9. Arrangement of a distillation laboratory, starting up distillation apparatus

9. Arrangement of a distillation laboratory, starting up distillation apparatus

9. Arrangement of a distillation laboratory, starting up distillation apparatus 9.1 Lay-out Points to be considered in designing a new laboratory ...

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9.

Arrangement of a distillation laboratory, starting up distillation apparatus

9.1

Lay-out

Points to be considered in designing a new laboratory are dealt with by Behre [l], Coleman [2] and Schramni [3], while the arrangement of a laboratory for analytical distillation i 4 gone into by Kincannon and Baker [4]. 9 distillation laboratory should have long, high wall surfaces for supporting the frameworks for apparatus. Examples of satisfactory arrangements in various spaces are given in Figs. 404 to 407. The location of pilot plants is illustrated in Figs. 140. 141, 146 and 160. There is a tendency for the manufacturers of distillation apparatus to run test centres for work on problems of inaterial and heat transfer. The testing apparatus is controlled froin a measuring room. An associated 18boratory is designed for coinplementary distillation experiments and the necessary analytical work on samples [21].

corridor

Fig. 404 Arrangement of a distillation laboratory (long type) with a well-ventilated roo111 and a separate pump room A = Laboratory bench, ;M = Framework, N A = Framework in fume c u p b o ~ r d . E = Laboratory bench

Lay-out I , Fig. 404 For the reduction of pump noise in the actual laboratory the vacuum pullips are placed in a separate pump room. The punips P are close to the wall between this I'OQI~I and the laboratory, SO as to make the vacuum lines as short as possible. The other side of this wall is provided with a framework M and is reserved for vacuum distillation. automatic pressure controllers and vacuum gauges are placed on or behind the framework where they are accessible and can easily be watched. The pump room can also serve as a small workshop. The window side of the laboratory is occupied b;v benches A with water and electricity supplies. This bench is intended for physical determinations, such as

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9. Arrangement of a distillation laboratory. starting up distillation apparatus

refractive index, solidification point, melting point, dielectric constant and optical rotation. The centralbench E is reserved for chemical work. The main wall adjoining the passage is also provided with a framework. For the distillation of unpleasant or poiaonous compounds such as ether, benzene, chlorinated hydrocarbons or organic nitro-compounds, a separate space is provided. It may be regarded as a large futne cupboard which can beentered; a 40-fold renewal of its air every hour ensures sufficient ventilation. The screen separating it from the laboratory is of wire-reinforced glaes, so that the apparatus can be supervised from the laboratory. If automatic apparatus is used in this chamber the measuring and control equipment should be mounted on the wall outside it. windows

lEkL cupboaid

corridor

t

I I

1

I

I

Fig. 406 Arrangement of a distilletion laboratory (square type) with a well-ventilated room and a separate pump room (for legend, see Fig. 404)

9.1 La.y-out

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Lapout I I , Fig. 405 The principle of this arrangement is the same as that of Fig. 404. 4 s the longest free surfacw are the dividing walls, the frameworks are attached to them. The mclosed, ventilated rooin is again intended for the distillation of noxions substances. 'Chr wntral laboratory bench here starts from the wall adjoining the passage and can b e fitted at its end with additional stands for small apparatus (Fig. 406). windows

corridor

Fig. 407 Srrangement of a distillation laboratory (short type) with a separate pump room a id high fume cupboards (for legend, s' e Figs. 404 and 405)

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Krell, Handbook

Fin. 408 Fu&e cupboard containing framework for apparatus

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9. Arrangement of a distillation laboratory, starting up distillation apparatus

Lug-out III, F ig . 407

ThiR laboratory, which is intended for distillations involving more extensive chemical work, is equipped with two large central benches. lnstead of the ventilated room, it only has two fume cupboards MA containing frames. One of these cupboards extends from the floor up to the ceiling (Fig. 408); the second starts from table level, but also contains st,ands for small apparatus. The air speed a t the openings of the cupboards is nmintained at 1-2 ftlsec.

9.2

Frameworks and services

Frameworks to carry distillation equipment can either be built with sets of parts or he Immanently attached to the walls. A framework which may he used to build any structure demanded by the apparatus, is shown in Fig. 409. Unit frames mounted on castors (Fig. 410) are obtainable, and have the advantage that t h e apparatus may be used anywhere in the laboratory. For extensive apparatus it is preferable to use frameworks fixed to the walls. Jordal rails (Fig. 411 a) which are embedded in the walls are designed to take up special clarnps (Fig.4 l l b ) at any desired height [ 5 ] . By the use of cross-bars of various lengths the framework can be made to match the apparatus (Fig. 408). The arrangenient used by the author is illustrated in Fig. 412. The. framework consists of ititerconnected unitsof 1 metre width, cemented into the wall; the wall is tiled to a height of Bfeet. On the floor below this franiework there is a brickwork trough, 2 ft. 6 inches in width, to catch any liquid that may he spilt by breakage. This trough will also localize a fire.

Fig. 409 Framew-ork for components

Fig. 410 Frame on castors

9.2 Frameworks and services

483

Fig. 41 1 Jordal rails a) rail with holes for insertion of special rlamps b) special clamp

2 and 3 phase sockets

Fig. 412 Framework unit with brickwork trough, piping and electric panel

31*

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9. Arrangement of a distillation laboratory, starting up distillation apparatus

The piping for water, gas, compressed air, vacuum and steam should be laid along the walls, together with a drain. Bench instruments may be placed on shelves behind the fmieworli. Electric power is taken froni panels; the most convenient position for these is hetween each pair of frames (Fig. 412). The panels have 8 to 10 sockets, rach with a switch and a neon laiiip, so that it can be seen at a glance which parts of the apparatus are in operation. -A main switch should be installed to cut off the whole electrical supply except lighting 111 the event of danger.

Fig. 413 Slotted angle iron for the conet,ructioii

of frames

Narrow sliding ladders, which can be kept in a corner hehind the framework when not in use, are employed for reaching all parts of the equipment. The wntilation should be so designed that fresh air enters along the floor behind the framework and the waste air leaves near the ceiling. Ten changes of air per hoiir is generally considered sufficient. If an appreciable quantity of gas is produced in a distillation it may be led awa? through the upper ventilation holes by tubes connected to condensers. Semi-technical dktillrrtim~u p a r a t w should be provided with specially constructed frames and platforms (Fig. 424), which may if desired be built up from unit parts. Slotted angle iron (Fig. 413) greatly facilitates the construction.

9.3

Building up the apparatus

Before the equipment is assembled i t is advisable, especially if the apparatus is complicated, to draw a sketch of it and, as a start, to arrange the components on the floor according to this plan. Next, the corresponding ground joints are examined

9.3 Building up the apparatus

44.5

by putting them together without grease and testing them for fit. By moistening the cone of the joint or drawing a circle of chalk on it, one can easily see whether irregularities are present. Loosely-fitting joints should be replaced. In vacuuiii distillation this procedure saves much time which would otherwise he spent in testing for lealib. Assembling of the parts should start from the bottom. In the firqt place it shoiild he possible to remove the still pot without dismantling other components. For thl. purpose flask heaters with a vertical adjustment (Fig. 327) can be used. Plain retort rings do not always give the flask a firin seating. In Tome cases the suspension of the flask in a spring cradle (Fig. 414)offers a solution. Thecolumn should bemounted exactly vertically by means of a plummet. The lateral parts of the apparatus must not be connected to the main, vertical parts before these have been tested for vacuum-tightness. Testing for leaks should, in fact, always he performed step by step, as this method is by far the most rapid. Ground joints should

Fig. 416 Clip for ball joint

Fig. 414 Spring cradle for flask

Fig. 415 Ground joint with metal clamps and springs

Fig. 417 Clip for plane joints

Fig. 418 Clip for ground joints (Edward & Co. London)

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9. Arrangement of a diatillation laboratory, starting up distillation apparatns

be secured by hooks and springs. Small joints usually have fused-on hooks; larger joints may be frtstened with metal clamps (Fig. 416). A clip for securing ball join& is shown in Fig. 416 and one for plane joints in Fig.417. The clip for ground joints which is manufactured by- Messrs. W. Edwards & Co, London, (Fig. 418) is easily detachable.

Fig. 419 Boae. 14 mm

Fig. 420 Rubber joint collars

Fig. 421 “Specco” hook-clamp

Rubber collars can be used for fastening ground joints and are manufactured for the sizes NS 12 to NS 29 (Fig. 420); they can be employed at temperatures up to 130°C [6]. Their main advantages are that the use of joint grease is unnecessary and that qtrains are unifornily distributed around the circumference. Bosses must be carefully machined so that, when the screws are tightened, the object connected is not forced out of position. If this happens, strains will ensue which may lead to the breakage of glass parts, usually after they have been h e a t d in the course of distillation. A reliable form of boss is shown in Fig. 419. The “Specco” hook clamp (Fig. 421) is intended specially for the construction of frameworks. The double three-point bearing ensures a tight hold free from movement. The standardized Gcru system consisting of a variety of components allows the constriiction of apparatus r a q y g from simple devices to large pilot plantn [7]. For supporting components that have to be adjusted exactly to a certain level, such au f h k heaters, levelling bottles etc., the variable height support due to Mannchen (Fig.422)is convenient, as it allows the position to be regulated to within a ndlimrtre. Ring clamps (Q. 423) are better than the customary jaw clamps for

9.3 Building up the apparatus

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Fig. 422 Variable height support (Mannchen-Riedel)

F1

'

Fig. 423 Ring clamps

a

Fig. 424 Framework for a 200 1 distillation plant. Galvanized tubes with galvanized coupling sleeves

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9. Arrangement of a distillation laboratory. starting up distillation apparatus

holding columns and other cylindrical parts. A systematic survey of supports for and the suspension of, chemical apparatus has been given by Schwarz [ 5 ] . Pilot plant and semi-technical distillation apparatus made of glass requires special connections, clamps and frameworks. It may suffice here to refer the reader to the catalogues of the glassware manufacturers. Some firms even send crews for the aasemblv of apparatus. As a n example Fig. 424 shows a framework of galvanized tubes joined by means of socket,s with Iinhus screws.

9.4

Sealing ground joints

In most cases the problem of ensuring that ground joints and taps are leakproof needs attent.ion. The substances to be distilled have widely different solvent powers for joint greases, so that preliminary tests may be necessary to find the most suitable lubricant. Some data on the subject are given in Table 79. The experience obtained with silicone greases is not yet sufficient to allow a definite judgment. There is some danger that coniponents of the grease will enter the column and affect the wetting of the packing, and it is difficult to remove the white, powdery filler which remains when the silicone itself has been leached out. ,4s a general rule it can be said that taps and stop-cocks should be lubricated with n softer grease than ground joints. Lithelen (Table 79) cont8ainslithium soaps and undergoes little change in consistency with temperature. It, can therefore be used for greasing taps at temperatures from below 0" up to 150°C. A review on the preparation of special laboratory greases has been compiled by Brooke [8].The various lubricants Table 79 Greases for ground j0int.s and taps

Type of grease

Ramsay greaae

Maximum Composition or manufacturer operating temp. ("C)

Application

6 pts. vaseline 1 pt. paraffin wax 6 pts. Para rubber

General work

E. Leybold's Xachf., Cologne, Germany

High-vacuum work

kipsenberg grease

1 pt. soluble starch

BZ 6364; BZ 6563 Sirnpy phosphoric acid Graphite

E. Merck, Darmstadt, Germany

For powerful greave solvents. such as diethylether or chloroparaffins

High vacuumgreaae P High vaouum grease R Lit helm

25

25 30 150

1 pt. glycerin

As graphite powder or a mirture of graphite and paraffin wax, or as colloidal graphite suspension in wat,er

High-temperatnre distillation

9.4 Sealing ground joints

489

have been extensively discussed by Wagner [9]. Bernhauer [ 101, Wittenbergcr [ 111. Wolf [12] and Friedrichs [13] have given detailed instructions for the handling of ground glass joints and glass taps, with particular consideration of how ground joints that have seized should be treated. I n molecular distillation it is essential to use a thoroughly degassed lubricant with a low vapour pressure, for instance the high-vacuum greases P and R. Ground joints with a mercury seal (Fig. 425), though providing a n entirely tight seal, should be employed only in exceptional cases, owing to the poisonous nature of mercury : the cup is better filled with vacuum oil or grease. An ungreased joint - even one having the finest ground surfaces - will never be entirely vacuum-tight or, conversely, will not prevent the escape of some vapour. Greasing is carried out by coating the upper half of the cone with a uniform layer of

n u

Joint Fig.425 with mercury seal

the lubricant in question. This is best done with a smooth wooden spatula; greasing with the finger gives a uniform coating, but has the disadvantage that dirt or moisture may be introduced into the lubricant. Another method, particularly suitable for Ramsay or Apiezon grease, is to warm the cone gently over a hot-plate (not an open gas flame) until the lubricant flows, after which i t is distributed by rotating the cone. It is then inserted into the socket and pressed in with a turning motion until the joint appears uniform and transparent. If this does not happen at once the process should be repeat
Krell, Handbook

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9. Arrangement of a distillation laboratory, aterting up distillation apparatus

those pieces, called “Rodets”, in sizes suited for the commonly used joints. In chap. 3.1 it wtm pointed out that precision ground joints may ale0 do without grease. In pilot and semi-technical plants Teflon rings and sleeves are preferably used for sealing ball and flat joints.

9.5

Starting up distillation apparatus

When the apparatus haa been assembled the chasge is put into the still pot. It should be filled to at most two-thirds of ite nominatkvohune, or to one-half in vamum distillation. Boiling chips are added to the contents. The volume of charge should be measured at the same temperature 88 the distillate fractions to be collected later, and this temperature may be relatively high if the fractions are solid at room temperature. Poisonous substances and those with a high vapour pressure are hest forced by gw pressure from a bottle into the still pot, which should then immediately be Htoppered. In order to emure good wetting of the packing it is customary to pour the charge in through the condenser if possible. If it is essential for the apparatus to be completely free from moisture it can be dried by blowing in hot air with the jacket heater in operation. Stress should again be laid on the importance of a thorough cleaning of the packing material before it is put into the column. It is not sufficient to rinse it a few times, say with carbon tetrachloride or trichloroethylene. The adhering layer can be removed by a treatment with hot benzene (poisonous; use fume cupboard) followed by a rinse with trichloroethylene [14]. For vacuum distillation, a preliniinary test for leakage is necessary. The apparatus is evacuated; when the required pressure has been reached the vacuum pump is fitopped and the mte of increaae of pressure is observed (section 5.4.1). A further test for tightness is performed when the column is in operation and the thermal load has been established. The still pot heater is switched on only when the desired pressure is attained, and the column jacket heater as soon aa vapour evolution starts. The cooling water should be turned on before the heaters are put into operation; during the initial period its rate of flow should be checked at intervals since it usually tends to vary somewhat at the start with the expansion of tap washers. When the vapour has reached the colmm head the load is adjusted to the required value (section 4.10.7) unless the column is to be flooded (section 4.10.8) to wet the packing. The apparatus ifi then allowed to run for at least half an hour at total reflux, so as to allow the initial h o w p i n t to be accurately determined, and only then is it adjusted to the required reflux ratio (section 4.10.4). As mentioned before, a few boiling c h i p are added to the still pot in order to promote regular ebullition. Generally speaking the use of boiling capillaries cannot he recommended, since their presence makes it difficult to determine the effective distillation pressure and air sometimes gives rise to polymerization. The “boiling chips” may be small pieces of earthenware (flower pots) or pumice, platinum tetrahedra and in some cmes even hits of wood. For alkaline materials, tin dust may be employed. It should be noted that boiling stones lose their activity if a vacuum

9.6 Safety measures

491

distillation is interrupted and air is admitted. Their action is connected with the small bubbles of air clinging to their surface; if the vacuum is interrupted it is therefore necessary to add fresh boiling chips [15]. If foaming occurs to a troublesome extent a t the beginning of distillation, a n attempt may be made to reduce it by the addition of an anti-foaming agent [16]. Silicone oils have recently been used with success for this purpose. If the material to he distilled is highly viscous it is advisable to keep the still pot contents in constant. motion with a magnetic stirrer or the stirrer due to Hubner [17].

9.6

Safety measures

I n laboratory practice it is frequently necessary to distil combustible, poisonoils or explosive substances; in vacuum distillation there is the danger that vessels may collapse: I t is therefore essential to observe certain safety measures [ 181. Data on combustible gases and vapours which are of importance from the point of view of laboratory safety have been collected by Dittmar [19]. In every case it shonld be decided whether or not an explosion-proof electric installation is required. Very poisolzous niaterinls should always be handled and distilled in the wellventilated room or in a fume cupboard. Explosive substances such as ether should be distilled only in a room especially designed for such operations unless work in the open air is preferred. If the charge contains poisonous gases in solution, the condenser should be connected to a tube leading to the atmosphere or to a fume cupboard. When distilling substances which injure the skin the operator should wear rubber gloves and goggles since it is difficult to avoid contact with traces of such materials; it may also be advisable to wear protective clothing. Vacuum distillations require special precautions. Safety spectacles or, rather, a face shield should be worn for work at reduced pressures. Heaters give sonie protection from flask and column. In addition, glass-wool sheaths rnay be applied to the other parts for insulation and protection. If this is not possible for experimental reasons, for instance because the separation process should be visible throughout its course a wire gauze or plane glass screen must be placed in front of the apparatus. Bnffer vessels can be fitted into wooden boxes lined with glass wool or completely encased in a wire gauze cage. If the vacuum pumps have a belt transmission, the latter miist he provided with an effective guard. The safety measures that are nesessary in a high-pressure laboratory and in work with toxic substances are considered in detail by Craig and Dew 1201.