EXPLOSION-SAFE LIQUID CONTAINER

Abstract: The present disclosure relates to a container (101, 11) adapted for holding liquid compounds liable to exothermic decomposition, said container (101, 11) provided with at least one explosion-safe liquid release system (104, 105, 106) (13, 14, 15)) comprised of a conduit (104, 13) having an inlet (105, 14) and an outlet (106, 16), wherein said inlet (105, 14) is fixed at or near the bottom of said container (101, 11). Containers provided with such explosion-safe liquid release systems (104, 105, 106)(13, 14, 15)) are particularly suitable for use with organic per­ oxides. Also disclosed are methods for storing or transporting liquid (102, 12) com­ pounds liable to exothermic decomposition in containers (101, 11) of the present dis­ closure. Containers used in such methods may optionally hold inert par­ ticles (110, 18) and/or liquid diluents.

Description: The present invention relates to a transportable container adapted for holding liquid compounds liable to exothermic decomposition, said container provided with at least one explosion-safe liquid release system wherein said liquid release system is operated by pressure less than the maximum pressure rating of said container, said liquid release system comprised of a conduit having an inlet, an outlet and a rupture disk positioned in said conduit, characterized in that said inlet of said conduit is fixed at or near the bottom of said container, the ratio of the cross-sectional area of said conduit to the container volume being more than 0.005 m⁻¹. Liquid compounds liable to exothermic decomposition decompose above certain critical temperatures to produce gas and heat. The heat produced further promotes the decomposition. Such compounds, and solutions, dilutions, suspensions, and emulsions containing such compounds, arc thus referred to as "self-heating" or "exothermically decomposing compounds". Examples of such compounds are liquid organic peroxides with explosive properties, such as tert.-butyl peroxybenzoate, tert.-butyl peroxypivalate (up to 77% in solution), tert.-butylperoxy-2-ethylhexanoate and tert.-butylperoxy isopropylcarbonate (up to 77% in solution); other organic peroxides, such as 2,5-dimethyl-2,5-ditert.-butyl peroxyhexane, tert.-butyl peroxy acetate (up to 52% in solution), di(3,5,5-trimethyl hexanoyl) peroxide (not more than 77% in solution), and methyl ethyl ketone peroxides (not more than 40% in diisobutyl nylonate); inorganic peroxides, such as hydrogen peroxide, ammonium peroxydisulphate, alkaliperborates, alkalipercarbonates, ammonium peroxymonosulphate, alkaline earth peroxyborates, and alkaline earth persulphates; azo compounds, such as 2,2'-azo di-(2,4-dimethyl)valeronitrile; nitrile compounds, such as pentylnitrite; and sulphohydrazides, such as benzenesulphohydrazide, N-nitroso compounds, nitro compounds and organic nitrates. The storage and transportation of exothermic decomposition compounds are particularly troublesome in that the build-up of decomposition gases in the transporation or storage container may cause violent, hazardous explosions, bursting the container holding the compound. In recognition of this problem, international safety laws and standards regulate the size and construction of containers used to store and transport such compounds. For example, the standards of the UN publication "Recommendations on the Transport of Dangerous Goods" limit the transportation of certain liquid organic peroxides to 50 kg plastic containers. International regulations for the transportation of organic peroxides are also contained in the "European Agreement Concerning the International Carriage of Dangerous Goods by Road" (ADR) and the "International Code for the Transport of Dangerous Goods by Ship" (IMDG-code). These and other limitations on container design and compound concentration hamper the efficient storage and transportation of compounds liable to exothermic decomposition. The paper "Safety Aspects of Organic Peroxides in Bulk Tanks" by Jan J. de Groot, Dick M. Groothuizen and Jaap Verhoeff, "I & EC process Design and Development", 1981, Vol. 20, pp. 131-138 (referred to as "Safety Aspects") discusses a tank designed for the bulk handling of diluted organic peroxides. The bulk storage tank in "Safety Aspects" is provided with a carbon rupture disk on top of the tank. During an accident in which the dilute organic peroxides explode, the rupture disk allows venting of the decomposition gases (and entrained liquid) to prevent bursting of the tank. German Patent 149,086 discloses a container for holding hazardous liquids such as petroleum and gasoline, which container is provided with a conduit having an inlet positioned near the bottom of the container. In case of fire, the liquid in the container is pressed through said conduit into a closed overflow container. The closed overflow container has, at the top thereof, a safety valve to allow the escape of pressurized gases. In U.S. Patent 3 945 941, polyolefin particles, traps and/or liners are added to containers holding a mixture of 70% tertiary butyl hydroperoxide (TBHP) and 30% water. The polyolefin additives were found to inhibit rapid combustion of the TBHP mixture. Currently available methods do not meet the needs of industry to safely store and transport bulk volumes of concentrated compounds liable to exothermic decomposition. Indeed, with currently available designs, decomposition and the resulting explosion and/or container rupture occur too quickly to safely reduce pressure by gas release and prevent explosion. Surprisingly, in view of the long felt need in the art, the container of the present invention provides pressure release which avoids explosion in the container. The present invention relates to a container of the type indicated above and is characterized in that the conduit inlet is at or near the bottom of the container, the ratio of the cross-sectional area of said conduit to the container volume being more than 0.005 m⁻¹. Pressure inside such container is generated by the decomposition of liquid compounds liable to exothermic decomposition. When the pressure in the container reaches a certain predetermined pressure, the liquid release system is operated by the pressure in the container to discharge substantially all the liquid compound. By quickly releasing substantially all liquid from the container, explosion is avoided. The "predetermined pressure" must be less than the maximum pressure rating of the container in order to maintain the structural integrity of the container. Generally, the maximum pressure rating of most industrial containers built for storage and/or transportation purposes is about 500 or 600 KPa (5 or 6 bar). However, containers having higher or lower maximum pressure ratings are not uncommon. In one embodiment of the present invention, the explosion-safe liquid release system employs a dip pipe as the conduit. In accordance with the present invention, the inlet of the dip pipe is located at or near the bottom of the container. If, due to the decomposition of the liquid, the pressure in the container increases to the predetermined design pressure, the liquid in the container is pushed out and explosion is avoided. In another embodiment of the present invention, the conduit is an opening at or near the bottom of the container. A rupture disk is positioned at the inlet of the conduit, at the outlet of the conduit, or between the inlet and the outlet of the conduit. The rupture disk is set to burst at a predetermined pressure as defined above. If the pressure in the container reaches the predetermined pressure level, the rupture disk breaks, quickly releasing the liquid in the container and avoiding explosion. Fig. 1 is a representation of a container for storage or transportation of liquid compounds liable to exothermic decomposition, the container being equipped with an explosion-safe liquid release system comprised of a dip pipe having an inlet at or near the bottom of the container. Fig. 2 is a cross-sectional representation of a container for storage or transportation of liquid compounds liable to exothermic decomposition, the container being equipped with an explosion-safe liquid release system comprised of a conduit having an inlet located near the bottom of the container and a rupture disk at the outlet of the conduit. Specific embodiments of the present invention are further described by reference to Figs. 1 and 2. Fig. 1 is a representation of a container designed in accordance with the present invention. The particular embodiment illustrated in Fig. 1 may be referred to as the "dip pipe" release system. Container 101 holds a liquid 102 liable to exothermic decomposition. The size, shape and construction material of container 101 will depend on factors such as intended use, liquid 102, and operating temperature and pressure. Liquid 102 may be diluted with a solvent or other liquid. Examples of such diluents for use with liquids liable to exothermic decomposition are water, hydrocarbons such as isododecane, esters such as dimethyl phthalate and mineral spirits such as methyl ethyl ketone. Additionally, liquid 102 may contain inert particles 110 such as Raschig rings, Solef balls, Berl saddles, Pall rings or other packing materials, preferably those made from inert materials such as glass, steel or olefins. Fitted in container 101 is a pressure-operated, explosion-safe liquid release system comprised of inlet 105, conduit 104 and outlet 106. Conduit 104 may be constructed of any material compatible with both the construction material of container 101 and the liquid 102. When liquid 102 is an organic peroxide, a preferred construction material for conduit 104 is stainless steel type AISI 316 or 304. The size of conduit 104 is dependent on the type, amount and concentration of liquid 102 and the maximum pressure rating of container 101. In general, the cross-sectional area ("A") of the conduit 104 should be about 0.005 m⁻¹ to about 0.05 m⁻¹ of the container volume ("V") (where V is expressed in m³). Typically, A is about 0.01 m⁻¹ to about 0.02 m⁻¹ of V. However, more violently decomposing liquids require a larger cross-sectional area. With further reference to Fig. 1, container 101 is also equipped with a liquid inlet 107 for addition of liquid 102 to the container. To ensure proper operation of the liquid release system in the event that liquid inlet 107 is inadvertently left open, liquid inlet 107 should be small (less than about 1 / 10 the cross-sectional area of conduit 104) and/or be fitted with a one-way "check" valve. Since container 101 is particularly designed as a reactor feed vessel, it is also equipped with liquid removal line 108. Opening 109 is provided to equalize pressure inside and outside container 101 during filling and emptying of container 101. Opening 109 should be small (less than about 1 / 10 the cross-sectional area of conduit 104). An additional feature illustrated in Fig. 1 but possible for any container of the current invention is cooling jacket 103. Cooling jacket 103 is particularly desirable when container 101 is used as a storage vessel or when container 101 is filled with a liquid which requires refrigeration. Fig. 2 is a cross-sectional view of another container designed in accordance with the present invention. Container 11 holds liquid 12 liable to exothermic decomposition. The size, shape and construction material of container 11 will depend on factors such as intended use, liquid 12, and operating temperature and pressure. Liquid 12 may be diluted with a solvent or other liquid as described above in relation to the embodiment in Fig. 1. Additionally, liquid 12 may contain inert particles 18, such as inert particles 110 also described in relation to Fig. 1. With further reference to Fig. 2, fitted at or near the bottom of container 11 is one embodiment of a pressure-operated, explosion-safe liquid release system comprised of conduit 13, inlet 14, rupture disk 15 and outlet 16. The size and release pressure of rupture disk 15 are determined based on criteria such as the type, amount, and concentration of liquid 12, the maximum pressure rating of the container, and the system operating temperature. Rupture disks of various sizes and bursting strength are available commercially from suppliers such as Berta under the tradename Fike®. The cross-sectional area of both conduit 13 and rupture disk 15 may be determined based on the guidelines discussed above for sizing conduit 104 in Fig. 1. The container of Fig. 2 is also fitted with liquid inlet 17. As in Fig. 1, the container represented in Fig. 2 may optionally contain liquid feed and removal lines, openings for pressure equalization, etc. based on the intended use of the container. Sizing such liquid feed and removal lines may be based on the guidelines discussed regarding liquid inlet 107 and opening 109 in Fig. 1. The advantages of the present invention are demonstrated by the examples which follow. The maximum pressure rating for containers in Comparative Examples A-E and Examples 1-5 is approximately 600 KPa (bar). The examples are summarized in Table 1. Comparative Example A A 20 litre aluminum container (0.3 m dia. x 0.4 m) was constructed. The container was completely closed except for a 2 mm diameter opening in the top. Eighteen litres of tert.-butylperoxy-2-ethylhexanoate (technically pure) were placed in the container. The container was heated until peroxide decomposition was self-sustaining. The container pressure reached 1700 KPa (17 bar) and the container exploded. Explosion shock waves measured 100 KPa (1 bar) overpressure at a distance of 1 m from the container and 20 KPa (0.2 bar) overpressure at a distance of 2 m. Comparative Example B An 8.3 litre (0.2 m dia. x 0.25 m) stainless steel container was built with a 1.8 mm dia. relief opening and a 12 mm dia. opening in the top. Bis(3,5,5-trimethylhexanoyl)peroxide (6.7 litres of a 37.5% solution diluted with isododecane) was placed in the container. The container was heated until peroxide decomposition was self-sustaining. Decomposition gases were vented through the top opening. Nevertheless, the pressure inside the container reached the dangerous value of more than 1300 KPa (13 bar), at which point part of the container wall broke. Comparative Example C A test identical to Comparative Example B was carried out except the 12 mm opening was replaced by an 18 mm opening in the top of the container and the container was filled with Rashig rings. The container was heated until peroxide decomposition was self-sustaining. The internal pressure reached 170 KPa (1.7 bar). Comparative Example D A test identical to Comparative Example C was carried out except the peroxide concentration was increased from 37.5% to 50%. The container was heated until peroxide decomposition was self-sustaining. The internal pressure reached 520 KPa (5.2 bar), at which point part of the container wall broke. Comparative Example E An 8.3 litre stainless steel container (0.2 m dia. x 0.25 m) was built with an 18 mm dia. conduit in the bottom and a 1 mm relief vent on top. Tert. butylperoxy pivalate (6.7 litre of a 75% solution diluted in isododecane) was placed in the container. The violence of decomposition of tert. butylperoxy pivalate is substantially equivalent to that of tert. butylperoxy-2-ethylhexanoate used in Comparative Example A. The container was heated to cause peroxide decomposition. Some peroxide was released through the conduit. However, the container internal pressure reached 780 KPa (7.8 bar) at which point part of the container wall broke. Example 1 A test identical to Comparative Example B was carried out except the 12 mm dia. opening was replaced by a 12 mm dia. rupture disk in the bottom of the container. At an internal pressure of 50 KPa (0.5 bars), the rupture disk burst, releasing the container liquids and avoiding explosion. The internal pressure reached only 50 KPa (0.5 bar). Example 2 A test identical to Comparative Example E was performed except 90 Raschig rings (34 mm I.D., 40 mm O.D., 40 mm L) were placed in the container. The peroxide was heated and peroxide decomposition occurred. The rupture disk burst and the container contents were released. The container internal pressure reached less than 5 KPa (0.05 bar). No explosion occurred. Example 3 A test identical to Example 2 was performed except 45 hollow spheres (type Solef PVDF, available from Euromatic) of 38 mm diameter were floating on top of the peroxide. The container was filled with bis (3,5,5-trimethylhexanoyl)peroxide (6.7 litres of a 75% solution diluted with isododecane) and heated until peroxide decomposition occurred. The container contents were released. The container internal pressure reached less than 10 KPa (0.1 bar). No explosion occurred. Example 4 A 65 litre container (0.4 m dia. x 0.6 m) constructed of stainless steel was built with a 22 mm dia. dip pipe substantially in accordance with the design of Fig. 1. The dip pipe inlet was located 11 mm from the bottom of the container. The dip pipe outlet was secured at the top of the container. The container was also fitted with a 3 mm dia. relief vent on top. The container was filled with 600 Rashig rings and 50 litre of a 75% tert.butyl peroxypivalate. The container was heated until peroxide decomposition was self-sustaining and liquid was released through the conduit. The internal pressure of the container reached 45 KPa (0.45 bar). No explosion occurred. Example 5 A test identical to Example 4 was performed except the container was filled with tert.-butyl peroxy-2-ethylhexanoate (rather than 75% butyl peroxypivalate) and the top-mounted relief vent had a diameter of 2 mm. The container was heated to self-sustaining decomposition. The internal pressure reached a maximum of 42 KPa (0.42 bar). No explosion occurred.

Claims: A transportable container adapted for holding liquid compounds liable to exothermic decomposition, said container provided with at least one explosion-safe liquid release system comprised of a conduit having an inlet, an outlet and a rupture disk positioned in said conduit, wherein said liquid release system is operated by pressure less than the maximum pressure rating of said container, characterized in that said inlet of said conduit is fixed at or near the bottom of said container, the ratio of the cross-sectional area of said conduit to the container volume being more than 0.005 m⁻¹. The container of claim 1 characterized in that said rupture disk is positioned at or near said outlet of said conduit. The container of claim 1, characterized in that said outlet is located at or near the top of said container. The container of any one of claims 1-3 characterized in that container has a maximum pressure rating of about 600 KPa (6 bar). The container of any one of claims 1-4 characterized in that said container further contains inert particles selected from Raschig rings, Berl saddles, Pall rings and olefin particles. A method of storing or transporting in a container a liquid liable to exothermic decomposition characterized in that use is made of a container acording any one of the proceeding claims. The method of claim 6 characterized in that said container holds both liquid liable to exothermic decomposition and inert particles. The method of claim 7 characterized in that said inert particles are selected from the group consisting of Raschig rings, Berl saddles, Pall rings and olefin particles. The method according to any one of claims 6, 7 or 8 characterized in that said liquid liable to exothermic decomposition is chosen from the group consisting of organic peroxides, inorganic peroxides, azo compounds, oxidizing compounds, thermally unstable compounds and mixtures thereof. The method according to any of one of the claims 6, 7, 8 or 9 characterized in that said container additionally holds at least one liquid diluent.

Inventors: DE GROOT, JOHANNES JACOBUS, SIKKENS, PAUL JOHAN
Applicants: AKZO N.V.
Application year: 1987
Main classification: B65D90
IPC codes: B65D90, A62D3, F16J12