Petrol rafinerisi katalitik dönüşüm ünitesinde işlenen naftanın kinetik modellemesi
Kinetic model for catalytic reforming  of naphtha in the oil refinery
Yazar: BURCU KEÇECİLER
Danışman: PROF. DR. DURSUN ALİ ŞAŞMAZ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Kimya Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2014
Konu: Kimya Mühendisliği = Chemical Engineering
Dizin: Ham petrol = Crude oil ; Kimyasal bileşim = Chemical composition ; Kinetik modeller = Kinetic models

Özet:
Petrol rafinerilerinde atmosferik distilasyon sonucu elde edilen ve benzinin hammaddesini oluşturan naftanın yapısında parafin ve naften gibi düşük oktanlı hidrokarbonlar bulunmaktadır. Hidrojen ile muamele görmüş nafta şarjı, aralarında fırınların bulunduğu dört adet dönüştürücü reaktöründen oluşan sürekli katalizör rejenerasyon (CCR) ünitesinin reaktör kısmına gönderilmekte ve burada dönüştürücü katalizörü üzerinde yüksek sıcaklık ve çok düşük basınçta, yüksek oktanlı izoparafin ve ağırlıklı olarak aromatik moleküllere dönüştürülmektedir. CCR ünitesi reaktör kısmında katalitik dönüştürücü reaksiyonları hareketli katalizör yataklar içerisinde meydana gelmekte ve dehidrojenasyon, izomerizasyon, dehidrosiklizasyon, dehidroalkilasyon, hidrojenle kırılma reaksiyonları sonucu üretilen ve reformat adını alan yüksek oktanlı benzinin yanı sıra hidrojence zengin gaz ve az miktarda sıvılaştırılmış petrol gazı (LPG) elde edilmektedir.
Benzin oktan sayısının (RON) arttırıldığı CCR ünitesinin üretim kapasitesi, benzin talebine göre değişiklik göstermektedir. Günlük operasyon koşullarında bu parametrelerin devamlı değişmesi RON değerinin de değişmesine neden olmaktadır. Bu değişiklik, son ürün olan benzinin RON değerini etkilemekte, kontrol edilemeyen zararlar meydana gelmektedir. Bu çalışma ile CCR ünitesi reaktör kısmındaki kinetik modelleme ile dördüncü dönüştürücü reaktöründen çıkan ürün bileşiminin öngörülmesi ve pratik bir şekilde oktan sayısının belirlenmesi için bir yöntem geliştirilmiştir. Ayrıca oktan arttırıcı katkı maddesi olan metil tersiyer bütil eterin (MTBE) karışım içerisindeki oranlarının azaltılması, böylece hem üretim maliyetlerinin düşürülmesi, hem de kimyasal madde kullanımının azaltılması ile çevreye verilen zararın en aza indirgenmesi amaçlanmıştır.
Tez çalışması ile geliştirilen yöntem, CCR ünitesi reaktör kısmına giren nafta şarjı bileşiminin kümeleme yöntemi ile tanımlanması, reaksiyon hız sabitlerinin hesaplanması, reaksiyonların ısı kapasitelerinin hesaplanması, reaksiyon ısılarının hesaplanması, reaksiyon ısıları kullanılarak nafta dönüştürücü reaksiyonlarına ait denge sabitlerinin hesaplanması, hız sabitlerinin ve denge sabitlerinin kullanılması ile nafta dönüştürücü reaksiyonlarına ait reaksiyon hızlarının belirlenmesi, reaksiyon hızları kullanılarak boru tipi reaktör (BR) modeline göre kütle ve enerji eşitliklerinin Matlab ile çözülmesiyle CCR ünitesi reaktör kısmındaki dördüncü dönüştürücü reaktöründen çıkan ağırlıkça ürün kompozisyonunun belirlenmesi, saha verilerini modelde kullanırken 'En Küçük Kareler Yöntemi' (EKK) ile uygulanması, model parametreleri tahmini yapılması, dördüncü dönüştürücü reaktöründen çıkan ürün kompozisyonunun hacminin hesaplanması, hesaplanan ürün kompozisyonunun hacmi, tanımlanan parafin, izoparafin, naften ve aromatik (PONA) kümelerinin saf bileşen oktan sayıları ve bu kümelerin nafta şarjındaki oktan sayısına etki katsayıları kullanılarak CCR ünitesi reaktör kısmındaki dördüncü dönüştürücü reaktöründen çıkan benzin oktan sayısının belirlenmesi adımlarını içermektedir.

Abstract:
The raw material gas in forming the structure of naphtha has low-octane hydrocarbons  such as paraffin,  naphthene and is obtained by atmospheric distillation  in the oil refinery. Naphtha feed is  flowing with  in the excess  hydrogen to transforming to high-octane hydrocarbons such as isoparaffins, aromatics in  reactor  section of  continuous catalyst regeneration unit (CCR). A petroleum refinery includes many unit operations and unit processes. The latest and most modern  type of catalytic reformers are called continuous catalyst regeneration (CCR)  reformers. Such  units  are characterized  by continuous  in-situ  regeneration of part of the catalyst in a special regenerator, and by continuous addition of the regenerated catalyst to the operating reactors..
Many of the earliest catalytic reforming units were non-regenerative in that they  did not  perform in situ catalyst  regeneration. Instead,  when  needed,  the  aged  catalyst was replaced by fresh catalyst and the aged catalyst was shipped to catalyst manufacturers  to  be either regenerated or to recover  the platinum  content  of  the aged catalyst. Very few, if any, catalytic  reformers  currently  in operation  are non-regenerative
The first unit operation in a refinery is the continuous  distillation of  the  petroleum crude oil being refined. The overhead liquid distillate is called naphtha and will become  a major  component  of  the  refinery's gasoline  (petrol)  product after it is further  processed  through a catalytic  hydrodesulfurizer to remove  sulfur-containing hydrocarbons and a catalytic reformer to reform its hydrocarbon molecules into more complex molecules with a higher octane rating value. The naphtha  is a mixture of very many different hydrocarbon compounds. It has an initial boiling point of about 35 °C and a final boiling point of about 200 °C, and  it contains paraffin, naphthene (cyclic paraffins) and aromatic hydrocarbons ranging from those containing 4 carbon atoms to those containing  about 10 or 11 carbon atoms. The naphtha from the  crude oil distillation is often further  distilled to produce a  "light"  naphtha containing  most but not all of  the  hydrocarbons  with 6 or fewer carbon atoms and a "heavy"  naphtha  containing most, but not all, of  the  hydrocarbons with more than 6 carbon atoms. The heavy naphtha  has an initial boiling  point of about  140  to 150 °C  and a final boiling point of about 190  to 205 °C. The naphthas  derived from the  distillation of crude oils are referred to as "straight-run"  naphthas.
It is the straight-run  heavy naphtha  that is usually  processed  in a catalytic reformer because  the light naphtha has  molecules with 6  or  fewer  carbon  atoms  which, when reformed, tend to  crack into butane and  lower molecular  weight hydrocarbons  which  are not  useful as high-octane  gasoline  blending  components. Also, the molecules  with 6 carbon atoms tend to form aromatics which is  
undesirable because governmental environmental regulations in a number of countries  limit the amount of aromatics , most particularly benzene, that gasoline may contain.
Catalytic  reforming  reactions  occur on moving-bed  reactors with  low  pressure  and high  temperature  in CCR unit. Catalytic  reforming  is a chemical process used to convert petroleum refinery  naphthas distilled  from crude oil (typically having low octane ratings) into high-octane liquid products called reformates, which are premium  blending stocks  for  high-octane gasoline. The process converts low-octane  linear  hydrocarbons (paraffins)  into branched alkanes  (isoparaffins) and cyclic naphthenes, which  are  then  partially  dehydrogenated  to produce  high-octane aromatic hydrocarbons. These reforming reactions are dehydrogenation, isomerization, dehydroxylation, dehydroalkylation  and   hydrocracking. There are many  chemical  reactions  that  occur  in  the  catalytic reforming process,  all of which  occur  in  the  presence  of  a catalyst  and a high partial pressure  of hydrogen. Depending  upon  the  type  or  version  of  catalytic reforming  used  as well  as  the desired reaction severity, the reaction conditions range from temperatures  of  about 495  to 525 °C  and  from  pressures  of  about 5 to 45 atm. The  dehydrogenation  also produces significant  amounts of  by product  hydrogen gas, which is fed into other refinery processes such as hydrocracking. The dehydrogenation  of  naphthenes  to convert  them  into  aromatics  as exemplified  in the conversion methylcyclohexane (a naphthene) to toluene (an aromatic). A side reaction  is  hydrogenolysis,  which  produces  light  hydrocarbons of  lower  value, such as methane, ethane, propane and butanes. In addition  to a gasoline blending stock, reformate  is the main source of aromatic  bulk  chemicals  such  as  benzene, toluene,  xylene  and  ethylbenzene  which  have  diverse  uses,  most  importantly  as raw  materials  for  conversion  into  plastics. The dehydrogenation  and aromatization of paraffins to aromatics (commonly called dehydrocyclization) as exemplified  in  the  conversion  of  normal  heptane  to tolüene. However, the benzene  content  of  reformate  makes it carcinogenic, which has led to governmental regulations effectively requiring further processing to reduce its benzene content. The isomerization of normal paraffins to isoparaffins as exemplified in the conversion of normal octane to 2,5-Dimethylhexane (an isoparaffin). The  hydrocracking  of  paraffins  into  smaller molecules as exemplified by  the cracking of normal heptane  into isopentane  and ethane. The hydrocracking of paraffins is the only one of the above four  major reforming reactions  that consumes  hydrogen.  The  isomerization  of  normal paraffins  does not consume or produce hydrogen. However, both  the  dehydrogenation of naphthenes  and  the  dehydrocyclization  of  paraffins  produce hydrogen.  The overall  net  production  of  hydrogen  in  the  catalytic  reforming of  petroleum naphthas  of  hydrogen gas  (at 0 °C and 1 atm) so excess meter of  liquid  naphtha feedstock. The  hydrogen  is  also  necessary  in  order  to  hydrogenolyze  any polymers  that  form  on  the  catalyst.
Furthermore, increased gasoline octane number  (RON) has been produced  in CCR so that CCR  unit  production  capacity  is  affected  by gasoline demand varies. Daily changeable operating conditions affect on RON, means occuring undesirable give-away. The success of this project is to obtain the composition of the 4th reactor exit and is able to predict the RON. Furthermore, it is possible to prevent RON give-away.
In this work, lump model is used to define naphtha reforming reactions and also, plug flow reactor (PFR) model is used for mass and energy balances. Moreover, at least square method is used for tuning. Finally, it is able to predict the model parameters and 4th reactor exit composition. Also, gasolin octane number (RON) can be determined.  All conclusions are suitable for real process variable so the simulation is very successful.