Introduction
Sodium methoxide (Sodium methanolate) is also known as sodium methoxide, molecular formula: CH3ONa, CAS (US Chemical Abstracts Number): 124-41-4. Sodium methoxide is divided into two types: liquid sodium methoxide and solid sodium methoxide. Liquid sodium methoxide is actually a methanol solution of solid sodium methoxide. The main production process is to put metal sodium or caustic soda into the reaction kettle under nitrogen protection, and then add excess methanol to react to generate liquid sodium methoxide. The liquid sodium methoxide is distilled under reduced pressure and dried to obtain white powdery solid sodium methoxide. Sodium methoxide is an important pharmaceutical intermediate that can be used to produce vitamin A, vitamin B, sulfonamide drugs, etc. It can also be used in the pesticide industry, edible catalysts and analytical reagents.
Liquid sodium methoxide and solid sodium methoxide are hazardous chemicals clearly listed in the 2015 edition of the “Catalogue of Hazardous Chemicals” organized by the State Administration of Work Safety (hereinafter referred to as the “2015 edition of the Catalog”). Solid sodium methoxide reacts easily with water to generate strong corrosive agents sodium hydroxide and methanol. Methanol is a highly flammable liquid that is volatile and toxic. If the packaging is not tightly sealed during transportation, the solid sodium methoxide product will easily deteriorate when exposed to water or humid air, and the methanol generated will be toxic to the transporter. In 2004, the “Yinghua” ship sailing from Dalian to Penglai Port was illegally carrying solid sodium methoxide on board the ship. During the journey, the Eastman packaging was damaged and chemically reacted with water, causing a fire. Thanks to proper handling, the ship was saved and the economic loss was more than one million yuan. Therefore, analyzing the hazardous characteristics of solid sodium methoxide and selecting appropriate packaging forms based on its properties is of great significance for promoting domestic and export trade of sodium methoxide and ensuring the safety of people’s lives, property and the environment during transportation.
1 Analysis of Hazard Characteristics of Solid Sodium Methoxide
1.1 Transportation Hazards of Solid Sodium Methoxide
The United Nations Recommendation on the Transport of Dangerous Goods (hereinafter referred to as ” Recommendation”) Dangerous goods are divided into explosives, gases (including flammable gases, toxic gases, non-flammable and non-toxic gases), flammable liquids, flammable Combustible solids (including substances that are prone to spontaneous combustion and substances that release flammable gases when exposed to water), oxidizing substances and organic peroxides, toxic substances and infectious substances, radioactive substances, corrosive substances, miscellaneous hazardous substances and articles (including hazardous Environmental substances) and other 9 categories.
Dangerous goods packaging is divided into three packaging categories according to the degree of danger of the contents: the most dangerous substances are packed in Class I packaging; the medium-dangerous substances are packed in Class II packaging; light Highly hazardous substances should be packed in Class III packaging. In the “List of Dangerous Goods” in the “Recommendation”, the United Nations number of solid sodium methoxide is UN1431. The main hazard is Class 4.2 self-heating substances, the minor hazard is Class 8 corrosive substances, and Class II packaging. According to the provisions of the Recommendation 2.0.3.3 “Hazard Sequence List”, when dangerous goods have Class 4.2 hazardous characteristics and are packed in Class II, they also have Class 8 corrosive hazards and are packed in Class II or III. , the overall risk should put Category 4.2 hazards before Category 8, that is, the goods have dual hazard characteristics when transported. The self-heating hazard of solid sodium methoxide is the gradual reaction of the substance with oxygen in the air to generate heat. If the rate of heat generation exceeds the rate of heat loss, the temperature of the substance will rise and, after an induction period, it may spontaneously ignite or ignite. Solid sodium methoxide is transported in Class II packaging, that is, in the self-heating hazard experiment, a 25mm cube sample is used for testing at 140°C. When the external ambient temperature is 140°C, the temperature inside the sample can exceed the ambient temperature by 60°C, reaching Above 200℃, it is the most dangerous self-heating substance.
The corrosive danger of solid sodium methoxide means that it easily reacts with water to form the strong corrosive sodium hydroxide, which will cause skin corrosion if the human body comes into contact with it. The reaction equation is: H2O+CH3ONa→CH3OH+NaOH. Skin corrosion refers to irreversible damage to the skin. The corrosive reaction is characterized by ulcers, bleeding, bloody scabs and, at the end of the 14-day observation period, discoloration of the skin, areas of complete alopecia and scabs due to bleaching. In experiments, a substance is corrosive to the skin if it causes skin damage to at least one test animal, that is, visible epidermal and dermal necrosis, after contact with the skin for up to 4 hours.
From the dangerous characteristics of sodium methoxide mentioned above, it can be seen that the use of packaging containing less goods to prevent heat accumulation, avoid contact with air and moisture, and maintain the sealing of its packaging are key factors to ensure transportation safety.
1.2 GHS classification of solid sodium methoxide
The United Nations’ Globally Harmonized System of Classification and Labeling of Chemicals (hereinafter referred to as GHS) is a chemical classification and labeling system used to unify The classification and labeling of chemicals in different countries and regions around the world are jointly prepared and formulated by the Globally Harmonized System Subcommittee of the Organization for Economic Cooperation and Development (OECD), the International Labor Organization and the United Nations Economic Commission for Europe. The first edition was officially published in December 2002. After further revision and improvement by experts from various countries, the latest version is the sixth revised edition published in 2015. GHS focuses on the entire life cycle of chemicals including production, transportation, sales, and use. The classification of chemicals includes 17 physical categories.Internal inflation stabilizes a constant internal pressure inside the package, and then detects whether there is any leakage. However, for plastic film bags, this method requires drilling an inflation hole on the bag and fixing the inflation pipeline, and ensuring that the position of the inflation hole is leak-proof, which is not easy to achieve for very thin flexible bags. As for the plastic film bags used to contain hazardous chemicals, in addition to the 50kg bags used in 200L open steel drums, there are also some larger 200kg bags. In view of this situation, we developed and researched a new sealing test method for inner packaging plastic film bags based on the pressure resistance test of plastic bags and films based on the existing laboratory equipment. If the plastic film bag can pass the sealing test after passing the drop test, it can meet the air tightness requirements of the overall packaging and reduce the sealing cost of the outer packaging.
2.4 Plastic film bag sealing test method
Test equipment: Microcomputer controlled stacking testing machine, model:
CPT5504, Meters Industrial Systems (China ) Co., Ltd., maximum test force 50kN; moisture permeability tester, model: TSY-T3, produced by Jinan Languang Mechanical and Electrical Technology Co., Ltd.
Test principle: Gas pressure is the macroscopic statistical force generated by the irregular motion of gas molecules impacting the surface of an object. The pressure inside the film bag can be considered to change uniformly, and the pressure is equal to the parts in contact with the bag body and the pressure plate and other parts of the bag body. Increase the internal pressure of the plastic film bag to the standard required value through external pressure, and observe whether there is any leakage.
Film bag sample requirements: The sample must be sealed by the company submitting it for inspection according to the actual sealing method during use. It must be filled with air in an atmospheric pressure environment but must not generate internal pressure. The film bag body should be flat, without wrinkles or damage. During the test, the sample should be placed flat in the middle of the pressure plate to minimize the local stress in irregular parts such as corners and seams.
Test method: Weigh the plastic film bag sample. Use a stacker to apply pressure to the sample, and calculate the platen pressure value by determining the effective area of contact between the stacker platen and the sample and the pressure value that the sample needs to reach. Since the film bag will expand horizontally during the pressure resistance process, the contact area with the pressure plate will become larger. It is necessary to re-determine the effective contact area after the pressure stabilizes, recalculate the pressure value based on the new contact area, and gradually increase the effective contact area to Close to a stable value, make the relative gas pressure inside the film bag reach 20kPa and maintain it for 5 minutes. Apply soap solution to the sealing area and observe whether the film bag sample leaks. After the test, the sample is weighed again, and the mass is compared with the mass before the test. After deducting the moisture permeability of the sample itself, it is checked whether there is air leakage in the sample.
3 Test results
We selected three thicknesses of plastic film bags for comparative testing and found that the test results of the two methods were completely consistent, as shown in Table 2:
Table 2 Comparison of results of two air tightness test methods
4 Conclusion
Sodium methoxide is prone to spontaneous combustion if the amount of transportation in the package is too large, and it is easy to react with water, so the airtightness of its transportation packaging is required to be very high. In order to meet its air tightness, this requirement can be achieved from both the outer packaging performance and the inner packaging performance. Using sealed plastic film bags as inner packaging can reduce the sealing requirements of the outer packaging, thereby greatly reducing transportation costs. The newly developed plastic film bag sealing test method can conveniently and effectively test the sealing of the bag body. The samples that pass the test can meet the requirement of no leakage under the 20kPa pressure specified in the “Recommendation” and national standards. Since this method was put into use in 2014, a total of more than 200 batches of plastic film bag samples have been tested in Shandong, Hebei and other regions to ensure the transportation safety of dangerous chemicals such as sodium methoxide, sodium ethoxide, and nitrocellulose that require airtight packaging. of great significance.
