Establishing the Appropriate Conditions of Regeneration of Cataytic Reforming Pt/AL2O3 Catalyst

Catalyst deactivation, the loss over time of catalytic activity and selectivity is a problem of great and continuing concern in the practice of industrial catalytic processes. Catalyst regeneration procedures for fixed-bed reforming units can vary widely. While all regeneration procedures share common elements, it is very common for the procedures to have evolved over years as unit configurations and throughputs have changed. Sub-optimal regeneration procedures can have a number of negative impacts on subsequent operation. In this study two samples of catalytic reforming Pt/Al2O3 catalysts were obtained from operating fixed bed semi regenerative reactors which has run for 10,000 and 14000 hours. These samples which have undergone deactivation in the course of the operations were regenerated under varying conditions of temperature, pressure and chlorination to establish the appropriate regeneration conditions. The progress and extent of regeneration were monitored using FTIR, SEM, XRD, GC-MS and XRF. The carbon content and effectiveness of the regenerated catalysts were determined and the values were compared with that of fresh catalysts. The regenerated catalysts showed 98 – 99.5% of the catalyst activity under the conditions of temperature and pressure of 500°C and 15psi respectively. The established conditions are to guide economic operations of such units which to realize high quality reformates and long life of the catalysts.


Introduction
Catalytic reforming is a chemical process used to convert petroleum refinery naphthas distilled from crude oil (typically having low octane ratings) into high-octane liquid products called reformates, which are premium blending stocks for high-octane gasoline [1]. The process converts low-octane linear hydrocarbons (paraffins) into branched alkanes (isoparaffins) and cyclic naphthenes, which are then partially dehydrogenated to produce high-octane aromatic hydrocarbons. The dehydrogenation also produces significant amounts of byproduct hydrogen gas, which is fed into other refinery processes such as hydrocracking. A side reaction is hydrogenolysis, which produces light hydrocarbons of lower value, such as methane, ethane, propane and butanes. It is also the conversion of straight chains of alkane catalytically [2].
In addition to a gasoline blending stock, reformate is the main source of aromatic bulk chemicals such as benzene, toluene, xylene and ethylbenzene which have diverse uses, most importantly as raw materials for conversion into plastics. However, the benzene content of reformate makes it carcinogenic, which has led to governmental regulations effectively requiring further processing to reduce its benzene content.
There are many chemical reactions that occur in the catalytic reforming process, all of which occur in the presence of a catalyst and a high partial pressure of hydrogen. Depending upon the type or version of catalytic reforming used as well as the desired reaction severity, the reaction conditions range from temperatures of about 495 to 525°C and from pressures of about 5 to 45 atm [3]. The commonly used catalytic reforming catalysts contain noble metals such as platinum and/or rhenium, which are very susceptible to poisoning by sulfur and nitrogen compounds. Therefore, the naphtha feedstock to a catalytic reformer is always pre-processed in a hydrodesulfurization unit which removes both the sulfur and the nitrogen compounds. Most catalysts require both sulphur and nitrogen content to be lower than 1 ppm.
Most catalytic reforming catalysts contain platinum or rhenium on a silica or silica-alumina support base, and some contain both platinum and rhenium. Fresh catalyst is chlorided (chlorinated) prior to use.
The noble metals (platinum and rhenium) are considered to be catalytic sites for the dehydrogenation reactions and the chlorinated alumina provides the acid sites needed for Isomerization, cyclization and hydrocracking reactions [4]. The biggest care has to be exercised during the chlorination. Indeed, if not chlorinated (or insufficiently chlorinated) the platinum and rhenium in the catalyst would be reduced almost immediately to metallic state by the hydrogen in the vapour phase. On the other an excessive chlorination could depress excessively the activity of the catalyst The activity (i.e., effectiveness) of the catalyst in a semi-regenerative catalytic reformer is reduced over time during operation by carbonaceous coke deposition and chloride loss. The activity of the catalyst can be periodically regenerated or restored by in situ high temperature oxidation of the coke followed by chlorination. As stated earlier herein, semi-regenerative catalytic reformers are regenerated about once per 6 to 24 months.. The higher the severity of the reacting conditions (temperature), the higher is the octane of the produced reformate but also the shorter will be the duration of the cycle between two regenerations. Catalyst's cycle duration is also very dependent on the quality of the feedstock. However, independently of the crude oil used in the refinery, all catalysts require a maximum final boiling point of the naphtha feedstock of 180°C [5]. Performance of the catalyst decreases with respect to time due to deactivation. Deactivation can occur by a number of different mechanisms, both chemical and physical in nature. These are commonly divided into classes, namely coke formation or fouling, poisoning, sintering contamination on active sites and agglomeration. Other mechanisms of deactivation include masking and loss of the active elements via volatilization, erosion and attrition [6]. For catalytic reactions involving hydrocarbons (or even carbon oxides) side reactions occur on the catalyst surface leading to the formation of carbonaceous residues (usually referred to as coke or carbon) which tend to physically cover the active surface. Coke deposits may amount to 15% or even 20% (w/w) of the catalyst and accordingly they may deactivate the catalyst either by covering of the active sites, and by pore blocking. Sometimes a distinction is made between coke and carbon [7]. The difference is however somewhat arbitrary: usually carbon is considered the product of CO disproportionation (2CO →C+CO 2 ), whereas coke is referred to the material originated by decomposition (cracking) or condensation of hydrocarbons.
The chemical nature of the carbonaceous deposits depends very much on how they are formed, the conditions of temperature and pressure, the age of the catalyst, the chemical nature of the feed and products formed. Several authors pointed out a direct relationship between the amount of coke deposited and the aromatic and polynuclear aromatic content of the feed. Also, it has been reported that coke formation occurs more rapidly when a hydrogen acceptor, such as an olefin, is present, in line with the hypothesis of a carbonium ion chemistry for coke formation. In practice, the coke deposition may be controlled to a certain extent by using an optimal catalyst composition and an appropriate combination of process conditions [8].
During the reaction an equilibrium is reached between the rate of coke production and the rate of coke removal by gasifying agents (e.g. H 2 , H 2 O and O 2 that remove coke as CH 4 , CO and COx, respectively) so that steady-state conditions, corresponding to a certain level of coke present on the catalyst surface, are eventually reached. Otherwise, if the rate of coke deposition is higher than that of coke removal, a suitable regeneration procedure must be applied [9].
Catalysts used in naphtha reforming processes are bifunctional, as they contain a metal or dehydrogenation and hydrogenation functionality and acid-catalyzed isomerization functionality. The metal site is provided by platinum and metals promoters such as rhenium, tin, germanium, and iridium. The alumina support and chloride provide the acidcatalyzed isomerization functionality for the catalyst. The major goal of catalyst regeneration is to restore the catalyst to almost its fresh activity state where metal and acid sites are functioning as before coke deposition. To achieve this goal, the catalyst coke is burned off in a controlled manner, platinum and promoter metals are redispersed, and catalyst chloride is restored either to a fresh catalyst level or to a prescribed regenerated catalyst chloride level [10].
Catalyst deactivation, the loss over time of catalytic activity and/or selectivity is a problem of great and continuing concern in the practice of industrial catalytic processes. Costs to industry for catalyst replacement and process shut downs total billions of dollars per year [11] Catalyst regeneration is aimed at achieving the following objectives; a. High surface area, b) High dispersal of metal(Pt), c) Proper acidity level, d) decoking of the catalyst surface. Time scales for catalyst deactivation vary considerably for example in case of cracking catalysts, catalyst mortality may be I the order of seconds while in ammonia synthesis the iron catalyst may last 5-10 years. However it is inevitable that all catalyst will decay [12]. Poor catalyst regeneration will lead to low product yields and increased operating expense, so good regenerations can improve catalyst performance, reduce operating costs, and lower catalyst management costs [13].
The unit studied in this work is SRR [14] which has three reactors, each with a fixed bed of catalyst, and all of the catalyst is regenerated in situ during routine catalyst regeneration shutdowns which occur approximately once each 6 to 24 months. Such a unit is referred to as a semiregenerative catalytic reformer (SRR). The unit is currently plagued with challenges of poor quality reformate yield and high costs of inputs due to high foreign exchange rates. This work is therefore directed at establishing appropriate conditions for catalyst regeneration, to achieve high/optimal activity of the catalyst that will enhance production of high quality reformates.

Experimental Procedures Regeneration
The procedures followed were adopted from literature [15]. And the nitrogen flow kept constant at 2kg/cm 2 . The two spent catalyst sourced were calcined at different temperatures (400°C, 500°C, 600°C, 700°C, 800°C), at constant air flow rate of 15psi for a reaction time of 4hrs each to obtain the optimum temperature. The spent catalyst was also calcined at optimum temperature and reaction time of 4hrs while the flow rate was varied @ 10psi, 15psi, 20psi, 25psi and 30psi. The spent catalyst was also calcined at optimum temperature and flow rate while the reaction time was varied @ 2hrs, 4hrs, 6hrs and 8hrs This is to study the effect of temperature; time and flow rate on the nature or pattern of regeneration i.e. amount of coke burnt off. This is shown in Figure 1 Catalysts' Reformation/Activity Performance Evaluations In a typical run, about 2.0g of the catalyst sample was packed (loaded) halfway within a tubular reaction vessel, a 56cm long by 1.0cm internal diameter stainless 'silica tube'. The diagrammatic set-up is as shown in Figures 3. Glassfibres were placed before and after the catalyst bed to homogenize the reactant mixture and temperature. Prior to any reaction, the reactor's temperature was steadily increased to the desired reaction temperature (465°C) and held at that temperature.
Treated Heavy Naphtha in a flask was heated (to vaporize) and the vapor was channeled downstream into the reactor. The vapor outlet (reformate) from the reaction zone was condensed as it passed through the condenser. The condensed reformate was collected as product. The procedure was done for fresh and the two spent catalyst at the same reaction temperature 465°C and feed flowrate. The constituents and compositions of reformate obtained in each case was determined with the aid of a QP2010 PLUS GC-MS machine. The reformate yield was later compared to check the activity of the catalyst. This is shown in Figure 3.

Product Characterization
The elemental composition (in oxide form) of product obtained was determined using the Energy Dispersive X-Ray Florescence (ED-XRF) machine (Minipal 4), and the X-ray diffraction (XRD) patterns were obtained using Empyreal, PANalytical diffractometer employing Cu Kα radiation (λ=0.154nm), Scanning Electron Microscopy (SEM) imaging and Surface area using sear's method were conducted, Fourier Transform Infrared spectroscopy (FTIR) and Gas Chromatograph/Mass Spectrometry (GCMS) were obtained using SHIMADZU FTIR spectrometer and QP2010 PLUS GC-MS.

FTIR Analysis of the Catalysts
The operation conditions variation done on the two spent catalyst A & B to obtain the optimum operating parameters for the regeneration process were all characterize using FTIR to affirm the best conditions observing the different functional groups present on the catalyst. Also the main objective is to ascertain the nature of coke species especially the soft coke. The main absorption band in Figure 1 of Fresh catalyst at 3466.20 cm -1 corresponded to NH stretching vibrations of NH 2 in aromatic amines and amides group. The absorption band at 1638.58cm -1 corresponded to C=C stretching of C=C in alkenes. Likewise, the band observed at 564.20 cm -1 corresponded to chain deformation modes of alkyl group. This is in consonance with what was reported by Mario [16].
The absorption bands 3466.20, 3486.45 & 3462.34 cm -1 in the figure 4 of fresh, Spent A and Spent B respectively still affirmed NH stretching vibrations of NH 2 in aromatic amines and amides group. The absorption band between 3000 and 2800cm -1 are assigned to aromatic and aliphatic rings probably produced by polycyclic aromatics like chrysene. The absorption bands at 2946.23 cm -1 2937.68 cm -1 (Spent A and Spent B)corresponded to CH antisym and sym stretching of -CH 3 and -CH 2 -in aliphatic compound which agree with symmetric and asymmetric flexion vibration of the C-H bonds associated with CH 3 [17]. All these can be linked to presence of commercial coke which is as a result of heavy unsaturated product from hydrocracking reaction during reforming such as poly-aromatics. Spent A with a band of 2039.79 cm -1 confirms the presence of structure of aromatic compounds from the pattern of the weak overtone and combination tone bands. Also absorption band at 1643.41cm -1 (Spent A) and 1642.44cm -1 (Spent B) also confirmed C=C stretching of C=C in alkenes i.e showing traces of heavy olefins and di-olefines that promote coking from the hydrocracking reaction effect on the catalyst. 1533.46cm -1 absorption band on Spent A shows the presence of aromatic ring. Likewise the band 1442.80 cm -1 on Spent B corresponded CH 3 antisym deformation of CH 3 in aliphatic compounds as also seen on fresh catalyst.
The entire absorption band below 900 cm -1 confirms C-H out of plane bending, i.e. 743.5 cm -1 of spent B shows phenyl ring substitution bands as reported by Mario [16 ].
The deactivated (spent) catalysts were calcined at varying temperature, time and air pressure (oxygen level) using unifactorial method to know the range of operating conditions to be used for proper regeneration of the spent catalyst. The various results were characterized using FTIR and the spectra for each operating conditions can be seen cascaded in Figures 1-5.    Comparing surface analysis technique showing the spectra of the fresh catalyst and deactivated spent catalysts subjected to different calcination temperatures. Figures1 -4 present the spectra of calcined Spent A and B at 400°C, 500°C and 600°C. it can be seen that the coke precursor from the deactivated spent catalyst that initially shows presence of coked catalyst (2937.68cm -1 and 2946.23cm -1 ) on Figures 2-4 but after the catalyst was calcined at different temperature (400°C, 500°C and 600°C) under nitrogen gas. It shows that these coke precursors can be eliminated and there was reduction in adsorption of the olefin and the aromatic on the catalyst metal surface but much more lesser @ 400°C but at calcined temperature of 700°C and 800°C in Figure 2 shows same adsorption of olefin and aromatic and much more presence of coke on Figure 6 (2956.01cm -1 on Spent A) and sintering were still observed.
From these observations, it can be concluded that a lower ramp rate is much more preferred for regeneration studies and it is in agreement with most industrial application as noted by previous workers [18] that showed that low temperatures are usually employed to enhance better control of the coke combustion.
Temperature effect on the spent catalyst under nitrogen gas in Figure 2 of 400°C, 500°C, 600°C also produces absorption bands range 2100 -2270cm -1 showing small but exposed presence of CC triple bond distribution (corresponding to CC triple bond stretching) presence of combustion which is as a result of hydrocracking not needed in reforming process leading to coke formation.
Considering time variation with optimum temperature (500°C) and a lower air pressure (15psi) chosen as a result of conditions with highest percentage weight loss of deposit on the two deactivated spent catalyst. Figure 4-6 showing cascaded time variation for spent A & B respectively shows little or no variation change in peaks i.e. showing all functional group that can be seen in the fresh catalyst but in terms of percentage weight loss for 2, 6 and 8hrs are lower compare to that of 4hours. Meaning that coke combustion occurs more within 4hours and reduces with any further increase in time. Figure 6 [20,16]. The results also confirmed that, the industrial or commercial coke catalyst 3000 and 2800cm -1

are missing. This shows that eliminated of these coke precursors after treatment under nitrogen gas in the presence of controlled air is possible but it can't show how active the regenerated spent catalysts except a catalyst performance test is done.
For further comparison, some other cascading was done and shown in figure 6 and 7 comparing each spent catalyst with the fresh and its regenerated catalyst.

Carbon Composition of Catalyst
The organic carbon content composition was carried using the Walkley black method. The percentage carbon on each catalyst was tabulated in Table 1. The composition in table 1 shows considerable deposition of carbon on the catalyst during reforming at the specific collected life cycle of the spent catalyst A & B. it was observed that there was much deposit of carbon on the first collected catalyst (Spent B) possibly due to the presence of more hydrocracking reaction that took place. The high carbon deposits found on the deactivated catalyst were decrease after regeneration due to the burning off the coke (carbon) deposited on the catalyst. The presence of carbon on the fresh catalyst could be as a result of sample of having been exposed to atmosphere and being a catalyst it can adsorb.

Morphology of Catalysts
The SEM image of the fresh catalyst and XRD patterns of the fresh and spent catalysts are shown in Figures 9-10.  The XRD diffractograms obtained from Empyreal PANalytical Diffractometer for the catalysts (fresh, Spent A & B) are as shown in Figure 9 above.
The low intensity counts and the broad peaks that characterized the diffractographs of the support (γ-Al 2 O 3 ) averred to the fact that the gamma-alumina is amorphous.
The platinum catalysts have closely related bragg angles (2θs) with those of the support (alumina), but little or no significant difference with their intensity counts.
Platinum and the Alumina are dominant as also reflected from XRF. Despite the heat effect on regeneration of the catalysts it shows that thermally the structure is not destroyed and carbon has no much significance on the structure of the catalysts.

XRF Analysis
The XRF of the fresh, spent and regenerated catalysts are shown in Table 2.  Table 2 shows the percentage oxide form of elemental composition using XRF. The alumina (Al 2 O 3 ) and the platinum were more dominant and it could be seen that there was a proportional increase in the support (alumina) after reforming has taken place on the deactivated catalyst compared to fresh catalyst (89.9% to 92.23% Spent A 89.9% to 92.2% Spent B). While little decrease in platinum (2.47% to 2.38% Spent A and 2.47% to 2.13 Spent B) and loss of chlorine which was completely used up during reforming process.
Majorly the fluctuation of the oxide was as a result of the loss of chlorine which was completely used up spreading across some of the other oxides for example alumina material increased probably as a result of chlorine loss and decrease of masses of other oxides. And due to the effect of calcinations (regeneration) burning or removal of some carbonaceous material, chlorine which was earlier used up resurfaced on the catalyst after the activity was boosted with dichloropropane and the alumina (support) decreases while other oxides too regained almost their original compositions. The pore fibre length of and pore distribution the fresh, spent and regenerated catalysts are shown in Figures 10 -17.           (Figure 13a and 13b), the carbon deposit are reduced, more opened pores are observed and we could observe clusters appearing back majorly in Figure 19a with less carbon deposit.
Also from Figures10a-10c of the fresh, spent A & B and regenerated spent A& B respectively. It can be seen that the SEM image surface area is divided into micro, meso and macro pore group. The surface area became more opened on regeneration of the catalyst for both spent A&B after chemical and thermal treatment burnt off some of the carbonaceous material deposited on the catalyst. This was clearly shown in the increment in the small, average and large surface area as shown in the summary given in Table 3. The catalysts textural properties are also shown in Table 4. The specific surface area was determined using Sear's method and presented in Table 4. There were significant increases in the regenerated catalyst compare to the deactivated catalyst (spent A & B). SSA (Specific surface area) for of spent A increased by 41% while spent B increased by 17%. The large percentage increase was as a result of the method used to obtain the surface area, but increase in surface area results to slight improvement in the surface morphology.
All deactivated catalysts have smaller specific surface area than the fresh catalyst. Comparatively the spent A deactivated catalyst has the least specific surface area, this is because organic compounds with higher boiling points have covered the catalyst surface more than that of spent B which results in the decrease of the specific surface area compared to fresh catalyst.

Catalysts' Performance Evaluations
The catalyst performance evaluation was examined on the basis of catalyst's ability to enhance the yield of reformate from treated heavy naphtha. The treated heavy naphtha feed was not pure The assumed composition of the byproducts (i.e the dry gases) in the entire products was cited from the work of Karla [23]. The operating reaction temperature used for the reforming was 465°C for the various catalysts packed. Hence, from the chromatograms of each sample analyzed, the area assigned to the unconverted treated heavy naphtha was taken as N, while the total area assigned to all reformates was taken as R.

Quantitative analysis
The quantitative analysis of the reformate obtained from the regenerated and fresh catalysts was carried using the GC-MS.. The GC-MS system used, have computer software used to draw and integrate peaks, and thus match the obtained MS spectra to library spectra. Thus, an analytes present in a sample eluting from the column was named by matchmaking, and the most likely analyte's names were given (in order of probability; SI) in each spectrum. For instance, the spectrum (connoted by the GC-MS machine as Hit# 1) shown in Figure 20 is "Benzene"-which is the compound name with its isomers (each placed within the two doubledollar-sign). The performance evaluation results are presented in Table 5. From Table 5 it can be seen that the fresh catalyst has the highest yield of reformate (84.24%) produce and that of the deactivated catalyst dropped a little due to the presence of carbonaceous material deposited on them, after regeneration the percentage reformate yield increased but still very close to the fresh in terms of percentage. In terms of activity of the catalyst, the before and after the extent the catalyst went through during regeneration the activity is still high for the deactivated and regenerated catalyst showing that the performance is very close to fresh catalyst which was taken as basis. Taking Spent A for example has 95.75% activity compare to fresh (100%) and also after regeneration the activity increase a little but still within the limit.

Conclusion
The catalyst life span and catalyst efficiency is critical to the operation of catalytic reforming units. This work has established a technological range of conditions for regeneration of Pt/Al 2 O 3 . catalyst employed in a fixed bed semi regenerative catalytic reforming unit. This work established that all deactivated catalysts have smaller specific surface area than the fresh catalyst. Comparatively the spent A deactivated catalyst has the least specific surface area, this is because organic compounds with higher boiling points have covered the catalyst surface more than that of spent B which results in the decrease of the specific surface area compared to fresh catalyst. The investigation also showed that the surface area became more opened on regeneration of the catalyst for both spent A&B after chemical and thermal treatment burnt off some of the carbonaceous material deposited on the catalyst. This was clearly shown in the increment in the small, average and large surface area in addition, the high carbon deposits found on the deactivated catalyst were decreased after regeneration due to the burning off the coke (carbon) deposited on the catalyst. The progress and extent of regeneration were monitored using FTIR, SEM, XRD, GC-MS and XRF. The carbon content and effectiveness of the regenerated catalysts were determined and the values were compared with that of fresh catalysts. The regenerated catalysts showed 98 -99.5% of the catalyst activity under the conditions of temperature and pressure of 500°C and 15 psi respectively. This work has opened a window to refiners in undertaking in house assessment and troubleshooting of the catalytic reforming units which will ensure optimal operation of the units. It is recommended that refiners should regularly carryout such investigations on their units to ensure that optimal conditions for operations are employed.