Ind. Eng. C h e m . Res. 1990, 29, 707-709
V1 = projected volume from apex to dryer bottom, ft3 V , = initial dryer volume, ft3 Wi = initial dryer charge, lb x , = wall thickness, ft a = projected cone angle, deg 8 = total drying time, h h = latent heat of vaporization, -1000 for water, BTU/lb J. = weight fraction removed based on initial charge
Literature Cited Shevlin, E. J. The Day-Nauta Mixer-Processor. Pharm. Technol. 1978, March, 56-59.
707
Updegrove, L. B. Batch Drying in a Nauta Mixer. Chem. Eng. Prog. 1977, April, 107-112. van den Bergh, W. J. B.; Scarlett, B. Some Improved Scale-up Rules for a Conventional Nautamixer. Zntl. Symp. Mixing 1984, 537-546.
Dennis M. Johns Agricultural Chemicals Process Research 969 Building T h e Dow Chemical Company Midland, Michigan 48667 Receiued for reuieui December 13, 1989 Accepted J a n u a r y 18, 1990
'H NMR Composition Analysis of Styrene-a-Methylstyrene-Butadiene Terpolymer A method for the determination of styrene-a-methylstyrene-1,2- and 1,Cbutadiene terpolymer based on 'H NMR spectrometry data is developed. Lacking any reference method, the accuracy and reproducibility were examined for the mixture of appropriate homopolymers. T h e method is additionally verified by analyzing the dependence of the obtained results for terpolymer compositions upon the conversion as well as upon the chemical composition of the starting monomer mixtures. T h e observed regularities as well as the standard deviation and the difference of the average confirm the applicability of the developed method for terpolymer analysis. Composition and configuration of copolymers affect their physical properties and use. These data are also important for the study of copolymerization reactions. Styrene (S)-a-methylstyrene (MS)-butadiene (B) terpolymers are difficult systems for composition analysis due to the structural similarity of styrene and a-methylstyrene. Most analytical methods are not applicable in that case. As far as 'H or 13C NMR spectrometry is considered, there are many papers dealing with styrene-a-methylstyrene and styrene-butadiene copolymer analysis but none dealing with styrene-cu-methylstyrene-butadiene terpolymer analysis. This is a very specific case as far as 'H NMR spectrometry is considered due to the almost complete overlapping of signals of S, MS, and B in the aromatic and aliphatic parts of the spectra, and thus, a different approach in the analysis is required. In this paper, a method for the determination of S, MS, 1,2B, and 1,4B terpolymer based on 'H NMR spectrometry data is presented. Lacking any standard method, the accuracy and reproducibility were examined based on a mixture of appropriate homopolymers. The terpolymer spectrum is not a simple superposition of homopolymer spectra, due to the impact of distribution of individual monomer units on the chemical shift. Thus, it was necessary to check the applicability of the method on terpolymer samples. This was done by analyzing the dependence of the obtained results on conversion as well as on the chemical composition of starting monomer mixtures. The observed regularities only served to validate the presented analytical method, without intending to explain the reactivity ratios.
Experimental Data Samples. Homopolymers polystyrene, poly(a-methylstyrene), and polybutadiene, prepared by suspension (PS) or emulsion (PMS, PB) polymerization, were precipitated (benzene/methanol) and dried under vacuum until constant weight. Their limiting viscosity numbers [?] determined in toluene at 25 "C were 0.50 for PS, 0.20 for PMS, and 1.39 dL/g for PB. 0888-5885/90/2629-0707$02.50/0
Terpolymers were prepared from three different mixture of monomers: S/MS/B 20/10/70,10/30/60, and 10/60/30 mol % . Reactions were performed in a 1-L autoclave using a "cold" (at 5 "C) emulsion process initiated by the hydroperoxide-iron-sodium formaldehyde sulfoxylate system. Samples of the terpolymers, taken out at different conversions, were terminated, purified by coagulation, precipitated, and dried under vacuum until constant weight was reached: reaction system S, 59 g; MS, 33.4 g; B, 108 g; water, 405 g; potassium myristate, 1.8g; Dresinate 515, 6.75 g; Orotan N, 0.3 g; tert-dodecylmercaptan, 0.3 g; 2,4,4-trimethylpentyl-2-hydroperoxide, 0.253 g; FeS0,-7H20, 0.3 g; EDTA, 0.06 g; sodium formaldehyde sulfoxylate, 2.4 g. NMR Spectrometry. The 'H NMR spectra are recorded on a Varian EM-390 NMR spectrometer (90 MHz) at room temperature. CCl, was used as the solvent (-20% w/v) and Me,Si as the internal standard.
Results and Discussion Figure 1 presents the 'H NMR spectrum of the styrenea-methylstyrene-butadiene terpolymer. The protons of the styrene and a-methylstyrene aromatic rings resonate from 6.8 to 7.4 ppm. Assignations of the olefinic part of the spectra were performed according to Mochel (1967): from 4.6 to 5.0 ppm resonating 2.5 protons on the double bond of 1,2-butadiene; from 5.0 to 5.7 ppm resonating 0.5 proton on the double bond of 1,2-butadiene and 2 protons on the double bond of 1,4-butadiene. The protons of the methyne, methylene, and methyl groups of the aliphatic part of all monomer units, more or less mutually covered, resonate in the area from 0.9 to 2.9 ppm. The signal of the methyl group of a-methylstyrene at 1.2 ppm is the least overlapped by other signals. Therefore, it is used in the analysis of the terpolymer as the characteristic signal for a-methylstyrene. It is better resolved in the terpolymer spectrum, and it resonates at weaker field than in the pure homopolymer spectrum. The areas of the aforementioned regions were denoted by a, b, c, and d respectively (Figure 1). 0 1990 American Chemical Society
708 Ind. Eng. Chem. Res., Vol. 29. No. 4, 1990 Table 11. Reproducibility of Results Determined via 1,2and 1,4-Butadiene Content in Homopolymer Mixtures (mol % ) (1,2B)100/ sample 1,2B 1,4B (1,2B + 1,4B) A 12.5 73.1 14.6 B 11.6 67.9 14.6 C 9.7 59.7 14.0 D 10.1 57.8 14.9 E 9.5 51.8 15.5 F 11.1 59.7 15.7 9
a
7
5
6
3
L
2
i
OPPM
+0.02
Figure 1. 'H NMR spectrum of styrene-a-methylstyrene-butadiene terpolymer. Table I. Comparison of the Known and the Experimentally Determined Composition of Homopolymer Mixtures (mol 7 0 ) homoNMR polymer weighted S MS B S MS B mixture A 9.7 4.2 86.1 9.4 5.0 85.6 B 9.2 79.5 10.4 80.4 8.8 11.7 19.4 69.4 71.3 11.2 C 11.6 17.1 67.3 14.5 17.6 67.9 D 16.3 16.4 13.3 25.4 61.3 25.3 61.2 E 13.5 11.4 70.8 70.9 17.8 F 19.0 10.1 d
-0.72 1.92
ri
+1.17 3.13
-0.47 1.83
The following equations for S-MS-B terpolymer analysis are developed: mMS= d / 3
(1)
ms = a / 5 - d / 3
(2)
m1,2B= b/2.5
(3)
m1,4B= c / 2 - 0.25m1,2B
(4)
mi Emi
(5)
M . = -100
'
1.33
Table 111. Results of the Analysis of Styrene-a-Methylstyrene-Butadiene Terpolymer by 'H NMR Spectrometry (mol % ) sample convsn, % S MS 1,2B 1,4B Starting Monomer Mixture S / M S / B (mol % ) 20/10/70 1 7.6 10.7 8.6 12.4 68.3 2 10.6 10.5 10.5 11.9 67.1 3 12.6 11.0 10.5 13.0 65.5 4 19.7 12.5 7.9 10.9 68.7 5 22.8 9.9 10.2 13.1 66.8 11.1 8.6 12.3 68.0 6 30.3 I 33.5 9.3 10.4 12.5 67.8 Starting Monomer Mixture S/MS/B (mol % ) 10/30/60 8 13.7 11.9 15.4 13.9 58.9 9 19.6 10.2 14.7 11.9 63.2 10 21.1 6.4 17.7 13.0 62.9 11 28.0 9.4 15.8 12.7 62.1 12 30.3 7.8 16.7 12.4 63.1 Starting Monomer Mixture S/MS/B (mol 70)10/60/30 13 8.5 18.4 21.0 60.6 14 20.1 20.0 21.3 58.7 15 27.7 24.6 19.5 55.9 50
tI
where m is the number of moles, M is the mole percent, and i is S, MS, 1,2B, and 1,4B. The repeatability and reproducibility were examined on the prepared mixtures of homopolymers of styrene, CYmethylstyrene, and butadiene. The obtained results, together with the difference of the average (d) as well as the standard deviation ( a ) , eqs 6 and 7 , for all three compo20/ 10/ 70
~ ( N M R-, w,) d =
i=1
n
n-1
Chemical
(6)
(7)
nents are exhibited in Table I. The obtained results exhibit a satisfactory accuracy level for this type of analysis. The best results are obtained for butadiene. The relation between the standard deviation and the difference of the average indicates that there is no systematic error in the butadiene content determination. The results for styrene and a-methylstyrene presented in Table I show that there might be systematic errors in their structure determination. All the results for a-methylstyrene are higher, and for styrene lower, then the reference values.
m
COmpOSiriOn
10/30/60
10/60/30
of t h e starting monomer mixtures,
r I , S/WS/B
Figure 2. Dependence of S + MS content in terpolymer upon the chemical composition of the starting monomer mixtures.
This systematic error is most likely caused by signal overlap in the a-methylstyrene methyl group area. The reproducibility of results is determined by the 1,2and 1,4-butadiene content in the homopolymer mixtures. Their ratio should be constant due to the fact that all homopolymer mixtures were prepared from the same polybutadiene sample. The results are exhibited in Table 11. The obtained reproducibility of the results is considered to be very good ( d = +0.02%; a = 1.33%). The applicability of the method to terpolymer analysis was tested on a number of terpolymer samples prepared by certain conversions and under selected starting monomer mixtures (Table 111). Since no reference method exists, we tried to verify the obtained results by testing
I n d . Eng. C h e m . Res 1990, 29, 709-711
709
the mentioned starting monomer mixtures were not examined. Figure 3 shows that the ratio S/MS for monomer mixture 20/10/70 varies about 0.9 for different conversions. For the monomer mixture 10/30/60, it grows with conversion, increasing from 1.3 to 2.2, and for mixture 10/ 60/30, it slowly falls with conversion from 1.1to 0.8. The observed regularities as well as the results obtained for homopolymer mixtures confirm the applicability of the developed method for terpolymer composition analysis.
0
10
20
30
10 5 conversion
Figure 3. Dependence of the molar ratio MS/S in terpolymer upon the conversion.
their dependence on conversion as well as on the composition of the starting monomer mixtures. It has been determined that the dependence of both styrene and cy-methylstyrene in the terpolymers on the starting monomer composition is very significant (Figure 2). The same is true for the dependence of the molar relationship S/MS in the terpolymer on conversion (Figure 3). For all the samples prepared with the starting monomer mixture S/MS/B 20/10/70, the S + MS content is a p proximately constant and on the average amounts to 2070, for the monomer mixture 10/30/60 amounts to 2570, and for the mixture 10/60/30 amounts to 42% irrespective of the conversion. The minor differences in terpolymer composition (depending on the conversion) within each of
Conclusion The presented method can be applied with satisfactory level of accuracy and reproducibility of results to the analysis of the styrene-a-methylstyrene-butadiene terpolymers. The obtained data make the research of copolymer reactions and reactivity ratios, as well as characterization of terpolymer products, possible. Registry No. (S)(MS)(B)(copolymer), 26376-43-2.
Literature Cited Mochel, V. D. NMR Composition Analysis of Copolymers. Rubber Chem. Technol. 1967, 40 (41, 1200.
Jasenka Muhl,* Vlasta SriBa Vida Jarm, Margita KovaE-FilipoviC INA-Industrija nafte Research and Development 41000 Zagreb, Yugoslavia
Received for review April 20, 1989 Revised manuscript received October 10, 1989 Accepted J a n u a r y 3, 1990
Improving Intermediate Product Yield in Simple Consecutive Reactions
--
An earlier paper discussed a scheme for improving the yield of the intermediate product, R, in the simple series reaction A R S, by removal of intermediate product R t o an inert phase. T h e design charts t h a t were presented are applicable only if t h e residence time of t h e inert phase is extremely small. In this work, design charts are presented for a more general case using the residence time of the inert phase as a separate design variable.
--
The maximum yield of intermediate R for the simple consecutive reaction A R S for a once-through plug flow reactor and first-order kinetics was given by Levenspiel (1975) as
CRmax/CAO =
(kl/k2)k2/(kz-kl'
(1)
where 7P,OPt
- In ( W k J - k, - k l
If k l and k , have different activation energies, eq 1 can be used to choose an optimal temperature to obtain higher yields of R. Alternatively, Kambitsis et al. (1987) presented two schemes for improving the yield of intermediate R during isothermal operation. One of these schemes removed intermediate product from the reaction mixture to an inert phase; thus, A k ' - R & S
R' (inert phase)
where 0888-5885/90/2629-0709$02.50/0
kla = (mass-transfer coefficient)(interfacial area)
-
( m3 transferred) (m2 surface)
(m2 surface)(s)(m3reacting phase) In the solution of the reactor and inert phase balances given by Kambitsis et al. (1987), the concentration of R in the inert phase was assumed to be negligible. This is a good assumption only when the residence time of the inert phase in the reactor is very small, implying a very large flow rate of the inert phase. Herein the equations for the inert and reactor phase balances are derived, accounting for the presence of a finite concentration of R (CRJ in the inert phase. These equations reduce to those presented by Kambitsis et al. (1987) under the limiting condition of C R I = 0.
Cocurrent and Countercurrent Operation A schematic diagram showing both countercurrent and cocurrent contacting between phases is shown in Figure 1. A cocurrent contacting pattern between the inert phase and the reactant mixture is preferred because the driving force for mass transfer of R into the inert phase, i.e., the concentration difference (C, - CRI),has to be sustained to obtain a better overall yield of R. In the countercurrent scheme, a t the feed introduction point, the driving force 1990 American Chemical Society
