CoatAlloy Barrier Coating for Reduced Coke Formation in Steam

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CoatAlloy ™ Barrier Coating for Reduced Coke Formation in Steam Cracking Reactors: Experimental Validation and Simulations Natalia Olahova, Steffen H. Symoens, Marko R Djokic, Nenad Ristic, Stamatis A Sarris, Mathieu Couvrat, Fanny Riallant, Hugues Chasselin, Marie-Françoise Reyniers, and Kevin Marcel Van Geem Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b04271 • Publication Date (Web): 20 Dec 2017 Downloaded from http://pubs.acs.org on December 28, 2017

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Industrial & Engineering Chemistry Research

CoatAlloy™ Barrier Coating for Reduced Coke Formation in Steam Cracking Reactors: Experimental Validation and Simulations

Natália Olahová1, Steffen H. Symoens1, Marko R. Djokic1, Nenad D. Ristic1, Stamatis A. Sarris1, Mathieu Couvrat², Fanny Riallant², Hugues Chasselin², Marie-Françoise Reyniers1, Kevin M. Van Geem1,* 1

Ghent University, Laboratory for Chemical Technology, Technologiepark 914, 9052 Gent,

Belgium. 2

Manoir Industries, 12 Rue des Ardennes BP8401 - Pitres 27108 VAL DE REUIL Cedex,

France. *

Corresponding author: Technologiepark 914, 9052 Gent, Belgium; [email protected]

1 ACS Paragon Plus Environment

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Abstract: The coking tendency under steam cracking conditions of CoatAlloy™, a newly developed multilayered Al barrier coating deposited on a commercial 25/35 Cr-Ni base alloy and aimed at reducing the coke formation under hydrocarbon atmosphere at > 1100 K temperatures was investigated. It was benchmarked to the uncoated commercial 25/35 Cr-Ni base alloy with a known low coking tendency in ethane steam cracking in a pilot plant. The influence of process conditions, such as coil outlet temperature, pre-sulfidation, continuous sulfur addition and aging was evaluated. The applied coating resulted in a reduced coking tendency as well as reduced yields of both CO and CO2 compared to the uncoated coil. The surface of both tested reactor materials was studied by means of SEM and EDX analysis. Further scale up was assessed by simulations of an industrial ethane cracker. All the findings show that the CoatAlloyTM barrier coating is capable of reducing coke formation and maintains its anti-coking activity over multiple cracking-decoking cycles. Keywords: steam cracking, ethane, coke formation, barrier coating, sulfur addition, pilot plant, SEM and EDX, run length simulations


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1

Introduction

Steam cracking of hydrocarbons will no doubt remain the main process for the production of valuable base chemicals such as olefins (ethylene, propylene and butadiene) and aromatics (benzene, toluene and xylenes). One of the process’ major unwanted byproducts is a carbonaceous residue, coke, deposited on the inner walls within the reactor tube and transfer line heat-exchanger (TLE)1,2. The coke layer strongly affects both the production and energetic efficiency and the economics of the process. Therefore the development of novel coke-reducing technologies is of interest to the academic and industrial community . In general, all the available technologies can be divided into three main groups, as mentioned below:

•

Feed additives

•

Three dimensional (3D) reactor configurations

•

Surface technologies

The focus in this paper is on the third category of anti-coking solutions. Since the reactor material is one of the most important factors that determine the amount of coke formed, surface technologies such as low-coking alloys and coatings have gained in importance over the last decades3. Increasing the Cr and Si content in alloys is believed to reduce coke formation. However, their increase is restricted by the negative impact on the mechanical properties. A recent method consisted in the addition of aluminum to the cracking coils, i.e. coating the surface with alumina, which is much more stable than chromia at higher temperatures4. Several companies have publicized coils with inner surfaces that result in an important reduction of coke formation. In all cases, rather thin coatings have been formed on the inner surfaces of hightemperature alloy steels. These coatings have low concentrations of nickel, iron, and other metals 3 ACS Paragon Plus Environment


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that produce filamentous coke5. The main advantage that coatings offer is that they can be applied (often in-situ) over a regular base alloy. Distinction can be made between coatings that passivate the inner coil wall6,7 and catalytic coatings that convert coke to carbon oxides8. A barrier coating passivates the catalytically-active sites of the reactor alloy and therefore eliminates catalytic coke formation. However, the non-catalytic coke formation is not prevented. While catalytic coatings convert deposited coke to carbon oxides and hydrogen through gasification reactions with steam. Two examples of catalytic coatings are CAMOL (CatalyzedAssisted Manufacture of Olefines)9, acquired by BASF and YieldUP8, property of General Electric Company. CAMOL coatings can reach 1-2 year run lengths for light feedstocks and when using appropriate feedstock qualities and operation conditions. When heavier feedstocks are used, run lengths of 100-400 days can be obtained. CAMOL also shows a high operatingtemperature stability (>1400 K)9. On the other hand, application of the YieldUp coating resulted in a coke reduction by 76% compared to the reference alloy reactor. Pilot scale experiments showed that the coating is robust and maintains anti-coking activity even after >10 coking/decoking cycles8. The increased levels of CO and CO2 are expected to generate operational difficulties. However, Petrone et al.9 claimed that the impact of CAMOL-coated coils on the total CO/CO2 production is both manageable and tunable. YieldUp also increased the yields of CO and CO2, but due to the high surface to volume ratio of the reactor that was used, this effect should be significantly reduced when applying the coating in an industrial reactor. Additionally, by tuning the coating formulation, the CO and CO2 yield could be further reduced. A special diffusion coating AlcroPlex® processed by Alon Surface Technologies, Inc. has been tested in a thermobalance system for pyrolysis10. The well-established technology comprises migration of Cr into the uppermost surface of the tube and a chemical vapor deposition that creates the aluminum rich layer. Laboratory tests showed a decrease of the coking rates by 80 and 4 ACS Paragon Plus Environment

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90 % in case naphtha and ethane were used as a feedstock, respectively. That was achieved by blocking the active surface sites which leads to a suppression of the catalytic coke formation. Besides that, the application of the AlcroPlex® results in a lowered production of CO/CO2 comparable with a continuous addition (CA) of sulfur to the feed. In this work the main focus was to investigate the potential anti-coking capability of CoatAlloy™, a barrier coating on a 25/35 Cr-Ni base alloy as compared to the uncoated 25/35 Cr-Ni base alloy. CoatAlloy™, reduces the coke formed on the inner wall by passivating the catalytically-active sites of the reactor alloy and thus eliminating catalytic coke formation. The heterogeneous non-catalytic coking mechanism, however, is not suppressed. The performance of the reference material and the coating applied on the inner wall of the coil was assessed under industrially relevant conditions. The influence of several process conditions, such as the coil outlet temperature (COT), pre-sulfidation, continuous addition of dimethyl disulfide (DMDS) and aging was investigated during steam cracking of ethane. The surface of both tested materials was further investigated by means of Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) spectroscopy. Next to this, the application of the barrier coating on run length and product yields in an industrial unit was evaluated by performing reactor simulations using COILSIM1D.



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Experimental section

2.1 25/35 Cr-Ni alloy Commercially applied 25/35 Cr-Ni alloy is primarily tested as a reference material for the coated coil is that this type of alloy is widely applied for steam cracking reactors, particularly for high temperature section of the reactor. The composition is presented in Table 1.

2.2 Coating CoatAlloy™ is a multilayered coating with a diffusion barrier which serves to isolate the coating from the base alloy. The top surface is an aluminum-containing layer which gives the material its anticoking performance. The coating is applied on the inner surface of the cracking coil and heattreated just after the deposition step to activate it. The total coating has a thickness of roughly 200 µm. The new generation of the CoatAlloy™11,12 provides high resistance to coking, carburization, and hot erosion.

2.3 Pilot plant setup To investigate the coating’s performance ethane steam cracking experiments were executed in the pilot plant setup available at the Laboratory for Chemical Technology at Ghent University. The experimental setup, shown schematically in Figure 1, consists of three main sections: the feed section, the reaction section and the analysis section. Since all the sections have been described by several authors8,13-18 elsewhere, only a short description will be given here. The feed section consists of different tanks from which several types of hydrocarbon feedstock can be fed, both liquid and gaseous feedstocks. To add the sulfur-containing compound (DMDS) 6 ACS Paragon Plus Environment

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uniformly and precisely, it is dissolved in hexane and introduced into the cracking coil using an ISCO 500D syringe pump having a capacity of 0.5 L. The de-ionized water flow, which is used to produce steam, as well as the hydrocarbon flow, is set using computer controlled pumps and/or Coriflow™ mass flow controllers. The furnace section divided into 7 cells is built of silica/alumina bricks and is about 4 m long, 0.7 m wide and 2.6 m high. The cells are heated by means of 90 premixed gas burners placed on the side walls in such a way as to provide a uniform distribution of heat. The fuel supply system contains a combustion controller that regulates the fuel-to-air ratio. The furnace is divided into seven separate cells that can be heated independently so that any temperature profile can be employed. In the first two cells, the feedstock is preheated, evaporated and mixed with the diluent (steam), allowing homogeneous conditions at the beginning of the actual cracking reactor. Steam cracking and coke deposition only occur in the last five cells, where the temperature is above 873 K. The reactor outlet pressure is controlled by a computer regulated restriction valve. The temperature and pressure of the reacting gas is measured by means of twenty-two thermocouples and five pressure transducers that are mounted along the coil. The reactor coil used for the barrier coating experiments is made out of two heatresistant tube alloys welded together: Incoloy 800HT and 25/35 Cr-Ni alloy, with an optional CoatAlloy™ coating attached on its surface. The first part of the tube is almost 4.8 m long, made of Incoloy 800HT with an internal diameter of 9 mm and is placed in cell 3 and cell 4. The second part (Figure 1, green) is located in cell 5 and cell 6 and is manufactured out of commercial 25/35 Cr-Ni alloy. This part is about 6.2 m long and has an internal diameter of 26 mm and an outer diameter of 40 mm. As can be seen from Figure 1 (red), the coil in the last cell is connected to a 0.6 m long straight tube made of Incoloy 800HT with an internal diameter 9 mm. As depicted in Figure 1, the CoatAlloy™ coating was applied on the reactor inner wall in cell 5 and



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cell 6. The alloy composition of the reactor material applied in the first four cells, as well as the reference material is specified in Table 119,20. The analysis section allows on-line identification and quantification of the entire product stream, i.e. a wide boiling point mixture, containing all permanent gases, such as H2, CO, CO2 and N2 which is used as an internal standard, and hydrocarbons ranging from methane to polycyclic aromatic hydrocarbons. After passing through the reactor coil, the effluent is quickly cooled in the TLE to stop unwanted reactions. Analysis samples are taken on‐line at different points of the setup. For C5+ analysis, this sampling point is located just before the TLE. After the TLE cooling and separation of the heaviest hydrocarbons and water, the remainder of the effluent is sent towards the flare. Before reaching the flare, a sampling point for C4- compounds is available. After passing through a condenser and a dehydrator, the branch ends in two separate GC’s, a refinery gas analyzer (RGA) and a permanent gas analyzer (PGA). This analysis allows detection of all permanent gasses present in the effluent and additional analysis of the lighter hydrocarbons. An infrared (IR) detector can be used to measure continuously the CO and CO2 content of the effluent, on‐line or during decoking.

2.4 Experimental procedure Experiments executed in the pilot plant setup consist of several steps: pre-oxidation, presulfidation (optional), cracking and decoking. Detailed information on the experimental conditions for each process step is given in Table S1 in the Supporting Information. In total 3 experiments were performed, hereafter referred to as Pre-S + CA, COT max and Aging. Each experiment comprises 1 cracking cycle, except for the aging procedure, in which eight


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cycles were executed. For comparison, we additionally performed experiments Blank and Pre-S and the results can be also found in the Supporting information. Pre-oxidation of the reactor is carried out only prior to the first cracking experiment for both tested materials. For subsequent experiments pre-oxidation is not necessary because of the decoking step implemented after cracking. The inner surface of the reactor is pretreated under a steam/air mixture and a set temperature profile for 1 hour. This step provides a protective layer formed of oxides which prevents the gas phase from being in contact with the catalytic active sites, present in the alloy21. For the experiments with Pre-S and Pre-S + CA, an additional pretreatment of the inner reactor surface is applied. Similarly to the pre-oxidation, pre-sulfidation with DMDS is performed before cracking under the conditions specified in Table S1. In particular, the reactor is heated under a flow of 1.11 x 10-3 kg.s-1 steam to achieve the desired temperature profile. When the temperature profile remains stable, sulfur is introduced to the reactor with a concentration of 750 ppmw DMDS / H2O. Prior to the introduction of the hydrocarbon feed, the reactor is heated under a steam flow of 0.80 x 10-3 kg.s-1 till the desired temperature profile is reached. Then, the flow rate of ethane is set to the desired value giving the dilution of 0.385 kgsteam.kgethane-1. Due to the introduction of hydrocarbons the temperature of the cracking coil decreases approximately 20 K due to the endothermic nature of the cracking reactions. After about 1.2 x 103 seconds the temperature of the cracking coil reaches the set values (see Table S1). Different durations of cracking were applied, ranging from 1 hour to 6 hours. Prior to the start of a new cracking run, burning of the coke deposited during cracking is necessary. To start a decoking procedure, the reactor is heated to 1073 K under a helium flow of 0.08 x 10-3 kg.s-1 and then steam (0.28 x 10-3 kg.s-1) is introduced into the reactor. After 0.3 x 10-3 s, the helium flow is stopped and air at a flowrate of 0.28 x 10-3 kg.s-1 is admitted to the reactor. 9 ACS Paragon Plus Environment


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As can be seen from Table S1, once the concentration of CO2 in the effluent gas is lower than 1 vol %, the temperature is increased to 1173 K in the last three cells. When practically all the coke is gasified and the concentration of CO2 in the effluent gas is lower than 0.1 vol %, the steam flow is stopped and decoking occurs in an air atmosphere. To prevent a pressure build-up in the outlet of the coil during the cracking run, the coke needs to be removed from that part as well. When the decoking procedure is over, the temperature in the last cell 7 is increased to 1023 K and decoking only with air takes place. During the decoking of the reactor coil, a connection with the infrared CO/CO2 analyzer is established, which allows a continuous measurement of the content of CO and CO2 in the effluent. All experimental runs were carried out at a constant coil outlet pressure, COP, of 2.0 bar abs and a constant hydrocarbon feed flow rate of 2.08 x 10-3 kg.s-1, while maintaining a steam flow rate of 0.8 x 10-3 kg.s-1 (steam dilution: 0.385 kgsteam.kgethane-1). The performance and the coking tendency of the CoatAlloyTM coating were assessed under the same cracking conditions as the reference alloy. Pre-sulfidation of the coil with a steam/DMDS mixture prior to the continuous sulfur addition of 50·10-6 kgDMDS.kgethane-1 was evaluated in the experiment Pre-S + CA. In experiment COT max, the effect of a higher coil outlet temperature of 1143 K was studied with the adopted temperature profile shown in Table S1. All other process conditions were kept the same as the experiments when DMDS was continuously added. Eight cracking cycles were performed evaluating the effect of aging and sulfur addition on the product distribution. Aging means the repetitive switching between cracking/decoking cycles, and thus switching between mildly reducing and highly oxidizing atmospheres. The aging procedure consists of three longer cracking (2, 2, and 6 hrs respectively) cycles followed by three cracking short (1 hr) cycles and finally repeating a long cycle of six hours with intermittent decoking. To validate a harmful effect 10 ACS Paragon Plus Environment

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of the sulfur continuous addition, the last short cycle was performed without sulfur. For further surface analysis of the coked coils, one additional short cycle with continuous DMDS addition was executed in the end.

2.5 Scanning electron microscopy and Energy dispersive X-ray analysis The coked coils were dismounted from the pilot plant setup, samples were cut and analyzed by means of SEM and EDX. The detailed procedure of the sample preparation is addressed in the Supporting information. First, the coked surface of the coil is examined (top view analysis). Afterwards, cross-sectional elemental analyses are performed. Both, the top surface analyses and cross-sectional analyses are performed on a Jeol JSM-7600F scanning electron microscope, which uses a Schottky field emission gun as electron source, and are described in detail in the Supporting information. It provides an ultrahigh resolution with a wide range of probe current for all applications. The Jeol can apply accelerating voltages of 0.1 to 30 kV and magnifications between 25 to 1 000 000 x.

2.6 Coupled simulations of an industrial ethane cracker To evaluate the effect of the improved performance by application of the coating on the run length of an industrial furnace, an accurate simulation model represents a requisite tool. In this work, the in-house developed model COILSIM1D, which allows simulating the run length of industrial steam cracking coils, was employed. In the next paragraphs, the simulations model as well as the description of the simulated cracking unit is presented.



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2.6.1 Kinetic reactor model COILSIM1D is a single event microkinetic model developed for simulating the steam cracking process22,23. Two main parts are essential to conduct the reactor simulations, namely a set of reactor model equations and a reaction network. The reaction network containing a monomolecular µ network and a β network is especially developed for the steam cracking process. The model equations based on a 1-dimensional reactor model comprise the continuity equations for the different species, an energy balance and a momentum equation. Solving results in the product yields and the pressure and temperature profiles along the reactor length see Figure S4 in the Supporting Information. The simulation of the run length of an industrial steam cracker is conducted by the incorporation of a coking model that is developed to determine the coking rates for steam cracking of light hydrocarbon feedstocks24 Only the contribution of the heterogeneous non-catalytic coke formation is considered in this model. To account for the effect of the CoatAlloyTM , the pre-exponential factors of reactions responsible for coke formation were fitted according to the coking rates obtained during the experiments. The pre-exponential factors for the coating differ from the ones for the reference alloy.

2.6.2 Simulated cracking unit The reactor configuration used for the simulation of the run length consists of a serpentine coil with 8 passes suspended in the cracking furnace. The detailed description of the ethane cracking unit has been already given in the work of Schietekat et al.8. To perform a simulation of the industrial cracking coil, the input of the cracking conditions is required. In this study, the simulations have been performed aiming to impose fixed coil outlet conditions, the COT and the COP, see Table S2 in the Supporting Information. An ethane feed with a purity of 97.7 % was


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used. The hydrocarbon and steam flow rate were set to 0.903 kg.s-1 and 0.316 kg.s-1 respectively, resulting in a steam dilution of 0.35. The reactor inlet and outlet temperature were equal to 876 K and 1123 K, respectively, while the coil outlet pressure was set to be 2.0 bars. Moreover, an initial heat flux profile from the furnace to the cracking coil needs to be inserted. The shooting method25 adjusts the inlet pressure and the heat flux profile aiming to meet the requested cracking severity indices at the reactor outlet.

3

Experimental results and discussion

3.1 Product yields The aim of the performed pilot experiments was to study the anti-coking capability of a coating over a reference 25/35 Cr-Ni alloy during ethane steam cracking. The barrier coating, CoatAlloy™, was applied on the pilot reactor inner wall. In the following paragraph, a comparison of the product distribution for both materials under various process conditions is made. It was shown by Froment et al.26 and Wang et al.13 that pre-sulfidation reduces the peak of CO that is detected during the initial stages of a cracking run. In order to suppress the CO production in the asymptotic stage of cracking, the use of continuous added DMDS is necessary. During presulfidation of the coil with a steam/DMDS mixture prior to the continuous DMDS addition, a minor selectivity drop of olefins is noticed with the application of the coating. The decreased carbon oxide values indicate that the coating is capable of reducing the steam reforming reactions. As can be seen in Table 2 and Table 3, the effluent contained less CO and CO2 than during the experiment without the coating (the yields of CO and CO2 were 0.17 and 0.01 wt% 13 ACS Paragon Plus Environment


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respectively for the uncoated coil and those for the coated one were 0.11 and 0.01 wt% respectively). Hence continuous addition of DMDS can mitigate CO and CO2 production when this is necessary for downstream units. The reduced CO and CO2 formation is in line with experiments found in literature

13,14,26

. The increase of the COT to 1143 K shows the expected

result on the yields: as ethane conversion increases, the yields of ethylene, propylene and 1,3butadiene increase too. A slight selectivity drop towards olefins is observed. However the CO and CO2 yields are increased significantly in comparison with the previous experiment. In agreement with previous results, the yields of CO and CO2 are decreased when comparing CoatAlloy™ to the bare MXM reactor; CO yields are decreasing from 0.29 to 0.14 wt% and CO2 yields are decreasing from 0.012 to 0.009 wt%, which is a reduction of 50.7 and 25.0% respectively (see Table 2 and Table 3). This can again be attributed to the application of the coating on the surface and thus blocking the active catalytic sites for steam reforming/coke gasification reactions8. For the first cycle during the aging procedure, a CO and CO2 reduction of 65.5 and 45.0% was obtained compared to commercial 25/35 Cr-Ni alloy. Again, the second cycle shows a reduction of the CO and CO2 yields of 57.0 and 50.0% in comparison with the reference. The reduction of carbon oxides by the coating amounted to 61.9 and 75.0% for CO and CO2 respectively, in the third cycle. The yields of CO and CO2 were again lower for the experiments were CoatAlloy™ was used in the following two 1-hour cycles. CO reduced with 58.3 and 69.3% compared to 25/35 Cr-Ni alloy and CO2 showed a reduction of 70.0 and 76.2%. In the sixth run of the aging experiment, where no continuous addition of DMDS was applied, the yields of CO and CO2 were highly elevated for both commercial 25/35 Cr-Ni alloy and CoatAlloy™, which is caused by steam reforming reactions consuming methane and olefins. Hence continuous sulfur addition affects the carbon oxide production to a large extent. The CO and CO2 yields were much lower in the experiments were the coating was applied; the CO yield 14 ACS Paragon Plus Environment

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for 25/35 Cr-Ni and CoatAlloy™ were 11.11 and 2.87 wt% respectively and the CO2 yields were 1.16 and 0.28 wt% respectively which is a reduction of 74.1 and 76.0%. The coating had a good performance in the seventh cycle, showing a reduction of 64.7 and 77.8% for CO and CO2 respectively compared to the reference 25/35 Cr-Ni commercial alloy. The ethane conversion is more or less stable for all experiments, keeping the same P/E ratio of 0.02 wt%.wt%-1. Overall, it can be seen that during short cycles, the yields of CO and CO2 are higher than during longer cycles, which is logical due to the higher initial CO and CO2 formation during the first hours.

3.2 Coke formation The coking tendency of both tested materials, commercial 25/35 Cr-Ni alloy and CoatAlloy™, is summarized in Figure 2 for all the experiments as well as in Table S4 in the supporting information. The total coke after a cracking run is represented by the coke burnt off from the reactor measured by the infrared CO/CO2 gas analyzer during the decoking procedure. The total amount of coke formed in these experiments depends on the respective contribution of the initial catalytic as well as the asymptotic, free-radical coke formation. However, in the pilot plant setup, the coking rate is determined by the value averaged over the total run length and over time. The amount of coke formed on the inner wall of the reactor decreases in all the experiments by the application of the coating compared to the reference 25/35 Cr-Ni alloy. Only in the case for the sixth cycle of the aging experiment, where 25/35 Cr-Ni alloy and CoatAlloyTM show a similar coking rate. For the experiment where pre-sulfidation of the coil with a steam/DMDS solution was performed prior to cracking with a continuous addition of DMDS, 391.0 g of coke was measured with the non-coated coil. As expected, a smaller amount of 271.4 g was measured after applying the coating. 15 ACS Paragon Plus Environment


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The experiment with the highest temperature profile, denoted as high COT, showed a substantially higher coke formation. Comparing both materials, it is observed that the amount of coke deposited was reduced by 31% when the coil was coated with CoatAlloy™ compared to the 25/35 Cr-Ni reactor alloy. A significant pressure build-up was measured during the experiment with reference alloy which caused an interruption of the cracking run after 4 hours. This means that the coating performs better at a higher coil outlet temperature than the reference material and hence longer run lengths are possible. In the end, the effect of aging on the durability of the coating is evaluated. This experimental procedure consists of two 2-hours cycles, one long cycle (6 hours) followed by three short cycles (1 hour) and finally repeating the long cycle of 6 hours. In order to validate a harmful effect of the sulfur continuous addition, the last short cycle was performed without the addition of sulfur. It is believed that sulfur-containing compounds can have a negative effect on the amount of coke formed during the steam cracking process27. This is explained by the passivation of the inner metal wall associated with the absorption of the sulfur species on its surface. The catalytic performance of the metal surface is mainly affected by the blockage of the catalytic active sites responsible for steam reforming reactions. The formed thyil radicals can further react with radicals in the coke layer which leads to more active sites at surface available to gas-phase radicals for non-catalytic heterogeneous coke formation. It was demonstrated that the coking rates were increased when a certain amount of sulfur-containing compound was continuously added to the feed13,14,27,28. This is consistent with the measured lower amount of coke during this cycle compared to the previous cycles. This implies that the continuous addition of DMDS enhances coke deposition. While the reduction in the coking rates is much more apparent without sulfur addition, the increase in CO and CO2 yields is also pronounced (see Table 2 and Table 3). To keep the reactors coked for further analyses of the surface, one additional short cycle with continuous DMDS addition was executed in the end. Also in these experiments, application of the tested coating is seen to reduce


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coke formation. Again, the CoatAlloy™ has a better performance, showing a reduction of the coke deposition by 42, 50 and 57% compared to the reference alloy for the first, second and third cycles, respectively. For the fourth and fifth cycle of 1 hour, coke reductions of 42 and 45%, respectively, were obtained compared to the commercial 25/35 Cr-Ni material. The reduced catalytic activity of the inner wall results in a lower amount of deposited coke results as well as in lower carbon oxides yields during the CoatAlloy™ experiments. The absence of continuous DMDS addition was assessed in the sixth cycle of 1 hour. While the decrease in CO and CO2 yields is much more apparent when the coating is applied, the reduction in coke formation is not so pronounced (from 13.8 g.h-1 to 12.9 g.h-1). The lower reduction of 32 % in coke amount was obtained for the 7th cycle.

3.3 SEM and EDX: Cross sectional analysis 3.3.1 Non-coated samples The elemental mapping of the cross section of a blank 25/35 Cr-Ni coupon is shown in Figure 3 (a). No oxide layer can be seen; a protective oxide layer is formed after pre-oxidation and during decoking. The carbon at the top of the sample originates from the embedment or from the coke layer. The bulk of the material is mainly composed out of Ni, Cr and Fe. This is in accordance with the specifications of the commercial 25/35 Cr-Ni reactor material (see Table 1). In Figure 3 (b), the elemental mapping of the cross section of a coked 25/35 Cr-Ni sample taken at the inlet of coil 5 can be observed. The oxide layer exhibits a rather continuous oxide layer of approximately 3 µm. In accordance with the published literature29,30, the Cr, Si and Mn diffused from the bulk of the material to the top layer to form a protective layer. Under these layers, some areas can be found where Si and O overlap. The elemental mapping of the cross section of a coked 25/35 Cr-Ni sample taken at the outlet of coil 5 is presented in Figure 3 (c). An oxide layer of almost 5-8 µm is present. Oxygen overlaps with Cr, Si and Mn. Cr, Si and Mn diffused from 17 ACS Paragon Plus Environment


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the bulk of the material to the top. This corresponds to the previous sample. Again, no Ni and Fe oxides are formed. The oxide layer does not fully cover the Fe and Ni of the bulk material which can lead to an increased catalytic activity. In Figure 3 (d), the elemental mapping of the 25/35 CrNi sample ‘inlet coil 6’ is presented. The oxide layer has a thickness of approximately 3-4 µm. The oxygen overlaps mainly with Cr. However, also some Fe, Ni, Si and Mn overlay with oxygen. They diffused from the bulk of the material to the surface layer. The elemental mapping of the cross section of a coked 25/35 Cr-Ni sample taken at the outlet of coil 6 is shown in Figure 3 (e). Cr, Mn and Si diffused to the top of the material to form an oxide layer. The oxide layer has a thickness of approximately 5 µm. No Ni diffused in this sample to the upper part of the material. The bulk of the material consists mainly out of Ni, Cr, Fe and Mn. The oxide layer formed during on the surface of 25/35 Cr-Ni do not change with the axial distance along the coil. According to the obtained observations, the main elements present on the surface and compose the oxide layer are Cr, Mn and Si. This implies the presented oxide layer could be composed out of SiO2, MnSiO3, MnCr2O4 and Cr2O3. They are thinner that the oxide layers that of the CoatAlloy TM (Figure 4).

3.3.2 Coated samples The elemental mapping of the cross section of a blank CoatAlloy™ coupon is given in Figure 4 (a). The continuous oxide layer that was developed during the manufacturing process is formed out of Al2O3 and has a thickness of 5-7 µm. However, the layer seems to be split by preparation. The bulk of the material is mainly composed out of Al and Ni. Spots with a higher concentration of Cr are present under the oxide layer. The elemental mapping of the cross section of a coked CoatAlloy™ sample taken at the inlet of coil 5 is shown in Figure 4 (b). It can be noticed that Al and O overlay. Some Ni and Cr also overlay with O. An oxide layer of almost 15 µm is present. 18 ACS Paragon Plus Environment

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In Figure 4 (c), the elemental mapping of the cross section of a coked CoatAlloy™ sample taken at the outlet of coil 5 is shown. It can be noticed that an Al2O3 layer is present. Also, some Ni, Mn and Cr can be found at the surface. A rather thick oxide layer of almost 10-15 µm is observed. The elemental mapping of the cross section of a coked CoatAlloy™ sample taken at the inlet of coil 6 can be observed in Figure 4 (d). An oxide layer with a thickness of 2-5 µm and consisting out of Al and O can be seen. However, no complete oxide layer is present. The oxide layer can be destroyed due to the polishing procedure or due to the applied cooling rate. The bulk of the material consists mainly out of Ni, Al and Cr. Again, the impurities of Si that are found at the top surface analysis cannot be seen in the cross sectional analysis. The elemental mapping of a coked CoatAlloy™ sample (coil 6 outlet) is presented in Figure 4 (e). It can be seen that Al, some Cr and O overlay. A continuous oxide layer of 2-5 µm can be observed. Under the oxide layer, the material consists mainly out of Ni and Al. Spots with a higher concentration of Cr can also be noticed. Again, no Si impurities are found in the cross sectional analysis. SEM and EDX analysis indicate that the oxide layers on CoatAlloyTM is mostly composed out of Al2O3. It is observed that some amount of Cr and Mn, leading to the assumption that MnCr2O4 and Cr2O3 are also present. The thickness of the oxide layer decreases along the axial position of the coil. Closer to the COT measurement, the thickness was smaller.

3.4 Run length simulations of an industrial ethane cracker Simulations of an industrial ethane cracker were performed by means of COILSIM1D to assess the effect of the barrier coating on the run length. The run length versus the wall temperature for both tested materials is plotted in Figure 5. The maximum wall temperature is predicted to be attained after 172 and 400 hours for the non-coated and coated coil, respectively. Overall, the application of the barrier coating increases the run length of the furnace by more than 130 %. 19 ACS Paragon Plus Environment


Page 20 of 53

The results of the simulations at the start of the run (SOR) as well as the end of the run (EOR) are summarized in Table 4. It is clear that reduced yields are measured in the EOR, mainly for the coated tube. The decreased ethylene selectivity is attributed to the larger pressure drop at the end of the reactor caused by a thicker layer of coke, agreeing with the work of Schietekat et al.8. Since the concentration of ethylene increases along the axial position of the reactor, thus more of ethylene is converted into coke by bimolecular reactions. Predicted profiles of the pressure drop at the end of the reactor corresponding to the run length are shown in Figure 6. The pressure drop does enhance with run length for both, the uncoated and uncoated coil. The simulation results show that pressure drop can be reduced throughout the run compared to the uncoated coil by application of the coating.

4

Conclusion

A novel barrier coating, CoatAlloy™ that eliminates coke formation by passivating the catalytically-active sites of the reactor inner surface was tested during steam cracking pilot plant experiments. The aim of these experiments was to study the anti-coking capability of the coating over a reference alloy, commercial 25/35 Cr-Ni alloy. The applied coating showed a better coking resistance by reducing coke formation, and lower CO and CO2 yields compared to the uncoated coil. Higher coking rates were observed after pre-sulfidation with a steam/DMDS mixture prior to a blank cracking run while decreased yields of carbon oxides were obtained only with the CoatAlloy™. Pre-sulfidation with a steam/DMDS mixture prior to continuous DMDS addition of mitigated the CO and CO2 production further. However, a higher coking rate was measured in comparison with the blank run and the Pre-S experiment which is consistent with previous 20 ACS Paragon Plus Environment

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results. Working at higher COT gave a higher conversion, olefin yields as well as higher CO and CO2 yields, but a higher coking rate. CoatAlloy™ was less affected by the increased COT compared to commercial 25/35 Cr-Ni alloy and showed a better performance. The samples were embedded and cross-sectional elemental analyses were performed. The oxide layer was not always fully continuous, which could be caused by preparation of the sample. An oxide layer enriched in aluminum was already present before preoxidation and cracking, this could be seen on the blank CoatAlloy™ sample. It is coherent with the alumina forming nature of the coating. The protective oxide layer of the commercial 25/35 Cr-Ni alloy is formed during preoxidation and during decoking. The oxide layers of the samples were mainly enriched in chromium, it is a typical Cr2O3 forming alloy with additional mixed spinel oxides and SiO2 layers. The oxide layers of the commercial 25/35 Cr-Ni alloy were thinner than the oxide layers presented on the CoatAlloy™ samples with a thickness of approximately 3 – 8 µm. The thickness of the oxide layer was homogeneous along the axial distance of the coil. Supporting information: The Supporting Information is available free of charge on the ACS Publications website. -

Experimental procedure. Details on scanning electron microscopy and energy-dispersive X-ray analysis

-

Details on the coupled simulations of an industrial unit

-

Experimental results: product yields, coke formation and elemental analyzer

Acknowledgements:



Page 22 of 53

Authors acknowledges financial support from a doctoral fellowship from the Fund for Scientific Research Flanders (FWO). The authors also acknowledge the financial support from the Long Term Structural Methusalem Funding by the Flemish Government – grant number BOF09/01M00409


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Nomenclature Abbreviations 3D

Three-Dimensional

CA

Continuous addition

-

CAMOL Catalyzed-Assisted Manufacture of Olefins

-

CIT

Coil Inlet Temperature

K

COP

Coil Outlet Pressure

bar abs

COT

Coil Outlet Pressure

K

DMDS

DiMethyl DiSulfide

-

EDX

Energy Dispersive X-ray

-

EOR

End Of Run

-

IR

InfraRed

-

MERT

Mixing Element Radiant Tube

-

PGA

Permanent Gas Analyzer

-

Pre-S

Pre-sulfidation

RGA

Refinery Gas Analyzer

-

SOR

Start Of Run

-

TLE

Transfer Line heat Exchanger

-



Page 24 of 53

References (1) Mahamulkar, S.; Yin, K.; Agrawal, P. K.; Davis, R. J.; Jones, C. W.; Malek, A.; Shibata, H., Formation and Oxidation/Gasification of Carbonaceous Deposits: A Review. Ind. Eng. Chem. Res. 2016, 55, (37), 9760-9818. (2) Kucora, I.; Paunjoric, P.; Tolmac, J.; Vulovic, M.; Speight, J. G.; Radovanovic, L., Coke Formation in Pyrolysis Furnaces in the Petrochemical Industry. Pet. Sci. Technol. 2017, 35, (3), 213-221. (3) Muñoz, A. E.; Van Geem, K. M.; Reyniers, M.-F.; Marin, G. B., Influence of the Reactor Material Composition on Coke Formation During Ethane Steam Cracking. Ind. Eng. Chem. Res. 2014. (4) Prescott, R.; Graham, M. J., The Formation of Aluminum-Oxide Scales on High-Temperature Alloys. Oxid. Met. 1992, 38, (3-4), 233-254. (5) McKimpson, M. G.; Albright, L. F., Future Coils for Ethylene Furnaces: Reduced or No Coking and Increaed Coil Longevity Prepr. Pap. - Am. Chem. Soc., Div. Fuel Chem. 2004, 49, (2), 776-777. (6) Ropital, F.; Broutin, P.; Reyniers, M. F.; Froment, G. F., Anticoking Coatings for High Temperature Petrochemical Reactors. Oil Gas Sci. Technol. 1999, 54, (3), 375-385. (7) Ganser, B.; Wynns, K. A.; Kurlekar, A., Operational experience with diffusion coatings on steam cracker tubes. Mater. Corros. 1999, 50, (12), 700-705. (8) Schietekat, C. M.; Sarris, S. A.; Reyniers, P. A.; Kool, L. B.; Peng, W.; Lucas, P.; Van Geem, K. M.; Marin, G. B., Catalytic Coating for Reduced Coke Formation in Steam Cracking Reactors. Ind. Eng. Chem. Res. 2015, 54, (39), 9525-9535. (9) Petrone, S.; Deuis, R. L.; Kong, F.; Unwin, P., Catalyzed-Assisted Manufacture of Olefins (CAMOL): Year-(4) Update on Commercial Furnace Installations. In 2010 Spring National Meeting San Antonio, AICHE: Texas, 2010; Vol. 88a. (10) Zychlinski, W.; Wynns, K. A.; Ganser, B., Characterization of material samples for coking behavior of HP40 material both coated and uncoated using naphtha and ethane feedstock. Mater. Corros. 2002, 53, (1), 30-36. (11) Redmond, T.; Bailey, A.; Chen, Y.; Fisher, G.; Miller, R. In Performance of Coatalloy Coating Systems In Ethylene Pyrolysis Furnaces Using Different Feedstocks, Session 86: Fundamental Topics in Ethylene Production, 12th Ethylene Producers' Conference, Atlanta, Georgia, USA, 2000; Atlanta, Georgia, USA, 2000. (12) Bergeron, M.; Maharajh, E.; McCall, T. In A Low Coking Environment for Pyrolysis Furnace – CoatAlloy, Session 63: Ethylene Furnace Technology and Operations, 11th Annual Ethylene Producers Conferenc, Houston, Texas, USA, 1999; Houston, Texas, USA, 1999. (13) Wang, J.; Reyniers, M.-F.; Marin, G. B., Influence of Dimethyl Disulfide on Coke Formation during Steam Cracking of Hydrocarbons. Ind. Eng. Chem. Res. 2007, 46, (12), 41344148.


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(14) Dhuyvetter, I.; Reyniers, M.-F.; Froment, G. F.; Marin, G. B.; Viennet, D., The Influence of Dimethyl Disulfide on Naphtha Steam Cracking. Ind. Eng. Chem. Res. 2001, 40, (20), 43534362. (15) Pyl, S. P.; Schietekat, C. M.; Reyniers, M.-F.; Abhari, R.; Marin, G. B.; Van Geem, K. M., Biomass to Olefins: Cracking of Renewable Naphtha. Chem. Eng. J. 2011, 176-177, (Supplement C), 178-187. (16) Pyl, S. P.; Dijkmans, T.; Antonykutty, J. M.; Reyniers, M.-F.; Harlin, A.; Van Geem, K. M.; Marin, G. B., Wood-Derived Olefins by Steam Cracking of Hydrodeoxygenated Tall Oils. Bioresour. Technol. 2012, 126, (Supplement C), 48-55. (17) Van Geem, K. M.; Pyl, S. P.; Reyniers, M.-F.; Vercammen, J.; Beens, J.; Marin, G. B., Online analysis of complex hydrocarbon mixtures using comprehensive two-dimensional gas chromatography. J. Chromatogr. A 2010, 1217, (43), 6623-6633. (18) Dijkmans, T.; Pyl, S. P.; Reyniers, M.-F.; Abhari, R.; Van Geem, K. M.; Marin, G. B., Production of bio-ethene and propene: alternatives for bulk chemicals and polymers. Green Chem. 2013, 15, (11), 3064-3076. (19) Xu, L. Y.; Zhu, P.; Jing, H. Y.; Guo, K.; Zhong, S. X.; Han, Y. D., Failure Analysis of Incoloy 800HT Pipe at High Temperature. Eng. Fail. Anal. 2013, 31, (Supplement C), 375-386. (20) Heat Resistant Alloys for Hydrocarbon Processing. http://www.manoirindustries.com/site/docs_wsw/fichiers_communs/docs/MI_Manaurite_XM.pdf (November 2017), (21) Fedorova, E.; Monceau, D.; Oquab, D., Quantification of growth kinetics and adherence of oxide scales formed on Ni-based superalloys at high temperature. Corros. Sci. 2010, 52, (12), 3932-3942. (22) Van Geem, K. M.; Hudebine, D.; Reyniers, M. F.; Wahl, F.; Verstraete, J. J.; Marin, G. B., Molecular Reconstruction of Naphtha Steam Cracking Feedstocks based on Commercial Indices. Comput. Chem. Eng. 2007, 31, (9), 1020-1034. (23) Van Geem, K. M.; Reyniers, M.-F.; Marin, G. B., Challenges of Modeling Steam Cracking of Heavy Feedstocks. Oil Gas Sci. Technol. 2008, 63, (1), 79-94. (24) Plehiers, P. M.; Reyniers, G. C.; Froment, G. F., Simulation of the run length of an ethane cracking furnace. Ind. Eng. Chem. Res. 1990, 29, (4), 636-641. (25) Meade, D. B.; Haran, B. S.; White, R. E., The Shooting Technique for the Solution of TwoPoint Boundary Value Problems. MapleTech 1996, 3, 85-93. (26) Oil & Gas Science and Technology-Revue De L Institut Francais Du PetroleReviews in Chemical EngineeringFroment, G. F., Coke formation in the Thermal Cracking of Hydrocarbons. Rev. Chem. Eng. 1990, 6, 35. (27) Reyniers, M.-F. S. G.; Froment, G. F., Influence of Metal Surface and Sulfur Addition on Coke Deposition in the Thermal Cracking of Hydrocarbons. Ind. Eng. Chem. Res. 1995, 34, (3), 773-785. (28) Olahova, N.; Djokic, M. R.; Van de Vijver, R.; Ristic, N. D.; Marin, G. B.; Reyniers, M.-F.; Van Geem, K. M., Thermal Decomposition of Sulfur Compounds and their Role in Coke Formation during Steam Cracking of Heptane. Chem. Eng. Technol. 2016, 39, (11), 2096-2106. 25 ACS Paragon Plus Environment


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(29) Bao, B.; Liu, J.; Xu, H.; Wan, S.; Zhang, W., Effect of Selective Oxidation and Sulphur/Phosphorus-Containing Compounds on Coking Behaviour during Light Naphtha Thermal Cracking. Can. J. Chem. Eng. 2017, 95, (8), 1480-1488. (30) Sarris, S. A.; Olahova, N.; Verbeken, K.; Reyniers, M.-F.; Marin, G. B.; Van Geem, K. M., Optimization of the in Situ Pretreatment of High Temperature Ni–Cr Alloys for Ethane Steam Cracking. Ind. Eng. Chem. Res. 2017, 56, (6), 1424-1438.

Figures

Figure 1: Schematic overview of the pilot plant setup during the experiments with the barrier coating, Incoloy 800HT (red), tested material commercial 25/35 Cr-Ni or with the applied CoatAlloy™ (green). ((○): process gas temperature, (●): reactor outer wall temperature, 1: electronic balance, 2: demineralized water reservoir, 3: liquid hydrocarbons reservoir, 4: heated sampling oven (573 K), 5: heated transfer lines (573 K), 6: oil cooled heat exchanger, 7: water cooled condenser, 8: cyclone, 9: thermal mass flow controller, 10: outlet pressure regulation valve, 11: water cooled heat exchanger, 12: dehydrator, 13: ISCO 500D syringe pump).


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Figure 2: Effect of different process conditions and the application of the coating on the amount of coke.



Page 28 of 53

(a)

(b)

(c)


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(d)

(e)

Figure 3: Elemental mapping of the cross section of a blank 25/35 Cr-Ni coupon (a), a coked 25/35 Cr-Ni sample (b) inlet cell 5, (c) outlet cell 5, (d) inlet cell 6 and (e) outlet cell 6 (3000 x, 15 kV). Steam cracking of ethane: Fethane = 2.08 x 10-3 kg.s-1, Fsteam = 0.80 x 10-3 kg.s-1, δ = 0.385 kgsteam.kgethane-1 , COP = 2.0 bara, FDMDS = 100 ppmw S.gHC-1 ,T5in = 1023 K, T5out = 1073 K, T6in = 1073 K, T6out = 1123 K.



Page 30 of 53

(a)

(b)

(c)


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(d)

(e)

Figure 4: Elemental mapping of the cross section of a blank CoatAlloy™ coupon (a), a coked CoatAlloy™ (b) inlet cell 5, (c) outlet cell 5, (d) inlet cell 6 and (e) inlet 7 (3000 x, 15 kV). Steam cracking of ethane: Fethane = 2.08 x 10-3 kg.s-1, Fsteam = 0.80 x 10-3 kg.s-1, δ = 0.385 kgsteam.kgethane-1 , COP = 2.0 bara, FDMDS = 100 ppmw S.gHC-1 ,T5in = 1023 K, T5out = 1073 K, T6in = 1073 K, T6out = 1123 K.



Page 32 of 53

Figure 5: Run length [hours] vs. wall temperature [K] of the COILSIM1D simulations.


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Figure 6: Run length [hours] vs. pressure drop [atm] of the COILSIM1D simulations.


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Page 34 of 53

Tables Table 1: Composition of the reactor material Incoloy 800HT and commercial 25/35 Cr-Ni alloy. Reproduced with permission from ref.19. Copyright 2013 Elsevier Ltd. and ref.20. Material Incoloy 800 HT Commercial 25/35 Cr-Ni alloy

Composition [wt %] Fe

Ni

Cr

C

Si

Al

Mn

S

Ti

Co

Cu

Nb

45.19

31.22

20.06

0.08

0.34

0.51

0.71

< 0.001

0.52

0.61

0.41

-

> 36.40

35.00

25.00

0.40

< 1.50

-

< 1.00

-

-

-

-

0.70


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Table 2: Product yields summary from the experiments performed with 25/35 Cr-Ni.

Pre-S + CA*

Experiment

COT max*

Aging 1CC*

2CC*

3CC*

4CC*

5CC*

6CC

7CC*

8CC*

2.08

2.08

2.08

2.08

Commercial 25/35 Cr-Ni alloy

Material Conditions Ethane flowrate [10-3 kg.s-1] -3

-1

2.08

2.08

2.08

2.08

2.08

2.08

0.80

0.80

0.80

0.80

0.80

0.80

0.80

0.80

0.80

0.80

0.385

0.385

0.385

0.385

0.385

0.385

0.385

0.385

0.385

0.385

ࢍࡰࡹࡰࡿ [ppmw]

100

100

100

100

100

100

100

0

100

100

COT [K]

1123

1143

1123

1123

1123

1123

1123

1123

1123

1123

COP [bara]

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

Duration [h]

6

4

2

2

6

1

1

1

6

1

XC2H6 [%]

64.72

74.71

64.20

65.07

64.96

64.42

64.97

66.06

63.74

64.24

∑C4-

99.63

97.32

99.87

99.72

99.47

100.27

99.76

106.80

99.58

100.00

H2

4.31

4.61

4.08

4.10

4.05

4.31

4.04

5.82

3.98

4.22

CH4

5.48

8.13

5.24

5.32

5.50

5.17

5.29

4.81

4.97

5.23

C2H6

35.28

25.29

35.80

34.93

35.04

35.58

35.03

33.94

36.23

35.76

C2H4

50.38

54.06

50.37

51.01

50.64

50.469

50.92

46.92

50.34

50.58

C3H6

1.27

1.54

1.21

1.22

1.28

1.15

1.15

0.97

1.21

1.17

1,3-C4H6

1.57

2.04

1.55

1.58

1.63

1.52

1.52

1.22

1.55

1.48

CO

0.17

0.29

0.52

0.46

0.15

0.98

0.74

11.11

0.14

0.49

CO2

0.022

0.012

0.025

0.022

0.008

0.050

0.042

1.156

0.009

0.020

Coke formed [g]

391.0

406.8

192.2

211.2

364.8

145.4

143.0

13.8

290.7

n.a.

Steam flowrate [10 kg.s ] Dilution

[kgsteam.kgethane-1]

**

Yields

C1-C4 Species

* **

Presulfidation and continuous addition conditions as specified in Table S1. Product yields averaged over effluent analyses per experiment. Asymptotic carbon oxides and hydrogen yields reported.


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Page 36 of 53

Table 3: Product yields summary from the experiments performed with CoatAlloy™.

Pre-S + CA*

Experiment

COT max*

Aging *

1CC

*

*

2CC

3CC

*

4CC

5CC*

6CC

7CC*

8CC*

2.08

2.08

2.08

2.08

2.08

CoatAlloy™

Material Conditions Ethane flowrate [10-3 kg.s-1] -3

-1

2.08

2.08

2.08

2.08

2.08

0.80

0.80

0.80

0.80

0.80

0.80

0.80

0.80

0.80

0.80

0.385

0.385

0.385

0.385

0.385

0.385

0.385

0.385

0.385

0.385

ࢍࡰࡹࡰࡿ , ppmw

100

100

100

100

100

100

100

0

100

100

COT [K]

1123

1143

1123

1123

1123

1123

1123

1123

1123

1123

COP, bara

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

2.0

Duration, h

6

4

2

2

6

1

1

1

6

1

XC2H6 [%]

63.50

74.10

63.30

63.32

63.60

64.24

64.34

63.52

63.32

63.91

∑C4- [wt %]

99.07

99.11

100.12

99.13

99.47

97.19

99.62

100.92

99.55

99.45

H2

4.19

4.86

4.15

4.09

4.10

4.07

4.20

4.48

4.06

4.36

CH4

4.98

7.63

4.68

4.63

4.62

4.42

4.87

4.42

4.57

5.11

C2H6

36.50

25.90

36.70

36.68

36.40

35.76

35.66

36.49

36.68

36.21

C2H4

49.14

55.64

50.48

49.91

50.59

49.12

50.96

49.03

50.55

50.08

C3H6

1.40

1.43

1.16

1.14

1.16

1.07

1.15

1.07

1.13

1.13

1,3-C4H6

1.57

2.09

1.51

1.43

1.44

1.35

1.48

1.33

1.45

1.51

CO

0.11

0.14

0.18

0.20

0.06

0.41

0.23

2.87

0.05

0.36

CO2

0.016

0.008

0.014

0.011

0.002

0.015

0.010

0.278

0.002

0.018

Coke formed [g]

271.4

226.1

118.9

106.0

158.2

85.0

78.8

12.9

198.7

n.a.

Steam flowrate [10 kg.s ] Dilution

[kgsteam.kgethane-1]

**

Yields

C1-C4 Species

*

presulfidation and continuous addition conditions as specified in Table S1.

**

Product yields averaged over effluent analyses per experiment. Asymptotic carbon oxides and hydrogen yields reported.


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Table 4: Results obtained by the simulations of an industrial ethane cracker at the start and end of the run for the coated and uncoated coil. Reactor

Non-coated

Coated

186

433

Run length [hours] SOR

EOR

SOR

EOR

CIP [atm]

3.007

3.396

3.007

3.398

Residence time [s]

0.669

0.683

0.669

0.684

950

1072

950

1070

P/E [wt%.wt% ]

0.023

0.024

0.023

0.024

XC2H6 [%]

74.71

73.04

74.71

72.70

H2

2.81

2.69

2.81

2.68

CH4

3.82

3.68

3.82

3.62

C2H4

37.99

36.77

37.99

36.55

C3H6

0.87

0.88

0.87

0.88

1,3-C4H6

1.213

1.12

1.21

1.10

C6H6

0.30

0.25

0.30

0.24

Wall temperature [K] -1

Yields [wt%]



Page 38 of 53

Figure captions Figure 1: Schematic overview of the pilot plant setup during the experiments with the barrier coating, Incoloy 800HT (red), tested material commercial 25/35 Cr-Ni or with the applied CoatAlloy™ (green). ((○): process gas temperature, (●): reactor outer wall temperature, 1: electronic balance, 2: demineralized water reservoir, 3: liquid hydrocarbons reservoir, 4: heated sampling oven (573 K), 5: heated transfer lines (573 K), 6: oil cooled heat exchanger, 7: water cooled condenser, 8: cyclone, 9: thermal mass flow controller, 10: outlet pressure regulation valve, 11: water cooled heat exchanger, 12: dehydrator, 13: ISCO 500D syringe pump). Figure 2: Effect of different process conditions and the application of the coating on the amount of coke. Figure 3: Elemental mapping of the cross section of a blank 25/35 Cr-Ni coupon (a), a coked 25/35 Cr-Ni sample (b) inlet cell 5, (c) outlet cell 5, (d) inlet cell 6 and (e) outlet cell 6 (3000 x, 15 kV). Steam cracking of ethane: Fethane = 2.08 x 10-3 kg.s-1, Fsteam = 0.80 x 10-3 kg.s-1, δ = 0.385 kgsteam.kgethane-1 , COP = 2.0 bara, FDMDS = 100 ppmw S.gHC-1 ,T5in = 1023 K, T5out = 1073 K, T6in = 1073 K, T6out = 1123 K. Figure 4: Elemental mapping of the cross section of a blank CoatAlloy™ coupon (a), a coked CoatAlloy™ (b) inlet cell 5, (c) outlet cell 5, (d) inlet cell 6 and (e) inlet 7 (3000 x, 15 kV). Steam cracking of ethane: Fethane = 2.08 x 10-3 kg.s-1, Fsteam = 0.80 x 10-3 kg.s-1, δ = 0.385 kgsteam.kgethane-1 , COP = 2.0 bara, FDMDS = 100 ppmw S.gHC-1 ,T5in = 1023 K, T5out = 1073 K, T6in = 1073 K, T6out = 1123 K. Figure 5: Run length [hours] vs. wall temperature [K] of the COILSIM1D simulations. Figure 6: Run length [hours] vs. pressure drop [atm] of the COILSIM1D simulations. 38 ACS Paragon Plus Environment

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For Table of Contents Only



234x139mm (120 x 120 DPI)

ACS Paragon Plus Environment

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182x73mm (120 x 120 DPI)


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182x73mm (120 x 120 DPI)


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127x76mm (150 x 150 DPI)


CoatAlloy Barrier Coating for Reduced Coke Formation in Steam

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