Leaving the "Red Ocean" of the Gasoline Market - Naphtha to Chemicals Refining Routes

Introduction and Context

The current scenario present great challenges to the crude oil refining industry, prices volatility of raw material, pressure from society to reduce environmental impacts and refining margins increasingly lower. 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 – Global Oil Demand by Derivative (Wood Mackenzie, 2020)

According to Figure 1, is expected a growing demand by petrochemicals while the transportation fuels tend to present falling consumption. Still according to Wood Mackenzie data, presented in Figure 2, due to the higher added value, the most integrated refiners tend to achieve higher refining margins than the conventional refiners which keep the operations focused on transportation fuels.

Figure 2 – Refining Margins to Integrated and Non-Integrated Refining Hardware (Wood Mackenzie, 2020)

NCM = Net Cash Margins

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.

Figure 3 present an overview of the trend of growing to the petrochemical market in short term.

Figure 3 – Growing Trend in the Demand by Petrochemical Intermediates (Wood Mackenzie, 2020)

As presented in Figure 3, some of the most promising petrochemical intermediate is the aromatics benzene and p-xylene. The maximization of aromatics in the refining hardware is possible through the installation of catalytic reforming technologies associated with a separation unit.

Beyond the aromatics production, in markets with surplus of gasoline, some alternatives like blend the heavier fraction of naphtha with diesel and jet fuel can be an interesting strategy, but this alternative presents limitations due to the middle distillates specifications like volatility and Reid Vapor Pressure (RVP). In this case, technologic routes capable to manage naphtha molecules aiming to direct these streams to petrochemical intermediates can ensure closer integration with petrochemical assets as well as higher added value to refiners. Some markets already are facing with the gasoline surplus, in these cases, directing naphtha to petrochemicals against gasoline can be an attractive way to ensure competitiveness to refiners. It's interesting to quote the potential competitive imbalance of the downstream industry in short term due to the growing demand for petrochemicals. Based on data from 2019 the total capital investments in crude to chemicals refineries is 300 billion US dollars and 64 % of this investment was made by Asian players, to reinforce this trend Figure 4 present a comparison between the relation of crude oil distillation capacity and the integrated refinery capacity for each continent.

Figure 4 – Crude Oil Distillation Capacity and Integrated Refinery Capacity for Each Continent (Wood Mackenzie, 2023)

Figure 4 shows that the Asian players have a superior integration capacity of their refining assets in comparison with another continents, as mentioned above, this can be translated in a significant competitive advantage to the Asian players and a great potential o competitive imbalance of the downstream market considering the recent forecasts which indicates growing demand for petrochemicals. Furthermore, it’s possible to see the power of the China in the Asian and global downstream market.

Again, being a high demand and most profitable market, the alternative to convert naphtha to petrochemicals should be a trend to refiners inserted in markets with gasoline surplus in the next years. According to data from Wood Mackenzie Company (2021), the highly integrated refiners can add from US$ 0,68 to US$ 2,02/ bbl. Still according to Wood Mackenzie, the Asian Market presents the major concentration of integrated refining plants.

According to the recent forecasts, the Asian market tends to respond by 90 % of the expected growth of world crude oil consumption considering the 2019 to 2026 period and the most part of this growth is related to petrochemicals demand. According to data from Asian Downstream Insights (2021) is expected an annual growth of 4,25 % in the petrochemicals demand in the Asian Market considering next five years, this scenario is leading the players of the Asian downstream sector to lead the world efforts to petrochemical integration, this is translated into high capital spending into crude to chemicals refineries, especially in China.

As presented in Figure 5, the petrochemicals demand tends to drive the crude oil demand for the next years.

Figure 5 – Growth of Petrochemicals as Driver for Crude Oil Consumption (IEA, 2021)

Additionally, it’s important to quote that the gasoline demand will be sustained by the in developing economies, as presented in Figure 6.

Figure 6 – Growth of Gasoline Demand for the Next Years (IEA, 2021)

This fact tends to restrict the consumer market which tends to offer lower refining margins, another great advantage to refiners capable to convert naphtha to petrochemicals against gasoline.

Based on description above it’s possible to apply the article published by W. Chan Kim and Renée Mauborge called “Blue Ocean Strategy” in Harvard Business Review, to classify the competitive markets in the downstream industry. In this article the authors define the conventional market as a red ocean where the players tend to compete in the existing market focusing on defeat competitors through the exploration of existing demand, leading to low differentiation and low profitability. The blue ocean is characterized by look for space in non-explored (or few explored markets), creating and developing new demands and reaching differentiation, this model can be applied (with some specificities once is a commodity market) to the downstream industry, considering the traditional transportation fuels refineries and the petrochemical sector.

Due his characteristics, the transportation fuels market can be imagined like the red ocean, where the margins tend to be low and under high competition between the players with low differentiation capacity. On the other side the petrochemicals sector can be faced like the blue ocean where few players are able to meet the market in competitive conditions, higher refining margins, and significant differentiation in relation to refiners dedicated to transportation fuels market. Figure 7 present the basic concept of blue ocean strategy in comparison with the traditional red ocean where the players fight to market share with low margins.

Figure 7 – Differences between Blue and Red Ocean Strategies (KIM & MAUBORGNE, 2004)

As presented above, the market forecasts indicates that the refiners able to maximize petrochemicals against transportation fuels can achieve highlighted economic performance in short term, in this sense, the crude oil to chemicals technologies can offer even more competitive advantage to the refiners with capacity of capital investment.

Can be difficult to some people to understand the term “differentiation” in the downstream industry once this is a market that deal with commodities, but the differentiation here is related to the capacity to reach more added value to the processed crude oil and, as presented above, nowadays this is translated in the capacity to maximize the petrochemicals yield, creating differentiation between integrated and non-integrated players. In other words, it’s possible to adapt the strategy to ensure more added value to the processed crude leaving the “red ocean” of transportation fuels enjoying the growing market of petrochemicals.

Higher Added Value to the Naphtha – Petrochemical Integration Concept

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

Figure 8 – Synergies 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, pyrolysis 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 9.

Figure 9 – Petrochemical Integration Levels (IHS Markit, 2018)

According to the classification proposed, the crude to chemicals refineries is considered the maximum level of petrochemical integration where the processed crude is totally converted into petrochemical intermediates like ethylene, propylene, and BTX.

Catalytic Reforming Technologies – Naphtha to Aromatics

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 significantly raise 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 has 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 10 present a basic process flow diagram for a typical semi-regenerative catalytic reforming unit.

Figure 10 – 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 has 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 11 presents a flow diagram to Aromazing? catalytic reforming unit.

Figure 11 – Aromizing? Reforming Technology by Axens Company

Both technologies are commercial and some process plants with these technologies are in operation around the world. ?Figure 12 presents a basic process flow diagram to CCR Platforming? developed by UOP Company.

Figure 12 – 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.

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, 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.

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 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.

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 Para-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). Figure 13 present the chemical arrangement of the xylenes isomers.

Figure 13 – Chemical Arrangement of the Xylene Isomers

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 14.

Figure 14 – 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 15.

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 15 – 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. As presented in Figure 14, the main reactions carried out in the aromatics production process aiming to improve the yield of benzene and xylenes are the toluene transalkylation presented in Figure 16 and the toluene disproportionation, presented in Figure 17.

Figure 16 – Toluene Transalkylation Reaction

Figure 17 – Toluene Disproportionation

Fluid Catalytic Cracking Technologies – The Maximum Olefins Operation Mode

According to the market demand, the FCC units can be optimized to produce the most demanded derivatives, refiners facing gasoline surplus markets can operate the processing unit in maximum olefins operation mode, to minimize the production of cracked naphtha.

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 18.

Figure 18 - 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.

The Petrochemical FCC Alternative – Complying with Current Market Demand

As quoted earlier, in markets with high demand by petrochemicals, the petrochemical FCC can be an attractive alternative to refiners aiming to ensure higher added value to bottom barrel streams. An example of FCC technology developed to maximize the production of petrochemical intermediates is the PetroFCC? process by UOP Company, this process combines a petrochemical FCC and separation processes optimized to produce raw materials to the petrochemical process plants. Other available technologies are the HS-FCC? process commercialized by Axens Company, and INDMAX? process licensed by Lummus Company.

To petrochemical FCC units, the reaction temperature reaches 600 oC and higher catalyst circulation rate raises the gases production, which requires a scaling up of gas separation section. ?The higher thermal demand makes advantageous operates the catalyst regenerator in total combustion mode leading to the necessity of installation a catalyst cooler system.

Figure 19 presents the results of a comparative study, carried out by Technip Company, showing the yields obtained by conventional FCC units, optimized to olefins (FCC to olefins), and the HS-FCC? designed to maximize the production of petrochemical intermediates.

Figure 19 – Comparative Study between Conventional FCCs and Petrochemical FCC (HS-FCC?)

It’s observed a higher reaction temperature (TRX) and a cat/oil ratio five times higher when are compared the conventional process units and the petrochemical FCC (HS-FCC?), leading to a growth of the light olefins yield (Ethylene + Propylene + C4=’s) from 14 % to 40%.

The installation of petrochemical catalytic cracking units requires a deep economic study taking into account the high capital investment and higher operational costs, however, some forecasts indicate growth of 4,0 % per year to the market of petrochemical intermediates until 2025. In this scenario can be attractive the capital investment aiming to raise the market share in the petrochemical sector, allowing then a favorable competitive positioning to the refiner, through the maximization of petrochemical intermediates. Figure 20 presents a block diagram showing a case study demonstrating how the petrochemical FCC unit, in this case the INDMAX? technology by Lummus Company, can maximize the yield of petrochemicals in the refining hardware.

Figure 20 – Olefins Maximization in the Refining Hardware with INDMAX? FCC Technology by Lummus (SANIN, A.K., 2017)

In refining hardware with conventional FCC units, further than the higher temperature and catalyst circulation rates, it’s possible to apply the addition of catalysts additives like the zeolitic material ZSM-5 that can raise the olefins yield close to 9,0% in some cases when compared with the original catalyst. This alternative raises the operational costs, however, as aforementioned can be economically attractive considering the petrochemical market forecasts.

Among another petrochemical FCC technologies, it’s possible to quote the Maxofin? process developed by KBR Company and the SCC? technology developed by Lummus Company.

Due to the higher production of light olefins, mainly ethylene, another important difference between conventional and petrochemical FCC units is related to the gas recovery section, while in conventional FCC is applied absorber columns, in petrochemical units is applied cryogenic processes though refrigeration cycles in similar conditions which are applied in steam cracking units, as presented in Figure 21 for the ACO? technology developed by KBR Company.

Figure 21 – Olefins Recovery Section of ACO? Technology by KBR Company (TALLMAN et. al., 2010)

The cryogenic processes applied to olefins recovery raises, even more, the capital requirement to petrochemical FCC units when compared with conventional FCCs, despite this, the growing market for petrochemicals and falling demand for transportation fuels, tends to compensate the higher investment.

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 consider 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 22.

Figure 22 – Typical Process Flow Diagram for an 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).

Naphtha Steam Cracking Process – More Olefins and Less Fuels

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 needs to present high paraffin content (higher than 66 %). Figure 23 presents a typical steam cracking unit applying naphtha as raw material to produce olefins.

Figure 23 – Typical Naphtha Steam Cracking Unit (Encyclopedia of Hydrocarbons, 2006)

Due to his relevance, great technology developers have 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 technologies 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. Another commercial technology dedicated to optimizing the yield of ethylene is the SCORE? technology developed by KBR and ExxonMobil Companies which combines a selective steam cracking furnace with high performance olefins recovery section.

The cracking reactions occurs in the furnace tubes, the main concern and limitation to operating lifecycle of 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. 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. Despite be possible to operate with naphtha, nowadays the steam cracking operators have chosen to operate with ethane or LPG against naphtha due to the competitive prices related to the new sources of NGL (Natural Gas Liquid), despite this trend over the last years, in markets where is observed a gasoline surplus, naphtha can still an attractive alternative as feedstock to steam crackers.

According to some forecasts, the demand by propylene will raise from 130 million metric tons in 2020 to around to 190 million metric tons in 2030. Facing the increasingly light feed to refineries and steam cracking units which tends to favor the ethylene production in detriment of propylene, the propylene demand tends to be supplied by on-purpose propylene production routes like propane dehydrogenation, methanol to olefins (MTO), and olefins metathesis.

Light Paraffin Dehydrogenation Technologies

Another alternative to improve the yield of light olefins in the refining hardware is to apply paraffin dehydrogenation technologies. Light paraffin is normally commercialized as LPG or gasoline and present reduced added value when compared with light olefins.

Dehydrogenation process involves the hydrogen remove from paraffinic molecule and consequently hydrogen production, according to the reaction (1):

R2CH-CHR2? ? R2C=CR2 + H2 (1)

The dehydrogenation reactions have strongly endothermic characteristics, and the reactions conditions include high temperatures (close to 600 oC) and mild operating pressures (close to 5 bar). The catalyst normally applied in the dehydrogenation reactions are based on platinum carried on alumina (others active metals can be applied).

Figure 24 shows a schematic process flow diagram for a typical dehydrogenation process unit.

The main processes that can produce streams rich in light paraffin are physical separation processes as LPG from atmospheric distillation and units dedicated to separate gases from crude oil.

Figure 24 – Process Flow Diagram for a Typical Light Paraffin Dehydrogenation Process Unit.

The feed stream is mixed with the recycle stream before to entre to the reactor, the products are separated in fractionating columns and the produced hydrogen is sent to purification units (normally PSA units) and, posteriorly sent to consumers units as hydrotreating and hydrocracking, according to refining scheme adopted by the refiner. Light compounds are directed to the refinery or petrochemical complex fuel gas pool, after adequate treatment while the olefinic stream is directed to petrochemical intermediates consumer market.

During the dehydrogenation process there is a strong tendency to coke deposition on the catalyst surface and, periodically is carried out the regeneration of the catalytic bed through controlled combustion of the produced coke. Some process arrangements present two reactors in parallel aim to optimize the processing unit operational availability, in these cases while a reactor is in production the other is in the regeneration step.

Due to the growing market and high added value of light olefins, great technology developers have been dedicated his efforts to develop paraffin dehydrogenation technologies. The UOP company developed and commercialize the OLEFLEX? that is capable to produce olefins from paraffin dehydrogenation with a continuous catalyst regeneration process, despite the higher initial investment, this technology can minimize the unavailability period to regenerate the catalyst. Figure 25 presents a basic process flow diagram for the OLEFLEX? technology by UOP Company. Another paraffin dehydrogenation technology from UOP Company is the PACOL? process.

Figure 25 – Basic Process Flow Diagram for the OLEFLEX? Technology by UOP Company (MARSH & WERY, 2018)

Another available technology is the CATOFIN? process, licensed by Lummus Company, as aforementioned, in this case, is applied two reactors in parallel, as presented in Figure 26.

Figure 26 – Simplified Process Scheme to CATOFIN? Dehydrogenation Technology, by Lummus Company.

Others dehydrogenation technologies available are the processes STAR? commercialized by ThyssenKrupp-Uhde Company and the process FBD? by SnamProgetti Company. ?The STAR? process is presented in Figure 27.

Figure 27 – Process Flow Diagram for the STAR? Paraffin Dehydrogenation Technology by ThyssenKrupp-Uhde Company (YOUSSEF et. al., 2008).

Due to his chemical characteristics, olefinic compounds can be employed in the production of a large quantity of interest products as polymers (polyethylene and polypropylene) propylene oxide and oxygenated compounds production intermediates (MTBE, ETBE, etc.).

As a process of high energy consumption, there is a great variety of research in the sense of developing more active and selective catalysts that reduce the need for energetic contribution to the dehydrogenation process. One of the main variations of the dehydrogenation process is the process called oxidative dehydrogenation that occurs according to reaction 2.

R2CH-CHR2 + O2 ? R2C=CR2 + H2O (2)

This reaction is strongly exothermic, and this is the main advantage in relation of the traditional dehydrogenation process, due to the high risk of paraffin combustion against the dehydrogenation reaction. Figure 28 presents the main characteristics of the quoted paraffin dehydrogenation technologies.

Figure 28 – Main Characteristics of Commercial Paraffin Dehydrogenation Technologies (YOUSSEF et. al., 2008).

Olefins Metathesis

The olefins metathesis process involves the combination of ethylene and butene to produce propylene as presented in reaction 3.

H2C=CH2 + H3C-HC=CH-CH3 → 2 H2C=HC-CH3 (3)

The main technology licensors for olefins metathesis processes are the Lummus Company, and IFP (Institut Fran?ais du Pétrole). Figure 29 presents a basic process flow arrangement for the OCT? technology, developed by Lummus Company.

Figure 29 – Process Flow Diagram for OCT? Olefins Metathesis Technology by Lummus Company.

The economic viability of olefins metathesis units relies on the price gap between propylene and ethylene as well as the ethane availability in the market.

The Combination of FCC and Steam Cracking Units – Maximum Olefins Yield

As aforementioned, maximize the light olefins yield in the refining hardware can be an attractive way to ensure competitiveness in the downstream market according to the recent forecasts. The combination of FCC and steam cracking units in the refining hardware can be an alternative to achieve this goal. Table 2 presents a comparison between steam cracking and FCC technologies.

The characteristics of the FCC and steam cracking units allows high yield of olefins in the refining without competition for feedstocks, once the FCC is a bottom barrel conversion technology based in carbon rejection that applies mainly gasoil as feed stream while the steam cracking process produces mainly ethylene through thermal cracking of ethane and high paraffinic naphtha.

The yield of propylene in the steam cracking units relies on the feedstock quality, being higher in units processing naphtha. In the last years, some refiners are adopting the ethane as main feedstock due to his lower prices, this fact reduces the propylene offer from steam crackers, raising the relevance of the propylene from FCC units to ensure the market supply.? This fact has been the main driver to the growing of propylene on purpose technologies like propane dehydrogenation, methanol to olefins, and metathesis. Despite this recent trend, the steam cracking units remain the main propylene source to the market with close to 48 % of the market.

An example of refining configuration relying on FCC and steam cracking units is presented in Figure 30.

Figure 30 – Integrated Refining Scheme Base on FCC 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 FCC and steam cracking units an attractive way to maximize the petrochemicals production in the refining hardware.

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 strategic mistake.

Conclusion

Nowadays, is still difficult to imagine the global energetic matrix free of fossil transportation fuels, especially for in developing economies. Despite this fact, recent forecasts, growing demand by petrochemicals, and the pressure to minimize the environmental impact produced by fossil fuels creates a positive scenario and acts as main driving force to closer integration between refining and petrochemical assets, in the extreme scenario the zero fuels refineries tend to grow in the middle term, especially in developed economies.

The synergy between refining and petrochemical processes raises the availability of raw material to petrochemical plants and makes the supply of energy to these processes more reliable at the same time ensures better refining margin to refiners due to the high added value of petrochemical intermediates when compared with transportation fuels. The development of crude to chemicals technologies reinforces the necessity of closer integration of refining and petrochemical assets by the brownfield refineries aiming to face the new market that tends to be focused on petrochemicals against transportation fuels, it’s important to note the competitive advantage of the refiners from Middle East that have easy access to light crude oils which can be easily applied in crude to chemicals refineries. As presented above, closer integration between refining and petrochemical assets demands high capital spending, despite this fact, the installation of refining units capable to add value to the naphtha can be a significant competitive advantage among the refiners, especially those players inserted in market with gasoline surplus. The advantage of the naphtha to chemicals routes can be exemplified through the growing “propylene gap” present in the text where the refiners capable to maximize the propylene yield both to on-purpose or traditional production (FCC of Steam Cracking) can enjoy a significant competitive advantage in the market.

Although the benefits of petrochemical integration, it’s fundamental taking in mind the necessity to reach a circular economy in the downstream industry, to achieve this goal, the chemical recycling of plastics is essential. As presented above, there are promising technologies which can ensure the closing of the sustainability cycle of the petrochemical industry.

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Dr. Marcio Wagner da Silva is Process Engineering Manager at a Crude Oil Refinery based in S?o José dos Campos, Brazil. He earned a bachelor’s in chemical engineering from the University of Maringa (UEM), Brazil and a PhD. in Chemical Engineering from the University of Campinas (UNICAMP), Brazil. He has extensive experience in research, design and construction in the oil and gas industry, including developing and coordinating projects for operational improvements and debottlenecking to bottom barrel units, moreover Dr. Marcio Wagner earned an MBA in Project Management from the Federal University of Rio de Janeiro (UFRJ), and in Digital Transformation at Pontifical Catholic University of Rio Grande do Sul (PUC/RS), and is certified in Business from Getulio Vargas Foundation (FGV).