Ammonia and ammonium hydroxide stabilizers for paraformaldehyde

Abstract

To provide a process for forming stabilized paraformaldehyde.SOLUTION: A process for forming stabilized paraformaldehyde includes exposing solidified paraformaldehyde to gas containing 50 ppm to 500 ppm of ammonia and / or ammonium hydroxide stabilizer. It is preferable that the solidified paraformaldehyde is free of organic amine. It is preferable that a supply source of the ammonia and / or ammonia hydroxide stabilizer is urea.SELECTED DRAWING: None

Description

Technical Field

[0001]

[0001] This disclosure relates to improvements in the storage life, handling, and transportation of paraformaldehyde.

Background Art

[0002]

[0002] Paraformaldehyde is a solid form of formaldehyde that is 80% or more. Typically, the formaldehyde concentration ranges from 90% to 96%. Paraformaldehyde is considered to be poly(oxymethylene) glycol, HO--(CH2O) n --H (n = 8 to 100). Generally, paraformaldehyde is produced by concentrating an aqueous solution of hot formaldehyde under reduced pressure. When cooled, the resulting solution solidifies into prills for storage and / or transportation.

[0003]

[0003] Paraformaldehyde exhibits excellent solubility in water and organic solvents such as butanol immediately after production. It readily dissolves in water or alcohol by hydrolysis or depolymerization to form methylene glycol or formal. However, its solubility in water and solvents decreases over time or when stored at temperatures generally exceeding about 35°C. This change in solubility is probably due to changes in the molecular weight (or the value of n) and end-capping of the paraformaldehyde chains by methanol. The solubility and reactivity of paraformaldehyde decrease with an increase in molecular weight.

[0004]

[0004] The presence of methanol in the reaction mixture also leads to the formation of insoluble matter. Insoluble matter is generally paraformaldehyde with its ends capped by alcohol, forming ethers. These high molecular weight ethers are insoluble in any solution unless they contain a strong acid. Paraformaldehyde typically contains insoluble matter at a concentration of about 10 ppm to 20 ppm. As paraformaldehyde is stored for a period of time, the small amount of alcohol in the pryl reacts with the paraformaldehyde to form even more insoluble matter. For example, after storage at ambient temperature, the concentration of insoluble matter can exceed 100 ppm, and in some cases, it can exceed 350 ppm if high concentrations of methanol are present. The industry standard for an acceptable amount of insoluble matter is less than 100 ppm. Therefore, the shelf life of paraformaldehyde is very short.

[0005]

[0005] To mitigate this problem, many stabilizers and inhibitors have been proposed. For example, amines such as hexaethylamine and triethylamine have been used. It is thought that stabilizers slow down chain growth and slow down the end encapsulation of paraformaldehyde, thereby reducing the formation of insoluble material over time. However, stabilizers also increase the stickiness of the prill, making manufacturing and handling very difficult.

[0006]

[0006] The following drawings are included to illustrate certain aspects of the embodiments and should not be considered exclusive embodiments. The disclosed subject matter can be modified, altered, combined and equivalent in form and function as can be imagined by those skilled in the art who will benefit from this disclosure. [Brief explanation of the drawing]

[0007] [Figure 1]

[0007] Figure 1 shows a diagram of an apparatus simulating a quenching vessel. [Overview of the project]

[0008]

[0008] The present disclosure relates to improving the shelf life, handling, and transport of paraformaldehyde using ammonia and / or ammonium hydroxide as stabilizers. [Modes for carrying out the invention]

[0009]

[0009] As used herein, the term “prill” refers to a pellet or a small solid ball. The final product of paraformaldehyde may also be in the form of flakes, lumps, granules, etc., depending on the method of solidification and drying of the paraformaldehyde. In this specification, the final product of paraformaldehyde is described in the form of “solidified (or solidified) paraformaldehyde,” which may be any suitable solidification form, including but not limited to prills, flakes, lumps, granules, etc.

[0010]

[0010] At low concentrations, hydrocarbon amines can stabilize solidified paraformaldehyde without making it sticky. However, the concentration of hydrocarbon amines is not high enough to noticeably extend the shelf life of solidified paraformaldehyde. At high concentrations, hydrocarbon amines make solidified paraformaldehyde so sticky that it cannot be transported by conventional means such as compressed air.

[0011]

[0011] It has been found that using ammonia and / or ammonium hydroxide as a stabilizer for paraformaldehyde allows for use at high concentrations, thus enabling the production of solidified paraformaldehyde that is non-sticky and has a long shelf life. Urea can be used as a source of ammonia by mixing urea with water and heating it.

[0012]

[0012] Though not limited to theory, ammonia and / or ammonium hydroxide react with the ends of the paraformaldehyde chain to form crystalline oximes and also neutralize any acidic catalyst. Both of these effectively inhibit chain growth and alcohol end encapsulation of solidified paraformaldehyde.

[0013]

[0013] Generally, the production of solidified paraformaldehyde involves heating a formaldehyde solution containing 30 wt% or more of formaldehyde (for example, about 30 wt% to 90 wt% formaldehyde) to a temperature of about 70°C to about 130°C, preferably about 80°C to about 100°C. The formaldehyde solution is held at this temperature for about 0.1 hours to about 3 hours, preferably about 20 minutes to about 40 minutes, more preferably about 20 minutes to about 30 minutes. This is often called maturation. During maturation, the formaldehyde polymerizes to form paraformaldehyde. Once the maturation process is complete, the paraformaldehyde product solidifies. In particular to form prills, the paraformaldehyde is passed through a nozzle to form prills, which are then dropped into a countercurrent gas in a prilling tower. This causes the paraformaldehyde to solidify. Polymerization reactions can still occur even during the solidification of paraformaldehyde. Optionally, the solidified paraformaldehyde is transferred to a quenching vessel, typically using compressed air, and further cooled. The solidified paraformaldehyde can be dried at a temperature of about ambient temperature to about 150°C, preferably about 50°C to about 100°C, for about 15 minutes to about 20 hours, preferably about 1 hour to about 2 hours. Polymerization reactions can still occur even during the drying of the solidified paraformaldehyde. The solidified paraformaldehyde is then stored or transported to the customer. Handling and transport of solidified paraformaldehyde within the plant or in storage is typically carried out using compressed air. The use of ammonia and / or ammonium hydroxide stabilizers does not make the solidified paraformaldehyde sticky like other amine stabilizers, so handling and transport of solidified paraformaldehyde is essentially the same as that of untreated solidified paraformaldehyde. Ammonia and / or ammonium hydroxide stabilizers can be incorporated into any part of the production or storage of paraformaldehyde.

[0014]

[0014] Exemplary aspects of the present disclosure include heating a formaldehyde solution containing 30 wt% or more of formaldehyde and about 50 ppm to about 1000 ppm, preferably 100 ppm to 500 ppm, more preferably 150 ppm to 250 ppm of ammonia and / or ammonium hydroxide stabilizer to a temperature in the range of about 70°C to about 130°C; and heating the formaldehyde solution to The method comprises allowing the formaldehyde to mature for a sufficient time to polymerize and form paraformaldehyde, and then solidifying the paraformaldehyde (for example, passing the paraformaldehyde through a nozzle to form prills, which are then dropped into a countercurrent gas in a prilling tower for further polymerization and solidification). The method may further include drying the solidified paraformaldehyde.

[0015]

[0015] Another exemplary aspect of the present disclosure includes heating a formaldehyde solution containing 30 wt% or more of formaldehyde to a temperature in the range of about 70°C to about 130°C; aging the formaldehyde solution for a time sufficient for the formaldehyde to polymerize to form paraformaldehyde in the presence of about 50 ppm to about 1000 ppm, preferably 100 ppm to 500 ppm, and more preferably 150 ppm to 250 ppm of ammonia and / or ammonium hydroxide stabilizer; and solidifying the paraformaldehyde (for example, passing the paraformaldehyde through a nozzle to form prills, which are then dropped into countercurrent gas in a prilling tower for further polymerization and solidification). The method may further include drying the solidified paraformaldehyde.

[0016]

[0016] A further exemplary embodiment of the present disclosure includes heating a formaldehyde solution containing 30 wt% or more of formaldehyde to a temperature in the range of about 70°C to about 130°C; aging the formaldehyde solution for a time sufficient for the formaldehyde to polymerize to form paraformaldehyde; and solidifying the paraformaldehyde in a prilling tower in the presence of a gas containing about 10 ppm to about 1000 ppm, preferably 25 ppm to 500 ppm, more preferably 50 ppm to 150 ppm of ammonia and / or ammonium hydroxide stabilizer (for example, passing the paraformaldehyde through a nozzle to form prills and dropping them into a counterflowing gas), and further polymerizing and solidifying it. The method may further include drying the solidified paraformaldehyde.

[0017]

[0017] Another exemplary aspect of the present disclosure includes heating a formaldehyde solution containing 30 wt% or more of formaldehyde to a temperature in the range of about 70°C to about 130°C; aging the formaldehyde solution for a time sufficient for the formaldehyde to polymerize to form paraformaldehyde; solidifying the paraformaldehyde (for example, by passing the paraformaldehyde through a nozzle to form prills, which are then dropped into a countercurrent gas in a prilling tower for further polymerization and solidification); drying the solidified paraformaldehyde; and exposing the solidified paraformaldehyde during and / or after drying to a gas containing about 10 ppm to about 1000 ppm, preferably 25 ppm to 500 ppm, and more preferably 50 ppm to 150 ppm of ammonia and / or ammonium hydroxide stabilizer.

[0018]

[0018] Another exemplary aspect of the present disclosure includes heating a formaldehyde solution containing 30 wt% or more of formaldehyde to a temperature in the range of about 70°C to about 130°C; aging the formaldehyde solution for a time sufficient for the formaldehyde to polymerize to form paraformaldehyde; solidifying the paraformaldehyde (for example, by passing the paraformaldehyde through a nozzle to form prills, which are then dropped into countercurrent gas in a prilling tower for further polymerization and solidification); drying the solidified paraformaldehyde; transporting the solidified paraformaldehyde to a storage facility; and exposing the solidified paraformaldehyde during transport or in the storage facility to a gas containing about 10 ppm to about 1000 ppm, preferably 25 ppm to 500 ppm, more preferably 50 ppm to 150 ppm of ammonia and / or ammonium hydroxide stabilizer.

[0019]

[0019] Combinations of the methods described above can be used. For example, the ammonia and / or ammonium hydroxide stabilizer can be used in one or more of the heating, aging, solidification, drying, or storage steps. If two or more steps involve exposure to the ammonia and / or ammonium hydroxide stabilizer, a lower concentration of the ammonia and / or ammonium hydroxide stabilizer can be used in each step.

[0020]

[0020] In each of the above embodiments, urea can be used as a source of ammonia and / or ammonium hydroxide stabilizer.

[0021] In each of the embodiments described above, the formaldehyde solution may contain 30 wt% or more of formaldehyde (for example, about 30 wt% to 90 wt% of formaldehyde), preferably about 35 wt% to 75 wt% of formaldehyde, and more preferably about 36 wt% to 50 wt% of formaldehyde.

[0021]

[0022] In each of the embodiments described above, the formaldehyde solution may be heated to a temperature of about 70°C to about 130°C, preferably about 80°C to about 100°C.

[0023] In each of the foregoing embodiments, the formaldehyde solution can be held (aged) at a temperature of about 70°C to about 130°C, preferably about 80°C to about 100°C, for about 0.1 hour to about 3 hours, preferably about 20 minutes to about 40 minutes, and more preferably about 20 minutes to about 30 minutes.

[0022]

[0024] In each of the foregoing embodiments, the solid paraformaldehyde can be dried at a temperature of about ambient temperature to about 150°C, preferably about 50°C to about 100°C, for about 15 minutes to about 20 hours, preferably about 1 hour to about 2 hours.

[0023]

[0025] Exposure of the solid paraformaldehyde to an ammonia and / or ammonium hydroxide stabilizer at any point from formation through storage, including during formation and storage, can include exposing the solid paraformaldehyde to a gas containing about 10 ppm to about 1000 ppm, preferably 25 ppm to 500 ppm, and more preferably 50 ppm to 150 ppm of an ammonia and / or ammonium hydroxide stabilizer. The ammonia and / or ammonium hydroxide stabilizer may be diluted in a carrier gas. Examples of carrier gases include, but are not limited to, air, oxygen, nitrogen, carbon dioxide, argon, etc., and any combination thereof.

[0024]

[0026] In each of the foregoing embodiments, the formaldehyde solution can further contain an acidic or basic catalyst. Examples of catalysts include, but are not limited to, formic acid, boric acid, sodium tetraborate, oxalic acid, and any combination thereof.

[0025]

[0027] In each of the foregoing embodiments, the formaldehyde solution, paraformaldehyde, and solidified paraformaldehyde may be without an organic amine. As used herein, the term "organic amine" includes low molecular weight compounds (less than 500 g / mol, preferably less than 300 g / mol) composed of carbon, hydrogen, nitrogen, and optionally oxygen. Examples of organic amines include, but are not limited to, methylamine, ethylamine, n-propylamine, n-butylamine, iso-butylamine, tert-butylamine, dimethylamine, diethylamine, di-n-propylamine, di-iso-propylamine, dibutylamine, triethylamine, and triethanolamine, hexamethylenetetramine, 2-ethylhexylamine, 2-aminopropanediol, hexylamine, ethanolamine, mixed C 20 amines, mixed C 10 amines, cyclohexylamine, 1,2-dimethoxypropanamine, triethylamine, ethanolamine, 1-amino-1,3-propanediol, 1-aminopentane, 2-methyloxypropylamine, and any combination thereof, etc.

[0026]

[0028] In each of the foregoing embodiments, the method further includes storing the solidified paraformaldehyde at ambient temperature to 50 °C for longer than 30 days (e.g., 30 days to 1 year or more) without increasing the insoluble matter concentration in the solidified paraformaldehyde beyond about 150 ppm, preferably about 120 ppm, more preferably about 100 ppm.

[0027]

[0029] An additional embodiment of the present disclosure is a paraformaldehyde composition comprising from about 1 ppm to 100 ppm, preferably from about 5 ppm to about 50 ppm, more preferably from about 10 ppm to about 25 ppm of an ammonia and / or ammonium hydroxide stabilizer and from about 80 wt% to about 99.9 wt%, preferably from about 90 wt% to about 99.9 wt%, more preferably from about 95 wt% to about 99.9 wt% of paraformaldehyde.

[0028]

[0030] The paraformaldehyde composition may also contain insoluble matter in an amount of about 1 ppm to about 200 ppm, preferably about 5 ppm to about 100 ppm, and more preferably about 10 ppm to about 50 ppm.

[0029]

[0031] In each of the embodiments of the paraformaldehyde composition described above, the paraformaldehyde composition may further contain an acidic or basic catalyst. Examples of catalysts, but not limited to these, include formic acid, boric acid, sodium tetraborate, oxalic acid, and any combination thereof.

[0030]

[0032] The source of the ammonia and / or ammonium hydroxide stabilizer is urea. In each of the embodiments of the paraformaldehyde composition described above, the paraformaldehyde composition may be in the absence of organic amines. Examples of organic amines, but not limited to these, include methylamine, ethylamine, n-propylamine, n-butylamine, iso-butylamine, tert-butylamine, dimethylamine, diethylamine, di-n-propylamine, di-iso-propylamine, dibutylamine, triethylamine, and triethanolamine, hexamethylenetetramine, 2-ethylhexylamine, 2-aminopropanediol, hexylamine, ethanolamine, and mixed C 20 Amine, mixed C 10 These include amines, cyclohexylamine, 1,2-dimethoxypropanamine, triethylamine, ethanolamine, 1-amino-1,3-propanediol, 1-aminopentane, 2-methyloxypropylamine, and any combination thereof.

[0031]

[0033] In each of the embodiments of the paraformaldehyde composition described above, the solidified paraformaldehyde may be in the form of prills, flakes, lumps, granules, or the like.

[0034] An exemplary embodiment of the present invention is a method comprising: heating a formaldehyde solution containing 30 wt% or more formaldehyde to a temperature in the range of about 70°C to about 130°C; aging the formaldehyde solution for a time sufficient for the formaldehyde to polymerize and form paraformaldehyde; solidifying the paraformaldehyde; and contacting the formaldehyde solution before and / or during heating, the formaldehyde solution during aging, the paraformaldehyde, and / or the solidified paraformaldehyde with ammonia and / or an ammonium hydroxide stabilizer. Optionally, the method may include one or more of the following: Element 1: The formaldehyde solution during heating further contains about 50 ppm to about 1000 ppm of ammonia and / or ammonium hydroxide stabilizer; Element 2: The formaldehyde solution during maturation further contains about 50 ppm to about 1000 ppm of ammonia and / or ammonium hydroxide stabilizer; Element 3: The solidification of paraformaldehyde comprises contacting the paraformaldehyde with a gas containing about 10 ppm to about 1000 ppm of ammonia and / or ammonium hydroxide stabilizer; Element 4: The method further comprises drying the solidified paraformaldehyde; Element 5: Element 4 and the method further comprises drying the solidified paraformaldehyde during and / or after drying Element 6: Element 4 or 5 and the method further include exposing the solidified paraformaldehyde to a gas containing approximately 10 ppm to approximately 1000 ppm of ammonia and / or ammonium hydroxide stabilizer; Element 7: Element 6 and the method further include exposing the solidified paraformaldehyde during transport and / or in the storage facility to a gas containing approximately 10 ppm to approximately 1000 ppm of ammonia and / or ammonium hydroxide stabilizer; Element 8: Element 6 or 7 and the method further include storing the solidified paraformaldehyde at ambient temperature ~ approximately 50°C for longer than 30 days, maintaining the insoluble matter concentration in the solidified paraformaldehyde at less than approximately 150 ppm. Element 9: The aging of the formaldehyde solution is approximately 0.1 hours to approximately 3 hours; Element 10: The method does not include organic amines; Element 11: The method further includes transporting the solidified paraformaldehyde to a storage facility; Element 12: The aging of the formaldehyde solution is 70°C to 130°C; and Element 13: The source of the ammonia and / or ammonium hydroxide stabilizer is urea. Examples of combinations, though not limited to these, include: combinations of elements 1, 4, and 11; combinations of elements 2, 4, and 11; combinations of elements 3, 4, and 11; combinations of elements 4, 5, and 11; combinations of elements 4, 6, and 7 (and optionally 8); combinations of elements 1, 4, 6, and 8; combinations of elements 2, 4, 6, and 8; combinations of elements 3, 4, 6, and 8; combinations of two or more elements 1, 2, 3, 4, and 5 (optionally further combinations of elements 6 and 7); and combinations of elements 9, 12, and / or 13 with any of the aforementioned elements.

[0032]

[0035] Another exemplary embodiment of the present invention involves exposing solidified paraformaldehyde to a gas containing about 10 ppm to about 1000 ppm of ammonia and / or ammonium hydroxide stabilizer. Optionally, the solidified paraformaldehyde is free of organic amines, and / or the source of the ammonia and / or ammonium hydroxide stabilizer is urea.

[0033]

[0036] A further exemplary embodiment of the present invention is a solidified paraformaldehyde comprising about 1 ppm to about 100 ppm of an ammonia and / or ammonium hydroxide stabilizer; and about 80 wt% to about 99.9 wt% of paraformaldehyde. Optionally, the solidified paraformaldehyde may comprise one or more of the following: Element 14: The solidified paraformaldehyde is in the absence of organic amines; Element 15: The solidified paraformaldehyde further comprises less than 150 ppm of insoluble matter; and Element 16: The solidified paraformaldehyde is in the form of prills, flakes, lumps, or granules.

[0034]

[0037] Unless otherwise indicated, all numerical values ​​used in this specification and the accompanying claims, such as quantities of components, properties like molecular weight, and reaction conditions, shall be understood in all cases to be modified by the term "approximately." Accordingly, unless otherwise shown, the numerical parameters set forth in the following specification and the accompanying claims are approximations that may vary depending on the desired properties to be obtained by the embodiments of the invention. At a minimum, and without attempting to limit the application of the doctrine of equivalents to the claims, each numerical parameter should be interpreted by applying common rounding techniques, at least in light of the reported number of significant figures.

[0035]

[0038] One or more exemplary embodiments incorporating aspects of the invention disclosed herein are shown herein. For clarity, not all features of physical implementations are described or shown in this application. In developing physical embodiments incorporating aspects of the invention, it should be understood that a number of implementation-specific decisions must be made, including compliance with system-related, business-related, government-related, and other constraints that vary by implementation and over time, in order to achieve the developer's objectives. While the developer's efforts are time-consuming, such efforts are still routine for those skilled in the art who benefit from this disclosure.

[0036]

[0039] While compositions and methods are described herein in terms of "containing" various components or processes, such compositions and methods may also "essentially consist of" or "consist of" various components and processes.

[0037]

[0040] To facilitate a better understanding of the embodiments of the present invention, preferred or representative embodiments are shown below. These embodiments should not be read in any way as limiting or defining the scope of the present invention. [Examples]

[0038]

[0041] Example 1. Apparatus 100 as shown in Figure 1 was used to simulate a quenching vessel. Apparatus 100 includes a dryer tube 102 (radius 2.5 inches (6.35 cm), height 11 inches (27.94 cm)) with a perforated plate 104 located 1.75 inches (4.445 cm) from the bottom, a gas inlet 106 between the bottom of the dryer tube 102 and the perforated plate 104, and a vent 108 at the top of the dryer tube 102. Furthermore, a thermocouple 110 extends from the top of the dryer tube 102 up to the perforated plate to measure the temperature inside the dryer tube 102. The gas inlet 106 is fluidically connected to a source 112 of ammonia and / or ammonium hydroxide stabilizer (e.g., a tank of ammonia, a tank of ammonia dilution in air, an aqueous solution of urea, an ammonium hydroxide solution, etc.). Wherever two components are described as being fluidically connected in this specification, there is hardware connecting the two components so that fluid can flow from one component to the other. This hardware may consist of two or more components, including lines, pipes, tubes, pumps, connectors, heat exchangers, valves, and the like.

[0039]

[0042] A heat exchanger 114 is located between the ammonia and / or ammonium hydroxide stabilizer supply source 112 and the dryer tube 102, and is used to heat the ammonia and / or ammonium hydroxide stabilizer before it is introduced into the dryer tube 102. Optionally, a gas (e.g., plant air) can be taken in from line 116 and combined with the ammonia and / or ammonium hydroxide stabilizer to dilute the ammonia and / or ammonium hydroxide stabilizer to the desired concentration.

[0040]

[0043] In this embodiment, 350 grams of paraformaldehyde prill were added to the dryer tube 102. As a result, the height of the prill reached 2.5 inches (6.35 cm) from the top of the dryer tube 102. A tank of 100 ppm ammonia in air was used as the source 112 for the ammonia and / or ammonium hydroxide stabilizer. The heat exchanger 114 was set to 200°F (93.3°C). 100 ppm ammonia in air was passed through the apparatus 100 at 30 standard cubic feet / min (0.85 cubic meters / min). As a result, the prill became a fluidized bed in the dryer tube 102. The fact that the prill maintained a fluidized bed indicates that the ammonia and / or ammonium hydroxide stabilizer did not make the prill too sticky for transport.

[0041]

[0044] The same experiment was conducted except that ethylhexylamine was used as a stabilizer. Prill became too viscous in the dryer tube 102 and did not flow.

[0045] Example 2. In a full-scale plant, paraformaldehyde prill was exposed to various concentrations of ammonium hydroxide in a prilling tower. More specifically, a 19% aqueous solution of ammonium hydroxide was heated to approximately 90°C. The resulting steam was passed through the prilling tower. Optionally, the steam could be diluted with plant air. Next, the prill was aged at 50°C for 4 days. This simulates 6 months of aging under normal storage conditions (approximately 23°C to 38°C). The amount of insoluble matter after aging is shown in Table 1. Here, the control is prill that was not exposed to ammonium hydroxide.

[0042] [Table 1]

[0043]

[0046] In all cases, the prill did not become sticky and was easily transported using standard methods and equipment.

[0047] These examples demonstrate that the use of ammonia and / or ammonium hydroxide stabilizers can maintain a low concentration of insoluble matter in solidified paraformaldehyde during storage, thereby maintaining conventional handling and transport capabilities.

[0044]

[0048] Thus, the present invention is well adapted to achieve not only the stated objectives and advantages but also the inherent objectives and benefits. The present invention can be modified and implemented in different but equivalent ways, which will be obvious to those skilled in the art who benefit from the teachings herein. The specific embodiments disclosed above are illustrative only. Furthermore, no limitations are intended to the configuration or design details shown herein other than those set forth in the following claims. Therefore, it is clear that the specific exemplary embodiments disclosed above are modifiable, combined, or modified, and all such variations are considered to fall within the scope and spirit of the invention. The invention as illustrated herein can be adequately implemented without any elements not specifically disclosed herein and / or any optional elements disclosed herein. Compositions and methods “comprising” various components or steps… Although described in terms of “containing” or “including,” the composition and method may also “essentially consist of” or “consist of” various components and processes. All numerical values ​​and ranges disclosed above are subject to some degree of variation. Whenever numerical ranges with lower and upper limits are disclosed, any numerical values ​​and any inclusions that fall within that range are specifically disclosed. In particular, any value range disclosed herein (in the form of “about a to about b” or equivalently “approximately a to b” or equivalently “approximately a ~ b”) is understood to indicate any numerical values ​​and ranges that fall within a broader range of values. Furthermore, terms in the claims have their obvious and ordinary meanings unless explicitly and clearly defined by the patentee. In addition, the indefinite article “a” or “an” used in the claims is defined herein to mean one or more of the elements it introduces. The following is a description of the claims as they were at the time of filing the application. [Claim 1] A formaldehyde solution containing 30 wt% or more formaldehyde is heated to a temperature in the range of approximately 70°C to approximately 130°C; The formaldehyde solution is allowed to mature for a sufficient amount of time for the formaldehyde to polymerize and form paraformaldehyde; The paraformaldehyde was solidified; and The formaldehyde solution before and / or during heating, the formaldehyde solution during maturation, paraformaldehyde, and / or solidified paraformaldehyde are brought into contact with ammonia and / or ammonium hydroxide stabilizer. A method that includes the act of doing so. [Claim 2] The method according to claim 1, wherein the formaldehyde solution being heated further comprises about 50 ppm to about 1000 ppm of ammonia and / or ammonium hydroxide stabilizer. [Claim 3] The method according to claim 1 or 2, wherein the formaldehyde solution during maturation further comprises about 50 ppm to about 1000 ppm of ammonia and / or ammonium hydroxide stabilizer. [Claim 4] The method according to any one of claims 1 to 3, wherein the solidification of paraformaldehyde comprises contacting the paraformaldehyde with a gas containing about 10 ppm to about 1000 ppm of ammonia and / or ammonium hydroxide stabilizer. [Claim 5] The method according to any one of claims 1 to 4, further comprising drying the solidified paraformaldehyde. [Claim 6] The method according to claim 5, further comprising exposing the solidified paraformaldehyde during and / or after drying to a gas containing about 10 ppm to about 1000 ppm of ammonia and / or ammonium hydroxide stabilizer. [Claim 7] The method according to claim 5 or 6, further comprising transporting solidified paraformaldehyde to a storage facility. [Claim 8] The method according to claim 7, further comprising exposing solidified paraformaldehyde during transport or in a storage facility to a gas containing about 10 ppm to about 1000 ppm of ammonia and / or ammonium hydroxide stabilizer. [Claim 9] The method according to claim 7 or 8, further comprising storing the solidified paraformaldehyde at ambient temperature ~50°C for longer than 30 days and maintaining the concentration of insoluble matter in the solidified paraformaldehyde at less than approximately 150 ppm. [Claim 10] The method according to any one of claims 1 to 9, wherein the formaldehyde solution is aged for approximately 0.1 hours to approximately 3 hours. [Claim 11] The method according to any one of claims 1 to 10, wherein the formaldehyde solution is matured at 70°C to 130°C. [Claim 12] A method according to any one of claims 1 to 11, wherein an organic amine is not included in the method. [Claim 13] The method according to any one of claims 1 to 12, further comprising transporting solidified paraformaldehyde to a storage facility. [Claim 14] The method according to any one of claims 1 to 13, wherein the source of the ammonia and / or ammonium hydroxide stabilizer is urea. [Claim 15] A method comprising exposing solidified paraformaldehyde to a gas containing approximately 10 ppm to approximately 1000 ppm of ammonia and / or ammonium hydroxide stabilizer. [Claim 16] The method according to claim 15, wherein the solidified paraformaldehyde does not contain an organic amine. [Claim 17] The method according to any one of claims 15 or 16, wherein the source of the ammonia and / or ammonium hydroxide stabilizer is urea. [Claim 18] The method according to any one of claims 15 to 17, further comprising storing solidified paraformaldehyde at ambient temperature ~50°C for longer than 30 days and maintaining the concentration of insoluble matter in the solidified paraformaldehyde at less than approximately 150 ppm. [Explanation of symbols]

[0045] 100 devices 102 Dryer tube 104 Perforated plate 106 Gas Inlet 108 Bent 110 Thermocouple 112 Sources of ammonia and / or ammonium hydroxide stabilizers 114 Heat exchanger 116 lines

Claims

1. A method comprising exposing solidified paraformaldehyde to a gas containing 50 ppm to 500 ppm of ammonia and / or ammonium hydroxide stabilizer.

2. The method according to claim 1, wherein the solidified paraformaldehyde does not contain an organic amine.

3. The method according to claim 1 or 2, wherein the source of the ammonia and / or ammonium hydroxide stabilizer is urea.

4. The method according to any one of claims 1 to 3, further comprising storing the solidified paraformaldehyde at 50°C above ambient temperature for more than 30 days, and maintaining the concentration of insoluble matter in the solidified paraformaldehyde at less than 150 ppm.

5. A method according to any one of claims 1 to 4, Drying the solidified paraformaldehyde; and Exposure of the solidified paraformaldehyde during and / or after drying to a gas containing 10 ppm to 1000 ppm of ammonia and / or ammonium hydroxide stabilizer. The method further includes the method described above.

6. The method according to claim 5, wherein the drying is performed at a temperature of ambient temperature to 150°C for 15 minutes to 20 hours.

7. The method according to any one of claims 1 to 6, wherein the gas comprises 50 ppm to 155 ppm of ammonia and / or an ammonium hydroxide stabilizer.

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