Coke formation during naphtha pyrolysis in a tubular reactor

The effect of run time, temperature, conversion and inlet steam-to-naphtha ratio on the rate of coke deposition during naphtha pyrolysis in an annular tubular reactor has been investigated. Rates of coke deposition increased with increasing temperature, conversion and inlet naphtha partial pressure. Pyrolysis and coking models available for naphtha cracking were used to calculate the total coke deposited by treating the temperature difference between the reacting fluid and the outer reactor wall as a parameter. For all the runs, the experimental and calculated coking rates were in close agreement for an assumed temperature difference of 35-45°C.     

渣油加氢裂化反应中油溶性催化剂的抑焦性能

以辽河常压渣油为研究对象,通过高压釜模拟渣油加氢裂化反应,对不同油溶性催化剂体系反应后的生焦量、生焦状况及产物进行分析,深入研究渣油加氢裂化反应中油溶性催化剂的抑焦性能.研究表明,随着活性金属含量的增大,油溶性单金属Co催化剂和Ni催化剂的生焦量减少,Co - Fe或Ni - Fe复配体系具有协同效应,抑焦性能增强,由...     

催化裂化结焦反应的研究进展

综述了近年来催化裂化结焦反应的研究进展情况,重点介绍了结焦反应的影响因素、焦炭对催化反应的影响、结焦机理以及焦炭的表征4个方面。研究认为,原料的性质、反应温度、催化剂的类型等因素均会对焦炭的生成产生影响。焦炭可以导致催化剂的失活,而位于孔道内部的焦炭对反应物或产物的扩散不利,进而影响产物的分布。研究表明,各种烃类组分形成焦炭的过程都必须经历芳香烃这一步。对于结焦催化剂可以采取多种表征手段,其中利用XPS以及GC-MS对焦炭进行表征的报道日益增多。尽管国内外对于催化裂化结焦反应的研究开展较早,然而探究焦炭的具体成分仍存在不小的困难,通过先进的表征手段鉴定焦炭中高缩合度芳烃组分以及如何减小催化裂化催化剂的结焦量将成为未来的研究方向。     

Deactivation by Coking of Platinum/Alumina Catalysts: Effects of Operating Temperature and Pressure

Coke deposition is a complex reaction that results from the production of coke precursors and from their destruction. At low temperatures, when the destruction reaction (high apparent activation energy) is negligible, the coking rate is increased owing to increasing metal accessibility. In contrast, at high temperatures the coking reaction is hindered by an increasing metal loading. A change in the coking temperature does not alter the chemical nature of the carbonaceous deposits and their distribution between the metallic and acidic phases of a bifunctional catalyst. On the other hand, an increase in coking pressure (with a constant hydrogen:hydrocarbon molar ratio) promotes the graphitization of coke on the support, protecting the catalytic activity of the metallic phase.     

对焦炭塔塔鼓变形失效的机理分析

焦炭塔是延迟焦化反应的反应釜,是延迟焦化装置的重要组成部分,其长期安全的运行是炼油企业取得高效益的前提和保障.但由于工作条件的恶劣,焦炭塔普遍存在着塔体变形、裙座及塔体焊接开裂等问题,严重影响着焦炭塔的安全运行.究其原因目前主要有以下几种情况:高温蠕变的结果;低周热疲劳的结果;高温蠕变与低周热疲劳共同作用的结果冷;急热温差热应力引起的局部塑性变形.通过对高温蠕变与低周热疲劳的产生条件以及损坏特征的仔细研究,并辅助以各种试验的结果,用排除法确定了焦炭塔的腰鼓变形失效的原因为急冷、急热温差热应力导致的局部塑性变形,并且总结出了其变形失效的规律和防治的具体方法.     

结焦时间与焦炭质量关系的20kg小焦炉实验分析

通过20kg小焦炉实验,探讨了在相同炼焦温度和同一配煤比条件下,结焦时间对焦炭质量的影响。结果显示,适当延长结焦时间能有效地提高焦炭的抗碎强度和反应后强度,而焦炭的耐磨强度和反应性明显降低,并从微观角度解释了焦炭质量变化的原因。建议在生产条件允许的情况下,应适当延长结焦时间,可以改善焦炭的冷热态强度。     

Coke formation on metal foils from heavy oils

The coke deposition on nickel and steel foils during pyrolysis of heavy oils has been studied. The amount of coke deposited on the foils was found to be dependent on foil type, reactor history, feed type and reaction conditions. On nickel, an asphaltene-containing feed gave more coke than an asphaltene-free feed. The coking on the metal foils increased in the order SS-302 < Inconel 718, Inconel X < Nickel. Introducing a rougher surface by rubbing the foils increased the coking. Scanning electron micrographs of the coked foils are presented and reveal details of two types of deposit. Type i is a catalytically formed deposit found only on nickel. The surface is covered in grains, crystalline in appearance. The grains are either irregular or needle-shaped, depending on the feed. The structure of the grains is not affected by the reaction conditions. Type ii is a deposited layer of coke, often containing droplets or mesophase spheres. The thickness and structure of the layer depends on the feed and the reaction conditions. This coke is formed in the liquid phase and deposited onto the surface. Surface roughness is important in determining the amount of coke deposited. A mechanism explaining these phenomena is suggested.     

异丁烷脱氢过程催化剂结焦与焦性质研究

在固定床反应装置上,采用YBD型Cr/Al_2O_3催化剂催化异丁烷脱氢,通过热分析技术研究结焦催化剂,考察反应条件对催化剂结焦量及焦性质的影响。结果表明,Cr/Al_2O_3催化剂对异丁烷脱氢有较好的催化活性,当反应温度580℃,空速800 h^(-1)时,异丁烷转化率60%以上,异丁烯选择性90%以上,异丁烯收率约60%。反应温度、空速以及异丁烯对结焦催化剂的焦含量有明显影响,当反应温度超过580℃,随着原料气中异丁烯含量的增加,催化剂的结焦量迅速增加。     

Open loop response to changes of coke-precursors during fluidised-bed catalytic cracking

Management of coke is very important during industrial operation of fluidised-bed catalytic cracking units; this coke can be classified into two categories. The first one is “additive coke”, which comes as precursors in feedstock from up-stream processes such as vacuum distillation; this coke is deposited on the catalyst surface independently from kinetic rates, catalyst/oil ratio or kind of catalyst. The second one is coke produced in cracking reactions, which depends on catalyst activity and catalyst/oil ratio. Both kinds of coke, additive and product, are deposited on catalyst surface and busted during regeneration. Due to normal changes in feedstock composition, the amount of coke precursors might oscillate during industrial operation. This situation would be seen as a change in the effective yield to coke in the riser and, consequently, a variation in the heat production rate during regeneration reactions, which could modify regenerator operating temperature; therefore several control studies are focused to the rejection of this disturbance. In this work, a mathematical model of industrial FCC units is used to simulate open-loop responses to different changes of coke precursors, it is found that FCC units are able to manage these disturbances without control actions, up to certain limits around the operating region; therefore control studies should consider this self-stabilisation ability prior to propose closed-loop operating policies.     

焦炉燃烧室-炭化室耦合热过程模拟研究

利用仿真软件,模拟了结焦周期内焦炉燃烧室-炭化室耦合热过程,获取了炭化室内焦炭温度随时间的变化趋势,分析燃烧室内的温度场、流场,进一步探讨了燃料种类、供热结构等因素对焦饼温度场和结焦时间的影响。结果表明:模拟结果与测量数据、设计数据吻合较好,验证了数理模型的可靠性和准确性,多点供热结构较好改善了高向加热均匀性,改善了煤饼中心高向温差,优化了焦炉的运行。     

焦炭强度与热性质控制因素分析

在20kg小焦记上进行了11种单种煤和8种配煤方案的炼焦试验,建立了焦炭质量预测模型。结果表明,单一的煤质指标与焦炭强度的关系不明显,多因素指标进行焦炭质量的预测效果较好;焦炭反应性与单一煤质指标中Vd、^—Rmax^0、Ad之间有较好的关系,且随反应温度的升高而增大。     

Single-event microkinetics for coke formation during the catalytic cracking of (cyclo)alkane/1-octene mixtures

A single-event microkinetic model (SEMK) is applied to model initial coking rates during the catalytic cracking of (cyclo)alkane/1-octene mixtures at 693–753 K and (cyclo)alkane and 1-octene inlet partial pressures of 26.6 and 4.8 kPa on a REUSY equilibrium catalyst. Three types of irreversible alkylations involving both gas phase and surface coke precursors, viz., alkylation of phenyl substituted carbenium ions with C₃–C₅ alkenes, alkylation of the nucleus of monoaromatics with C₃–C₅ alkylcarbenium ions, and alkylation of C₈–C₁₀ alkylcarbenium ions with C₃–C₅ alkenes, have been considered as rate-determining steps in coke formation. The bulky alkylated species formed out of these alkylations are considered as coke. The activation energies for these alkylations obtained via non-isothermal regression are independent of the feedstock within the parameters confidence limits reflecting the fundamental character of the SEMK. The negative effect of temperature on the experimentally observed coking rates is qualitatively described and is explained in terms of an overcompensation of the increase of the rate coefficient by a lower surface coke precursor concentration.     

焦炭质量与高炉冶炼关系的再思考

不断追求高的焦炭热强度与炼焦煤资源短缺的矛盾在不断加剧,直接威胁到高炉工艺的可持续发展和生存.从冶金反应工程学的视角对焦炭质量问题进行了讨论.由于浮氏体气相还原和焦炭气化是一对耦合反应,焦炭在高炉内气化的多少主要由矿石的还原性决定,在使用高还原性铁矿石时,提高焦炭的反应性对改善高炉效率有利.实验研究证明,影响高炉强化和喷煤比提高的限制性因素是高炉下部的多相正常对流运动,而通过提高焦炭的抗粒度降级能力能够增大焦炭料层的透气性和透液性,促进高炉的顺行.建议开展炼铁、焦化和煤炭地质等多学科研究,尽快制定新的焦炭质量标准.     

硫化物和硫/磷化合物的添加方式对石脑油热裂解结焦影响的研究

以石脑油为裂解原料,考察了硫化物和硫/磷化合物的添加方式对热裂解结焦行为的影响。采用Raman光谱、XRD、SEM和XPS等检测手段表征了HP40试样的氧化层和焦炭的形貌与结构。结果表明,原料连续注入硫化物条件下,磷化物的加入使得焦炭结构改变,显示出优异的抗结焦效果。硫化物和硫/磷化合物预处理导致氧化层中Fe含量升高,抑制结焦效果有限。硫/磷预处理与原料连续注入硫/磷化合物联合方式与原料连续注入硫/磷化合物方式的抗结焦效果接近,但前者在初期的抑制效果更明显。所有添加方式都会引起结焦层中无定形焦炭含量升高,焦炭的石墨化程度降低。热裂解焦炭缩合程度较高,硫化物和硫/磷化合物减少了催化结焦的生成,在一定程度上提高了焦层中氢含量。     

石油加工过程中焦炭形成的原因、类型及影响因素

回顾了多种烃类分子裂解生焦的机理,指出多环芳烃是石油加工过程中焦炭形成的反应中间体。从分子化学反应水平上综述了3种生焦机理:多相催化结焦、多相非催化结焦、均相非催化结焦,研究表明:较高温度下烷烃催化裂解过程中,焦炭的组成与裂解反应深度有关,但不受烷烃分子结构的影响;热裂解过程中,异构烷烃的生焦速率大于正构烷烃,烯烃、芳烃具有较大的生焦趋势,且芳烃裂化的生焦量与物质的碱性对数线性相关。依据显微结构的不同,焦炭可以分为3类:点状焦炭、镶嵌状焦炭和纤维状焦炭,相关研究表明:焦的结构特性与中间相形态有关,可塑性好的碳质中间相易聚合、溶并形成各向异性的纤维状焦炭。工艺过程中,原料的性质、催化剂及添加剂种类、工艺操作条件等因素都会影响焦炭的生成。     

Addition methods of sulfur and sulfur/phosphorus-based compounds on coking behavior during thermal cracking of naphtha

Using naphtha as raw material for cracking, the effects of adding sulfides and sulfur/phosphorus compounds on the coking behavior of thermal cracking were investigated. The morphologies and structures of the pretreated HP40 alloy specimen and coke deposits were characterized by Raman spectroscopy, XRD, SEM and XPS. The results showed that the addition of phosphide into the sulfide additives led to the change in the structure of coke deposits under the condition of continuous addition of additives into the feed. The method with continuous addition of sulfur/phosphorus-based compounds showed excellent anti-coking properties. The surface pretreatment with sulfur or sulfur/phosphorus-based compounds made the increase of Fe content in the oxide film on the specimen. So anti-coking effect was limited when the pretreatment method was applied. The coking inhibition property of the application of surface pretreatment with sulfide/phosphide followed by continuous addition of sulfur/phosphorus-based compounds were similar to that of the application of continuous addition of sulfur/phosphorus-based compounds in the feed. However, the combination method showed the better anti-coking effect during the initial cracking process. All the addition methods led to the increased amounts of amorphous coke in the coke layer and the decreased graphitization degree of cokes. The results of the low H/C ratios showed the highly condensed structure of the coke deposits during thermal cracking process. The addition of sulfur and sulfur/phosphorus-based compounds could influence the dehydrogenation reaction to some extent during the coke formation by reducing catalytic coking.     

On the Confinement Effect During Catalytic Reaction Over Al-MCM-41

A comprehensive study has been made on the cracking abilities of mesoporous aluminosillicate MCM-41 materials with different Si/Al ratios (15–∞) and pore diameters (1.6–3.0 nm) by using 1,3,5-triisopropylbenzene (1,3,5-TiPB) cracking as the test reaction. The roles of Al content and pore diameter on the catalytic features of the samples were evaluated by the conversion of 1,3,5-TiPB, coke content and deactivation parameters. It is found that the catalytic activity is mainly controlled by adsorptive properties towards the reactant and the dispersion of acid sites. In terms of their catalytic performances, cracking reaction over aluminosilicate mesoporous materials is more favorable for catalysts with smaller pore size and higher Al concentration. Moreover, coking is found responsible for catalyst deactivation during 1,3,5-TiPB cracking reaction over Al-MCM-41.     

Preparation and Anti-coking Property of SiO2/S Coating on HP40 Tube

SiO2/S coating was prepared on the inner surface of an HP40 tube using dimethyldisulfide and tetraethylorthosilicate by atmospheric pressure chemical vapor deposition (APCVD) to alleviate catalytic coking on the inner surface of radiant tube for ethylene production in petrochemical plants. The comparative coking experiments with the coated and uncoated HP40 tubes were carried out under the same cracking conditions. SiO2/S coating was compact and had excellent anti-coking property. The coke on the coated HP40 tube was about 22% of that on the uncoated HP40 tube, and only small granular coke was deposited on the coated HP40 tube. However, the filamentous coke formed on the uncoated HP40 tube. The thermal stability of SiO2/S coating was satisfactory at cracking temperature, and the anti-coking property of SiO2/S coating was still over 60% after 3 coking and decoking cycles.     

配合煤配比对焦炭综合热性质的影响

以企业生产实践为背景,研究在配合煤中增配肥煤和1/3焦煤对焦炭综合热性质的影响。对不同配比配合煤的性质指标进行检测,采用40 kg焦炉实施炼焦试验,并对炼制焦炭的传统国家标准热性质指标和利用自主研制装置测得的综合热性质指标进行测定。结果表明:增配肥煤和1/3焦煤,均会使配合煤的变质程度降低,挥发分含量升高,胶质体的黏结能力下降,但胶质体的量保持不变。配比变化引起的配合煤性质指标的变化没有显现在焦炭的传统国家标准热性质指标反应性CRI和反应后强度CSR上。以往的研究都是以CRI和CSR指标为目标量判断配合煤的配比是否合适,本研究除此之外还采用了自主提出的焦炭综合热性质指标。配合煤配比变化引起的焦炭的综合热性质指标变化比国家标准热性质CRI和CSR指标变化敏感,这可能与其反映了焦炭某些新的特征有关。基于焦炭综合热性质指标的变化规律,考虑到1/3焦煤具有经济性,生产上增配某些特定的1/3焦煤,可以同时达到提高焦炭质量和降低配煤成本的目的。