ISO 975-2021 pdf free download – Brown coals and lignites — Determination of yield of benzene- soluble extract — Semi-automatic method.
This document specifies a semi-automatic method for determination of the yield of benzene-solubleextract in brown coals and lignites.
Normative references
The following documents are referred to in the text in such a way that some or all of their contentconstitutes requirements of this document.For dated references, only the edition cited applies. Forundated references, the latest edition of the referenced document(including any amendments) applies.ISO 5068-2,Brown coals and lignites —Determination of moisture content — Part 2: lndirect gravimetricmethod for moisture in the analysis sample
ISO 13909-4,Hard coal and coke —Mechanical sampling — Part 4:Coal —Preparation of test samplesISO 18283,Coal and coke — Manual sampling
3Terms and definitions
No terms and definitions are listed in this document.
ISO and lEC maintain terminological databases for use in standardization at the following addresses:— ISO online browsing platform: available at https://www.iso.org/obp
一IEC Electropedia: available at https://www.electropedia.org/
4Principle
A test portion of the brown coal or lignite is extracted with benzene in a semi-automatic extractioninstrument. The solvent is then removed by evaporation and the soluble residue dried to constant mass.The percentage of benzene-soluble extract is calculated from the mass of residue after drying and isreported on the dry basis.
5Reagent
5.1 Benzene, of analytical reagent grade, p20 =0,876 g/ml, distillation range 80 °C to 81°C.At least95 % shall distil within this range.
WARNING — Benzene is flammable and toxic by inhalation, ingestion or skin absorption.Thetest must be carried out in a hood and the benzene must be recovered as completely as possible.
6 Apparatus
6.1 Semi-automatic extraction instrument,containing mainly two units: the continuousextraction-evaporation device and the controller. The continuous extraction-evaporation deviceconsists of a 100 ml conical flask, an extraction chamber and a condenser. The extraction chamber
8.3Procedure
Transfer a mass of about 2 g (determined to the nearest 0,1 mg) of general analysis test sample to theextraction thimble (6.2) and cover with a pad of absorbent cotton, which is fitted snugly on the wall ofthe thimble.
Place the extraction thimble with sample in the extraction chamber (6.1).
Add 60 ml to 70 ml of benzene to a previously dried flask of known mass(determined to the nearest0,1 mg).
Assemble the instrument.
Switch on the electrical power.Push down the programme button.The instrument will automaticallyperform the experiment in accordance with the following sequence:
The extraction-evaporation device is lowered until the flask is immersed in the water bath as inthe preliminary adjustment and the condenser is in an inclined position permitting refluxing.Theheating of the water bath is started simultaneously.
When the extraction temperature previously set is reached, the pump begins to circulate the hotwater between the bath and the jacket of the extraction chamber. The benzene vapour from theflask passes through the extraction chamber and reaches the condenser, where it is condensed anddrips onto the thimble. The extraction stage is thus in progress.
After 180 min, or an otherwise set time, the pump stops and extraction is finished.Hot water flowsback to the bath. The temperature of the extraction chamber drops to a temperature at which thebenzene vapour can only reach the extraction chamber and condenses there.Thus a rinsing actionis achieved,by means of which the benzene-soluble extract adhered to the wall is washed down intothe flask by the condensed benzene.This is the rinsing stage.
After 10 min, rinsing is finished.The condenser is automatically changed to an inverted positionpermitting distillation.The pump works again so as to resume hot-water circulation. T’he benzenevapour condenses in the condenser and flows to the receiver. The stage of evaporation starts.
After 50 min of evaporation is finished, the extraction-evaporation system is elevated to the originalposition, permitting the flask to be detached from the extraction chamber. The programme is thusterminated.
Detach the flask with soluble residue. Dry it in the air oven (6.3) maintained at 105 °Cto 110 Cor inthe vacuum oven (6.3) maintained at 80 °C± 2 °C and about 50kPa to constant mass after allowingit to cool to ambient temperature.
NOTE Constancy in mass is considered to have been achieved when the difference between successivedryings does not exceed 0,001 g.ISO 975 pdf download.