Naphtha Pyrolysis Research Articles

Catalytic pyrolysis of straight-run naphtha to light olefins: Experiment and molecular-level kinetic modeling study

In this work, molecular-level kinetic modeling was developed for the fluid catalytic pyrolysis of straight-run naphtha based on the structural unit and bond-electron matrix framework. The kinetic parameters were tuned and optimized using systematic experimental data from a fluidized bed under different conditions, the predicted values of the fraction yield, naphtha composition, and gas product yield were in agreement with the experimental data. The model can obtain the typical reaction rate of naphtha with different carbon numbers and structure compositions at the molecular level under typical conditions. The model can also quantify and compare the effects of eliminating different side reactions on the light olefins production, and different optimized reaction types of naphtha feedstocks under two typical conditions were revealed, quantitative model calculations show a significant boost in light olefin yield of 15–33 percentage points without hydrogen transfer.

Separation of ethylene and ethane using Co-Gallate pellets in a vacuum swing adsorption process

This work reports a vacuum swing adsorption (VSA) process that utilizes Co-gallate pellets to produce high-purity ethylene. The process is tested on two feed streams generated from the pyrolysis of naphtha and steam cracking of ethane, respectively. The VSA cycle consists of four steps: pressurization, adsorption, replacement with ethylene product and blowdown. A cyclic steady state (CSS) is reached for every test condition, verified by checking the profiles of column pressure, gas composition, and solid loading, which remain constant for ten subsequent cycles. Through analysis of the independent decision variables that affect the performance of the 80/20 (v/v) ethylene/ethane mixture separation, we identify desorption pressure and the replacement flowrate to feed flowrate ratio as the most significant factors. By optimizing these variables, we achieve an exceptional purity of 99.90% for ethylene with a 46.45% recovery and a productivity of 1.05 mol kg−1 per cycle. The Co-gallate adsorbent has a high affinity for ethylene and a low diffusion limitation, thus demonstrating superior potential for industrial ethylene/ethane separation compared to zeolite 4A and Ag+-Amberlyst 35.

Thermodynamic appraisal of naphtha to light olefins based on different reaction pathways and independent chemical reactions

Catalytic pyrolysis of naphtha involves a series of complex acid-catalyzed reaction pathways, that significantly affect the distribution of pyrolysis products. To determine the optimal catalyst characteristics for enhancing light olefins, n-pentane and cyclopentane were used as model compounds to analyze cracking pathways, including the protolytic, dehydrogenation, and hydrogen transfer cracking pathways based on thermodynamic methods. The effects of temperature and pressure on cracking pathways are also discussed. The results indicate that the optimum cracking pathways for enhancing light olefins were the dehydrogenation cracking pathway of n-paraffins and the protolytic cracking pathway of cycloparaffin. Therefore, the design and development of catalysts with dehydrogenation and acidic active sites have become particularly important for the efficient conversion of n/cyclo-paraffins. Furthermore, a thermodynamic equilibrium model based on one set of independent reactions in the catalytic pyrolysis process was established to analyze the effects of the operating conditions on the equilibrium yields. Under these operating conditions, as determined by applying the thermodynamic equilibrium model, the production of light olefins can be tailored.

Thermodynamic analysis of reaction pathways and equilibrium yields for catalytic pyrolysis of naphtha

Thermodynamic analysis of reaction pathways and equilibrium yields for catalytic pyrolysis of naphtha

Pyrolysis and oxidation of a light naphtha fuel and its surrogate blend

An experimental and kinetic study on pyrolysis and oxidation of a real light naphtha fuel and its surrogate blend were conducted. Based on the chemical functional group method, a three-component surrogate blend for the target naphtha was formulated, which contains 64.2 mol% iso-pentane, 21.0 mol% n-hexane, and 14.8 mol% methylcyclopentane. The pyrolysis and oxidation characteristics of the target naphtha fuel and the formulated surrogate were compared using a jet-stirred reactor (JSR) at the equivalence ratios of 0.5, 1.0, 2.0 and ∞, across the temperature range from 700 to 1100 K, and at atmospheric pressure. Mole fractions of the three components, oxygen, hydrogen, CO, CO2, and C1-C4 hydrocarbons were measured by gas chromatograph. Similar global reactivities between the two test fuels were observed in both pyrolysis and oxidation experiments. In addition, a detailed chemical kinetic model was constructed and validated against the species mole fraction profiles measured in JSR experiments. The present model can provide reasonable prediction of the experimental measurements of the species mole fractions in pyrolysis and oxidation of the surrogate blend. Uncertainty-weighted sensitivity analysis indicates that the model prediction of the consumption of the three components of the surrogate blend in pyrolysis are dominated by the rate constants for H-abstraction reactions of isopentane, n-hexane, methylcyclopentane and propene by H atom and methyl radical. The model predictions of the oxidation reactivity of the surrogate blend mainly depend on H-abstraction reactions from the three surrogate components by HO2 radical at 800 K, while the H-abstraction reactions from aldehyde and alkene intermediates become more significant at 950 K.

Propylene yield from naphtha pyrolysis cracking using surface response analysis

Propylene yield from naphtha pyrolysis cracking using surface response analysis

Anti-coking performance of Cr/CeO2 coating prepared by high velocity oxygen fuel spraying

The coke in the coils has a serious impact on the long-term and stable operation of the ethylene plant. Inhibiting coking of the cracking furnace is an important issue. In this paper, the Cr/CeO2 coatings were prepared on the surface of 310S stainless steel by high-velocity oxygen-fuel (HVOF) spraying. The anti-coking performances of the bare 310S specimen and the Cr/CeO2 coatings were tested by using the pyrolysis of naphtha. The results show that the coating with the thickness of 10–15 μm and a very small number of pores was built up by the obviously deformed splats and the coating/substrate interface is jagged bond. The white area on the surface of Cr/CeO2 coatings mainly includes CeO2. However, the gray area is made of Cr or Cr2O3. Compared with the bare 310S specimen, the coking inhibition rates of coatings are 48.7%, 58.9%, 76.1% and 88.9% when the ratio of Cr and CeO2 powder is 19:1, 9:1, 4:1 and 3:2, respectively. With increasing the relative ratio of CeO2, more white areas without coke are exposed. The CeO2 surface can not only inhibit catalytic coking, but also promote the reaction of water vapor and coke.

Activity and sulfur resistance of co-impregnated bimetallic PdNi/γ-Al2O3 catalysts during hydrogenation of styrene

Pyrolysis gasoline (PyGas) is an unstable byproduct of the pyrolysis of naphtha and other hydrocarbons for the production of olefins. PyGas is stabilized by hydrogenation at mild conditions. The hydrogenation of styrene to ethylbenzene is considered a model test reaction for studying the selectivity of the catalysts because it has the slowest rate of conversion. The catalytic activity and selectivity of two bimetallic co-impregnated Pd–Ni catalysts supported on γ-alumina were assessed and compared to those of a commercial monometallic Pd catalyst (AXENS LD265). The laboratory-prepared catalysts had different metal content and Pd:Ni atomic ratios (1:1 and 1:7). Catalytic tests of selective hydrogenation of styrene to ethylbenzene were made in a batch stirred tank reactor and in a continuous fixed bed trickle bed reactor. The sulfur resistance of the bimetallic catalysts in semicontinuous condition, was assessed by means of the same operational conditions using thiophene as a model poison compound. The support, Pd–Ni co-impregnated catalysts and LD265 commercial catalysts were further characterized by N2 chemisorption, EPMA, OM, ICP elemental analysis, temperature programmed reduction, XPS and X-Ray diffraction. The results indicated the presence of different metal species: Pd0, Pdδ+, Ni0 and NiO. The lab-prepared bimetallic catalysts were found to be active for the selective hydrogenation of styrene (both in the batch and continuous system). During the continuous evaluations, the commercial LD265 catalyst had an intermediate activity level that lied between the values corresponding to the Pd–Ni bimetallic catalysts: PdNi(1:1) $$ \gg $$ LD265 > PdNi(1:7). During the poison free semicontinuous evaluations, the pattern of conversion as a function of contact time of co-impregnated Pd–Ni catalysts are quite similar to that of commercial LD265 catalyst, though the catalytic activity is slightly better for PdNi(1:1). After 90 min of contact time the order of conversion was: PdNi(1:1) > LD265 > PdNi(1:7). On the other hand, during the poison semicontinuous tests (with 300 pp of thiophene), the initial reaction rates of the co-impregnated catalysts decreased, pointing a poisoning of the active sites by thiophene. PdNi(1:1) had higher initial reaction rate than PdNi(1:7) during poison free or poisoned in both conditions. PdNi(1:7) was more sulfur resistant than PdNi(1:1). The higher activity of the PdNi(1:1) catalyst was attributed to the presence of Pd0 and Pdn+/Nim+ species that favored respectively, the homolytic cleavage of the H–H bond and the adsorption of styrene. The higher sulfur resistance of the PdNi(1:7) catalyst would be associated with the higher Cl/Al surface atomic ratio in this catalyst (electronic effect) and the presence of electrodeficient species of Pd (Pdxδ+OyClz) that prevented the adsorption of thiophene by steric hindrance (geometrical effect of the large species) or by electronic effects.

Ethylene Yield from a Large Scale Naphtha Pyrolysis Cracking Utilizing Response Surface Methodology

Statistical software is a robust application that has proven reliable worldwide. However, it is not normally used in the actual large scale olefin plant as it relies on the simulation software by Olefin Licensor should any issue rises. The study was conducted in a newly commissioned large scale olefin plant to see the impact of various operating variables on the ethylene yield from Short Residence Time (SRT) VII Furnace. The analysis was conducted utilizing statistical analysis, Response Surface Methodology (RSM) in Minitab Software Version 18 to develop a reliable statistical model with a 95% confidence level. The historical data was taken from the Process Information Management System (PIMS) Software, PI Process Book Version 2015, and underwent both residuals and outliers removal prior to RSM analysis. 10 variables were shortlisted from the initial 15 identified variables in the studied SRT VII via Regression analysis due to RSM limitation to conduct the larger analysis in Minitab Software Version 18. The Response Optimizer tool showed that the ethylene yield from naphtha pyrolysis cracking in the studied plant could be maximized at 34.1% with control setting at 600.39 kg/ hr of Integral Burner Flow, 6.81% of Arch O2, 113.42 Barg of Steam Drum Pressure, 496.96°C of Super High Pressure (SHP) Temperature, 109.11 t/hr of SHP Boiler Feed Water (BFW) Flow, 92.78 t/hr of SHP Flow, 63.50 t/hr of Naphtha Feed Flow, and -13.38 mmHg of Draft Pressure.

Investigation into the Anticoking Performances of Sol–Gel-Derived SiO2 and SiO2–CeO2 Coatings during Thermal Pyrolysis of Light Naphtha

CeO2-based materials are widely applied in a three-way catalyst framework for catalytic combustion of diesel soot. For the application of CeO2 in coking inhibition during thermal cracking of hydroc...

Solvolysis of Bituminous Coal in Coal- and Petroleum-Derived Commercial Solvents.

The solvolytic conversion of softening bituminous coal at 380 °C in solvents derived from the commercial hydrocarbon byproducts and residues from coal and petroleum processing was studied. Hydrogen-donor tetrahydronaphthalene (THN) and nondonor 1-methylnaphthalene (MN) were also used for comparison. The high-boiling solvents of different chemical classes (highly aromatic coal tar, its anthracene fraction, and low-aromatic heavy gas oil of catalytic cracking of the oil residue) and the H-donor THN solvent were found to exhibit high efficiency for coal conversion into quinoline-soluble products. The chemical and molecular compositions of coal, solvents, and dissolved products were characterized in detail by different techniques, including chemical analysis, group analysis, infrared Fourier transform (IRFT) spectroscopy, X-ray diffraction (XRD), liquid chromatography, and thermal analysis to reveal the chemical transformations of the coal–solvent mixture during the dissolution reaction. The solvolysis of coal in the liquid phase of both highly aromatic and low-aromatic solvents was found to involve selective depolymerization of polymer-like coal via breaking of weak linkages between the aromatic units, resulting in the formation of soluble pitchlike products. The effective dissolution of coal in the H-donor THN solvent resulted probably from a combination of the nonselective thermal fragmentation of the coal structure to smaller radical intermediates and their stabilization by hydrogen from THN, producing mainly tar and a few gases. The low-boiling solvents of both predominantly aromatic and aliphatic classes (gas oils from naphtha pyrolysis and delayed coking of the petroleum residue) and MN exhibited poor efficiency for coal dissolution. The concentrations of carcinogenic benzo(a)pyrene (BaP) in the solvents used and in the toluene fractions of the resulting extracts were analyzed. The remarkable result was that coal extracts, compared to solvents, contained much less BaP, probably due to its conversion with coal and/or solvent molecules during coal dissolution.

Optimization of SRT-VI Pyrolysis Furnaces of High-Capacity Ethylene Plant

The development and solution of an optimization model of real-time control of pyrolysis of straight-run naphtha are considered. The model takes into account the constraints imposed by downstream units of a high-capacity production plant on the pyrolysis process, among which are the primary pyrolysis-gas fractionation unit, pyrolysis-gas compression unit, pyrolysis-gas separation unit, ethylene and propylene refrigeration cycles, reactors of hydrogenation of acetylenic compounds, and separation columns. Optimization is performed using a mathematical model comprising three parts: calculation of the physicochemical characteristics of straight-run naphtha from data of density measurements and Engler distillation, calculation of the kinetic parameters of the process, and determination of the yields of 14 main products of the pyrolysis. The errors of modeling the yields of various pyrolysis products are as follows (rel %): ethylene ±1.5, propylene ±2.8, butadiene ±3.3, and benzene ±3.1. In the optimization, “light” (density 0.706 kg/L) and “heavy” (0.72 kg/L) straight-run naphthas were studied. For both types of feedstock at a target ethylene yield of 10.45 t/(h furnace) under the target constraints, the profit was maximized and the standard naphtha consumption was minimized. The results were compared with the requirements for the pyrolysis according to the standard operating procedures, according to which the ethylene yield did not reach the target value for either type of feedstock and was 10.32 and 9.68 t/(h furnace), respectively. After optimization, the maximum profit was 1143 and 935 cu/(h furnace), respectively. The minimization of the standard consumption gave 1.79 t/t for light naphtha and 1.84 t/t for heavy naphtha. The constraints were met, and the target ethylene yield was reached. It was concluded that the pyrolysis of straight-run naphtha taken directly from a supplier’s pipe is inefficient and that the feedstock should be prepared in stirred intermediate tanks, with naphtha density measurements and Engler distillation performed according to the standard operating procedures, the data of which should then be used in the optimization.

Improving the steam-cracking efficiency of naphtha feedstocks by mixed/separate processing

Naphtha feedstock used for the steam-cracking process is typically blended from several hydrocarbon source streams of composition varying in a broad range. This study aims at evaluation of the potential yield improvement, which could be obtained by separate steam-cracking of light and heavy sub-streams using tailored process parameters for each of the sub-streams. Laboratory pyrolysis reactor was used for both separate and blend processing of the naphtha feedstocks in the temperature range of 760–810 C, and different blending ratios. At maximum temperature, pyrolysis of light naphtha provides ethylene yield 24.1 wt. %, while only 13.6 wt. % of ethylene was obtained from heavy naphtha. Both, ethylene and propylene yield express decreasing trend with increasing content of heavy naphtha in blended feedstock. Obtained results suggest possibility of mutual effects between components resulting in non-linear dependence of products yields on the blending ratio, therefore a principle of additivity cannot be assumed. A potential for improvement of ethylene yield by 1.1 wt. % is shown on example of processing scenario.

Optimization of the Pyrolysis of Naphtha Fractions of the West Siberian Gas Condensate to Obtain Lower Olefins and Divinyl

Naphtha fractions of the West Siberian gas condensate were evaluated as feedstock for thermal pyrolysis performed in the temperature interval 750–900°C at the conventional contact time of 0.2–0.4 s and steam-to-feed weight ratio of (0.5; 0.8): 1.0. Statistical models of the process, based on the experimental dataset obtained, were constructed and used for multicriteria optimization with respect to the key products: ethylene, propylene, divinyl, pyrogas, and coke. The optimum process parameters for pyrolysis of light and heavy naphtha of the gas condensate to reach the maximal yield of target products (ethylene, propylene, divinyl) under the conditions of compromise solutions were found. The influence of the group and individual hydrocarbon composition of the naphtha fractions of the gas condensate on the yield and distribution of the major products was demonstrated.

Application of convolutional neural networks to large-scale naphtha pyrolysis kinetic modeling

Abstract System design and optimization problems require large-scale chemical kinetic models. Pure kinetic models of naphtha pyrolysis need to solve a complete set of stiff ODEs and is therefore too computational expensive. On the other hand, artificial neural networks that completely neglect the topology of the reaction networks often have poor generalization. In this paper, a framework is proposed for learning local representations from large-scale chemical reaction networks. At first, the features of naphtha pyrolysis reactions are extracted by applying complex network characterization methods. The selected features are then used as inputs in convolutional architectures. Different CNN models are established and compared to optimize the neural network structure. After the pre-training and fine-tuning step, the ultimate CNN model reduces the computational cost of the previous kinetic model by over 300 times and predicts the yields of main products with the average error of less than 3%. The obtained results demonstrate the high efficiency of the proposed framework.

Coupled simulation of recirculation zonal firebox model and detailed kinetic reactor model in an industrial ethylene cracking furnace

Abstract A coupled system simulating both firebox and reactor is established to study the naphtha pyrolysis in an industrial tubular furnace. The firebox model is based on zone method including combustion, radiation, and convection to simulate heat transfer in the furnace. A two-dimensional recirculation model is proposed to estimate the flow field in furnace. The reactor model integrates the feedstock reconstruction model, an auto-generator of detail kinetic schemes, and the reactor simulation model to simulate the reaction process in the tubular coil. The coupled simulation result is compared with industrial process and shows agreement within short computation time.

Molecular characterization of petroleum fractions using state space representation and its application for predicting naphtha pyrolysis product distributions

Molecular model of petroleum fractions plays an important role in the designing, simulation and optimization for petrochemical processes such as pyrolysis process, catalytic reforming and fluid catalytic cracking (FCC). However, it is very difficult to exactly characterize the composition distributions due to its internal complexity and containing numerous redundant information and measuring errors although many efforts have been made so far. As an improvement of the work in Mei et al. (2016), a molecular-based representation method within a multi-dimensional state space is developed in this paper. In this method, each pure component in the petroleum mixtures is defined as a state variable and any petroleum fractions can be geometrically represented as a point in a multi-dimensional linear state space, in which a conception of basis fractions is further introduced by defining a group of linear independent vectors so that any petroleum fractions within the specified range (e.g. naphtha) can be obtained through a linear combination by such basis fractions. The redundant information and measuring errors in the pre-determined petroleum fraction samples are eliminated through the procedure of calculating the basis fractions with non-negative matrix factorization (NMF) algorithm, meanwhile the scale of the feedstock database is highly decreased. As an application example of the basis fractions, a quick prediction approach on naphtha pyrolysis product distributions is developed by linearly combining the pyrolysis products of the basis fractions. In contrast to mechanistic models, this proposed method is more suitable for real-time control and optimization purpose with little loss of accuracy.

Self-adaptive multi-objective teaching-learning-based optimization and its application in ethylene cracking furnace operation optimization

A self-adaptive multi-objective teaching-learning-based optimization (SA-MTLBO) is proposed in this paper. In SA-MTLBO, the learners can self-adaptively select the modes of learning according to their levels of knowledge in classroom. The excellent learners are more likely to choose the learner phase to enhance population diversity, and the common learners are tend to choose the teacher phase to improve the convergence ability of the algorithm. So learners at different levels choose appropriate modes of learning and carry out corresponding search function to efficiently enhance the performance of algorithm. To evaluate the effectiveness of the proposed algorithm, SA-MTLBO is firstly compared with other algorithms in twelve test problems. The results demonstrate that SA-MTLBO can generate Pareto optimal fronts with good convergence and distribution. Finally, SA-MTLBO is used to maximize the yields of ethylene, propylene, and butadiene of the naphtha pyrolysis process. The computational results of SA-MTLBO indicate that the operation of ethylene cracking furnace can be improved by increasing the yields of ethylene, propylene, and butadiene.

Multi‐Objective Optimization of Pseudo‐Dynamic Operation of Naphtha Pyrolysis by a Surrogate Model

AbstractA simple pseudo‐dynamic surrogate model is developed in the framework of the state space model with the feed‐forward neural network to replace the complex free radical pyrolysis model. The surrogate model is then applied to investigate the multi‐objective optimization of two key performance objectives with distinct contradiction: the mean yields of key products and the day mean profits. The ϵ‐constraint method is employed to solve the multi‐objective optimization problem, which provides a broad range of operation conditions depicting tradeoffs of both key objectives. The Pareto‐optimal frontier is successfully obtained and five selected cases on the frontier are discussed, suggesting that flexible operations can be performed based on industrial demands.

Olefin profile prediction of naphtha pyrolysis using a feeding-independent continuous lumping method with mechanism analysis

By avoiding the massive calculations of complicated reaction networks, the continuous lumping method has been welcomed as a means of describing hydrocarbon pyrolysis processes. In our work, with the introduction of a new distribution function representing different structure effects on kinetic parameters, a mechanism-oriented continuous lumping model is proposed to acquire the olefin profile of naphtha pyrolysis with experimentation independent of different feeding compositions. Meanwhile, micro-reactor pyrolysis experiments are conducted to analyze the structure mechanism and to obtain the pyrolysis parameters. The analytical results indicate that long-chain molecules with higher degrees of branching react faster, and long-chain alkanes with fewer side chains are more inclined to form ethylene product. The prediction results of the simulation method are consistent with the experimental results. The prediction performance is comparatively accurate and independent of feeding.