Deactivation patterns of Mo/Al2O3, Ni–Mo/Al2O3 and Ni–MoP/Al2O3 catalysts in atmospheric residue hydrodesulphurization

In the present work, a comparative study on the deactivation behavior of three types of industrial hydrotreating catalysts, namely, Mo/Al₂O₃, Ni–Mo/Al₂O₃ and Ni–MoP/Al₂O₃, that are used to promote primarily hydrodemetallization (HDM), hydrodesulphurization (HDS) and hydrodesulphurization + hydrodenitrogenation (HDS/HDN) reactions, respectively, in the first, second and third reactor of commercial atmospheric residue desulfurization (ARDS) units was carried out. The main objective of the study was to contribute to a better understanding of the relationship between catalyst type and catalyst deactivation patterns. The used catalysts from these experiments were fully characterized to determine the extent and the cause of deactivation. Special emphasis was paid to understanding the nature of the coke and metal deposition on the used catalysts by applying chemical analysis and various advanced analytical techniques, such as solid-state carbon-13 nuclear magnetic resonance spectroscopy (¹³C NMR), temperature-programmed oxidation (TPO), electron probe micro-analysis (EPMA), and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The results are discussed scientifically based on the physico–chemical properties of the three catalysts.     

Coking behavior and catalyst deactivation for catalytic pyrolysis of heavy oil

For the catalytic pyrolysis of heavy oil on catalyst CEP-1, coking behavior was investigated in a confined fluidized bed reactor. Coke content on the spent catalyst decreases with the increase of H/C mol ratio of feeds and catalyst-to-oil weight ratio, while it increases with the enhancement of reaction temperature. An empirical model is proposed to predict the coke content based on feed properties and operating conditions. The predicted coke content is close to the experimental data. The relationship between micro-activity index of catalysts and coke content is studied. A coking deactivation model for pyrolyzing catalysts is established, and then model parameters are determined by the least square regression analysis. According to the deactivation model, the variations of relative activity of catalysts with both residence time of catalysts and catalyst-to-oil weight ratio are predicted.     

Analysis of coke deposition profiles in commercial spent hydroprocessing catalysts using Raman spectroscopy

The distribution of coke inside the pellets of several industrial spent hydroprocessing catalysts was analyzed using Raman spectroscopy. The shape of the coke profiles gives us information on the deactivation mechanism and the magnitude of diffusion limitations. Samples taken at the end of run showed the most pronounced coke profiles. Typical M-shaped profiles observed in a guard bed catalyst suggest a sequential deactivation mechanism and a strong diffusion resistance. Consequently, it is concluded that near the end of life the catalyst effectiveness factor can be significantly reduced by coke deposition.     

Deactivation and regeneration of hybrid catalysts in the single-step synthesis of dimethyl ether from syngas and CO2

Synthesis of dimethyl ether (DME) has been studied in a single reaction step, from H₂ + CO and H₂ + CO₂, in a fixed bed reactor on CuO-ZnO-Al₂O₃/γ-Al₂O₃ and CuO-ZnO-Al₂O₃/NaHZSM-5 hybrid catalysts. It has been proven that water content in the reaction medium (which is higher when CO₂ is fed) contributes to efficiently decreasing deactivation by coke in both catalysts and, consequently, when water is in the feed deactivation is insignificant for 30 h reaction. Nevertheless, water also decreases the activity of γ-Al₂O₃ acid function, due to its high adsorption capacity on the acid sites. Due to its importance in the viability of the industrial process, a study has been carried on the regeneration of both catalysts by coke combustion under controlled conditions (in order to avoid CuO sintering). For this study, the catalysts have been used under severe deactivation conditions. It has been proven that γ-Al₂O₃ does not have a suitable hydrothermal stability and that CuO-ZnO-Al₂O₃/NaHZSM-5 catalyst has an excellent performance and is suitable for using it in uninterrupted reaction–regeneration cycles.     

A comparative study for heavy oil hydroprocessing catalysts at micro-flow and bench-scale reactors

CoMo and NiMo catalysts were prepared and the catalytic activities were evaluated in fixed bed micro-flow and bench-scale reactors with different feed composition. Experiments were conducted at conditions close to those that exist in the industrial practice. Due to the different nature of the feeds, the conditions were varied with respect to both evaluation scales. The fresh and spent catalysts were characterized. Spent catalyst textural properties indicated that catalysts were deactivated and the surface area and pore volume dropped by 20–60%. The adsorption–desorption hysteresis of spent catalysts indicated that cylindrical pores are deactivated at the pore mouth and played an important role in modification by either closing one end of the pore or forming a narrow neck pore, which is indicative of the formation of “ink-bottle” type pores. Thus, the deposition of metal and carbon takes place preferentially at the pore entrance, which causes pore mouth plugging. These results are also supported by the SEM–EDAX analysis, where metal and carbon depositions are evident and taking place at the superficial region of a catalyst particle. The increase in absolute area of hysteresis is based on the catalyst's average pore diameter: the higher the average pore diameter, the lower the area of the spent catalyst. The activity and deactivation of the catalyst are discussed on the basis of catalyst porosity and deposited metal characterization. The composition of catalysts varies, considering two applications in a multi-reactor system: a CoMo catalyst for the first reactor, and a NiMo in the second reactor; the former is supported on γ-Al₂O₃ and the latter on TiO₂/Al₂O₃. As a comparison, the CoMo catalyst exhibited better hydrogenolysis while the NiMo catalyst showed better hydrogenation activity in both micro-flow and bench-scale reactors. It appears that there is a moderate effect of TiO₂ content in support on Ni and V hydrodemetallization (HDM) while hydrodeasphaltenization (HDAs) and hydrodesulfurization (HDS) activities were slightly improved when a partially hydrotreated feed, which contains more refractory compounds than virgin feedstock, was employed.     

CH4-CO2 reforming over Ni/Al2O3 aerogel catalysts in a fluidized bed reactor

Ni/Al₂O₃ aerogel catalysts were synthesized by a sol-gel method combined with a supercritical drying route. The catalytic performances of the catalysts in methane reforming with CO₂ were investigated in a quartz micro-reactor. The results indicated that the aerogel catalyst showed higher specific surface area and higher dispersivity of nickel species than those of impregnation catalyst. The excellent catalytic performances and stabilities were achieved over the aerogel catalysts in the fluidized bed reactor. Comprehensive characterization with TG, XRD and FESEM revealed that the aerogel catalyst in the fluidized bed had much lower carbon deposition than that in the fixed bed. The fluidization of the aerogel catalyst greatly improved the contact efficiency of gas-solid phase, which accelerated the gasification of the deposited carbon. In contrast, the deactivation of the aerogel catalyst was caused by the carbon deposition due to the catalyst without moving in the fixed bed. Moreover, decreasing activity of the impregnation catalyst in the fluidized bed resulted from the poor fluidization state of catalyst particles and low effective active sites on surface of catalyst.     

Deactivation Analysis of Industrial Spent Catalysts Applied to Lube Oil Hydrotreating in a Pilot Plant

Industrial spent catalysts taken from different beds of industrial lube oil hydrotreating reactors were investigated in a pilot plant. Experiments to quantify the catalytic activity loss for hydrodesulfurization, hydrodenitrogenation, and aromatic hydrogenation reactions were carried out using an industrial feedstock under operational conditions similar to the industrial ones. Characterization of the spent catalysts was performed to demonstrate the relative influence of different possible deactivation causes. Depending on the position of the catalyst inside the industrial reactor, different deactivation causes were evaluated. At the top of the reactor, poisoning by silicon, arsenic, and iron was the main cause, while at the bottom, coke deposition was predominant.     

Syngas production from methane reforming with CO2/H2O and O2 over NiO–MgO solid solution catalyst in fluidized bed reactors

Catalyst performance of NiO–MgO solid solution catalysts for methane reforming with CO₂ and H₂O in the presence of oxygen using fluidized and fixed bed reactors under atmospheric and pressurized conditions was investigated. Especially, methane and CO₂ conversion in the fluidized bed reactor in methane reforming with CO₂ and O₂ was higher than those in the fixed bed reactor over Ni_0.15Mg_0.85O catalyst under 1.0 MPa. In contrast, conversion levels in the fluidized and fixed bed reactor were almost the same over MgO-supported Ni and Pt catalysts. It is suggested that the promoting effect of catalyst fluidization on the activity is related to the catalyst reducibility. On a catalyst with suitable reducibility, the oxidized and deactivated catalyst can be reduced with the produced syngas and the reforming activity regenerates in the fluidized bed reactor during the catalyst fluidization. In addition, the catalyst fluidization inhibited the carbon deposition.     

沸腾床渣油加氢处理催化剂失活研究

沸腾床催化剂失活主要是由于金属和焦炭沉积导致的,同时在沸腾状态下催化剂的物理和机械性质也发生了改变。使用后的催化剂向小的粒度分布方向偏移;催化剂沉积了大量的金属和焦炭,使催化剂的堆积密度增加,同时导致催化剂的孔结构、酸性质发生了变化。失活催化剂沉积的金属和焦炭在颗粒内外分布均匀,表明催化剂利用率较高。     

碱改性HZSM-5催化热解木质素催化剂失活分析

对0.3 mol·L^-1 NaOH改性后的HZSM-5以及未改性HZSM-5催化剂进行循环和再生评价实验以考察催化剂的寿命。对反应后和再生的催化剂进行N₂吸脱附以及NH₃-TPD表征,并通过对反应后的催化剂进行SEM、TGA、FTIR、UV-Vis等表征分析催化剂积炭。两种催化剂的活性均随着循环实验次数的增加而逐渐降低,经4次循环实验的改性HZSM-5催化剂的催化活性远高于4次循环实验的未改性HZSM-5催化剂。反应过的催化剂经高温煅烧再生后其活性都有所恢复,再生后的改性HZSM-5的催化活性仍高于未改性催化剂。对两种不同催化剂积炭分析,改性后催化剂的积炭量少于未改性的催化剂,其积炭组分中高聚芳烃的含量相对较多。     

Studies on nickel-based catalysts for carbon dioxide reforming of methane

The catalytic activity and coke resistance of La₂O₃ promoted nickel-based catalysts are investigated in a fixed-bed flow reactor. The contents of carbon deposited on catalysts were measured by a carbon combustion method. Catalysts were characterized by CO–TPD, CO₂–TPD, TPR, XPS and XRD techniques, and the results were correlated with the coke resistance of the catalysts. It is found that the catalytic activity, resistance to carbon deposition and the stability of the catalysts can be greatly improved with the addition of a rare earth oxide. It is found that BaTiO₃ is an ideal support. Thus 5.0 wt.% Ni–0.75 wt.% La–BaTiO₃ catalyst shows great resistance to coke formation and higher thermal stability as well as higher catalytic activity, than the catalysts 5.0 wt.% Ni/La–BaTiO₃ (Ba/La = 1/0.002) and 5.0 wt.% Ni–1.5 wt.% La/BaTiO₃.     

Deactivation of metal catalysts in liquid phase organic reactions

The paper gives a general survey of the factors contributing to the deactivation of metal catalysts employed in liquid phase reactions for the synthesis of fine or intermediate chemicals. The main causes of catalyst deactivation are particle sintering, metal and support leaching, deposition of inactive metal layers or polymeric species, and poisoning by strongly adsorbed species. Weakly adsorbed species, poisons at low surface coverage and solvents, may act as selectivity promoters or modifiers. Three examples of long term stability studies carried out in trickle-bed reactor (glucose to sorbitol hydrogenation on Ru/C catalysts, hydroxypropanal to 1,3-propanediol hydrogenation on Ru/TiO₂ catalysts, and wet air oxidation of paper pulp effluents on Ru/TiO₂) are discussed.     

Study of accelerated deactivation of hydrotreating catalysts by vanadium impregnation method

The main causes of catalysts deactivation for hydrotreating are coking and metals deposition. In this present work, accelerated deactivation of hydrotreating catalysts was studied. In this respect, vanadium which is deposited with nickel during hydrotreating reaction was impregnated into the fresh hydrotreating catalyst. Different percentage of vanadium was impregnated and their hydrodemetalization (HDM) and hydrodesulfurization (HDS) activities were studied in bench-scale reactor of heavy crude oil. Accelerated deactivations for both HDM and HDS were observed on vanadium impregnated catalysts. The rate of HDS deactivation was faster than that of HDM reaction. The rapid deactivation of HDS may be due to the coverage of active sites by impregnated vanadium atom. The deactivation is slower when the V loading is low; but above 10 wt% loading a rapid deactivation is observed. A comparison of deactivation is made in between normal deactivation and the deactivation by vanadium impregnation. It was found that deactivation by vanadium impregnation is lower than that of normal deactivation. It suggests that at initial stage the formation of coke causes deactivation of the catalyst whereas at later stage when metals sulfides deposition is quite high, these sulfides take part in deactivation.     

Spectroscopic investigations on deactivation of zeolite catalysts during reactions of olefins

Coke formation over acidic zeolite catalysts upon reaction of olefins is investigated using in-situ IR spectroscopy, i.e. an IR cell which simultaneously serves as a fixed-bed flow reactor and is attached to a gas chromatograph. Zeolites HY, dealuminated H-MOR with two different Si/Al ratios and H-ZSM-5 are compared. The effects of the number of active sites and the pore volume of the zeolites on the initial rate of coke formation and the final coke level are studied.

The final level of coke deposition reflects to some extent the pore volume of the zeolite catalyst. In all cases a considerable amount of coke formed remained inside the pore structure but another fraction was deposited onto the external surface. Both findings were confirmed by sorption measurements on samples before and after loading with coke.

Possible mechanisms of deactivation through coke formation, viz, poisoning, consumption or blockage of sides are briefly considered. In-situ IR spectroscopy revealed that at most a small fraction of the active sites of HY, HMOR or HZSM-5 disappeared during coke deposition suggesting that deactivation is caused by site blocking rather than by poisoning or consumption of the acidic centres.

Finally, in-situ IR spectroscopy turned out to be a useful tool for discriminating between low-temperature coke (formed below about 500 K) and high-temperature coke (deposited above 500 K).     

钴基费托合成催化剂失活机理及再生研究进展

综述了钴基费托合成催化剂的失活机理、催化剂再生工艺及如何延长催化剂寿命的研究进展,通过分析催化剂失活原因,认为中毒、Co颗粒烧结、积炭、氧化、固相反应、晶相重构、表面阻塞和催化剂磨损等因素造成催化剂不同程度失活,其中积炭和Co颗粒烧结是催化剂失活的最主要原因,延长催化剂寿命的关键是提高催化剂的抗烧结能力和抑制积炭生成。增强活性金属Co和载体间的相互作用,保持Co晶粒分布均一或采用包覆、限域等策略可提高催化剂的抗烧结能力,通过添加助剂、调整氢碳比和空速等工艺参数亦可抑制积炭的生成。采用氢处理、脱蜡-氧化-还原和脱蜡-氧化-溶液处理-还原等工艺可实现催化剂的再生,对催化剂进行再生时要结合催化剂失活的主要原因,选择合适的再生工艺来最大限度地恢复催化剂活性。今后,提高催化剂的稳定性以及开发催化剂再生工艺技术路线是提高钴基费托合成技术竞争力的关键。     

基于甲烷化反应的催化剂颗粒设计与过程强化

甲烷化反应过程的主要问题是“烧结”和“积炭”。基于甲烷化反应的强放热、减分子特性和对反应机理的认识,从催化剂与反应器的匹配性角度,论述了当前的主要甲烷化工艺、甲烷化催化剂、甲烷化反应及过程强化方法。流化床技术可有效防止催化剂的积炭和烧结,从与流化床反应器匹配的催化剂结构设计源头出发,制备具有耐磨损、易流化、低密度的高活性甲烷化催化剂,是流化床甲烷化发展的一个重要途径。     

Investigation of carbonaceous compounds deposited on NiMo catalyst used for ultra-deep hydrodesulfurization of gas oil by means of temperature-programmed oxidation and Raman spectroscopy

NiMo/Al₂O₃ catalyst used for ultra-deep HDS of several gas oils at various conditions was characterized by both temperature-programmed oxidation combined with mass spectroscopy (TPO–MS) and/or gas chromatography (TPO–GC), and Raman spectroscopy to make clear how the catalyst was deactivated. TPO–MS showed the presence of carbonaceous compounds containing H and N atoms on the used catalysts. TPO–GC showed that the combustive property of the carbonaceous compounds sensitively changes depending on the HDS reaction conditions and the position of the catalyst charged in the HDS reactor. A curve fitting analysis of TPO–GC profiles indicated that the carbonaceous compounds combusted below 680 K during TPO were observed on all the spent catalysts examined here whereas more refractory carbonaceous compound (combusted at around 690 K during TPO) was observed on the catalyst that had experienced severe HDS reaction conditions. More refractory carbonaceous compound was preferentially observed on the catalyst charged near the outlet of the HDS reactor. Raman spectra of the carbonaceous compounds indicated that the carbonaceous compounds combusted below 680 K during TPO has an amorphous-like structure whereas the refractory carbonaceous compound has a graphite-like one. Raman spectra also indicated that the graphite-like carbonaceous compound possesses a greater lateral size than the amorphous-like one, implying that the refractory carbonaceous compound can cover the catalyst surface more effectively. The carbonaceous compound having a graphite-like structure is one of main reasons for the catalyst deactivation. It is suggested that the precursor for this type of carbonaceous compound is not formed directly from the feed, but indirectly formed during the HDS of gas oil, because of its preferential deposition on the catalyst charged near the outlet of the HDS reactor.     

甲苯甲醇烷基化制对二甲苯催化剂中试反应性能研究

经过多步改性制备了负载二氧化硅（SiO₂）、氧化镁（MgO）、五氧化二磷（P₂O₅）、贵金属铂（Pt）的纳米ZSM-5分子筛催化剂,并在六段固定床反应器上分段装填该催化剂720 g进行甲苯、甲醇烷基化制对二甲苯反应活性评价。实验结果表明,通过调变甲醇和甲苯物质的量比可以使甲苯转化率在22%~30%可调,烷基化液相产物中二甲苯选择性保持在95%以上,二甲苯中对二甲苯选择性保持在95%以上;催化剂单程寿命达到1 300 h,随着反应时间延长催化剂的活性有所下降。通过X射线衍射（XRD）、热重分析（TG-DTG）和氮气吸附-脱附等手段对参加反应前后的催化剂进行了表征,结果表明反应中生成的积炭堵塞了分子筛的孔道或覆盖了催化剂的活性位;经过在反应器内原位再生,催化剂的反应活性基本恢复到新鲜催化剂水平。     

Performance of spent sulfide catalysts in hydrodesulfurization of straight run and nitrogen-removed gas oils

After the test run of several months two kinds of commercial catalysts (NiMo/Al₂O₃ and CoMo/Al₂O₃) were examined in hydrodesulfurization (HDS) of straight run (SRGO) and nitrogen-removed gas oils, at 340 °C under 50 kg/cm² H₂. Hydrogen renewal between stages was attempted to show additional inhibition effects of the by-products such as H₂S and NH₃. Spent NiMo/Al₂O₃ and CoMo/Al₂O₃ catalysts showed contrasting activities in HDS and susceptibility to nitrogen species, according to their catalytic natures, compared to those of their virgin ones. HDS over spent NiMo/Al₂O₃ was significantly improved by removal of nitrogen species, while that over spent CoMo/Al₂O₃ was much improved by H₂ refreshment. The activity for refractory sulfur species such as 4,6-dimethyldibenzothiophene was reduced more severely than that for the reactive sulfur species such as benzothiophenes over spent catalysts. The effects of both two-stage hydrodesulfurization and nitrogen-removal were markedly reduced over the spent NiMo when compared with those over virgin NiMo one. The acidity of the catalysts was correlated with the inhibition susceptibility by nitrogen species as well as H₂S and NH₃. Spent catalysts apparently lost their activity due to the carbon deposition, which covered the active sites more preferentially. The spent NiMo catalyst carried more deposited carbon with larger C/H ratio and nitrogen content. Higher acidity was found to be present on the NiMo catalyst, but this was greatly decreased by the carbon deposition. Additionally, the reactivity of nitrogen species in HDS was briefly discussed in relation to the acidity of the catalyst and its deactivation by carbon deposition.