THE COLLIERY GUARDIAN AND JOURNAL OF THE COAL AND IRON TRADES. Vol. CX. FRIDAY, DECEMBER 24, 1915. No. 2869. Coke Oven Managers’ Association. PAPER ON BENZOL. quently may give rather high pressures for the percentages of benzol in oil used. Nevertheless, they show that in most plants, the rich oil is far from being saturated, and that the effect of temperature on the return gas is very consider- able. What was described as the first of the educational meetings of the newly-formed Coke Oven Managers’ Association, was held at the Applied Science Depart- ment of Sheffield University on Saturday, December 18, when a very satisfactory attendance of members followed with keen interest, and subsequently discussed with animation, a paper on “ Benzol,” by Mr. George Taylor (Silverwood Collieries). The President (Mr. George Chrisp), in opening the proceedings, announced that the membership of the association now stood at 75 — including 48 coke oven members, 23 associates, and four honorary members. Considering the very short time the association had been in existence, he thought that was a very satis- factory achievement, and he believed that the number could be considerably augmented if every member did his best towards that end. The association had arranged to hold its first annual dinner on January 15; and another, paper on the subject of ammonia would be considered a fortnight later. With regard to the paper to be read that evening, owing to the prime import- ance of this product at the present time, the council of the association felt that the first of their educational papers might very appropriately deal with benzol. People who were not intimately connected with the business scarcely realised how important it was that the country should have an ample supply of benzol at the present time. The council felt, therefore, that any- thing that could be done in the way of publicity or helping the members of the association in this matter, would serve a useful public service. It had been said that if the coke oven plants of the Central Empire® were destroyed, the war would not last another month. They might not be able to do much to destroy the enemy plants, but they could work their own to the fullest capacity, and if the reading of the paper and the dis- cussion it evoked resulted in a few more gallons of petrol being produced in this country, the council of the association would feel that their choice of this sub- ject had been amply justified. With regard to the author of the paper, the president 'added that Mr. Taylor had devoted much study to the subject, and had had considerable experience with its working; and what he did not know about benzol was not worth knowing. Benzol. Mr. George Taylor then read his paper on “ Benzol.” One of the most important matters at present before the carbonising world is the recovery and rectification of benzene and its homologues from the gases evolved in the destructive distillation of coal. Before the general adoption of coal gas as an illuminant, a certain amount of gas was manufactured from oil, and delivered to consumers in cylinders, under pressure, in a similar fashion to oxygen at the present time. Benzene was discovered by Faraday in 1835 in the liquid condensed by cooling this oil gas in freezing mixture. In 1833, Mitscherlich prepared benzene from calcium benzoate, nitrified it, and recorded the char- acteristics of nitro-benzene (1834). It was not until the year 1845 that the presence of benzene was observed in coal tar, and identified by conversion to nitro-benzene by A. W. Hofmann. Charles Mansfield, who originated the methods for rectification of benzene, and utilised for the purpose the still then employed for the production of alcohol, lost his life (1854) when preparing benzene for the Paris Exhibition. So far benzene had been manufactured for the purpose of carburetting gas. Then came the discovery of aniline dyes (Perkin, 1856; Hof maim, 1859), which gave the needed impetus to the industry, and since that time progress has steadily been made. Knowledge not Conclusive. Knowledge of the formation of benzene in gas is not very conclusive. It has been found that, in distilling coal at low temperatures, paraffins result, and that, on increasing these temperatures, a diminution in the amount of paraffins takes place, along with the production of benzols, until at 650 degs. Cent, the condensable hydrocarbons are almost exclusively those of the benzene series. In coke oven gas, the volume due to the presence of benzol, as vapour, ranges from about 0-8 to 1-6 per cent, of the total, which corresponds to 2—4 galls, of benzol per ton of coal distilled. The removal of the benzol is, of course, attended by a corresponding diminution in the volume of the gas, a falling off in calorific value of from 32—64 British thermal units per cubic foot gross, and a considerable loss in illuminating power. In order that little of the benzol shall be removed in tar extrac- tion, it is necessary that this process be carried out at a temperature of not less than 35 degs. Cent., the gas being suitably cooled for ammonia scrubbing afterwards. In the case of direct processes, where the tar fog is extracted from hot gas, there is no risk of benzol being removed with the tar. Before entering the benzol scrubbers the gas should be freed from water by a trap. Washing Media and Plant. Presuming then that the gas is freed from ammonia, tar and mechanically carried moisture, and that its temperature is below 25 degs. Cent., the next problem is the absorption of the benzol as completely as possible. Two absorbing mediums are in general use—coal tar creosote and blast furnace oil. The methods of using these oils being different, it is necessary that they should not be mixed. Considering that the ultimate aim of the process is the production of pure benzene, etc., it is advisable to use oils that contain the smallest possible amounts of matters not helpful to Q o 8 o n S3 r g g 00 i 05 04 08 07 06 02 QI 09 >0 i 0 13 1-2 II 050 075 13 30 30 120® C Benzol in 14® Tw CrooscU. Percentage of 70 per cent at absorption. Such are phenols, phenoloids, basic com- pounds, naphthalene, and tarry substances. If present, these impurities should be removed from the oil before its use as an absorbent, as by this procedure the life of the oil is prolonged, and the loss in washing the recovered benzols is much reduced; also, the water separates more easily from the oil in the storage tanks. With regard to the plant necessary for oil washing, tower scrubbers of about the same capacity as those used for ammonia extraction are usual, and oil is circulated through them in a manner similar to that in which liquor is circulated in ammonia scrubbers. There is, however, a growing tendency to adopt rotary scrubbers, usually of the brush type. These scrubbers are highly efficient, and by reason of the more intimate contact of oil with the gas a higher percentage absorption is obtained than is the case with tower scrubbers; also, the plant can be arranged so that the power expended in circulating the oil is les®. Another advantage is economy of ground space. A rotary scrubber of 8 ft. internal diameter, with eight to ten washing chambers, is capable of dealing with the gas from 200 tons of coal per diem. The above chart gives curves showing the amounts of 70 per cent, benzol vapour in gas, which is in equilibrium with benzolised creosote of 14 degs. Twaddle, at various temperatures. These vapour pressure determinations were obtained by the increase-in-volume method, and conse- According to the quantity of coal carbonised, the circulat- ing stock should be from 40 to 80 tons, and the fresh oil required to replace losses runs from 20 to 35 galls, per 100 galls, of benzol made—unless it is salty, when somewhat more will be used. Provision should be made for the separation of water from the circulating oil, as watery oil is one of the principal causes of benzol loss. This is, of course, general know- ledge ; but it is surprising to find on how few plants arrange- ments are made for dealing efficiently with water. Distillation. The benzol is driven off the benzolised or rich oil by distillation. Formerly this was accomplished in a manner similar to tar distillation, but now the whole of the benzol is produced by the continuous system; the rich oil circulates through a cap-and-plate still, meeting a current of steam, which drives off the benzol; the spent oil, after cooling, being re-circulated through the scrubbers. Many types of distilling plant are in use, with more or less success. It is generally admitted that, for economy, an exchange of heat should take place between the incoming rich oil and the hot debenzolised oil from the still. In some cases the rich oil is further heated by steam heaters. This is particularly the case where the still is being worked up to its full capacity, and space cannot be afforded to allow the dephlegmatory action of a colder oil. The stills them- selves fall into two classes : One in which powerful steam heaters are placed in a chamber at the base of the still, with the intention of drying the effluent oil, and the other which works with wet steam only. In the latter type provision should be made for separating the water from the oil whilst still hot. Vapours of water and benzol leave the still at about 100degs. to 112 degs. Cent., and must be partially condensed or dephlegmated in order that a 65 per cent, benzol may be obtained. The fraction which con- denses at a temperature of less than 95 degs. Cent, is the required material. The heavier matters consist of water, naphthalene, light oil and phenols, and are usually small in quantity. In connection with the condensing of the benzol it is highly important that no back pressure shrould be set up in this process, otherwise difficulty will be experi- enced in denuding the oil of benzol, and losses will take place. The table at top of next page gives the working data obtained from plants in various parts of the country. It can be seen from these figures that a high saturation of oil, where consistent with a good return gas, is much to be desired; also, the oil should certainly be heated to 110degs. Cent, in the still. Should this not be the case, and the effluent oil contains over 0-5 per cent, of benzol, the steam supply should be superheated. From information to hand, concerning two plants, the introduction of superheated steam increased the yields of benzol about 5 per cent. Purification and Fractionation. In order that coke oven benzol may be of use in the arts it must be subjected to a purifying process, and separated