生物柴油产品与质量ASTMD6751

Biodiesel Production and Quality

Last updated April 26, 2007

The production processes for biodiesel are well known. There are three basic routes to biodiesel production

from oils and fats:

* Base catalyzed transesterification of the oil.

* Direct acid catalyzed transesterification of the oil.

* Conversion of the oil to its fatty acids and then to biodiesel.

Most of the biodiesel produced today is done with the base catalyzed reaction for several reasons:

* It is low temperature and pressure.

* It yields high conversion (98%) with minimal side reactions and reaction time.

* It is a direct conversion to biodiesel with no intermediate compounds.

* No exotic materials of construction are needed.

The chemical reaction for base catalyzed biodiesel production is depicted below. One hundred pounds of fat

or oil (such as soybean oil) are reacted with 10 pounds of a short chain alcohol in the presence of a catalyst to

produce 10 pounds of glycerin and 100 pounds of biodiesel. The short chain alcohol, signified by ROH

(usually methanol, but sometimes ethanol) is charged in excess to assist in quick conversion. The catalyst is

usually sodium or potassium hydroxide that has already been mixed with the methanol. R', R'', and R'''

indicate the fatty acid chains associated with the oil or fat which are largely palmitic, stearic, oleic, and

linoleic acids for naturally occurring oils and fats.

The Biodiesel Reaction

CH2OH R'''COOR

CH2OCOR'''

| Catalyst

|

CH2OCOR'' + 3 ROH ------> CH2OH + R''COOR

|

|

CH2OCOR' CH2OH R'COOR

100 pounds 10 pounds 10 pounds 100 pounds

Oil or Fat Alcohol (3) Glycerin Biodiesel (3)

The National Biodiesel Board does not get involved with commercial biodiesel production or the design and

construction of biodiesel facilities, but we have provided an example of a simple production flow chart along

with a short explanation of the steps involved to acquaint the reader with the general production process.

Biodiesel Production ProcessCatalyst

Catalyst-MixingMethanolPurificationMethanol-RecoveryQuality

ControlMethylEster

Vegetable Oils, UsedRecycledMethanolCooking Oil,Animal FatsTransesterificationPharmaceuticalGlycerinCrude BiodieselGlycerinPurificationIf desiredNeutralizing AcidNeutralizationPhase SeparationRe-neutralizationMethanol-RecoveryCrudeGlycerin

The base catalyzed production of biodiesel generally occurs using the following steps:

Mixing of alcohol and catalyst. The catalyst is typically sodium hydroxide (caustic soda) or potassium

hydroxide (potash). It is dissolved in the alcohol using a standard agitator or mixer.

Reaction. The alcohol/catalyst mix is then charged into a closed reaction vessel and the oil or fat is added.

The system from here on is totally closed to the atmosphere to prevent the loss of alcohol. The reaction mix

is kept just above the boiling point of the alcohol (around 160 °F) to speed up the reaction and the reaction

takes place. Recommended reaction time varies from 1 to 8 hours, and some systems recommend the

reaction take place at room temperature. Excess alcohol is normally used to ensure total conversion of the fat

or oil to its esters.

Care must be taken to monitor the amount of water and free fatty acids in the incoming oil or fat. If the free

fatty acid level or water level is too high it may cause problems with soap formation and the separation of the

glycerin by-product downstream.

Separation.

Once the reaction is complete, two major products exist: glycerin and biodiesel. Each has a

substantial amount of the excess methanol that was used in the reaction. The reacted mixture is sometimes

neutralized at this step if needed. The glycerin phase is much more dense than biodiesel phase and the two

can be gravity separated with glycerin simply drawn off the bottom of the settling vessel. In some cases, a

centrifuge is used to separate the two materials faster.

Alcohol Removal. Once the glycerin and biodiesel phases have been separated, the excess alcohol in each

phase is removed with a flash evaporation process or by distillation. In others systems, the alcohol is

removed and the mixture neutralized before the glycerin and esters have been separated. In either case, the

alcohol is recovered using distillation equipment and is re-used. Care must be taken to ensure no water

accumulates in the recovered alcohol stream.

Glycerin Neutralization. The glycerin by-product contains unused catalyst and soaps that are neutralized

with an acid and sent to storage as crude glycerin. In some cases the salt formed during this phase is

recovered for use as fertilizer. In most cases the salt is left in the glycerin. Water and alcohol are removed to

produce 80-88% pure glycerin that is ready to be sold as crude glycerin. In more sophisticated operations,

the glycerin is distilled to 99% or higher purity and sold into the cosmetic and pharmaceutical markets.

Methyl Ester Wash. Once separated from the glycerin, the biodiesel is sometimes purified by washing gently

with warm water to remove residual catalyst or soaps, dried, and sent to storage. In some processes this step

is unnecessary. This is normally the end of the production process resulting in a clear amber-yellow liquid

with a viscosity similar to petrodiesel. In some systems the biodiesel is distilled in an additional step to

remove small amounts of color bodies to produce a colorless biodiesel.

Product Quality and Registration. Prior to use as a commercial fuel, the finished biodiesel must be analyzed

using sophisticated analytical equipment to ensure it meets ASTM specifications. Additionally, all biodiesel

produced must be registered with the Unites States Environmental Protection Agency under 40 CFR Part 79.

The most important aspects of biodiesel production to ensure trouble free operation in diesel engines are:

* Complete Reaction

* Removal of Glycerin

* Removal of Catalyst

* Removal of Alcohol

* Absence of Free Fatty Acids

These parameters are all specified through the biodiesel standard, ASTM D 6751. For a complete copy of

ASTM D 6751 contact ASTM at . This standard identifies the parameters the pure biodiesel

(B100) must meet before being used as a pure fuel or being blended with petrodiesel. The National Biodiesel

Board has adopted ASTM biodiesel specifications. The specification is listed on the following page.

The NBB has also formed the National Biodiesel Accreditation Commission that has put into place an

accreditation program for companies selling biodiesel and biodiesel blends. It is a Good Housekeeping™

type seal of approval for biodiesel marketers, and provides the consuming public with additional assurances

and confidence that biodiesel purchased form a Certified Biodiesel Marketer will meet ASTM specifications.

Certifications are pending, and will be posted on the NBB web site at . Once the program

has been fully implemented, NBB recommends that all biodiesel marketers become certified, and that all

biodiesel consumers specify the purchase of biodiesel from NBAC Certified Marketers.

SPECIFICATION FOR

BIODIESEL (B100) – ASTM D6751-07a

March 2007

Biodiesel is defined as the mono alkyl esters of long chain fatty acids derived from vegetable oils or animal

fats, for use in compression-ignition (diesel) engines. This specification is for pure (100%) biodiesel prior to use

or blending with diesel fuel. #

Property

Calcium & Magnesium, combined

Flash Point (closed cup)

ASTM Method

EN 14538

D 93

Limits

5 max

93 min.

Units

ppm (ug/g)

Degrees C

Alcohol Control (One of the following must be met)

1. Methanol Content

2. Flash Point

Water & Sediment

Kinematic Viscosity, 40 C

Sulfated Ash

Sulfur

S 15 Grade

S 500 Grade

Copper Strip Corrosion

Cetane

Cloud Point

Carbon Residue 100% sample

Acid Number

Free Glycerin

Total Glycerin

Phosphorus Content

Distillation, T90 AET

Sodium/Potassium, combined

Oxidation Stability

Workmanship

EN14110

D93

D 2709

D 445

D 874

D 5453

D 5453

D 130

D 613

D 2500

D 4530*

D 664

D 6584

D 6584

D 4951

D 1160

EN 14538

EN 14112

0.2 Max

130 Min

0.05 max.

1.9 - 6.0

0.02 max.

0.0015 max. (15)

0.05 max. (500)

No. 3 max.

47 min.

Report

0.05 max.

0.50 max.

0.020 max.

0.240 max.

0.001 max.

360 max.

5 max

3 min

% volume

Degrees C

% vol.

mm2/sec.

% mass

% mass (ppm)

% mass (ppm)

Degrees C

% mass

mg KOH/g

% mass

% mass

% mass

Degrees C

ppm

hours

Free of undissolved water, sediment, & suspended matterBOLD = BQ-9000 Critical Specification Testing Once Production Process Under Control

* The carbon residue shall be run on the 100% sample.

# A considerable amount of experience exists in the US with a 20% blend of biodiesel with 80% diesel fuel (B20).

Although biodiesel (B100) can be used, blends of over 20% biodiesel with diesel fuel should be evaluated on a

case-by-case basis until further experience is available.