Classification of Chemical Reactions Useful in Reactor Design

Classification of Reactions


Table 1 shows the classification of chemical reactions according to our scheme with a few examples of typical reactions for each type.

Classification of Chemical Reactions Useful in Reactor Design

First Postulate and Second postulate (principle of equal priori probabilities) of Statistical Thermodynamics

Statistical thermodynamics used in predicting the macroscopic properties of a system consisting of large number of particles.

Gibbs proposed a method called ensemble method based on two simple postulates

First Postulate:

It states that the time averaged value of thermodynamic property (which is not related to temperature )is equal to the ensemble average value of the same property.

• For this ensemble has to be considered such that it covers all the possible quantum states of the system. i.e. the ensemble should contain all possible stationary states of the system.

Second postulate:(principle of equal priory probabilities)

It states that in an ensemble, formed by all the possible quantum states of an isolated thermodynamic system in equilibrium all the quantum states will be found with equal probability.

• This postulate is known as "principle of equal priori probabilities".

Therefore the postulates put together imply that the system spends equal amount of time in each and every possible quantum state. These two postulates made use of in estimating the thermodynamic properties of the system.

The validity of these postulates depends on the agreement between the experimental values and deductions made from the postulates.

Postulates of statistical thermodynamics

Postulates of statistical Thermodynamics:

Statistical thermodynamics used in predicting the macroscopic properties of  a system consisting of  large number of particles.

Gibbs proposed a method called ensemble method based on two simple postulates

First Postulate:

It states that the time averaged value of thermodynamic property (which is not related to temperature )is equal to the ensemble average value of the same property.

For this ensemble has to be considered such that it covers all the possible quantum states of the system. i.e. the ensemble should contain all possible stationary states of the system.

Second postulate:(principle of  equal priory probabilities)

It states that in an ensemble, formed by all the possible quantum states of an isolated thermodynamic system in equilibrium all  the quantum states will be  found with equal probability.

This postulate is known as "principle of  equal priory probabilities".

Therefore the postulates put together imply that the system spends equal amount of time in each and every possible quantum state. These two postulates made use of in estimating the thermodynamic properties of the system.

The discovery of graphene-----Andre K. Geim,Konstantin S. Novoselov

The discovery of graphene—a one-atom-thick sheet of carbon atoms arranged in a honeycomb pattern that boasts outstanding mechanical and electronic properties--has won physicists Andre K. Geim, 51, and Konstantin S. Novoselov, 36, both of the University of Manchester, in the U.K., the 2010 Nobel Prize in Physics. The researchers will share nearly $1.5 million in prize money.

The idea that a single "freestanding" sheet of graphene—meaning a one-atom-thick carbon film that rests on or is suspended from but is not tightly attached to a support—could be isolated, had been investigated since the 1980s, when carbon nanotubes and buckeyballs were discovered.

Yet after years of trying unsuccessfully to separate graphite into its constituent graphene sheets, researchers had concluded by the early part of this decade that freestanding graphene could not be isolated. Thermodynamics principles predicted that the material would spontaneously roll up into a nanotube or other curved structure. "At that time, graphene was considered a hypothetical or academic material," Geim told C&EN in 2009 .

THE STORY could start even earlier because graphite has been used as pencil "lead" for centuries, which means that graphene actually has been close at hand for a very long time. Every time someone scribes a line with the ubiquitous pencil, the resulting mark contains bits of this hot "new" material, Geim says. But graphene isn't readily available in freestanding, single-sheet form in ordinary pencil markings, so its properties cannot be explored or exploited.

Not surprisingly, scientists have been trying for a long time to split graphite into its constituent parts. For years, their efforts met with little success. Early on, researchers tried a chemical method for thrusting molecules or atoms in between graphite's layers to pry apart the graphene sheets. This chemical exfoliation technique generally yielded a slurry or sludge of graphitic particles similar to wet soot. The chemical method soon gave way to a mechanical approach to cleaving graphite.

By rubbing or scraping graphite against a surface, researchers managed to peel off microscopic chunks as thin as roughly 100 atomic layers. Referred to as micromechanical cleavage, that method was taken up by scientists in many labs and worked well enough almost 20 years ago to produce graphite slivers that were optically transparent. Yet the slices still weren't atomically thin.

Yet in 2004, Geim and Novoselov, who was a postdoc at that time, worked out a surprisingly simple method for exfoliating little chips of graphite by folding adhesive tape against the crystals and peeling apart the tape repeatedly. The team showed that not only could single sheets of graphene be isolated, but they remain particularly stable at room temperature (Science 2004, 306, 666).

The discovery of that rudimentary method for isolating graphene sheets led to an explosion in graphene research. The material has quickly become a top choice for advanced computing applications, digital displays and other types of flexible electronics, and advanced composite materials. Experts contend that graphene's usefulness is only just beginning to be discovered.

Multi loop and multi variable control for distillation operation, Degrees of freedom for distillation tower, composition(temperature) and pressure control stategies

Basics of Distillation column control

For Basics of distillation and distillation column control follow the following below links.

These covers Vapor liquid equilibrium calcculations also.

Basics of Distillation(Click Here)

Basics of Distillation column control(Click Here)

Electrochemical Techniques for monitoring and understanding the actual electrochemical process taking place on the metal surface

Corrosion of metal occurs through electrochemical reactions at the metal-solutioni nterface. Understanding the electrochemical phenomenon of a corrosion process will help to monitor and mitigate corrosion reaction. By using electrochemical methods, it is possible to monitor as well as understand the actual electrochemical process taking place on the metal surface. Unlike weight loss or gravimetric methods, electrochemical methods are fast in determining and analyzing the electrochemical properties. The electrochemical methods used for this study are described in the following sub-sections.

Linear polarization method

In a corroding electrode, a region of linear dependence exists between current and the potential applied over a small range close to the free corrosion potential. Free corrosion potential is the potential measured when no current flows through the electrode. This linear currentpotential response is due to the exponential relation of anodic and cathodic currents of a corroding electrode to potential, derived from Butler-Volmer equation45. Over a small potential range (<20 mV), the difference between cathodic and anodic exponential curves is almost linear. This linear dependence was first noted by Stern and Geary in 1957 and they derived an equation known as Stern-Geary equation, relating the slope of the linear region to the Tafel slopes and corrosion current.

   Stern − Geary Equation ∶Rp = (ba . bc) /(2.303*(ba + bc)*icorr) = ∆E/∆l ------------(5)

where, Rp is the polarization resistance, icorr is the corrosion current and ba , bc are anodic and cathodic Tafel slopes respectively. Eqn 5 served as an important tool for a new experimental approach to study the electrochemistry of corrosion reactions. The Linear polarization resistance (LPR) technique is based on the above mentioned theoretical fact. It is a non destructive method used for calculating polarization resistance which in turn used for calculating corrosion rate.

LPR technique generates a plot of current verses potential over a small potential range. In this method the metal sample is polarized step-wise, starting below the corrosion potential (usually -20 mV) and ending above the corrosion potential (usually +20 mV). The plot of current versus potential is linear, the slope of which gives the polarization resistance (Rp)46. The polarization resistance is inversely proportional to the uniform corrosion rate and can be used in the Stern-Geary equation to determine the corrosion current and corrosion rate47. A plot of current verses potential using LPR technique is shown below in Figure 2.1. The grey line on the graph is the sample plot of experimental data obtained using LPR technique. The linear fit of experimental data was performed using “Gamry- Echem analyst”
software and shown as a black line. From the experimental fit line the corrosion rate and polarization resistance are calculated. The calculation of corrosion rate using LPR technique is based on few fundamental assumptions such as the corrosion rate is uniform, both anodic and cathodic reactions are under activation control (kinetic control), a negligible solution resistance and most importantly known values of Tafel slopes.

The advantage of LPR technique is that data acquisition can be done quicker compared to other electrochemical methods. This method is non destructive since the potential applied to the sample is very small. The main demerit of this technique is that it needs Tafel data to calculate corrosion rate, which must be obtained either from literature or from other experiments.

Carbon Dioxide CO2 Corrosion Mechanism(In pipe lines of natural gas and oil transportation)

Carbon dioxide which is present naturally is also injected purposely into gas wells to enhance oil recovery. In the process of recovery it is required to sustain CO₂ environment also.

Carbon Dioxide CO₂ Corrosion Mechanism

Although a lot of reaction mechanisms exist for CO₂ corrosion, the most widely accepted

Mechanism is given as follows.

CO₂ hydration:

CO₂g ↔ CO₂ aqu --------------- (1)

CO₂ aq + H₂O (l) → H₂CO₃ aq -------------(2)

The carbonic acid dissociates into bicarbonate and carbonate ions in two cathodic steps. The cathodic reaction also includes reduction of hydrogen ions.

2 H₂CO₃+ 2e^- → H₂+ 2HCO₃^{- -----------------} (3)

2HCO₃^-+ 2e^- → H₂ + 2CO₃^2- -----------(4)

2H⁺+ 2e^- → H₂  -------------------(5)

The CO2 corrosion reaction includes the anodic dissolution of iron at the metal surface and given by,

Fe → Fe⁺²+ 2e^-  -------------------(6)

The overall electrochemical reaction of CO2 corrosion is given by,

Fe + CO₂ + H₂O → FeCO₃ + H₂ ------------------------------(7)

Thus, the overall reaction of CO₂ corrosion leads to the formation of FeCO₃ with the liberation of hydrogen gas. FeCO₃, if precipitated, could form a protective film on the metal surface and prevent the metal from further corrosive attack. The properties of the FeCO₃ layer are greatly influenced by the corrosion rate and environmental conditions.

In spite of extensive research on CO₂ corrosion over decades, it is still unclear which of the three cathodic reactions dominates the corrosion reaction in different environmental conditions. The net cathodic reaction current is assumed to be the sum of all the three cathodic reaction currents and according to mixed potential theory this sum must equal the total anodic dissolution current. From this complex corrosion mechanism it can be expected that the corrosion rate of carbon steel can be greatly affected by the environmental factors like fluid hydrodynamics which might affect the rate of the reaction.

See Also:

Carbon Dioxide CO₂ Corrosion Mechanism in steel pipe lines

Effect of pH on Carbon Dioxide CO2 corrosion on carbon steel pipe lines

Effect of temperature on Carbon Dioxide CO2 corrosion on carbon steel pipe lines


Effect of hydrodynamics on Carbon Dioxide CO2 corrosion on carbon steel pipe lines 


Effect of CO2 partial pressure on  CO2 corrosion on carbon steel pipe lines


Effect of Fe²⁺ concentration on Carbon Dioxide CO2 corrosion on carbon steel pipe lines