CHEMICAL ENGINEERING RESOURCES

OIL PRICES

2016-02-07T23:44:00.001-08:00

The price of oil, or the oil price, generally refers to the spot price of a barrel of benchmark crude oil. The price of a barrel of oil is highly dependent on both its grade, determined by factors such as its specific gravity or API and its sulphur content, and its location.

As with all commodities, the oil price is determined by the balance between supply and demand. The supply of oil is dependent on geological discovery, the legal and tax framework for oil extraction, the cost of extraction, the availability and cost of technology for extraction, and the political situation in oil-producing countries. Both domestic political instability in oil producing countries and conflicts with other countries can destabilise the oil price. For example, the Iranian Revolution of 1979 led to a jump in oil prices.

The demand for oil is dependent on global macroeconomic conditions. According to the International Energy Agency, high oil prices generally have a large negative impact on global economic growth.

The oil price appears to be at a critical junction from which it could turn back sharply lower in the coming months or embark on a sustained rally.

Having hit a near 13-year low earlier this month of around $27 a barrel, international benchmark Brent crude has been rising over recent sessions and peaked at close to $36 in Asia overnight. The price has long since decoupled from the actual cost of production and is now dependent on whether there will be a deal to cut global supplies, which still exceed demand by at least one million barrels a day.

Speculation that such a deal is close has driven the rally of the past few sessions. Russian officials claimed to have received an offer from the Saudi Arabia-dominated Opec cartel for a coordinated production cut of five per cent and said a meeting could take place in February. But there is considerable debate that this apparent rapprochement will lead to material actions.

"We do not expect such a cut will occur unless global growth weakens sharply from current levels, which is not our economists' forecast," Goldman Sachs analysts wrote, in a note reported by Reuters. Goldman was last year the first to predict the oil price could drop to $20 or below – there have since been forecasts of as low as $10 a barrel.

Doubts on the deal are widespread and are based, says the Wall Street Journal, on the fact Saudi Arabia has denied being the source of the offer to Russia, as well as another Opec oil power, Iran, remaining locked in proxy wars with the Saudis and so being unlikely to participate in any agreement after re-emerging from export sanctions. This, in turn, "makes it hard for Saudi Arabia to take the lead".

On the other hand, Saudi officials have said, according to a report on state television cited by CNBC, that while it was not the source of the five per cent cut offer, it will "cooperate with other oil producers to support the oil market". Fellow member Iraq, which recently reported record oil output, will also "agree and cooperate" with any agreed cut, said its oil minister Adel Abdul Mahdi.

Finally, there is US shale production, which has remained resilient so far but many expect to fall off soon. Financing arrangements are coming to an end and the economics of the business amid the price slump are punishing, which, notwithstanding any deal, should help ease production pressure elsewhere.

All of these issues should finally come into sharper focus over the next month and the oil price will move accordingly. The pessimists still outnumber the optimists but in truth, it could yet go either way.
Excerpt: theweek.co.uk

MATLAB APPLICATION IN CHEMICAL ENGINEERING

2010-11-28T07:15:00.000-08:00

MATLAB is a powerful code-based mathematical and engineering calculation
program. It performs all calculations using matrices and vectors in a logical programming
environment. This guide is a brief introduction to MATLAB in chemical engineering, and
in no way attempts to be a comprehensive MATLAB learning resource. This guide is a
starting point for the new MATLAB user, and as such no prior MATLAB experience is
necessary. Further help can be found in the MATLAB help files or at Mathworks website
at www.mathworks.com and in the help section at
http://www.mathworks.com/access/helpdesk/help/techdoc/matlab.shtml
Section I: How MATLAB works
Most MATLAB commands can be run from the command window (shown below,
on the right hand side of the interface). MATLAB commands can also be entered into a
text file labeled with the ‘.m’ extension. These files are known as ‘m-files’. These
commands can be broken down into scripts and programming. Scripts can be thought of
as commands that instruct MATLAB to execute a particular function or pre-made
program, and programming can be thought of as the raw code required to construct
functions and programs within MATLAB. Generally, all programming must be contained
within a file used by MATLAB (called an m-file), but script can be entered either in an
m-file or directly into the command window. An image of the MATLAB interface is
shown below

MATLAB contains many ready-made programs or functions that are conveniently
arranged into different toolboxes. When using MATLAB, these toolboxes and their
functions can be called upon and executed in any MATLAB script. In the above image,
the toolbox selection or launch pad is shown (at the left hand side of the interface).
Basic MATLAB: The language
MATLAB uses a language that is somewhat similar to that of Maple1. The scripts
or calling functions have a particular name and argument that must be entered into the
function execution call. For example, to plot the sine function in MATLAB between 0
and 6 using the fplot command, the following code can be entered directly into the
command window, or into an m-file:

(One can define the function sin(x) in an m-file and replace the fplot command to be
fplot(‘filename’,[0,6]))
Before going much further, an understanding of the structure of a MATLAB
simulation or execution must be developed.
M-files
M-files contain programming, scripts, equations or data that are called upon
during an execution. If the m-file is a function definition, then the most important part of
this type of m-file is the first line. The first line must contain the function definition so
that MATLAB can find those m-files that are called upon. These types of m-files are
called function m-files or function files. The code used to define the function file is as
follows:

‘file_name’ is simply the name of the m-file (the filename must be the same in the
definition and the file-name), z is the dependant variable, and x and y are the independent
variables. (Of course, one can have less or more independent variables depending upon
the complexity of the problem and the equations involved.) The next few lines of script in
the m-file can define the function or functions and label any required variables. The
following is an example of an m-file used to plot the natural logarithm2 function.
To produce a plot of this function, the following code is entered into the command
window:
This yields a plot of ln(x) between x= 1 and x= 5.
2 MATLAB uses ‘log’ as the natural logarithm function, and ‘log10’ as logarithm base ten.

to be continued...

NUMERICAL METHODS IN CHEMICAL ENGINEERING

2010-11-28T06:54:00.000-08:00

Course Description
Numerical methods for solving problems arising in heat and mass transfer, fluid mechanics, chemical reaction engineering, and molecular simulation. Topics: numerical linear algebra, solution of nonlinear algebraic equations and ordinary differential equations, solution of partial differential equations (e.g. Navier-Stokes), numerical methods in molecular simulation (dynamics, geometry optimization). All methods are presented within the context of chemical engineering problems. Familiarity with structured programming is assumed. The examples will use MATLAB®.

EXPRESSING SYSTEMS OF LINEAR ALGEBRAIC EQUATIONS AS: Ax=b

We wish to solve systems of simultaneous linear algebraic equations of the general form:

a11x1 + a12x2 + … + a1nxn = b1

a21x1 + a22x2 + … + a2nxn = b2

::

::

an1x1 +an2x2 + … + annxn = bn (1.1.1-1)

Where we have N equations for the N unknowns x1, x2, …, xn.

As a particular example, consider the following set of these three equations (N=3) for the three unknowns x1, x2, x3:

x1 + x2 + x3 = 4

2x1 + x2 + 3x3 = 7

3x1 + x2 +6x3 = 2 (1.1.1-2)

aij = constant coefficient (usually real) multiplying unknown xj in equation #i.

Bi = constant “right-hand-side” coefficient for equation #i.

For the system (1.1.1-2) above,

a11 = 1 a12 = 1 a13 = 1 b1 = 4

a21 = 2 a22 = 1 a23 = 3 b2 = 7

a31 = 3 a32 = 1 a33 = 6 b3 = 2

It is common to write linear systems in matrix/vector for as:

Ax=b (1.1.1-3)

Where the vector of unknowns x is written as:

x = (1.1.1-4) n::21xxx

The vector of right-hand-side coefficients b is written:

b = (1.1.1-5) n::21bbb

The matrix of coefficients A is written in a form with N rows and N columns,

A = (1.1.1-6) nna ...aaa: : : :: : : :a ...aaaa ...aaa n3 n2 n12n 23 22 211n 13 12 11

We see that row ‘i’ contains the values ai1, ai2, …, aiN that are the coefficients multiplying each unknown x1, x2, …, xN in equation #i.

Rows �� equations Columns �� coefficients multiplying a specific unknown in each equation.

aij = element of A in ith row and jth column

= coefficient multiplying xj in equation #i.

After we will write the coefficients in matrix form explicitly, so that we may

write Ax=bas:

nna ...aaa: : : :: : : :a ...aaaa ...aaa n3 n2 n12n 23 22 211n 13 12 11N21x::]xx = (1.1.1-7) n::21bbb

For the example system (1.1.1-2):

x1 + x2 + x3 = 4

2x1 + x2 + 3x3 = 7

3x1 + x2 +6x3 = 2 (1.1.1-2, repeated)

We have:

A = 6 1 33 1 21 1 1b = (1.1.1-8) 



274

As we will represent our linear systems as matrices “acting on” vectors, some review of basic vector notation is required.
For full lecture on this course and lecture notes, email us at millenniumtutors@yahoo.com

Second Module
http://clickserve.cc-dt.com/link/tplclick?lid=41000000011066022&pubid=21000000000269318

1.2.3 Pivoting Techniques in Gaussian Elimination

Let us consider again the 1st row operation in Gaussian Elimination, where we start with the original augmented matrix of the system. to get the full articles, email us at millenniumtutors@yahoo.com

POLYMER TECHNOLOGY

2010-04-21T08:36:00.000-07:00

Introduction to the World of Polymers
What is the meaning of polymer?
This word stems from Greek: Poly = many, mers = particles. So this
term describes a molecule composed of many identical parts, called mers.
The large molecule is therefore termed: macromolecule. What is left for us,
is the practical definition of the term “many”. The minimum considers hundreds
of mers. However, there are no sigdicant mechanical properties below
about 30 mers, while the useful average reaches 200-2,000 mers. If one wants
to speak about molecular weights (which is usually done in chemistry) a
broad range between 5,000 up to 2 x IO6 may be representative, while in
some cases it may reach 10’.
The sheer existence of such a broad range of molecular weights indicates
that we deal with long molecules that have no fixed or standard length (or
weight). This presents a most comprehensive difference between macromolecules
and the smaller molecules that are characterized by a smgle and fixed
molecular weight (e.g. water = 18). Prior to delving deep into the world of
polymers, it is essential also to explain the common term “plastics”. The
name itself actually, describes the stage of processing the polymer while it is
plastic or soft-enabling smooth flow and shaping. On the other hand, plastics
(or the scientific term, plastomers) refer to the major group of polymers
that in combination with various additives leads to materials of construction.
In addition to plastomers, polymers are also used as elastomers (rubber like), textiles, coatings and adhesives. Many polymers may appear in various
utility groups, determined by the final desired composition. Because plastics
use is dominated by polymers, many people do not care about the difference
between those two terms, which are similar but by no means identical.
While the synthetic polymers are, for good reasops, of major interest in
this book one should acknowledge the historical role of natural polymers
since the beginning of mankind: in food [protein, starch and others); in clothing
(wool, cotton, silk); and in various other uses (cellulose for writing and
natural resins for ornaments). Later (in the 18th century) the resin exuded
from rubber trees (Hevea Braziliensis) turned into a very useful product in
transportation (wheels and tires), in industry (conveyor belts) and in general
uses, including toys. Even today, many natural polymers are still in use, reaching highly developed processing methods. However, modem industry is
mady based on raw material that is suitable for mass production. Hence the
vitality of the synthetic polymers.
In intermediate stages (the 19th century) polymers made by the modification
of natural resins have appeared, the most prominent ones being the
cellulose derivatives. Celluloid (obtained by nitration of cellulose ) represents
the first semi-synthetic polymer. It became useful after compounding with a
plasticizer (mainly camphor) to reduce its brittleness. Many cellulose derivatives
are still currently in use (as plastomers, textiles or coatings) but the
major development in the 20th century is definitely attributed to many families
of synthetic polymers-the era of polymers.
Table 1-1 presents by historical year, the beginning of commercial production
of the most useful polymers. While many useful polymers appeared in
the 1930s, the process of introducing new polymers continued during the
1950s, 1960s and so on. It apparently takes about 10 years for a newborn
polymer to reach maturity. During this period it has to undergo infant development
and compete with other polymers or nonpolymeric materials. The
major issue has become the tremendous cost of commercialization of a new
polymer, because the period of research and development (including marketing)
is long and costly. In spite of all this, novel polymers appear every year,
as long as they demonstrate uniqueness. However, there appears an increasing
trend towards polyblends (mixtures of existing polymers). There is a distinction
between homogeneous polymers (homopolymers), consisting of
identical mers, and heterogeneous ones made of a random combination of
two (or more) mers, namely, the copolymers. The latter may involve various
compositions differing in the type, concentration and order of the distinct
mers in the macromolecule.
In conclusion, a wide array of polymers is already in use, so that a systematic
presentation of their chemical structure, as well as the relationship between
structure and behavior at the final stage, is essential.
[ 3 ]
PROBLEMS
1. Describe 3 products made of plastics. What are the advantages over
other materials? State other options.
2. Describe 3 natural polymers and the scope of applications. What synthetic
polymers may replace them and what are their advantages?
3. Describe 5 thermoplastic polymers and 5 thermosetting polymers.
What are the principal differences between the two groups? Give details on
the structure of the mer in each case.
4. Can you convert thermoplastic polymers to thermosetting polymers?
Thermosets to thermoplastics? Describe hybrids.
5. Find the output of polymer production in the recent two years in the
US. Give details of production of the major polymer families and state the
changes for each of them.
6. Which polymers are products from the coal industry and which are
produced by the petrochemical industry?

IN THIS CHAPTER we deal with a very basic concept-from
where does everything start? We begin with the raw materials for the polymer
industry, the so-called monomers, and explain how they are produced. The
process for polymer synthesis - polymerization - should be well understood
regarding both the mechanism as well as the industrial technology. We avoid
going into too many details but still point out the basic principles.
Polymerization reactions involve careful control of purity of monomers,
ratio of reactants, special additives, temperature and pressure, separation and
recovery. Each family of polymers represents a wide range of variables. They
appear in a large number of grades, differing in molecular weght, distribution,
degree of crystallinity, size of particles and types of special additives.
The polymer leaves the reactor as a powder or as pellets (often, after passing
through extrusion and granulation). Some stabilizers are directly added in the
polymerization or granulation stage. The polymer is then stored in big silos
for homogenation. This process is mostly carried out at special compounding
units, which are responsible for exact mixing and composition.
2.2 THE PETROCHEMICAL INDUSTRY
The petrochemical industry, that branch of the chemical industry which
is based on the exploitation of the crude-oil distillation products has turned out to be the leading industry in chemistry, wherein most monomers and
polymers are produced. It was preceded by the coal industry, developed
mainly in Germany and Britain during the 19th century. By decomposition of
coal at high temperature (an anaerobic process called cracking) products llke
acetylene, methanol, or phenol are derived. These chemicals serve as the
primary source for an extended array of polymers.
Acetylene is derived from carbide, the latter obtained by a reaction between
lime and coke (the major solid fraction obtained from coal pyrolysis).
The basic chemical reactions are as follows:
CaO + 3C --* CaCz + CO (2-1)
CaC, + 2Hz0 + Ca(OH)z + HC=CH
(acetylene)
Just another step leads to the manufacture of one of the oldest monomers
-vinylchloride - along with other vinyl derivatives (including acrylonitrile).
CHsCH + HCl + CHz=CHC1
(vinylchloride)
(2-3)
Ethylene, which serves as a source of many other monomers, can also be
synthesized by the hydrogenation of acetylene.
CHzCH + Hz + CHz=CHz (2-4)
Methanol is obtained in another process, by oxidizing coke with steam to
form a mixture of carbon monoxide and hydrogen, as follows:
C + HzO -, CO + Hz (2-5)
Next steps will lead to the formation of methanol via a catalytic reaction:
CO + 2Hz + CH30H (2-6)
Methanol may be further oxidized to formaldehyde:
CHjOH + %Oz --* HCOH
(formaldehyde)
(2-7)
A whole family of polymers is derived from formaldehyde: polyacetal
(polymethylene oxide), phenol-formaldehyde, urea-formaldehyde and melamine-
formaldehyde. It is interesting to note that the other components (phenol,
urea and melamine) are also products of coal pyrolysis. Like many other aromatics, phenol is produced from another fraction of
the cracking of coal, coal-tar. These aromatics serve as the basis for a large
list of other polymers, like nylons, epoxides and polycarbonates, in addition
to polystyrene and other styrenic derivatives (ABS, SB rubber) and polyesters.
The petrochemical industry (based on crude oil and partly on natural gas)
essentially replaced the coal industry as the major source of monomers. This
industry was developed in Europe during the 1950s, but started in the United
States as early as 1920.
The lowest homolog in the paraffin family, methane (CH,), (derived from
crude oil but frequently found in natural gas), serves as the basis for the
manufacture of methanol:
[ 7 ]
CH, + H20 -+ CO + 3Hz (2-8)
CO + 2H2 -+ CHBOH (2-9)
Alternatively, methane can be converted to acetylene, and through it to all
kinds of monomers.
(2-10)
Currently, by cracking the light fraction naphtha (with a boiling point
between gasoline and kerosene), the unsaturated gases that serve the primary
monomers -ethylene, propylene and butylene - as well as aromatics (including
phenol) are obtained. From these, many monomers are derived. By the
1960s, 90% of all organic chemicals were derived from oil, and this trend
continued growing. Only 3% to 5% of crude oil is used as chemicals, while
the major portion is utilized as fuel. The world forecast for production of
petrochemicals during 1996 was:
Ethylene 65 million tons
Propylene 40 million tons
Butadiene 7 million tons
Benzene 38 million tons
Xylenes 28 million tons
Let us describe the routes to some selected monomers, produced by the petrochemical
industry.
Monomers Derived from Ethylene
(VCM) CH,=CHCI
(vinyl chloride) CH2=CH2 + 2HC1 + Y202 + CH2Cl-CH2Cl -+
CH,=CHCl + HC1
(2-1 1)
VCM can also be manufactured by an alternative reaction:
Styrene can be synthesized by reacting ethylene with benzene (the latter
present in the aromatic fraction of the oil cracking process- benzene, toluene
and xylene).
2CH2=CH2 + 2C6H6 -+ CbHS-C2H5 + CH,=CH I (2-13)
C6H5
(styrene)
Styrene serves as the monomer for the well-known polymer-polystyrene. It
also serves as the source of many copolymers, that is polymers made from
two monomers at varying compositions, such as SAN = styrene-acrylonitrile;
SBR = styrene-butadiene rubber (the major synthetic rubber); SBS =
styrene-butadiene-styrene (a modern family of thermoplastic rubbers which
are not cross-linked); and the well-known terpolymer ABS which is based on
3 monomers - acrylonitrile-butadiene-styrene.
Vinyl acetate (a monomer frequently used in adhesives and coatings) may
also be synthesized by reacting ethylene with acetic acid:
H2C=CH2 + CH3COOH + CH2=CH-O-C-CH3 8
Monomers Derived from Propylene
Acrylonitrile is obtained by reacting propylene with ammonia:
(2-14)
(2-15)
Another important monomer, methylmethacrylate (acrylic), is obtained
by reacting propylene with carbon monoxide, oxygen and methanol:

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FREE CHEMICAL ENGINEERING SOFTWARES

2010-04-21T07:27:00.000-07:00

Publisher: Springer | ISBN: 0306457261 | edition 1997 | PDF | 263 pages | 13,3 mb This ideal introductory text covers the basics of polymer chemistry and engineering, as well as structure-property relationships in plastics, in a concise manner. Technically authoritative and up-to-date, the volume offers a survey of the basic chemistry of monomers and their conversion to the various polymers, the essentials of structure and performance, rheology of polymers as liquids and solids, and mechanical properties. Problem sets enhance the book's suitability for advanced undergraduates in chemical engineering or materials science. zarksentinel@TP
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ChemMaths contains information on 3000+ chemical compounds allowing predition of chemical compound properties, critical constants, thermodynamic properties, surface tension, gas & liquid diffusivitiy, viscosity calculations etc, periodic table, solves 500+ chemical/civil/electrical/mechcanical engineering, distillation, design, physics and mathematical equations. Contains 200+ unit conversions.

Contains a graphical program to draw 2D/3D graphs, general chemical sturcture drawing program, process simulation program. Solve for matrices, triangles, finance, geometry, area/surface/volume,statistics and many other mathematical problems and equations.
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3. Engineering Chem Calculator
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It is EniG. Chemistry Assistant is an expression calculator for fast calculation of molecular weight of compounds by simple entry of chemical formula, and replaces the element symbols with their atomic weight. The program translates texts with chemical element symbols or without them into a mathematical expression and calculates them. The program includes functions for statistical analysis, solving the quadratic equation, physical constants, and prepare solution calculator.

The element symbols can be written in lowercase letters, and the intelligent routine in the program will try to translate them and will show the result of translation - or it will report an error. The appearance of mathematical expressions, which are the result of the translation, can be seen if the mouse pointer is held over the entry field. The right mouse button has several often used anions and molecules.

The calculator feature is a list with task history in that storing all of your recent inputs and results. Chemistry Assistant also included a detailed help file that containing syntax, usage, and examples for all of the supported functions. The calculator also provides a list of common physical constants and performs various conversions between English and metric units.

Every function that is supported by Chemistry Assistant can be inserted by clicking on the button with function name or by typing its name on the physical keyboard. Some functions are not associated with the buttons, but every function can be called by typing its name. Examples are available from Help menu.
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CHEMICAL REACTION ENGINEERING

2010-04-17T04:47:00.000-07:00

Every industrial chemical process is designed to produce economically a desired
product from a variety of starting materials through a succession of treatment
steps. Figure 1.1 shows a typical situation. The raw materials undergo a number
of physical treatment steps to put them in the form in which they can be reacted
chemically. Then they pass through the reactor. The products of the reaction
must then undergo further physical treatment-separations, purifications, etc.-
for the final desired product to be obtained.
Design of equipment for the physical treatment steps is studied in the unit
operations. In this book we are concerned with the chemical treatment step of
a process. Economically this may be an inconsequential unit, perhaps a simple
mixing tank. Frequently, however, the chemical treatment step is the heart of
the process, the thing that makes or breaks the process economically.
Design of the reactor is no routine matter, and many alternatives can be
proposed for a process. In searching for the optimum it is not just the cost of
the reactor that must be minimized. One design may have low reactor cost, but
the materials leaving the unit may be such that their treatment requires a much
higher cost than alternative designs. Hence, the economics of the overall process
must be considered.
Reactor design uses information, knowledge, and experience from a variety
of areas-thermodynamics, chemical kinetics, fluid mechanics, heat transfer,
mass transfer, and economics. Chemical reaction engineering is the synthesis of
all these factors with the aim of properly designing a chemical reactor.
To find what a reactor is able to do we need to know the kinetics, the contacting
pattern and the performance equation.

Classification of Reactions

There are many ways of classifying chemical reactions. In chemical reaction
engineering probably the most useful scheme is the breakdown according to
the number and types of phases involved, the big division being between the
homogeneous and heterogeneous systems. A reaction is homogeneous if it takes
place in one phase alone. A reaction is heterogeneous if it requires the presence
of at least two phases to proceed at the rate that it does. It is immaterial whether
the reaction takes place in one, two, or more phases; at an interface; or whether
the reactants and products are distributed among the phases or are all contained
within a single phase. All that counts is that at least two phases are necessary
for the reaction to proceed as it does.
Sometimes this classification is not clear-cut as with the large class of biological
reactions, the enzyme-substrate reactions. Here the enzyme acts as a catalyst in
the manufacture of proteins and other products. Since enzymes themselves are
highly complicated large-molecular-weight proteins of colloidal size, 10-100 nm,
enzyme-containing solutions represent a gray region between homogeneous and
heterogeneous systems. Other examples for which the distinction between homogeneous
and heterogeneous systems is not sharp are the very rapid chemical
reactions, such as the burning gas flame. Here large nonhomogeneity in composition
and temperature exist. Strictly speaking, then, we do not have a single phase,
for a phase implies uniform temperature, pressure, and composition throughout.
The answer to the question of how to classify these borderline cases is simple.
It depends on how we choose to treat them, and this in turn depends on which description we think is more useful. Thus, only in the context of a given situation
can we decide how best to treat these borderline cases.
Cutting across this classification is the catalytic reaction whose rate is altered
by materials that are neither reactants nor products. These foreign materials,
called catalysts, need not be present in large amounts. Catalysts act somehow as
go-betweens, either hindering or accelerating the reaction process while being
modified relatively slowly if at all.
Table 1.1 shows the classification of chemical reactions according to our scheme
with a few examples of typical reactions for each type.

Variables Affecting the Rate of Reaction

Many variables may affect the rate of a chemical reaction. In homogeneous
systems the temperature, pressure, and composition are obvious variables. In
heterogeneous systems more than one phase is involved; hence, the problem
becomes more complex. Material may have to move from phase to phase during
reaction; hence, the rate of mass transfer can become important. For example,
in the burning of a coal briquette the diffusion of oxygen through the gas film
surrounding the particle, and through the ash layer at the surface of the particle,
can play an important role in limiting the rate of reaction. In addition, the rate
of heat transfer may also become a factor. Consider, for example, an exothermic
reaction taking place at the interior surfaces of a porous catalyst pellet. If the
heat released by reaction is not removed fast enough, a severe nonuniform
temperature distribution can occur within the pellet, which in turn will result in
differing point rates of reaction. These heat and mass transfer effects become
increasingly important the faster the rate of reaction, and in very fast reactions,
such as burning flames, they become rate controlling. Thus, heat and mass transfer
may play important roles in determining the rates of heterogeneous reactions.

Definition of Reaction Rate

We next ask how to define the rate of reaction in meaningful and useful ways.
To answer this, let us adopt a number of definitions of rate of reaction, all interrelated and all intensive rather than extensive measures. But first we must
select one reaction component for consideration and define the rate in terms of
this component i. If the rate of change in number of moles of this component
due to reaction is dN,ldt, then the rate of reaction in its various forms is defined
as follows. Based on unit volume of reacting fluid,

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UNIT OPERATION

2010-04-12T06:25:00.000-07:00

EVAPORATION

Evaporation is a type of vaporization of a liquid, that occurs only on the surface of a liquid. The other type of vaporization is boiling, that instead occurs on the entire mass of the liquid. Evaporation is also part of the water cycle.
Evaporation is a type of phase transition; it is the process by which molecules in a liquid state (e.g. water) spontaneously become gaseous (e.g. water vapor). Generally, evaporation can be seen by the gradual disappearance of a liquid from a substance when exposed to a significant volume of gas. Vaporization and evaporation however, are not entirely the same processes.
On average, the molecules in a glass of water do not have enough heat energy to escape from the liquid. With sufficient heat, the liquid would turn into vapor quickly (see boiling point). When the molecules collide, they transfer energy to each other in varying degrees, based on how they collide. Sometimes the transfer is so one-sided for a molecule near the surface that it ends up with enough energy to escape.
Liquids that do not evaporate visibly at a given temperature in a given gas (e.g. cooking oil at room temperature) have molecules that do not tend to transfer energy to each other in a pattern sufficient to frequently give a molecule the heat energy necessary to turn into vapor. However, these liquids are evaporating, it's just that the process is much slower and thus significantly less visible.
Evaporation is an essential part of the water cycle. Solar energy drives evaporation of water from oceans, lakes, moisture in the soil, and other sources of water. In hydrology, evaporation and transpiration (which involves evaporation within plant stomata) are collectively termed evapotranspiration. Evaporation is caused when water is exposed to air and the liquid molecules turn into water vapor which rises up and forms clouds.

Theory

For molecules of a liquid to evaporate, they must be located near the surface, be moving in the proper direction, and have sufficient kinetic energy to overcome liquid-phase intermolecular forces.^[1] Only a small proportion of the molecules meet these criteria, so the rate of evaporation is limited. Since the kinetic energy of a molecule is proportional to its temperature, evaporation proceeds more quickly at higher temperatures. As the faster-moving molecules escape, the remaining molecules have lower average kinetic energy, and the temperature of the liquid thus decreases. This phenomenon is also called evaporative cooling. This is why evaporating sweat cools the human body. Evaporation also tends to proceed more quickly with higher flow rates between the gaseous and liquid phase and in liquids with higher vapor pressure. For example, laundry on a clothes line will dry (by evaporation) more rapidly on a windy day than on a still day. Three key parts to evaporation are heat, humidity and air movement.
On a molecular level, there is no strict boundary between the liquid state and the vapor state. Instead, there is a Knudsen layer, where the phase is undetermined. Because this layer is only a few molecules thick, at a macroscopic scale a clear phase transition interface can be seen.

Evaporative equilibrium

Vapor pressure of water vs. temperature. 760 Torr = 1 atm.

If evaporation takes place in a closed vessel, the escaping molecules accumulate as a vapor above the liquid. Many of the molecules return to the liquid, with returning molecules becoming more frequent as the density and pressure of the vapor increases. When the process of escape and return reaches an equilibrium,^[1] the vapor is said to be "saturated," and no further change in either vapor pressure and density or liquid temperature will occur. For a system consisting of vapor and liquid of a pure substance, this equilibrium state is directly related to the vapor pressure of the substance, as given by the Clausius-Clapeyron relation:

where P₁, P₂ are the vapor pressures at temperatures T₁, T₂ respectively, ΔH_vap is the enthalpy of vaporization, and R is the universal gas constant. The rate of evaporation in an open system is related to the vapor pressure found in a closed system. If a liquid is heated, when the vapor pressure reaches the ambient pressure the liquid will boil.
The ability for a molecule of a liquid to evaporate is largely based on the amount of kinetic energy an individual particle may possess. Even at lower temperatures, individual molecules of a liquid can evaporate if they have more than the minimum amount of kinetic energy required for vaporization.

Factors influencing the rate of evaporation

Concentration of the substance evaporating in the air: If the air already has a high concentration of the substance evaporating, then the given substance will evaporate more slowly.
Concentration of other substances in the air: If the air is already saturated with other substances, it can have a lower capacity for the substance evaporating.
Concentration of other substances in the liquid (impurities): If the liquid contains other substances, it will have a lower capacity for evaporation.
Flow rate of air: This is in part related to the concentration points above. If fresh air is moving over the substance all the time, then the concentration of the substance in the air is less likely to go up with time, thus encouraging faster evaporation. This is the result of the boundary layer at the evaporation surface decreasing with flow velocity, decreasing the diffusion distance in the stagnant layer.
Inter-molecular forces: The stronger the forces keeping the molecules together in the liquid state, the more energy one must get to escape.
Pressure: In an area of less pressure, evaporation happens faster because there is less exertion on the surface keeping the molecules from launching themselves.
Surface area: A substance which has a larger surface area will evaporate faster as there are more surface molecules which are able to escape.
Temperature of the substance: If the substance is hotter, then its molecules have a higher average kinetic energy, and evaporation will be faster.
Density: The higher the density, the slower a liquid evaporates.

In the US, the National Weather Service measures the actual rate of evaporation from a standardized "pan" open water surface outdoors, at various locations nationwide. Others do likewise around the world. The US data is collected and compiled into an annual evaporation map.^[2] The measurements range from under 30 to over the120 inches (3,000 mm) per year.

Applications

When clothes are hung on a laundry line, even though the ambient temperature is below the boiling point of water, water evaporates. This is accelerated by factors such as low humidity, heat (from the sun), and wind. In a clothes dryer hot air is blown through the clothes, allowing water to evaporate very rapidly.

Combustion vaporization

Fuel droplets vaporize as they receive heat by mixing with the hot gases in the combustion chamber. Heat (energy) can also be received by radiation from any hot refractory wall of the combustion chamber.

CRYSTALLIZATION

Crystallization is the (natural or artificial) process of formation of solid crystals precipitating from a solution, melt or more rarely deposited directly from a gas. Crystallization is also a chemical solid-liquid separation technique, in which mass transfer of a solute from the liquid solution to a pure solid crystalline phase occurs.

Crystallization in nature

There are many examples of natural process that involve crystallization.

Geological time scale process examples include:

Natural (mineral) crystal formation (see also gemstone);
Stalactite/stalagmite, rings formation.

Usual time scale process examples include:

Snow flakes formation (see also Koch snowflake);
Honey crystallization (nearly all types of honey crystallize).

Process

The crystallization process consists of two major events, nucleation and crystal growth. Nucleation is the step where the solute molecules dispersed in the solvent start to gather into clusters, on the nanometer scale (elevating solute concentration in a small region), that becomes stable under the current operating conditions. These stable clusters constitute the nuclei. However when the clusters are not stable, they redissolve. Therefore, the clusters need to reach a critical size in order to become stable nuclei. Such critical size is dictated by the operating conditions (temperature, supersaturation, etc.). It is at the stage of nucleation that the atoms arrange in a defined and periodic manner that defines the crystal structure — note that "crystal structure" is a special term that refers to the relative arrangement of the atoms, not the macroscopic properties of the crystal (size and shape), although those are a result of the internal crystal structure.

The crystal growth is the subsequent growth of the nuclei that succeed in achieving the critical cluster size. Nucleation and growth continue to occur simultaneously while the supersaturation exists. Supersaturation is the driving force of the crystallization, hence the rate of nucleation and growth is driven by the existing supersaturation in the solution. Depending upon the conditions, either nucleation or growth may be predominant over the other, and as a result, crystals with different sizes and shapes are obtained (control of crystal size and shape constitutes one of the main challenges in industrial manufacturing, such as for pharmaceuticals). Once the supersaturation is exhausted, the solid-liquid system reaches equilibrium and the crystallization is complete, unless the operating conditions are modified from equilibrium so as to supersaturate the solution again.

Many compounds have the ability to crystallize with different crystal structures, a phenomenon called polymorphism. Each polymorph is in fact a different thermodynamic solid state and crystal polymorphs of the same compound exhibit different physical properties, such as dissolution rate, shape (angles between facets and facet growth rates), melting point, etc. For this reason, polymorphism is of major importance in industrial manufacture of crystalline products.

Artificial methods

For crystallization (see also recrystallization) to occur from a solution it must be supersaturated. This means that the solution has to contain more solute entities (molecules or ions) dissolved than it would contain under the equilibrium (saturated solution). This can be achieved by various methods, with 1) solution cooling, 2) addition of a second solvent to reduce the solubility of the solute (technique known as antisolvent or drown-out), 3) chemical reaction and 4) change in pH being the most common methods used in industrial practice. Other methods, such as solvent evaporation, can also be used. The spherical crystallization has some advantages (flowability, bioavailability, ...) for the formulation of pharmaceutical drugs (see ref Nocent & al., 2 Applications

There are two major groups of applications for the artificial crystallization process: crystal production and purification.

Crystal production

From a material industry perspective:

Macroscopic crystal production: for supply the demand of natural-like crystals with methods that "accelerate time-scale" for massive production and/or perfection.
- Ionic crystal production;
- Covalent crystal production.
Tiny size crystals:
- Powder, sand and smaller sizes: using methods for powder and controlled (nanotechnology fruits) forms.
  - Mass-production: on chemical industry, like salt-powder production.
  - Sample production: small production of tiny crystals for material characterization. Controlled recrystallization is an important method to supply unusual crystals, that are needed to reveal the molecular structure and nuclear forces inside a typical molecule of a crystal. Many techniques, like X-ray crystallography and NMR spectroscopy, are widely used in chemistry and biochemistry to determine the structures of an immense variety of molecules, including inorganic compounds and bio-macromolecules.
- Thin film production.

Massive production examples:

"Powder salt for food" industry;
Silicon crystal wafer production.
Production of sucrose from sugar beet, where the sucrose is crystallized out from an aqueous solution.

Purification

Thermodynamic view

Low-temperature SEM magnification series for a snow crystal. The crystals are captured, stored, and sputter coated with platinum at cryo-temperatures for imaging.

The nature of a crystallization process is governed by both thermodynamic and kinetic factors, which can make it highly variable and difficult to control. Factors such as impurity level, mixing regime, vessel design, and cooling profile can have a major impact on the size, number, and shape of crystals produced.

Now put yourself in the place of a molecule within a pure and perfect crystal, being heated by an external source. At some sharply defined temperature, a bell rings, you must leave your neighbours, and the complicated architecture of the crystal collapses to that of a liquid. Textbook thermodynamics says that melting occurs because the entropy, S, gain in your system by spatial randomization of the molecules has overcome the enthalpy, H, loss due to breaking the crystal packing forces:

T (S l i q u i d - S s o l i d) > H l i q u i d - H s o l i d

G l i q u i d < G s o l i d

This rule suffers no exceptions when the temperature is rising. By the same token, on cooling the melt, at the very same temperature the bell should ring again, and molecules should click back into the very same crystalline form. The entropy decrease due to the ordering of molecules within the system is overcompensated by the thermal randomization of the surroundings, due to the release of the heat of fusion; the entropy of the universe increases.

But liquids that behave in this way on cooling are the exception rather than the rule; in spite of the second principle of thermodynamics, crystallization usually occurs at lower temperatures (supercooling). This can only mean that a crystal is more easily destroyed than it is formed. Similarly, it is usually much easier to dissolve a perfect crystal in a solvent than to grow again a good crystal from the resulting solution. The nucleation and growth of a crystal are under kinetic, rather than thermodynamic, control.

Equipment for crystallization

1. Tank crystallizers. Tank crystallization is an old method still used in some specialized cases. Saturated solutions, in tank crystallization, are allowed to cool in open tanks. After a period of time the mother liquid is drained and the crystals removed. Nucleation and size of crystals are difficult to control. Typically, labor costs are very high.

2. Scraped surface crystallizers. One type of scraped surface crystallizer is the Swenson-Walker crystallizer, which consists of an open trough 0.6 m wide with a semicircular bottom having a cooling jacket outside. A slow-speed spiral agitator rotates and suspends the growing crystals on turning. The blades pass close to the wall and break off any deposits of crystals on the cooled wall. The product generally has a somewhat wide crystal-size distribution.

3. Double-pipe scraped surface crystallizer. Also called a votator, this type of crystallizer is used in crystallizing ice cream and plasticizing margarine. Cooling water passes in the annular space. An internal agitator is fitted with spring-loaded scrapers that wipe the wall and provide good heat-transfer coefficients.

4. Circulating-liquid evaporator-crystallizer. Also called Oslo crystallizer. Here supersaturation is reached by evaporation. The circulating liquid is drawn by the screw pump down inside the tube side of the condensing stream heater. The heated liquid then flows into the vapor space, where flash evaporation occurs, giving some supersaturation.The vapor leaving is condensed. The supersaturated liquid flows down the downflow tube and then up through the bed of fluidized and agitated crystals, which are growing in size. The leaving saturated liquid then goes back as a recycle stream to the heater, where it is joined by the entering fluid. The larger crystals settle out and slurry of crystals and mother liquid is withdrawn as a product.

5. Circulating-magma vacuum crystallizer. The magma or suspension of crystals is circulated out of the main body through a circulating pipe by a screw pump. The magma flows though a heater, where its temperature is raised 2-6 K. The heated liquor then mixes with body slurry and boiling occurs at the liquid surface. This causes supersaturation in the swirling liquid near the surface, which deposits in the swirling suspended crystals until they leave again via the circulating pipe. The vapors leave through the top. A steam-jet ejector provides vacuum.

6. Continuous oscillatory baffled crystallizer (COBC). The COBC is a tubular baffled crystallizer that offers plug flow under laminar flow conditions (low flow rates) with superior heat transfer coefficient, allowing controlled cooling profiles, e.g. linear, parabolic, discontinued, step-wise or any type, to be achieved. This gives much better control over crystal size, morphology and consistent crystal products. For further information see oscillatory baffled reactor.

Filtration

Filtration is a mechanical or physical operation which is used for the separation of solids from fluids (liquids or gases) by interposing a medium through which only the fluid can pass. Oversize solids in the fluid are retained, but the separation is not complete; solids will be contaminated with some fluid and filtrate will contain fine particles (depending on the pore size and filter thickness).
Applications
* Filtration is used to separate particles and fluid in a suspension, where the fluid can be a liquid, a gas or a supercritical fluid. Depending on the application, either one or both of the components may be isolated.

* Filtration, as a physical operation is very important in chemistry for the separation of materials of different chemical composition. A solvent is chosen which dissolves one component, while not dissolving the other. By dissolving the mixture in the chosen solvent, one component will go into the solution and pass through the filter, while the other will be retained. This is one of the most important techniques used by chemists to purify compounds.
* Filtration is also important and widely used as one of the unit operations of chemical engineering. It may be simultaneously combined with other unit operations to process the feed stream, as in the biofilter, which is a combined filter and biological digestion device.
* Filtration differs from sieving, where separation occurs at a single perforated layer (a sieve). In sieving, particles that are too big to pass through the holes of the sieve are retained (see particle size distribution). In filtration, a multilayer lattice retains those particles that are unable to follow the tortuous channels of the filter. Oversize particles may form a cake layer on top of the filter and may also block the filter lattice, preventing the fluid phase from crossing the filter (blinding). Commercially, the term filter is applied to membranes where the separation lattice is so thin that the surface becomes the main zone of particle separation, even though these products might be described as sieves.
* Filtration differs from adsorption, where it is not the physical size of particles that causes separation but the effects of surface charge. Some adsorption devices containing activated charcoal and ion exchange resin are commercially called filters, although filtration is not their principal function.
* Filtration differs from removal of magnetic contaminants from fluids with magnets (typically lubrication oil, coolants and fuel oils), because there is no filter medium. Commercial devices called "magnetic filters" are sold, but the name reflects their use, not their mode of operation.
The remainder of this article focuses primarily on liquid filtration.
There are many different methods of filtration; all aim to attain the separation of substances. Separation is achieved by some form of interaction between the substance or objects to be removed and the filter. The substance that is to pass through the filter must be a fluid, i.e. a liquid or gas. Methods of filtration vary depending on the location of the targeted material, i.e. whether it is dissolved in the fluid phase or suspended as a solid.
Two main types of filter media are employed in the chemical laboratory— surface filter, a solid sieve which traps the solid particles, with or without the aid of filter paper (e.g. Büchner funnel, Belt filter, Rotary vacuum-drum filter, Crossflow filters, Screen filter), and a depth filter, a bed of granular material which retains the solid particles as it passes (e.g. sand filter). The first type allows the solid particles, i.e. the residue, to be collected intact; the second type does not permit this. However, the second type is less prone to clogging due to the greater surface area where the particles can be trapped. Also, when the solid particles are very fine, it is often cheaper and easier to discard the contaminated granules than to clean the solid sieve.
Filter media can be cleaned by rinsing with solvents or detergents. Alternatively, in engineering applications, such as swimming pool water treatment plants, they may be cleaned by backwashing. Self-cleaning screen filters utilize point-of-suction backwashing to clean the screen without interrupting system flow.
Fluids flow through a filter due to a difference in pressure - fluid flows from the high pressure side to the low pressure side of the filter, leaving some material behind. The simplest method to achieve this is by gravity and can be seen in the coffeemaker example. In the laboratory, pressure in the form of compressed air on the feed side (or vacuum on the filtrate side) may be applied to make the filtration process faster, though this may lead to clogging or the passage of fine particles. Alternatively, the liquid may flow through the filter by the force exerted by a pump, a method commonly used in industry when a reduced filtration time is important. In this case, the filter need not be mounted vertically.
Certain filter aids may be used to aid filtration. These are often incompressible diatomaceous earth or kieselguhr, which is composed primarily of silica. Also used are wood cellulose and other inert porous solids such as the cheaper and safer perlite.
These filter aids can be used in two different ways. They can be used as a precoat before the slurry is filtered. This will prevent gelatinous-type solids from plugging the filter medium and also give a clearer filtrate. They can also be added to the slurry before filtration. This increases the porosity of the cake and reduces resistance of the cake during filtration. In a rotary filter, the filter aid may be applied as a precoat; subsequently, thin slices of this layer are sliced off with the cake.
The use of filter aids is usually limited to cases where the cake is discarded or where the precipitate can be separated chemically from the filter.
Filtration is a more efficient method for the separation of mixtures than decantation, but is much more time consuming. If very small amounts of solution are involved, most of the solution may be soaked up by the filter medium.
An alternative to filtration is centrifugation — instead of filtering the mixture of solid and liquid particles, the mixture is centrifuged to force the (usually) denser solid to the bottom, where it often forms a firm cake. The liquid above can then be decanted. This method is especially useful for separating solids which do not filter well, such as gelatinous or fine particles. These solids can clog or pass through the filter, respectively.

Examples
Examples of filtration include

* The coffee filter to keep the coffee separate from the grounds
* HEPA filters in air conditioning to remove particles from air
* Belt filters to extract precious metals in mining.
* Furnaces use filtration to prevent the furnace elements from fouling with particulates.
* Pneumatic conveying systems often employ filtration to stop or slow the flow of material that is transported, through the use of a baghouse.
* In the laboratory, a Büchner funnel is often used, with a filter paper serving as the porous barrier.

An experiment to prove the existence of microscopic organisms involves the comparison of water passed through unglazed porcelain and unfiltered water. When left in sealed containers the filtered water takes longer to go foul, demonstrating that very small items (such as bacteria) can be removed from fluids by filtration.
In the kidney, renal filtration is the filtration of blood in the glomerulus, followed by selective reabsorbtion of many substances essential for the body.

References
1. Lecture notes, Postgraduate course on Filtration and Size separation at the Department of Chemical Engineering, University of Lougborough, England

2. Sterlitech

3. How does a Brita water filter work FAQ

4. Eclipse Magnetics – Magnetic filter supplier

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Introduction to Chemical Engineering

2010-04-10T05:32:00.000-07:00

Who is an engineer?

“Engineers can do for 1p what a scientist can do for £1”

Unknown

“Engineering is the art of directing the great sources of power in

nature for the use and convenience of man” Thomas Tredgold, 1828

“Part Einstein, part bulldog. Somebody who makes the difficult

routine and the impossible probable” Unknown Engineers find and implement solutions for the needs of society that are economically, environmentally and morally sound.

Where did chemical engineering come from?

Prehistory:

Mechanical engineers + chemists designed, built and ran processes.
Concerned with getting the job done.
Little standardization.
Gross inefficiencies and large environmental impact.

Founding of discipline:

George E. Davis and the IChemE – 1880 onwards.
First departments - MIT in the US (1887), UMIST (1900s).
Unit operations and the AIChE in 1915.
Many countries did without them until more recently (Germany)

What is chemical engineering by definition?

Definition found in a standard dictionary:

“A branch of engineering which involves the design and operation of large scale chemical plants, petrochemical refineries, and the like.” Hmmm …

Another definition (from the WWW):

“Concerned with processes that cause substances to undergo required changes in their chemical or physical composition, structure, energy content or physical state.”
Chemical engineers are everywhere?

Oil industry

Chemical and allied products
Process plant manufacture and construction
Pharmaceutical (aspirin, hormones, …, drug delivery)
Personal care (cosmetics, moisturizers, …)
Household products (washing powder, …)
Food and drink
Materials (silicon chips, porous media, catalysts, …)
Consultants
Academia