Coke Accumulation Research Articles

Coke accumulation and deactivation behavior of microzeolite-based Mo/HZSM-5 in the non-oxidative methane aromatization under cyclic CH4-H2 feed switch mode

The lifetime deactivation patterns of a microzeolite-based 6wt%Mo/HZSM-5 in the non-oxidative dehydroaromatization of methane were measured first at 1073K and a space velocity of 12,000ml/g-Cat/h in continuous CH4-feeding, cyclic 5min CH4–5min He feed switch and cyclic 5min CH4–5min H2 feed switch modes. Appearance of an obvious inflection point in the course of benzene selectivity under the cyclic CH4-H2 feed switch operation mode revealed the two stages deactivation feature of the catalyst: the deactivation was first slow and then accelerated. TG and TPO measurements of the spent samples were performed and the results exhibited strong similarity in the total coke content and the intensity and area of the low temperature TPO-COx peak. Then, a set of tests under the cyclic CH4-H2 feed switch mode over different time frames, followed by the TPO measurements of the spent samples, was performed to pursue the coke accumulation behavior of the catalyst over its lifetime. The low-temperature burning coke defined by the low-temperature TPO-COx peak was confirmed to be the dominant type of coke, reside on the external surface of the zeolite and in the inner mouth region of the zeolite channels, and accumulate over the catalyst lifetime at a constant rate. In parallel, a constant rate was also observed for the decrease of the benzene formation rate itself over the slow deactivation period. While these observations suggest the possible existence of a cause and effect relationship between the low-temperature burning coke and catalyst deactivation, a detailed discussion was made on the dominant effect of accumulation of graphite-like coke on the slow deactivation of catalyst.

Steam reforming of n-dodecane over K2Ti2O5-added Ni-alumina and Ni-zirconia (YSZ) catalysts

The steam reforming of n-dodecane over 35 wt% Ni supported on alumina (Ni-Al2O3) and yttrium-stabilized zirconia (Ni-YSZ) at 800 °C for 10 h with a steam-to-carbon ratio of 3 was tested in the presence and absence of 10 wt% of K2Ti2O5 (KTO) particles. The suppression of coke formation by KTO was investigated using various characterizations, including BET, TPO, TGA, TEM, and EELS. After the addition of 10 wt% of KTO particles by ball milling, Ni-YSZ exhibited stable performance with negligible coke formation at space velocities of less than 20,000 h−1. The addition of KTO to Ni-Al2O3 did not yield any improvements because the majority of Ni particles in alumina pores are not directly in contact with the KTO phase. The dispersion of finely divided KTO particles on the surfaces of both Ni and the support effectively suppressed coke formation by steam gasification of the deposited coke into CO and H2. First, the gradual accumulation of coke during the course of the reaction deactivated the Ni sites, which presented activity for the steam reforming of methane. The Ni and acidic sites, which were effective for the hydrogenolysis of n-dodecane to methane and ethylene (or ethane in the presence of KTO), were eventually deactivated. An overall reaction pathway was then proposed based on the results.

The multiple benefits of glycerol conversion to acrolein and acrylic acid catalyzed by vanadium oxides supported on micro-mesoporous MFI zeolites

The ZSM-5 zeolite (MFI structure, Si/Al=40) was treated using NaOH and either oxalic acid or HCl to obtain hierarchical materials with different characteristics, followed by impregnation with vanadium oxides (V2O5) to generate redox-active sites. The impact of the multiple treatments on the efficiency and stability of the catalysts in the conversion of glycerol to acrolein and acrylic acid was investigated and correlated with catalyst porosity, acidity, and chemical composition. The treated and impregnated V2O5 catalysts were subjected to XRD, 27Al NMR, nitrogen physisorption, TPD-NH3, TG, and UV–Vis analyses, in order to associate the properties of the catalysts with their activities. The studies showed that the catalytic performance of the materials depended on the acidic and textural properties of the zeolites, which influenced both the dispersion of V2O5 and its interaction with the acid sites of the supporting zeolites. All the catalysts provided conversion values exceeding 65%, even after 6h on glycerol stream. The distribution of products strongly reflected the effects of pore formation, acid treatment with oxalic acid or HCl, and the presence of vanadium oxide. The effects of these modifications resulted in higher selectivity to acrolein and acrylic acid, a reduced rate of coke accumulation in the zeolite, and a longer catalyst lifetime.

The Chemical-Loop Reforming of Alcohols on Spinel-Type Mixed Oxides: Comparing Ni, Co, and Fe Ferrite vs Magnetite Performances

Ferrospinels with different metals—Fe, Ni, Co, and Cu—were investigated as oxygen ion and electron carrier materials for the chemical-loop reforming of ethanol, aimed at the production of H2 with intrinsic separation from CO and CO2. The materials used showed different behaviours both during the first step of the loop—the reduction of the annealed spinel with ethanol—and the second step—the re-oxidation with steam—as well as with the increasing cycle number. The differences shown were rationalised in terms of redox behaviour, carbon residue accumulation during the cycle, and ability to restore the starting spinel structure during cycling. Mixed ferrospinels showed enhanced reducibility when compared to magnetite; however, since coke accumulation was unavoidable, the best-performing material amongst the materials tested was Co ferrite, which underwent the greatest reduction and was able to maintain it throughout repeated cycles.

Advances in the study of coke formation over zeolite catalysts in the methanol-to-hydrocarbon process

Methanol-to-hydrocarbon (MTH) process over acidic zeolite catalysts has been widely utilised to yield many types of hydrocarbons, some of which are eventually converted into the highly dehydrogenated (graphitized) carbonaceous species (cokes). The coking process can be divided into two parallel pathways based on the accepted hydrocarbon pool theory. From extensive investigations, it is reasonable to conclude that inner zeollite cavity/channel reactions at acidic sites generate cokes. However, coke formation and accumulation over the zeolite external surfaces play a major role in reaction deactivation as they contribute a great portion to the total coke amount. Herein we have reviewed previous literatures and included some recent works from KOPRC in understanding the nature and mechanism of coke formation, particularly during an H-ZSM-5 catalysed MTH reaction. We specially conclude that rapid aromatics formation at the zeolite crystalite edges is the main reason for later stage coke accumulation on the zeolite external surfaces. Accordingly, the catalyst deactivation is in a great certain to arise at those edge areas due to having the earliest contact with the incoming methanol reactant. The final coke structure is therefore built up with layers of poly-aromatics, as the potential sp2 carbons leading to pre-graphite structure. We have proposed a coke formation model particularly for the acidic catalyst, which we believe will be of assistance in understanding—and hence minimising—the coke formation mechanisms.

Effects of Ga doping on Pt/CeO2‐Al2O3 catalysts for propane dehydrogenation

This paper describes catalytic consequencesThis paper describes catalytic consequences of Pt/CeO2‐Al2O3 catalysts promoted with Ga species for propane dehydrogenation. A series of PtGa/CeO2‐Al2O3 catalysts were prepared by a sequential impregnation method. The as‐prepared catalysts were characterized employing N2 adsorption‐desorption, X‐ray diffrtaction, temperature programmed reduction, O2 volumetric chemisorption, H2‐O2 titration, and transmission electron microscopy. We have shown that Ga3+ cations are incorporated into the cubic fluorite structure of CeO2, enhancing both lattice oxygen storage capacity and surface oxygen mobility. The enhanced reducibility of CeO2 is indicative of higher capability to eliminate the coke deposition and thus is beneficial to the improvement of catalytic stability. Density functional theory calculations confirm that the addition of Ga is prone to improve propylene desorption and greatly suppress deep dehydrogenation and the following coke formation. The catalytic performance shows a strong dependence on the content of Ga addition. The optimal loading content of Ga is 3 wt %, which results in the maximal propylene selectivity together with the best catalytic stability against coke accumulation. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4365–4376, 2016

Cenosphere formation from heavy fuel oil: a numerical analysis accounting for the balance between porous shells and internal pressure

Heavy fuel oil (HFO) as a fuel in industrial and power generation plants ensures the availability of energy at economy. Coke and cenosphere emissions from HFO combustion need to be controlled by particulate control equipment such as electrostatic precipitators, and collection effectiveness is impacted by the properties of these particulates. The cenosphere formation is a function of HFO composition, which varies depending on the source of the HFO. Numerical modelling of the cenosphere formation mechanism presented in this paper is an economical method of characterising cenosphere formation potential for HFO in comparison to experimental analysis of individual HFO samples, leading to better control and collection. In the present work, a novel numerical model is developed for understanding the global cenosphere formation mechanism. The critical diameter of the cenosphere is modelled based on the balance between two pressures developed in an HFO droplet. First is the pressure (Prpf) developed at the interface of the liquid surface and the inner surface of the accumulated coke due to the flow restriction of volatile components from the interior of the droplet. Second is the pressure due to the outer shell strength (PrC) gained from van der Walls energy of the coke layers and surface energy. In this present study it is considered that when PrC ≥ Prpf the outer shell starts to harden. The internal motion in the shell layer ceases and the outer diameter (DSOut) of the shell is then fixed. The entire process of cenosphere formation in this study is analysed in three phases: regression, shell formation and hardening, and post shell hardening. Variations in pressures during shell formation are analysed. Shell (cenosphere) dimensions are evaluated at the completion of droplet evaporation. The rate of fuel evaporation, rate of coke formation and coke accumulation are analysed. The model predicts shell outer diameters of 650, 860 and 1040 µm, and inner diameters are 360, 410 and 430 µm respectively, for 700, 900 and 1100 µm HFO droplets. The present numerical model is validated with experimental results available from the literature. Total variation between computational and experimental results is in the range of 3–7%.

Elucidating Zeolite Deactivation Mechanisms During Biomass Catalytic Fast Pyrolysis from Model Reactions and Zeolite Syntheses

Zeolites are crystalline microporous aluminosilicates that have numerous applications in industry, specifically in catalysis, separation and adsorption. Zeolites catalyze the conversion of biomass-derived pyrolysis vapors into hydrocarbons; however, zeolites frequently suffer from rapid deactivation under pyrolysis conditions. Methanol-to-hydrocarbon processes are closely related to biomass upgrading reactions and several proposed mechanisms are discussed to provide mechanistic insight for biomass upgrading with zeolites. Syntheses of novel zeolites have potential to relieve deactivation factors including mass diffusion limitations of bulky molecules and accumulation of carbonaceous coke on the catalyst surface. Catalytic activity of conventional zeolites is presented to provide insights to evaluate the novel zeolites. Recent advances of the new zeolite structures are also presented in the context of potential future directions for the field.

Optimization of Heavy Oil Upgrading Using Dispersed Nanoparticulate Iron Oxide as a Catalyst

It has previously been shown that in situ upgrading of heavy oil by toe-to-heel air injection (THAI) can be augmented by surrounding the horizontal production well with an annulus of pelleted catalyst. Despite the further upgrading achieved with this configuration, the accumulation of coke and metals deposits on the catalyst and pore sites, resulting from cracking of the heavy oil, have a detrimental effect on the catalyst activity, life span, and process. An alternative contacting pattern between the oil and nanoparticulate catalysts was investigated in this study, to mitigate the above-mentioned challenges. The Taguchi method was applied to optimize the effect of reaction factors and select the optimum values that maximize level of heavy oil upgrading while suppressing coke yield. The reaction factors evaluated were reaction temperature, H2 initial pressure, reaction time, iron metal loading and speed of mixing. An orthogonal array, analysis of mean of response, analysis of mean signal-to-noise ratio (S/N) and analysis of variance (ANOVA) were employed to analyze the effect of these reaction factors. Detailed optimization of the reaction conditions with iron oxide dispersed nanoparticles (≤50 nm) for in situ catalytic upgrading of heavy oil was carried out at the following ranges; temperature 355–425 °C, reaction time 20–80 min, agitation 200–900 rpm, initial hydrogen pressure 10–50 bar, and iron metal loading 0.03–0.4 wt %. It was found that the optimum combinations of reaction factors are temperature 425 °C, initial hydrogen pressure 50 bar, reaction time 60 min, agitation 400 rpm and iron–metal loading 0.1 wt %. The properties of upgraded oil at the optimum condition are API gravity 21.1°, viscosity 105.75 cP, sulfur reduced by 37.54%, metals (Ni+V) reduced by 68.9%, and naphtha plus middle distillate fractions (IBP: 343 °C) increased to 68 wt % relative to the feed oil (12.8° API, 1482 cP, sulfur content 3.09 wt %, metals (Ni+V) content 0.0132 wt %, and naphtha plus middle distillate fractions 28.86 wt %).

Biogas to syngas conversion without carbonaceous deposits via the dry reforming reaction using transition metal catalysts

This study investigates how morphology, active metal content and oxygen storage capacity of various bimetallic NiCo/CeZrO2 materials influence their catalytic activity and stability in the methane dry reforming reaction. Catalyst preparation procedure and chemical composition were steered to finally obtain materials, which do not accumulate carbon during the CH4/CO2 reforming reaction. Oxygen storage capacity of the CeZrO2 catalyst support was identified to play a vital role in retarding carbon accumulation over the tested NiCo/CeZrO2 materials. This property can be fully developed when a nanocrystalline solid solution of CeO2 and ZrO2 is formed. Secondly, a high dispersion of nickel and cobalt is crucial for two reasons: (i) catalysts which contain larger NiCo bimetallic particles (for example with 12–18wt.% active metal loading) exhibit a low metal-support interphase that results in enhanced coke formation rates; (ii) additionally, only a marginal gain in methane reforming rates are achieved at higher loadings, compared to catalysts with a 3–6wt.% active metal content. We demonstrated that a NiCo/CeZrO2 catalyst under relevant operating conditions after 400h TOS maintains 79 and 84% conversion of CH4 and CO2, with negligible coke accumulation.

High catalytic performances of CeO2–CrOx catalysts for chlorinated VOCs elimination

A series of porous CeO2–CrOx mixed oxides are synthesized using different precipitants (NaOH, NH4OH, (NH4)2CO3 and urea) and evaluated for deep oxidation of various chlorinated VOCs (CH2Cl2, C2HCl3, C2H4Cl2 and C6H5Cl). The results show that all these materials represent porous structures and small particle sizes (2–8nm). Part of Cr element can go into the lattice of CeO2, resulting in the formation of Ce–Cr–O mixed oxide. Compared with pure CeO2 and Cr2O3, the amount of Cr6+ species and oxygen vacancies in CeO2–CrOx mixed oxides are significantly increased, due to the strong interaction between CeO2 and CrOx. Thus, all the CeO2–CrOx mixed oxides exhibit high catalytic activity and good durability for deep oxidation of chlorinated VOCs, especially the CeO2–CrOx prepared using (NH4)2CO3 as precipitant. Moreover, only slight chlorinated byproducts are detected in the process of chlorinated VOCs oxidation, and the surface accumulation of coke and Cl species as well as the loss of Cr element is slight during the long-term reaction at 265°C, indicating that these CeO2–CrOx materials possess interesting fundamental result, deserving more research before conclusion on practical value.

Zinc Accumulation and Behavior in Tuyere Coke

A case study of zinc oxide, which represents the first report on the occurrence, crystalline features, formation mechanism, and influence of this mineral in tuyere coke, was conducted in this study. A number of zinc oxides, some of which were in hexagonal wurtzite habit, were observed to distribute mainly in coke pores, cracks, surfaces, and around coke minerals. The accumulation of zinc in tuyere coke may enhance the degradation of coke and increase the generation and accumulation of coke fine in a blast furnace, which would cause bad effect on blast furnace operation. Investigations into zinc behavior in tuyere coke can be important for further interpretations of coke degradation in the high temperature zone of a blast furnace.

Textural and catalytic properties of Mo loaded hierarchical meso-/microporous lamellar MFI and MWW zeolites for direct methane conversion

The consequences of meso-/microporous zeolite structures on distribution and activity of active sites (Brønsted acid and metal sites) in molybdenum (Mo) impregnated lamellar MFI and lamellar MWW zeolites were investigated in direct methane aromatization (DMA) reactions. In comparison with their microporous analogies (Mo/MFI and Mo/MWW), the mesopores in the Mo/lamellar MFI and Mo/lamellar MWW zeolites facilitated the dispersion of Mo in zeolite micro-channels. The catalytic DMA reactions showed that the Mo loaded lamellar MFI and lamellar MWW zeolites enabled efficient methane conversion, aromatic product formation, and coke accumulation in the initial stage of reaction, while their performances were similar to those of Mo/MFI and Mo/MWW catalysts in the long term run. A plausible explanation to this scenario is that active sites in Mo/lamellar MFI and Mo/lamellar MWW can be accessed by reactants through both micropores and mesopores. The facilitated transport and accessibility to active sites by mesopores accounted for initial fast reaction and deactivation rates of Mo loaded lamellar zeolites. After mesopores were clogged by deposited coke in DMA reactions, micropores of zeolites were responsible for the long term catalyst performances, which were similar to Mo loaded microporous zeolites.

Performance of a binder-free, spherical-shaped Mo/HZSM-5 catalyst in the non-oxidative CH4 dehydroaromatization in fixed- and fluidized-bed reactors under periodic CH4–H2 switch operation

There is a need to develop a fluidizable Mo/HZSM-5 catalyst for industrial application of the non-oxidative CH4 conversion to benzene. A binder-free, spherical-shaped Mo/HZSM-5 catalyst was applied for the first time to the non-oxidative CH4 dehydroaromatization and its activity and stability were examined in both fixed- and fluidized-bed reactors at atmospheric pressure, 1073–1173K and 10,000mL/g/h under periodic CH4–H2 switch operation modes. The fixed bed tests confirmed that this catalyst has the same high activity as a 100% zeolite-based Mo/HZSM-5 powder catalyst. The fluidized bed tests demonstrated further that, the combination of daily cyclic H2-regeneration and one-hour continuous H2-regeneration between daily cyclic tests enables the catalyst to exhibit well-duplicated activity–time curves over a period of 6-day. Hence, a three-bed circulating reactor system was proposed to realize continuous and highly efficient catalyst regeneration and stable production of benzene. Moreover, measurements of the particle size distribution revealed that the average particle sizes of the spent samples collected after the fluidized bed tests become slightly larger than that of the fresh catalyst. Coke accumulation on the external surfaces of catalyst particles is believed to be responsible for strengthened resistance of the catalyst toward abrasion under the fluidization conditions.

Outlet Temperature Correlation and Prediction of Transfer Line Exchanger in an Industrial Steam Ethylene Cracking Process

Predicting the best shutdown time of a steam ethylene cracking furnace in industrial practice remains a challenge due to the complex coking process. As well known, the shutdown time of a furnace is mainly determined by coking condition of the transfer line exchangers (TLE) when naphtha or other heavy hydrocarbon feedstocks are cracked. In practice, it is difficult to measure the coke thickness in TLE through experimental method in the complex industrial situation. However, the outlet temperature of TLE (TLEOT) can indirectly characterize the coking situation in TLE since the coke accumulation in TLE has great influence on TLEOT. Thus, the TLEOT could be a critical factor in deciding when to shut down the furnace to decoke. To predict the TLEOT, a parametric model was proposed in this work, based on theoretical analysis, mathematic reduction, and parameters estimation. The feasibility of the proposed model was further checked through industrial data and good agreements between model prediction and industrial data with maximum deviation 2% were observed.

The role of MoS2nano-slabs in the protection of solid cracking catalysts for the total conversion of heavy oils to good quality distillates

The total conversion of the oil barrel to good quality fuels and distillates has been an overriding goal in the oil refinery industry. Today, it is even more important to improve the effective use of the energy fossil reserves. The actual technologies still produce variable amounts of low quality fractions (e.g. fuel oil, bunker oil) or by-products (e.g. coke). The evolution of the slurry hydrocracking technology can open the way to achieve the objective. This technology was originally developed in Germany in the first half of the last century and reconsidered by several research groups in the past decades. The catalyst used in the slurry process is still constituted by the same materials developed by German scientists in the last century, i.e. bulk, crystalline, nano-sized iron, molybdenum or tungsten sulfide. We have demonstrated now that it is possible to improve the catalytic performances by combining the excellent hydrogenation, hydrodesulfurization and hydrodemetallation properties of dispersed MoS2 catalyst with those of a conventional cracking catalyst. This dual catalyst system demonstrates for the first time the ability of dispersed MoS2 particles to protect the cracking catalyst against rapid decay due to coke accumulation and metal poisoning.

Development of a High-Throughput Methodology for Screening Coking Resistance of Modified Thin-Film Catalysts

A high-throughput optical technique has been developed for the rapid screening of coking resistant composition-spread promoted-catalyst libraries during hydrocarbon cracking, in particular for Jet Propellant 8(JP-8) cracking. The libraries are screened by measuring changes in the catalyst's surface color due to the accumulation and burnoff of coke from the surface during JP-8 exposure and catalyst regeneration via oxygen burnoff. This rapid screening method was validated through a comparison of the coking properties of high-surface area powder cracking catalysts, and sputter deposited samples. Experiments on bimetallic (Pt-Gd) catalysts showed systematic trends consistently illustrating the superiority of Pt-Gd alloys to coking due to the presence of gadolinium.

Triple-Protected Nanoparticles

Applying a uniform oxide coating to metal nanoparticles used for catalytic hydrocarbon processing simultaneously protects the particles from three common deactivation processes that can lead to frequent chemical reactor shutdowns, according to a study conducted by researchers at Northwestern University and Argonne National Laboratory. The findings, which may help avoid costly chemical plant interruptions, were reported at the American Chemical Society national meeting last week in San Diego and in Science (DOI: 10.1126/science.1212906). A number of chemical and physical processes can rob nanosized metal catalyst particles of their ability to mediate chemical reactions. In hydrocarbon catalysis, the two most common routes to deactivation for such particles are sintering—which causes the particles to agglomerate and fuse together, thereby reducing the surface area available for chemical reactions—and accumulation of coke, a carbonaceous layer that blocks reactants’ access to catalytically active sites. Nano...

Effect of transition metal additives on the catalytic stability of Mo/HZSM-5 in the methane dehydroaromatization under periodic CH 4–H 2 switch operation at 1073 K

Eight 0.5 wt%M–5 wt%Mo/HZSM-5 catalysts (M = Cr, Mn, Fe, Co, Cu, Zn, Ru or Pd) prepared by co-impregnation method were tested for the non-oxidative methane dehydroaromatization at a practically required severe condition of 1 atm, 1073 K and 10,000 mL/g/h in periodic CH 4–H 2 switch operation mode. The aim was to investigate promotional effects of these transition metal additives on the activity and stability of Mo/HZSM-5 and find out a really effective promoter for the title catalytic system. While Fe, Co, Ru and Pd additions were found to enhance the catalyst's CH 4 conversion activity, only Fe was observed to remarkably improve the activity stability, and therefore another two Fe-modified catalysts with 0.3 and 1.0 wt% of Fe were prepared and tested to make further confirmation. Ascribed to the second group of metal additives, Cr, Mn, Cu and Zn additions exhibited little influence on the CH 4 conversion activity, and Cr and Mn caused even slight decreases in the activity stability. Similar tests were also conducted with the samples of 0.5 wt%M/HZSM-5s to confirm the negligibly low activities of all but Pd metal additive themselves. Then, all spent catalyst samples were subjected to TPO, TG, SEM and BET measurements to gain an insight into the promotion mechanisms of Fe additive. Consequently, the TPO and TG measurements revealed that the addition of all metals except Ru enhanced coke accumulation and only Fe induced the formation of a new type of coke. Well consistently, the SEM observations confirmed considerable amounts of carbon nanotubes formed in all Fe-containing spent samples, whereas no single carbon nanotube in all other spent samples. Furthermore, the BET measurements also confirmed that all Fe-containing spent samples had obviously higher BET surface areas and micropore volumes than all other spent catalyst samples. While all these, in addition to the test results, strongly suggest that the promotional effect of Fe additive is closely related to Fe-induced carbon nanotube formation and growth at the tested condition, three possible promotion effects were proposed in the article to explain all observations.

Synergy effect of MgO and ZnO in a Ni/Mg–Zn–Al catalyst during ethanol steam reforming for H 2-rich gas production

Nickel based mixed oxide catalysts derived from Ni–Mg–Zn–Al hydrotalcite-like precursors are prepared and evaluated for H 2-rich gas production via ethanol steam reforming. It has been found that the catalyst properties (e.g. BET surface area, Ni dispersion and reducibility) and catalytic performance depend on the Mg:Zn molar ratio. MgO and ZnO have a synergetic effect. At 700 °C, the quaternary catalyst with a Mg:Zn ratio of 4 exhibits the highest H 2 yield and best stability, viz. no apparent variation of the product distribution over 100 h operation, whereas the ternary catalyst without Mg suffers severe coke accumulation after 7 h on-stream. Two types of carbon (filamentous and amorphous) are found deposited on the catalyst surface. The carbon deposited is dominated by filamentous carbon, which is likely originated from the decomposition of methane, and does not cause immediate deactivation.