.

The following example shows the effect of 02 on reaction yield.

It is noteworthy that NO was converted to NO2 when 02 was introduced.

Example 7 About 51 sponge platinum was raised to 500°C under reducing conditions and subjected to a gas stream of 0.33% NO, 0.5% H2, 5.0% Co (balance H2).
, total gas pressure of 1 atm) was flowed into the system at a rate of 14 a/h.

Various percentages of 02 were introduced and conversions were measured.

The results are shown in FIG.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an apparatus suitable for carrying out the present invention. Figures 2-1 are graphs showing conversion under various reaction conditions. 1, 2.3...Reaction gas cylinder, 4...
...Inert carrier gas cylinder, 5,6
, 7, 8...Flow rate regulator, 9...Manifold, 10...Catalyst, 11...Reaction vessel, 12... Thermocouple, 14... Mixing coil, 15... Tube, 17... Trap, 20... Gas chromatograph, 22...
...Automatic analyzer, 25...Tube, 27...
...Heating coil.

Claims (1)

[Claims] 1. In the production of a compound of 2N2H4CO, in the presence of a hydrogenation catalyst, a) an oxide of composition NOx (in this case
is l or 2. ), b) carbon monoxide, and C) hydrogen source CO:NOx-
0.5:1~io:i, H2:NOx=1:1~10:
1. A process for the production of said compounds, characterized in that a gas mixture containing a proportion of 1:1 is reacted at a temperature in the range from 200 to 600 DEG C., and the resulting compound is collected. 2. Claim 1 provides that the method comprises 300
A method characterized in that it is carried out at a temperature in the range ~500<0>C. 3. In either claim 1 or 2, the hydrogenation catalyst contains platinum, rhodium, and palladium, as well as 67% nickel, 28% copper, 1 to 2% manganese, and 1.9 to 2.5% manganese. % iron. 4. A method according to claim 1, 2, or 3, characterized in that the hydrogen source is selected from molecular hydrogen and water. 5. A method according to any one of claims 1 to 4, characterized in that the obtained compound is collected by condensing at a temperature of 120° C. or lower. 6 In claim 5, the compound is converted into solid NH40C by condensing at a temperature of 60°C or less.
A method characterized by collecting as N. 7. A method according to claim 5, characterized in that the compound is collected as solid urea by condensation at a temperature of 60 to 120°C. 8. A method according to any one of claims 1 to 7, further comprising oxygen in the gas mixture. 9. A method according to any one of claims 1 to 8, characterized in that the ratio of carbon monoxide to NOx is selected from 1:1 to 4:1. 10. A method according to claim 9, characterized in that the ratio of N2 to NOx is selected from 121 to 2:1.