Aromatics and Olefins – Maximum Added Value to the Crude Oil

Introduction and Context

???????????The downstream industry faces a transition period where the focus of the players is changing from transportation fuels to petrochemicals aiming to ensure maximum added value to processed crude oils as well as to allow the growth of low carbon energies in the global energetic matrix.

???????????The newest threat to refiners is the reduction of the consumer market, in the last years became common, news about countries that intend to reduce or ban the production of vehicles powered by fossil fuels in the middle term, mainly in the European market. Despite the recent forecasts, the transportation fuels demand is still the main revenues driver to the downstream industry, as presented in Figure 1, based on data from Wood Mackenzie Company.

Figure 1 – Relation of Petrochemical Feedstock/Transportation Fuels Feedstock and Installed Capacity (Wood Mackenzie, 2019)

???????????According to Figure 1, the transportation fuels demand represents close to five times the demand by petrochemicals as well as a focus on transportation fuels of the current refining hardware, considering the data from 2019. Despite these data, is observed a trend of stabilization in transportation fuels demand close to 2030 followed by a growing market of petrochemicals. Still according to Wood Mackenzie data, presented in Figure 2, is expected a relevant growth in the petrochemicals participation in the global oil demand.

Figure 2 – Change in the Profile of Global Crude Oil Demand (Wood Mackenzie, 2019)

???????????The improvement in fuel efficiency, growing market of electric vehicles tends to decline the participation of transportation fuels in the global crude oil demand. New technologies like additive manufacturing (3D printing) have the potential to produce great impact to the transportation demands, leading to even more impact over the transportation fuels demand. Furthermore, the higher availability of lighter crude oils favors the oversupply of lighter derivatives that facilitate the production of petrochemicals against transportation fuels as well as the higher added value of petrochemicals in comparison with fuels. It’s interesting to note that even in a pandemic scenario, the sales of electric vehicles grow close to 40 % in 2020 and tends to grow even more in 2021 according to data from International Energy Agency (IEA), presented in Figure 3.

Figure 3 – Evolution of Electric Car Fleet (IEA, 2021)

???????????Facing these challenges, search for alternatives that ensure survival and sustainability of the refining industry became constant by refiners and technology developers. Due to his similarities, better integration between refining and petrochemical production processes appears as an attractive alternative, some forecasts indicates that the chemicals market will be doubled in 2030 in comparison with 2016 level, in general the refiners focused on transportation fuels are capable to add close to US$ 15 per processed barrel while the players focused on petrochemicals can achieve US$ 30 per processed barrel. In this sense, the petrochemical integration not only allow the participation in a most profitable market, but also in a growing and most resilient market when compared with the transportation fuels.

Although the advantages, it’s important consider that the integration between refining and petrochemical assets increase the complexity, requires capital spending, and affect the interdependency of refineries and petrochemical plants, these facts need to be deeply studied and analyzed case by case.

Synergies between Refining and Petrochemical Assets – Petrochemical Integration

The focus of the closer integration between refining and petrochemical industries is to promote and seize the synergies existing opportunities between both downstream sectors to generate value to the whole crude oil production chain. Table 1 presents the main characteristics of the refining and petrochemical industry and the synergies potential.

As aforementioned, the petrochemical industry has been growing at considerably higher rates when compared with the transportation fuels market in the last years, additionally, represent a noblest destiny and less environmental aggressive to crude oil derivatives. The technological bases of the refining and petrochemical industries are similar which lead to possibilities of synergies capable to reduce operational costs and add value to derivatives produced in the refineries.?

Figure 4 presents a block diagram that shows some integration possibilities between refining processes and the petrochemical industry.?

Figure 4 – Synergies Possible between Refining and Petrochemical Processes

???????????Process streams considered with low added value to refiners like fuel gas (C2) are attractive raw materials to the petrochemical industry, as well as streams considered residual to petrochemical industries (butanes, pyrolisis gasoline, and heavy aromatics) can be applied to refiners to produce high quality transportation fuels, this can help the refining industry meet the environmental and quality regulations to derivatives.

???????????The integration potential and the synergy among the processes rely on the refining scheme adopted by the refinery and the consumer market, process units as Fluid Catalytic Cracking (FCC) and Catalytic Reforming can be optimized to produce petrochemical intermediates to the detriment of streams that will be incorporated to fuels pool. In the case of FCC, installation of units dedicated to produce petrochemical intermediates, called petrochemical FCC, aims to reduce to the minimum the generation of streams to produce transportation fuels, however, the capital investment is high once the severity of the process requires the use of material with noblest metallurgical characteristics. ?

???????????The IHS Markit Company proposed a classification of the petrochemical integration grades, as presented in Figure 5.?

Figure 5 – Petrochemical Integration Levels (IHS Markit, 2018)

???????????According to the classification proposed, the crude to chemicals refineries is considered the maximum level of petrochemical integration.

???????????In this scenario, the synergy between refining technologies like catalytic reforming and petrochemical processes like steam cracking units can offer great operational flexibility to refiners, allowing higher added value to intermediate streams like naphtha against gasoline production that, as presented above, presents falling demand. The better integration between refining and petrochemical assets through more integrated refining configurations can be an important competitive differential in the downstream industry for the next years.

Producing Light Aromatics - 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, in the current scenario this a less attractive route.

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.

Figure 6 present a basic process flow diagram for a typical semi-regenerative?

Figure 6 – Typical arrangement to Semi-regenerative Catalytic Reforming Process Unit

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 7 presents a flow diagram to Aromazing? catalytic reforming unit.

Figure 7 – Aromizing? Reforming Technology by Axens Company

Both technologies are commercial and some process plants with these technologies are in operation around the world. ?Figure 8 presents a basic process flow diagram to CCR Platforming? developed by UOP Company.

Figure 8 – CCR Platforming? Reforming Technology by UOP Company

???????????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. ?Figure 9 presents a basic process flow for the catalyst regeneration sequence.?

Figure 9 – Catalyst Regeneration Sequence (DOMERGUE et. al., 2006)

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. ?As aforementioned, light aromatics (BTX) presents growing demand and high added value, Figure 8 presents the forecast of aromatics demand considering the Asian market.

Figure 10 – Aromatics Demand Forecast for the Asian Market (Wood Mackenzie, 2019)

Considering this market scenario, the maximization of light aromatics can be an attractive strategy to improve the revenues to some refiners that rely with more integrated refining hardware.

Aromatics Separation Section – Ensuring Maximum Added Value

As aforementioned, in markets where there is demand, the production of petrochemical intermediates is economically more advantageous than the production of transportation fuels, especially in countries with easy access to lighter oils. The production and separation of aromatics are processes with great capacity of adding value to crude oil.

The aromatics production complex is a set of processes intended to produce petrochemical intermediates from naphtha produced in the catalytic reforming process or by pyrolysis process. An aromatics production complex can take on different process configurations, according to the petrochemical market to be served, an example is shown in Figure 11.

Figure 11 – Basic Process Configuration for a Typical Aromatics Separation Unit

The naphtha rich in aromatics,?produced in catalytic reforming or pyrolysis units (in some cases from both), is fed to an extractive distillation column where the separation of aromatic compounds is conducted, which are withdrawn in the extract phase, are recovered at the bottom of the column while the non-aromatic compounds are withdrawn from the top in the raffinate phase. ?The aromatics are separated from the solvent in the solvent recovery column and directed to the fractionation section of aromatics where the essentially pure benzene and toluene streams and xylenes blend are obtained. The raffinate is sent to a wash column and the non-aromatic hydrocarbons are usually sent to the refinery's gasoline pool.

??????????The process shown in Figure 9 involves only physical separation steps, that is, the process yields in each stream depends on the concentration of this compound in the feed stream. ??

The growing demand for high-quality petrochemical intermediates and the higher added value of these products have made it necessary to develop conversion processes capable of converting lower interest aromatics (Toluene) into more economically attractive compounds (Xylenes).

Aromatics separation, mainly xylenes, is a great challenge to the modern engineering. The similarities between the molecules make the separation through simple distillation very hard, for this reason, several researchers, and technology licensors dedicate their efforts to develop new processes which can lead to pure compounds with lower costs. A basic scheme for a xylene separation process is shown in Figure 12.

Figure 12 – Basic Process for Xylenes Separation

The xylenes blend is fed to a distillation column where the ethylbenzene is separated in the top and sent to styrene production market while the bottom stream is pumped to another column where the mixture of Meta and Para-xylenes is withdrawn in the top and the Ortho-xylene and heavier compounds are removed in the bottom.

Ortho-xylene is separated from heavy aromatics in another distillation column while the Meta and Para-xylene are fed to a crystallization process, where is obtained a stream with a high concentration in Meta-xylene and the residual stream is directed to an isomerization unit, aiming to promote the conversion of residual Meta and Orto-xylenes in Para-xylene. The aromatics production units are normally optimized to maximize the Meta-xylene production because this is a petrochemical intermediate with higher interest, this compound is raw material to produce terephthalic acid that is used to produce PET (Polyethylene Terephthalate).

Improving the Yield of Paraxylene – Molecular Management

To raise the production of higher commercial and economic interest compounds (P-Xylene and Benzene), technology licensors developed several processes to convert streams with low added value in these compounds. One of the main developers of this technology is the UOP Company, the PAREX? process apply the separation through adsorption to obtain high purity P-xylene from xylenes blend. ?

?Another UOP technology is the ISOMAR? process, which promotes the xylenes isomerization to Para-xylene raising the recovery of this compound in the aromatic complex. TATORAY ? process was developed to convert toluene and heavy aromatics (C9+) in benzene and xylenes through transalkylation reaction. Another economically attractive technology is the SULPHOLANE ? process that applies liquid-liquid extraction operations and extractive distillation to reach high purity aromatics separation from hydrocarbon mixture. ?

The UOP Company developed an integrated aromatics complex aiming to maximize the production of benzene and P-xylene, which lead to a higher profitability to the refiner. A UOP Aromatics Complex scheme is presented in Figure 13.?

Figure 13 – Aromatics Complex by UOP Company

Other companies have attractive and efficient technologies to produce high purity aromatics, the Axens Company license an aromatics production complex also based on separation and conversion processes, called ParamaX? that can be optimized to produce P-xylene. This process is presented in Figure 14.?

The ParamaX? technology offers the possibility of Cyclohexane production (Raw material to synthetic fibers) through benzene hydrogenation beyond raise the production of this component through toluene HydroDealkylation (HDA). ?

Figure 14 – Schematic Process Flow Diagram for ParamaX? technology, by Axens Company.?

As aforementioned, the capital investment to installation of aromatics production complexes is high, however, the obtained products have high added value and rely on great demand, and even the compounds with low interest can be commercialized with high margin. ?In countries with easy access to light oil reserves as Saudi Arabia and United States (Tight Oil) the installation of these process plants is even more economically attractive.

In markets with over supply of LPG, it’s possible to improve the aromatics production applying commercial technologies like the Cyclar? process, developed by UOP Company, as presented in Figure 15.

Figure 15 – Process Flow Diagram for Cyclar? Process by UOP Company (BANACH, 2016)

???????????Despite the capital spending, the use of low added value streams can be an attractive alternative to refiners inserted in markets with high demand by BTX, like Asia. Another commercial technology with interesting potential is the GT-2A? process, developed by Sulzer-GTC Technology Company to produce BTX from methane and LPG. Figure 16 presents a basic process flow diagram for the GT-2A? process.

Figure 16 – Block Diagram for the GT-2A? Technology by Sulzer-GTC Company (Sulzer-GTC Company Website)

???????????Another alternative is the process GT-BTX Plus? technology, developed by Sulzer-GTC Company, which is capable to produce light aromatics from FCC naphtha, this process is presented in Figure 17.

Figure 17 – Process Flow Diagram for GT-BTX Plus? Process by Sulzer-GTC Company (Sulzer-GTC Company Website)

???????????It’s important considering the impact of these technologies over the remain markets once they reduce the availability of other crude oil derivatives like LPG and gasoline. As aforementioned, the use of on purpose technologies can be attractive to refiners inserted in markets with great demand by aromatics.

Naphtha Steam Cracking Process – Maximizing Light Olefins

???????????The Steam cracking process has a fundamental role in the petrochemical industry, nowadays the most part of light olefins light ethylene and propylene is produced through steam cracking route. The steam cracking consists of a thermal cracking process that can use gas or naphtha to produce olefins, in this review we will describe the naphtha steam cracking process.

???????????The naphtha to steam cracking is composed basically of straight run naphtha from crude oil distillation units, normally to meet the requirements as petrochemical naphtha the stream need to present high paraffin content (higher than 66 %). Figure 18 presents a typical steam cracking unit applying naphtha as raw material to produce olefins.

Figure 18 – Typical Naphtha Steam Cracking Unit (Encyclopedia of Hydrocarbons, 2006)

???????????Due to his relevance, great technology developers has dedicated his efforts to improve the steam cracking technologies over the years, especially related to the steam cracking furnaces. Companies like Stone & Webster, Lummus, KBR, Linde, and Technip develop technologies to steam cracking process. One of the most known steam cracking technology is the SRT? process (Short Residence Time), developed by Lummus Company, that applies a reduce residence time to minimize the coking process and ensure higher operational lifecycle.

????????????The cracking reactions occurs in the furnace tubes, the main concern and limitation to operating lifecycle o steam cracking units is the coke formation in the furnace tubes. The reactions carry out under high temperatures, between 500 oC to 700 oC according to the characteristics of the feed (inlet temperature). For heavier feeds like gas oil, is applied lower temperature aiming to minimize the coke formation, the combination of high temperatures and low residence time are the main characteristic of the steam cracking process.

Fluid Catalytic Cracking Technologies – Propylene Production Route

Fluid Catalytic Cracking (FCC) is one of the main processes which give higher operational flexibility and profitability to refiners. The catalytic cracking process was widely studied over last decades and became the principal and most employed process dedicated to converting heavy oil fractions in higher economic value streams.

The installation of catalytic cracking units allows the refiners to process heavier crude oils and consequently cheaper, raising the refining margin, mainly in higher crude oil prices scenario or in geopolitics crises that can become difficult the access to light oils. ?The typical Catalytic Cracking Unit feedstream is gas oils from vacuum distillation process. However, some variations are found in some refineries, like sending heavy coke naphtha, coke gas oils and deasphalted oils from deasphalting units to processing in the FCC unit.

The catalyst normally employed in fluid catalytic cracking units is a solid constituted by small particles of alumina (Al2O3) and silica (SiO2) (zeolite). By the catalyst characteristics and the operational conditions in the catalytic cracking process (temperature higher than 500 oC), the process is inefficient to cracking aromatic compounds, therefore, how much more paraffinic is the feedstream, higher is the unit conversion. Figure 19 presents a process scheme for a typical Fluid Catalytic Cracking Unit (FCCU).?

In a conventional scheme, the catalyst regeneration process consists in the carbon partial burning deposited over the catalyst, according to chemical reaction below:

C + ? O2 → CO

The carbon monoxide is burned in a boiler capable of generating higher pressure steam that supplies others process units in the refinery.?

Figure 19 – Schematic Process Flow for a Typical Fluid Catalytic Cracking Process Unit (FCCU)

The principal operational variables in a fluid catalytic cracking unit are reaction temperature, normally considered the temperature in the top of the reactor (called riser), feed stream temperature, feed stream quality (mainly carbon residue), feed stream flow rate and catalyst quality. Feedstock quality is especially relevant, but this variable is a function of the crude oil processed by the refinery, so is difficultly can be changed, but for example, aromatic feedstock’s with high metals content are refractory to cracking and conducting to a quick catalyst deactivation. ?

An important variation of the fluid catalytic cracking technology is the residue fluid catalytic cracking unit (RFCC). In this case, the feedstock to the process is basically residue from atmospheric distillation column, due to the high carbon residue and contaminants (metals, sulphur, nitrogen, etc.) are necessary some adaptations in the unit like catalyst with higher resistance to metals and nitrogen and catalyst coolers furthermore, it’s necessary apply materials with most noble metallurgy due the higher temperatures reached in the catalyst regeneration step (due the higher coke quantity deposited on the catalyst), that raises significantly the capital investment to the unit installation. Nitrogen is a strong contaminant to the FCC catalyst because they neutralize the acid sites of the catalyst which are responsible for the cracking reactions.??

When the residue has high contaminants content, is common the feed stream treatment in hydrotreating units to reduce the metals and heteroatoms concentration to protect the FCC catalyst.

Typically, the average yield in fluid catalytic cracking units is 55% in volume in cracked naphtha and 30 % in LPG. ?

The decanted oil stream contains the heavier products and have high aromatic content, is common that this product is contaminated with catalyst fines and normally this stream is directed to use like fuel oil diluent, but in some refineries, this stream can be used to produce black carbon.

Light Cycle Oil (LCO) has a distillation range close to diesel and normally this stream is directed to treatment in severe hydrotreating units (due to the high aromaticity), after this treatment the LCO is sent to the refinery diesel pool.

Heavy cracked naphtha is normally directed to refinery gasoline pool, however, in scenarios where the objective is to raise the production of middle distillates, this stream can be sent to hydrotreating units for further diesel production.

The overhead products from main fractionator are still in gaseous phase and are sent to the gas separation section. ?The fuel gas is sent to the refinery fuel gas ring, after treatment to remove H2S, where will be burned in fired heaters while the LPG is directed to treatment (MEROX) and further commercialization. ??The LPG produced by FCC unit have a high content of light olefins (mainly Propylene) so, in some refineries, the LPG stream is processed in a Propylene separation unit to recovery the propylene that has higher added value than LPG.

Cracked naphtha is usually sent to refinery gasoline pool which is formed by naphtha produced by other process units like straight run naphtha, naphtha from the catalytic reforming unit, etc. Due to the production process (deep conversion of residues), the cracked naphtha has high sulfur content and to attend the currently environmental legislation this stream needs to be processed to reducing the contaminants content, mainly sulfur. ??

The cracked naphtha sulfur removing represents a great technology challenge because is necessary to remove the sulfur components without molecules saturation that gives high octane number for gasoline (mainly olefins). ???

Usually, catalytic cracking units are optimized to aiming the production of fuels (mainly gasoline), however, some process units are optimized to maximize the light olefins production (propylene and ethylene). Process units dedicated for this purpose have his project and operational conditions significantly changed once the process severity is strongly raised in this case.

The reaction temperature reaches 600 oC and higher catalyst circulation rate raises the gases production, which requires a scaling up of gas separation section. ?

In several cases, due the higher heat necessity of the unit is advantageous to operate the regenerator with the total combustion of the coke deposited on the catalyst, this arrangement significantly changes the thermal balance of the refinery once it’s no longer possible to resort the steam produced by the CO boiler. ?

Over last decades, the fluid catalytic cracking technology was intensively studied aiming mainly the development of units capable of producing light olefins (Deep Catalytic Cracking) and to process heavier feedstocks. The main licensers for fluid catalytic cracking technology nowadays are the companies KBR, UOP, Stone & Webster, Axens, and Lummus Company.

Meeting the Market Demand through FCC Optimization – Maximum Olefins Operation Mode

In this operation mode the FCC unit operates under high severity translated to high operation temperature (TRX), high catalyst/oil ratio. The catalyst formulation considering higher catalyst activity through addition of ZSM-5 zeolite. There is the possibility to a reduction in the total processing capacity due to the limitations in blowers and cold area capacity.

???????????It’s observed an improvement in the octane number of cracked naphtha despite a lower yield, due to the higher aromatics concentration in the cracked naphtha. In some cases, the refiner can use the cracked naphtha recycle to improve even more the LPG yield.

???????????In the maximum LPG operation mode, the main restrictions are the cold area processing capacity, metallurgic limits in the hot section of the unit, treating section processing capacity as well as the top systems of main fractionating column. In markets with falling demand by transportation fuels, this is the most common FCC operation mode.

Through changing the reaction severity, it is possible to maximize the production of petrochemical intermediates, mainly propylene in conventional FCC units, as shown in Figure 20.

Figure 20 - Optimization of Process Variables in FCC Units to Improve the Yield of Petrochemicals Intermediates.

The use of FCC catalyst additives such as ZSM-5 can increase unit propylene production by up to 9,0%. Despite the higher operating costs, the higher revenues from the higher added value of derivatives should lead to a positive financial result for the refiner, according to current market projections. A relatively common strategy also applied to improve the yield of LPG and propylene in FCC units is the recycling of cracked naphtha leading to an over cracking of the gasoline range molecules.??

Propylene Recovery Section

The growing demand by petrochemicals lead some refiners to install propylene recovery units aiming to allow the maximization of light olefins yield in his refining hardware. Among the light olefins, the propylene is one of the most relevant petrochemical intermediate due to the high demand and added value.

The propylene can be applied as intermediate to the production some fundamental products, for example:

·??????Acrylonitrile;

·??????Propylene Oxide;

·??????Cumene;

·??????Acrylic Acid;

·??????Polypropylene;

Propylene can be produced through conventional processes like Steam Cracking and Fluid Catalytic Cracking (FCC) or through directed processes like metathesis of ethylene and butane, propane dehydrogenation, olefins cracking, Methanol to Olefins processes (MTO), among others. Currently a major part of the propylene market is supplied by steam cracking units, but close to 28 % of the global propylene demand is from the separation of LPG produced in Fluid Catalytic Cracking Units (FCC).

???????????Normally, the LPG produced in FCC units contain close to 30 % of propylene and the added value of the propylene is close to 2,5 times of the LPG. According to the local market, the installation of propylene separation units presents an attractive return over investment. Despite the advantage, a side effect of the propylene separation from LPG is that the fuel stays heavier leading to specifications issues, mainly in colder regions, in these cases alternatives are to segregate the butanes and send this stream to gasoline pool, add propane to the LPG or add LPG from natural gas. It’s important take into account that some of these alternatives reduce the LPG offer, which can be a severe restriction according to the market demand.

A great challenge in the propylene production process is the propane and propylene separation step. The separation is generally hard by simple distillation because the relative volatility between propylene and propane is close of 1.1. This fact generally conducts to distillation columns with many equilibrium stages and high internal reflux flow rates.

There are two technologies normally employed in propylene-propane separation towers that are known as Heat-Pump and High-Pressure configurations.

The high-pressure technology applies a traditional separation process that uses a condenser with cooling water to promotes the condensation of top products, in this case, it’s necessary to apply sufficient pressure to promote the condensation of products in the ambient temperature. Furthermore, the reboiler uses steam or another available hot source. The adoption of high-pressure separation route requires a great availability of low-pressure steam in the refining hardware, in some cases this can be a restrictive characteristic and the heat pump configuration is more attractive, despite the higher capital requirements.

The application of heat pump technology allows decrease the operating pressure by close of 20 bar to 10 bar, this fact increase the relative volatility propylene-propane, making the separation process easier and, consequently, reducing the number of equilibrium stages and internal reflux flow rate required for the separation.

???????????Normally, when the separation process by distillation is hard (with relative volatilities lower than 1.5) the uses of heat pump technology show more attractive.

???????????Furthermore, some variables need to be considerate during the choice of the best technology for the propylene separation process like availability of utilities, temperature gap in the column and installation cost.

???????????Normally, the propylene is produced in the refineries with to specifications. The polymer grade that is most common and have higher added value with a purity of 99,5 % (minimum) this grade is directed to polypropylene market. The chemical grade where the purity varies between 90 to 95% is normally directed to other uses. A complete process flow diagram for a typical propylene separation unit applying heat pump configuration is presented in Figure 21.

Figure 21 – Typical Process Flow Diagram for a FCC Propylene Separation Unit Applying Heat Pump Configuration

The LPG from FCC unit is pumped to a depropanizer column where the light fraction (essentially a mixture of propane and propylene) is recovered in the top of the column and sent to a deethanizer column while the bottom (butanes) is pumped to LPG or gasoline pool, according to the refining configuration. The top stream of the deethanizer column (lighter fraction) is sent back to FCC where is incorporated to refinery fuel gas pool, or in some cases can be directed to petrochemical plants to recover the light olefins (mainly ethylene) present in the stream while the bottom of the deethanizer column is pumped to the C3 splitter column, where the separation of propane x propylene is carried out. The propane recovered in the bottom of the C3 splitter is sent to LPG pool where the propylene is sent to propylene storage park. The feed stream passes through a caustic wash treating aiming to remove some contaminants that can lead to deleterious effect to petrochemical processes, an example is the carbonyl sulfide (COS) that can be produced in the FCC (through the reaction between CO and S in the Riser).

?The Synergy between Aromatics Production Complex, Steam Cracking and FCC Units

???????????As presented in Figure 3, light aromatics and olefins presents growing demand and high added value when compared with gasoline, in this sense, maximize the yield of these petrochemical intermediates in the refining hardware can ensure high economic result to refiners, despite the high capital spending and operation costs related to a more complex refining hardware.

???????????Among the synergy possibilities between steam cracking and aromatics production complexes is the use of pyrolysis gasoline produced in the steam cracking units as feed stream to aromatics production complex, improving the refinery capacity to produce aromatics against gasoline. By his turn, the raffinate stream from aromatics complex can be used to improve the olefins yield in steam cracking units, mainly ethylene and propylene.

An example of refining configuration relying on the synergy between aromatics production complex and steam cracking units is presented in Figure 22.

Figure 22 – Integrated Refining Scheme Base on Aromatics Complex and Steam Cracking Units (UOP, 2019)

???????????Considering the recent trend of reduction in transportation fuels demand followed by the growth of petrochemicals market makes the synergy between aromatics production complex and steam cracking units an attractive way to maximize the petrochemicals production in the refining hardware and achieve closer integration between refining and petrochemical assets, a growing trend in the downstream industry.

As aforementioned, face the current trend of reduction in transportation fuels demand at the global level, the capacity of maximum adding value to crude oil can be a competitive differential to refiners. Due to the high capital investment needed for the implementation that allows the conventional refinery to achieve the maximization of chemicals, capital efficiency becomes also an extremely important factor in the current competitive scenario as well as the operational flexibility related to the processed crude oil slate. ?

???????????Although the advantages presented by closer integration between refining and petrochemical assets, it’s important to understand that the players of downstream industry are facing with a transitive period where, as presented in Figure 1, the transportation fuels are responsible by great part of the revenues. In this business scenario, it’s necessary to define a transition strategy where the economic sustainability achieved by the current status (transportation fuels) needs to be invested to build the future (maximize petrochemicals). Keep the eyes only in the future or only in the present can be a competitive mistake.

Conclusion

???????????The scenario faced by the players of the downstream industry requires even more competitive capacity to ensure higher value addition to the processed crude oils, mainly considering the current trend of reduction in transportation fuels demand followed by the growing market of petrochemicals that requires a higher conversion capacity in the refining hardware aiming to ensure higher yields of added value derivatives. In this scenario, high integrated refining configurations based on residue upgrading and flexible refining technologies can be economically attractive.

?In this sense, the synergy between aromatics production complex and steam cracking units in the refining hardware can ensure a high yield of added value petrochemical intermediates, ensuring closer integration with petrochemical assets as well as better economic results when compared with gasoline production. Despite these advantages is important to take into account the high capital investment in petrochemical and integrated refining technologies and the time of these investments is a strategic decision to refiners aiming to be prepared to the future of the downstream market, although these risks, the petrochemical integration seems a significant driver to the future of the crude oil refining market and the synergy between aromatics production complex and steam cracking technologies can develop a highlighted role in this scenario.

References

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Deloitte Company. The Future of Petrochemicals: Growth Surrounded by Uncertainties, 2019.

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Encyclopedia of Hydrocarbons (ENI), Volume II – Refining and Petrochemicals (2006).

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OYEKAN, S.O. Catalytic Naphtha Reforming Process. 1st ed. CRC Press, 2019.

Refinery-Petrochemical Integration (Downstream SME Knowledge Share). Wood Mackenzie Presentation, 2019.

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Dr. Marcio Wagner da Silva is Process Engineer and Project Manager focusing on Crude Oil Refining Industry based in S?o José dos Campos, Brazil. Bachelor in Chemical Engineering from University of Maringa (UEM), Brazil and PhD. in Chemical Engineering from University of Campinas (UNICAMP), Brazil. Has extensive experience in research, design and construction to oil and gas industry including developing and coordinating projects to operational improvements and debottlenecking to bottom barrel units, moreover Dr. Marcio Wagner have MBA in Project Management from Federal University of Rio de Janeiro (UFRJ), in Digital Transformation at PUC/RS, and is certified in Business from Getulio Vargas Foundation (FGV).

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