4 Tips to Help You Survive the Dissertation Writing Process

Dissertation Writing Help

So you have been handed the task to write your undergraduate or postgraduate dissertation but are unsure about how to tackle it? Dissertation writing process is full of surprises and as such it requires students to put in several 100 hours of study to achieve a high academic grade. Are you struggling with your dissertation? If Yes, then trust me you are not the only one to have got stuck with it. As you initiate work on your dissertation, pieces of the puzzle will start to fall in place and your path ahead will become clearer.  So do not get frustrated with your shortcomings and meet the challenges head on.

P.S: It is possible for you to improve your dissertation writing skills and consequent academic grade by following some simple tips and techniques as discussed below in this article.

Start Early

It is vitally important to start your research work in a timely manner. Before doing anything else you will be required to choose an appropriate dissertation topic. There are many online academic sources that you can use to pick an interesting topic. Research Prospect Ltd provides hundreds of possible research topics in every academic discipline. Their writers can also do some initial research to suggest latest topics for you to choose from. Select a topic that is not only interesting but also with significant amount of literature available on it. Moreover, make sure that you are passionate about the research topic because it is likely that you will be spending hours thinking, writing and talking about.

Be Patient

While you should try and take ownership of what you can control, it is important not be impatient when things do not work out the way you hoped them to see. You need to be equally comfortable in the wait time. You will observe if you haven’t already than the dissertation writing process will be full of delays and waiting times because of your own unavailability and due to the time your supervisor takes to return feedback on your dissertation. Remember that it is humanly impossible to control such situations.

Get Help from Expert Academics

Your supervisor is surely your first line defense against your inabilities and shortcoming but that does not mean that you shouldn’t look for help from the best dissertation writing service in UK. If you find yourself with a part of your dissertation then it is recommended that you look for a reliable academic writing service before it’s too late. You may also choose to get your work polished by an editing service to improve the quality standard of your work from 2:2 to 2:1 or 1st class.

Learn to live with your limitations as a writer

If you are not an expert academic writer then you should not expect yourself to produce a top notch paper that will score a distinction. It is important for all of us to identify our limitations and then work our way around them. Romon B. Goings in his article at Inside Highered claimed that “Gaining this understanding was a major turning point in my development as a scholar. When I first began to conceptualize my dissertation, I was a little unsure of my ability to take on such a daunting task. As a result, I sometimes found it hard to write sentences because I was looking for the perfect one.”

Naphtha Catalytic Reforming Processes

Dissertation Writing Help

Catalytic Reforming Processes

In 1940, The Universal Oil Products (UOP) introduced a catalytic reforming process by using catalyst which contain platinum for production of high octane naphtha from low octane naphtha, and the process became known as the Platforming according to Mayers (2004), Sutton et al (1973) and Dachos et al (1997). Furthermore, these authors point out that over the years other version of UOP original process have been developed by various oil companies but UOP process is still widely employed in the refineries. Over the years UOP process has been improved by introduction of bimetallic catalysts (Platinum and Rhenium on a silica or silica aluminium base) according to Mayers (2004). The greater activity and stability of this catalyst resulted in production of high octane naphtha on reduction of pressure. Bimetallic platinum-rhenium catalysts are known as R-56, which is a preferred catalyst to be used on naphtha platforming plants. The performance comparison of the UOP catalysts including R-56 is shown in Figure 2.1.

Sutton et al (1973) states that the UOP catalytic reforming technology has evolved from semi regenerative, fixed-bed processes to the more energy efficient, highly reliable, low operating cost, continuous catalyst reforming technology for naphtha reforming. Dachos et al (1997), described Stacked-type CCR process design, which is basically similar to UOP. The stack type CCR design can cope with longer regeneration time period associated with semi regenerative (SR) process. However, the short regeneration time period lead to a high rate of deactivation upon reducing the pressure which consequently give lower hydrogen (H2) to hydrocarbons (HCs) ratio as mentioned by Mayers (2004), Sutton et al (1973) and Dachos et al (1997) . The low H2 to HC ratio effectively leads to higher C5+ molecules and hydrogen according to Mayers (2004), Sutton et al (1973) and Dachos et al (1997).

The process selected in this project was very much influenced by above factors. The features of SR and CCR were incorporated in process system using same catalyst. Three catalyst beds were operated in series with same cycle length. Anotos et al (2004) has mentioned that if fourth reactor is added to the process then more catalyst would be required due to longer cycle length. However it is possible to improve the improvement CCR arrangement by addition of fourth reactor adjacent to other stacked reactors. And the system has a common catalyst bed that moves from top to bottom of reactor section.

According to Antos et al ( 2004 ), Mayers (2004), Sutton et al (1973), Dachos et al (1997) and Doolin et al ( 2001 ) UOP CCR Platforming Process considered to be the most successful reforming process available for the reforming of the naphtha because in the CCR Platforming unit, the regenerated catalyst is continuously replaced with spent catalyst of reactor.

UOP Process

Dachos et al (1997) described UOP platforming process which combines the concept of CCR system with SR system. This arrangement allows the fresh catalyst fed to the reactor while maintaining minimal recycle gas circulation rate and low pressure at the steady state operational conditions. In order to maintain a steady state reforming operation process uses stacked radial flow reactors and a CCR section at optimum process operating conditions according to Mayers (2004), Sutton et al (1973) and Dachos et al (1997).

A simplified schematic flow diagram of the CCR Platforming process is presented in Fig 2.2. The catalyst flows vertically down the stack due to gravity. The feed flows radially across the annular catalyst bed. The catalyst is continuously withdrawn from the last reactor and transferred to the regenerator. The catalyst which requires the regeneration flows down to the regenerator where the accumulated carbon is burned off from the catalyst surfaces. Regenerated catalyst with hydrogen is reintroduced into the top of stack reactor. By this way the quality of catalysts is kept as nearly fresh as possible. Due to separate reactor and regenerator sections allow each of them to operate at their own optimal conditions of operation.

Modelling and Designing of Catalytic Reforming by UOP (Importance)

The literature review suggests that The Universal Oil Products (UOP) has developed a number of Catalytic reforming Processes to upgrade or replace low octane naphtha to the high octane naphtha for the petrol blending.

SR units consist of three or four reactors generally loaded with bifunctional catalyst and operating in the temperature range of 460 0C to 540 0C whereas pressure range of 7 to 40 bars with hydrogen H2 to hydrocarbons (HCs) ratio of 2 to 3. However, high H2/hydrocarbons ratios may minimize coke deposition over the catalyst. The coke deposition on the catalyst surfaces decreases naphtha reforming activity and shortens the run length depending on operational severity. The reformer can be optimized for product yield, product quality and the catalyst cycle life time by changing the reactor inlet temperature. The values of reactor inlet temperatures are known from the reactor temperature profile.

Sowel (1998), points out that mathematical model sometimes do not match the plant which one is trying to simulate for optimum operational conditions. However, understanding the reasons can assist one in using the model to maximum the capabilities of the plant. The reasons why simulations do not match the plant characteristics fall into three main categories according to Sowel (1998):

*          simulation effects or inherent errors

*          sampling and analysis effects or measurement errors

*          model misapplication effects

Sowel (1998)  suggests that a model must predict behaviour not only within the reactor but in the auxiliary areas of the unit as well. It should also consider the complex nature of the process and the reaction that takes place during the process of reforming. According to Mayers (2004) UOP provides a detailed outline of the steps in catalytic reforming modelling, including the definition of the modeling objective, process identification, model selection, data collection and validation, and, finally, model calibration and verification. Beside that the Modelling of UOP process provides additional operational rules. The UOP model also allows to simulates how feed composition and operating conditions affect product compositions and yields.

Meyers (2004) suggested that most important part of a plant design concepts are as follow:

Feed Should Have

  • Less Alkenes (olefins) because they are prone to coking of reactors.
  • More Cycloalkanes (Naphthenes) because they are good for increasing the naphtha octane number.
  • Less Alkanes (paraffinic) because they yield lower octane number naphtha.
  • High hydrogen to hydrocarbon ratio because this results a decrease in coking severity.
  • No nitrogen because nitrogen would produce ammonia and which will subsequently convert to ammonium chloride. This may decrease the chloride level in the reactor and cause scaling or physical deposits to accumulate.
  • About 20 parts per million (ppm) of water, which is required for the acid in the reactor to become active in ionizing. Acids are not effective in ionizing without the presence of

some form of ion transfer (i.e. water or water vapour).

Catalyst Activity

The catalyst activity is the most important consideration in naphtha reforming operations. If the catalyst activity is high say 1.0 for brand new or freshly generated catalyst, the time required for the conversion is significantly small, therefore, conversion of naphthenes to aromatics is very quick with lesser amount of catalyst or segment of reactor required. If the activity of the catalyst is low, there would be a lower conversion of naphthenes to aromatics. 

Reactor Pressure

The yield of reformer is directly linked with Pressure effect, temperature and Catalyst stability. However, there is no theoretical limitations for reactor pressure, although practical operating constraints have led to a historical range of operating pressures from 345 to 4830 kPa (50 to 700 psig) according to Mayers (2004), Sutton et al (1973), Dachos et al (1997) and Doolin et al (2001). By decreasing the reactor pressure  hydrogen production increases along with octane number naphtha (reformate) yield. However, at low pressures coke builds up quickly on the Platforming catalyst at reaction conditions. The high coking of catalyst associated with lower operating pressures require continuous catalyst regeneration.

Reactor Temperature

Temperature of the catalyst beds give the primary control of Product quality in the Platforming process. There are two ways to calculate the reactor temperature. First way is (WAIT) means Weighted Average Inlet Temperature, which can be obtained by summing the product of fraction of catalyst in each reactor. The result then multiplied with inlet temperature. Second way s (WABT) means Weighted Average Bed Temperature, which can be obtained by summing the product of each reactor, then result multiplied with average of its outlet and inlet temperature. Generally, it is referred to have WAIT calculations for temperature. For SR Platforming, WAIT ranges from 4900C to 5250C whereas for CCR Platforming, it is ranges from 5250C to 5400C.

Space LHSV

For lean naphtha [i.e. high Alkanes (paraffin) content] requires the feed to be operated at a higher LHSV. Otherwise Cycloalkanes (naphthenes) would convert rapidly, whereas the  Alkanes (paraffins) could crack if there residence in the reactor is prolonged. Furthermore, the temperature drop would be lower and the furnace firing requirements would not be that efficient. The yield is related to the residence of the feed. This important aspect made us adopt changes for the simulator.

Catalyst

The role of catalyst is to decrease the activation energy required for a particular reaction.     The kinetics are usually similar but the temperature requirements, physical requirements (attrition, surface etc), and selectivity are used in determination of catalyst selection. In naphtha platforming processes catalyst mostly contains platinum or rhenium on a silica-aluminium base or some contain both platinum and rhenium as stated by to Antos et al (2004)  , Mayers (2004), Sutton et al (1973), Dachos et al (1997) and Doolin et al (2001).

Rate Equations

The rate equations for platforming reactions are as follow:

  • Arene Formation:

                  r1 = ηkp1(PE –PAPH3 /Kp1)

Kp1 = 9.87 exp (23.21-34750/1.8T)

  • Alkane Formation:

r2 = ηkp2(PEPH –Pp/Kp2)

kp2   = 9.87 exp (35.98- 59600/1.8T)

  • Hydrocracking of Alkane:

r3 = ηkp3 Pp/P

kp3   = exp (42.97- 62300/1.8T)

  • Hydrocracking of Alkane:

r4 = ηkp4 PE/P

kp4   = exp (42.97- 62300/1.8T)

Here subscripts A, N, P and H means  aromatics, naphthenes (cycloalkanes), paraffins (alkanes) and hydrogen respectively. P represents system pressure and p represents the partial pressure of the components. T is the absolute temperature in Kelvin.

The physical model of catalytic reforming radial flow is shown in Figure 2.3. Ro and Ri represent the outer and inner radii of catalyst bed. For an element dR on bed at (R, R+dR), the material stream for inlet is Ni and temperature T. then outlet stream is N+dNi and temperature T + dt. From the mass and enthalpy balance five different differential equations are derived which is described by Smith (1959) as:-

dNA / dR  = 2  x  π  x  R  x  L  x ρC  x  (r1)

dNN / dR  = 2  x  π  x  R  x  L  x ρC  x  (-r1 – r2 – r4)

dN/ dR  = 2  x  π  x  R  x  L  x ρC  x  ( r2 – r3)

dNH   / dR  = 2  x  π  x  R  x  L  x ρC  x  [3 r1– r2-(n-3)/3 x r3 – (n/3) x r4 ]

dNT    / dR  = (2  x  π  x  R  x  L  x ρC) / Ʃ C pi Fi  x  -[(3 r1ΔH1  +  r2 ΔH2  +(n-3)/3 x  ΔH3  +(n/3) x ΔH4 ]

It is required to calculate first the rate by calculating partial pressure assuming ideal gas given to the system pressure and then calculate the rates at a particular temperature.

References

Dachos ,N., Kelly,A., Felch, D.,Reis,E. (1997) UOP platforming process.  Handbook of       Petroleum Refining Processes; Meyers, (R. Ed)., McGraw-Hill: New York, 2nd ed.    . Section 4.3.

Doolin, P.K., Zalewski, D.J. , Oyekan, S.O. (2001) Meeting the challenges of cleaner fuels, World Refining; Chemical Week Associates Production; pp.12

Smith, R.B. (1959) Kinetic analysis of naphtha reforming with platinum catalyst. Chem Eng Progr; 55(6):76–80.

Sutton, E.A.,Greenwood, A.R., Adams, F.H. (1973) A new processing concept for    continuous Platforming. Oil Gas J. 71 (20), pp 136.

 

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