Cleaner and Sustainable fuel: Ways of producing cleaner and high performing Gasoline.

Introduction and Context

Despite the trend of reduction in transportation fuels demand, these derivatives are still responsible by great part of revenues in the downstream industry and are fundamental to sustain the economic development of the nations, especially in development economies, according to Figure 1, the demand for gasoline tends to be sustained by in development economies in the short term.

Figure 1 – Growth of Gasoline Demand (IEA, 2021)

Minimize the consumption and the environmental impact of transportation fuels is a constant objective of researchers and some refining technologies was developed over the years aiming to improve the performance and reduce the environmental footprint. The gasoline is one of the most consumed crude oil derivative in the world and is normally composed by a blend of naphtha aiming to comply with strict regulations like sulfur content and octane number. An adequate octane number can optimize the performance of the gasoline in Otto cycle engines and minimize the consumption, in the refining hardware the refiners normally rely on dedicated refining technologies to improve the octane number of the final gasoline though the management of naphtha molecules.

The streams normally involved in the gasoline production process are straight run naphtha, cracked naphtha (after hydrodesulfurization), coke naphtha (after hydrotreatment) and reforming naphtha.

Reformed naphtha, produced in the catalytic reforming unit is one of the streams that contribute to raising the octane number in the final gasoline. However, due the severe restrictions related to the carcinogenic aromatic emissions, mainly benzene, some refiners have avoided the application of this stream to formulate gasoline, directing the reformed naphtha preferably to petrochemical intermediates production in aromatics complexes.

Gasoline Production Process

???????????The final gasoline is composed by a blending of different naphtha streams, as presented in Figure 2.?

Figure 2 – Example of Process Streams Blending to Produce Gasoline

The use of straight run and reformed naphtha is normally minimized, aiming to direct these streams to petrochemical intermediates market due to the higher added value of these streams in this market.

???????????Cracked naphtha (Naphtha from FCC) contributes positively to the octane number of the final gasoline, however, due to the current restrictions related to the sulfur content in the gasoline (maximum of 10 ppm), the use of cracked naphtha without treatment step is limited. Refineries that has catalytic alkylation units in his refining scheme normally direct this stream to produce aviation gasoline that have higher market value when compared with automotive gasoline, for this reason, the participation of the alkylation naphtha is minimized in the composition of this fuel.?

???????????Isomerization naphtha has low contaminants content (sulfur and nitrogen) and high octane number and, for these reasons, the participation of this stream in the formulation of gasoline is maximized in refineries that have isomerization units in the refining scheme. In markets with high demand for gasoline, refiners can add butanes to gasoline pool, however, the participation is limited due to the high vapor pressure of this stream that can lead to break quality requirements (Reid Vapor Pressure – RVP). Normally, butanes are added to LPG pool, respecting the limits to avoid breaking the mixture quality related to heavy limitations.

???????????Nowadays, due to the environmental and quality regulations over the gasoline the hydrodesulphurization of cracked naphtha is fundamental to be possible the refiners meet the sulfur content in the final gasoline that can be low than 10 ppm in most restrictive markets. In this short technical review we provide an introduction to the available technologies to improve the quality of the gasoline pool.

Isomerization Technologies

An alternative to the reforming naphtha is the production of branched hydrocarbons (with high octane number) through processes as Catalytic Alkylation and Isomerization.

Isomerization process involves the conversion of normal paraffin to branched paraffin, keeping the carbon number in the reactant molecule. The reactions are carried out in the presence of hydrogen under pressure and temperature mild conditions. The presence of hydrogen aims mainly to avoid coke deposition on the catalyst.

Isomerization reactions (1) are slightly exothermic, that is, are favored under lower temperatures. In order to balance the kinetic requirements and thermodynamic limits, are applied high activity catalysts which allow operating under lower temperatures.?

The catalysts applied in the isomerization processes have bifunctional characteristics containing acids and metallic sites, the most employed catalysts are platinum impregnated chlorided-alumina, zeolitic and oxide-based catalyst.

Isomerization process produces a light stream that can contribute to raising the octane number to the final gasoline and is practically free of contaminants like nitrogen and sulfur, however, due the high content of lighter compounds, the isomerate stream affects negatively the gasoline fugitive emissions specification (high Reid Vapor Pressure), that is, the isomerate need be blend with heavier streams to formulate gasoline that meet the current specifications.?

The typical feed stream to isomerization units is normally the lighter fraction (C5 – C6) of straight run naphtha when the objective is to produce isomerate naphtha which will be directed to gasoline pool.?Another process that has great interest to the refining industry is the isomerization of N-butane to isobutane, this product can be directed to the feed stream to catalytic alkylation units or to produce MTBE (Methyl-Tert Butyl Ether), in this case, the process feed stream is the heavier fraction of LPG obtained in debutanizers columns.?The isomerization catalyst is sensitive to contaminants as nitrogen and sulfur, and then normally the feed pass through a treating step to reduce the contaminant content (normally hydrotreatment).?

Figure 3 shows a process flow diagram for a typical isomerization unit.?

Figure 3 - Typical arrangement for Single reaction stage Isomerization Unit.

The feed stream is mixed with hydrogen and is pre-heated in heat exchangers, following is fed to the reactor, and the reactor effluent is cooled through heat exchange with the fresh feed and then is directed to a separation vessel where the major part of hydrogen is separated from the liquid phase.??Hydrogen is sent back to the process by the compressor while the liquid phase is sent to a distillation column where the isomerate naphtha is the bottom product and the light products are removed in the top.

The main process variables of the isomerization processes are temperature, operation pressure, and space velocity. As aforementioned, the temperature is normally reduced and can vary between 120 and 250 oC depending on the activity of the employed catalyst, due to the isomerization reactions characteristics, seek to operate under lower temperatures.

Operating pressure is normally close to 30 bar, higher pressures conducts the higher catalyst cycle life, on the other hand, favor hydrocracking reactions that are undesirable. The space velocity in the reactor is a design variable and express a relation among residence time and catalyst total cost, lower velocity results in higher catalyst mass and higher residence time which allow operates under lower temperature level.?

One of the most known isomerization technology is the PENEX ? process, developed by UOP Company that apply a platinum impregnated chlorinated-alumina as the catalyst.?Figure 4 presents a simplified scheme for this process.

PENEX ? technology applies dryer vessels containing molecular sieves aim to remove water from feed and hydrogen streams, preserving the catalyst.

Figure 4 – Simplified Process Scheme to PENEX? technology by UOP Company

The process applies two reactors in series and this arrangement allows operate one reactor while the other is under catalyst replacement or maintenance.

Another very employed isomerization technology is the PAR-ISOM? process also developed by UOP Company, in this case, is applied a sulfated-zirconia catalyst with the possibility of regeneration in the processing unit.?

GTC Technology Company developed the ISOMALK-2? technology that also applies platinum impregnated sulphated-zirconia as the catalyst, the process still apply pre-fractionating step and the recycle of poor octane index streams, the process is presented in Figure 5.

Figure 5 – Process Scheme for ISOMALK-2? technology by GTC Technology Company.

Despite need higher investment, the ISOMALK-2 ? technology can produce isomerate naphtha with higher octane index.?

As the isomerization reactions are limited by equilibrium conversion, some technologies involve removing isoparafinn formed during the process from the recycle stream, shift the reactional equilibrium and raising the quality of final product. These technologies applies sophisticated separation processes like simulated moving bed and molecular sieves, the technologies IPSORB? and HEXSORB? developed by AXENS Company and technologies MOLEX? e ISOSIV? developed by UOP company are examples of these processes.

???????????As mentioned above, the N-butane isomerization is economically attractive once the isobutane is applied like feedstock to catalytic alkylation processes, which is another process capable to produce high quality gasoline. Another use to isobutane is the MTBE production, however, face the current environmental regulations his use as a gasoline additive is falling down and in some countries is prohibited.

???????????The main butane isomerization technology is the BUTAMER? process, developed by UOP. Another available technology is the ISO C4?, developed by AXENS. The process is basically the same applied to C5-C6 fraction isomerization process as described above.?

Isomerization processes show advantages in relation to others gasoline upgrading technologies because can produce low contaminant stream (nitrogen and sulfur), without aromatic compounds and productive process safer when compared with catalytic reforming and alkylation technologies, respectively.

These characteristics make the isomerization processes attractive to refiners inserted in markets with high demand for gasoline and petrochemical intermediates.?

Catalytic Reforming Technologies

The main objective of the Catalytic Reforming unit is to produce a stream with high aromatics hydrocarbons content that can be directed to the gasoline pool or to produce petrochemical intermediates (benzene, toluene, and xylenes) according to the market served by the refiner, due the high content of aromatics compounds the reformate can raise significantly the octane number in the gasoline.

A typical feedstock to the catalytic reforming unit is the straight run naphtha, however, in the last decades due to the necessity to increasing the refining margin through installation of bottom barrel units, hydrotreated coke naphtha stream have been consumed like feedstock in the catalytic reforming unit.?

The catalyst generally employed in the catalytic reforming process is based on platinum (Pt) supported on alumina treated with chlorinated compounds to raise the support acidity. This catalyst has bifunctional characteristics once the alumina acid sites are actives to molecular restructuring and the metals sites are responsible for hydrogenation and dehydrogenation reactions.?

The main chemical reactions involved in the catalytic reforming process are:

·??????Naphthene Compounds dehydrogenation;

·??????Parafinns Isomerization;

·??????Isomerization of Naphthene Compounds;

·??????Paraffins Dehydrocyclization;

Among the undesired reactions can be cited hydrocracking reactions and dealkylation of aromatics compounds.

The naphtha feed stream is blended with recycle hydrogen and heated at a temperature varying 500 to 550 oC before to enter in the first reactor, as the reactions are strongly endothermic the temperature fall quickly, so the mixture is heated and sent to the second reactor and so on. The effluent from the last reactor is sent to a separation drum where the phases liquid and gaseous are separated.?

The gaseous stream with high hydrogen content is shared in two process streams, a part is recycled to the process to keep the ratio H2/Feed stream the other part is sent to a gas purification process plant (normally a Pressure Swing Adsorption unit) to raise the purity of the hydrogen that will be exported to others process plants in the refinery.

The liquid fraction obtained in the separation drum is pumped to a distillation column wherein the bottom is produced the reformate and in the top drum of the column is produced LPG and fuel gas.

The reformate have a high aromatics content and, according to the market supplied by the refinery, can be directed to the gasoline pool like a booster of octane number or, when the refinery has aromatics extraction plants is possible to produce benzene, toluene and xylenes in segregated streams, which can be directed to petrochemical process plants.?The gas rich in hydrogen produced in the catalytic reforming unit is an important utility for the refinery, mainly when there is a deficit between the hydrogen production capacity and the hydrotreating installed capacity in the refinery, in some cases the catalytic reforming unit is operated with the principal objective to produce hydrogen.??

The main process variables in the catalytic reforming process unit are pressure (3,5 – 30 bar), which normally is defined in the design step, in other words, the pressure normally is not an operational variable. The temperature can vary from 500 to 550 oC, the space velocity can be varied through feed stream flow rate control and the ratio H2/Feed stream that have a direct relation with the quantity of coke deposited on the catalyst during the process.?To semi-regenerative units, the ratio H2/Feed stream can vary from 8 to 10, in units with continuous catalyst regeneration this variable can be significantly reduced.??

Due to the process severity, the high coke deposition rate on the catalyst and consequently the quick deactivation leaves to short operational campaign periods to semi-regenerative units that employ fixed bed reactors.??

To solve this problem some technology licensors developed catalytic reforming process with continuous catalyst regeneration steps.?

The process Aromizing? developed by Axens company apply side by side configurations to the reactors while the CCR Platforming? developed by UOP apply the configuration of stacked reactors to catalytic reforming process with continuous catalyst regeneration. Figure 6 presents a flow diagram to Aromazing? catalytic reforming unit.

Figure 6 – Aromizing? Reforming Technology by Axens Company

Both technologies are commercial and some process plants with these technologies are in operation around the world.?Figure 7 presents a basic process flow diagram to CCR Platforming? developed by UOP Company.

Figure 7 – CCR Platforming? Reforming Technology by UOP Company - Source: UOP Company - www.uop.honeywell.com

In the regeneration section the catalyst is submitted to processes to burn the coke deposited during the reactions and treated with chlorinated compounds to reactivate the acid function of the catalyst.?

Despite the higher capital investment, the rise in the operational campaign and higher flexibility in relation of the feedstock to be processed in the processing unit can compensate the higher investment in relation of the semi-regenerative process.??

The catalytic reforming technology gives a great flexibility to the refiners in the gasoline production process, however, in the last decades there is a strong restriction on the use of reformate in the gasoline due to the control of benzene content in this derivate (due to the carcinogenic characteristics of this compound). This fact has been reduced the application of reformate in the gasoline formulation in some countries.?Furthermore, the operational costs are high, mainly due to the catalyst replacement and additional security requirements linked to minimize leaks of aromatics compounds.?

Face to the limitation of the aromatics content in the gasoline, mainly the benzene, the refiners has used alkylation or isomerization to produce streams capable of improving gasoline octane number in detriment of reformate naphtha. Like aforementioned, some refiners have aromatics extraction plants in his refining scheme, in this case, the production can be directed to produce benzene, toluene, and xylenes as intermediates products to petrochemical industries, despite higher capital and operational investments this configuration can be economically attractive, these products have commercialization prices higher than gasoline and this fact can be potentialized in scenarios like saturation of gasoline market.

Alkylation Technologies

Another alternative to improve the naphtha octane number is the production of branched hydrocarbons (with high octane number) through Catalytic Alkylation Process.?

The alkylation process involves the reactions between light olefins (C3 – C5) and isoparaffinic hydrocarbons like isobutane. The reaction product called alkylate is a mixture of branched hydrocarbons with higher molecular weight and higher octane number.

An example of typical alkylation reaction is represented below:?

C4H10 + C3H6→ C7H16 (2,3 Dimethylpentane)

???????????The reaction is catalyzed in strongly acidic reaction environment, the acids normally employed in the industrial scale technologies are Hydrofluoric Acid (HF) and Sulfuric Acid (H2SO4).

The main advantage of alkylation process is the production of a stream with high octane number, high chemical stability and practically free of contaminants as nitrogen and sulfur. These characteristics turn the alkylate a component attractive to the gasoline formulation to the automotive and aviation industries.?

???????????Alkylation process feed streams are generally obtained from LPG produced in deep conversion units, mainly Fluid Catalytic Cracking (FCC) and Delayed Coking. The LPG produced in these process units have high olefins content, ideal for the alkylation process. The isobutane stream is normally obtained through separation of LPG produced in the atmospheric distillation unit, FCC or Delayed Coking in deisobutanizer towers.?

???????????Like aforementioned, the acids generally employed as the homogeneous catalyst to the alkylation process are HF and H2SO4.?Figure 8 presents a process flow diagram to the alkylation process catalyzed by HF.

???????????The feed stream goes through a pretreatment (generally molecular sieves or alumina) before being pumped to the reactor, the objective is to remove process contaminants mainly water, diolefins and sulfur and nitrogen compounds. Water is especially damaging to the process, once accelerates piping and equipment corrosion process, and beyond requires higher HF reposition.

???????????After pretreatment the hydrocarbons streams are put in contact with the hydrofluoric acid in the reactor and the hydrocarbons mixture and HF solution is separated through gravity in a settler vessel, the hydrocarbon phase is sent to the fractionating section while the aqueous phase (containing the most of HF) is cooled and sent back to the reactor. As alkylation reactions are exothermic, the reactor is continuously refrigerated aim to keep the reaction ideal conditions.?

Figure 8 – Typical Process Flow Diagram to Catalytic Alkylation Unit using HF as Catalyst

A part of hydrofluoric acid is sent to the stripping column where the acid is stripped with isobutane. The top product is a mixture of HF and isobutene and sent back to the reactor while the bottom stream containing an azeotropic mixture of water and HF, beyond hydrocarbons, this step is responsible to keep the HF free of contaminants and with adequate concentration to the alkylation process.

???????????After the separation columns, butane and propane streams go to a treatment with alumina aim to decompose organic fluorides and with KOH to neutralize the remaining acidity. The alkylate stream is treated with NaOH to neutralize the remaining acidity. Currently, the main alkylation technology licensors with HF are the companies UOP and CONOCO-PHILLIPS.

???????????Alkylate stream is normally directed to the refinery gasoline pool to the production of high octane automobile gasoline or aviation gasoline, however, in petrochemical plants this stream can be used as intermediate to produce ethyl-benzene (to produce Styrene), isopropyl-benzene (to produce Phenol and Acetone) and dodecyl-benzene used to produce detergents. Propane and butane streams can be sent to the LPG pool of the refinery or commercialized separately.?

???????????The alkylation process with sulfuric acid as catalyst has similarities with the hydrofluoric acid process, however, the sulfuric acid regeneration step is more complex and involves the H2SO4 decomposition in SO2 and SO3 and the subsequent condensation of concentrated sulfuric acid, this regeneration can be conducted in the processing site or in an external process plant, consequently the acid sulfuric consumption in the process is much higher than HF, furthermore, the solubility of sulfuric acid in hydrocarbons is lower, requiring greater agitation?to maintain the contact between the phases in ideal conditions to the process.?

The alkylation technologies with sulfuric acid most applied in industrial scale are the processes STRATCO Effluent Refrigerated Alkylation Process?, licensed by STRATCO Engineering Company and EXXON MOBIL Cascade Auto refrigerated Process?, licensed by EXXON MOBIL Company. Figure 9 shows a simplified process flow diagram to the alkylation technology with H2SO4, licensed by STRACTO Engineering.??

Figure 9 – Basic Process Flow Diagram to the Alkylation Process Catalyzed by H2SO4, developed by STRATCO Engineering Company.

Olefins feed stream go to a coalescer to remove water, after the mixture with isobutane recycle, in the sequence the mixture is sent to the reactor. The mixture of hydrocarbons and acid follow to a settler where the phase separations occurs, organic phase is sent back to reactor, a control valve promotes the necessary pressure reduction to vaporize the lighter hydrocarbons and remove heat from the reactor, controlling the equipment temperature which raises due the exothermic characteristics of alkylation reactions.

???????????The hydrocarbons blend is sent to a flash drum where the lighter phase is directed to a compressor to condense in an accumulator vessel and the propane is recovered in the depropanizer tower while the heavier hydrocarbons (essentially isobutane) are recycled to the reactor. The stream containing the alkylate is directed to a caustic treatment and posteriorly to a deisobutanizer column where the alkylate are removed in the bottom.

???????????As aforementioned the need of catalyst replacement is higher in the process with sulfuric acid, however, the HF process needs higher Isobutane/Olefins ratio, which means a greater separation system. Over the last decades, the refiners have opted to the HF alkylation technologies due to the higher simplicity of this process and the lower need of catalyst replacement that leaves to lower operational costs.?

However, regulatory pressures have led some refiners to convert her their HF alkylation units to operate with H2SO4, due the high volatility and higher risks presented by the hydrofluoric acid, some licensers developed technologies to convert HF units to operate with sulfuric acid like the ALKYSAFE? technology, licensed by STRATCO Engineering Company and the?ReVap? process, developed by the companies EXXON MOBIL and CONOCO-PHILLIPS which uses additives to reduce the HF volatility, making the unit operation safer.?

Acid purity must be maintained higher as possible through the removal of ASO (Acid Soluble Oil), water and dissolved reactants in the HF case and through fresh acid replacement in processes with acid sulfuric as the catalyst.?

???????????The main disadvantage of the alkylation processes with homogeneous catalyst (HF or H2SO4) is the need to handling strong acid highly concentrated, that leave a greater process safety risks and high maintenance costs, mainly related to avoid corrosion in piping and equipment and, as aforementioned, equipment failures with contention losses can have dramatic consequences.

Aiming to eliminate these risks, some licensors have dedicated his efforts to develop heterogeneous catalysts that can replace the strong acids in the alkylate production processes, the UOP Company developed the process called ALKYLENE?, that apply a solid catalyst with continuous regeneration during the process. Among other technologies can be cited the processes LURGI EUROFUEL?, developed by Lurgi Engineering Company in cooperation with SUD-CHEMIE, the ALKYCLEAN? process, developed by the companies ABB-Lummus and Akzo Nobel and the process FBA?, developed by Haldor Topsoe.

Light Olefins Condensation

The process consists in an olefins combination and the consequent production of high molecular weight olefins, as presented as following.?

n CH2=CH2?→ H-(CH2CH2)n-H?(1)

???????????This process is controlled to maintain the products in the gasoline distillation range.?

???????????The reactions are carried out under mild temperature conditions (between 15 and 25 oC) and pressures that vary between 10 and 80 bar, according to the process feed stream. The condensation reactions are exothermic and the reaction is controlled by heat removing from the reactor, normally through cold streams injection between the catalytic beds (quench streams). The process can be conducted under thermal or catalytic conditions, however, the commercial units normally apply the catalytic route using acid catalyst, mainly phosphoric acid deposited on an adequate carrier.??

???????????Raw-material (light olefins) for the process is normally from fluid catalytic cracking units (FCC), catalytic dehydrogenation or thermal cracking units.

???????????A typical process flow diagram for a gasoline production unit through olefins condensation is presented in Figure 10.?

Figure 10 – Typical Process Flow Diagram for Light Olefins Condensation Process to produce Gasoline

The feed stream passes through a process to remove contaminants, mainly sulfur compounds that are a catalyst poison. From the feed drum, the olefinic stream is pumped to the reactor where the temperature control is realized by the injection of reactants under a reduced temperature between the catalytic beds, as aforementioned.

???????????After the reaction step, the reactor effluent is separated in a flash distillation column where the bottom product is sent to a stabilizer column that aims to removing the light compounds from the naphtha stream and the top product is recycled to the process. Normally the gasoline produced by this route is called polymerization gasoline.?

???????????This process is capable to produce high octane gasoline, however, the high olefin content makes the polymerization gasoline chemically unstable, leading to gum producing in the short term. The polymerization gasoline is normally directed to the refinery gasoline pool and mixed with the others naphtha streams to contribute to raising the octane index of the final gasoline, however, his adding is limited too by his high volatility (high Reid Vapor Pressure). The remaining olefins stream can be directed to petrochemical intermediates market or to the refinery LPG pool.?

???????????The gasoline production process by olefins condensation or polymerization, lost space to other technologies like isomerization, alkylation and catalytic reforming that can produce more chemically stable naphtha with the same octane index (in some cases higher).

???????????Nowadays, light olefins are intended to consumption as petrochemical intermediates due the higher profitability offered to the refiner, however, refiners inserted in markets with high gasoline demand can apply this process to quickly raise the high-quality gasoline production.

???????????Some important technology developers as UOP Company and Shell Global Solutions developed contributions to improve the olefins condensation process. Among the commercial technologies dedicated to produce naphtha from olefins polymerization we can quote the Catolene? process by UOP Company and the Polynaphtha? technology developed by Axens Company. Taking into account the growing demand by petrochemicals, the naphtha polymerization units are being applied to improve the yield of light olefins through the recycling of polymerized naphtha to an FCC unit, as presented in Figure 11.

Figure 11 – Processing Scheme Relying on UOP Catolene? Olefins Polymerization Technology - Source: UOP Company - www.uop.honeywell.com

???????????As aforementioned, the polymerization or olefins condensation can contribute an agile and relatively cheap way to raise the gasoline production, mainly in extreme scenarios of the shortage of derivatives. In some refining configurations, these processing units can be also applied to produce diesel.

Etherification Processes – The Oxygenated Alternatives

Among the additives that were widely applied in the gasoline formulation, it’s possible to highlight oxygenated compounds as the ethers MTBE (Methyl Tert Butyl Ether), ETBE (Ethyl Tert Butyl Ether), and TAME (Tert-Amyl Methyl Ether).

These additives are produced through etherification reactions, which consist in the addition of an alcohol to olefins producing ethers. The MTBE and TAME are produced from Methanol while the ETBE is produced from Ethanol.

Due to his characteristics (total miscibility whit hydrocarbons, high octane number, and low volatility), MTBE is the ether most widely employed. The MTBE production chemical reaction is presented in Figure 12.??

Figure 12 – MTBE Producion Chemical Reaction

The reaction is catalyzed by acid catalyst with cationic resins as the carrier.

In refineries with MTBE producing units, the Isobutene is normally obtained through fractionating of LPG from Fluid Catalytic Cracking Unit (FCC). MTBE production reaction is exothermic and is carried out under mild conditions, normally the pressure varies from 10 to 20 bar and the temperature is controlled from 40 to 70 oC. Figure 13 shows a typical process flow scheme for MTBE production.?

Figure 13 – Typical Process Arrangement to MTBE Production Process Unit

???????????The methanol fresh feed is mixed with the recycled methanol and posteriorly mixed with the isobutene stream before to enter in the first reactor. The first reactor effluent is sent to a fractionating tower where the bottom product is the MTBE and the top stream is directed to the second reaction stage, the effluent of this reactor is pumped to another distillation column where the MTBE is removed from the bottom and the top is directed to a water washing column. In this column, the remaining Isobutene is removed in the top and the Methanol/Water mixture is removed in the bottom. This mixture is separated in another fractionating column and the remaining Methanol is recycled to the process while the water is removed to treatment or partially recycled to the washing tower.

???????????The principal process variables for MTBE production process are the pressure and temperature that need to be controlled at the lower possible level to attend the compromise between the kinetic requirements and the exothermic characteristics of the reaction.

???????????Main process technology licensors developed technologies to produce oxygenated additives for the gasoline, mainly MTBE.

???????????One of the main commercialized technologies is the ETHERMAX? process developed by UOP Company, this process is presented in Figure 14.?

Figure 14 – Simplified Process Flow Diagram for ETHERMAX ? technology by UOP Company

???????????This process is capable to produce MTBE, ETBE, and TAME according to the raw material applied, this fact gives a great flexibility to the process which is a considerable advantage. A major part of the etherification reactions occurs in the reactor and the remaining alcohol is partially converted in the reactive distillation column.

???????????As aforementioned, some of the main technology licensors developed processes aiming to produce oxygenated additives, mainly in the 80s and 90s with the objective to maximize the production of these compounds in substitution of lead-based additives. Among the main commercially available technologies we can cite the CDMTBE ? process, developed by McDermott Company and the CATACOL? technology developed by Axens Company.??

Conclusion

???????????As aforementioned, high quality gasoline still present great demand especially in growing economies. The octane boosting technologies can help refiners to comply with the market requirements at same time that reduce the consumption and environmental impact of fossil fuels that is an urgent requirement of our society. Flexible refining technologies capable to be directed to petrochemicals like catalytic reforming units gives competitive advantage to refiners considering the growing demand by petrochemicals, especially light aromatics, but the remain octane boosting technologies can still offer great contribution to the refining margins according to the market supplied to the refiners.

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ZHOU, T.; BAARS, F.?Catalytic Reforming Options and Practices.?PTQ Magazine, 2010.