HUNGARIAN JOURNAL OF INDUSTRIAL CHEMISTRY VESZPREM Vol. 30. pp. 177 -180 (2002) INVESTIGATION OF THE PRODUCTION OF GAS OIL OF LOW AROMATIC CONTENT J. HANCSOK and Z. VARGA (Department of Hydrocarbon and Coal Processing, University ofVeszprem, H-8201 Veszprem, P.O. Box 158, HUNGARY) Received: May 21,2002 The demand on gas oil of low aromatic content was increasing significantly in the last years. The reasons of this the more and more stricter quality requirements of dieseL fuels, partly the extending use of these products as good quality feedstocks of steam cracking for producing light olefms. In Hungary, the growing demand on gas oil of low aromatic content is expected in the near future. Its reason is that the restriction of the polyaromatic content of diesel fuels came into force in the European Union in the year 2000 and the assumed growing in the quantity requirements of ethylene and propylene may cause extended inquiry for this base stock. The experimental results of producing gas oil of low aromatic content are presented. In the first step of the dual stage process the sulphur content of the gas oil was reduced (slO ppm), in the second one the hydrodearomatization of the product on Pt/Al20 3 catalyst was studied. The effects of the process parameters (temperature, LHSV, pressure, etc.) on the yield and product quality are discussed. On the base of experimental results the advantageous key process parameters were determined. The possible applications of the obtained gas oils as diesel fuel blending components and the feedstock of the steam cracking were examined. Keywords: hydrodearomatization, gas oil, emission reduction, steam cracking feed, noble metal catalyst Introduction The restriction of the exhaust gas emission (CO, S02, NOx, particulate matter) have been kept stricter in Europe (for example the emission limits of light duty diesel engines are given in Table 1) and other parts of the world [1, 2, 3, 4, 5, 6]. To satisfy all requirements is only possible by developing of engine construction, improving the quality of fuels and using exhaust gas treating system (oxidizing catalysts, particle filters, NOx-trap) [7, 8, 9, 10, 11]. The present and the future quality requirements of diesel fuels are summarized in Table 2. From the aspect of exhaust gas emissions of the diesel engine very important compounds are the aromatics, mainly the polyaromatics, which have carcinogenic effect in themselves, further the soot originating from the partial burning of these compounds in the engine are carcinogen as well [12, 13, 14, 15). Besides the human health and environmental effects the aromatic compounds may cause problems in the engine because they have low cetane number. In addition to diesel fuel the petrochemical industry uses gas oil in growing quantity as base stock of steam cracking, where the aromatic compounds have also harmful effect, as they increase the quantity of the less valuable fuel oil, tar and coke Il6, 17]. The aim of the present study was to identify and quantify the key process parameters for the hydrodearomatization (HDA) of a previously hydrodesulphurized gas oil fraction on Pt/A120 3 catalyst. We studied the effects of key process parameters on the saturation of aromatic compounds. On the basis of the experimental results the advantageous process parameters were determined. The obtained products were qualified from the point of view using them as blending components of diesel fuel and feedstock of steam cracking. Experimental The experiments were carried out in a high pressure twin reactor system at the University of Veszprem department of Hydrocarbon and Coal Processing. This system consists of a tubular reactor of 100 cm3 efficient volume, as well as equipment and devices applied in tbe reactor system of hydrotreating plants (pumps, 178 Table 1 The emission limits of light duty diesel engines in the European Union Standard Emission limits, g/km PM NO, HC co HC+NO, Euro2- 0.080 1.06 0.71 1996 Euro 3- 0.050 0.50 0.64 0.56 2000 Euro 4- 0.025 0.25 0.50 0.30 2005 Table 2 The present and the future quality requirements of diesel fuels EN590 EU Requirements (2000) (2005) Cetane number, min. 51 51 Density kg/~' 820-845 820-845 15°C,max. Polyaromatics, %,inax. Total aromatic content, %, max. Distillation of 95lv% ac, max. 11 360 Sulphur content 350 ppm, max. 11 360 50* EU (2008/ 2009) ? ? ? ? ? 10 World Wide Fuel Charter, Category 3 4 55 55 820-840 820-840 2 2 15 15 340 340 30 5-10 *From the year 2003 tax allowance in Germany for motor fuels having 10 ppm separators, heat exchangers, temperature and pressure regulatorS, gas flow regulators), see Fig.l. The feedstock was a light gas oil fraction previously hydrodesulphurized to avoid the poisoning of the Pt/Al20 3 catalyst; its main properties before and after the treatment are given in Table 3. The temperature range of the experiments was 180- 3000C, the total pressure 40 bar; the liquid hourly space velocity {LHSV) varied between 0,5 h-1 and 2,0 h-1 and the volume ratio of hydrogen-to-hydrocarbon was 600 dm3b:Im3• The experiments were carried out on a Pt/y-Ah03 type catalyst having 0.58 % Pt-content. The properties of the feedstock and products were determined by standard test methods: sulphur content by X-ray fluorescence spectrometry, aromatic content by HPLC. The experiments were carried out on catalyst of permanent activity and by continuous operation. The repeatability of the experimental results was higher than 95% considering the ensemble errors of the technological experiments and test methods. Table 3 The main properties of the feedstock before and after the hydrotreating' Properties Method Feed untreated treated Density, 15°C, kg/m3 ASTM D4052-96 826 816 Cetane number MSZ EN ISO 5165 49 54.5 Cold Filter Plugging Point, MSZEN 116 -30 CFPP, oc Sulphur content, ASTM D2622-98 650 <2 ppm Aromatics, % IP 391:1995 Mono 8.8 9.9 Di 7.5 7.0 Poly 1.7 1.0 Total 18.0 17.9 Distillation data ASTMD86-97 Initial bp., oc 198 190 10 vol. %, oc 219 216 50 vol. %, ac 245 243 90vol. %, oc 283 286 Final bp., °C 297 294 BMCI* 27.6 23.0 *Bureau of Mine Correlation Index Fig.l The flow diagram of the reactor system; Notations: 1, 6, 11, 13, 14, 18, 20, 22, 30, 34, 36, 37, 38: closing valves; 2, 8, 31, 39: control valves; 3, 7, 9, 15: manometers, 4: oxygen converter; 5: dryer; 10, 32: gas filter; 12: gas flow meter/controller; 16, 23: back valve; 17, 19: liquid feeds burettes; 21: liquid pump; 24: pre-heater; 25: reactor, 26: sampling valve, 27, 29: cooler, 28: separator; 33: pressure recorder; 35: pressure controller; 40: wet gas flow meter Results and Discussion After the experiments we determined the yields of the liquid product which were above 99% in every case. These results showed that hydrocracking reactions take place only a little extent or not at all. Fig.2 displays the change of total aromatic content of the products as function of temperature and LHSV. It shows that both process parameters have significant effect on the saturation of aromatics. Studying the effect of temperature on the reduction of aromatic content in case of LHSV o~s and 0.8 b"1, Table 4 Summary of the results of the advantageous experiments Properties Experiment AM/I AM/2 AM/3 AM/4 Process conditions Temperature, oc 280 280 300 300 Pressure, bar 40 40 40 40 LHSV,h'1 0.5 0.8 1.2 2.0 H2/HC, dm 3 /dm3 600 600 600 600 Yield,% 99.6 99.7 99.5 99.6 Product quality Density, kg/m3 810 811 811 813 Sulphur content, <2 ppm <2 <2 <2 Aromatics, % mono 0.5 1.6 2.9 3.6 di 0.08 0.09 0.1 0.4 poly 0.05 O.D7 0.08 0.09 total 0.63 1.76 3.08 4.09 Distillation data, D86, oc initial bp. 185 186 187 187 10 vol.% 214 215 215 215 50vol.% 241 242 242 243 90vol.% 285 285 285 284 final bp. 294 294 295 296 Flash point, oc 78 78 78 79 Cetane number 57.5 57.0 57.0 56.5 CFPP, °C -30 -30 -31 -31 BMCI 20.5 20.8 20.8 21.8 respectively, it . can be assessed that the increase in temperature to about 280°C reduces the aromatic content to a minimum point and then it rises gradually. It can be explained that from the point of view of kinetics the increase of temperature is advantageous for the saturation of aromatic rings until a point where thermodynamic hindrance, which arises from the exothermity of the reaction, begins to exert a significant effect on the rate of reaction. In case of higher LHSV 1.2 and 2.0 h-1, respectively, we found that the aromatic content did not reach a minimum point, but it is expected that further increase in temperature would have the same effect. Studying the effect of the LHSV it can be stated that lower LHSV, that is longer mean residence time, is favourable for reducing the aromatic content. . On the basis of experimental results we assessed that the maximum of the saturation of aromatics was in the temperature range of 280-300°C, within the applied process conditions (e.g. catalyst, feedstock, etc.). So the other properties of products obtained in this range were determined; the results are given in the Table 4. These data display that the aromatic content of the products is significantly lower compared to the feedstock, that caused improve in other properties as well (e.g. cetane number), further the properties of the products meet all the demands of EN 590 standard. 179 Table 5 Emission potential of the products and feedstock Emission, g/km co HC NOx PM 18 ;;:. 16 114 = B 12 ~ 10 ~ 8 " :a 6 Feed untreated treated 1.230 0.092 0.920 0.044 1 '-+-0,Si .--~~--o,sJ ~-r-1,21 1.201 0.065 0.918 0.037 Experiment AM/1 AM/2 AM/3 AM/4 1.185 1.188 1.188 1.194 0.055 0.057 0.057 0.060 0.917 0.917 0.918 0.918 0.035 0.035 O.D35 0.036 ~ 4 2 o+-~~~~~2~'~--~~~+-~~~~~~~ 160 170 }80 190 200 210 220 230 240 250 260 270 280 290 300 310 Temperatul'l), "C Fig.2 Effect of temperature and LHSV on the reduction of the total aromatic content In addition the polyaromatic content and the cetane number of the products satisfy the EC limits which came into force in the year 2000 and the quality requirements of the World Wide Fuel Charter Categories 3 and 4. We estimated the emissions of the products of the experiments. The equations approved by the EPEFE (European Programme on Emissions, Fuels and Engine Technologies) for the light duty diesel vehicles were used to determine the potential of emitting CO, hydrocarbon (HC), NOx and particulate matter (PM) [18]. CO(g I km) = -1.3250726+0.003037 ·d- - 0.025643. cPA -0.015856. CN + (1) +0.0001706·795 HC(gl km) =-D.293192+0.0006759·d- - 0.0007306. cPA - 0.0032733. CN- (2) -0.000038 · Tg5 NOX(g J km) = 1.0039726-0.0003ll3·d + + 0.027263. cPA -0.0000883. CN- (3) -0.0005805 • T95 PM(g I km) = [-{).3879873+0.0004677 ·d + where + 0.0004488. cPA + 0.0004098. CN + (4) + 0.0000788 · T95 1· ·[1-0.00016· (450-c.)J d ·density,. kg/m3 c,. - polyaromatic content, % 180 CN - cetane number T9s -back-end volatility, oc c., - sulphur content, ppm. The data concerning the products and the feedstock are summarized in Table 5. On the basis of these data we established that reduction of the aromatic and sulphur content significantly contributes to the decrease of emission, except NOx. On the basis of these data it can be assessed that production of good quality diesel fuel blending components is only possible by using HDS and HDA processes together. To determine the applicability of the products as base stocks of the steam cracking we applied the Bureau of Mine Correlation Index (BMCI), see Eq.(5), which refers to the hydrocarbon types in the petroleum products. Polyaromatic hydrocarbons have the highest BMCI values (above 100) and paraffin hydrocarbons the smallest ones (below 20). BMCI = 48640 +473.7 ·d15.6 -456.8 VABP 15.6 where V ABP -volume average boiling point, K di;:~ -density, g/cm3 (5) The decrease in BMCI value of the products showed the saturation of the aromatic, mainly the polyaromatic compounds, that improves the quality of the products from the aspect of applying them as base stocks of steam cracking. Conclusions We were able to produce diesel fuel blending components on the applied catalyst which satisfy the present (year 2000) and the future (year 2005) requirements. The aromatic content of the feedstock can be reduced in one step to a great extent, and this decreases significantly the tailpipe emission of the diesel engine, except NOx content. The obtained product is applicable as diesel fuel blending component in itself or together with others in order to suit the standard specifications of commercial products that contributes to the reduction of emission of diesel engines. 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