WO1996006672A1

WO1996006672A1 - Molten urea dehydrate derived compositions

Info

Publication number: WO1996006672A1
Application number: PCT/US1995/010800
Authority: WO
Original assignee: Us Sulfamate, Inc.
Priority date: 1994-08-26
Filing date: 1995-08-25
Publication date: 1996-03-07
Also published as: AU3495195A

Abstract

A process for the production of a dehydrated molten urea composition which may be utilized to produce a dry, stable, granular and acidic composition of matter. Also disclosed are various compositions of matter produced from a dehydrated urea melt which may be reacted with proton donors to produce useful compositions.

Description

"MOLTEN UREA DEHYDRATE DERIVED COMPOS/T/ONS"

TECHNICAL FIELD

The present invention discloses a molten urea dehydrate suitable for preparing dry proton donors such as a dry, stable, granular, acidic and non-catalytic composition of matter, employable as a substitute for dry acids. The composition has a pH of « 1.2 and consists primarily of ammonium hydrogen sulfate, cyanuric and sulfuric acids. Additionally disclosed is a process for the preparation of the foregoing composition through reaction of species of dehydrated urea, sodium hydroxide and aqueous sulfuric acid.

BACKGROUND ART

Urea is the amide of carbamic acid (NH₂COOH) or the diamide of carbonic acid CO(OH)₂. Urea is a colorless, oderless, tasteless composition at standard temperature and pressure. If dissolved in water urea hydrolyzes into ammonium carbamate and then into ammonia and carbon dioxide.

Urea is typically produced by direct dehydration of ammonium carbamate (NH₂COONH₄). At its melting point urea decomposes to ammonia, biuret, cyanuric acid, ammelide, and triuret. Urea is a monobasic substance which forms salts with acids. See, for example, Encyclopedia of Chemical Technology (Vol. 23 "Urea" p. 548 et seq.).

Sulfamic acid (HSO₃NH₂) is an inorganic, dry acid produced and sold in the form of water-soluble crystals and granules. Its principal commercial application has been as a scale remover in chemical cleaning operations. Salts of sulfamic acid are used in electroplating and electroforming operations and in the manufacture of flame retardants and herbicides. Although sulfamic acid has been produced in the laboratory for more than a hundred years, it was not until 1936 that a process of commercial preparation was discovered. First disclosed by Baumgarten in USPN 2,102,350, the process involves reacting urea with sulfuric acid and sulfur trioxide (either separately or as oleum). This process, with modifications, has been the primary method of commercial production since 1936 (even though the reaction is strongly exothermic).

Over the years, numerous modifications of this process have been introduced in an effort to improve yields and overcome the hazards arising from the inherent exothermia. The prior art discloses two main methods of preparing sulfamic acid. The first method involves a reaction between anhydrous ammonia and sulfuric anhydride, resulting in the formation of ammonium sulfamino salts. These salts must then be acidified and hydrolyzed with sulfuric acid, thus leading to the formation of sulfamic acid and a greater or smaller quantity of a by-product known as ammonium hydrogen sulfate

(ammonium bisulfate). This by-product is separated through crystallization and filtration in the form of ammonium sulfate (after neutralization of the mother liquors of crystallization of the sulfamic acid). This type of low-yield process has the disadvantage of leading to the formation of, at best, one molecule of ammonium hydrogen sulfate per molecule of sulfamic acid formed.

The second method involves the formation of sulfamic acid from sulfuric acid, sulfuric anhydride and urea according to the general reaction scheme: H₂S0₄ + S0₃ +C0₂(NH₂)₂ → 2 HS0₃NH₂ + C0₂

This method has the theoretical advantage of not resulting in the formation of ammonium sulfate. There are two embodiments of this second process. In the first, urea is reacted with a substantial excess of sulfuric acid and anhydride. These two reactants are added either separately or in the form of mixtures of oleum and sulfuric acid, giving a suspension of sulfamic acid in a weak oleum or in sulfuric acid. In order to obtain separation of the sulfamic acid, it is necessary to filter and wash the cakes obtained in increasingly dilute sulfuric liquors. Filtering and washing operations are difficult and expensive, they always cause partial hydrolysis of the sulfamic acid, leading to a loss of this product in the form of ammonium hydrogen sulfate.

An alternative embodiment of this second type of process involves the reaction of sulfuric acid and urea in stoichiometric proportions with a quantity of sulfuric anhydride which may be in excess at a temperature below 50°C. Then in a second phase, the liquid complex formed is decomposed at a temperature of 60 to 100°C while the excess S0₃ and the C0₂ formed are entrained by means of an inert gas. In USPN 2,408,492, Tauch proposed to effect this decomposition in the presence of a third substance, a solid pulverulent diluent, which would ensure the mass retains the appearance of a dry product. The decomposition is then carried out in a reactor with vigorous agitation so as to break the sulfamic acid into small granules. One of the difficulties of this technique, which is otherwise useful, is the elimination of the heat released by the reaction for forming the complex since the very viscous liquid obtained has to be conveyed to a heat exchanger outside the reactor. Efforts have been made to control the heat of the reaction by, for example, using excess liquid sulfur trioxide [Tauch, USPN 2,408,823 and USPN 2,851 ,336 and McQuald USPN 2,436,658] or by premixing the urea, sulfur trioxide and sulfuric acid in a pre-mix reaction with cooling to give a liquid mass which is then heated to form sulfamic acid [Hill, USPN 2,390,648 and USPN 2,191,754] or by cycling the reacting mass through an external cooling mechanism [Leonard, USPN 2,409,572]. In 1983, Leclercq disclosed in USPN 4,386,060, a process for the preparation of sulfamic acid which involved a two stage process wherein the sulfuric anhydride used in the first stage is dissolved at a temperature less than 50°C in a halogenated fluorocarbon or a mixture of halogenated fluorocarbons having a boiling point of from 273.16 K to 323.16 K (0.0 to 50°C) or, alternatively, in a one-stage process at 60°C to 100°C with the sulfuric anhydride dissolved in a halogenated fluorocarbon or a mixture of halogenated fluorocarbons have a boiling point below 100°C at atmospheric pressure. The halogenated fluorocarbon serve to remove the heat generated by the exothermic formation of the sulfamic acid from the original reactants. However, the expense of production is increased by the need to utilize this additional reactant.

All of the methods provided by the prior art utilize the three reactants (urea, sulfur trioxide and sulfuric acid) in varying proportions. All have the disadvantage of being expensive and time-consuming. As a result of these disadvantages, today there are no manufacturers of sulfamic acid located within the United States. It is therefore the primary objective of this invention to produce a composition of matter employable as a substitute for sulfamic acid (and other dry acids) in many commercial applications. Another objective of the present invention is to provide a composition of matter which is (and will remain) dry and solid under generally normal atmospheric conditions.

Still another object of the present invention is to provide a method for the conversion of a urea melt to a form whereas it may react directly with sulfuric acid and other proton donors.

Yet still another objective of the present invention is to provide a commercially feasible method of preparation of the foregoing composition being attractive to U.S. manufacturers because of its simplicity, safety and economy. Also disclosed is a method of producing a dehydrated urea melt

(Green Liquor Reactant [GLR]) which may be reacted with proton donors to produce useful compositions. DETAILED DESCRIPTION OF THE INVENTION I. Preparation of Green Liquor Reactant

The present invention may be utilized to produce various compositions including a dry, stable, granular, acidic and non-catalytic composition of matter, employable as a substitute for sulfamic acid and/or other dry acids and salts in many commercial applications.

The green liquor reactant (GLR) is produced by first dehydrating urea into one or more of its four condensed species in accordance with the following reactions:

UREA + HEAT — ► NH₂CONHCONH₂ + NH₃ BIURET

UREA + HEAT → N^CONHCONHCONH, + 2NH₃ TRIURET

UREA + HEAT → NHCONHCONHCO + 3NH₃ CYANURIC

ACID

UREA + HEAT → NH₂CONHNHCONC + 2NH₃ + H₂0 AMMELIDE

All four species will be present in some proportion in the molten dehydrated urea. In order to maximize the efficiency of the dehydration, the reaction should be conducted in such a way as to allow the reacting mixture to have a high surface area in order to maximize NH₃ and H₂0 evolution and preventing re-hydration (stainless steel [or similar alloy] reaction vessels are preferred). Additionally, a small amount of sodium hydroxide (5%) is added to the urea melt has a catalytic effect.

Insoluble forms of these species (biuret and cyanuric acid) will be produced in too great a proportion if the dehydration is carried out too quickly or too long at temperatures in excess of 160°C. If present in too high of a proportion, these insoluble species will cause the molten urea to appear whitish in color indicating it has become unreactive with the sulfuric acid. When the desired species are present in high proportion, the dehydrated molten urea will appear as a dark green liquid or a yellow-green melt.

The GLR may be utilized to produce many useful compositions of matter pursuant to several reaction pathways and procedures and several heretobefore unknown qualities and features.

II. Composition Consisting Essentially of Ammonium Hydrogen

Sulfate and Cyanuric Acid and a Sodium Molecule a. Production The present invention discloses a dry, stable, granular, acidic and non-catalytic composition of matter, employable as a substitute for sulfamic acid in many commercial applications. The composition has a pH of 2.0 and consists primarily of ammonium hydrogen sulfate, cyanuric and sulfuric acids. Additionally, a process is disclosed for the preparation of the present composition through a reaction of dehydrated urea, sodium hydroxide and aqueous sulfuric acid. The product, while providing a effective substitute for sulfamic acid in many commercial applications, does not require sulfur trioxide, either separately or as a component of oleum in its production. Also eliminated is the need for time consuming and labor intensive filtration and washing steps as typically disclosed in prior art processes for the production of sulfamic acid. The method described herein additionally does not require the use of fluorocarbons or any other mechanisms to control the heat of reaction. This process results in a high yield of commercial grade product which does not require separation from by-products. The disclosed product, while possessing many similar characteristics to that of sulfamic acid has the advantage of being able to be produced faster and more inexpensively while it remains solid under atmospheric conditions.

The process requires as a first step that urea be dehydrated into one or more of its four condensed species in accordance with the following reactions (as disclosed previously as GLR):

UREA + HEAT → NH₂CONHCONH₂ + NH₃ BIURET

UREA + HEAT → N^CONHCONHCONH, + 2NH₃ TRIURET

UREA + HEAT → NHCONHCONHCO + 3NH₃ CYANURIC ACID

UREA + HEAT → NH₂CONHNHCONC + 2NH₃ + H₂0 AMMELIDE All four species will be present in some proportion in the molten dehydrated urea. In order to maximize the efficiency of the dehydration, the reaction should be conducted in such a way as to allow the reacting mixture to have a high surface area in order to maximize NH₃ and H₂0 evolution and preventing re-hydration. Additionally, a small amount of sodium hydroxide (5%) added to the urea melt has a catalytic effect.

Insoluble forms of these species (biuret and cyanuric acid) will be produced in too great a proportion if the dehydration is carried out too quickly at temperatures in excess of 160°C. If present in too high of a proportion, these insoluble species will cause the molten urea to appear whitish in color indicating it has become unreactive with the sulfuric acid. When the desired species are present in high proportion, the dehydrated molten urea will appear as a dark green liquid or a yellow-green melt.

The advantage of dehydrating the urea is that, in this form and with the proper proportion of condensed species present, it will react directly with sulfuric acid to form ammonium bisulfate. Thus, dehydration eliminates the need for sulfur trioxide, thereby reducing the costs of production.

In order that the nature of my novel process may be more clearly described, reference will be made hereinafter, by way of example, to specific embodiments of the processes, but it will be apparent many variations and modifications may be made in the particular conditions set forth.

The preferred embodiment of the process is described as follows: Urea (NH₂-CO-NH₂) in any form, but preferably in the form of 287% granular fertilizer or feed grade, is slowly heated to a temperature in excess of its melting point but less than 160°C and until dehydrated/condensed into a mix of four species: Biuret (NH₂-CO-NH- CO-NH₂), Cyanuric Acid (NH-CO-NH-CO-NH-CO), Ammelide (NH₂-CO- NH-NH-CO-N-C) and/or Triuret (NH₂-CO-NH-CO-NH-CO-NH₂). In order to prevent re-hydration and provide for a high yield of the dehydrated species, the dehydration should be performed in such a manner as to afford the reaction mixture with a high surface area so as to provide for maximum NH₃ and H₂0 evolution. Additionally, a small amount of sodium hydroxide (5%) has been found to have a catalytic effect on the urea. Complete dehydration of the urea generally occurs within 30 to 45 minutes depending upon the volume of urea being heated. Under manufacturing conditions, the urea has been found to have become sufficiently dehydrated upon the lose of between 8 and 15 percent of its weight and appearing greenish in color. At this point, the reaction mixture will be nearly to the point of solidification, but still capable of being poured and stirred.

Once the urea has been sufficiently dehydrated, about 50 pounds (~ 20.0 kg) of finished dry acid is introduced into the discharge spout of a well ventilated ribbon or paddle mixer (or an amount sufficient to plug the discharge spout of the mixer). The mixer should be preferably one made of stainless steel (although carbon steel which has been treated with a baked-on corrosion inhibitor is acceptable). This finished product, as introduced to the discharge spout of the mixer, acts as a plug which will contain the yet added sulfuric acid and keep it from leaking out of the bottom of the mixer. Next, an appropriate amount of 93 to 98 percent sulfuric acid (H₂S0₄), preferably 93 percent should be added to the mixture. Upon the introduction of the urea melt to the mixer containing the acid, a boiling, foaming reaction takes place giving off C0₂, water vapor and small amounts of S0₂ while yielding the claimed composition of matter. The rate of addition of the dehydrated urea to the sulfuric acid should be such that the foaming mix does not overflow the mixer. Thus, the rate of addition is dependent upon the size and depth of the mixer.

During the mixing process, a small amount of dodecylbenzene sulfonic acid (DBSA), a surfactant, may be added to the reaction mixture. DBSA causes larger crystals to be formed, resulting in a less hygroscopic and larger finished crystal. As the reaction proceeds, the mixture first forms a white liquid which then begins to solidify after a few minutes to a white paste. After further cooling (15 - 20 minutes), the reaction mixture further solidifies into a white granular powder. At this stage, a silicon dioxide coating is added to the mixture to improve flowability. After continued drying of the reaction mixture, the resultant granular powder may be discharged from the mixer through a bottom gate, into a drum where it continues to cool, forming a large stable crystalline solid. This final curing stage has become known as the "denning" stage. After the product has been in the "denning" drum for 2 to 12 hours, it may be fed into an auger and delivered to a bin above a grinder and ground to a fine powder, suitable for commercial use in descaling and other chemical cleaning applications.

Since the reaction is strongly exothermic and results in the evolution of C0₂, S0₂ and water vapor, care must be taken to protect workers from splashing. The preferred method of safely mixing these reactants is to always add, at a slow rate, the dehydrated urea to the sulfuric acid and not vice versa. b. Example

To produce 411 pounds (187 kg) of the product, approportion 114 pounds (52 kg) of urea into 12 stainless steel pans respectively containing 9.5 pounds (4.3 kg) each. Slowly heat the urea to between

138 and 160°C (280 and 320°F), being careful not to exceed the latter temperature, until it reaches a condensed form, greenish in color and nearly solid, but molten enough to be poured. Then, add V≥ pound NaOH to each pan and continue heating for 10 to 12 minutes. Once finished heating the urea melt, pour the composition into a 55 gal drum (208 liters).

Into the discharge spout of a well ventilated large stainless steel or carbon steel mixer which has been treated with a baked-on corrosion inhibitor, add about 50 pound (23 kg) of the finished product to keep the sulfuric acid from leaking out the bottom. Into the sealed mixer, carefully add 240 pound (110 kg) of 93 percent sulfuric acid. Then, slowly add, over a period of 2 to 5 minutes, the molten dehydrated urea into the mixer while stirring. The reaction which occurs becomes very hot 177 to 204°C (350 to 400^'F) and gives off huge volumes of steam, C0₂ and small amounts of S0₂. The rate of addition should be slow enough to avoid having the resulting foam overflow the mixer. After all the reaction ingredients are in the mixer, add 14 pound of the surfactant dodecylbenzene sulfonic acid. As the reaction proceeds, the mixture first forms a white liquid which then begins to solidify after a few minutes to a white paste. After further cooling (15 to 20 minutes), the reaction mixture further solidifies into white granules. At this stage, % pound of silica dioxide may be added to the mixture as a flow agent. After further drying of the reaction mixture, the resultant granular powder is discharged from the mixer through a bottom gate and into a drum where it continues to cool, forming a large stable crystalline solid. After the product has been "denning" for 2 to 12 hours, it may be ground and fed into 50 pound (25 kg) bags, thus, ready for sale without further processing.

AHSSASM has been determined under Department of Transportation (DoT) testing (Title 40, Code of Federal Regulations) to be as follows: Corrosivity Not a corrosive

Oral toxicity Not a poisonous material

Dermal toxicity Not a poisonous material Eye irritation Severe eye irritation

Conversely, sulfamic acid causes permanent eye damage and is considered to have dermal toxicity. c. Industrial Applicability

1. Fire Prevention

The composition consisting essentially of ammonium hydrogen sulfate and cyanuric acid and a sodium molecule (AHSCASM) may be utilized as a flame retardant in clothing, in plastics, and paper products.

Likewise, AHSCASM may be utilized in fire extinguishing and fire fighting equipment when added with sodium bicarbonate, a surfactant and water. 2. Phosphate Rock Beneficiating

The composition consisting essentially of ammonium hydrogen sulfate and cyanuric acid and a sodium molecule (AHSCASM) may be utilized for beneficiating phosphate ores containing dolomite. III. Composition Consisting Essentially of Ammonium Hydrogen

Sulfate and Sulfamic Acid and a Sodium Molecule a. Production

Production GLR is mixed hot with oleum (sulphur trioxide) so as to produce an ammonium hydrogen sulfate and sulfamic acid and a sodium molecule (AHSSASM) composition.

In accordance with the discussion infra regarding the production of GLR, urea is melted (dehydrated) with ammonia and some water vapor as a product of the dehydration. Once the urea is dehydrated (loss of 8.0 to 12.0 percent of original mass or until substantially no NH₂ remains) the NH-CO strings are reacted with sodium hydroxide (0.25 to 2:9.5 by weight) in two additions. Water vapor evolution stops once the sodium hydroxide is added to the melt. The sodium hydroxide converts carbon dioxide in the dehydrated urea into sodium carbonate/bicarbonate and NH oligomer of unknown composition. If the available NH is high in the resultant composition then sulfamic acid will be a product if the mixture is reacted with sulfuric acid. Likewise, if insufficient ammonia was driven off during urea dehydration ammonium bisulfate will form.

In a 1 :2 ratio GLR is added slowly while mixing to the oleum in a jacketed and chilled mixer. The product of this reaction (AHSSASM) is a strong dry acid with a pH of less than 1 (<1). b. Industrial Applicability

The AHSSASM of the present invention may be utilized with a high degree of efficacy as a replacement for sulfamic acid, ammonium hydrogen sulfate, or any other strong dry acid. IV. Composition Consisting Essentially of GLR Molecules

(Nitrogen Containing Molecules) and Acetic Acid and a

Sodium Molecule a. Production

Production GLR is mixed hot with acetic acid so as to produce a GLR acetate. The hot GLR is added very slowly to acetic acid in a chilled jacketed mixer so the acid does not combust. b. Industrial Applicability

The GLR acetate may be utilized in feed additive for stock animals such as cattle, dairy cows, and other ruminants. For example, cattle are typically fed urea and a drug such as lasolocid sodium so as to increase acetic acid production in the rumen. Use of the GLR acetate effectively replaces both the urea and the drug application. The GLR acetate is preferably fed at a rate of 0.1 percent of body weight daily for each animal. V. Composition of GLR with other Proton Donors (H⁺)

When hot GLR is added and mixed with other proton donors a variety of new dry acids with unique properties are formed. The temperature of reaction, mixing ratio, and vessel composition, all effect the physical properties of the end product. By adding GLR to conventional organic and inorganic acids stable dry acids which are non- hygroscopic are formed. These new acids generally form anhydrous sodium carbonate molecules which co-precipitate and confers unique safety and anti-corrosive properties not found in the conventional non- GLR based organic or inorganic acid.

While the invention has been described in connection with preferred procedures, it will be understood that it is not intended to limit the invention to those procedures. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.

Claims

1. A process for the preparation of a composition of matter comprising the steps of:

(a) heating urea until it is dehydrated and condensed into a molten mixture of biuret, triuret, cyanuric acid, and ammelide; and

(b) mixing the molten dehydrated and condensed species of urea into a crystal forming amount of aqueous sulfuric acid.

2. The process of claim 1 further comprising drying said mixture.

3. The process of claim 2 further comprising grinding said dried mixture into a particulate state.

4. The process of claim 1 wherein said urea is heated between its melting point (* 135°C) and 160°C.

5. The process of claim 4 whereupon said urea is heated between said temperature for between 20 and 45 minutes.

6. The process of claim 1 wherein said species of urea are mixed with 93 to 98 percent sulfuric acid.

7. The process of claim 6 wherein said sulfuric acid is 93 percent sulfuric acid.

8. The process of claim 1 wherein said urea is heated until it loses between 20 and 30 percent of its mass.

9. The process of claim 8 wherein said urea is heated until it has a greenish colour and is a molten solid.

10. The process of claim 1 further comprising adding a catalyst during said heating step.

11. The process of claim 10 wherein said catalyst is sodium hydroxide (NaOH).

12. The process of claim 11 wherein said sodium hydroxide is in a five percent concentration.

13. The process of claim 1 further comprising adding an emulsifier in said mixing step.

14. The process of claim 13 wherein said emulsifier is a surfactant.

15. The process of claim 14 wherein said surfactant is dodecylbenzene sulfonic acid (DBSA).

16. The process of claim 3 further comprising adding a flow agent to said mixture.

17. The process of claim 16 wherein said flow agent is silica dioxide.

18. A dry, stable, non-catalytic composition of matter consisting essentially of:

(a) ammonium bisulfate (NH₄HS0₄); and

(b) cyanuric acid (C₃H₃N₃0₃).

19. The composition of matter of claim 18 wherein said composition is between 5 and 15 percent cyanuric acid.

20. The composition of matter of claim 18 wherein said composition is between 85 and 95 percent ammonium bisulfate.

21. The composition of matter of claim 18 wherein said composition is 11 percent cyanuric acid and 89 percent ammonium bisulfate.

22. The composition of matter of claim 18 further consisting of the group selected from ammonium sulfamate (NH₄S0₃NH₂), ammonium sulfate (NH₄S0₄), and sulfamic acid (H₂NS0₃H).

23. A process for the preparation of a composition of matter comprising the steps of:

(a) heating urea until it is dehydrated and condensed into a molten mixture of biuret, triuret, cyanuric acid, and ammelide; and (b) mixing the molten dehydrated and condensed species of urea with sodium hydroxide so as to produce a molten green liquor reactant.

24. The process of claim 23 further comprising adding said molten green liquor reactant with a proton donor so as to produce a dry acid.

25. The process of claim 24 wherein said proton donor is selected from the group consisting of (i) cyanuric acid, (ii) sulfuric acid, sodium trioxide, and acetic acid.

26. A composition of matter consisting essentially of (a) ammonium hydrogen sulfate, (b) cyanuric acid, and (c) a sodium molecule.

27. A composition of matter consisting essentially of (a) ammonium hydrogen sulfate, (b) sulfamic acid, and (c) a sodium molecule.

28. A composition of matter consisting essentially of (a) a nitrogen containing molecule derived from green liquor reactant, (b) acetic acid, and (c) a sodium molecule.

29. A composition of matter consisting essentially of (a) a nitrogen containing molecule derived from green liquor reactant, (b) a proton donor, and (c) a sodium molecule.

30. A method of beneficiating phosphate from dolomite (MgCa(CO._j)₂) and phosphate, comprising the step of treating the ore with AHSCASM.

31. A method of increasing the acetic acid content in the rumen of a ruminant comprising the step of supplementing the feed of said ruminant with a composition consisting essentially of a nitrogen containing molecule derived from GLR and acetic acid and a sodium molecule.