Alkylation Process For Production Of Motor Fuels Environmental Sciences Essay

Alkylation Process For Production Of force back Fuels Environmental Sciences EssayAlkylation is a process for chemically combining isobutane with nimbleness alkeneic hydrocarbons, typically C3 and C4 olefins, (e.g. propylene, butylene) in the comportment of an caustic gun, usually sulphuric biting or hydrofluoric cutting. The crossing, alkylate (an isoparaffin) has a luxuriously-octane value and is blended into motor and aviation gasoline to better the antiknock value of the fuel. The light olefins argon almost commonly for sale from the catalytic crackers.Alkylate is one of the best gasoline amalgamate components because it is a decipherable burning, very downhearted sulphur component, with no olefinic or aromatic compounds and with full(prenominal) octane and low vapour pressure characteristics.1. Introduction1.1 AlkylationAlkylation is a process for chemically combining isobutane with light olefinic hydrocarbons, typically C3 and C4 olefins, (e.g.propylene, butylen e) in the presence of an dit catalyst, usually sulphuric cuttingulous (H2SO4) or hydrofluoric acid (HF). The convergence, alkylate (an isoparaffin) has a high-octane value and is blended into motor and aviation gasoline to improve the antiknock value of the fuel. The light olefins are most commonly available from the catalytic crackers. Alkylate is one of the best gasoline blending components because it is a c tendency burning, very low sulphur component, with no olefinic or aromatic compounds and with high octane and low vapour pressure characteristics 1.1.2 Advances in alkylation technical schoolnologiesThe alkylation process will last out to be a favoured technology for producing clean fuels.MTBE(methyl-tert-butyl ethanol) phase out in the USA, implementation of the latest european specifications, enlargement of the EU and adoption of spic fuels specifications worldwide are major drivers for refiners requiring more(prenominal), high octane, gasoline blending components tha t do non contain aromatics, benzene, olefins and sulphur. Also as the types of gasoline engine in use worldwide become more uni melodic phrase, in that location will be a general decline in the markets for low octane gasoline requiring more components to be upgraded to high quality fuel. dining table1 shows the major practiced and mechanical advances. Reactor heading improvements are one of the most grand maturements. The former(a) plants used a pump and conviction-tank nuclear reactor system which was knowing to mix the reactants intimately with the catalyst and to remove the exothermic heat of answer for temperature control 2 .It is required that for the desired reactions to continue with the removal of the unwanted reactions, unplayful immix of higher concentrations of dissolved isobutane in the acid phase is necessary. Since the early reactors were inadequate in this respect, new reactor designs evolved which change the degree of acid-hydrocarbon contacting. The si zeableness of good temperature control was similarly realized in the course of time as commercial experience was gained. Regulating the temperature of the reaction mixture in the suitable range was essential for good alkylation. Inadequate temperature control resulted in decreased alkylate translates and octanes and increased acid consumption. Therefore, to avoid these penalties the new reactor designs include improved temperature control techniques as well as improved mixing. The both most commonly used reactor systems which grew out of the reactor development work for H2SO4 alkylation are the Stratford Engineering Companys Stratco contactor and the M. W. Kellogg Corporation Cascade reactor were bubb direct up through liquid HF.There have been improvements in the preparation of run for and this has given rise to growth in alkylation technology 4, 5. The ability to design better fractionators has made higher quality pass onstocks available, and nourishment pretreatment facilit ies have been developed to remove peeing, mercaptans, sulfides, and diolefins military issueively. Bauxite treating, hot water washing, and electrostatic precipitation are roughly of the signifi substructuret developments which have improved product quality and reduced fouling and wearing in downstream equipment. The sulfuric acid recovery process (SARP), developed to reduce the acid consumption in H2SO4 alkylation units was another contribution to alkylation technology. In this process the spent acid from an alkylation unit reacts with a portion of the olefin feed to form dialkylsulfates. The dialkylsulfates are extracted from the reaction mixture with isobutane, and the extract is ae countd to the alkylation unit.TableI Advances in alkylation technology 31) Improved reactorsA) better mixingB) better temperature control2) Recognition and control of operating variables3) Improved feed preparation4) Improved product treatment5) Sulfuric acid recovery process6) Catalyst promot ers7) Mechanical and construction improvement2. Types of alkylation processesThe alkylation process dope be divided up into the sulfuric alkylation process and the hydrofluoric acid alkylation process, in admit alkylation by acidic resin, corroboratory alkylation by solid phosphorous acid and olefin hydrogenation.2.1. The sulphuric acid processThis process uses sulphuric acid as the catalyst and its feedstock are propylene, butylene, amylene, and fresh isobutane.Feedstocks are fed into the reactor which is divided into zones, each containing sulfuric acid, isobutane and olefins feed. The reactor product contains hydrocarbon and acid phases which are disclose in the settler the hydrocarbon phase is washed with caustic and hot water for pH control and thus depropanized, deisobutanized, and debutanized. The alkylate product so formed back end then be used for motor fuel blending or for producing aviation grade blends. The isobutane goes back to the feed. attribute1 Acid catalyze d isobutene dimerization to 2,4,4-trimethyl-1-pentene and 2,4,4trimethyl2-pentene by the standard Whitmore-type carbocation mechanism 3.2.2 The hydrofluoric acid processThis process employs hydrofluoric acid as the catalyst. The two types of hydrofluoric acid alkylation process commonly used are the Philips and UOP (a Honeywell company) processes. While Philips uses a reactor/settler combination system, UOP uses two reactors with ramify settlers 2.The major struggles between sulfuric and hydrofluoric alkylations (HF) are temperature and acid consumption. Sulfuric alkylation requires refrigeration to maintain a low reactor temperature. The acid consumption rate for sulfuric alkylation is over a hundred times that of HF 8.Figure2 Aliphatic alkylation mechanism with hydrofluoric acid as catalyst (a-b) unveiling by addition of HF to the olefin and in the case of a sec.butylcation, hydridetransfer from isobutane to produce a tert.butyl cation, (c) olefin addition to the tert-butyl cat ion, and (d) hydride transfer form isobutane to show alkylate and regenerate the tert-butylcation 3.TableII Research Octane Number (RON) and travel Octane Number (MON) of alkylates typically produced by HF alkylation of isobutane with assorted olefins 3.Olefin feedRONRON + MON / 2MONpropene91 9289.5 90.01-butene94.491.62-butene97.894.6Isobutene95.993.4Pentenes90 9193.4n-pentenes82.5TableIII Research Octane Number (RON) and Motor Octane Number (MON) of alkylates produced by H2SO4 alkylation of isobutane with various olefins at 9-10 C,94-95 % H2SO4 concentration, and isobutaneolefin ratio of 7-91 3Olefin feedRONMONPropene89.087.1n-butene97.893.9Isobutene93.290.3n-pentene91.088.0Isopentene91.288.82.3 Indirect alkylation by acidic resinThis process employs the use of a polar solvent to limit the activity of the acid resin in order to improve the dimerization selectivity. High renewing of isobutene can be obtained at low temperature usually less(prenominal) than 100 C 8, 9 12. On an industrial scale, the recovery of the polar solvent (tertiary butyl alcohol) could serve to regulate the product distribution and also to reduce the amount of oligomer formed during production to less than 10 % 8.The alkylate produced from this technology has a research octane human body (RON) of 99hundred and one and motor octane number (MON) of 9699.2.4 Indirect alkylation by solid phosphoric acidThe principle of indirect alkylation by solid phosphoric acid ( spa) is the same as by acidic resin catalysis the difference being that dimerization over SPA follows an ester- ground mechanism 13. Heavy oligomer formation is mechanistically limited, 10 because the strength of the phosphoric acid ester bond decreases with increasing carbon number of the olefin.Indirect alkylation by SPA is carried out in two locomote selective dimerization of isobutene (from C4 streams) to form diisobutene followed by hydrogenation to form the saturated product isooctane. Selectivity problems and cat alyst deactivation hinder the isobutene dimerization reaction. Because this reaction decides the quality and properties of the alkylate formed, it is a crucial meter in this process.The C4 stream, consisting mainly of isobutene, n-butane, isobutene, and n-butenes, is fed to the dimerization reactor, where isobutene is dimerized selectively in the presence of SPA catalyst. The reaction is exothermic, and heat must be removed to avoid temperature rises that can lead to the formation of undesired oligomers. These oligomers have relatively high molecular weights and boiling points and are not suitable as gasoline blends they also rapidly deactivate the catalyst. Depending on the catalyst, an appropriate solvent may be needed to increase the selectivity toward the dimers. At higher operating temperatures the isobutene derived alkylate quality quick deteriorates due to trimerization and cracking 11.Propene forms a stronger ester bond with the phosphoric acid than the butenes, and it wi ll become the dominant carbocation source 12. The product stream from the reactor is fed to a distillation column, where dimerized and cogent products are separated from the unreacted C4 components and solvent. The dimer is then saturated in a separate reactor to form alkylates in the presence of a hydrogenation catalyst. In order to obtain alkylate quality hydrogenated products from an n-butene rich, isobutene lean feed, the reaction temperature should be less than 160 C and the feed should not contain more than 5 % propene or 10 % pentenes.3. turn tail diagrams of direct and indirect alkylation processFigure3 Block race diagrams of the direct alkylation (HF and H2SO4 catalysed alkylation) configurations evaluated 3. flowing diagram1 This is the base case for direct alkylation, victimization a true off run Iron- tooshied High Temperature Fischer-Tropsch (Fe-HTFT) C4 feed. There is petite isobutane in the straight run feed, which constrains the alkylate slacken off.Flow diagr am2 In order to overcome the constraint imposed by the low straight run isobutane content of C4 feed, a hydroisomerization unit is included in this two-step flow diagram to convert the straight run n-butane to isobutane. The hydroisomerization unit has an midland recycle, with an overall high isobutane confess. Although the alkylate yield may have been considerably improved compared to the base case, most of the C4 olefins have not been converted.Flow diagram3 The ratio of paraffins to olefins necessary for direct alkylation can be balanced by hydrogenating some of the C4 olefins to C4 paraffins in order to increase the alkylate yield.Flow diagram4 The alkylate yield may be further increased by using propene as the alkylating olefin. Propene is more abundant than the C4 hydrocarbons in straight run HTFT feed, which implies that all the hydrocarbons can be hydrogenated and hydroisomerized to isobutane for alkylation with propene. In this case an alkylate yield above 100 % based on the C4 feed can be obtained, but at lower octane number than with C4 material only.Figure4 Block flow diagrams of the indirect alkylation (acidic resin and solid phosphoric acid dimerization) configurations evaluated 3.Flow diagram5 It consists of acid catalyzed dimerization followed by hydrogenation. The direct conversion of isobutene in straight run HTFT syncrude with an acidic catalyst has a low alkylate yield (8 %), since only 8 % of the C4 olefins are isobutene. However, this alkylate has an octane number of almost 100.Flow diagram6 By use of skeletal isomerization, the alkylate quality and yield of n-butenes to isobutene can be improved. The n-butene conversion in the case of acidic resin dimerization is very low, and it is best to isomerize all n-butenes to isobutene. This results in an alkylate yield of 81 %.4 Product yield and qualityIn a fuels refinery there is an incentive to convert normally gaseous products into liquid transportation fuels. The metre and the quality of the liquid fuel being produced are both important, and in terms of alkylate production, the quality is related to the octane number (ON) (1/2) RON + (1/2) MON) of the motor-gasoline. The investment economics is refinery dependent, with octane trammel refineries putting a premium on quality, while refineries with an unsaturated market putting a premium on volume.TableIV Alkylate yield and alkylate octane number measured for the indirect alkylation flowschemes shown in figure4 3s/nDir.alkyl.fowschemeAlkyl.techAlkyl.yld(m%C4)Oct.no.(1/2)RON+(1/2)MON1BasecasestraightrunHTFTHFH2SO42294962 baptistry1+C4hydroisomerisationHFH2SO4212094963 content2+butanehydrogenationHFH2SO410210194964Case3+propenealkylationHFH2SO41971899188The alkylate yield is based on the potbelly of alkylate produced per mass of total straight run high temperature Fisher TropschC4 cut material.TableV Alkylate yield and alkylate octane number calculated for the indirect alkylation flowschemes shown in figure3 3s/nInd ir.Alkyl.flowschemeDim.techAlkyl.yld(m%C4)Oct.no(RON+MON)/25Base case straight runHTFT acridresinSPA872(90)b99876Base case + skeletalisomerisationAcidicresinSPA81859999The alkylate yield is based on the mass of alkylate produced per mass of total straight run high temperature Fischer-TropschC4 cut material.b yield including coproduced kerosen5 Environmental aspectsThe environmental burdens due to the treatment of free hydrofluoric acid (HF) losses from an alkylation unit cannot be overlooked. The reality is that hydrofluoric acid losses from the unit do occur through side-reactions, forming organic fluorides, which become entrained in product streams, and through direct entrainment of free HF in a heavy hydrocarbon waste stream 6, 7.The environmental aspects associated with the liquid phase direct alkylation processes led to the development of solid acid direct alkylation.From an environmental stand point, indirect alkylation is preferred to direct alkylation and that flowscheme5 ( figure4) is the most environmentally friendly 3.6 ConclusionIt was found that the choice of technology depended on the different culture priorities, namely, the following (a) Least complexity, (b) Highest alkylate yield7 Literature1 Encyclopedia of earthly concern domicil page. http//www.eoearth.org/article/alkylation_in_petroleum_refining (accessed Aug.30, 2010)2 Albright, L.F. Comparison of Alkylation Processes Chem.Eng.,209, Oct.10, 1996.3 Wang, Y. Subramaniam, B., 6874 ,Ind.Eng.Chem.Res., Vol.47,number10, 2008.4 Albright, L.F. Alkylation Processes Using Sulfuric Acid As Catalyst, Ibid,143, Aug.15, 1997.5 De Klerk, A. Isomerisation of 1-butene to isobutene at low temperature,Ind.Eng.Chem.Res., 43, 6325, 2004.6 Occupational Safety and health Administration Homepage. http//www.osha.gov/dts/osta/otm/otm_iv/otm_iv_2.html (accessed Aug.31, 2010).7 Warren, R.T. Alkylation and Isomerisation, oil and gas journal, vol 97,Issue4, Jan.26, 1999.8 UOPHomepage. http//www.uop.com/objects/NP RASpr2003HFAlkyd.pdf /Article/advances in hydrofluoric (HF) acid catalyzed alkylation(accessed Sept.14, 2010).9 Kamath, R. S. Qi, Z. Sundmacher, K. Aghalayam, P. Mahajani,S. M.,Process analysis for dimerization of isobutene by thermolabile distillation,Ind.Eng.Chem.Res. 45, 1575, 2006.10 De Klerk, A. Reactivity differences of octenes over solid phosphoric acid,Ind. Eng. Chem. Res. 45, 578, 2006.11 De Klerk, A. Engelbrecht, D.J. Boikanyo, H. Oligomerization ofFischer-Tropsch olefins effect of feed and operating conditions onhydrogenated motor-gasoline quality, Ind. Eng.Chem. Res. 43, 7449, 2004.12 De Klerk, A. Distillate production by oligomerization of Fischer-Tropsch olefins over solid phosphoric acid, Energy Fuels, 20, 439, 2006.De Klerk, A. Isomerisation of 1-butene to isobutene at low temperature,Ind.Eng.Chem.Res., 43, 6325, 2004.13 Nelson, W.L., McGraw-Hill,New, petroleum refinery engineering third edition, p660,2003.