CONFERENCE PROCEEDINGS HUNGAR~JOURNAL OF INDUSTRIAL CHEMISTRY VESZPRBM Vol. 2. pp. 48-52 (2000) PRODUCTION OF ENVIRONMENTALLY FRIENDLY DIESEL FUELS Z. VARGA, J. HANCSOK and F. KOVACS (Department of Hydrocarbon and Coal Processing, University ofVeszprem, P. 0. Box 158, Veszprem, H-8201, HUNGARY) This paper was presented at the Second International Conference on Environmental Engineering, University of Veszprem, Veszprem, Hungary, May 29 -June 5, 1999 This paper examines options for reducing emissions by improving fuel quality. In the scope, the importance of deep hydrodesulphurization and hydrodenitrogenation is discussed which reduce the formation of acid :rains and sulphate particles. The experimental results of the hydrotreating of a gas oil on Ni-Mo/ A}zO.;fpromoter catalyst are presented. The effect of the key process parameters (temperature, pressure, LHSV, hydrogen/hydrocarbon volume ratio) on the yield and quality of products are discussed. Based on experimental results, the advantageous process parameters were determined for producing diesel fuel blending components of 500, 400, 300, 200, 150 and 50 ppm sulphur content. The possible applications of the obtained diesel fuel blending components in themselves or together with others are examined to satisfy the standard specifications of commercial products. Keywords: hydrodesulphurization; diesel fuel; emission reduction Introduction The exhaust gases of diesel engines pollute the environment to a significant extent due to containing CO, COz, NO", S02 and particulates. Therefore, these contribute to the formation of acid rains, green house effect and the reduction of ozone level in the higher atmosphere, which may damage both the environment and human health [1-3]. The emissions of diesel engines which may cause cancers, are 25-35 times higher as compared to gasoline engines. The particles of smallest size are especially harmful; the effects of these were investigated by epidemology and breathing studies, and established to cause asthma, allergies and lung cancer [4]. For this reasons the sulphur and aromatic, mainly polyaromatic, content of automotive diesel fuels was tightened all over the world. For example sulphur content limit of 350 ppm will come into force in the European Union in the year 2000 and 50 ppm in the year 2005, respectively (Table 1) [5-8]. The emissions of diesel engines can be reduced partly by developing engine constructions, improving the quality of fuels and using exhaust gas treating systems (oxidising catalysts, particle filters, NOx~trap) [9-13}. The aim of the present study was to identify and quantify the key process parameters for the hydrotreating of a gas oil to produce diesel fuel blending components of various sulphur contents which meet the requirements of the year of 2000 and the following years. Table 1 Diesel fuel quality requirements at present and in the future MSZ· Requirements in the European Community Properties EN-590 1627 EC EP ECA ET EP ECA ET January 2000 Janu~2005 2010 Density at l5°C, kg m3, max. 820-860 850-860 845 845 845 845 825 825 Distillation 85 vol.% point, oc, max. 350 350 95 vol.% point, oc, max. 370 350 350 360 350 340 d 330 Cetan number, min. 49 48 51 51 51 53 58 d 58 Sulphur content, ppm, max. 500 500 350 200 350 200 50 50 50 Total aromatic content, %, max. Polycyclic aromatic content, %, max. 11 11 11 8 1 d 1 EC: European Council; EP: European Parliament; E CA: EU Conciliation Agreement on fuels and vehicles; ET: European Community Amendment; d: debated -< 98 97 96 LHSV,h"1 -+-1 95 -1,3 ....,._1,6 ~2 94"1"-~-- 320 330 340 350 360 Temperature, oc Fig.J Effect of temperature and LHSV on the yield of the stabilized liquid product We also studied the rate of hydrodenitrogenation (HDN) reactions, taking place parallel to the deep hydrodesulphurization (HDS). We considered this particularly important because only little information is available in the literature about the connection between the change of sulphur and nitrogen contents of the gas oil under the conditions of deep HDS, when the sulphur content of the products is 50-500 ppm [14·18]. However, from environmental aspects the reduction of the nitrogen content of diesel fuels is similarly important, because nitrogen oxides, which are also formed during the burning of the organonitrogen compounds, may cause pollution of the environment (acid rains, ozone formation), corrosion in the parts of the engine and its exhaust system, furthermore they decrease the base content of the engine oil. Experimental The experiments were carried out in the high pressure twin reactor system at our department. This system consists of a tubular reactor of 100 cm3 efficient volume, as well as equipments and devices applied in the reactor system of hydrodesulphurization plants (pumps, separators, heat exchangers, temperature and pressure regulators, gas flow regulators). The feedstock was a heavy gas oil fraction having sulphur content of 9300 ppm, nitrogen content of 217 ppm and total aromatic content of 27.5%. Its detailed properties are given later together with those of the products obtained in the case of using advantageous process conditions. The experiments were carried out on a Ni- Mo/AlzOipromotor type catalyst, which was available in presulphided form. The temperature range of the experiments was 320- 3600C, the pressure 40 bars; the liquid hourly space velocity (LHSV) varied between 1.0 h"1 and 2.0 h-1 and the volume ratio of hydrogen-to-hydrocarbon was 200 dm3 dm"3• 49 1400 1200 ~ 1000 1f ~ 800 <.> 600 ] ,9< :::1 400 --+-1 !;/) • 1,3 200 ... 1,6 • 2 0 320 330 340 350 360 Temperature, °C Fig.2 Effect of temperature and LHSV on the reduction of the sulphur content The properties of the feedstock and products were determined by standard tests methods: sulphur content by X-ray fluorescence spectrometry, aromatic content by HPLC (MSZ 10907/1998) and nitrogen content by the ASTM D 4629 method. 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 tests methods. Results and Discussion We plotted the yields of the stabilised liquid product as a function of temperature and LHSV. Fig.] demonstrates that both the increase in temperature and decrease in LHSV results in the reduction of the yields of liquid products. The effect of the change in temperature is more significant than that of LHSV. The decrease of the yield can be explained therewith that the rate of liDS, HDN and hydrocracking reactions increases with stricter process parameters. Above 340°C, the yield loss can be placed mainly to the account of the hydrocracking reactions. This is supported by the fact that the amounts of the gas and the gasoline fraction (boiling point < 200°C) increase above this temperature. Fig.2 displays the change of the sulphur content of the products as a function of temperature and LHSV. This demonstrates that both increase in temperature and decrease in LHSV reduces the sulphur content of the products. The effect of the change in temperature is in this regard, too, more significant than that of LHSV. In the case of LHSV values of 1.6 h-1 and 2.0 h- 1 the sulphur content decreases exponentially in the temperature range of 320-350°C and gradually above this. Applying LHSV values of 1.0 h-1 and 1.3 h"1 the rate of sulphur content decreases nearly exponentially with increasing temperature. 50 Table 2 Process parameters for producing products of various sulphur contents Process parameters Sulphur content, ppm Temperature, oc LHSV, h-1 <500 <400 <300 <200 <100 <50 340 1.0 and 1.3 350 1.0; 1.3 and 1.6 360 1.0; 1.3; 1.6 and 2.0 340 1.0 350 1.0 and 1.3 360 1.0; 1.3 and 1.6 350 1.0 and 1.3 360 1.0; 1.3 and 1.6 350 1.0 360 1.0 and 1.3 360 1.0 and 1.3 360 1.0 140,----------------------------, 120 s 100 ·g; 1 80 <=:: g ~ ~ :: ]~r-:-~:_.¥_s_,, -+-1 20 ---1,3 lj --lr--1,6 0 ll--*-2 'i 320 330 340 Temperature, °C I 350 360 Fig.3 Effect of temperature and LHSV on the reduction of the nitrogen content Products having sulphur content of max. 350 ppm (EC limit in 2000) can be obtained only above 340°C. The possible key process parameters for producing products of various sulphur contents are summarised in Table2. We also studied the change of nitrogen content of the products as a function of temperature and LHSV. The results are plotted in Fig.3, which displays that in contrast to the change of sulphur content that of the nitrogen content has a minimum point. The nitrogen content of the products decreases with rising temperature to 340-350"C, then it increases gradually. One explanation for this can be that the nitrogen content of the gas oil fraction is present in aromatic compounds, and the saturation of the rings occurs in the first step of the HDN reaction, before the nitrogen splits from the molecule 'in the second one. From the point of view of kinetics, the increase of temperature is advantageous for the saturation of the rings until a point where thermodynamic hindrance begins to exert a significant effect on the rate of reaction. Consequently, the rate of the HDN reactions is detennined by the rate of the saturation of the rings. Table 3 Summary of the results of the advantageous experiments Properties Feed Experiment stock VZ/1 VZ/2 VZ/3 VZ/4 VZ/5 Process conditions Temp., oc 340 350 350 360 360 Press., bar 40 40 40 40 40 LHSV, h-1 1.0 1.3 1.0 1.3 1.0 H2/HC, dm 3 dm-3 200 200 200 200 200 Yield,% Gas 1.6 2.2 3.2 3.8 5.3 Liquid <200°C both 0.7 1.4 3.3 4.9 >200°C 98.4 97.1 95.4 92.9 89.8 Density, kg rri3 Product quality 860 850 855 853 848 846 Sulphur cnt., ppm 9300 350 260 150 80 40 Nitrogen cnt., ppm 217 11 33 12 53 32 Aromatics, % mono 16.9 20.5 22.6 23.1 23.4 di 8.1 6.6 6.1 5.5 5.2 poly 2.4 1.6 1.4 L3 1.2 total 27.5 28.7 30.1 29.9 30.0 Assay ibp. 188 180 193 188 186 191 lOvol.% 284 268 274 272 269 267 30vol.% 309 303 307 305 301 299 50 vol.% 324 320 322 321 319 322 70vol.% 336 333 335 335 331 334 90vol.% 354 351 352 353 351 350 fbp., 369 362 363 365 362 361 Flash point, oc 70 58 79 70 62 66 Cetanindex 55 56 56 56 61 61 CFPP,OC 0 2 2 2 1 1 From the aspect of the environmental protection the reduction of both the sulphur and the nitrogen content of diesel fuels is very important. Therefore, we plotted the HDS and HDN activity in one diagram to determine the optimal process parameters for producing diesel fuel blending components of low sulphur and nitrogen contents (FigA). However, we assessed that the optimal process parameters for the HDS and HDN reactions differ from each other. In consequence. a compromise is necessary concerning the sulphur and nitrogen content of the products. For the time being only the sulphur content of diesel fuels is limited, we determined the process parameters for obtaining products, which can meet the present and the expected requirements. The results of the advantageous experiments are summarised in Table 3. These data display that the properties of the products meet the demands of EN 590 and MSZ 1627 standards, except CFPP. However, the CFPP requirements can be satisfied by blending the improper products with light gas oil or/and applying flow improving additives. The data concerning the distribution of the aromatic content support that saturation of aromatics also takes place parallel with the HDS and HDN reactions, though not to a considerable extent. We estimated jhe emissions of the products of the experiments. The equations approved by the EPEFE ·were used to determine the potential of emitting CO, Table 4 Emission potential of the products and feedstock Emission, Feed Experiment gkm"1 stock VZ/1 VZ/3 VZ/4 VZ/5 co 1.341 1.312 1.322 1.307 1.301 HC 0.093 0.083 0.086 0.066 0.065 NOx 0.943 0.942 0.942 0.942 0.942 PM 0.159 0.060 0.060 0.0582 0.057 hydrocarbon (HC), NOx and particulate matter (PM) [19]. CO (g km" 1 ) = -1.3250726 + 0.003037d- 0.025643cpA- 0.015856CN + 0.0001706T95 (1) HC (g ~-1) = -0.293192 + 0.0006759d- 0.0007306cpA - 0.0032733CN- 0.000038T95 (2) NOx (g km" 1 ) = 1.0039726- 0.0003113d + 0.027263cpA 51 100 100 90 90 80 80 ~ ~ :t 70 70 -~ ·E g g (/) 60 60 s @ LHSV,h-1 :r: 50 ......,._ 1 50 ---*--1 40 --1,3 40 ---1,3 30 30 320 330 340 350 360 370 Temperature, oc Fig 4 Effect oftemperature and LHSV on the HDS and HDN activities - 0.0000883CN- 0.0005805T9s PM (g km- 1 ) = [-0.3879873 + 0.0004677d + (3) products that contributes to the reduction of particulate emission of diesel engines. 0.0004488cpA + 0.0004098CN + 0.0000788T95] · · [1 - 0.00016(450- cs)] (4) where d- density, kg m·3; cpA- polyaromatic content, %; CN- cetan number; T95 - back-end volatility, °C; Cs - sulphur content, ppm. The data concerning the products and the feedstock are summarised in Table 4. Based on these data we established that reduction of the sulphur content significantly contributes to the decrease of the particulate matter emission. However, the values of the other emissions change little or not at all. Conclusions We were able to produce diesel fuel blending components on the applied catalyst which satisfy the present (year 2000) and the expected (year 2005) requirements. The sulphur content of the feedstock can be reduced in one step to a great extent, and this decreases significantly the emission of S02 and sulphate particles of the diesel engine, in addition the products are less poisonous for the oxidising and NOx converting catalysts used in the exhaust gas system that leads to further reduction of diesel engine emissions. The optimal process parameters of the HDN and HDS reactions do not coincide, so the products of low sulphur content have relatively high nitrogen content and this may result in emission problems in the future. 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 SYMBOLS LHSV liquid hourly space velocity HDS hydrodesulphurization HDN hydrodenitrogenation CFPP cold filter plugging point HC hydrocarbon PM particulate matter d density CpA polyaromatic content Cs sulphur content, ppm CN cetan number T9s back-end volatility REFERENCES 1. KNocHE A.: Air Quality and Fuel Specifications, The 1997 European Oil Refining Conference and Exhibition, Cascais (Portugal), 1997 2. PERERA P.: Future Air Quality Strategies and Integrated Assessment Post-2000, 3rd Annual World Fuels Conference, Brussels, 1-19, 1998 3. RAINBOW L.J.: European Programme on Emissions, Fuels and Engine Technologies (EPEFE) - Gasoline and Diesel Test Fuels Blending and Analytical Data, SAE Technical Paper Series, Nr 961066, 1996 4. 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