Production of Acetic Anhydride from Acetone

ii J. App]. Chem., 3, JUII~, 1953

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DAROUX-PRODUCTION OF ACETIC ANHYDRIDE

PRODUCTION OF ACETIC ANHYDRIDE FROM ACETONE*

By W. GERARD DAROVX

The pilot-plant process evaluation and full-scale design for the production of acetic anhydride from acetone are described. Pasic economics and alternative processes are briefly discussed.

Introduction

Acetic anhydride is a basic raw material for the cellulose acetate manufacturer and the bulk of world production is used for this purpose. Minor outlets for the chemical include acetylation reactions in organic chemistry, e.g. the production of aspirin. The reactivity of acetic anhydride with water is also employed in the manufacture of hexamethylenetetramine explosives. There is, however, a striking constancy in the ratio of acetic anhydride production to cellulose acetate output! in peace-time conditions. This shows quite clearly the importance of cellulose acetate manufacture as the main outlet for acetic anhydride.

It is characteristic of this cellulose-acetylation reaction that about half the acetic anhydride consumed is reconverted into acetic acid, in accordance with the simple scheme shown in Fig. I.

Each mole of acetic anhydride used for acetylation produces, in round figures, one mole of surplus acetic acid, which must be reconverted into the raw material.

The modern method of reconverting the acetic acid into anhydride is the acid-cracking process, in which catalysed vapour-phase cracking of acid is

FIG. 1. Basic scheme for cellulose acetylation much employed to give keten and water.s The keten is then absorbed in acetic acid to give anhydride, which is returned to the acetate process.

In this way the cellulose acetate manufacturer avoids the production of excess of acetic acid and reduces his net anhydride requirement to about o· 7 ton of anhydride per ton of cellulose acetate. This is sufficient to supply the acetyl content of the cellulose acetate flake and to make up the process losses.

The net amounts of acetic anhydride required may then be produced from any of the following basic raw materials, all of which have been employed on a large commercial scale: (a) calcium carbide or acetylene, (b) ethanol, or (c) isopropanol.

The processes are shown diagrammatically in Fig. 2.

RAW MATEAIAL rNTERAlEDIATE$

AcET rc ANHYDRIDE

____~ and lor AC ETIC

ACID

I METHANE

I ETHANOL

FIG. 2. Outline Of processes for the production of acetic anhydride

General economics In the immediate post-war period a study of the methods of producing anhydride indicated

that isopropanol gave the greatest promise as a basic raw material for economical anhydride production in the United Kingdom. Calcium carbide suffered from the major disadvantage of high power-cost and high coal-prices. The developments of methane cracking to produce acetylene

* Read before a joint meeting of the Chemical Engineering Group and the Institution of Chemical Engineers. on 31 March, 1953

ACID

J. appl, Chern., 3, June, 1953 F

DAROUX-PRODUCTlON OF ACETIC ANHYDRIDE

did not give high hopes of a specific cheap process. Ethanol based on molasses, a commodity which fluctuates very much in price, appeared in the long view to be faced with severe competition from petro-chemical processes, which were at that time developing rapidly.

It was then thought that the best hope of obtaining cheap anhydride lay in exploitation of the synthetic ethanol and isopropanol arising as by-products from the olefins produced in oil-cracking. The cost studies which were made at the time were very much hampered by the difficulty of assessing the true value of the unsaturated hydrocarbons produced as by-products and the real cost of the marginal facilities required to convert them into shippable products. This is a difficulty which always arises when a variety of products are being made in a single process. The costs may be loaded on one or the other product according to the circumstances.

The following main conclusions stood out clearly from the mass of economic detail: First, the cracking of crude oil mainly for the production of a single aliphatic alcohol, such as ethanol or isopropanol, was not likely to be economic, owing to the very heavy weighting of capital investment. Secondly, isopropanol was more likely to settle down, under conditions of large-scale production and free competition, to a basic cost and selling price substantially less than that of ethanol. Under these conditions, acetone, cheaply and simply produced by isopropanol dehydrogenation, would be a suitable material for anhydride synthesis.

These conclusions led to our interest in acetone-cracking and its process evaluation.

Basic reaction and chemistry

It is well known that acetone may be thermally decomposed in a copper or silica tube according to the reactiona, 4, 5 CH:J • CO· CH 3 -+ CH 4 -:-- CH 2 : CO, and that keten itself may decompose to ethylene and carbon monoxide thus:" --'~ ~- 2CO. Other possible reactions are:2CH 2·.CO C2H 4 dehydrogenation, which has been observed in our own work, CH 3 . CO . CH 3 ...,? 3H2 -+- CO ~- 2C; and polymerization of keten to diketen and high polymers, sometimes with the elimination of carbon dioxide. \

The main cracking reaction is slightly endothermic, to the extent of about 29,000 B.Th.U .jlb -rnol., a figure which is very small compared with the sensible heat of the cracking stock, which must be heated to 1200-1500" F. It has also been shown in early experiments that the molar yield of keten diminishes with increasing conversion per pass and that at over 50% conversion the yields become uneconomic. Nickel and iron have been reported to promote the dehydrogenation of acetone. Hinshelwood & Hutchison? have found that the thermal decomposition of acetone is first-order and homogeneous, though their conclusions have been questioned by Taylor."

Keten may be smoothly fixed in acetic acid to produce acetic anhydride, a reaction which evolves about 42,000 B.Th.U.jlb.-mol.

The published data on the cracking process are of only slight value to the designer, and it was therefore necessary to investigate the reaction on a pilot and laboratory scale before a full-scale plant could be worked out. This work was confined largely to the cracking step, as it appeared that the absorption, recycling and recovery units could be designed by normal methods after laboratory checking of the physical data.

Pilot plant

The chief problems investigated on the pilot plant were the general feasibility of the cracking reaction, materials of construction of the cracking tube and the conversion-selectivity relationship.

An outline flow-sheet of the pilot plant is shown in Fig. 3. It consists of a steam-heated acetone vaporizer, a preheating coil and cracking coil separately gas-fired, together with quench, absorption and distillation units. The cracked products were rapidly quenched with a recycle liquor which contained acetic anhydride and free acetic acid. This fixes the keten as rapidly as possible after its generation in the furnace. Unconverted acetone is rectified and returned to the process, and the by-product gas is scrubbed to remove its partial pressure of acetone and unreacted keten, the feed acetic acid being used as scrubbing liquid.

It was not considered necessary to include plant for the distillation of the crude anhydride, as this process is fairly straightforward and could be assessed much more economically in the laboratory. ,

The preheating and cracking tubes were constructed of solid-drawn 25/20 chromium-nickel steel of I in. nominal diameter. This material was selected for its good thermal and mechanical ! properties, which are necessary in the construction of a large-scale cracking unit. It was thought that the copper tubes used in the published work would be quite unsuitable for the plant scale; silica is also a most undesirable structural material and the nickel-free irons of the Sicromal type I suffer from the disadvantage of great brittleness, which makes fabrication and support design difficult. High mass-velocities in the range 10-30 ft.1b.sec. units were employed to give relatively

J. appl. Chern., 3, June, 1953

--------- 1_


CRUDE GAS

GAS SEPARATOR

ACETONE VAPORIZER

REC~CLE ACETONE

ABSORBER FEED PUMP

CRACKER TOWER

,-----------IG---+-----...---------.L--~FEED ACETONE

CRUDE PRODUCT

FIG. 3. Outline flour-sheet of pilot plant for acetone cracking

short contact-times and high productivity. High vapour-speeds also provide sufficient kinetic energy to scour the tube free from by-product coke. •

Initial operation of the pilot unit was hampered by excessive formation of coke, which quickly blocked the comparatively small tube. In some cases this coke was removed by steam and air purging. When the blockage was very severe, it was necessary to take out the tube and remove the coke mechanically. It was found that new 25/20 tubes give almost 100°" conversion of the acetone into hydrogen and carbon, but that after some time they become conditioned, so that the dehydrogenating character of the metal surface is gradually reduced. It reappears, however, after a tube has been purged with steam and air. Such a method of operation would obviously be too uncertain for full-scale plant working; subsequent work by Tyler led to the discovery that the addition of very small amounts of carbon disulphide to the acetone feed almost completely inhibited the dehydrogenation reaction."

Three months' intensive pilot-plant operation sufficed to give the hasic design-data for the consideration of a full-scale process. The important relationship between the selectivity and conversion per pass was then well established and it was satisfying to find that both the weight balances and the gas analyses and volume gave a good correlation. It had been thought that minor

90r---.,.--------,---------,

. c,

~ 80

~ .... u ~ I

~ 70 -;- ---l__ --- _ z . UI .... UI

" I

10 15 20 25 30 ACETONE CONVERSION. per cent

FIr;. 4. Conuersion-solccriricy relation for acetone cracking

impurities might build up in the recycle acetone during continued operation, but careful fractionation of the material failed to reveal any important accumulation, though, after continued recycling, the acetone had a I' ;, (molar) oxygen demand from acid permanganate at 860 F.

J. appl. Chcrn., 3, June, 1953


Owing to the urgency of the project, the pilot plant was built in the United States by arrangement with a leading oil company, and it is a pleasure to recall the harmonious co-operative atmosphere in which the work was carried out.

Selectivity, conversion and gas analysis

The general selectivity-conversion relationship for acetone-cracking to keten is shown in Fig. 4, which shows the trend of the data. It is not, however, claimed that the yields and operating data of the full-scale plant are precisely defined by this graph. It is interesting to derive the selectivity and conversion from the gas analysis and gas volume. These variables are usually much more quickly and easily measured on a plant than the overall mass-balance.

Consider a typical gas analysis from the thermal decomposition of acetone at about 100:j

conversion, given in Table 1.

Table I

Gas analysis from acetone decomposition: pilot plant run 17B mass velocity, 21 ft.lb.sec. units; contact time, 0'40 sec.

% (vjv)

Carbon dioxide

Unsaturated hydrocarbons 3'7

Carbon monoxide II ·8

Hydrogen 1·6

Methane 82'5

100'0

Moles of gasfmoles of feed .. o- Il6

The methane and hydrogen in the gas have obviously arisen from the thermal decomposition of the acetone according to the primary reaction CH 3·CO·CH;l·0>- CH 4 + CH 2:CO, and the dehydrogenation reaction CH3 · CO· CH3 -'~ 3Hz I CO -1- 2C; the conversion of the acetone, that is the number of moles of acetone decomposed, as a percentage of the number of moles of acetone fed, is:

Moles of (methane + o- 33 hydrogen) produced -~~~--~~_._---~- . -~ X 100

Moles of acetone fed

or, for this particular case, 0'Il6 X 0·83 X 100 = 9'6%. A weight balance gave 9'5%.

The selectivity to keten, that is the percentage of the acetone decomposed that produces a useful product, requires more careful evaluation. Considering the components of the gas in turn, carbon dioxide can arise only by a useless reaction which need not be postulated, but which must involve two molecules of acetone; unsaturated compounds and carbon monoxide, which should theoretically be in the ratio I: 2, come from the undesirable thermal decomposition of keten; and hydrogen arises from the slight dehydrogenation of the acetone. Expressed as a ratio, this gives:

Selectivity = Moles~facetone~eco~p()s~=...rn~les of ac~oI1e...llSelesslL~ac~dX 100 Moles of acetone decomposed

~ (CH4 -+- ~i~!:!zL~ICO_,,-:,,~.0 X 100 CH4 + 0'33Hz

which for the particular case gives

0.830 - o· 126Selectivity X 100

0·83°

85'8%


.--------------

Ii

P Sl

11

11

S

I

e v f t C c

DAROUX-PRODUCTION OF ACETIC ANHYDRIDE 245

The weight balance gave a selectivity of 82' 2~6, which, of course, includes the loss of some liquid product as polymers of keten.

The interpretation of the gas analyses has proved most useful in studying the course of the pilot-plant reactions, particularly in the initial stages, when dehydrogenation occurred with a keten selectivity of only 1 or 2% and the hydrogen selectivity was about 98%. There are of course minor deficiencies and inconsistencies in the gas-analysis figures. For example, the carbon monoxide: unsaturated ratio is never exactly 2 as the chemical equation requires, but the overall scheme showing the competing reactions is sound enough for practical purposes.

Full-scale plant design

The full-scale plant design involved as a first step several tentative calculations for the most economical unit. The variables were the conversion-selectivity relationship established by pilot work, the estimated plant cost for units having different conversions per pass, and the predicted future cost of acetone. The higher the price of acetone in relation to plant costs, the lower was the conversion that could be allowed to give an economical product. The unit was eventually designed for a conversion of 25% per pass for maximum output. Lower outputs could then be obtained, if desired, with enhanced chemical efficiency.

The overall flow-sheet of the process, as adapted for a full-scale plant, is shown in Fig. 5.

ACETIC ACID

SY5 TEM

, STRIPPING STillI

~~. GAS-SCRUBBING

FIG. 5. Basic flow-sheet for production of acetic anhydride

This shows the cracking furnace, quenching unit, condenser absorbers, gas-scrubbing plant and distillation units in the most elementary form.

After the leading dimensions of the units, as fixed by the overriding economic conditions, had been decided, the main technical problems were: (a) furnace design, (b) condensing and absorption

(a) Furnace design

J. appl. Chem., 3, June, 1953

The problem of designing a cracking furnace to operate under the desired conditions of close temperature-control, reasonable thermal economy, low pressure-drops and flexible operation, is a very common one for the oil-refining engineer, and there are almost as many types of gas-phase thermal cracking furnaces as there are designers. The cracking of acetone had, however, two special features which required more than usual emphasis. First, the feed stock is an extremely high-priced one, and hot acetone is a most searching material in finding leaks through jointed tubes. Secondly, the plant was to be geared to the needs of a very costly works, where any interruption of anhydride supply would be extremely expensive, if not catastrophic, so that immediate replacement of a split or faulty cracking tube was imperative.

A review of the available types of furnace did not disclose a standard unit exactly suited to

equipment and (c) distillation of the recycle and product streams. These are discussed below.


our needs and so the design of yet another type of furnace was undertaken. The general layout is shown in Fig. 6.

I

-~

, :

"

"

";,

PREHEATING CELL

FIG. 6. Diagrammatic view of fum ace

The unit consists of two identical circular cells, each designed to accommodate a 25/20 chromium-nickel welded solid-drawn coil about 400 ft. in length. Built into the walls of each cell of the furnace are 24 wedge-shaped ledges which mate with lands on the eight coil-supports. Each of these supports is built up from standard alloy-steel castings in three sections which are pin-jointed for flexibility. In this way the whole coil is allowed to float in the cell to avoid any stress due to thermal expansion. The first cell is used to preheat vaporized acetone to the incipient cracking temperature. The firing of the second coil is varied to give the desired degree of conversion. The cells are capped by sand-sealed refractory domed lids which support the four burners firing each cell. Dual burners are employed and steam-atomized distillate oil is used for starting up the unit; when gas production has been stabilized, the oil stems are withdrawn and inspirator gas burners are used.

Lobo & Evans have shown, in their invaluable paper.t" the great advantage of a high ratio of refractory area to furnace volume in obtaining good radiation coefficients in direct-fired furnaces. For


this reasc provides mean pos on the tu

Flue the come one of w to 4000]

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(b) Cond

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expansic consider expansic quench tubes.

Val acetone, combiru The es exercise the des

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Tlacetic a keten. acetic ~

temper effluent

J. app

DAROUX-PRODUCTION OF ACETIC ANHYDRIDE 247

this reason the circular cells have been divided into four sections by a battered cruciform wall which provides a good focus for flame radiation. The angle of inclination of the burners is variable, the meanposition being about 5°from vertical, facing towards the wall, so preventing flame-impingement on the tubes.

Flue gases from the cracking cell join the products of combustion in the preheating cell and the combined gases then pass to a convection section consisting of two sets of banked finned tubes, one of which is used to vaporize the feed. A second bank takes the flue-gas temperature down to 400° F. in preheating the feed to the acetone-distillation unit. The connecting bends are supported in davits with counterweighted wire ties to take up expansion strains. The flue gases are exhausted through a hot-gas fan to the stack, and the usual by-pass flues are provided to isolate the convection section or any cell, and run on natural draught.

The overall thermal efficiency of the furnace is about 85°;,. A diagrammatic view is shown in Fig. 6. A view of the installation is given in Fig. 7.

FIG. 7. Cracking furnace showing quench unit in foreground

(b) Condensing and absorption equipment

Once keten has been formed in the cracking unit it is very important to quench it as quickly as possible to prevent its thermal decomposition to ethylene and carbon monoxide. For this reason the cracked outlet gases are shock-cooled by injection of one of the recycle streams containing an excess of acetic acid. A simple four-jet unit is employed for this and an immediate volume expansion takes place on partial vaporization of the quench feed. The pipeline is therefore considerably expanded at this point and the severe thermal strain is taken up by generously-sized expansion bellows. A single equilibrium contact is then given in a packed tower over which liquid quench is circulated, with continuous filtration to remove suspended coke blown from the cracking tubes.

Vapour at about 300c F., leaving the so-called quench tower, and containing permanent gas, acetone, acetic acid, acetic anhydride and keten, is then condensed. During the condensation, combination of the keten with acetic acid takes place to form anhydride, with the evolution of heat. The estimation of condenser surface to deal with this poly-component gas mixture was a nice exercise in chemical engineering calculation. A trial and error step-wise method was evolved for the design and this was checked on a very small laboratory unit to give a basis for specification.

Here, as at other points in the plant, Rosenblad spiral-plate exchangers were successfully used, as it was found that the cost per equivalent square foot of stainless-steel surface was less than that of shell-and-tube or battery-type units.

The cracker products now separate into a crude liquid fraction containing the bulk of the acetic anhydride, and a gas stream containing a high concentration of acetone and some unabsorbed keten. The gas is therefore first scrubbed with a substantially acetone-free recycle stream containing acetic acid. A normal bubble-cap tower is used for this duty, but in order to keep the operating temperature low, internal recirculation through water-cooled Rosenblad exchangers is used. The effluent gas from this tower contains a little acetone, which is effectively removed by contact in a

J. appl, Chern., 3, June, 1953

--- ----=----=--- - - ~


second tower through which flows the acetic acid feed to the plant. The gas is now saturated with acetic acid, which is removed by water scrubbing, and the aqueous acetic acid is returned to the acetate unit for concentration. A final caustic wash is given before the gas passes to the holder for storage as furnace fuel.

(c) Distillation of recycle and product streams

The equipment is designed on normal lines, though it was necessary to check all vapour-liquid equilibria and thermal data in the laboratory before preparing final designs. An acetone still produces recycle acetone from the crude product and this overhead distillate passes back to the furnace. The low conversion makes the duty of the still relatively heavy and some thermal economy is achieved by preheating the feed in the convection section of the furnace. Also, as the feed rate is high in comparison with the overhead, the trays are split below the feed plate to accommodate the high liquid rates. The construction is entirely in stainless steel and much ingenuity has been exercised by E. W. Fletcher in designing the tray supports and structure to give maximum economy in material and very good standards of accuracy in the plate levelling.

The base product from the acetone still is cooled in a Rosenblad exchanger and used as the recycle feed to the quench unit and first gas-scrubber. A side stream passes forward for stripping to give an overhead of acetic acid and acetone and a bottoms product of strong anhydride and high-boiling polymers. This is distilled in a final column to give an overhead of acetic anhydride and a small residue of tarry compounds. In view of the unknown nature of these products it was considered desirable to fit this distillation unit with duplicate re-boilers arranged with valves, so that the spare could be cleaned without interruption of production.

The condensers for all the fractionating columns are of the spiral-plate type, and we have found them most suitable for their duty; in addition to relatively low cost, they have high heat-transfer coefficients and low pressure-drops.

Standardization

As far as possible, plant units have been standardized to reduce to the minimum the necessary stocks of spares. The cracking and preheating coils, the most expensive individual items, are identical, and the spares are therefore interchangeable. All the liquid exchangers are of the same pattern. Stainless-steel circulating pumps, of which there are 26, have been divided into three standard design groups, and the storage tanks, valves and pipelines have been reduced to standard sizes even where this has meant slight over-design, to allow rapid replacement from economically small stocks. This is particularly important with high-priced stainless-steel equipment in a new project where there may be unexpectedly high corrosion-rates.

Layout

After the major items of equipment have been designed, their disposition in the plant area becomes the major problem, and inexpensive rough models were found to be most effective in helping the visualizing of the appearance and convenience of the finished plant. This was particularly true of the pipe runs, which became complicated with a recycling process. The pipelines were simulated on the finished model by the piping contractor, who used different colours of insulated wire to represent the pipe sizes and indicated valves by simple paper-fasteners clipped to the wires. In this way it was possible to simplify and make more economical many of the process pipes. Two views of the models are shown as Figs, 8 and 9.

The general aim in the layout was to use structural members as supports for simple sheeting to give shelter at the focal points. Fire walls, fitted with steel partition doors, were used on one side of the furnace building, and the corresponding face of the pro:ess building was built as an almost blank wall to give additional protection. The storage tanks of highly inflammable materials were located on the side of the process building remote from the furnace.

As far as possible, most of the process pumps were sited together in a single gallery (Fig. 10) to allow easy access for packing and general maintenance, and this also simplified the installation of a ventilated pump-drip collection system, returning leakages to the crude-product storage tank. This is very necessary with lachrymatory materials like acetic acid and acetic anhydride.

Instrumentation

The plant is almost completely automatically controlled. A central control room, slightly pressurized with fresh air, provides the focal centre for plant operation, and there are few plantvariables that cannot be observed and corrected in the control room.

J. appl, Chem., 3, June, 1953

FIG. Prelimil/ary mOG

J. appJ

249 DAROUX-PRODUCTION OF ACETIC ANHYDRiDE

FIG. 8 (left).

Preliminary model of furnace room and annexe

FIG. 9 (right). Preliminary model of pr ccess building

FIG. 10 (left).

Pump gallery

J. appl, Chem., 3, June, 1953

DAROUX-PRODUCTJON OF ACETIC ANHYDRIDE

Furnace firing is controlled by selected thermocouple points in the preheating and cracking cell.

A generous allowance of spare thermocouples was made at critical points in the vapour stream and this has proved well worth while in practice. At the more important points we have fitted six thermocouples, and the main temperature recorder and controllers automatically select the surviving couples.

Burner trimming and air adjustment are done manually at infrequent intervals. Duplicate hand-operated and manually-controlled air-operated valves are provided in the furnace room for emergencies, and these are useful when the plant is being started up. Oil-firing is done under hand control.

Feeds to the cracking furnace, scrubbing towers and distillation units are regulated automatically with pneumatic control systems, usually operating through transmitting' flowrators '. A few orifice plates are used on gas lines and hot-liquid feeds. Each of the control valves is provided with a hand-operated by-pass, and, where possible, the corresponding' flowrator ' is conveniently sited so that the operator can see the flow changes if he should have to leave the control room and go over to hand operation.

Distillation-process temperatures, which guide the automatic reflux controllers, are measured by gas-filled bulbs and transmitted to the controllers and records pneumatically. Instrument supply is provided by a Nash pump on the plant, with an automatic switch to cut in the works air in the event of failure.

The instruments in the control room were arranged on a diagrammatic flow-sheet panel after much discussion, and operating experience has shown the advantage of this scheme in giving the operator a clear picture of the plant conditions. By using miniature instruments, a well spaced layout can be obtained, with very slight sacrifice of chart accuracy. Fig. II shows a general view of the control room.

FIG. I r. General view of control r,JQIII

Process temperatures, other than those recorded, are measured at a desk indicator with three 24 point banks of selecting switches. When a temperature is selected for measurement, a signal light appears on the flow-sheet panel, showing the location of the point whose temperature is being indicated.

Audible and visible alarms are fitted at all critical points and come into action for important pump-failures, flow-failure, high or low levels in any process vessel, higher-than-scheduled temperatures in the preheater or cracker cell, or unusually high gas-pressure in the scrubbing system.

Other instruments include a gas specific-gravity recorder, continuous gas-analyser, pneumatic tank-stock indicators, and integrators for power, steam, water, raw material and finished product.

Routine instrument maintenance on small parts is done in the control room behind the control panel. Major repairs on control valves are of course done in the workshop.

Our experience so far has been that full instrumentation and control have been well worth while. The advantages lie rather in precision of the operating variables than in major savings in labour cost. On the plant a large enough operating crew must always be available to cope with emergencies, and


this is 111

product working givesa.

Safety

Tt acetic a

Fi foam r fires c( instant tank is spindle tank, j the fu of the acetOl

i flame pumI foren

only requ with sup: COUI

Op

ter:

she in tel

J.

I .

,I


FIG. 12.

View behind control panel

this is more than the labour needed for plant running. With a plant producing a relatively expensive product, steady operating conditions, maintained with the least amount of tediousness in day-to-day working, leave plenty of scope for concentration on increased yields and better efficiencies. This gives a real boost to the productivity of the labour employed.

Safety

The main plant-hazards are fire and risk of injury from the very reactive chemicals, keten, acetic acid and acetic anhydride.

Fire precautions include a foam dowsing-system for the two 400-ton acetone tanks, and a foam manifold for general use. Experiments with artificial acetone fires showed that for open fires copious dilution with a water spray is most effective, and water screens can be turned on instantly from any floor of the process building to protect the stairways. A steam-purged dump tank is provided at the furnace outlet and the valves are operated from floor level with extended spindles. These valves are checked regularly as a routine. Excess pressure is also vented to this tank, in which about 1000 gallons of water are held to give dilution. The quantity of acetone in the furnace and tubes under normal operating conditions is relatively small, owing to the low density of the high-temperature vapour, but steam dowsing of the furnace and four ways of shutting off the acetone feed from safe positions have been installed.

A direct line connects the plant to the works fire-station in case of emergencies. Naturally, flame-proof electrical equipment has been used wherever acetone vapour or gas may leak. All pump starters are clearly labelled, and a flicker of the alarm light in the control room shows the foreman which pumps have been started up.

Keten itself has been reported to be highly toxic, but fortunately it is so reactive that there is only a slight risk of free keten escaping from the plant in any appreciable concentration. The main requirements for personal safety are good ventilation, free accessibility of the plant units, and, with dangerous operations, a proper supply of protective goggles, gloves and clothing, and supervision to see that these are fully used. The usual safety showers and eye douches are of course provided.

Operating results

As the plant has only recently begun to operate, it would be premature to discuss the longterm operating results.

We have confirmed a remarkable sensitivity of gas-make to operating temperature. This was shown by the pilot plant, but is much more marked on the full-scale unit. When a small change in the set point of the cracker-outlet temperature is made, the gas-make changes long before the temperature change is noticed, and during normal operation, where the temperatures are usually

J. appl. Chern., 3, June, 1953 F~


held to within 1° F., slight ripples in the gas-make chan show minor temperature variations in the cracking coil.

As the plant was completely new in our works experience, we thought it desirable to give qualified shift supervision for the first four operating weeks after routine testing and furnace drying-out. The shift chemical engineers did their training job so well that we were glad to hand the unit over to the shift foremen after this period, and we are very pleased with their handling of this complicated plant.

FIG. 13. General view of the plane

Acknowledgments

The author would like to pay tribute to the engineers and chemists who have formed the design team. In particular he acknowledges with gratitude the major pan played by the chief acetate engineer, Mr. E. Turney, in the successful implementation of the project. The work done by his assistant, Mr. E. W. Fletcher, has contributed very largely to producing a successful mechanical design and layout.

The instrument engineers, Messrs. E. W. Little and W. Hibbert, have met our most exacting requirements for process control. The construction was in the hands of Mr. W. Ellard, who built the plant in a very short time under difficult conditions, and Mr. D. L. Tyler's fundamental work in the chemistry and physical data of the process has been the essence of the full-scale design.

Finally, the author is glad to acknowledge the help of his friend and colleague Mr. J. D. Smith, who has spent so much of his time on the plant design and operation.

The author'S thanks are due to the directors of Courtaulds Ltd. for permission to publish this paper.

Courtaulds Ltd. Research Department (Chemical Engineering Section)

Coventry

Received '-7 February, 1953

References

1 Zakal, H. W., Chem, Ind., Philad. 1948, 63, 209 6 Peytral, E., Bull. Soc. chim, Pr., 1921,31, [iv], 122

, Loveless, L. W. J., Trans. lnstn chem. Engrs, Land., 7 Hinshelwood, C. N. & Hutchison, Proc, roy. Soc.,

1947, ~-7, 47 1926, [A] III, 245 3 Schmidlin, J. & Bergmann, M., Ber, dtsch, chem.

Ges., 1910,43,2821 • Taylor, H. S., J. phys. Chem., 1926, 30, 1433

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I. ARYLO HALOGEN

B

Sodium at proportions of hours at 200-2 phenols. Sod

General introd1 The work de

of the well know acidic carboxyl f amide (IV) grou

O'CH, ACl\ II ~/ CI (I)

It was not expel but the sulphir might well COD sulphinic analo growth-regulatl sequent develo of the type SOl simulate the ac remains, there!

However, tion of the suI conventional c phenoxrmeth: insectICIdes, C groupS of oH

Aryloxymel AryloxyJ

described in . HO·CHz·SI hydroxymetl acid itself re existence in

The n sulphonates no details t< sulphonate: thioethanel phenols5 t bisulphite, of sodium 2-hydroxy not to the

John: sodium f halogen a bound 3I

]. appl.

Production of Acetic Anhydride from Acetone

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