THE DISTILLATION OF COAL IN A VACUUM. 131XVI1I.-The Distillation qf Coal in a Vacuum.By MAURICE JOHN BURGESS and RICHARD VERNON WHEELER.IN the course of an investigation into the nature of coal, the effecthas been tried of distillation a t different temperatures and underdifferent conditions. Some account of the results obtained hasalready been communicated to the Society (T., 1910, 97, 1917;1911, 99, 649; 1913, 103, 1704). In the earlier stages of thisinvestigation, during the year 1909, distillations of coal weremade a t low temperaturm in a high vacuum, the main object beingto examine the liquid products. The gmeous products of distilla-tion in a vacuum were also studied, and the results obtained formthe subject of the present paper.It has already been shown that it8 the temperature of distillationof coal is increased from 500° to l l O O o the percentage of hydrogenin the gases evolved increases, whilst the percentages of methaneand ethane decrease, a decomposition point, marked by a rapidevolution of hydrogen, occurring at about 750O.Below 450° i twas stated (Zoc. cit.) that ‘‘ ethane, propane, and, probably, highermembers of the paraffin series form a large percentage of thegases evolved.”When coal that has been finely pulverised and thoroughly driedin air at 107O is exhausted a t room temperature, “occluded”gaees in small quantity can be pumped off. These gaees, unlike theoccluded gases that can be obtained, sometimes in large volume,from newly-won, undried cod, consist largely of carbon dioxideand carbon monoxide.On raising the temperature of the coal during exhaustion, thesuccession of events is^ as follows :l i 132 BURGESS AND WHEELER :Occluded or " condensed " gases (unextractable at atmospherictemperature) continue to be removed in small quantity up to 150°or 200O. These gases are mainly the paraffin hydrocarbons, thehigher members predominating.At about 200° there is a copious evolution of water (small quan-tities of gas being also evolved), and water continues to make itsappearance at successive stages in the distillation up to 45UO-thehighest temperature employed in this series of experiments.Thiswater, as has been pointed out in a previous paper, must be waterof constitution. The gases evolved during the period of mostrapid formation of water contain a high percentage of the oxidesof carbon.Between ZOOo and 300° decomposition occurs of some sulphur-containing organic conipound, for the gases evolved during thatperiod contain a considerable proportion of hydrogen sulphideand tarnish mercury.This decomposition, which begins a t about270°, is practically completed a t 300O. Simultaneously with thehydrogen sulphide the gases contain a considerable proportion ofthe higher olefines, the evolution of which does not, however, ceaseor fall off until a temperature of 350° is reached.Liquids other than water begin to distil a t about 310°, a t whichtemperature a thin, reddish-brown oil appears. There is nomarked evolution of gas a t this temperature, and i t seems probablethat the oil is not necessarily a product of decomposition, but maybe liquated out of the coal conglomerate.A decomposition point occurs a t about 350°, there being thena rapid evolution of gas and much viscid oil formed.Decomposi-tion then continues with increasing rapidity as the temperature isr aisecl .The mixtures of gases evolved a t the different temperatures arevery complicated, containing as they do hydrogen sulphide, ca.rbondioxide, ethylene and the higher olefines, carbon monoxide,hydrogen, and the paraffin hydrocarbons up to and includingpentaneThe presence or absence of benzene vapour could not bedefinitely established owing to the difficulty there is in estimatingit separately from the higher olefines*; but neither benzene norits homologues could be detected in the liquid products of distilla-tion in a vacuum up to 450°, so that the presence of the vapoursamongst the gaseous products is extremely doubtful.* I n the analysis of these mixtures of gases the reagent used for estimatingbenzenetogether with tne higher olefines, sepaisately' from ethylene, was concentratedsulphuric acid (D 1.84).Treatrneiit for a short tiriie with this reagent (the densityof which was wrongly stated to be 1.9 in a previons paper) removes benzene and t h ehigher oletines together, leaving ethylene practically untonchedTHE DISTTLLATION OF COAT, IN A VACUUM. 133Of the paraffin hydrocarbons, besides methane and ethane,propane and butane were isolated by fractionation with liquid airand solid carbon dioxide dissolved in ether, and the presence ofpentane established by explosion analysis.It is impossible in a mixture of more than two of the membersof the paraffin series to calculate the percentage of each constitu-ent present, but on explosion with excess of air the value of theratio CIA (contraction on explosion : absorption by potassiumhydroxide, that is, carbon dioxide formed) gives some indicationof their nature; chus the value of the ratio is for methane 2-00and f o r ethane 1.25, so that if a mixture of the paraffins gives onexplosion analysis a ratio CIA lying between 2.00 a.nd 1.25, it isgenerally safe t o say that both methane and ethane are containedin the mixture, and it is usual t o calculate the analysis on theassumption that no higher inember is present.It must be bornein mind, however, that the same analytical results are given onexplosion by a mixture of equal volumes of methane and propaneas by pure ethane.A method of calculation which gives, perhaps, a better idea ofthe nature of the gases present than does the ra.tio C / A is basedon the following considerations :41 volumes of any mixture of paraffin hydrocarbons containm CH, groups and n CH, groups (in the case of methane n=O).The carbon in the mixture of paraffins is equal to the carbondioxide produced on explosion (is equal to the absorption, A , bypotassium hydroxide after explosion); and if the letter G be takento represent the contraction on explosion, the hydrogen in themixture of paraffins is given by the expression 2/3(2.4 + 2C).From these two relationships we get:wz + n = carbon = A ,andwhence m=1/3(2C-A),and 72 = 2 I 3 (2 A - C) .volumes of the paraffins present, whatever their composition, so tbat :4nz + 2n = hydrogen = 2 / 3(2A + 2C) ;Now m, the number of CH, groups, givee also the number ofVolume of paraffins, Tr,=1/3(2Cf-9) .. . (1)The number cf CH2 groups per 7 1 ~ volumes of the paraffins isgiven by the equation:n = d - V . . . . . . , (2)So that n / V , the number of CH, groups per unit volume of theparaffins, can be obtained by means of these equations; or it canbe calciilated directly from the relation :. . . . . . I b - 2 ( 2 A - C ) _ - ~V 2C-I34 BURGESS AND WHEELER :The value n / V is in several ways more convenient than theratio ( ! / A usually employed, for it shows at a glance the averagenumber of CH, groups in the mixture of paraffin hydrocarbonsanalysed, and, in conjunction with the determination of V , enablesa record of the volume of the paraffins and a statement as to theirnature t.0 be made without entering into any hypothetical calcu-lation of the percentages of individual members present.Thevalue n / V for methane is, of course, 0; for ethane it is 1, forpropane 2, and so on.The higher paraffins mostly appear at the lower temperaturesof distillation, the range 100-300° being attended by thegreatest percentage evolution. Above 350°, the decompositionpoint of part of the coal substance, the percentage of methaneincreases, and that of the higher hydrocarbons decreases.It is conceivable that the paraffin hydrocarbons obtained byexhaustion from coal a t temperatures between ZOOo and 300° (thatis, below the decomposition point observed) are present as suchin the coaI, being held in a manner similar to, but more forciblethan, '' occluded '' methane at the lower temperatures.The factthat there is a simultaneous evolution of olefines, however, makesit more probable that both classes of hydrocarbons arise from thethermal decomposition of a solid paraffin or similar long-chaincompound.EXPERIMENTAL.The apparatus employed for the vacuum distillations underwentseveral modifications during the course of the research.Its finalform is depicted in Fig. 1. As will be seen from this diagram, theneck of the distillation retort (a round-bottom flask of Jena hardglass) pointed vertically downwards into a receiver attached by aground-glass joint. By distilling the coal in this manner refluxcondensation of liquid produck was avoided, and their thermaldecomposition prevented or minimised. A second and, in someexperiments, a third receiver was interposed between the firstand an autoniatically-acting mercury pump, fitted with twoSprengel tubes, used for withdrawing the gases as they wereevolved from the coal, The receivers nearest the pump were keptcooled throughout the distillations by a solution of solid carbondioxide in ether, or, in some experiments, by liquid air.Thewide-bore tap on the neck of the retort enabled the distillationsto be interrupted at different temperatures, and the condensing-tubes changed, without admitting air to the coal.The capacity of t.he retort in the experiments described in thispaper was such as to onable 200 grams of coal to be distilledTHE DISTILLATION OF COAL IS A VACUUM. 135the retort being filled to thO neck. In later experiments a retortcapable of holding about 1& kilos. has been employed.Method of Ezpwiment.-Fine dust obtained by pulverising nutcoal was employed; in som0 cases after drying at 1 0 7 O duringthree hours before use, in other cases without drying,The whole apparatus having been rapidly exhausted by meansof a Qeryk oil pump, thO last traces of air were removed a t atmo-spheric temperature by the Sprengel pump.When undried coalwas used, " occluded" gases continued to be pumped off forseveral days a t atmospheric temperature. These gases were, insome experiments, collected in fractions over successive periods oftime, and the fractions analpsed separately.All occluded gases having been removed at atmospheric tem-F:G. 1. F I ~ . 2.2'0 gan holderElcperature, an electric resistance furnace surrounding the retort wasgradually raised in temperature to looo, and exhaustion continuedat that temperature until no more gases could be pumped off,The temperature was then further raised, gradually, by 50° orlooo, and all the gases at this higher temperature collected. Thismode of procedure, which enabled decomposition points to bedetected, was followed up t o a temperature of 450°, each successivestage in the heating being maintained until no further gases wereevolved, and the condensing tubes being changed at each stage.The mercury pump used was rapid in its action, and, evenduring the period of maximum evolution of gases, did not allow136 BURGESS AND WHEELER :the pressure in the retort to fall below 20 mm.For the collectionof the comparatively large volumes of gases evolved at the highertemperatures the device shown in Fig. 2 was used, the globe A ,filled with mercury, being a, receiver from which the gases couldbe transferred to a gas-holder containing a mixture of equal partsby volume of glycerol and water.Each experiment lasted continuously during from four to eightweeks.Results of E’xperiments.-O*le or tv70 typical experiments onlyof the many that have been carried out need be recorded.Severaldifferent varieties of bituminous coal have been used, but noimportant differences have been observed in their behaviour onheating or in the products, whether gaseous or liquid, of theirdecomposition. The composition of the occluded gases, it is true,varies with the kind of coal and with its previous history (forexample, with the length of time since it was niined), but a studyof the occluded gases is but an incidental part of this research,and has, moreover, already received the attention of numerousinvestigators.The first experiment t o be described wm made with a sampleof Silkstone (bituminous) coal in the form of fine dust, obtainedby pulverising about 50 kilos.of washed “nuts,” and had beenpassed through a, 240-mesh sieve. This coal was from the sameseam as coal A of our previous work. The dust was not driedbefore use, and gave off a considerable volume of occluded gaseson exhaustion at atmospheric temperature. When these gases hadbeen removed the coal was heated to looo, exhaustion beingcontinued.Gases Evolved at looo.The volume of gases evolved a t looo amounted to 34 C.C. perTheir composition was as 100 grams of coal, measured a t N.T.P.follows :CO, ................................ 6-70 per cent.0, ................................. 1.66 ,,C, H, ...............................0 *85 , ,C,H,(n > 2) ..................... 1 *30 , ,CO .................................... 1.40 ,,H, .................................... 190 , ,CnH2n+Z .......................... 84 -55 , ,The walue n/V for the paraffins was 2.21, showing the presenceof homologues higher than propane.Gases Evolved at ZOOo.At 200° 65.5 C.C. per 100 grams of coal were collected. Acomplete analysis was made of a portion of this gas, and thTHE DISTILLATION OF COAT, IN A VACUUM. 137remainder passed into. a condensing apparatus surrounded by asolution of solid carbon dioxide in ether, whereby a temperatureof about -80° waa obtained. A portion of the gases (about7-5 per cent. of the total volume evolved from the coal at 2 0 0 O )liquefied a t this temperature.This gas gave on explosion analysisa ratio C/A =0*875, with a value' 12/ V=3*00, showing it to bebutane.The a.nalysis of the total gas evolved at 200° was:CO, ............................... 8-85 pvr relit.0, ................................ 0.70 ,,CTH4 ........................... 0.86 ,)C1&H2,& ............................ 2.90 ,) cot. .............................. 2 -60 , y11, .................................. 2-75 ),C,aH2rr+d .......................... S1*OO ,,The paraffins, which include the butane determined separately,had a; value n/ IT= 1-84.Gases Evolved qt 300O.The temperature of the coal was now gradually raised t,o 300'.There was no further evolut'ion of gas until a temperature ofabout 270° was reached, the gases then evolved tarnishing badlythe mercury over which they were collected.Heating and exhaustion were continued during two days, thetemperature being maintained a t 300O.Towards the end of theheating the gases evolved ceased to, ta.rnish mercury. Altogether,58.5 C.C. per 100 grams of coal were collected.Butane wa,s isolated from the gases by liquefaction, as in thecase of the gases evolved a t 2 0 0 O . The analysis of the total gasevolved showed :35-35 per cent. CO, and H,S .........C,H, .................. 0-55 .. C,H, ................. 1-05 .. C, H2?% ................. 1 8 '8 5 , . CO .................. 10.50 .. H, .................... 13.35 .. ClrH218+? ............. 18-85 ,,The valoe v / V flw t h e paraffins was 1.43.Decompositicn of eome part, or" the coal substance had obviouslytaken place between 270° and 300O; for, although the volume ofgases evolved was not large, their composition was very differentfrom that of the gases evolved below 2 0 0 O .No' separate estimationof the percentage of hydrogen sulphide present was made, but ibsprmence in considerable quantity was indicated by the yellowcolour imparted ' t o the' potassium hydroxide solution used forestimating carbOn dioxide138 BURGESS AND WHEELER :Gases Evolved at 350° and at 400O.On raising the temperature of the coal above 300° a rapidevolution of gas took place between 320° and 350°, and, aftermaintaining the temperature during eight days a t 350°, 985 C.C.of gas per 100 grams of coal were collected.The temperature of the coal was then gradually raised to 400°,and exhaustion continued at that temperature during sixteendays. Four litres of gas per 100 grams of coal were collected.The analyses of the gases collected at 350° and at 400° were:H,S ..................... co, ....................C,H, .....................C,H, ....................C,H, ..................co.......................H, ......................CnHm+2 ...............At 350".1.7020.950-151.9017-903'401.5 *3537'22A t 400".0 -702 -85trace2 -356.153.4036-9046.55The value of n / V for the paraffins was, for the gases obtainedat 350°, 0.311, and for those obtained at 400°, 0.302.Fractionation of the Gases by Liquid Air.-An experimenttypical of those in which fractionation by liquid air was resortedto was made with the Silkstone coal in the form of dust thatpassed a 1.00- and remained on a 150-mesh sieve.The dust wasdried a t 1 0 7 O in air before being put into the retort.Occluded gases having been removed, heating was carrieddirect to 340° (that is, just to the decomposition point of thecoal). Two main fractions of the gases were obtained: (a) gasescondensed by liquid air during distillation, and ( 6 ) gases notcondensed by liquid air.The uncondsnsed gases consisted mainly of carbon monoxide,hydrogen, methane, and nitrogen. The condensed gases were boiledinto a receiver, and treated in the following manner: the receiverwas cooled by a solution of solid carbon dioxide in ether, andfractions taken a t different pressures, thus :FriuAio11 KO.i. Withdrawn uuderFraction No. it.Fraction No. iii.Fnlction No. iv.Fractioii No. v.9 7 7 ,2 2 9 9* 2 9 . Receiver at atmospheric2 ) 9 7 :: 'z8 z::} teeipernture.Part of the last fraction (No. v.) showed a tendency to condenseto a mobile liquid at atmospheric temperature under slightpressureTHE DISTILI,ATION OF COAL IN A VACUUM.The analyses of these fractions were as follows:(i. 1Per cciit.CO, a d H,S ........ 8 1-00C2H, ..................... 0 -4 0C,H, ..................... 0.95C, H ................ 5 -2 5 co ........................ 0 9 5H, ....................... nil.C,, Hyz+2 ............. 8 -7 5n/V for paraffins ...... 1.93(ii )Per ct lit.70.050.350'4515-100.90nil.11.051'74(iii. )Per cent.48 000.650.957 .oo1.60i l i l .39TO2 *35(iv.)Per cent.8-100.751-107.451.50nil.82.452.77139(v- 1Per ccnt.4.10nil.1'7510.201.50nil,82.453.00It will be noticed that analysis No. iv. adds up to more than100 per cent. Occasionally, particularly with gases obtained fromcoal a t 200°, it has been found that, the volume of gases (assumingthem to be paraffins) given by explosion analysis has caused thecomplete analysis to add up to slightly more than 100. This resultis, so far as can be ascertained, due t o the fact that minute tracesof gas in the mixture of paraffins had a tendency to condense toliquids under pressure, so that in transferring them over mercuryfrom one part of the aiia.lysis apparatus to another some condensa-tion may have taken place and a slightly greater volume of gasesthan appeared on measurement burned during the explosionanalysis.Gases Evolved at 400O.The gases were fractionated with liquid air as before.Theportion uncondensed consisted mainly of carbon monoxide,hydrogen, and methane. The gases condensed by liquid air weretreated in the same way as those obtained at 340°, six fractionsbeing taken as follows:Frsztion No. i. Withilratin underFraction No. ii.Fraction No. iii. Y , 9 23 ) $ 3Fraction No. iv. 7 . 9 , 9 ' 'ij \ nrceiver a t atinospliericFraction No. v.Fraction No. vi. Last ;t'aces of ;:wlily c&dcusible gases. tc'i'I'erature'The analyses of these fractions were :(i. 1Per rent.CO, and H,S ......... 8.65C,H, ................... 0 60CzH4 .................... 7.75C,H,, ................ 3 90 co ...................... 3.35H, ....................... nil.C,Hp+% i...... ...... 69.90n/V for paraffins ...... 0.59(ii.)Per cell t.7 -000'400 *459-052 -50nil.77-100 *95(iii )Per ceut.4 -500.455 *0515.102 20nil.69.751.28(iv.) (v.) (vi.)Per cent. Percent. P1-r cent.0.70 1-65 11.800.60 nil. nil.0.50 0.65 2 0535.75 38-90 38-650.40 0'45 1-30nil. iiil. nil.60.80 55-85 41-852-00 2-46 3.65In other experiments, details of which need not be given, differen140 JONES APU’D WHEELER : THE COJIPOSITION OF COAL.boiling fractions of the liquefied gases were taken, reliquefied, andfractionated several times. I n this manner i t was possible to makea nearly complete separation of the paraffin hydrocarbons, and t oestablish the presence of all members up t o and including pentaneESRBIEALS,__ - - - _. - __ - - CUMBERLASD