HUNGARIAN JOURNAL OF INDUS1RIAL CHEMISTRY VESZPREM Vol. 30. pp. 299 ~ 303 (2002) HYDROTREATING OF FULL RANGE FCC GASOLINE J. HANCSOK, S. MAGYAR and A. LENGYEL1 (Department of Hydrocarbon and Coal Processing, University of Veszprem, H-8201 Veszprem, P.O. Box 158, HUNGARY 1MOL- Hungarian Oil and Gas Co., H-2443 Szazhalombatta, P.O. Box 1, HUNGARY) Received: November 20, 2002 Sulphur content of engine gasoline must be reduced below 50 ppm in the European Union from 2005, and gasoline containing 10 ppm sulphur will have tax allowance [1 ,2]. FCC gasoline is one of the blend stocks being applied in largest amount (about 20-50%). The sulphur content of this is significant (about 50-2000 ppm), therefore 50-95% of the sul~hur species of gasoline originates from this stream. Selective hydrotreating of FCC gasoline may be a fav~urable techmque among the numerous new desulphurising methods. Achievements of a research work, made for hydrotreating a £?11 r~ge of FCC gasoline, are presented in this paper. The authors were able to find combinations of process parameters bemg smtable to produce gasoline blend stock of 11 ppm sulphur content with only 2 units loss of octane number. Keywords: FCC gasoline, desulphurization, olefin saturation, octane loss Introduction Further reduction of the automotive emission can be achieved effectively with complex development of fuels, engine construction, lubricants and other parts of vehicles (catalytic converter, tyre etc.). Currently the sulphur specifications have dominant importance from the point of view of engine gasoline, because combustion products of sulphur species - beside air pollution- are poison the vehicle catalysts. Thus further significant reduction of sulphur content can be expected (Table I) [3]. Three main long-run methods are offered for reducing sulphur content of gasoline, each of which results in lower sulphur content of FCC gasoline: reduction by hydrofining of FCC feed, application of new catalysts and catalyst additives in the FCC unit and desulphurisation of FCC gasoline [4, 5]. These strategies can be used either in themselves or in combination. Nevertheless, desulphurisation of FCC gasoline cannot generally be avoided to meet ultra low sulphur specifications of engine gasoline. The loss of octane number can be very significant (up to 10-15 units) applying conventional hydrotreating of FCC gasoline. Accordingly, this process is not economical from two aspects: partly due to considerable loss of octane number, partly because significant hydrogen consumption. A number of desulphurising processes for FCC gasoline have ~n develope4 which can economically be used to produce low sulphur FCC gasoline with acceptable loss of octane number [6-1_7]. The new desulphurising processes are Wldel y diversified in respect of their principle and technical configuration (selective hydrotreating, adsorption. extractive distillation, caustic extraction etc.). Options for desulphurisation of FCC gasoline are summarized in Table 2 [18]. Some of these processes treat full range FCC gasoline, but others accomplish desulphurisation with only a portion of FCC gasoline. It is extremely important in the latter processes tha~ the colun:n for the distillation of gasoline has to be optunally destgned and the cut point well selected [19]. . Fig.} illustrates the major optional pathways tor post-treating of FCC gasoline: The main features of the processes indicated on th1s figure . were . a~eady presented in Table 2. In some cas~s th~ hght fracuon_ of FCC gasoline is sent to an ethenficatto~ or alkylatl?n unit for boosting the octane number, while the ~ea~1er fraction is hydrotreated. This kind of combmatmn reduces the overall octane loss of tx>SHreating. These processes were not indicated on Fig.l. During the research, the possibility of desulphurisation of a full. range FC~ gasoline on Pt,Pdlzeolite has been investigated. The rum of the study was to examine the effect of process parame~ers (primarily temperature and liquid hourly space veloc1ty} on the yield and quality of liquid product and to determine the advantageous process parameters. 300 Region, country, state USA California EU Japan Process Naphtha hydro- treating (NHT) NHT+octane increase Selective NHT Selective NHT + octane increase Adsorption Extractive distillation Oxidation Alkylation Bio processing Table 1 Actual and planned motor gasoline specifications Maximum sulphur content ppm Maximum olefin content V N % (actual) (planned) (actual) (planned) 500 30 (2006) 25 no change 30 15 (end of2002) 4 no change 150 50 (2005) 18 still not decided 100 10 (2008?) not specified still not decided Table 2 Options for the desulphurisation of FCC gasoline Key feature Industrial application conventional yes zeolite+ isomerisation yes RT-225 yes dual catalyst yes catalytic distillation yes combination yes Zn adsorbent yes alumina adsorbent pilot selective solvent sys. yes peroxyacid pilot ultrasou,nd pilot solid acid pilot bio catalysis no H2-consumption Octane loss high high high low medium low medium low medium low medium low low low none none none low none low low low low low low low ISAL I Octgaln I Prlme-G+I SCAN fining Conventional hydrotratlng I !SAL I Octgaln I Prlm&-G+I Name of process various Octgain, Isal SCAN fining Prime-G+ CD Hydro/ CDHDS SCANfining II SZorb Irvad GT-DeSulf . . CED SulphCo OATS Fig, J Major optional pathways for the desu1phurisation of FCC gasoline Licensors a number of firms ExxonMobil, UOP ExxonMobil IFP CD Tech ExxonMobil Philips Alcoa GTC Petro star Bechtel BP Enchira ~ydrogen, ·-t>~~ m1rogen 1 2 3 31 ~LiqUid product 301 Fig.2 Simplified drawing of the test apparatus. 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 Experimental Apparatus Desulphurisation of FCC gasoline has been carried out in a high-pressure reactor system (Fig.2) at the Department of Hydrocarbon and Coal Processing, University of Veszprem. This consists of a tubular reactor of 100 cm3 efficient volume and is free of back mixing. It contains the same equipments and devices applied in the reactor system of desulphurising plants (pumps, separators, heat exchangers, as well as regulators of temperature, pressure and gas flow). Catalysts The hydrodesulphurising experiments were carried out on Pt,Pd/zeolite catalyst, applying 80 cm3 of it. Feedstock As feedstock of the desulphurising experiments a full boiling range (data of simulated distillation: 6-228 °C) FCC gasoline were used. The major quality features are summarised in Table 3. Methods Compositions of feedstock and liquid products were analysed by gas chromatography (CHROMOCf ANE} and the quality characteristics were calculated by a software from these compositions. Composition of gas products was determined, by gas chromatography (ASTM D 5134-90). Sulphur content was measured by pyro- fluorescence method (ASTM D 5453). The experiments were carried out on catalyst of steady-state activity. by continuous operation. Results and discussion Process parameters of the experiments (Table 4) were selected and based on literature data and on earlier results of the Department. From the results of the experiments it can be stated that crack reactions - resulting in lighter hydrocarbons - have not proceeded in the investigated temperature range, because the yield of liquid products was high (>99.5 %) at every combination of process parameters. The degree of desulphurisation of FCC gasoline depended on the process conditions. Sulphur content of the products (Fig.3) became lower with increasing temperature and decreasing LHSV. The highest level of desulphurisation (80 %) was reached at 280 oc and IRSV = 1.0 (Fig.4). Under these conditions the product contained 11 ppm sulphur. 302 Table 3 Main properties of the feedstock Density (15,6°C), g/cm3 0.7423 Sulphur, ppm 63 Nitrogen, ppm 13 Research octane number 93.4 Motor octane number 81.7 (RON+ MON)/2 87.6 Composition. % n-paraffins 4.0 i-paraffins 31.8 ole fins 24.9 aromatics 31.7 naphthenes 7.6 i 35 ~30+---~~~~~~~----------------~ .:r !~+---------~~~~~~~----------~ ~ 20 r-------------=~~...2~~::------~ ~ 15 5+---~--------~--~----~----~--~--~ 220 230 240 250 270 280 TIH!lperatuno, •c Fig.3 Sulphur content of products as function of temperature 100 ~ 90 .: ao ~ ~ 70 i 00 l 50 40 :t: 30 20 220 230 Fig.4 Hydrodesulphurisation as function oftemperature Taking into account the composition of the feedstock and products it can be stated that the olefin content of each product decreased in proportion to the feedstock. The degree of saturation of olefins as function of temperature is shown on Fig.5. Higher temperature and tower LHSV resulted in higher olefin saturation. The highest olefin saturation (approx. 50%) occWTed when desulphurisation was the lowest. ~iainly paraffins have formed from the olefins. but in a less degree also aromatics and naphthenes. Evaluating the change of the concentration of paraffins it was stated that more n~paraffins than i~paraffins were formed from the olefins. Every product had lower iso/normal paraffin ratio than the feedstock (8.0). This ratio is presented on Fig.6 as function of temperature. The ratio was lower at higher temperatures and lower LHSV. This can be attributed to thermodynamic reasons. because higher temperature binders isomerisation. Table 4 Applied process parameters Parameter Reaction temperature, oc Reaction pressure, bar Liquid hourly space velocity, h" 1 Hzfhydrocarbon ratio, m3/m 3 60 50 ;.!: g 40 ~ 30 = c i 20 '6 10 0 220 230 240 250 260 270 Property 230-280 30 1,0-3,0 300 280 290 Temperature, •c Fig.5 Olefin saturation as function of temperature 7,0 .2 6,0 'E ~ 5,0 ; ~ .!! 4,0 3,0 220 230 240 250 260 270 280 290 Temperatura, •c Fig.6 Iso/n-paraffin ratio as function of temperature 2,5 ~ z 0 2,0 ~ 0 1,5 !!:. ~ 1,0 . ~ 0,5 8 0,0 220 230 240 250 260 270 280 200 Temperatuta, ·c Fig.7 Loss of octane number as function of temperature The outcome of the mentioned chemical changes was the lower octane number of the products. Fig. 7 illustrates the loss of octane number as function of temperature. The largest loss of octane number (2 units in [RON+MON]/2: the average of RON and MON) was observed at 280 °C, LHSV = 1.0 h- 1• Sensibility of every product became lower due to saturation of olefins. By desulphurisation to the same degree, the lowest loss of octane number could be reached with the largest LHSV (3.0 n·1). Removal of the light fraction of FCC gasoline could result in significant reduction of the loss of octane number. or lower sulphur content could be reached with the same loss of octane number. Conclusions From the results of the investigation carried out on Pt,Pd/zeolit catalyst with the use of full range FCC gasoline, having 63 ppm sulphur content it can be stated that at advantageous process conditions (280°C; JO bar; LHSV=l,O; H2/HC = 300) FCC gasoline of 11 ppm sulphur content can be produced with high yield and only 2 units decrease of octane number ([RON+MON]/2: average of RON and MON). About 75 %of the olefins are in the light fraction of the feedstock (below 70 °C). This light fraction may contain very little sulphur, because it was passed through a Merox unit in the refinery, which extracts the mercaptans from the light fraction. Below 70 oc thiophenes are not present. This means that if we would cut the feedstock at 70 oc and we would only hydrotreat the heavier fraction, significant octane loss reduction could be reached, but only about 2 or 3 ppm of sulphur wou~d bypass the desulphurisation with the light fractron. Furthermore, we can raise the temperature of the reactor, and we can reach higher level of desulphurisation without facing further significant octane loss. However, we have to confirm this with further experiments, and this is the aim of our next research work. Nevertheless, our results confirm the opinion that hydrodesulphurisation of FCC gasoline can mainly be accmr~plished effectively and economically by expedient refinement of light and heavy fractions gained by fractionation. ACRONYMS FCC - fluid catalytic cracking HCN - heavy cracked naphtha LCN - light cracked naphtha LHSV - liquid hourly space velocity MCN - medium cracked naphtha MON - motor octane number RON - research octane number REFERENCES 1. DIXON-DECLEVE S.: World Refining, 2001, 12(9), 8 303 2. ANON.: Oil Gas European Magazine 2001 27(1) 42-43 ' , ' 3. SWEED N. H.: Petroleum Technology Quarterly, Autumn, 2001, 6(3), 45-51 4. REIDT. A., BREVORD E. and LAAN M. N. T.: The Challenge of Meeting Future Gasoline Specifications: Pre-treating vs. Post-treating Options around the FCCU, European Catalyst Technology Conference, Antwerp, 2001 5. BAVARO V.: World Refining, 2000, 10(2), 30-37 6. MAPLE R. E.: Hydrocarbon Engineering, 2000. 5~,%~2 . 7. BURNEIT P. A., HUFF G. A., PRADHAN V. R., GLASEIT J. A. and HURST P.: BP Low Gasoline Technology OATS™, ERTC 5th Annual Meeting, Rome,2000 8. GENTRY J., KHANMAMEDOV T., and WYTCHERLEY W.: Hydrocarbon Engineering, 2002, 7(2), 43-44 9. 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