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PROEFSCHRIFT
TER VERKRIJGING VAN DE GRAAD VAN DOCTOR IN DE TECHNISCHE WETENSCHAP AAN DE TECHNISCHE HOGESCHOOL TE DELFT, OP GEZAG VAN DE RECTOR MAGNI-FICUS DR. O . B O T T E M A , HOOGLERAAR IN DE AFDELING DER ALGEMENE WETENSCHAPPEN VOOR EEN COMMISSIE UIT DE SENAAT TE
VERDEDIGEN OP WOENSDAG 23 APRIL 1958 DES NAMIDDAGS TE 1 UUR
DOOR
RADEN MAS SOEMANTRI
SCHEIKUNDIG INGENIEUR GEBOREN TE SEMARANG (INDONESIA)
het Delfts Hogeschoolfonds voor de financiële steun en het verleende stipendium.
Voorts gaat mijn dank uit aan allen, die in enige vorm heb-ben medegewerkt aan het tot stand komen van dit proef-schrift.
T A B L E O F C O N T E N T S
Chapter I. The separation of naphthalene and its hydro-genated products by gas-liquid
chromato-graphy 7 1. Introduction 7
2. Description of the apparatus 8
3. Experimental 13 4. Methods of calibration 16
5. Conclusions 17 Chapter II. The separation of mixtures of biphenyl,
cyclohexylbenzene and bicyclohexyl by
gas-liquid chromatography 21 1. Introduction 21 2. Experimental part 21
3. Method of calibration and results, 24
4. Discussion of the results 29 Chapter HI. Correction-factors in quantitative analysis
by gas-liquid chromatography with thermal
conductivity detection 33 1. Introduction 33 2. Experimental part 33
3. Discussion of the r e s u l t s ' 37
4. Conclusions 43 Chapter IV. Selective hydrogenation of olefins in
olefin-aromatic mixtures 44 1. Introduction 44 2.' Experimental part 44
3. Discussion of the results 47
4. Conclusion 51 Chapter V. Hydrodesulphurization of thiophene
contain-ing mixtures.
Part I: thiophene-aromatic mixture
Part II: thiophene-olefinic mixture 55
1. Introduction 55 2. P a r t i :
Experimental part 56 Discussion of the results 59
Regeneration of the catalyst 62
3. P a r t II:
Experimental part 64 Discussion of the results 64
Summary 70 Samenvatting (summary in Dutch) 72
Ringkasan (summary in Indonesian) 74
References 75
C h a p t e r I
THE SEPARATION OF NAPHTHALENE AND ITS HYDROGENATED PRODUCTS BY GAS-LIQUID
CHROMATOGRAPHY *)
Introduction
Vapour-phase chromatography (now officially named gas chromatography), first suggested by Martin and Synge (1), has now become a very important tool for the analysis of volatile compounds. In fact it is at the moment of the same impor-tance as the infra-red-, ultra-violet spectroscopy, and in some cases even supersedes the mass-spectrometry.
This tremendous extension of this relatively new analytical method is due to the following features of the gas chromato-graphy, viz its versatility, its relative simplicity in opera-tion and in apparature, its low price, yet offering a rapid and direct quantitative analysis of practically all kinds of volatile mixtures.
Application of this analytical separation technique to gas and liquid mixtures have been described by Martin and James (2), Ray (3), Bradford et al(4), van der Craats (5), James (6), James and Phillips (7), Keulemans and Kwantes (8), Lichten-fels et al (9) and several others (21-51).
These references, dealing with different aspects of gas chromatography, can be classified as follows:
14, 24,27, 33, 47,48 dealing with adsorption chromatography, 4 , 5 , 3 0 , 4 0 , 4 1 , 4 3 , 4 6 dealing with qualitative aspects of the method,
23, 35,42 compilation of the applications,
3, 4, 25, 29, 32, 33, 34, 36 dealing with quantitative aspects, 4, 5, 9, 25, 39, 44 studying the influence of operating variables, 28, 31, 37 application to fluor-, sulphur-, boron-compounds. 38,45 application to preparative scale,
3, 5, 20, 28, 49, 50, 51 constructional aspects of the apparatus, 2, 21, 22 application to fatty acids,
4, 5,14, 26, 27, 33 application to hydrocarbon- and permanent gases,
4, 8, 9, 30, 32, 36, 49 application to liquid hydrocarbons.
Gas chromatographical methods can be divided into two e s -sentially different groups:
1. Gas-solid adsorption chromatography (10) (14), employing a solid adsorbing agent. This method can be sub-divided into two groups
a. Separation by displacement: the gaseous mixture is ad-sorbed on to active charcoal or silicagel and then de-sorbed by raising the temperature, or it is displaced by a vapour that is more strongly adsorbed.
b. Separation by elution: the adsorbed components are eluted by means of an inert stripper gas, (3) (11) mostly nitrogen or hydrogen.
2. Gas-liquid partition chromatography, employing a liquid agent for partition. This thesis is dealing only with this latter method.
Principle
In gas-liquid partition chromatography the moving phase is a gas-vapour mixture, and the stationary phase consists of a non-volatile high-boiling liquid, supported on an inert solid c a r r i e r . Due to the difference in partition coefficient of the several components, they will be separated and leave the column one after another by stripping with the carrier gas. Method of detecting
Several detecting devices have been developed and are suitable for detecting and measuring the separated compo-nents :
1. measuring of thermal conductivity
2. measuring the pressure increase or volume increase, after chemically binding the c a r r i e r gas (5,14)
3. automatic titration (for acids) (2) 4. p-ray ionization cell (20)
5. microflare detection (Scott) (15) 6. Martin's gas density balance (16) and several other devices.
The measuring of thermal conductivity is relatively simple, sensitive and reliable.
Description of the apparatus *)
In the present apparatus the thermal conductivity cell (katharometer) is of the Bureau of Mines type (12). It con-*) Construction by H.D.F.Bagmeyer.
cm in length. Both wires form two a r m s of a Wheatstone bridge and are fed with a 100 nxA. current from an accumu-lator. Through one of these bores (reference channel) streams the c a r r i e r gas only, while through the other channel streams the c a r r i e r gas and the separated component. Due to the dif-ference in thermal conductivity in both bores, the Wheatstone bridge will be out of equilibrium and the overpotential is fed to an automatic Brown potentiometer, coupled with a pen r e -corder.
The c a r r i e r gas nitrogen is drawn from a bomb via a r e -ducing valve. As a constancy of the gasflow is essential for the chromatogram, nitrogen is led to a precision reducing valve (Negretti and Zambra). An accurate and constant p r e s -sure drop can thus be maintained over the column.
In order to eliminate any pressure variations, a buffer vessel is attached after the precision reducing valve. The column and the katharometer are immersed in the oil bath, so that they have the same temperature. The column is coiled into a spiral to save space. The gas flow is measured by means of a flowrator at the inlet, and by a soapfilm flow-meter at the outlet. The flowrator serves merely for the flow indication, the exact gas velocity is measured with the soapfilm flowmeter.
"The inlet system consists of a valve, over which a rubber serum cap is attached. In this way leakage of the system during the injection of a sample is eliminated. A schematic flow-sheet of the apparatus is given in the figure below.
s sr
: N I T I ( O 0 E N - C Y L I N D E R PRECISION REtXJCINO VALVE (NEGRETTI & ZAMBRA) ;BUFFER VESSEL
OPEN MANOMETER •
FLOWRATOR FOR FLOW-INDICATION DRYING CHAMBER (Co CI2 ) KATHAROMETER OR THERMAL CONDUCTIVITY CELL THERMOSTATED OIL BATH CHROMATOGRAPHIC COLUMN ( C a L E D AROUND THE KATHAROMETER) SAMPLING SYSTEM
BROWN r » c o r d » r
E L E C T R I C CIRCUIT
Fig. lb
The katharometer and the chromatographic column, mounted on a tripod
and on the detection, a constancy of temperature is absolute-ly necessary. For this reason, the katharometer and the chromatographic column are immersed in an oil thermostat. For the two units for gas chromatography, now in operation, two different methods of temperature regulation a r e applied. 1. An oil bath, consisting of about 8 liters of sesame oil, is contained in a cast iron cylindric vessel. The katharometer and the chromatographic column a r e immersed in here. At the bottom and the middle of the vessel are situated two isolated electrical heating elements. The energy to these elements is supplied via a "Variac" transformer, by which the energy supply can be regulated.
The cylindric vessel is isolated from its surrounding by asbestos paper and asbestos cord. A certain energy supply from the Variac corresponds to a certain temperature of the oil bath. This rather simple system of temperature regula-tion proves to be satisfactory: a constancy of ± 0.5°C at e.g.
140^0 can easily be reached -during long periods (24 hours and longer).
The disadvantage of this kind of temperature regulation is a. it takes a relatively long time to reach its equilibrium. b. it is not suited for the purpose of rapid changing of
temperature, due to the thermal inertia of the oil.
Beside the disadvantages, it has several advantages, as simplicity, no stirring required, and particularly well suited for continuous work at constant conditions, e.g. for serie analyses.
2. The katharometer and chromatographic column are im-mersed in an oil bath of silicone MS 550 contained in a modified "Wobser Universal Thermostat". This contains a p r e -heating device, a motor driven s t i r r e r and two electrical heating coils of 1.0and 1.5kW respectively. The temperature regulation is here accomplished by a contact thermometer, coupled to a relay. The silicone oil is chosen because of its low vapour p r e s s u r e , as the apparatus is to be operated at high temperatures (circa 200OC).
This thermostating device has many advantages, as rapid equilibrium, and the possibility of rapid changing of tempe-r a t u tempe-r e . But it has one main disadvantage, namely this:
When the temperature is somewhat too low, then the heating s t a r t s , and this large sudden energy input in the oil bath, affects the chromatogram seriously (disturbing the base line), probably due to an inhomogeneous temperature profile in the oil bath. To eliminate this trouble, the thermostating device is modified as follows:
heat-ing elements, but only a part of these. Thus a part of the heating elements is continuously supplying energy to the oil bath, and the other part is connected or cut off, if the tem-perature is too low or too high respectively, via the relay, directed by the contact thermometer.
With a choice of the temperature desired by means of the contact thermometer and an appropriate choice of the portion of the heating elements to be regulated (with "Variac" t r a n s -former), the desired temperature can be reached and kept constant, without the disturbing large energy input as men-tioned before. The temperature constancy is + 1"C at 200^0, during 24 hours or longer.
With the modifications, mentioned above, the Wobser Universal Thermostat is made suitable for gas chromato-graphic apparatus for high temperature operations.
The "Brown continous balance" recorder
Two r e c o r d e r s are now in use in combination with our chromatographic units. One is a recorder with a fixed span (2.5 mV), the other one with a variable span, with continuous regulation from 0 to 2.5 mV.
This last feature is of practical importance, especially in trace analysis. If for instance cyclohexane (minor concentra-tion) must be separated from the bulk, consisting of n-hep-tane, then a relatively large sample has to be introduced, because of the limited sensitivity of the detector. But with this large dose of sample the column tends to be overloaded, giving rise to a bad separation. Now, in lowering the span to 0.5 mV, then the "sensitivity" is increased five times. Con-sequently only one fifth of the sample size is necessary for detecting the cyclohexane, and the risk of column overloading is avoided. The cyclohexane peak is then well separated from the bulk.
The separation
Martin (2) and others have given a theory of gas-liquid partition chromatography. This theory gives indications as to how to achieve a good separation, but due to the fact that a large number of factors play a part in the process, it is still difficult to predict the optimum conditions for each problem. Some of the important factors for separation are (5):
1. The nature of the absorption liquid and the column tempe-r a t u tempe-r e , as these detetempe-rmine the Hentempe-ry coefficient and therefore the partition coefficient.
2. The velocity of the carrier gas, column diameter, size of the sample, and type of the solid c a r r i e r .
Experimental part
The intention is to study the separation of naphthalene and its hydrogenated products for the analysis of the products obtained in semi-technical dehydrogenation processes of decalin. Table of components Naphthalene Decahydronaphthalene (decalin) trans cis Tetrahydronaphthalene (tetralin) b . p . , o c 217.9 185.5 194.6 207.2
For this purpose several accurately weighed mixtures of these components were prepared and analysed by means of gas-liquid chromatography. Before analysing these mixtures all the components were first tested for purity (see Table I). Choice of conditions of analysis
1. The chromatographic column: analyses were carried out on two kinds of column:
a. Dow Corning Silicone 702, impregnated on Celite, col-umn diameter 12 mm.
b. dioctylphtalate, impregnated on ground firebrick, col-umn diameter 6 mm.
The column length is 180 cm (coiled copper tube).
These columns have been used successfully for analyses of hydrocarbon gases and gasoline fractions.
The columns were prepared as follows:
a. Kieselguhr (Celite 545, Johns Manville Corpn) was size-graded by repeated suspension in water, heated in a muffle for three hours at 300^0, and purified by treatment with HCl 1.19, to remove iron and basic impurities. After washing with water until acid-free, Celite was dried at 145°C (2). The liquid phase, consisting of Silicone 702, dissolved in pentane was added to the Celite (0.5 g sili-cone/l g Celite), stirred well, and the pentane evaporated at 70OC.
The mixture is packed down to a known density (0.4 g/cc) and the two ends plugged with glass-wool.
b. Screen fractions of firebrick (40-100 mesh), after suspen-sion in water to remove dust, and drying at ISQOC, were impregnated with dioctylphtalate, diluted with a volatile solvent (0.3 g dioctylphtalate/l g brick).
The packing density in the column is 0.6 g/cc. 2. The operational variables.
a. the temperature: a few analyses were done at 140°C, the others at 170° and 180°C. The influence of the tempera-ture on the shape of the peaks and the time of analysis is illustrated in figs. 2 and 3. The lower the temperature, the broader the peaks and the longer the time of analysis. At 170OC the peaks are relatively sharp and symmetrical and sufficiently separated for quantitative work.
Of course a higher temperature can be chosen for these analyses in order to shorten the time of analysis, but this is limited to a certain extent:
(i) At higher temperatures the silicone or dioctylphtalate have still higher vapour p r e s s u r e s , so they can be stripped by the c a r r i e r gas. The column will be in this way seriously damaged.
At 170°-180OC no decline could be detected in the sep-arating efficiency of our columns.
(ii) As tetralin and decalin are relatively unstable, very high temperatures have to be avoided in order to p r e -vent any dehydrogenation of these components at the hot Pt wire or at the walls of the bores of the katharo-meter.
b. Velocity of the carrier gas : 5.5 L nitrogen/hour for the dioctylphtalate, 6.5 L nitrogen/hour for the silicone col-umn.
c. Size of the samples : 0.15-0.20 ml (benzenic solution). The limitations of the size of the samples a r e :
upper limit: the column must not be overloaded and the peaks must not run out of the recorder scale.
lower limit: determined by the sensitivity of the katharo-meter.
According to Ray (3), the samples were put on to the chromatographic column by means of a calibrated syringe p r o -vided with a long needle.
Note.
The mixtures that were not liquid were liquefied by heating at 70OC. From the homogeneous liquid a sample was then taken in the preheated syringe, in order to prevent solidifi-cation.
This method has the disadvantage that there might be loss of the most volatile component, due to evaporation during the heating. The most elegant method is to add benzene or other
or influence the ratio of the other components. Fig. 5 shows a chromatogram obtained in these analyses and Fig. 6 shows a chromatogram of a mixture to which benzene was added. Qualitative and quantitative interpretation of the chromato-grams.
Qualitative: the retention volupie, or at a given velocity of the c a r r i e r gas, the retention time of a component, is determined by the nature of the stationary phase (absorption liquid), the temperature, and the velocity of the c a r -r i e -r gas. At constant ope-rating conditions, the -retention time (volume) of a* component is specific and constant (VR). A component can thus be identified by means of its retention time.
Quantitative: the area of a peak is directly proportional to the quantity of the corresponding component (4, 5,13). In most cases it is not necessary to measure the actual peak area, but it is sufficient to measure it by multiplying the height by the half-band width of the peak (a x b). This method is first suggested by Cremer and Muller (33), and is now commonly used.
• I N J E C T I O N — * POINT
F I G . 2 ( a ) FIG 2 (b)
Q U A U T A T I V E Q U A N T I T A T I V E
If the thermal conductivities of the components are equal, or when the differences are negligible, then the area of a peak is directly proportional to the mol-concentration of the corresponding component. According to Phillips (13), this will be the case when hydrogen or helium a r e used as c a r r i e r gas. These have very high thermal conductivity in compar-ison with other vapours and gases.
The total sum of the areas of the peaks is taken as 100 per cent 'and the ratio between the peak area and this sum gives the mol-percentage of the corresponding component. In this case, helium being unavailable, nitrogen is used as c a r r i e r
gas. The thermal conductivity of nitrogen differs only little from that of the other vapours.
In following the method described above, the values found differ considerably from the values calculated from the p r e -paration of the mixtures.
The values found for naphthalene were all too high and deviations as large as 6.6% absolute were encountered. Thus it was necessary to carry out calibration and to make some corrections. Evidently in using nitrogen as c a r r i e r gas, the difference in thermal conductivity of the components is not negligible.
Methods of calibration
1. According to Bradford et al (4) by the "internal standard" method. This method has the following disadvantages: first, it is very difficult to add an accurate fixed amount of the "in-ternal standard" to all mixtures to be analysed, secondly, several calibration mixtures must be prepared and analysed to obtain accurate calibration lines for all components.
2. Another method is to measure the peak area corresponding to an accurately known amount of a component. This method is rather time-consuming and complicated: the peak area is influenced by the operation variables, and it is not possible to inject an accurate amount with a common syringe.
3. The method of calibration used in these analyses is as follows: equimolar mixtures of decalin and tetralin and equi-molar mixtures of tetralin and naphthalene were prepared. Assuming equality of thermal conductivities, the peaks of the components of such equimolar mixtures must have the same area.
Table of calibration
tetralin naphthalene tetralin
decalin (trans + cis)
prepared,% 49.6 50.4 50.0 50.0 area of peak square mm 1 495.0 576.3 660.0 756.0 20«5.5 3333.0 1900.6 3171.8 1 From this table it is clear that naphthalene gives a larger area than tetralin, and decalin gives a smaller area than tetralin. Therefore the a r e a s of the components are not d i -rectly proportional to their mol-concentrations, but the fol-lowing corrections must be applied.
Area of decalin xl.07
By applying these correction-factors in interpreting the chro-matograms, it is found that the values (mol-percentages) ob-tained for the components are correct. The mean deviation is about 1.5% absolute (see Table I). This method "of calibra-tion is relatively simple and accurate compared with other calibration methods. The ratio of the peak areas of the com-ponents (correction-factors) is temperature-independent in the temperature range 140O-180OC.
Conclusions
1. On both columns the components are readily separated and leave the column according to their boiling points.
2. No influence of the column diameter on the separating ef-ficiency can be observed. Apparently no disturbing radial diffusion occurs. Both columns are stable at these operat-ing conditions.
3. Gas-liquid partition chromatography offers a simple, rapid, and accurate method of analysis for these high-boiling, sometimes solid, mixtures, and requires only very small samples. This method has great advantages over other possible methods, like analytical distillation or combined ultra-violet and infra-red spectroscopy.
4. No dehydrogenation of decalin and tetralin can be detected. Above 200OC some dehydrogenation might occur, which will render the analysis inaccurate and complicated.
5. Concentrations as small as l%can be detected quantitativ-ely.
Mol, % Mixture Commercial decalin Dg Tz = tetralin obtained by distillation . N = recryatallized naphthalene TB = commercial tetra-lin . cis-Decalin . Commercial decalin + cis-Decalin I . Commercial decalin -|-ci«-Decalin I I . - D ^ r ^ I I . ND„I NTz I . . . NTzïl D„TBI . NDBTZÏ . NDHTZ I I . NDHTZ I I I NDHTZ I V . NDHTZ Y . ND„Tz VI NDnTz V I I NDaTz V I I I NDBTZ I X ND„Tz X . «rans-Decalin c — — — — — 17-9 46-5 39-2 70-9 1-9 1 0 36-2 46-9 25-6 7-2 3-2 73-7 3-7 56-3 31-3 32-7 13-8 ƒ 79-6 2-3 — — — 16-2 47-9 3 9 0 7 1 0 2-5 1-3 34-4 44-5 26-6 7-0 2 0 73-4 3-5 57-9 31 4 3 2 5 1 5 0 d — — — — — - 1 - 7 -fl-4 - 0 - 2 -fO-1 -foe -fO-3 - 1 - 8 - 2 - 4 - f l O - 0 - 2 - 1 - 2 - 0 - 3 - 0 - 2 -fl-6 + 0-1 - 0 - 2 + 1-2 cis-Decalin c — — — — — 82-1 53-5 11-3 1 8 1 2-7 1-4 9-2 1 3 0 7-3 4 0 1-2 1 9 0 2-2 14-5 8-5 9-4 4-5 ƒ 20-4 3-2 — — 1000 83-8 52-1 11-7 18-9 3 0 2-2 8-4 14-4 8-3 4-3 0-7 19-2 2-6 1 7 0 8-8 9-4 5 0 d c Tetralin f
Very nearly the value
— — — — + 1-7 - 1 - 4 + 0-4 + 0-8 - f 0 3 -I-0-8 - 0 - 8 + 1-4 + 1 0 -1-0-3 - 0 - 5 -fO-2 -fO-4 + 2-5 •fO-3 0 -1-0-5 — — — — — — 49-5 — 83-4 46-3 54-5 38-4 31-3 8 5 1 14-8 5-8 5 0 0 4-4 20-4 3 9 0 36-9 and i.r 94-5 — 1000 — — — 49-3 — 80-5 4 7 0 57-2 38-1 32-6 83-5 14-3 5-9 50-7 4 0 21-3 4 0 0 3 8 0 d Naphthalene c ƒ d
"ound by analytical distillation spectrography — — — — — — - 0 - 2 — - 2 - 9 -1-0-7 -f2-7 - 0 - 3 - H - 3 - 1 - 6 - 0 - 5 - f O l -fO-7 - 0 - 4 -t-O-9 - f l O + 1 1 — — — — — — — 10-3 1 2 0 51 3 — 1-8 35-8 3-7 80-9 1-6 44-2 24-8 39-8 18-9 44-8 — 1000 — — — — — 1 0 1 13-9 49-5 — 3 0 32-5 5-3 8 3 0 1-5 42-2 21-2 38-6 18-2 4 2 0 — — — — -^ — — - 0 - 2 -H-9 - 1 - 8 — - H - 2 - 3 - 5 + 1-8 -f-2-1 - 0 1 - 2 0 - 3 - 6 - 1 - 2 - 0 - 7 - 2 - 8 c = calculated. ƒ = found from chromatogram after correction. d = deviation.
COUJMN : DKX:nrLPHTALATE TEMP. . 1 7 0 * 0 FLOW .5.S l ^ , N j , Fio 3 CCXUMN DIOCTYLPHTALATE TEMP 1 4 0 ' C f LOW 5 . » l • / ^ " J .t-Fia 4
J
COUJMN : SUOONC 7 0 2 TEMP : l e O ' C n-ow ••sVt.N, —i— 6 0 30 ao F I O 5 COLUMN; DIOCTYLPHTALATE TEMP 1 7 0 * 0 FLOW * • * % , • FlQ 6
C h a p t e r II
THE SEPARATION OF MIXTURES OF BIPHENYL, CYCLOHEXYLBENZENE, AND BICYCLOHEXYL
BY GAS-LIQUID CHROMATOGRAPHY •)
Introduction
The intention is to study the quantitative separation of mixtures of biphenyl, cyclohexylbenzene, and bicyclohexyl for the analysis of the products, obtained in continuous dehy-drogenation and hydehy-drogenation studies with these compounds, and in hydrodesulphurization studies with dibenzothiophene.
Table of components bicyclohexyl cyclohexylbenzene biphenyl
(H)
{
H J
(_M_>
m.w. 166.30 160.25 154.20 b . p . 760 mm Hg 2350c 2380C 255OC Mixtures of these components have been subjected to gas-liquid partition chromatography, and it is shown that this method offers an excellent quantitative separation of the components mentioned above.This simple, rapid, and accurate method, for which only very small samples are required, offers great advantages over other analytical methods, such as analytical distillation and ultra-violet and infra-red spectroscopy.
Experimental part
1. For the principle of the method and the description of the apparatus and other experimental details, one is referred to the former chapter.
*) Published paper: W.J.Hendriks, R.M.Soemantri and H.I.Waterman, J.Inst.Petrol. ,12. 1957. 288.
2. The chromatographic columns and operating variables Two chromatographic columns were used for the analyses:
a) dioctylphtalate on ground firebrick b) silicone 702 on Celite,
6 mm in diameter and 180 cm in length.
The operating temperatures were 180.Ö and 190OC. Too high temperatures have to be avoided for the same reason as de-scribed in Chapter I.
In all analyses no dehydrogenation was observed. 3. The stability of the columns.
After some orientating experiments to find the most suit-able conditions for this separation, the analyses of the mix-tures were carried out continuously. The chromatographic column was thus subjected day and night to these severe con- * ditions. After about 50 hours the first symptoms of decline in separating efficiency could be observed, and after about 60 hours the separating efficiency of the columns had declin-ed so much that they could be usdeclin-ed no more for this purpose.
This decline in separating efficiency of the chromato-graphic column is caused by the fact, that at these high tem-peratures the immobile phase is stripped away by the c a r r i e r gas, owing to its high vapour p r e s s u r e . By this decrease of the amount of the immobile phase the retention times of the components become smaller.
Some investigators indeed use small amounts of immobile phase (15-20wt%) in order to shorten the time of analysis and to improve the separation (5).
If, however, the amount of the immobile phase is too small, the separating efficiency decreases sharply.
The stability of two chromatographic columns, expressed in t e r m s of the decrease of the retention time of a component is illustrated in both figures below. With a fresh column a separation of t r a n s - and cis-decalin is obtained as shown in a. After about 50 hours the separation is only as shown in b. At the end there is practically no separation of both compo-nents, as shown in c.
Another stationary phase tested, a bitumen (blown asphalt), has practically the same stability as the "residue" column. 4. The analyses
As is shown in Chapter I in the case of the separation of naphthalene, tetralin, and decalin, the areas of the peaks are not directly proportional to the mol-concentrations of the corresponding components in using nitrogen as c a r r i e r gas. An analogous case is to be expected in the separation of these mixtures of biphenyl, cyclohexylbenzene, and bicyclohexyl.
Z in
u z
COLUMN : COILED COPPER TUBE 4 m m I D , LENGTH 2 7 0 cm
STATIONARY PHASE DIOCTYLPHTALATE ON GROUND riREBRICK 3 0 V . (IKi») OPERATED AT ; TEMP 1 6 0 ' C t l ' C ""iNLET ' * ' " " " '
FLOW 2 0 L ^ n N j ^OUTLET ATMOSPHERIC INJECTED S A M P 1 . E S DISTILLING FRACTIONS.CONTAINING TRANS - AND
C I S - D E C A L I N , AND SMALL QUANTITIES OF TETRALIN - NAPHTHALENE
RETENTION D I S T A N C E S ; MEASURED TOR TRANS - D E C A U N PEAKS, UNCORRECTED r o R D E A D - V O L U M E
2 0 3 0 4 0 50 8 0 70 8 0 5o ioiT"
HOURS ( T I M E IN OPERATION) STABILITY O T A CHROMATOGRAPHIC COLUMN, EXPRESSED IN TERMS o r THE DECREASE Or THE RETENTION DISTANCE OF A COMPONENT AS FUNCTION OF THE AGE OF THE COLUMN ( T I M E IN O P E R A T I O N )
COLUMN COILED COPPER TUBE 4 m m I D , .LENGTH 2 7 0 c m
STATIONARY PHASE : „ R E S I D U E ' O N GROUND FIREBRICK ( 4 0 - t O O ME SH) 2 0 V . ( " ^ ) ,.RESI0UE":RESIDUEOF MOLECULAR DISTILLATION
TEMP 1 B 3 ' C t i c
FLOW 2 5 l ^ B N j ** INLET '*^* ^"^ *^3 ' ' O U T L E T ' ^ * ° " » ! H j
OPERATED AT
INJECTED SAMPLES
RETENTION D I S T A N C E S ; MEASURED FOR TRANS-DECALIN PEAKS , UNCORRECTED FOR DEAD VOLUME CRUDE PRODUCTS OF DEHYDROGENATION PROCESSES O F DECALIN.
CONTAINING DECAUN, TETRALIN, AND NAPHTHALENE. DISSOLVED IN BENZENE
_L
OPERATED AT SOO'C 3 0 l-^R Ng FOR MIXTURES CONTAI-NING BIPHENYL
_L
3 0 4 0 SO SO 7 0 SO 9 0 10O n o
fc HOURS(TIME IN OPERATION) STABILITY O F A CHROMATOGRAPHIC COLUMN, EXPRESSED IN TERMS OF THE DECREASE O F THE RETENTION DISTANCE OF A COMPONENT AS FUNCTION OF THE AGE OF THE COLUMN ( T I M E IN OPERATION)
k k l\
a b c
1 = TRANS DECALIN 2 r CIS DECALIN
Several binary mixtures of biphenyl and bicyclohexyl, bi-phenyl and cyclohexylbenzene, cyclohexylbenzene and bicyclo-hexyl, and ternary mixtures of these three components were accurately prepared in the most varying mol-ratios. Every component is first tested for purity.
As some mixtures were liquid and others were solid-liquid, a roughly known amount of purified benzene was added to all mixtures. The roughly known amount of benzene added is of practical use in order to be able to inject samples that will give chromatograms of the same order of size so that the accuracy of the measuring of the peak areas is the same. The c a r r i e r gas used is again nitrogen and the peak areas are taken as the product of the height and the half-band width of the peak.
5. Method of calibration and results.
In the case of the quantitative separation of the system naphthalene-tetralin-decalin the correction-factors for the a r e a s of the peaks of the chromatograms were determined by means of measurement of the chromatograms of equimolar mixtures of, respectively, tetralin and naphthalene and tetra-lin and decatetra-lin.
The method used here is principally the same, but it is extended in order to improve the accuracy:
a) The correction-factor for biphenyl is taken as 1.
This choice is of course quite arbitrary: cyclohexylben-zene or bicyclohexyl can also be taken as 1.
b) The determination of the correction-factor (a) of cyclo-hexylbenzene is carrier out as follows: for a binary mix-ture of biphenyl and cyclohexylbenzene,
i.u 107 1 u IV, « C h B z - A c h B z the mol% cyclohexylbenzene = r , . . — 100%
BPh = biphenyl
ChBz = cyclohexylbenzene Bch = bicyclohexyl
Thus achBz = mol% ChBz A mol% B P h • AchB2 •BPh 1)
A s the mol r a t i o s of the m i x t u r e s a r e known from the p r e p a r a t i o n and the peak a r e a s can be m e a s u r e d on the c h r o m a t o -g r a m s , achBz can be d e t e r m i n e d with f o r m u l a 1). T h e a v e r a -g e value found for achBz = 1.20. With t h e s e c o r r e c t i o n - f a c t o r s , ttBPh = 1 and achBz = 1.20 the c h r o m a t o g r a m s of t h e s e binary m i x t u r e s w e r e calculated. The r e s u l t is shown in Table I.
Table I S y s t e m : Biphenyl-cyclohexylbenzene , Number of m i x t u r e 9 10 11 12 13 Mol % Biphenyl Found 46.5 76.4 26.3 91.7 12.2 C a l c . 48.6 75.8 26.4 91.2 11.6 Cyclohexylbenzene Found 53.5 23.6 73.7 8.3 87.8 A a v e r a g e : 0.8%, A m a x i m u m : 2.1% A = (mol% found)-(mol% calculated)
C a l c . 51.4 24.2 73.6 8.8 88.4 A + 2.1 - 0.6 + 0.1 - 0.5 - 0.6
c) The c o r r e c t i o n - f a c t o r of bicyclohexyl is d e t e r m i n e d in the s a m e way a s for cyclohexylbenzene, with b i n a r y m i x t u r e s of biphenyl and bicyclohexyl.
T h e a v e r a g e value found for asch = 1.35. T h i s value i s used in calculating the c h r o m a t o g r a m s of t h e s e b i n a r y m i x -t u r e s . See Table H.
Table II S y s t e m : Biphenyl-bicyclohexyl N u m b e r of m i x t u r e 4 5 6 7 8 M o l % Biphenyl Found 52.3 26.9 76.9 96.3 10.7 C a l c . 53.2 27.2 75.8 95.95 9.05 Bicyclohexyl Found 47.7 73.1 23.1 3.7 89.3 C a l c . 46.8 72.8 24.2 4.05 90.95 A a v e r a g e : 0.9%, A m a x i m u m : 1.7%
A= (mol% found)-(mol% calculated)
A + 0.9 + 0.3 - 1.1 - 0.4 - 1.7 d) T h u s the t h r e e c o r r e c t i o n - f a c t o r s a r e «BPh = 1 (by definition) «ChBz = 1 . 2 0 OtBch = 1 . 3 5
To t e s t these d e t e r m i n e d a - v a l u e s , they a r e applied to the c h r o m a t o g r a m s of b i n a r y m i x t u r e s of cyclohexylbenzene and bicyclohexyl, and to t e r n a r y m i x t u r e s of biphenyl, c y c l o -hexylbenzene, and bicyclohexyl, the r e s u l t s of which a r e shown in T a b l e s III and IV.
Table III S y s t e m : Cyclohexylbenzene-bicyclohexyl N u m b e r of m i x t u r e 14 15 16 17 18 Mol % Cyclohexylbenzene Found 48.7 76.8 24.7 90.0 11.9 C a l c . 47.7 75.2 25.5 90.7 11.3 Bicyclohexyl Found 51.3 23.2 75.3 10.0 88.1 C a l c . 52.3 24.8 74.5 9.3 88.7 A - 1.0 - 1.6 + 0.8 + 0.7 - 0.6 A a v e r a g e : 0.9% A m a x i m u m : 1.6%
Number of mixture 19 20 22 23 24 25 26 28 29 31 32 33 Mol% Biphenyl Found 34.4 49.9 39.1 25.2 40.0 18.9 4.3 50.0 13.1 56.2 42.3 36.9 Calc. 35.5 51.6 41.5 26.3 40.6 18.9 4.3 49.6 12.2 55.6 44.3 35.6 A -1.1 -1.7 -2.4 -1.1 -0.6 0.0 0.0 +0A +0.9 •HO.6 -2.0 -I-1.3 Cyclohexylbenzene Found 31.4 25.2 22.4 51.5 42.4 42.1 47.2 47.0 33.7 35.1 15.9 55.6 Calc. 32.8 24.4 19.4 49.4 39.6 43.0 48.0 46.5 33.3 34.1 14.6 55.4 A -1.4 -1^0.8 -1-3.0 +2.1 +2.8 -0.9 -0.8 +0.5 +0.4 +1.0 +1.3 +0.2 Bicyclohexyl Found 34.2 24.9 38.5 23.3 17.6 39.0 48.5 3.0 53.1 8.7 41.8 7.5 Calc. 31.7 23.9 39.1 24.3 19.9 38.1 47.7 3.9 54.5 10.3 41.1 8.9 A +2.5 +1.0 -0.6 -1.0 -2.3 +0.9 +0.8 -0.9 -1.4 -1.6 +0.7 -1.4 A maximum 2.4 3.0 2.5 A average 1.0 1.3 1.3
A= {mol% found)-(mol% calculated)
T h e s e t a b l e s show c l e a r l y that the d e t e r m i n e d a - v a l u e s for bicyclohexyl and cyclohexylbenzene a r e c o r r e c t .
e) In the s y s t e m naphthalene, t e t r a l i n , and decalin, the c o r -r e c t i o n - f a c t o -r s found w e -r e a s follows: (see c h a p t e -r I)
aN = 1/1.3
ttT = 1 (by definition) ao = 1.07
In o r d e r to have a c o r r e l a t i o n between t h i s s y s t e m and the s y s t e m biphenylcyclohexylbenzenebicyclohexyl, the c o r r e c tionfactor of naphthalene (ON) with r e s p e c t to biphenyl i s d e -t e r m i n e d wi-th b i n a r y m i x -t u r e s of biphenyl and naph-thalene, in the way a s d e s c r i b e d under b).
The a v e r a g e value found for aN = 1.60. T h i s value, applied t o the calculation of the c h r o m a t o g r a m s of t h e s e b i n a r y m i x -t u r e s , gives -the r e s u l -t s a s shown in Table V.
f) The c o r r e c t i o n - f a c t o r of naphthalene (ON) being 1.60, the c o r r e c t i o n f a c t o r s of t e t r a l i n and decalin b e c o m e r e s p e c -tively:
ax = 1-60 X 1 . 3 - a T = 2.10
T a b l e V S y s t e m : Biphenyl-naphthalene N u m b e r of m i x t u r e 41 42 43 44 45 M o l % Biphenyl Found 43.7 26.0 59.1 13.7 66.5 C a l c . 43.55 25.8 59.7 12.8 66.65 Naphthalene Found 56.3 74.0 40.9 86.3 33.5 C a l c . 56.45 74.2 40.3 87.2 33.3 A - 0.2 - 0.2 + 0.6 - 0.9 + 0.2 A a v e r a g e : 0.4%. A m a x i m u m : 0.9%. A = (mol% found)-(mol% c a l c u l a t e d ) . F o r the s i x - c o m p o n e n t s y s t e m : biphenylcyclohexylbenzeneb i c y c l o h e x y l n a p h t h a l e n e t e t r a l i n d e c a l i n , the c o r r e c t i o n -f a c t o r s a r e shown in the table below.
Table of c o r r e c t i o n - f a c t o r s OBPh = 1 ttBch = 1-35 ttx = 2.10 achBz = 1.20 ttN = 1.60 ttQ = 2.20
g) In applying these c o r r e c t i o n - f a c t o r s to binary m i x t u r e s of b i p h e n y l - d e c a l i n b i p h e n y l - t e t r a l i n cyclohexylbenzene -decalin cyclohexylbenzene - t e t r a l i n cyclohexylbenzene - naphthalene bicyclohexyl-decalin b i c y c l o h e x y l - t e t r a l i n bicyclohexyl-naphthalene the a - v a l u e s p r o v e to be c o r r e c t . T h e r e s u l t s a r e shown in Table VI.
A c o r r e l a t i o n i s thus made between t h e s e two s y s t e m s . h) A s an i l l u s t r a t i v e e x a m p l e , the a n a l y s e s of six-component m i x t u r e s consisting of all the components mentioned above a r e shown in Table VII.
H e r e w i t h is shown the possibility and a c c u r a c y of the quan-t i quan-t a quan-t i v e s e p a r a quan-t i o n of m i x quan-t u r e s of quan-these high-boiling, s o m e of which a r e c l o s e b o i l i n g , components by gasliquid c h r o m a t o -g r a p h y .
Note: In the d e t e r m i n a t i o n of the c o r r e c t i o n - f a c t o r s «chBz, aBch, ttN, a s shown in T a b l e s I, II, and V, the r e s u l t s w e r e obtained in p r a c t i c a l l y a l l c a s e s from at l e a s t two c h r o m a t o -g r a m s p e r m i x t u r e . F o r p r a c t i c a l l y all other m i x t u r e s only one c h r o m a t o g r a m p e r m i x t u r e is used for the d e t e r m i n a t i o n of the composition.
B i p h e n y l - t e t r a l i n B i p h e n y l - d e c a l i n C y c l o h e x y l b e n z e n e -n a p h t h a l e -n e C y c l o h e x y l b e n z e n e -t e -t r a l i n C y c l o h e x y l b e n z e n e -d e c a l i n B i c y c l o h e x y l -n a p h t h a l e -n e B i c y c l o h e x y l -t e -t r a l i n B i c y c l o h e x y l -d e c a l i n i of m i x t u r e 55 56 52 53 54 50 51 49 H i g h e s t b o i l i n g c o m p o n e n t F o u n d 4 2 . 8 51.6 4 4 . 9 4 3 . 6 4 8 . 5 45.4 27.3 4 6 . 7 C a l c . 4 5 . 0 49.9 4 3 . 7 4 5 . 0 49.6 4 2 . 8 29.4 4 6 . 5 L o w e s t b o i l i n g c o m p o n e n t | F o u n d 57.2 48.4 55.1 56.4 51.5 54.6 72.7 53.3 C a l c . 55.0 50.1 56.3 55.0 50.4 57.2 70.6 53.5 A 1 + 2.2 - 1.7 - 1.2 + 1.4 + 1.1 - 2.6 + 2.1 - 0.2 A = (mol% found) - (mol% c a l c u l a t e d )
Table VII
System: Biphenyl cyclohexylbenzene bicyclohexyl -naphthalene -tetralin-decalin Number of m i x t u r e 46 60 Mol% found c a l c . A found c a l c . A B i -phenyl 11.8 14.1 -2.3 20.8 22.0 -1.2 cyclo- hexyl-benzene 13.8 14.7 -0.9 22.3 21.6 +0.7 b i c y c l o -hexyl 12.4 13.5 -1.1 20.6 21.1 -0.5 naphtha-lene 25.5 23.55 +2.0 7.4 6.9 +0.5 t e t r a -lin 21.6 18.9 +2.7 5.7 6.6 -0.9 d e c a -lin 14.8 15.25 -0.5 23.1 21.8 +1.3 A = (mol% found) - (mol% calculated)
Discussion of the results
As can be seen from Tables I-V, this method of calibra-tion results in an average accuracy of the analyses of ± 1 per cent absolute. The maximum deviation observed in all ana-lyses was 3 per cent absolute.
It is remarkable that the highest-boiling components in the systems biphenyl-cyclohexylbenzene-bicyclohexyl and
naphthalene-tetralin-decalin respectively, which are both total aromatics, have the smallest correction-factor. The lowest boiling components, both totally saturated, have the highest correction-factor.
These results suggest a certain relationship between the type of hydrocarbon and the correction-factor or thermal con-ductivity.
For an understanding of the physical meaning of the cor-rection-factor, the response of the thermal conductivity cell to the signals, caused by the change in the composition of the effluent gas stream, must be considered. See Fig. 1
The signal is thus the difference between the thermal con-ductivity of pure nitrogen and the thermal concon-ductivity of a mixture of nitrogen and a component. Thus the same mol-concentration of biphenyl, cyclohexylbenzene, or bicyclohexyl in the effluent gas stream gives r i s e to different signals in
ratio a / c . It means that the higher the thermal conductivity of a component, the greater the correction-factor (a).
In using hydrogen or helium as c a r r i e r gas, which have thermal conductivity eight times as high as nitrogen, the situation is given in fig. 1. It can readily be seen that the
a-values will be smaller and are nearly equal to 1. That is why for most purposes it is not necessary to carry out cali-bration to determine the correction-factors of the several components in using hydrogen or helium as c a r r i e r gas (13).
For accurate work and for components mutually differing very much in thermal conductivity, it is yet necessary to carry out calibration to determine the a-values.
In this method to every component an average a-value is given, as determined from the chromatograms of known mix-tures. That means that a is considered to be concentration-independent. This is strictly only correct in assuming the lines, connecting the XN2 and iVcomp (fig- 1) to be straight: the thermal conductivity of mixtures of nitrogen and a com-ponent varies linearly with the concentration of that compo-nent in the nitrogen gas. If these lines a r e curved, then a will be a function of the concentration.
However, considering the fact, that the vapour concentra-tion of a component in the c a r r i e r gas is usually very small, it is quite justifiable to consider the lines to be straight in this small interval. With this assumption the use of one value of a for a component is justified.
The relationship between correction-factor and thermal conductivity as illustrated above, is investigated for com-pounds with known thermal conductivities, namely the system n-hexane, cyclohexane and benzene, and the system n-hep-tane-toluene. The thermal conductivity of the compounds a r e as listed below. T h e r m a l at 200OF ( 9 4 ^ 0 n i t r o g e n n - h e x a n e cyclohexane benzene n - h e p t a n e toluene conductivity a a t a *) 17.7 X 10-3 12.0 10.4 e x p r e s s e d in 9.1 B T U / h r . O F . f t 11.6 11.5
Analyses were carried out at lOO^C with nitrogen as c a r r i e r gas. For the system n-hexane-cyclohexane-benzene the fol-lowing a-values were obtained
«^benzene = I'.QO (by definition) ^tyclohexane - 1-02
"n-hexane =1-27
From fig. 2 it can be seen, that the following signal ratios signal to benzene signal to cyclohexane signal to benzene signal to n-hexane = 1.18 = 1.51 hold.
In the system n-heptane-toluene, practically not differing in thermal conductivity, the a is found to be one (no correction). These data qualitatively confirm the postulated relationship between thermal conductivity and correction-factor.
tignql t o bcnz«n« . 0 . 6 , , , g signal to cyclofwxan* T 5 tignol to bonzenc ^ B . 0 _ . >. ftignai t o n-h«)<an« i 7 kN2 12 0 . 1 0 ^ X n-lwxane 10 4 . 1 0 " ^ X cyclohexane 9 1 . 1 0 " ^ X benzene ot 9 4 ' C l O O V . l O 2 0 3 0 4 0 5 0 « 0 7 0 8 0 9 0 1 0 0 V . Nn component Fig. 2
It is to be noted, that in the system n-hexane-cyclohexane-benzene the same tendency is observed, namely that the aro-matic has the lowest a-value, as in the system biphenyl-cy-clohexylbenzene-bicyclohexyl and the system naphthalene-tetralin-decalin.
C h a p t e r I I I
CORRECTION-FACTORS IN QUANTITATIVE ANALYSIS BY GAS-LIQUID CHROMATOGRAPHY WITH THERMAL
CONDUCTIVITY DETECTION
Introduction
In the quantitative analysis of mixtures by gas-liquid chro-matography with thermal conductivity detection it was shown by several investigators (32) (13) (25) that the areas of the peaks of the chromatograms are not directly proportional to the concentration (mol- or weight-concentration) of the com-ponents. Especially in using nitrogen as c a r r i e r gas, con-siderable deviations are obtained in assuming proportionality of the a r e a s to the concentrations, as shown in Chapter I and II. The use of hydrogen or helium as c a r r i e r gas will give r i s e to a closer proportionality (13) (19), as is discussed also in the former chapter. It is now generally accepted that in using thermal conductivity detection calibration is neces-sary, especially if a high accuracy is required.
The method of calibration used and investigated for the quantitative analysis of naphthalene-tetralin-decalin mixtures and for biphenyl-cyclohexylbenzene-bicyclohexyl mixtures is described in the former chapters.
Until now very little or none is published about c o r r e c -tion-factors of the compounds with molecular weights above 100. In this paper therefore the correction-factors of a num-ber of bicyclic compounds are given.
In order to test the general applicability and validity of the method of calibration and to investigate the correction-fac-tors at varying operating conditions, the following experi-ments were carried out.
Binary mixtures of known composition and of approximat-ely equimolar composition of several components were sub-jected to gas-liquid chromatography at varying operating conditions. From the chromatograms obtained the c o r r e c -tion-factors were calculated. It is proved, that the influence of the operating conditions e.g. temperature, kind of station-ary phase, gas-flow system, on the value of the correction-factor is only small.
In order to show the relation between correction and the accuracy of the analysis, the deviation between "corrected" and "uncorrected" areas is discussed.
Experimental part
1. The compounds used in this investigation a r e mentioned in table I. Table I compound t r a n s d e c a l i n c i s d e c a l i n t e t r a l i n d i h y d r o n a p h t h a l e n e 1-2 d i h y d r o n a p h t h a l e n e 1-4 b u t y l b e n z e n e indane indene benzothlophene 3 m e - b e n z o t h l o p h e n e 1 m e - n a p h t h a l e n e 2 m e - n a p h t h a l e n e c o n s t a n t s ngo^ 1.4695 = 1.4810 = 1.5415 n6"= 1.4896 = 1.5385 = 1.5765 %S = 22.5 %S = 20.8 n2»= 1.6173 m . p . = 3 1 - 3 3 0 c quality p u r e p u r e p u r e containing naphthalene » p u r e y) " » » V » m . w . from the f o r m u l a 138.24 138.24 132.21 130.18 130.18 134.21 118.17 116.16 134.19 148.21 142.19 142.19 f o r m u l a
CO
CO
a)
CO
00
Q c . c . „U Q
UD
W
uoo
00
000
The highest boiling components a r e 1 me-naphthalene and 2 me-naphthalene with boiling points respectively 245° and 241°C.
2. Binary mixtures of approximately equimolar concentration were prepared of these compounds, as shown in table II. 3. These mixtures were analysed by gas-liquid
chromato-graphy. From the chromatograms the correction-factors were calculated as follows:
assuming the correction-factor of tetralin or decalin = 1, the correction-factor of the compound A
mOl% A O A . +• r X A
«A = ^-.r.^& p • T>r in which: aA = correction-factor A mol% B OB ^ ^ compound A
.IS described in chapter II.
B = decalin or tetralin O = peak area
t r a n s d e c a l i n c i s d e c a l i n t r a n s d e c a l i n t e t r a l i n butyl benzene t e t r a l i n indene t e t r a l i n indene t r a n s d e c a l i n indane t e t r a l i n 51.2 48.8 48.2 51.8 49.6 50.4 50.5 49.5 34.1 65.9 49.0 51.0 2 m e - n a p h t h a l e n e t e t r a l i n benzothlophene t e t r a l i n 3 me-benzothlophene t e t r a l i n 1 m e - n a p h t h a l e n e t e t r a l i n dihydronaphthalene 1-2 t r a n s d e c a l i n dihydronaphthalene 1-4 t r a n s d e c a l i n 37.4 62.6 48.2 51.8 52.6 47.4 54.8 45.2 51.4 *) 48.6 51.9 **) 48.1 *) dihydronaphthalene contained naphthalene a s i m p u r i t y
the exact composition i s dihydronaphthalene 1-2 49.0
naphthalene 2.4 t r a n s d e c a l i n 48.6 **) the exact composition i s dihydronaphthalene 1-4 50.4
naphthalene 1.5 t r a n s d e c a l i n 48.1 T h e naphthalene a s impurity was d e t e r m i n e d from the c h r o
-m a t o g r a -m in c o -m p a r i n g the peak a r e a of naphthalene to that of t r a n s d e c a l i n with the c o r r e c t i o n - f a c t o r a l r e a d y known for naphthalene.
Before the analyses of the mixtures, the compounds were subjected separately to gas-liquid chromatography to test the purity. It was shown that all components were pure, except dihydronaphthalene 1-2 and 1-4 which contained naphthalene as impurity.
4. The analyses were carried out at varying operating condi-tions to investigate the influence of these on the value of the correction-factors.
The following conditions were varied: a. the temperature (160° - 180° - 2 0 0 ^ 0 b. the immobile phase (partition liquid)
dioctylphtalate on ground firebrick (parts by weight 30-100)
"bitumen" *) on ground firebrick (parts by weight 20-100) c. the gas-flow system:
the reference and column side of the katharometer in serie or separated (parallel), as shown in fig. 1
s e r i e S = s a m p l i n g s y s t e m R= r e f e r e n c e s i d e C : c o l u m n side r e f e r e n c e - a n d c o l u m n s i d e in s e r i e r e f e r e n c e - a n d c o l u m n s i d e s e p a r a t e d Fig. 1
The c a r r i e r gas used, was nitrogen, the column diameter 0.4 cm and the column length 270 cm. The bridge current was 100 mA. The conditions d u r i n g the analyses were kept c o n s t a n t . The samples injected were approximately of the same size in order to have the same measuring accuracy. 5. Interpretation of the chromatograms.
The area of a peak is calculated as the height times half-band width. From the known mol-ratio and the calculated a r e a - r a t i o from the chromatogram, the correction-factor was calculated. The correction-factor found, is then ap-plied to calculate the mol-concentration.
ttAOA
I X O B
"^01% B = ^ ^ ^ 0 ^ ^ . 100% The results are shown in table III.
mixture t r a n s decalin cis decalin t r a n s decalin t e t r a l i n butyl benzene t e t r a l i n indene t e t r a l i n indene t r a n s decalin indane t e t r a l i n dihydronapht. 1-2 t r a n s decalin dihydronapht. 1-4 t r a n s decalin 2 me-naphthalene t e t r a l i n benzothlophene tetralin me-benzothiophene t e t r a l i n 1 me-naphthalene t e t r a l i n operating conditioni^ mol r a t i o 1.050 0.931 0.984 1.020 0.517 0.961 1.010 1.048 0.597 0.931 1.110 1.212 A a r e a r a t i o 0.950 1.168 0.888 1.093 2.002 1.070 0.938 0.900 1.388 a 1.00 1.08 0.87 1.11 1.035 1.03 0.95 0.94 0.83 B a r e a r a t i o 1.067 a 1.09 c a r e a r a t i o 1.175 0.848 1.045 0.916 0.826 a 1.09 0.83 1.00 0.85 0.92 D 1 a r e a r a t i o 1.403 0.784 0.705 a. 0.84 0.87 0.85 Operating conditions: A: t e m p e r a t u r e 160OC B; 160Oc gas flow s e r i e p a r a l l e l gas velocity 1.8L n i t r o g e n / h r . column side 2.4L n i t r o g e n / h r .
r e f e r , side 3.0 „ immobile phase dioctylphtalate dioctylphtalate C; t e m p e r a t u r e IBOOC D: 200OC
gas flow p a r a l l e l p a r a l l e l gas velocity column side 1.6L 1.6L n i t r o g e n / h r .
n i t r o g e n / h r .
r e f e r , side 1.44L 1.44 „ n i t r o g e n / h r .
immobile phase bitumen bitumen
A = (mol% found)-(mol% prepared) is theoretically z e r o . The a found in these analyses is + 0.2%
This shows the good reproducibility of the analyses.
Discussion of the results
1. As can be seen from table III, the correction-factors a r e influenced by the operating conditions, though only to a minor extent. Due to these small variations, no attempts
will be made to c o r r e l a t e t h e s e v a r i a t i o n s of the c o r r e c -t i o n - f a c -t o r s -to -the opera-ting condi-tions.
T o show the r e l i a b i l i t y of the a - v a l u e s found in this t a b l e , the a - v a l u e s will be checked one with the other for two c a s e s :
a. F o r the m i x t u r e i n d e n e - t r a n s decalin, the a indene i s found t o be 1.035 (atransdecalin =1)
F o r the m i x t u r e i n d e n e - t e t r a l i n , the a indene is found to b e 1.10 (atetralin =1)
In calculating the a indene with the c o r r e c t i o n - f a c t o r for d e c a l i n , being 1.08 (atetraiin =1), we find 1 . 0 3 5 x 1 . 0 8 =
1.12. T h i s i s in good a g r e e m e n t to the value found (1.10). b . In applying the value of a dihydronaphthalene 1-4 = 0 . 9 4
(atransdecalin =1) to a m i x t u r e of dihydronaphthalene 1-4-t e 1-4-t r a l i n , 1-4-taking 1-4-the a1-4-te1-4-traiin = 1 , we find
«•dihydronaphthalene 1-4 = 0 . 9 4 X 1 . 0 8 = 1 . 0 2
Using this value of adlhydronaphthalene 1-4 m i x t u r e t e t r a l i n naphthalene dihydronaphthalene 1-4 mol% p r e p a r e d 48.7 1.4 49.9 mol% found 49.0 1.4 49.6 A
-0.3
1
p r o v e s to be c o r r e c t .2. Due to the s m a l l v a r i a t i o n s of the c o r r e c t i o n - f a c t o r , it i s
in m o s t c a s e s convenient to take the a v e r a g e value of the c o r r e c t i o n - f a c t o r s for each component, although of c o u r s e the a c c u r a c y will be l e s s .
F o r a r e q u i r e d a c c u r a c y of ±1% absolute, this i s quite p e r m i s s i b l e a s shown in table IV. In this table a r e shown a l s o the Auncorrected, i . e . the deviation between mol% found, if the a r e a i s not c o r r e c t e d , and mol% p r e p a r e d .
2a. In an a t t e m p t to c o r r e l a t e the value of the c o r r e c t i o n -factor to the s t r u c t u r e of the c o r r e s p o n d i n g component, the following can be stated:
a. the m e t h y l - g r o u p has a r a t h e r g r e a t influence on the value of the c o r r e c t i o n - f a c t o r ,
b . the place of the m e t h y l - g r o u p in the molecule has no influence on the value of a. T h i s is a l s o the c a s e for the p l a c e of the double bond in the molecule and for the c i s - t r a n s i s o m e r i s m .
c. the h e t e r o - a t o m has a g r e a t influence on the value of a. Due to the limited data a v a i l a b l e , it is not p e r m i s s i b l e to
c o n s i d e r a, b , and c a s a g e n e r a l r u l e .
formula
CO
00
00
CO
QV
OJ
cn
ro
00
Q.C-C.C.C
CO
00
00"'
^XJ
ex?
0U-'
t ={ ^umcorr. - ^ *) wiUi cL^eci component naphthalene dihydronaphthalene 1-2 dihydronaphthalene 1-4 tetrahydronaphthalene (tetralin) trans decahydronaphthalene (decalin) cis decahydronaphthalene indene indane tetralin butyl benzene naphthalene 1 me-naphthalene 2 me-naphthalene indene benzothlophene 3 me-benzothiophene tnol% found)-(mol% prepared) iol% found, if not corrected -ilin=l. T h u s w i t h a t e t r a l i n = l - ' corr.fact. 0.77 0.95 0.94 1.00 1.08 1.08 1.10 1.02 1.00 0.85 0.77 0.85 0.84 1.10 0.85 0.90 mol% prepaj '«dihydron. "dihydron. A -±0.1 +0.1 -+0.2 ±1.0 +0.3 +0.2 -±0.5 -±0.2 ±0.3 ±0.3 ±0.9 ±0.6 ^uncorr. - see chapter I +1.3 •) +1.3 •) definition -2.2 --2.0 -0.7 definition +3.8 - see chapter I +3.8 +4.0 -2.0 +4.0 +3.0 red. 1-2=0.95x1.08=1.03 1.4=0.94x1.08=1.02can see the tendency of increasing avalues with i n c r e a s ing saturation. In the serie biphenylcyclohexylbenzene -bicyclohexyl the same tendency is found (see chapter II). In comparing the a-values of ethylbenzene and ethylcyclo-hexane, the saturated component has again the highest a-value.
This holds only for comparing aromatics and the c o r r e -sponding saturates, not for olefins and the corre-sponding saturates (compare indene-indane). Due to a complete lack of thermal conductivity data for these components, it is impossible to check the relation of the correction-factor with the thermal conductivity.
In reference to the procedure and data described above, it is interesting to examine the accuracy, implied with the use of the correction-factors in the quantitative interpre-tation of the chromatograms.
If, for instance, a correction-factor different from 1.00 is found, what is then the accuracy in using a correction-factor of 1.00, viz not correcting the a r e a ?
Another question is how the accuracy will be for mixtures of other than equimolar composition, as in these experi-ments it was dealt only with equimolar mixtures.
To show the relation between the accuracy and the value of the correction-factor as function of the composition of the mixtures, the following procedure is followed:
2 components give rise to the peak areas Oi and O2. defining a^^l, then mol% comp.2 = Q Q . 100% without correction mol% comp. 2 = Q Q„ . 100%
a2= correction-factor component 2.
Thus the deviation between corrected and uncorrected mol-concentrations in mol% absolute is
^ = ( 0 1 ^ - 0 1 ^ ^ ) 0 ^ ^ 1 0 0 % 1) If the mol-concentration of component 2=x, then
a02
^ = ü r ? ^ ^ i o o % 2)
Combining 1) and 2) and substituting C for ^
Taking the differential quotient of 3) as zero, the value of X, at which Amax will occur, can be calculated.
xmax. = C ± A/CMÖÖC 4) and herewith Amax. can be calculated. For different values
of a, equation 3) is shown graphically in fig. 2. From this figure one can see clearly, that when a correction-factor of 1.02 is found, it is convenient to neglect this factor, viz it is not necessary to correct the a r e a s , if the required accuracy is ± 0.5% absolute, as the maximum deviation is exactly 0.5% absolute.
If the accuracy required is ±1% only, then a correction-factor of 0.96 or 1.04 can be neglected, viz one does not need apply correction.
Equation 3) and fig. 2 also justify the use of approximately equimolar mixtures, as at this concentration the maximum deviation is obtained. The deviations at other mol-concen-trations will be smaller. The data presented above are thus not flattering.
In relation to this, s t r e s s must be laid on the results and conclusions, stated in chapter II, viz the value of the cor-rection-factor is concentration-independent, under the experimental conditions used. In the investigation as d e -scribed in chapter II the most varying mol-concentrations were used, but it was shown that for a component one value of the correction-factor could be used for the whole con-centration range.
4. An equation can also be derived which shows the direct relation between the value of Amax. (the maximum devia-tion between corrected and uncorrected mol-concentradevia-tion) and the value of a.
Substituting 4) in 3), then it can be derived, that
'Amax. = ^^y^Tj^Y . 100 5) This equation is shown graphically in figure 3.
From figures 2 and 3 it is easy to see, what the maximum deviation will be for a certain value of the correction-fac-tor, and at which mol-concentration this maximum value will occur. In this way one can see directly, whether cor-rection is necessary or not, according to the accuracy required.
5. In the literature the quantitative interpretation of the chro-matograms is often related to the weight-concentrations
there exists a simple relation between the correction-factors for mol-concentrations and the correction-correction-factors for weight-concentrations.
defining a = correction-factor for mol-concentration, and a' = correction-factor for weight-concentration, then Q Q . 100% = mol% component 1.
a ' O i
a'Oi+02 • "^00% = weight% component 1
Then it can simply be derived that the following relation holds:
a' _ M l .
a - M ^ 6^ The question whether the peak areas can be better related
to the weight-concentrations rather than to the mol-con-centrations (29) is conveniently answered by this simple relation.
e . g . w i t h atetralin = 1 , 100 94
adecaiin=1.08 - . a ' = 1.08 X J 3 2 2 1 t h u s a' > a anaphthaiene=0.77—»a' = 0 . 7 7 x ^ ^ 2 2 1 ^^^^ a' < a
Relating the peak areas to the weight-concentrations im-plies m o r e correction in this case.
In another case, e.g. benzene-decalin
78 1
adecalin = 1, OCbenzene = 1.6 — a' = 1 . 6 x J33724 ^^^^ a' < tt
In this case the relation of the peak a r e a to weight-con-centration implies l e s s c o r r e c t i o n .
Conclusions
1. This investigation has shown that the correction-factors vary only little with the operating conditions (variables). 2. The question whether one has to apply correction or not, is directly related to the accuracy required, and to the value of the a. If a differs only little from unity, then correction is not necessary, if an accuracy of ± 1% is r e -quired.
3. This investigation has clearly shown the value of the calibration method, based on correction-factors, and the accuracy implied with the use of the correction-factors.
C h a p t e r IV
SELECTIVE HYDROGENATION OF OLEFINS IN OLE FIN-AROMATIC MIXTURES *)
Introduction
The intention is to study the selective hydrogenation of olefins in an olefin-aromatic mixture. This kind of selectiv-ity is perhaps not of technical importance, but it is interest-ing for analytical purposes.
A study of this selectivity has already been made by sev-eral authors: Waterman et al (52), Vlugter (53), de Kok et al (54), Ipatief and Corson (55), Waterman et al (56). Most of the experiments mentioned above, were carried out in batch, mostly in rotating autoclaves. The experiments dealt with here, were carried out continuously in a small pilot plant. Thus it was possible to study the effect of several reaction variables more definitely. According to Waterman et al (56), in batch experiments with olefinic distillates, the
Pt. Si02. AI2O3 catalyst showed a very good selectivity at 1200c and 10 atm. H2 p r e s s u r e . The Pt.Al2O3.Cl catalyst showed a somewhat irregular behaviour.
In the continuous operations of the present investigation the following catalysts were studied:
1. Pt. Si02. AI2O3: platinum on commercial cracking catalyst 2. Pt.Al2O3.Cl : platforming catalyst
3. Si02.A]203 : commercial cracking catalyst 4. WS2 : tungsten sulphide catalyst
Besides these catalytic runs, thermal runs were carried out also.
Experimental part 1. F e e d s t o c k :
For reason of simplicity of the analysis and to have an a r t i -ficial unsaturated mixture in the gasoline range, a feedstock is prepared by mixing a mixture of hexenes, obtained from the Koninkliike/Shell Laboratorium Amsterdam (from the wax-cracker), and a technical mixture of xylenes (o-p- and *) to be published: R.M.Soemantri and H.I. Waterman, Chimie et Lidustrie.
2. P r e p a r a t i o n of t h e c a t a l y s t : 1. Platinum on silica alumina (56)
Commercial cracking catalyst, pressed into pellets, was impregnated with a solution of chloroplatinic acid in wa-ter. After drying at 100°C for 16 hours, it was reduced in a hydrogen flow at 580°C for 16 hours. The catalyst con-tained 0.5% platinum.
2. Platforming catalyst
A full description of the preparation is given in (56). In the experiments the catalyst was activated at 400OC in a hydrogen flow for one hour prior to use.
3. Silica alumina
A commercial cracking catalyst was pressed into pellets. It was heated for 2 hours at400<^C in a hydrogen flow prior to use.
4. Tungsten sulphide
WS2 pellets, obtained from the Koninklijke/Shell Labora-torium Amsterdam.
5. For the thermal runs the reactor was filled with clean glass balls.
3. D e s c r i p t i o n of t h e a p p a r a t u s (see fig. 1)
The liquid feed is pumped into the preheater. At the en-trance of the preheater hydrogen is supplied from a cylinder via a reducing valve. The gas-liquid mixture is warmed up in the preheater and then enters in the gaseous phase the reactor, filled with the catalyst (reactor volume 50 ml).
The reaction products leave the reactor at the bottom, pass a water cooler and enter the high-pressure separator, in which separation is achieved of the gas and the liquid p r o -duct.
The off-gas is released via a back-pressure, passes an aceton-solid CC^-cooled condenser and finally a gasmeter. The liquid product is collected in a bottle and the evolving dissolved gas joins the off-gas.
The feed-pump is a high-pressure displacer pump. The feed-velocity can be adjusted by varying the stroke of the pump. The preheater and the reactor are electrically heated, the temperatures are measured by means of thermocouples and automatically registered. The pressure in the system is measured by means of a manometer. The gas-velocity can be
regulated by manipulating the reducing valve and the back-p r e s s u r e . It is measured by a wet gasmeter.
FEED-STOCK
0
TC H 7 \ / \ / \ / \ . PREHEATER J ^ M « M A N O M E T E R F P = F E E D PUMP T C = T H E R M O C O U P L E R =REACTOR W C = WATER COOLER S "SEPARATOR B P - B A C K PRESSURE G M = 6 A S - M E T E R JCONDENSER PRODUCT F I G I SCHEMATIC F L O W - S H E E T 4. P r o c e d u r eAfter charging the catalyst to the reactor, air in the s y s -tem was removed by purging the sys-tem with hydrogen and blowing off repeatedly.
After pressure testing the unit, the desired temperature, p r e s s u r e and hydrogen flowrate were established.
Hereafter the feed-pump was started and the feed-rate was adjusted to the desired value.
Before starting a test-run, first a pre-test period was run, in which the desired reaction variables were carefully adjusted. After removal of the product in this pre-test period a test-run was started.
As the high-pressure separator never can accomplish a complete separation of the gas and liquid product, the off-gas is passed via a condensing flask, cooled in an aceton-solid CO2 mixture, to condense out any condensables.
The evolving dissolved gas from the product-bottle passes also this condenser.
5. M e t h o d of a n a l y s i s
The feedstock and hydrogenated products were analysed according to the Fluorescent Indicator Adsorption Method, as described by Criddle and le Tourneau (57). In this method, based on chromatographic separation over silicagel, separa-tion is accomplished between aromatics, olefins and satu-r a t e s , i . e . vesatu-ry suitable fosatu-r this pusatu-rpose.
