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10. Frequently Asked Questions

1. What are the standards for unloading bulk MDI from truck or rail?

The operation of unloading (or loading) any tank truck, iso tank container, tank car, or small container of MDI is potentially hazardous. Unloading facilities must be designed and located giving due regard to the potential hazards of MDI products.

Written operating procedures covering all aspects of the unloading operation of MDI products must be prepared and available to all involved parties. All necessary PPE and emergency equipment must be available for the unloading operations. Personnel must be trained in correct use of all protective clothing and emergency equipment (see Section 5).

Unloading of MDI products from bulk containers should be performed with a self-priming, seal-less pump and a vapor return line connected between the storage tank and the bulk delivery container. The seal-less design eliminates potential seal failure. Due to the MMDI freezing point, MMDI transfer lines must be heated. Dry air or nitrogen must be available to purge the unloading lines and vapor return line after unloading is completed. The storage tank must be equipped with a high-level device which will stop the unloading automatically if the maximum tank level is reached.

If dry air or nitrogen pressure is used to transfer MDI products from a bulk container to the storage tank, the pressure must be regulated below the maximum safe operating pressure of the bulk container, and the storage tank vent must be sized accordingly. After disconnecting hoses, all exposed fittings and hoses must be protected with caps or plugs.

The dimensions and physical arrangement of bulk containers vary. Contact your local BASF office for unloading instructions on specific container types.

2. Can MDI be stored in an outdoor bulk storage tank?

Yes, but the tank should be insulated, have a heating source if necessary (e.g., heating jacket, heating coils, or heat exchanger), and a top mounted agitator to avoid local overheating if necessary. All MDI storage tanks should be located above ground and be certified for positive pressure for unloading or if contamination occurs. Storage tanks are recommended to be placed indoors for spill containment and to prevent the effects of weather variation on the product.

3. What occurs during an isocyanate reaction with water?

The reaction of isocyanates with water will produce polyurea solids and CO2 gas. These insoluble polyureas will deposit on surfaces of pipes and tanks causing line restrictions and filtration problems. The generated CO2 could present a pressure hazard, including the potential of a violent rupture of an under-vented tank or vessel.

4. Do you need a nitrogen pad for an MDI bulk storage tank?

MDI storage tanks should be blanketed with dry air or nitrogen (-40°F/°C dew point). Storage tanks should be maintained under slight positive pressure (1 mbar) and should be pressure-controlled by nitrogen or dried air. Storage tank vents must be sized to adequately protect the tank against pressure buildup during unloading operations or the generation of pressure from moisture contamination. Storage tank ventilation can be accomplished by pressure control through an activated carbon filter or knockout pots.

5. What do you do if someone is sprayed with MDI?

Immediately move the affected person to a safety shower or other source of large amounts of water. Remove all contaminated clothing while under the shower and thoroughly wash affected areas with soap and water or
polypropylene glycol. Medical treatment should be given if skin irritation persists (e.g., redness, swelling, or burning sensation). Soak contaminated clothing in decontaminating solution and launder before reusing or destroy in cases of severe contamination. Take precautions against additional exposure when completing these activities.

6. What do you do if MDI is ingested?

If MDI is ingested immediately contact the Human Poison Control Center (1-800-222-1222). The affected person should immediately drink large amounts of water to reduce the concentration of the chemical. Vomiting should not be induced. Keep the individual calm and protect against loss of body heat. The person should be transported to a medical facility as quickly as possible. If vomiting should occur, more water should be given immediately. Never give fluids or induce vomiting if the person is unconscious or having convulsions.

7. What do you do in the event of an MDI spill?

Perform the following steps in response to an MDI release.

  1. Evacuate nonessential personnel from the area
  2. Notify emergency centers and management if required
  3. Use proper protective equipment
  4. Contain spill
  5. Transfer spilled MDI to open container using pump or absorbent material
  6. Neutralize spilled MDI
  7. Decontaminate surfaces
  8. Isolate/dispose of waste
  9. Monitor for residual diisocyanate
  10. Perform additional decontamination if diisocyanate is detected

Depending upon the size, location, and type of release, government agencies or authorities may require notification. In the United States, any release of over 5,000 lbs. to the environment must be reported to the NRC (1-800-424-8802) and the local planning commission as outlined under EPCRA regulations. Transportation incidents involving MDI must be reported to the NRC for any release over the reportable quantity of 5,000 lbs. (approximately 500 gallons). This is a requirement of U.S. Federal CERCLA regulations.

For transportation incidents in Canada, Transport Canada operates Canutec. Transportation incidents in Canada should be reported to Canutec (1-613-996-6666).

8. What do you do if your MDI drums are bulging?

A bulging drum of MDI should be assumed to be the result of contamination, usually with water. This slow but unstoppable reaction with a diisocyanate produces CO2, which increases the pressure inside the container. Since it is not easy to judge the acute risk of bursting, the drum under pressure should not be moved. A tarpaulin should be placed over the drum.

It is necessary to relieve this pressure safely before the drum bursts. This is best accomplished by puncturing the top of the drum with a long-handled spike. Some response companies have specialized drum de-pressurization devices. During this action, all uninvolved persons must be removed from the area and the working personnel must use complete chemical protection. The punctured drum must then be placed in an oversized drum with pressure venting capabilities. It must be remembered that the original contamination will probably continue to cause a pressure increase. The container must be regularly vented using proper safety precautions and BASF
contacted for disposal recommendations.

9. Does BASF have a recommended Piping & Instrumentation Diagram for the design of isocyanate bulk storage?

No. There is no specific layout or equipment design that must be used for isocyanate bulk storage. Multiple options are possible and should be evaluated as part of a standard engineering design process.

10. What products should be stored in a warm room? At what temperatures?
11. Why does my MDI product appear cloudy?

There are several reasons why an MDI product may appear cloudy. The product may be old and may have exceeded its shelf-life. Over time, some MDI products will form increasing amounts of dimeric species (uretdiones), often referred to as “dimer.” MDI dimer has limited solubility in the product and, at some point, the level of dimer may exceed its saturation point. When this occurs, the dimer will begin to precipitate out of solution, causing the product to become cloudy. After extended periods of time, the dimer may even begin to settle out of solution at the bottom of the container as a fine white solid.

Other causes of cloudiness in the product include contamination by water or other foreign chemicals. Some MDI products, mostly those with high monomeric MDI content, especially 4,4’- MDI, are very sensitive to contamination by small amounts of water. Sometimes even exposure to humidity in the air in the headspace above some product may eventually cause the product to become cloudy. The cloudiness is caused by the reaction of small amounts of humidity with MDI, primarily 4,4’-MDI, which results in the formation of MDI urea species. These MDI ureas have limited solubility in the product, causing the product to appear cloudy. At higher concentrations these MDI ureas may even precipitate out of solution as white solids.

Certain chemicals, solids or liquids, may have limited solubility or compatibility in MDI products. Thus, contamination with these chemicals, even in small amounts, may cause the MDI product to appear cloudy. Other
chemicals may be completely compatible with MDI but may react with MDI to form products that are incompatible, resulting in a cloudy appearance.

12. My MDI shipment is a different color than usual. Is there a problem with it?

If the product contains PMDI, the color may range from light amber to dark brown, depending on the composition. PMDI is manufactured in a highly energetic process, using extremely reactive reagents. As a result, varying amounts of color bodies are formed in the process. These color bodies could come from extremely small amounts of contaminants in the raw materials used to make PMDI or could be inherent in the process chemistry. The concentration of these by-products is very low, but since they are highly colored the presence of these by-products causes the final PMDI product to have an appearance ranging from light amber to brown. Batch-to-batch variation may result in slightly more or less of these colored by-products, resulting in some variation in the color of the final product. It is important to realize, however, that these colored species do not, in any way, affect the quality or performance properties of the final polyurethane prepared from the PMDI. In general, if lower color is desired in the final polyurethane, one normally selects products that are based on 100% monomeric MDI, or those that have minimal PMDI content.

Products based on only MMDI typically have colors ranging from water white to yellow. In MMDI products the color arises from very small amounts of by-products formed by the reaction of MDI with other ingredients in the product. The color does not, in any way, affect the quality or performance properties of the final polyurethane prepared from the MDI.

13. What materials are safe to expose to MDI?

MDI reacts with acids, alcohols, basic materials (e.g., sodium hydroxide, ammonia, and amines), magnesium and aluminum (and their alloys), metal salts (e.g., tin, iron, aluminum, and zinc chlorides), strong oxidizing agents (e.g., bleach and chlorine), polyols, and water (CPI, July 2003). These reactions may be violent, generating heat, which can result in an increased evolution of isocyanate vapor and/or a buildup of pressure within closed containers.

Tanks may be fabricated of unlined carbon steel. The steel tanks should be rust-free because trace iron contamination may affect the MDI reactivity. Other satisfactory materials include stainless steel, glass-lined steel, or nickel-clad steel; however, these configurations are more expensive. Stainless steel is the recommended material of construction for pumps, discharge pipelines, and valves. MDI is not generally corrosive towards metals or other materials at room temperature, but the presence of a small amount of acidity in PMDI can produce some corrosion with copper alloys and aluminum. Copper, zinc, or their alloys must be avoided as they may cause product deterioration. MDI will attack and embrittle many plastic and rubber materials in a short time, which may cause these materials to crack. Flex Hose must be Teflon®-lined or specially sold and labeled for isocyanate handling.

14. My product has exceeded its recommended shelf life. Can I still use it in my process?

The shelf life or storage lifetime of MDI products vary with composition. Refer to the Technical Data Sheets for each product for information concerning shelf life. Many MDI products, however, will be usable well beyond the shelf life stated in the Technical Data Sheets. Customers with appropriate analytical capabilities can verify that a product is still good to use by re-running its specifications. If the specifications are still within the ranges indicated on the products Certificate of Analysis (COA), then the product can still be used. Customers without the appropriate analytical capabilities may contact their distributor or their BASF salesperson to request recertification of their product.

15. My product froze and contains a large amount of white solid material. Can the product be “melted” again? What should I do?

When some MDI products are exposed to temperatures lower than those recommended in the Technical Data Sheets for that specific product, the product “freezes”. When a product freezes monomeric MDI (primarily 4,4’-MDI) crystallizes out of solution as a white solid. The ease at which a product freezes when subjected to low temperatures depends on its composition. Typically, product containing high levels of monomeric MDI, especially 4,4’-MDI, tends to freeze more readily.

When an MDI product freezes, sometimes warming the product to warm room temperature (75 to 85ºF or 24 to 29ºC) is all that is required to melt the MDI crystals and result in a clear product. Other MDI products need to be warmed to higher temperatures, 110 to 122ºF (43 to 50ºC), to melt all the MDI crystals. Other products, however, are more sensitive and even when heated to 110 to 122ºF, some undissolved white solids may remain on the bottom of the container. These insoluble white solids are MDI dimers, and once formed cannot be dissolved back into solution. They can only be removed by filtering the product.

The tendency to form insoluble MDI dimer increases with time after a product freezes. Therefore, it is important not to keep an MDI product frozen for a long period of time. If a product shows evidence of freezing, after exposure to temperatures lower than that recommended in the Technical Data Sheets, it is best to immediately warm the product to either warm room temperature (75 to 85ºF), or higher temperatures (110 to 122ºF). In many cases, prompt warming to melt the MDI crystals will result in a clear product that can be used without any change in performance properties.

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