Standard Test Method For Moisture in Activated Carbon – ASTM D 2866-89

Standard Test Method For Moisture in Activated Carbon – ASTM D 2866-89

1-Scope.

1.1 This test methods provide two procedures for the determination of the moisture content of activated carbon. The procedures may also be used to dry samples required for other tests. The oven-drying method is used when water is the only volatile materials present and is in significant quantities, and the activated carbon is not heat sensitive (some activated carbons can ignite spontaneously at temperature as low as 150⁰C). The xylene-extraction method is used when a carbon is known or suspected to be heat sensitive or to contain non water-miscible organic compounds instead of or in addition to water. The over- drying method described in these test methods may be used as the reference for development of instrumental technique for moisture determination in activated carbon. 

1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

2. Referenced documents

2.1 ASTM Standards

E 177 Practice for Use of the Term Precision and Bias in ASTM Test Methods.

E 691 Practice for conducting an Interlaboratory Study to Determine Precision of Test Method.

3. Summary of Test Method

3.1 Oven-Drying Test Method- A sample of carbon is put into a dry, closed capsule ( of known weight) and weighed accurately. The capsule is opened and place with the lid in a preheated oven. The sample is dried to constant weight then removed from the oven and with the capsule closed, cooled to ambient temperature. The closed capsule is weighed again accurately. The weight loss is expressed as a percentage of the weight of the original sample.

3.2 Xylene-Extraction Test Method- A known, accurate weight of carbon is put into a boiling flask. A known volume of xylene is added to the flask and the flask then connected to a water trap. A hot place is used to heat the xylene until boiling. The temperature is controlled to allow steady reflux. Reflux continues until no further water can be collected in the trap. The weight of water collected is expressed as a percentage of the weight of the original sample.

4. Significance and Use

4.1 The moisture content of activated carbon is often required to define and express its properties in relation to the net weight of the carbon.

5. Apparatus and Materials

5.1 Moisture Oven-Most commercial, electrically heated, forced-circulation drying ovens capable of temperature regulation between 145 and 155 ⁰C may be used.

5.2 Capsules with Cover-Low form glass weighing bottles with ground-glass stoppers or seamless metal boxes with cover may be used. They should be as shallow as possible, consistent with convenient handling.

5.3 Desiccator.

6. Materials

6.1 Desiccant- Anhydrous calcium chloride or other suitable desiccant.

7. Procedure for Activated Carbon Passing A No. 50 sieve

7.1 Dip out with spoon or spatula from the sample bottle a 1 to 2-g representative sample. Put this into a pre-dried tarred capsule with lid, close and weigh at once to the nearest 0.5 mg. The depth of the carbon in the capsule must not exceed 1.25 cm

7.2 Remove the cover and place the capsule and cover in a preheated forced circulation oven (at 145 to 155 ⁰C). Close the oven and dry to constant weight (3 h normally sufficient). Open the oven and cover the capsules quickly. Cool in a desiccator to ambient temperature and weigh.

8. Procedure for Activated Carbon Larger Than A No. 50 sieve

8.1 Use a 5 to 10 g representative sample and weigh to the nearest 2 mg. Complete the determination as described in section 7.

9. Calculation

9.1 Calculate the moisture content as follows:

Moisture, weight % = [(C-D)/(C-B])x100

Where:

B = Weight of capsule with cover, g

C= weight of capsule with cover plus original sample, g, and

D = weight of capsule with cover plus dried sample, g.

    XYLENE-EXTRACTION METHOD

10. Apparatus

10.1 Boiling Flask –A 300 mL flat-bottom Erlenmeyer ask with ground glass joints

10.2 Condenser- A300 mm water- cooled condenser of the Allihn type with ground- glass joint

10.3 Drying Tube, containing a suitable desiccant with fiber-glass filter.

10.4 Water trap- A Bidwell and Sterling 10 mL or Dean and stark receiver with ground-glass joint. The water trap should be clean so that the shape of the meniscus at the end of the test is the same as at the beginning.

NOTES 1 – The trap may be coated with a silicone resin to give a uniform meniscus. To coat the trap, first clean it with a suitable cleaner. Rinse the clean trap with a silicone resin and after draining for a few minutes, bake for 1h at approximately 200 ⁰C

10.5 Hot Plate-An electrically heated hot plate with enclosed elements and temperature control.

11. Regent

11.1 Xylene- Reagent grade in accordance with the specifications of Committee on Analytical Reagent of the American Chemical Society.

12. Hazards

12.1 The use of hot xylene presents a continual fire hazard and suitable fire extinguishing equipment  should be available.

13. Preparation of Apparatus

13.1 Clean the condenser, flask and trap and carefully dry to ensure that is free of water. Assemble the condenser and water trap as shown in Fig. 1     

FIG 1 Moisture Determination Apparatus

14. Procedure 

14.1 Weigh the sample bottle. Dip out with a spoon from the sample bottle 25 to 50 g of the sample. Put this into the boiling flask and reweigh the sample bottle to the nearest 0.1 g. Add 100 mL of xylene and connect the boiling flask to the water trap. For carbons having density less than 0.30 g/cm³, 200 mL of xylene should be used for a 25g sample.

14.2 Place the hot plate under the boiling flask and heat to boiling. Adjust the temperature control so as to reflux the xylene at the rate of about 1 drop/s from the tip of the condenser. Continue to reflux until there is no further increase in the water layer in the trap over a 30- min period (from 2 to 8 h may be required).

15.Calculation:

15.1 Calculate the moisture content as follows:

Moisture, weigh % = [V / (C-E)] x 100

Where:

V = water collected, ml

C = initial weight of sample bottle, g, and

E = weight of sample bottle after removing moisture sample, g

15.2 Calculate for the correction for moisture in carbon to determine the weight of a carbon sample on the dry basic as follows:

Corrected weight (dry basic) =

initial weight of carbon(undried)x (100-% moisture from 15.1)/100%

16. Precision and Bias

16.1 An interlabotory test which included four laboratories testing in triplicate, activated carbon sample with nominal moisture levels of 1 weight %, 5 weight %, and 12 weight %, was conducted according to Practice E 691. Results of these test yielded repeatability coefficients at 95% confidence level as listed in Table 1

16.1.1 The high coefficients of variation for both test methods when the moisture is nominally “1 weight % or less.” If greater precision is needed, the amount of carbon sample can be increase over that specified in Sections 7,8 and 14

17. Keywords   

17.1 Activated carbon, moisture.