What is Diesel Exhaust Fluid
Diesel Exhaust Fluid, also known as DEF, AUS 32 and AUS 40, is a chemical solution commodity standardized for use in diesel fuel combustion vehicles, machinery, and equipment. Diesel exhaust fluid is defined as a nitrogen oxide (NOx) reducing agent where NOx refers to nitric oxide, (NO), and nitrogen dioxide (NO2). DEF is used as a consumable reactant in motors built with a Selective Catalytic Reduction (SCR) system to convert regulated, regulated NOx exhaust into non-polluting nitrogen gas and water vapor.
Solutions of DEF are a mixture of only two ingredients: urea and water, both of high purity quality. Urea is a nitrogen-based molecule that belongs to the amide, carbonyl reactivity group. It is a white, crystalline, stable and nonhazardous solid with high water solubility. Urea is known also as carbamide, isourea, and has the chemical formula CO(NH2)2 or CH4N2O. In DEF-SCR systems, urea is used as source of ammonia. Outside of DEF, urea is commonly used in agriculture for fertilizers.
In DEF production, the urea used must be pharmaceutical or automotive grade. This quality grade ensures any impurities are limited that could cause damage to the expensive and specialized diesel exhaust fume catalyst over time. The water specified for DEF products must also be of analytical quality and is often purified by distillation, deionization, ultrafiltration and/or reverse osmosis.
Aqueous DEF is considered a weak base with a pH range of 7.0 – 9.5. Solutions are clear to colorless and have the potential for a slight ammonia odor. DEF is fairly stable, non-flammable, non-combustible, non-toxic, and non-hazardous per UN / DOT handling standards. DEF solutions must have only trace amounts of restricted elements and be free of certain contaminants such as biuret and aldehydes. The International Standardization Organization (ISO) requires a select level of purity and regulates the production, concentration and composition of DEF products and bulk solutions.
DEF Applications
Diesel exhaust fluid is used by many modern diesel fuel vehicles and equipment. The most common DEF applications include highway and rail freight transport, semi-truck trailers, farm tractors and combines, maritime vessels, cargo ships, construction machinery, as well as earth moving and forestry equipment.
The use of DEF in vehicle systems is the direct result of government and authority requirements set in place as a collective effort to reduce the amount of NOx pollutants emitted from diesel burning engines to better protect our planet’s atmosphere and environment.
How Does Diesel Exhaust Fluid Work | The DEF – SCR Process
Diesel fuel burning engines of a specific strength and exhaust output must meet governmental emission restrictions. There are several technologies that exist for OEMs to achieve the necessary reduced emissions, but many choose Selective Catalytic Reduction (SCR) due to its ease of integration, ability to break down NOx pollutants, and benefit of increased total engine efficiency. On DEF-SCR equipped vehicles, a DEF holding tank stores diesel exhaust fluid where it is then pumped and injected into the SCR exhaust system after the engine and fuel combustion.
Selective Catalytic Reduction systems work by using DEF as a source for ammonia that can react with NOx gasses as DEF is injected into the exhaust chamber during vehicle operation. The urea in DEF is hydrolyzed by the elevated temperatures and a catalyst (a Vanadium metal alloy) to yield ammonia gas. The hot ammonia gas then reacts with nitric oxide, NO, and nitrogen dioxide, NO2, to produce non-polluting nitrogen gas and water vapor. The system also works to reduce the overall amount of carbon monoxide (CO) and hydrocarbons (HC) being emitted.
The following infographic provides an overview of the DEF-SCR injection and exhaust fume breakdown system.
Diesel Exhaust Fluid Types
DEF: AUS 32
AUS 32 is an acronym for Aqueous Urea Solution with 32.5% urea, otherwise known as diesel exhaust fluid. AUS 32 is 32.5% by weight pure grade urea dissolved in 67.5% pure water. AUS 32 is also known as Transit DEF and is the most commonly used DEF type and concentration.
AUS 32 is the standard diesel exhaust fluid used in land-based road and off road vehicles such as highway transport trucks, construction machinery, and agriculture equipment. The implementation of AUS 32 in diesel burning engines is associated with 2007-2010 U.S. EPA Tier 4 Regulations concerning air pollution control.
Transit DEF solutions are standardized by ISO 22241 to a 32.5% urea content. This concentration gives DEF solutions the lowest freezing point possible at 12°F (-11°C) while still providing the optimal catalytic activity for NOx reduction. AUS 32 concentrations allow DEF to freeze and thaw without damage to quality or strength and without concern of over-concentrating or salting out in equipment lines and storage tanks.
DEF: AUS 40
AUS 40 is Aqueous Urea Solution with 40% by weight urea in water and standardized according to ISO 18611. AUS 40 is also known as Marine DEF and is most used in maritime cargo vessels that feature SCR-DEF technology for compliance with 2014-2017 EPA regulation and enforcements. AUS 40 also sees use in train and rail applications for diesel engine locomotives.
Difference Between DEF Products
The technical difference between AUS 32 and AUS 40 is in the urea content. AUS 40 has 6.5% more urea by weight dissolved into the water solution. This additional urea content increases DEF’s catalytic ability to breakdown NOx emissions, making AUS 40 more effective and therefore better at treating larger combustion engine exhausts such as those found on container vessels or train engines. The additional urea strength also raises AUS 40’s freezing point up to 35°F (1.7°C) making it more prone to freezing and better suited for geographic locations, environments and work conditions where cold temperatures are not as much of a concern.
For store bought products such as bottles and jugs of diesel exhaust fluid, or service station DEF pumps, these will be transit DEF (AUS 32). To be listed for sale, all DEF products must be ISO 22241 compliant and therefore, due to standard and regulations, are all the same. The main difference is in the manufacturer. API certification is optional and serves as an additional accreditation that the DEF product meets the set purity requirements.
How to Store Diesel Exhaust Fluid
DEF stock solutions and products should be stored with the goal to maintain optimal purity, solution strength, and temperature to maximize DEF service life and effectiveness. Diesel exhaust fluid is best stored in a closed, airtight container kept in a cool location out of direct sunlight. Successful long-term DEF storage will consider temperature requirements of the solution, sunlight exposure, material compatibility, purity management, and average shelf life.
Use Compatible, Corrosion Resistant Materials
When storing and handling DEF, use only materials that have been determined compatible with DEF for tanks, fittings, pipes, and equipment such as pumps, hoses, and dispensing nozzles. Diesel exhaust fluid should be stored in nonreactive, noncorrosive materials made from plastic, such as polyethylene or polypropylene, stainless steel, glass, and glass reinforced polymers also known as fiberglass.
Polyethylene plastic is the most commonly used material type for DEF storage due to its characteristics, compatibility, low weight, and lost cost, and is the reason why most vehicle’s on-board DEF tanks are made from the material.
Compatibility is vital in DEF storage to prevent potential damage to equipment and to keep DEF from being contaminated by materials, trace minerals, or elements through unwanted corrosion or chemical interactions. All equipment in contact with DEF should be clean, without rust, kept free of any foreign matter, and should not be used with any other solution, cargo, or chemical, including tap water.
Use New or DEF Only Equipment
DEF storage is not recommended in vessels or service lines that have been previously used unless prior use was of certified DEF. Contamination through non-ideal storage conditions or exposure to incompatibles can reduce DEF effectiveness as well as cause potential damage to the SCR catalyst.
Non-ideal storage conditions are a leading reason for occurrences such as clogged injectors, lower than required emissions reduction, and catalyst replacement. Therefore, use new or DEF only equipment for diesel exhaust fluid.
DEF Temperature Maintenance
Temperature maintenance is also recommended to improve the storage, stability, and usability of DEF solutions. AUS 32 DEF storage temperatures should range between 14°F and 75°F (-10°C – 24°C). AUS 40 storage temperatures should range between 50°F and 85°F (10°C – 29°C). This ideal storage range for DEF solutions creates a unique protection need at both freezing and elevated temperature extremes.
Below freezing, AUS 32 DEF will coagulate, eventually coalesce, and will not be able to be used until thawed. AUS 40 DEF begins to thicken around 50°F (10°C), salt out near 38°F (3.3°C) and freeze around 35°F (1.7°C).
Above the recommended DEF storage temperatures and the urea in DEF can begin to hydrolyze and degrade into ammonia gas (NH3). How fast DEF will break down to ammonia is dependent on how high the temperature is, direct sunlight exposure, and the total length of time this occurs. With extended heat exposure, DEF breakdown will shorten its shelf life by reducing the urea content available for catalytic activity and can also result in pressure buildup if the container is not vented.
Recommended DEF Storage Tanks and Components
Commonly used and recommended DEF storage tanks, options, and components are detailed below. In general, the most used options are storage tanks made from high density polyethylene plastic, intermediate bulk containers (IBC totes), DEF transfer tanks, fiberglass tanks, rubber-lined carbon steel, and stainless steel.
High Density / Cross Linked Polyethylene
High density polyethylene (HDPE) is an industrial strength thermoplastic that is resistant to DEF corrosion and environmental concerns such as rusting. Due to its unreactive nature, polyethylene HDPE is a common material choice for small to bulk volume DEF containers. Cross linked polyethylene (XLPE) storage tanks are also compatible with DEF solutions but in general do not offer enough advantage to outweigh the increased cost when compared to HDPE.
HDPE storage tanks are produced through rotational mold fabrication that creates a durable, seamless chemical handling tank that is fully compatible with all DEF solutions and urea concentrations. Polyethylene tanks are offered up to a maximum capacity around 20,000 gallons. In scenarios that require even larger volumes of DEF, poly tanks are engineered to easily allow multi-tank connections to increase the total capacity of a DEF system.
The polyethylene materials and resins used to make chemical storage tanks can vary by manufacturer in grade, purity and extent of additives. Our poly DEF tanks are fabricated according to FDA, CFR and ANSI / NSF standards using virgin resin to produce potable water grade tanks that are top in quality in terms of material and engineering. These factors are important when using HPDE in high purity contact scenarios such as diesel exhaust fluid.
Poly IBC Totes for DEF
Rigid HDPE intermediate bulk containers (IBCs) and poly caged totes are also frequently used for DEF in smaller yet still significant volumes and/or high mobility applications such as agriculture and construction. Many DEF totes feature a pump and transfer system, making them an all-in-one option for DEF dispensing and refueling. Due to the temperature-sensitive nature of diesel exhaust fluid, DEF Powerblanket® IBC tote heaters are available to prevent freezing concerns.
Stainless Steel
Stainless steel is a versatile and commonly used material due to the intrinsic mechanical and chemical durability of this refined metal alloy. Stainless steel 304/316 tanks for DEF storage are often reserved for large (> 20,000 gallon) applications such as in DEF production or distribution. However, stainless steel metal and installation costs are often greater than the other storage tank types.
Also, chemical compatibility tests for stainless steel indicates some long term sensitivity to urea, making the material better suited for low duration contact applications such as with tanker trucks and in dispensing equipment.
Lined Carbon Steel
Carbon steel is susceptible to corrosion by DEF, which can cause solution impurities and affect application performance as well as eventual tank failure. Use is not recommended without an interior liner that is compatible and resistant to DEF and potential urea breakdown products. When used with a compatible inner liner, the mechanical integrity of carbon steel can make these tanks and materials suitable for use in bulk DEF storage and transport.
When compared to HDPE, carbon steel tanks are potentially susceptible to environmental corrosion and rust and often carry greater purchase and installation costs.
Fiberglass Reinforced Plastic
Fiberglass reinforced plastic, (FRP, also fiber-reinforced polymer), is a compatible option for bulk DEF storage. Fiberglass tanks are perhaps less common in DEF applications compared to polyethylene due to increased production costs and increased handling difficulties. With this said, FRP tanks make an excellent choice for underground storage and dispensing applications, which they are often used for.
Similar to stainless steel, FRP tanks can express long-term sensitivity to DEF that arises from DEF’s potential urea to ammonia degradation. FRP tanks without the right resin or production specifics can be sensitive to ammonia and ammonium hydroxide, which forms as ammonia gas dissolves in water.
Premium, alkaline resistant resins should be used in FRP tanks for DEF storage. Insulation, heat tracing, or underground tank installation is also recommended to ensure DEF stability and minimize potential ammonia gas production from sunlight exposure.
Recommended DEF Storage Tank Components
DEF storage tank components and installation fittings should be selected based on their corrosive compatibility and durability with diesel exhaust fluid urea and water. Compatibility is important to avoid equipment or tank failure as well as maintain DEF purity. Components should be inert to reactivity and resist degradation on extended exposure if long term, repeat use is expected or desired. For example, CPVC and PVC materials are not recommended for handling DEF long term due to potential amine sensitivity.
DEF storage is recommended in chemical polyethylene tanks built to handle 1.35 specific gravity liquids or greater. Recommended fittings include bulkheads made from polypropylene or 316 SS, recommended gasket materials include Viton or EPDM, and recommended bolts include Hastelloy or 316 SS. Recommended hose materials include EPDM and natural rubber.
The chart below compiles material resistance and chemical sensitivity to aqueous DEF urea solutions for common tank fittings and components.
Material | Compatibility / Damage |
---|---|
ABS Plastic | Good / Minor |
CPVC | Fair / Moderate |
PVC | Good / Minor |
XLPE | Excellent / None |
HDPE | Excellent / None |
LDPE | Excellent / None |
Polypropylene | Excellent / None |
Nylon | Excellent / None |
Neoprene | Good / Minor |
PTFE (Teflon) | Excellent / None |
PVDF (Kynar) | Excellent / None |
Viton | Excellent / None |
Hastelloy-C | Excellent / None |
Fluorocarbon (FKM) | Excellent / None |
Nitrile (Buna-N) | Good / Minor |
EPDM | Excellent / None |
Natural Rubber | Excellent / None |
304 SS | Good / Minor |
316 SS | Good / Minor |
Aluminum | Not Recommended / Severe |
Brass | Not Recommended / Severe |
Carbon Steel | Not Recommended / Severe |
Cast Iron | Fair / Moderate |
Copper | Not Recommended / Severe |
Titanium | Excellent / None |
*The above DEF / material compatibility statements are recommendations only and provided for reference. No guarantee is expressed or implied given the usefulness of any one material for DEF storage and handling. The above data is sourced from multiple reputable sources and is based on chemical compatibility tests. Always contact the chemical supplier or manufacturer when making modifications or designing a unique system. DEF products available for purchase are made from and installed with materials with known DEF compatibility.
Heating & Insulating DEF Tanks
Diesel exhaust fluid is sensitive to both hot and cold temperature extremes. High temperatures are more problematic and damaging to DEF. Extended exposure to temperatures above 85°F to 100°F can reduce DEF total urea content which will shorten DEF shelf life and its effectiveness for use in diesel SCR systems. Freezing and thawing, on the other hand, even repeatedly, will not harm DEF but solutions cannot be used when frozen.
Storage applications that require outdoor and bulk volumes of DEF often add tank insulation and/or heating devices to provide stable temperatures and help maintain DEF’s chemical integrity.
Polyurethane Insulation & Solution Heating
For DEF tank insulation, a polyurethane spray foam that is coated and weatherproofed with a mastic sealant is recommended. Polyurethane insulation can greatly increase a DEF tank’s resistance to temperature change and direct sunlight effects. This in turn can extend the useful service life of both the stored DEF solution and the poly tank.
Tank heat tracing, or other solution heating methods such as IBC tote heat blankets, can also be recommended for outdoor DEF storage. DEF heating is most reserved for uses that face extended subfreezing temperatures and limited sun-exposure, such as is common in more northern applications.
We are a leader in heat tracing and plastic tank insulation, see here for more details on our custom tank options. For more on poly tank insulation, see our post here.
Underground DEF Storage
Underground tank installation is an acceptable method for DEF temperature maintenance and sunlight protection. Underground storage tanks (USTs) make use of the earth’s natural heat to maintain stable temperature levels. Underground tanks do not require further heating or insulation considerations. In the United States, an underground tank must be properly installed according to overseeing laws and regulations, all of which can vary on location and what will be stored.
Underground DEF storage tanks are often made from rubber-lined carbon steel or fiberglass.
- Carbon steel is a durable material good for large UST storage needs; however, is long term susceptible to DEF when used without a resistant liner and to acidic soil chemistry, making it more prone to eventual UST replacement.
- FRP tanks can be more sensitive to accidental impact damage, but overall, fiberglass tanks are the best option for underground bulk DEF storage and are therefore, commonly used.
Further DEF Storage Considerations
Maintaining DEF Purity
Maintaining DEF purity is critical to successful DEF storage, to retain effectiveness for use, and to prevent damage or problems in a vehicle’s DEF-SCR system. To maintain DEF purity:
- Use compatible materials for storage and handling.
- Keep storage units closed.
- Use closed-loop transfer systems.
- Keep any dirt and debris out of the container and equipment.
- Limit the duration that lids, containers or bungs are open.
- Keep transfer equipment clean.
- Perform final rinses with demineralized water or DEF; do not use tap water.
- Do not use DEF containers or equipment for anything other than certified DEF.
- Store away from incompatible chemicals.
- Avoid extended sunlight exposure.
- Avoid elevated temperatures.
- Do not mix or add anything to DEF.
Causes of DEF Impurity or Contamination
Common elements that cause DEF impurity include copper, iron, zinc, nickel, aluminum, calcium, phosphate, and sodium. These impurities can result from using incorrect, aged, or rusting equipment in DEF handling. Other contaminants include dirt, dust, and debris originating from the environment and nature and often results from using an unsealed DEF container or leaving a container open.
In bulk DEF production, use, and handling scenarios, trace elements must be analytically tested and proven to be below ISO-specified concentration limits. These limits are fairly small in effect. For example, a single tablespoon of table salt, (NaCl) has the potential to contaminate 3 gallons of DEF with enough sodium ions, Na+ to exceed the ISO-allowed maximum of 0.5 ppm (0.5 mg/mL)*.
The following table lists DEF purity limits.
Contaminant | Purity Limit | Contaminant | Purity Limit |
---|---|---|---|
Alkalinity, NH3 % by weight maximum | 0.2 | Iron, ppm maximum | 0.5 |
Biuret % by weight maximum | 0.3 | Copper, ppm maximum | 0.2 |
Insolubles, ppm maximum | 20 | Zinc, ppm maximum | 0.2 |
Aldehyde, ppm maximum | 5 | Chromium, ppm maximum | 0.2 |
Phosphate (PO4), ppm maximum | 0.5 | Nickel, ppm maximum | 0.5 |
Aluminum, ppm maximum | 0.5 | Magnesium, ppm maximum | 0.5 |
Calcium, ppm maximum | 0.5 | Sodium, ppm maximum | 0.5 |
Potassium, ppm maximum | 0.5 |
*ISO limit: 0.5 ppm Sodium (Na+) = 0.5 mg/mL = 1892 mg/gal. 1 Tablespoon NaCl ≅ 17.06 grams = 17060 mg NaCl. Atomic mass of Na vs Cl is about ⅓ Na+, ⅔ Cl– meaning 17060 mg NaCl ≅ 5687 mg Na+; 5687 mg / 1892 mg/gal = 3 gallons. Meaning 1 Tablespoon NaCl could contaminate 3 gallons of DEF.
DEF Shelf Life & Ideal Conditions
DEF shelf life averages 12 to 18 months and is directly dependent on purity, long term storage temperature, and total exposure to sunlight UV energy. Ideal storage conditions for DEF will limit these effects. Following the projected shelf life, remaining DEF can be analyzed for purity to determine if it is still suitable for use. DEF analysis can be analytically performed by a lab or by a DEF concentration tool engineered for this purpose. If DEF testing indicates urea content has been lost or contamination has occurred, shelf life should be considered zero and the stock no longer suitable for use.
Temperature & Maximum DEF Shelf Life
Cool temperatures and storage away from direct sunlight are best for maximizing DEF’s shelf life. When capable, bulk volumes of DEF are preferred over repeated small quantities. Larger volumes have greater heat capacities and therefore a greater resistance to temperature changes and influence from heat sources. This means the solution will take longer to warm and will stay cooler longer.
To provide maximum shelf life, diesel exhaust fluid has an ideal temperature range between 40°F to 60°F. ISO specification 22241-3 reports AUS 32 solutions that are kept between 10 to 90°F will have at least a one year shelf life. To achieve a two year shelf life, long term storage temperatures should not exceed 75°F. For a three year shelf life, DEF should be kept under 60°F.
The following table demonstrates the average shelf life of DEF at different storage temperatures.
DEF Shelf Life vs Temperature | |
---|---|
Storage Temperature | Shelf Life Months |
≤ 60°F | 36 |
≤ 75°F | 24 |
≤ 77°F | 18 |
≤ 85°F | 12 |
≤ 95°F | 6 |
≤ 104°F | 2 |
≤ 120°F + | 1.5 |
Sunlight’s Effect on DEF Shelf Life
Diesel exhaust fluid storage tanks, IBC totes, and transfer tanks are recommended to be installed or kept in a location that minimizes the amount of direct sunlight exposure. Sunlight can provide thermal energy and high-wavelength (ultraviolet, UV) energy that can cause unwanted effects on stock DEF solutions. Over time, the sun’s energy input is capable of causing heat-induced hydrolysis of the urea in DEF and direct hydrolysis through ultraviolet energy and amine molecular interactivity.
Sunlight exposure and these resulting hydrolysis reactions can irreversibly reduce DEF’s concentration, therefore reducing its effectiveness and its useful shelf life. It is due to the potential for heat-induced hydrolysis that DEF is recommended to be stored at lower temperatures and that higher temperatures lead to a shorter shelf life.
Important Note on DEF Tanks and Sunlight Exposure
Remember, these reactions take time, so taking a 135 gallon DEF IBC tote out of the storage shed to top-up field equipment on a hot summer day is not likely to cause much damage to your DEF stock. On the other hand, leaving the DEF tote out in the field all summer will more than likely cause significant breakdown and may even result in the total loss of your supply.
For a more sun-resistant alternative to the caged IBC tote, consider Enduraplas® DEF tanks or NTO® portable DEF tanks manufactured from rigid, opaque high-density polyethylene and designed for DEF transport and outdoor dispensing applications.
Summarizing Indoor and Outdoor DEF Tank Storage
Indoor storage is recommended for all volumes of diesel exhaust fluid. Indoor storage will eliminate or at least significantly reduce the concerns from solar radiation and elevated temperatures.
When outdoor installation and applications are required, DEF tanks are recommended to feature a polyurethane foam insulation and weather-proofing to better protect stock solutions and the container from environmental effects. Underground fiberglass tanks are also an effective, reliable option.
Outdoor HDPE tanks, if not insulated, are recommended to be opaque and white in color to limit sunlight penetration and reduce the amount of heat energy absorbed. Consider NTO® DEF vertical storage tanks which are an all-in-one solution to stock DEF storage, handling, filling, and dispensing for long-term, repeat applications.
Building structures and/or natural shade can also be an effective means to help minimize sun exposure and associated heating for permanent DEF tank installations.
DEF Properties
DEF properties refer to the chemical characteristics and standard measurements of diesel exhaust fluid. As a chemical, DEF is considered a non volatile, non flammable, non hazardous solution with a negligible vapor pressure.
The standard properties of both AUS 32 and AUS 40 DEF solutions are fairly similar except for their maximum and minimum temperature ratings that results from the difference in urea content. DEF solutions have a specific gravity rating around 1.09, and a density around 9.10 ± 0.025 lbs/gal, making DEF heavier than water (8.34 lbs/gal) and common fuels of diesel (6.90 lbs/gal) and gasoline (6.22 lbs/gal).
The following table is an overview of DEF properties:
DEF Property | Value |
---|---|
Specific Gravity at 68⁰F (20⁰C) | 1.09 |
Density at 68°F (20°C) | 9.07 – 9.12 lbs/gallon |
Refractive Index at 68°F (20°C) | 1.3814 – 1.3843 |
AUS 32 Urea % by weight | 32.5 ± 0.7 |
pH | 7.0 – 8.5 |
Freeze / Salt-Out Temperature | 12°F (-11°C) / N/A |
Recommended Storage Temperatures | 14 – 75°F (-10 – 23.9°C) |
AUS 40 Urea % by weight | 40.0 ± 1.0 |
pH | 8.0 – 9.5 |
Freeze / Salt Out Temperature | 35°F (1.7°C) / 38°F (3.3°C) |
Recommended Storage Temperatures | 40 – 85°F (4.4 – 29.4°C) |
AUS 32 Transit DEF has a minimum recommended service temperature of 14°F (-1.1°C) while AUS 40 has a minimum recommended service temp of 50°F (10°C). Aqueous urea solutions have a lower temperature range that varies on concentration. The chemical eutectic point (point of lowest freezing) for DEF is at 32.5% urea in water. Any concentration above or below 32.5% will have a higher freezing point measurement as demonstrated in the accompanying DEF freezing point chart.
Incompatible Materials & Reactivity
In general, DEF is considered stable and unreactive under its normal conditions of handling and use for diesel SCR systems. Due to the urea content, solutions of DEF report a general incompatibility and reactivity with strong acids and bases, strong oxidizing agents, chlorates and chlorides, hypochlorite compounds, chromates and manganates, iron, mild steel, and nonferrous metals. Care should be exercised between DEF and these chemical and material types.
Additional and specific DEF incompatibilities include elemental fluorine, hydrogen peroxide, lead dioxide, and titanium tetrachloride; mixing with hypochlorite / phosphorus pentachloride can form nitrogen trichloride, an unstable combustible; direct contact with over-heated surfaces can produce toxic vapors of ammonia and nitrous gas; contact with ammonium nitrate can ignite or explode.
DEF Evaporation
Diesel exhaust fluid can experience evaporation, which can affect its suitability for use. The water in DEF can evaporate if kept in an open tank or used from an open storage system. As the amount of water by weight % decreases, the concentration of urea in weight % will increase per unit of volume. This can result in a stronger urea concentration being injected into a vehicle SCR system originally designed for AUS 32. The increase in urea concentration can cause not all of the urea to be used in the catalytic reaction, resulting in salt buildup, clogs, and a DEF-SCR system that is not fully effective.
For DEF spills, drips and remaining liquid, such as on dispensing nozzles or around lids, the resulting white powder or crystal is the urea salt leftover after all the water has evaporated. This is harmless, although it may cause irritation if you get it in your eyes. Dry DEF can be easily washed away with water.
DEF Crystallization
DEF crystallization can happen when enough water evaporates that the remaining water content cannot support the amount of urea present. In other terms, the water volume has decreased beneath urea’s maximum solubility levels and therefore begins to salt out (precipitate) as the water has reached saturation. Note, however, this is fairly unlikely except for neglected DEF stock and very poor care conditions.
Urea has a very high solubility in water, often reported around 1.08 g/mL at 68°F (20°C). This means every 1 mL of water can support 1.08 grams of urea. After doing some math and using the 32.5% urea content of DEF, around 64% of a total DEF solution would have to evaporate before precipitation begins to occur. This is a significant volume; for a 50 gallon DEF tank, this means 32 gallons of water would have to evaporate to reach urea saturation. If storage conditions allow for 32 gallons to evaporate, then it is also very likely that the DEF stock is contaminated or has degraded from poor storage conditions, and considering the remaining solution will now be much greater than the required 32.5% urea concentration, will no longer be suitable for use.
DEF Manufacturing
North America reported 230 million gallons of DEF produced and imported for use in 2012 with projections estimating DEF consumption to reach 1.5 billion gallons by 2022. Both AUS 32 and AUS 40 DEF solutions are manufactured using what is termed automotive grade urea (AGU, pharmaceutical, non-fertilizer grade urea). This high-quality urea is dissolved in purified, demineralized water until the desired concentration has been reached.
Newly produced DEF solutions are then laboratory certified per ISO standards prior to being approved for sale and use in diesel SCR systems. Urea solutions up to 70% are also manufactured for distribution and use in DEF production through dilution.
DEF manufacture requires a supply of analytically pure urea where the most common source option is to produce urea on-site by reacting ammonia and carbon dioxide gas together. DEF manufacturing is further divided into domestic urea production and dilution plants that specialize in making DEF from concentrated volumes.
The majority of DEF is made at domestic facilities that focus on producing urea for DEF manufacture. Final certified DEF products are then distributed to truck fleets, truck stops, OEMs, dealers, marine yards, train yards, gas stations, and local retailers. DEF is often packaged and distributed under common brand names such as AdBlue®, BlueDEF®, and AUS32®.
Diesel exhaust fluid distribution is often performed and handled by tanker trucks, shipped in ISO containers, IBC totes, and drum barrels. We provide a full selection of high density plastic tanks for DEF storage by manufacturers, distributors, and service stations.
DEF Safety & Handling
Diesel exhaust fluid is a non-hazardous material as defined by UN / DOT shipping and handling regulations for personnel and the environment. However, in terms of physical handling, DEF solutions can be mildly caustic and corrosive to equipment if made from incompatible materials.
Exposure to DEF in the eyes, sensitive tissues or long-term skin contact can cause irritation and/or pain. Direct contact with DEF should be avoided without proper protective equipment.
Harmful exposure should always be addressed according to the recommendations of specific product safety data sheets. If looking for more information on DEF handling, see this quality assurance guidance document here.
DEF Storage Takeaways
Due to international regulations, diesel exhaust fluid has become an essential product for diesel fuel engines. DEF serves as a consumable chemical reactant to provide emission control for many modern vehicles. DEF is defined, handled and traded as a fuel commodity, which, along with its standardization, has produced a non-proprietary, consistent solution that is certified to meet the purity requirements for its use and storage. (For more information concerning DEF, see the EPA on diesel engines, transportation, emissions and regulations)
Polyethylene storage tanks are a common and effective choice used in many industries that handle and use DEF. Stainless steel and other durable plastics are also common for DEF related equipment, components, fittings and plumbing. When seeking to store bulk volumes of diesel exhaust fluid, it is important to communicate to providers your specific handling needs and anticipate your DEF storage conditions and understand how geographic and seasonal temperature factors can influence the storage and equipment requirements for your DEF stock solutions.
As America’s liquid tank superstore, we provide high-density polyethylene tanks, dispensing tanks, DEF transfer tanks, DEF IBC totes, poly caged totes, fiberglass tanks, and much more.
If you need assistance or would like more information concerning DEF tanks, transfer products, or portable DEF solutions, contact us. We work directly with top manufacturers and producers in North America and will work directly with you for a solution to your unique application needs.
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- Diesel Exhaust Fluid Safety Data Sheet (greatlakespetroleum.com)
- Automotive Grade Urea Quality Assurance Guidance Document (novax-material.com)
- Diesel Fuel Standards – EPA (epa.gov)
- State and Local Transportation Resources – EPA (epa.gov)
- Smog, Soot, and Other Air Pollution from Transportation – EPA (epa.gov)
- EPA Emission Standards Regulations – EPA (epa.gov)