Szebényi, Imre

Széchy, Gábor

English

Periodica Polytechnica (Budapest University of Technology and Economics)

POLYMETHYLBENZENES IN REFORMATES OBTAINED FROM NAPHTHA FRACTIONS By I. SZEBENYI and G. SZECHY Department of Chemical Technology, Technical University Budapest Received May 25, 1974 Polymethylhenzenes - compounds characterized by having three or more methyl groups on a benzene ring - find an increasing importance as starting materials for the synthetic chemical industry. This is due to some advantageous properties of these compounds, e.g. the ring-substitution re-action rates of the polymethylhenzenes are much higher than those of benzene, toluene or even xylenes [1]. At the same time, the steric position of the methyl groups of the in-dividual isomers results in high selectivity in case of chemical reactions. The structure of polymethylbenzenes is generally suitable for the pro-duction of starting materials for heat resistant polymers and cross-linking agents, plasticizers and dyes. Presently the following three polymethylhenzenes are of industrial and commercial importance: 1,2,4 trimethylbenzene (pseudocumene) 1,3,5 trimethylbenzene (mesitylene) 1,2,4,5 tetramethylhenzene (durene) The polymethylbenzene produced in the greatest quantity is pseudo-cumene, the world production of which was about 50,000 tons in 1970 [2]. In Fig. 1 utilization routes are shovt'D. for the three polymethylhenzenes mentioned [2]. Trimethylhenzenes and tetramethylhenzenes are known to be found in the liquid product of catalytic gasoline reforming [3]. In order to devise a scheme for the separation of polymethylhenzenes, the concentration of the compounds in these reformates must be kno'W-n first and the optimum boiling ranges of feedstocks to be reformed must be determined. As a consequence, the aim of the presented experimental work was to determine the concentration of polymethylbenzenes in reformates obtained from feedstocks with different boiling ranges. The effect of the temperature of reforming on trimethylhenzene formation was also studied. 3 Periodica Polytechnica CH. XIX. 1-2. 34 I. SZEBENYI and G. SZECHY O=C-o <Y /Polyesters -::fY I ""0"-.... Epoxy curing agents CH 'ori~ ~ Coaltngs JOp QCH CaOH 1 J Trlmellilic anhydride ~ 4,<;,; re '?9-"A NH2 V Dyes <:>&, ., CH Pseudocumene ". 0 CH3 C'~a -::fY 3 H3Cy~ CH Vilamin£ 3 Pseudocumidtne ~H2 H3COl CH3-Dyes/uffs ~ol\ ~\\\'Q ~c\\ol\ ~ H3CQ CH3 /1es~I~~ Chemical reaction A I· . .J I ~ Q • • n IOXluan ~Ob;'~ ~ /1esitYI~~~ HOOCn~Development product Y hi"gh temperature application possible CaOH Trimesic acid 0"" "",0 O ",cXXc"'" -' Polymers H3C 11 CH3~0 1 oL-£poxyresins H3C ~ CH3 ""'c ~ c'" ~ Dye stuffs 0"'" ""0 Durene Pyromelllfic anhydride Fig. 1. Utilization routes of three polymethylbenzenes Experimental As starting material in the experiments a desulphurized naphtha of Ro-maskino origin was used, obtained from the feedstock of a reforming unit in the Danube Refinery, Szazhalombatta. Three fractions obtained by laboratory distillation from this naphtha were used as feedstocks. Characteristic properties of the starting naphtha and the three fractions are given in Table 1. The expe-riments were first carried out in a high-pressure microreactor apparatus and then repeated in a larger experimental reactor system [4]. Microreactor was chosen because several experiments have been carried out also ,~ith pure model compounds and small quantities of these compounds were at disposal. At the same time, it was desirable to maintain the com-parability between the experiments with naphtha fractions and pure model POLY21JETHYLBENZENES IN REFORMATES 35 Table 1 Properties of de sulphurized feedstocks Straight-run Fraction distilled Straight-run naphtha of from base material naphtha from Romaskino ori"ain (basic I I the Srony material) A B C refinery ASTM Distillation, DC I I Initial boiling point 75 100 126 154 82 10% 98 I 109 136 I 158 100 50% 129 I 128 147 165 130 90% 164 151 164 176 166 End point 185 164 178 189 188 Density, dio 0.740 0.743 0.758 0.772 0.741 Hydrocarbon composi-tion % by weight CB paraff:\ns 15.4 21.6 12.0 1.3 14.7 Cs + paraffins 24.8 22.7 40.2 51.8 30.8 total paraffins 56.2 56.1 53.5 51.3 56.1 CB naphthenes 8.6 11.6 6.9 La 8.1 C9 naphthenes 9.0 9.9 13.0 7.9 9.6 <;'0+ naphthenes 7.0 3.9 11.2 20.7 9.5 total naphthenes 33.2 33.3 32.4 29.6 33.8 Cs aromatics 4.1 5.5 6.2 2.9 3.8 CH aromatics 3.8 2.2 7.0 14.1 4.6 Trimethylhenzenes 1.1 0.6 1.6 3.3 I 0.9 total aromatics 10.3 10.4 13.9 17.0 9.8 total olefins \ 0.3 0.2 I 0.2 0.3 I 0.3 Per cent by weight I \ of the basic material I 100 30.6 22.1 12.1 -compounds. The catalyst applied in all experiments was a commercial platinum catalyst, which is presently used in Hungarian reforming units. The micro-reactor had an inner diameter of 6.8 mm, therefore the commercial catalyst had to be crushed and the fraction v"ith particle size 0.63 to 0.80 mm was filled into the reactor tube. In case of the larger reactor, the catalyst was used in its original form. Product gases were not recycled to the reactor in either case, but instead, hydrogen from a cylinder was led through the reactor. The microreactor tube contained 2 ml of crushed catalyst, the experiment-al reactor had a catalyst volume of 100 ml. Because of the small size of the microreactor, in general no quantitative relationships valid for large scale operations can be established. For this reason, material balances were not 3* 36 1. SZEBENYI and G. SZECHY considered in the present work, although the liquid yields (reform ate percent-ages by volume and by weight of feedstock) were determined. However, in order to compare yields of our microreactor unit with those of the industrial plant, several runs were carried out with the same naphtha feedstock as used in the reforming plant in the Szony refinery. Of course, no parameter values completely equivalent to the large scale parameters· could be set, as the industrial unit contained three adiabatic reactors connected in series, and our apparatus contained a single isothermic reactor. Hence, temperature drop and reheating could not be simulated. The test parameters were the following: temperature: 500 DC pressure: 32 kp/cm2 liquid hourly space velocity: 2.2 ml/ml hour gas/liquid ratio: 1380 ml/ml feed (H2: CH mole ratio 11:1) The industrial reformate and products of two microreactor runs are compared in Table 2. Table 1 shows the hydrocarbon composition of the naphtha feedstock. Table 2 shows that beginning at isopropylbenzene, hence just in the range of Cg aromatics, there is quite a good agreement between the industrial reform ate and the two microreactor products. In spite of the great difference in size, our experiments permit to draw conclusions of quantitative rather than only of qualitative character. Table 2 Composition of reformates from industrial and microreactor units Quantity in the reformate, per cent by weight Component Industria! Microreactor Microreactor reformate product product run No. 1 run No. 2 Methylbenzene 10.8 6.9 6.9 Ethylbenzene 3.7 2.S 3.1 1,3 and 1,4 dimethylbenzene 10.0 6.9 7.1 1,2 dimethylbenzene 4.1 2.8 2.9 Isopropylbenzene 0.4 0.5 0.4 n-propylbenzene 1.3 1.4 1.1 1,2,4 trimethylbenzene S.O 4.4 4.S 1,3,S trimethylbenzene l.S 1.2 1.3 1,2,3 trimethylbenzene 1.6 1.6 1.8 In the reforming experiments, only the temperature was change d (be-tween 470 and 530 DC), the other three parameters were held at the follo,ving constant values: POLYMETHYLBENZENES IN REFORMATES 37 pressure: 30 kpjcm 2 liquid hourly space velocity: 3 mljml hour gasJIiquid ratio: 1300 mljml feed The value of the gasJIiquid ratio corresponds to ~ : CH mole ratios of 10.9 : 1. 9.2 : 1 and 10.2 : 1 in case of fractions A, B and C, respectively. The products of the reforming experiments were analyzed by a gas chromatographic method developed for this purpose at our Department [5]. Results Table 3 shows the trimethylbenzene content of the reformates obtained from fractions A, Band C at different reforming temperatures in the micro-reactor. The data in Table 3 are represented in Figs. 2, 3 and 4. Fig. 2 shows that the reformate obtained from fraction A contains 4.5 to 5 per cent by weight of 1,2,4 trimethylbenzene, while the other two isomers are present wt; l 3 2 1,2,3 trimelhylbenzene ~-~====~~====~!=====5t :::z 1,3,5 trimethylbenzene "70 480 "90 500 510 520 530 Temperature °C Fig. 2. Trimethylbenzenes in reformates obtained from fraction A in microreactor in quantities of only about 1 %. This can be explained by the fact that 1,2,4 trimethylbenzene has a far greater thermodynamic stability than the other two isomers. The rise of temperature slightly increases the 1,2,4 trimethyl-benzene content of the reformate, but it practically does not affect the for-mation of the other two trimethylbenzenes. Fig. 3 shows the trimethylbenzene content of the reform ate obtained from fraction B at different temperatures. In this case, rising of the reforming temperature had a much more marked effect on the formation of 1,2,4 tri-methylbenzene than in case of the first fraction. The quantity of the other two isomers increased but slightly with the temperature. 38 "'~ I : r 5 3 2 I. SZEBENYI and G. SZECHY 1.2,4 trimethylbenzene F3 Irimethylbenzene _-!L---------•• --------~:r-------_::: • c 1,70 480 1,90 500 510 520 530 Temperature °C Fig. 3. Trimethylbenzenes in reformates obtained from fraction B in microreactor wt% 8 1, 2/1 trimethylbenzene 7 6 5 F,3 trimelh!//~nzene 3 1,3,5 trimethylqenzene • 2 1 470 480 "90 500 510 520 530 Temperature cC Fig. 4. Trimethylbenzenes in reformates obtained from fraction C in microreactor POL YMETHYLBENZENES IN REFORMATES 39 Fig. 4 shows the results obtained with the highest boiling fraction. The effect of temperature increase is the most advantageous in this case. The reformate obtained at 530°C had a 1,2,4 trimethylbenzene content of 8.7% by weight. The rise of temperature enhances also the formation of 1,3,5 and 1,2,3 trimethylhenzenc, and the 1,2,3 trimethylhenzene (hemimellitene) content of the reformate is as high as 3 % by weight. Results of the experiments carried out in the larger reactor (100 ml volume of catalyst) are given in Table 4. Comparison of Tables 3 and 4 shows Table 3 Concentration of trimethylbenzenes in reformates obtained in microreactor (catalyst volume: 2 ml) Percentage by weight of the refannate obtained from fraction A B C Component Reforming Reforming Reforming temperature, °C temperature, °C temperature, QC 470 490 510 530 470 490 510 530 470 490 510 1,2,4 trimethylbenzene 4.4 4.5 4.9 5.6 5.1 5.7 6.7 8.2 4.1 5.5 6.9 1,3,5 trimethylbenzene 1.0 1.0 1.1 1.3 1.2 1.4 1.5 1.8 1.1 1.5 1.9 1,2,3 trimethylbenzene 1.1 1.2 1.2, 1.3 2.3 2.3 2.5 2.6 2.3 3.0 3.3 I Table 4 Concentration of trimethylbenzenes in reformates obtained in a reactor containing 100 ml of catalyst Percentage by weight of the reformate obtained from frac tion Component temperature, °C I temperature, QC temperature, cC 530 8.7 2.3 3.3 RefO~g I Refo:mg 1\ RefO~g 470 , 490 , 510 , 530 I 470 i 490 1 510 I 530 I 470 , 490 1 510 , 530 1,2,4 trimethylbenzene 1,3,5 trimethylbenzene 1,2,3 trimethylbenzene 4.81 4.9 5.1 5.3 4.8 4.9 6.2 1.0 \1.3 1.4 1. 7 1.1 1.3 1.6 1.2 [ 1.4 1.4 1.5 1.6 :U 2.2 I 7.2 4.1 1.7 1.2 2.3 2.2 I 6.0 7.0 7.8 1.2 1.5 2.1 2.3 2.41 2.7 a fair agreement between the results obtained in the latter case and in the mic-roreactor. As an illustration, the trimethylhenzene content of the reformate obtained from fraction C in the larger reactor system is shown in Fig. 5. The trimethylhenzene content of these reformates is very similar to those shown in Fig. 4. The trimethylhenzene yield is slightly lower than in case of the corresponding microreactor experiment. 40 I. SZEBENYI and G. SZECHY The 1,2,4,5,- and 1,2,3,5 tetramethylhen2<ene contents of the reformate. were also determined. These compounds were found in the experimental re-formates in concentrations always helow 1 % by weight. " 6 1,2,4 trimethyfbenzene 1.2,3 Irimethyfbenzene . ..---t' -!-__ -!----.cr---470 lt80 lt90 500 570 520 530 Temperature °C Fig. 5. Trimethylbenzenes in reformates obtained from fraction C in a reactor containing 100 ml of catalyst Discussion Two peculiarities were observed: the advantageous effect of the tem-perature rise on the trimethylhenzene yield (and especially on that of 1,2,4 trimethylbenzene), and the increase of this effect in case of the heavier fractions. In order to study these effects in more detail, experiments have been carried out ~ith different pure hydrocarbons; it was found that the quantity of alkylhenzenes formed by dehydrogenation of the corresponding alkylcyclo-hexanes did not increase at higher temperatures; on the contrary, the rise of temperature impaired the yield. Experiments with pure n-nonane and n-decane showed, however, that the increase of temperature greatly enhanced the dehydrocyclization of paraffins and the formation of 1,2,4 trimethylhenzene. Since Cg paraffin hydrocarbons occur in naphthas in much greater con-centrations than do trimethylcyclohexanes, the temperature rise is advan-tageous. This influence is especially marked in the case of the higher boiling frac-tions because these contain more Cg and heavier paraffins. In our case, for ins-POLYMETHYLBENZENES IN REFORMATES 41 tance, the CH paraffin content of fractions A, Band C was 22.7, 40.2 and 51.8% by weight, respectively. In case of the heavier fractions C10+ naphthenes may also yield trimethyl-benzenes by hydrocracking and dehydroisomerization. Our experiments have shown that by reforming heavier naphtha fractions (boiling above 130 °C), reformates containing approximately 9% by weight 1,2,4 trimethylbenzene can be obtained. Such streams can be considered as possible feedstocks for the pro-duction of 1,2,4 trimethylbenzene. As this compound is relatively easy to be separated by distillation from the reformate, the most suitable way for the production of other required polymethylbenzenes seems to be the separation of this compound and formation of other polymethylbenzenes by means of chemical conversion methods (isomerization, disproportionation, alkylation) from 1,2,4 trimethylbenzene as starting material. Summary Concentrations of tri- and tetramethylbenzenes in reformates obtained from three naph-tha fractions at temperatures between 470 and 530°C were determined. The experiments were carried out on a commercial Pt reforming catalyst in a microreactor and then repeated in a larger experimental reactor. Higher boiling fractions gave better trimethylbenzene yields and higher temperatures enhanced trimethylbenzene formation especially in case of higher boiling fractions. Max. 8.7 per cent by weight 1,2,4 trimethylbenzene was found in the reformate obtained at 530°C from the fraction boiling at 154 to 189 QC. Tetramethylbenzene content of the reformates was always below 1 % by weight. In the <; aromatics range, compositions of experimental reformates were in good agreement with an industrial reformate. References 1. CONDON, J.: Journal of the American Chemical Society 70, 1963 (1948) 2. OCKERBLOO::II, N. E.: Hydrocarbon Processing 51, No. 4. 114. (1972) 3. WINGERTER, K. H.: Chemische Technik 14, 333 (1962) 4. HEVESI, J.: Erdol und Kohle 24, 687-689 (1971) 5. ACKER1B.NN, L.-SZEBENxi, L-VER::IIES, E.: Periodica Polytechnica Chem. Eng. 16, 279-284 (1972) Dr. Imre SZEBENYI } Gc1bor SZECHY H-1521 Budapest 

POLYMETHYLBENZENES IN REFORMATES OBTAINED FROM NAPHTHA FRACTIONS

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POLYMETHYLBENZENES IN REFORMATES OBTAINED FROM NAPHTHA FRACTIONS

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Periodica Polytechnica (Budapest University of Technology and Economics)