HYDROTREATING OF FULL RANGE FCC GASOLINE.doc

HUNGARIAN JOURNALOF INDUSTRIAL CHEMISTRYVESZPRÉMVol. 30. pp. 299 - 303 (2002)HYDROTREATING OF FULL RANGE FCC GASOLINEJ. Hancsók, S. Magyar and A. Lengyel1(Department of Hydrocarbon and Coal Processing, University of Veszprém, H-8201 Veszprém, P.O. Box 158, HUNGARY1MOL Hungarian Oil and Gas Co., H-2443 Százhalombatta, P.O. Box 1, HUNGARY)Received: November 20, 2002Sulphur 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 sulphur species of gasoline originates from this stream. Selective hydrotreating of FCC gasoline may be a favourable technique among the numerous new desulphurising methods. Achievements of a research work, made for hydrotreating a full range of FCC gasoline, are presented in this paper. The authors were able to find combinations of process parameters being suitable 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 lossIntroductionFurther 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 1) 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 been developed which can economically be used to produce low sulphur FCC gasoline with acceptable loss of octane number 6-17.The new desulphurising processes are widely 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 that the column for the distillation of gasoline has to be optimally designed and the cut point well selected 19.Fig.1 illustrates the major optional pathways for post-treating of FCC gasoline. The main features of the processes indicated on this figure were already presented in Table 2. In some cases the light fraction of FCC gasoline is sent to an etherification or alkylation unit for boosting the octane number, while the heavier fraction is hydrotreated. This kind of combination reduces the overall octane loss of post-treating. These processes were not indicated on Fig.1.During the research, the possibility of desulphurisation of a full range FCC gasoline on Pt,Pd/zeolite has been investigated. The aim of the study was to examine the effect of process parameters (primarily temperature and liquid hourly space velocity) on the yield and quality of liquid product and to determine the advantageous process parameters.Table 1 Actual and planned motor gasoline specificationsRegion,country,stateMaximum sulphur content ppm(actual)(planned)Maximum olefin content V/V %(actual)(planned)USA50030 (2006)25no changeCalifornia3015 (end of 2002)4no changeEU15050 (2005)18still not decidedJapan10010 (2008?)not specifiedstill not decidedTable 2 Options for the desulphurisation of FCC gasolineProcessKey featureIndustrialapplicationH2-consumptionOctane lossName of processLicensorsNaphtha hydro-treating (NHT)conventionalyeshighhighvariousa number of firmsNHT+ octane increasezeolite + isomerisationyeshighlowOctgain, IsalExxonMobil, UOPSelective NHTRT-225yesmediumlowSCANfiningExxonMobildual catalyst yesmediumlowPrime-G+IFPcatalytic distillationyesmediumlowCDHydro/CDHDSCDTechSelective NHT + octane increasecombinationyesmediumlowSCANfining IIExxonMobilAdsorptionZn adsorbentyeslowlowS ZorbPhilipsalumina adsorbentpilotlowlowIrvadAlcoaExtractive distillationselective solvent sys.yesnonelowGT-DeSulfGTCOxidationperoxyacidpilotnonelowCEDPetrostarultrasoundpilotnonelowSulphCoBechtelAlkylationsolid acidpilotlowlowOATSBPBio processingbio catalysisnononelowEnchiraFig.1 Major optional pathways for the desulphurisation of FCC gasolineFig.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 meterExperimentalApparatusDesulphurisation 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 Veszprém. 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).CatalystsThe hydrodesulphurising experiments were carried out on Pt,Pd/zeolite catalyst, applying 80 cm3 of it.FeedstockAs 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.MethodsCompositions of feedstock and liquid products were analysed by gas chromatography (CHROMOCTANE) 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 discussionProcess 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 °C and LHSV = 1.0 (Fig.4). Under these conditions the product contained 11 ppm sulphur.Table 3 Main properties of the feedstockDensity (15,6°C), g/cm30.7423Sulphur, ppm63Nitrogen, ppm13Research octane number93.4Motor octane number81.7(RON + MON)/287.6Composition, %n-paraffins4.0i-paraffins31.8olefins24.9aromatics31.7naphthenes7.6Fig.3 Sulphur content of products as function of temperatureFig.4 Hydrodesulphurisation as function of temperatureTaking 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 lower LHSV resulted in higher olefin saturation. The highest olefin saturation (approx. 50 %) occurred when desulphurisation was the lowest. Mainly 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 hinders isomerisation.Table 4 Applied process parametersPARAMETERPROPERTYREACTION TEMPERATURE, °C230-280REACTION PRESSURE, BAR30LIQUID HOURLY SPACE VELOCITY, H-11,0-3,0H2/HYDROCARBON RATIO, M3/M3300Fig.5 Olefin saturation as function of temperatureFig.6 Iso/n-paraffin ratio as function of temperatureFig.7 Loss of octane number as function of temperatureThe 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 h-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.ConclusionsFrom 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; 30 bar; LHSV=1,0; 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 °C thiophenes are not present. This means that if we would cut the feedstock at 70 °C and we would only hydrotreat the heavier fraction, significant octane loss reduction could be reached, but only about 2 or 3 ppm of sulphur would bypass the desulphurisation with the light fraction. 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 accomplished effectively and economically by expedient refinement of light and heavy fractions gained by fractionation.ACRONYMSFCC- fluid catalytic crackingHCN- heavy cracked naphthaLCN- light cracked naphthaLHSV- liquid hourly space velocityMCN- medium cracked naphthaMON- motor octane numberRON- research octane numberREFERENCES1. Dixon-Decleve S.: World Refining, 2001, 12(9), 82. Anon.: Oil Gas European Magazine, 2001, 27(1), 42-433. Sweed N. H.: Petroleum Technology Quarterly, Autumn, 2001, 6(3), 45-514. Reid T. 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, 20015. Bavaro V.: World Refining, 2000, 10(2), 30-376. Maple R. E.: Hydrocarbon Engineering, 2000, 5(2), 46-527. Burnett P. A., Huff G. A., Pradhan V. R., Glasett J. A. and Hurst P.: BP Low Gasoline Technology OATSTM, ERTC 5th Annual Meeting, Rome, 20008. Gentry J., Khanmamedov T., and Wytcherley W.: Hydrocarbon Engineering, 2002, 7(2), 43-449. Debuisschert Q., Nocca J.L. and Cariou J.P.: Prime-G+TM: The Key to FCC Gasoline Desulfurization, Proceedings of the Interfaces2002 Conference, Budapest, 200210. Upson L. L. and Schnaith M. W.: Petroleum and Coal, 2001, 40(3), 139-14611. Shih S. S., Owens P. J., Palit S. and Tryjanowski D. A.: Mobils OCTGAINTM Process: FCC Gasoline Desulfurization Reaches a New Performance Level, NPRA 1999 Annual Meeting, San Antonio, Texas, 199912. Stuntz G. F. and Plantenga F. L.: New Technologies to Meet the Low Sulfur Fuel Challange, 17th World Petroleum Congress, Block 2:Excelling in Refining and Delivering Quality Petrochemicals, Rio de Janerio, 200213. Anon.: World Refining, 2001, 12(8), 2314. Rock K. L.: CDHydro/CDHDS for Ultra Low Gasoline Sulfur, ECTC 2002, Amsterdam, 200215. Irvine R. L. and Varraveto D. M.: Petroleum Technology Quarterly, Summer 1999, 37-4416. Gislason J.: Hydrocarbon Engineering, 2002, 7(2), 39-4217. Turk B., Gupta R. and Arena B.: A New Continuous Catalytic Process for Desulfurization of Syngas and Hydrocarbons, 2002 NPRA Annual Meeting, San Antonio, Texas, 200218. OConnor P. and Mayo S.: Division of Fuel Chemistry Preprints, 2001, 46(2), 381-38619. Golden S. W., Hanson D., W. and Fulton, S. A.: Hydrocarbon Processing, 2002, 81(2), 67-72