SANS 5941-2009 Carbon dioxide content of coal (titrimetric method)《煤中的二氧化碳含量(滴定法)》.pdf

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3、damage whatsoever than may result from the use of this material or the information contain therein, irrespective of the cause and quantum thereof. ISBN 978-0-626-22337-3 SANS 5941:2009 Edition 2SOUTH AFRICAN NATIONAL STANDARD Carbon dioxide content of coal (titrimetric method) Published by SABS Stan

4、dards Division 1 Dr Lategan Road Groenkloof Private Bag X191 Pretoria 0001 Tel: +27 12 428 7911 Fax: +27 12 344 1568 www.sabs.co.za SABS This standard may only be used and printed by approved subscription and freemailing clients of the SABS.SANS 5941:2009 Edition 2 Table of changes Change No. Date S

5、cope Foreword This South African standard was approved by National Committee SABS SC 27B Solid mineral fuels Test methods, in accordance with procedures of the SABS Standards Division, in compliance with annex 3 of the WTO/TBT agreement. This document was published in April 2009. This document super

6、sedes SABS SM 5941:1980 (edition 1). This standard may only be used and printed by approved subscription and freemailing clients of the SABS.SANS 5941:2009 Edition 2 1 Carbon dioxide content of coal (titrimetric method) 1 Scope This standard specifies a volumetric method for the determination of the

7、 carbon dioxide content of coal. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) ap

8、plies. Information on currently valid national and international standards can be obtained from the SABS Standards Division. ISO 3696, Water for analytical laboratory use. Specification and test methods. SANS 18283, Hard coal and coke Manual sampling. 3 Principle Coal passing a 212 m test sieve is t

9、reated with hydrochloric acid, which reacts with the carbonates present in the coal to liberate carbon dioxide. The carbon dioxide evolved from the decomposition of the carbonates is absorbed in benzylamine solution. The benzylamine salt formed is titrated with a solution of potassium methoxide in a

10、 mixture of toluene and methanol, using thymol blue as indicator. NOTE 1 Results obtained with this method should be comparable with results obtained using SANS 939 and SANS 940. NOTE 2 The determination is carried out in a closed circuit (see figure 1). 4 Apparatus 4.1 Absorption flask assembly, th

11、at is clean, dry, made up of boro-silicate glass and that consists of a 25 mL round-bottomed flask fitted (by means of ground joints) with a burette of capacity 10 mL graduated at 0,02 mL intervals, and an air inlet tube that reaches to the bottom of the flask (see figure 1). NOTE 1 The absorption f

12、lask assembly (and the assembly in 4.6) may be cleaned by means of a strong solution of potassium dichromate in sulfuric acid. NOTE 2 It is convenient to use an automatic type of burette fitted preferably with a polytetrafluoroethylene tap. This standard may only be used and printed by approved subs

13、cription and freemailing clients of the SABS.SANS 5941:2009 Edition 2 2 4.2 Balance, that has a sensitivity of 0,1 mg. 4.3 Flow meter, that is capable of measuring rates of flow of air up to 40 cm 3 /min. 4.4 Heating mantle, that is suitable for heating the reaction flask. 4.5 Pump, that is capable

14、of circulating air through the system at a rate of approximately 35 cm 3 /min. 4.6 Reaction flask assembly, that is clean, dry, made up of borosilicate glass, and that consists of a 50 mL, flat-bottomed flask fitted (by means of ground joints) with a tap funnel, a double-surface condenser of effecti

15、ve length of 100 mm, and an air inlet tube that reaches to the bottom of the flask (see figure 1). 5 Reagents NOTE Unless otherwise specified, use only water that complies with the requirements of ISO 3696, and that is free from carbon dioxide and reagents of analytical grade or (when such grade is

16、unobtainable) of the purest grade available. (Distilled or de-mineralized water may be freed from carbon dioxide by boiling it gently for 15 min.) 5.1 Hydrochloric acid, c(HCL) = 3 mol/L 5.2 Absorption mixture, prepared by mixing three volumes of 95 %(volume fraction) ethanol with 1 volume of benzyl

17、amine (C 6 H 5 CH 2 N 2 ) and 3 volumes of dioxan (OCH 2 OCH 2CH 2CH 2 ) 5.3 Standard potassium methoxide (CH 3OK.2CH 3OH) solution 0,1 mol/L, in a toluene-and- methanol mixture and standardized in triplicate as follows, using fresh portions of the sodium carbonate solution for each determination: P

18、ipette 10 mL of the standard sodium carbonate solution (see 5.4) into the reaction flask and carry out the test as described in clause 6, but omitting the coal sample. Calculate the carbon dioxide equivalent, F, of the potassium methoxide solution from the following formula and use the mean of the t

19、hree determinations: F = V 10where F is the carbon dioxide equivalent of the potassium methoxide solution in milligrams per millimetres V is the volume of potassium methoxide used in millilitres5.4 Standard sodium carbonate solution, 0,045 mol/L (1 mL = 1 mg CO 2 ). Dissolve 1,204 g of anhydrous sod

20、ium carbonate (previously dried at 260 C for 30 min) in water in a 500 mL volumetric flask, dilute to the mark with water, and mix well. 5.5 Thymol blue indicator, a mass fraction of 0,2 % i n dioxan solution. This standard may only be used and printed by approved subscription and freemailing client

21、s of the SABS.SANS 5941:2009 Edition 2 3 6 Procedure NOTE Before commencing any series of determinations check the apparatus for leaks. 6.1 Condition the 212 m sample, prepared in accordance with the relevant method in SANS 18283, by so exposing it for at least 30 min in a thin layer as to allow its

22、 moisture content to attain equilibrium with the laboratory atmosphere. 6.2 Mix the conditioned sample thoroughly (preferably by mechanical means) for at least 1 min. 6.3 Carry out duplicate determinations. 6.4 Accurately weigh out approximately 0,5 g of the coal sample, transfer it to the reaction

23、flask, and add 5 mL of water. Stopper the flask and wet the coal by shaking vigorously. Remove the stopper and wash any coal adhering to it and to the neck of the flask, back into the flask. 6.5 Pour 7 mL of the absorption mixture (see 5.2) into the absorption flask and add three drops of the thymol

24、 blue indicator (see 5.5). 6.6 With the tap funnel open, assemble the apparatus as shown in figure 1 but without connecting the ball-joint between the reaction and absorption flasks. Connect the inlet of the pump to the absorption flask assembly and the outlet to the reaction flask assembly. Switch

25、on the pump, connect the reaction flask assembly to the absorption flask assembly by means of the ball joint, and finally close the tap funnel. Adjust the air circulation rate to about 35 cm 3 /min and circulate the enclosed air through the system for 5 min to absorb the carbon dioxide present in th

26、e system. NOTE Follow the procedure described in 6.5 and 6.6 precisely to avoid “suckbacks“ in the apparatus. Reverse the sequence of operations given in 6.5 and 6.6 when shutting down the apparatus. 6.7 Titrate the contents of the absorption flask with the standard potassium methoxide solution to t

27、he blue end point and when this remains stable, place 2 mL of the hydrochloric acid in the tap funnel and admit the acid into the reaction flask, taking care not to admit air into the system. Wash the funnel three times with a small quantity of water, passing the washings into the reaction flask and

28、 finally leaving the funnel half full of water to act as a seal. Heat the contents of the reaction flask to boiling point. During this operation carbon dioxide is evolved and the colour of the absorption mixture changes from blue, through green, to yellow. After 5 min titrate the contents of the abs

29、orption flask with the standard potassium methoxide solution to the blue end point. Continue to boil the contents of the reaction flask while circulating air for a further 5 min, adjusting the end point at intervals. Decomposition of the carbonates in the test sample of coal and absorption of the ca

30、rbon dioxide evolved should be complete approximately 10 min after heating has begun. If the potassium methoxide fails to flow from the burette, remove the heat source and allow the flask to cool for 30 s. If undue frothing occurs, repeat the determination, adding a few drops of ethanol (95 %) to th

31、e mixture in the reaction flask. NOTE 1 Further determinations may be made without changing the absorption mixture until 5 mL of the potassium methoxide solution have been added. NOTE 2 A reference absorption mixture titrated to the blue end point, and kept in a closed flask can be used to compare t

32、he blue end point colour. This standard may only be used and printed by approved subscription and freemailing clients of the SABS.SANS 5941:2009 Edition 2 4 7 Calculation 7.1 Calculate the carbon dioxide (CO 2 ) content as a percentage from the formula: T = m V F 10where T is the carbon dioxide cont

33、ent, as a percentage; m is the mass of test sample used for the determination, in grams; F is the carbon dioxide equivalent to the potassium methoxide solution, in milligrams per millimetres;V is the volume of potassium methoxide solution used, in millilitres. 7.2 If the precision of the results is

34、not in accordance with clause 8, repeat the determination. 7.3 Report the result (the mean of duplicate determinations) to the nearest mass fraction of 0,1 %. 8 Precision 8.1 The precision of results achievable by this method is given in table 1. Table 1 Precision of results 1 2 3 Carbon dioxide con

35、tent % mass fraction Repeatability aReproducibility bUp to including 1 0,05 % absolute 0,10 % absolute Over 1 5 % of actual value 10 % of actual value aSame operator and same apparatus. bDifferent operators and different apparatus, with results expressed to the same moisture basis, preferably on the

36、 dry basis. This standard may only be used and printed by approved subscription and freemailing clients of the SABS.SANS 5941:2009 Edition 2 5 Figure 1 Assembled apparatus for the determination of carbon dioxide content in coal Bibliography SANS 939, Polished twines. SANS 940, Emulsion roof paint. S

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