Faculteit Ingenieurswetenschappen Vakgroep Chemische Proceskunde en Technische Chemie Laboratorium voor Petrochemische Techniek Directeur: Prof. Dr. Ir. G. B. Marin Modeling Steam Cracking of Complex Hydrocarbons Helge Dehandschutter Promotoren: Prof. dr. ir. G.B. Marin Prof. dr. lic. M.-F. Reyniers Begeleider: Dr. ir. K. Van Geem Scriptie ingediend tot het behalen van de academische graad van burgerlijk scheikundig ingenieur Academiejaar 2005-2006 Faculteit Ingenieurswetenschappen Vakgroep Chemische Proceskunde en Technische Chemie Laboratorium voor Petrochemische Techniek Directeur: Prof. Dr. Ir. G. B. Marin Modeling Steam Cracking of Complex Hydrocarbons Helge Dehandschutter Promotoren: Prof. dr. ir. G.B. Marin Prof. dr. lic. M.-F. Reyniers Begeleider: Dr. ir. K. Van Geem Scriptie ingediend tot het behalen van de academische graad van burgerlijk scheikundig ingenieur Academiejaar 2005-2006 Modeling Steam Cracking of Complex Hydrocarbons Helge Dehandschutter Scriptie ingediend tot het behalen van de academische graad van burgerlijk scheikundig ingenieur Academiejaar: 2005 – 2006 Promotoren: Prof. dr. ir. G. B. Marin en Prof. dr. lic. M.-F. Reyniers Begeleider: Dr. ir. K. Van Geem UNIVERSITEIT GENT Faculteit Ingenieurswetenschappen Vakgroep Chemische Proceskunde en Technische Chemie Laboratorium voor Petrochemische Techniek Directeur: Prof. Dr. Ir. G. B. Marin Abstract The main objective of this thesis is the validation and the improvement of the fundamental simulation models of Plehiers (1989) and Vercauteren (1991). The expansion in the petrochemical industry, the continuing demands for ethylene and propylene, the varying feedstock availability, and the rapidly changing market situation have brought and continue to bring research attention to the modeling of the steam cracking process. In the past few decades step by step new and better simulation models have been developed at the Laboratorium voor Petrochemische Techniek. However, the cracking behavior of toluene is still not accurately described in the studied models, as come forward in chapter 2. The reactions existing in the current reaction network disregard the actual cracking mechanism of toluene in which the benzyl radical plays a key role. The steps taken to eliminate this shortcoming are described in chapter 2 as well. By taking the real cracking mechanism of toluene into account excellent simulation results for the benzene and toluene yields are obtained. Furthermore, nowadays more and more heavy fractions (heavy naphtha, light gas oil or vacuum gas oil) are used as feedstock for steam cracking. The reason is that the demand for these fractions as fuel is becoming less and less important. This results in large remains of these low cost fuels. It is of great importance that the simulation models also accurately predict the product spectrum of these heavy fractions. In this respect the study of the cracking behavior of several gas condensates is carried out. In chapter 3, the results of these cracking and decoking experiments part of a new pilot campaign are discussed. Moreover, to use a simulation model, a detailed composition of the feedstock is often required. In chapter 3, the method for analyzing the feedstocks is described as well. Keywords: thermal cracking, modeling, pilot plant experiments FACULTEIT TOEGEPASTE WETENSCHAPPEN Chemische Proceskunde en Technische Chemie Laboratorium voor Petrochemische Techniek Directeur: Prof. Dr. Ir. Guy B. Marin Opleidingscommissie Scheikunde Verklaring in verband met de toegankelijkheid van de scriptie Ondergetekende, Helge Dehandschutter afgestudeerd aan de UGent in het academiejaar 2005 - 2006 en auteur van de scriptie met als titel: Modeling Steam Cracking of Complex Hydrocarbons verklaart hierbij: 1. dat hij/zij geopteerd heeft voor de hierna aangestipte mogelijkheid in verband met de consultatie van zijn/haar scriptie: de scriptie mag steeds ter beschikking gesteld worden van elke aanvrager de scriptie mag enkel ter beschikking gesteld worden met uitdrukkelijke, schriftelijke goedkeuring van de auteur de scriptie mag ter beschikking gesteld worden van een aanvrager na een wachttijd van jaar de scriptie mag nooit ter beschikking gesteld worden van een aanvrager 2. dat elke gebruiker te allen tijde gehouden is aan een correcte en volledige bronverwijzing Gent, 16 juni 2006 ___________________________________________________________________________________________ Krijgslaan 281 S5, B -9000 Gent (Belgium) tel. +32 (0)9 264 45 16 • fax +32 (0)9 264 49 99 • GSM +32 (0)475 83 91 11 • e-mail: [email protected] http://allserv.ugent.be/tw12/ IK DANK : voor het mogelijk maken en het begeleiden van dit stukje wetenschap: Prof. dr. ir. Marin Prof. dr. ir. Reyniers voor zijn enorme inzet, zijn enthousiasme, zijn goede raad, zijn kennis en de leuke samenwerking: Kevin voor het me wegwijs maken in de wondere wereld van de pilootinstallatie: Mister Wang en Michaël voor de leuke sfeer aan de koffietafel: iedereen van “Zwijnaarde” voor de ontspannende middagen, avonden en nachten: mijn medecollegastudenten voor hun diverse steun (want ook al snappen ze niets van chemie, van de rest begrijpen ze alles) mijn ouders Bjorn voor de computerlogistiek mijn broer, Bram Modeling Steam Cracking of Complex Hydrocarbons Helge Dehandschutter Promotors: Prof.dr.lic. Reyniers M.F., Prof.dr.ir. Marin G.B. Coach: Dr.ir. Van Geem K.M. Abstract: Fundamental simulation models are an indispensable of ethylene decreases and other products such as propylene, tool for the petrochemical industry. The development of an butadiene and benzene become more significant. In order to extensive database of pilot plant experiments has made it possible 1 improve the reliability of the single event microkinetic model to validate the simulation models of Plehiers (1989) and for heavier feedstocks, the cracking behavior of gas Vercauteren (1991) 2 for a first time in a very systematic manner. This validation reveals several shortcomings to both models. condensates is studied. Gas condensates are the liquid Some of the shortcomings can be overcome by introducing new condensate removed and recovered during the processing of reactions and species, e.g. reactions involving the benzyl radical. raw natural gas. These fractions show an approximate boiling However, this way of working does certainly not solve all the range between 50 and 350 °C. problems encountered. Therefore a completely new single event 3 microkinetic model is developed by Van Geem (2006) . This II. RESULTS model gives a good agreement for a wide range of pilot plant experiments with light and heavier fractions. However the database does not contain a lot of experiments with heavy A. Network improvement fractions. Nowadays more and more heavy fractions are used as 1) Validation feedstock for steam cracking. In this respect the study of the To validate the fundamental simulation models of Plehiers cracking behavior of several gas condensates is carried out. Eight (1989) 1 and Vercauteren (1991) 2 the simulation results are different gas condensates are cracked under identical conditions, compared with experimental data from the experimental while for one feedstock also the process conditions have been database. In this database over 400 experiments obtained with varied over a broad range. The detailed molecular composition of one specific fraction is also determined. mare than 50 different feedstocks are gathered. An interface is designed to make searching for data easy. One of the main steam cracking, modeling, pilot plant experiments Keywords conclusions of this comparison is that the cracking behavior of toluene is not accurately described. The reactions implemented in the current reaction network disregard the I. INTRODUCTION actual cracking mechanism of toluene in which the benzyl Steam cracking of hydrocarbons is one of the main radical plays a key role. The main reactions that appear during processes in the petrochemical industry. In this process the cracking of toluene are presented in Figure 1. hydrocarbon feedstocks ranging from light alkanes such as ethane and propane up to complex mixtures such as naphthas C-C & C-H scission of molecules and recombination and heavy gas oils are cracked into commercially more toluene benzyl + H valuable products such as light olefins and aromatics. Steam ethylbenzene benzyl + CH 3 cracking is carried out in tubular reactors suspended in large dibenzyl benzyl + benzyl gas-fired furnaces at temperatures ranging from 600-900 °C. The petrochemical industry is continually searching for Hydrogen abstraction higher performance and increased selectivity to increase their H + toluene H2 + benzyl profit margins. In this search accurate simulation models have CH 3 + toluene CH 4 + benzyl become indispensable tools. Several fundamental simulation C2H5 + toluene C2H6 + benzyl models for steam cracking have been developed at the LPT. However, the simulation results of some feedstocks are not Ipso addition always as accurate as one desires. These shortcomings can be H + toluene benzene + CH 3 partly explained by the absence of certain reaction pathways Figure 1: Cracking mechanism of pure toluene 4 and several important species. On the other hand, a new optimization of the kinetic parameters of the reaction network 2) Adaptations could also solve a lot of problems. These options are critically The reactions in Figure 1 are introduced in the reaction 1 evaluated in this work. network of Plehiers (1991) . The optimization of the Another important aspect is