Biodiesel Cold Flow Basics

Information for Petroleum Distributors, Blenders, and End-Users on Issues Affecting Biodiesel in the Winter Months

Prepared by the National Biodiesel BoardWinter 2007/2008

Diesel Fuel & Cold Weather Operability

Operability is defined as the lowest temperature a vehicle will operate without loss of power due to waxing of the fuel delivery system.

Diesel Fuel Background Information Relevant to Biodiesel

Diesel fuels composition and cold flow properties vary greatly across the United States. Cold flow characteristics of diesel fuels are influenced by the source of the crude oil they are made from, how they are refined and if they are blended to improve performance during cold weather.

The cold temperature properties of diesel fuel vary across the country depending on the time of year the fuel is produced and the climate. Generally, diesel fuels used in cold climates have better cold flow characteristics than diesel fuels used in warmer regions.

Both of these statements have a direct impact on the operability of biodiesel blends in cold weather

Cloud PointTemperature where crystals first appear

Cold Filter Plugging PointThe lowest operating temperature in which a vehicle will operate

Pour PointLowest temperature where fuel is observed to flow

Three Important Cold Weather Parameters that Define Operability for Diesel Fuels & Biodiesel

CRYSTALS GROW AND BEGIN TO ADHERE TO

ONE ANOTHER

Understanding the Cold Flow Mechanism in Diesel Fuel and Biodiesel

NUCLEI

LARGE CRYSTALSADHERE, TRAPPING LIQUID.

POCKETS ARE FORMED SIMILAR TO A HONEY COMB. FUEL GELLED.

Pour Point

VISIBLE CRYSTALSCloud Point

More wax precipitates as the temperature decreases

Typical Treatment of Diesel for Cold Weather Operation

Additives

All commercial cold flow additives work by modifying the wax crystal structure during crystal formation when cooling occurs.

Dosage level (expressed in parts per million (ppm)) of individual commercial additives varies depending on wax content and temperature.

Key Point: Additive must be added to fuel before it reaches cloud point temperature to be effective.

Kerosene (#1-D)

#1-D has excellent cold flow properties and is generally blended with #2-D in the winter months across the United States to meet customer cold flow specifications, improving/ insuring operability. Cloud and pour points, and CFPPs of some #1-D can be well below -30º F.

Typical Treatment of Diesel for Cold Weather Operation

Biodiesel and Cold Weather Operability

Basic Facts about Biodiesel & Cold Weather

B100 freezes faster than most US petrodiesel.

Untreated B20 freezes about 2-10° F faster than #2 petrodiesel, depending on:

• the cold flow properties of the biodiesel• the cold flow properties of the petrodiesel• at blend levels of 20% and less (< B20), the

cold weather parameters of the diesel fuel will dominate

Biodiesel Feedstock Composition and Cold Weather Operability

The cold flow properties of biodiesel fuels are dependant on the feedstock (specific type of oil, fat or grease) from which they are made and are a strong function of the level of saturated fat.

Animal fats, palm and coconut oils are more highly saturated—higher CN, higher cloud point.

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Saturated Monounsaturated Polyunsaturated

INCREASING CETANE NUMBER (CN) AND STABILITY

BETTER COLD FLOW PROPERTIES

Cloud Point (CP) Variation in 3 Different Diesel & Biodiesel Blends—Soy Methyl Ester (SME)

Cloud point for biodiesel blends made from 3 diesel

fuels and SME (SME cloud point = 34 o F)

-60

-50

-40

-30

-20

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0

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0 5 10 15 20

Blend Level (%)

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Pour point for biodiesel blends made with 3 methyl esters and

one diesel fuel (diesel pour point = -17 o F)

-20

-10

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0 20 40 60 80 100

Blend Level (%)

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SME ETME HYGME

Variation in Pour Point (PP) of 3 Different Biodiesel Base Feedstocks

Biodiesel Blends Cold Flow CharacteristicsCloud Point

(°F)Pour Point

(°F)Cold Filter Plugging Pt

Soy Methyl Esters 32 25 22

#2 Diesel 4 -30 1

2% Soy in #2 6 -25 1

5% Soy in #2 8 -20 -1

50% #1 and 50% #2 -6 -45 -12

2% Soy in 50/50 -6 -40 -14

5% Soy in 50/50 -6 -40 -14

#1 Low Sulfur Diesel -54 -70 <-30

2% Soy in #1 -45 -60 <-30

5% Soy in #1 -32 -55 <-30

ASTM D 6751-07a

Property Test Method Limits Units

Calcium & Magnesium EN 14538 5 max ppm (ug/g) Alcohol Control

either Flash Point D 93 130 min Degrees C or GC Methanol EN 14110 0.2 % Volume Flash Point D 93 93 min Degrees C Kin. Viscosity, 40C D 445 1.9 - 6.0 mm²/sec. Sulfated Ash D 874 0.02 max % mass Sulfur S500 D 5453 0.05 max (500) % mass (ppm)

S15 D 5453 0.0015 max (15) % mass (ppm) Copper Corrosion D 130 No. 3 max Cetane Number D 613 47 min

Cloud Point D2500 Report degrees C Carbon Residue D 4530 0.05 max % mass Acid Number D 664 0.50 max mg KOH/g Free Glycerin D 6854 0.020 % mass Total Glycerin D 6854 0.240 % mass Phosphorous Content D 4951 0.001 max % mass Distillation, T90 AET D 1160 360 max degrees C Na/K, Combined EN 14538 5 max ppm (ug/g) Oxidation Stability EN 14112 3 min hours (Visual Appearance) D 4176 Free of un-dissolved water, sediment and

suspended matter

Cold Weather Performance with Biodiesel

Establish a benchmark for cold flow protection based on the ASTM D975 “Tenth Percentile Minimum Ambient Air Temperature.”

the lowest ambient air temperature which will not go lower on average more that 10% of the time

Make sure the petroleum distributor is aware of this and incorporates it into blending operations

Biodiesel Blending and Cold Weather Operability

The impact of blending biodiesel with diesel fuel is dependent on the characteristics of the base diesel fuel and the methyl ester.

Generally, the better the cold flow characteristics of the base diesel fuel, the greater the effect of blending biodiesel on its cold flow properties. Blending biodiesel with #1-D and premium diesel fuels tends to affect cold flow properties more than blending biodiesel with #2-D.

Biodiesel Blending and Cold Weather Operability

Concerns arise when the fuel temperature falls below the cloud point of either fuel, independently, or as a finished blend fuel.

Biodiesel Blending and Cold Weather Operability

B100 Cold Weather Storage and Delivery Precautions B100 stored in cold temperatures (less than 40º F)

must be heated to at least 60ºF prior to distribution or blending into middle distillates of any grade.

If pumping biodiesel in cold weather through a conventional fuel pump, keep the hose and supply line to the pump equally protected with heat. An option to heating the systems is to blend B100 with 50% kerosene to dilute the cold weather properties of the biodiesel.

Cold Weather Blending Options and Precautions

With any type of blending (splash, in-tank or bottom loading), putting B100 into a cold empty truck can cause the fuel to gel, prohibiting proper mixing.

Always maintain biodiesel at 10–15º F above its cloud point prior to blending with diesel fuel.

Low Blends of Biodiesel and Cold Weather Operability

Blends of 2% and 5% biodiesel with diesel fuel have little impact on cold flow properties. Only small increases in cloud and pour point are observed, while the CFPP often decreases slightly when using B2.

As long as the B2 or B5 blend is made using an appropriate “winter grade” diesel fuel, no special provisions are required for storing, transferring or using the fuel.

Low Blends of Biodiesel and Cold Weather Operability

Biodiesel and Cold Flow Additives

Cold flow additives essentially work only on the diesel portion of the biodiesel blend as U.S. oils and fats contain too high a level of saturated compounds for most additives to be effective.

The cold flow additive effectiveness can also change dramatically depending on the exact type of biodiesel and the processing it has undergone; much like the situation found with diesel fuel.

Conclusions Cold flow properties of petrodiesel fuel vary widely.

One MUST be aware of the cold flow properties of both the biodiesel AND the petrodiesel.• With blends of 20% and below, petrodiesel is

dominant

Prepared properly, blends of B5 or less do not appear to be appreciably different from the base petrodiesel.

Blending biodiesel with #2 petrodiesel in blends of 20% (B20) does have an impact on the cold flow properties.• Saturated oils and fats have more of an effect on

cold flow properties.

Blending biodiesel with #1 petrodiesel in blends of 20% (B20) results in more of an impact on cold flow properties than with #2 petrodiesel.• But the resulting #1 blend still has better cold flow

values than #2.

Conclusions

Cool Customers

Cranmore Mountain ResortWhen snow falls at a rate of several inches per hour and all signs point to perfect weekend ski conditions, this ski resort has a lot riding on successful operation of its snow grooming equipment.

How others use biodiesel in cold climates

Cool Customers

City of Brooklyn Park, MN

The city has used biodiesel blends since 1999 in its fleet of over 100 vehicles— including fire trucks, utility and police vehicles.

How others use biodiesel in cold climates

Cool Customers

Yellowstone National Park

Biodiesel powers about 300 vehicles, boilers and other diesel equipment at the crown jewel of America’s National Park System.

How others use biodiesel in cold climates