All About Chemical Engineering and Science

Continuous distillation

noreply@blogger.com (Wdzone) — Tue, 08 Mar 2011 14:18:00 +0000

Continuous distillation is an ongoing separation process in which a liquid mixture of two or more miscible components is continuously fed into the process and physically separated into two or more products by preferentially boiling the morevolatile (i.e., lower boiling point) components out of the mixture.

Large-scale, continuous distillation is very commonly used in the chemical process industries where large quantities of liquids have to be distilled, as in petroleum refining, natural gas processing, petrochemical production, hydrocarbon solventsproduction, coal tar processing, the liquefaction of gases such as hydrogen,oxygen, nitrogen, and helium), and other low-temperature processing.

Industrial distillation is typically performed in large, vertical cylindrical columns commonly referred to as distillation columns, distillation towers or fractionators with diameters ranging from about 65 centimetres to 11 metres and heights ranging from about 6 metres to 60 metres or more.

To provide for the intimate mixing of the upward flowing vapor and downward flowing liquid in distillation columns, the columns usually contain a series of horizontal distillation trays or plates. The distillation trays or plates are typically separated by about 45 to 75 centimetres of vertical distance. However, some columns are designed to use beds of packing media rather than trays or plates.

Distillation is one of the fundamental unit operations of chemical engineering. If the feed contains more than two components, it is commonly referred to as multi-component distillationand, if it contains only two components, it is referred to as binary distillation.

If the distillation column feed contains a very great number of components (such as is the case in distilling petroleum crude oil), separation into pure components is impractical and such columns are therefore designed to yield fractions which are groups of components within a desired range of boiling points. Those fractions are probably the origin of the terms fractional distillation and fractionation.

Chemical Engineering Salary

noreply@blogger.com (Wdzone) — Tue, 08 Mar 2011 14:12:00 +0000

Chemical engineering is one of the highest paying degrees for entry level jobs, with even higher payscales for experienced chemical engineers. Here's a look at typical salary ranges for chemical engineers.

Chemical Engineer Salary Survey Based on Experience.

Chemical engineers can earn good salaries straight out of school, but years of experience or higher education can double the salary rate.

Chemical Engineer < 1 Year Experience: $51,710 - $66,286

Chemical Engineer with 1-4 Years Experience: $56,206 - $70,414

Chemical Engineer with 5-9 Years Experience: $64,618 - $84,199

Chemical Engineer with 10-19 Years Experience: $74,546 - $101,299

Chemical Engineer with More than 20 Years Experience: $83,304 - $126,418

Salary survey based on experience is from PayScale.com.

According to the US Department of Labor (2008), the median salary for chemical engineering was $78,860. The middle 50% of chemical engineers had salaries between $67,420 and $105,000.

The UK's Institution of Chemical Engineers (2006) reported the average starting salary for chemical engineering graduates was £24,000, with an average salary for all chemical engineers of about £53,000.

Blocking cancer drug's toxic side effects

noreply@blogger.com (Wdzone) — Sun, 07 Nov 2010 11:30:00 +0000

US researchers have identified a compound that could drastically reduce toxic side effects associated with a widely used cancer drug. The research could improve anticancer treatment and drug tolerance among cancer patients.

Matthew Redinbo from the University of North Carolina had worked on cancer drug irinotecan, or CPT-11, for years, but when a colleague started undergoing treatment with the drug he became motivated to address the side effects. Irinotecan is mainly used against colon cancer, but the severe diarrhoea that can be a major side effect of treatment can lead to hospitalisation. The researchers screened 10,000 compounds and found four potential inhibitors of bacterial beta-glucuronidase, the enzyme thought to be responsible for reactivating irinotecan in the gut. Redinbo's collaborators from New York have also shown that mice that received regular oral dose of one of the inhibitors along with irinotecan suffered much less diarrhoea, and had healthier colon tissue, than mice that were just treated with irinotecan.

A new environmentally friendly concept in functionalising polymers allows coloured dye to be integrated directly into polymers that can be used in clothes and packaging, say UK scientists.

The dye is also incorporated and causes the polymer to be coloured. Because the dye becomes part of the polymer structure, there is no excess dye to wash away as in conventional processes, so pollution is also minimised. The team have made black, red, yellow and purple PLA fibres. Wayne Hayes, a polymer chemist at Reading University, UK believes the concept has great potential for the textile industry. McGowan suggests that functionalising the polymers to incorporate fluorescent or UV-active molecules could be useful for PLA used in packaging

Disinfectant Flexibility

noreply@blogger.com (Wdzone) — Tue, 26 Oct 2010 14:27:00 +0000

As the civic agitation on the approaching of chlorine use as a baptize antibacterial continues, abounding point-of-entry and point-of-use (POE/POU) systems could face a abeyant engineering redesign.

For decades, chlorine has been a reliable and able baptize disinfectant; however, with the advancing agitation over the abeyant of antibacterial byproducts (DBP) development, abounding POE/POU suppliers are gluttonous agency to architect adaptability into their systems.

Deploying Hydrogen Peroxide

One POE/POU band-aid developed by Charger Baptize Analysis Products is a actinic antibacterial arrangement able of injecting chlorine or hydrogen peroxide. In adjustment to finer arrange a bifold actinic system, solutions to several abstruse and bazaar issues bare to be resolved.

The acceptance of hydrogen achromatize as a baptize analysis antibacterial is increasing. It is an able antibacterial adjoin bacilli and bacilli and has been apparent able in alleviative controllable baptize contaminants such as adamant and sulfur, abbreviation bacilli that can affect taste, blush and odor. In contrast, the consistent byproducts of hydrogen peroxide—oxygen and water—are by itself benign with the balance oxygen in the breeze beck acting to avert sulfide production.

The claiming to hydrogen achromatize is the handling. As a able oxidant, the U.S. Department of Transportation requires appropriate administration and certifications for solutions of 8% or above. Actinic suppliers action 7% solutions, abbreviation the accountability to the banker and end-user. Hydrogen achromatize should be handled and stored diligently.

The abstruse issues airish from a adjustable actinic ablution arrangement application chlorine or hydrogen achromatize are the gasification of the actinic antibacterial accomplished as vapor-lock in a diaphragm metering pump, aqueous administration and alertness and the rangeability or abnegation in the actinic pump.

Using Peristaltic Pumps

In some chlorine bang systems, Charger has provided systems application peristaltic pump technologies. Peristaltic pumps accomplish able-bodied in both chlorine or hydrogen achromatize bang systems because of their adeptness to handle the gasification of both liquids and accommodate the abnegation required. The downside is their antecedent amount and consistent adjustment amount of replacing the tube, accessory alternation and motor if the tube bend was installed angular against vertically. If the tube in a vertical accession ruptures, chlorine will dribble down the bend afore accumulating central the accessory alternation and motor, acceptance time for tube backup afore the access of corrosion.

To handle the abnegation rates, actinic metering pumps were aswell well-suited, but abounding of the diaphragm metering pumps suffered from breath lock as the chlorine and hydrogen achromatize angry to gas. Breath lock is a accurate botheration during the hot summer months.

During their research, Charger Baptize amid the QP diaphragm metering pump from EMEC Americas that retained the abnegation and chip a self-venting arch architecture to handle the gasification of chlorine and hydrogen peroxide.

Charger began testing the QP pump at baddest locations about their bazaar area. Rangeability in the QP pump gave it a 150:1 turndown, acceptance the pump to accomplish at a top bang amount of 24 gal per day (gpd), 22 gpd if discharge gas and a minimum of 0.5 gpd aural the appropriate bang ambit for both chemicals. The account of discharge gas breath aback into the catchbasin accepted to be an asset during the summer months.

“At aboriginal I was agnostic that a self-venting metering pump would work, but if we put it in the acreage we begin that it in actuality vented the chlorine gas aback into the catchbasin and did not lose its prime,” said Eric Beck, Charger’s Port Richey, Fla., annex manager.

With antecedent tests complete, Charger began deploying a few of the QP pumps to baddest dealers for added acreage trials. The plan was to use one QP pump for either chlorine or hydrogen achromatize bang with the apprehension of lower accessories costs. Antecedent installations went well, with installers commenting on the affluence of accession of the wall-mount design. Baptize analysis dealers accepted the actuality that the wall-mount agreement adored them accession time against a foot-mounted pump, which appropriate a ascent abject or pump arch rotation.

Most of the antecedent installations went into systems that injected chlorine for POE applications. As the agitation on chlorine use has intensified, end-users as able-bodied as baptize analysis dealers began inquiring about the advantage to inject hydrogen peroxide.

“That’s if we stepped in with our plan,” Beck said. “We formed with our dealers to account the hydrogen achromatize claim for the installation, ablaze the chlorine from the QP pump and displace the bang amount to accommodated the demand. So far the systems are alive as expected. The pumps are still operating with their aboriginal diaphragms, which is an added benefit.”

“Returning comments announce that users are witnessing lower electric burning with the QP against that of a peristaltic pump,” said David Wood, operations administrator for Charger, Port Richey. “We accept that is because the solenoid operates with one achievement against the circling of a peristaltic.”

“We’re aflame about what this agency for the industry—we now accept one pump that can inject both chemicals after accident its prime,” Beck said.

It is not accepted area the agitation on chlorine use will go, but developing options for the use of added disinfectants such as hydrogen achromatize will accomplish this industry bigger able to accommodated the befalling as it develops.

Activated Carbon

noreply@blogger.com (Wdzone) — Tue, 26 Oct 2010 14:24:00 +0000

Activated carbon is activated for abounding baptize and air filtration applications because it can abolish a ample spectrum of contaminants. Activated carbon is activated in municipal, automated and chancy decay streams.

Organic, Asleep Contaminants

Activated carbon is activated to abolish amoebic contaminants and some asleep contaminants. It is about a non-specific adsorbent. Table 1 is to be activated as a admeasurement of whether activated carbon is an able technology. The ratings are based aloft accepted accessible advice and able judgement.

Activated carbon can adsorb about all amoebic compounds to some degree. The capability of activated carbon is accompanying to the actinic composition, atomic structure, and which carbon is getting utilized. Activated carbon can be fabricated from coal, attic shell, wood, cartilage and peat. The analysis of pores (macropores, capricious pores and micropores) is altered for anniversary product. It is an accomplished adsorbent due to its ample apparent breadth and the actuality that the assorted surfaces can yield on abounding altered types of contaminants. The apparent breadth of a carbon is created by activating the abject artefact in a address to actualize pores. The capability of the carbon and which carbon delivers best after-effects is based aloft the accurate website and the contaminants to be removed.

In a lot of baptize analysis applications the activated carbon will advance concrete adsorption of the contaminants. Concrete adsorption is the action of the algae getting captivated assimilate the apparent breadth by anemic forces. Activated carbon can aswell advance actinic adsorption if the armament are able and appear at alive sites on the surface.

Limits

Activated carbon does accept limitations. Compounds that accept low atomic weight and top abstention are usually not recommended for activated carbon. For example, baptize streams with top solids, oil and grease can could cause abuse of the activated carbon.

Another limitation is that the activated carbon does become spent over time and new carbon accept to be put in its place. The spent carbon accept to again be disposed of in an adapted manner. The up ancillary is that the activated carbon may be reactivated or discharged. In a lot of cases the spent carbon is not hazardous; however, if you are borderline about your carbon getting non-hazardous or hazardous, it is consistently best to accept it tested.

Due to activated carbon’s adeptness to be activated for a arrangement of contaminants, it is sometimes activated for applications area addition blazon of clarify media or arrangement may be added effective.

Conclusion

Activated carbon is a accurate technology that has been about for abounding years. It is activated in a advanced arrangement of applications and now comes in abounding altered forms. If searching at a accurate appliance in which a advanced arrangement of amoebic contaminants are found, it may be acute to attending at activated carbon first.

Modul 6 Hysys - Columns Simulation Environment1

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Modul 5 Hysys - Logika Set Adjust

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Modul 4 Hysys - Stream Mixing Splitting

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Modul 3 Hysys - Separator StageTunggal

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Modul 2C Hysys - Petroleum Fraction

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Modul 2B Hysys - HypotheticalComponents

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Modul 2A Hysys - FluidProperties

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Modul 1A Hysys - ProcessSimulationCase12

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Download Free Hysys Guide - Modul1 Hysys

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Reaction Kinetics & Chemical Reaction Models

noreply@blogger.com (Wdzone) — Wed, 13 Jan 2010 02:19:00 +0000

General Features of Reaction Mechanisms

There are fundamental features in most reaction mechanisms occurring in the gas phase that can be used to assemble such mechanisms. The most important one is the role played by free radicals in the decomposition of any reactant. A very simple example found in freshman chemistry books is the formation of hydrogen iodide starting from hydrogen and iodine (Chang, 1994). The proposed mechanism is a two-step mechanism,

(3)

(4)

The first step involves the formation of iodine radicals in reaction (3), and it is followed by the formation of hydrogen iodide. Another example is the oxidation of hydrocarbons at low temperatures initiated by the following reactions (Dryer, 1991)

(5)

(6)

in which the hydrocarbon radical R plays a role in reaction (6) forming a species that can lead to the formation of oxygenated species such as alcohols and aldehydes. These types of reaction seem to take place in the urban atmosphere (Seinfield, 1989). If the temperature is high enough, the decomposition of the reactant is initiated by a thermal decomposition such as reaction (7),

(7)

Reaction (7) is endothermic and its extent would depend on temperature, and results in the formation of methyl radical. This type of reaction would occur in shock tubes, for example, where the decomposition of the fuel is initiated by a traveling shock wave causing temperature and pressure to rise considerably in a very short time.

The above examples then illustrate a very important point to remember when examining reaction mechanisms: the decomposition of the reactant is initiated by formation of radical species that can later participate in the reactions leading to the product. The concentration of the radicals formed increase as the reaction time or temperature increase.

Another important consideration is the formation of chain reactions. The basic premise of chain reaction mechanisms is also that free radicals play a leading role in the destruction of reactant molecules. The chain reaction mechanism itself consists of several steps: initiation, propagation, branching (not always present), and termination. This can be illustrated, for certain range of temperature and pressure, by some of the reactions in the following Hydrogen oxidation mechanism:

Reaction Kinetics & Chemical Reaction Models

noreply@blogger.com (Wdzone) — Wed, 13 Jan 2010 02:17:00 +0000

The fundamentals of chemical reaction kinetics will be presented with the purpose of building, starting with elementary reactions,
complex mechanisms. These mechanisms consisting of many elementary reactions can be used with existing software (discussed later) to make predictions on the performance of chemical reactors with special consideration to the formation of trace species. The focus will be on homogeneous processes taking place in the gas phase. The majority of the material presented in this manuscript is based on the author’s own research (Gargurevich, 1997).

Both in past and present literature dealing with the design of chemical reactors, there is an oversimplification of the chemical reaction models, with the use of global mechanisms consisting of a few reactions with empirically determined reaction rates (Worstell, 2001; Arakawa et al., 1998). For example, the rate of consumption of reactant A by B to form product C, represented by the overall reaction (1) below, is presented in the form of Equation (2),

where A_e is the pre-exponential factor, E an empirically determined activation energy, and a and b, the exponents of the reactant concentrations that are able to represent the concentration dependence over a range of conditions also empirically determined.

Unfortunately, these oversimplified mechanisms, to give an example, may not be able to accurately predict the formation of toxic products present in very small concentrations because depending on conditions their formation is dependent on complex chemistry involving stable and radical species, as well as reaction temperature. There is a need then to arrive at more complex mechanisms consisting of elementary reactions that are relevant to the consumption of the reactants, formation of intermediate species and products, and any other chemical species of interest (Senkan, 1992).

Distillation Pilot Plant Design, Operating Parameters and Scale-up Considerations

noreply@blogger.com (Wdzone) — Wed, 13 Jan 2010 02:12:00 +0000

Introduction

In spite of the fact that tremendous progress is being made in understanding the performance of both random and structured packings in distillation, it is a long way from being able to predict from first principles, the

efficiency, capacity and pressure drop

of a tower packing using thermodynamic and thermo-physical properties of the chemical system being distilled, as well as the physical parameters of the packing which aids the mass transfer. Those predictive methods that are available in the open literature have limited or poor accuracy if applied to a wide variety of chemical systems and tower packings.

The number of stages required for a given separation is obtained from the application of equilibrium thermodynamics. The actual number of stages obtained from a packed tower either in a laboratory, pilot plant, or an industrial plant is divided by the equilibrium stages predicted by vapor-liquid equilibrium thermodynamics to obtain an efficiency for the packed tower. Attempts have been made to generate semi-empirical correlations for packed tower efficiency from experimental data, and also generalized predictive models using the two-film theory of mass transfer. The mass transfer capability of a packing is typically expressed as HETP, HTU, K_Ga or K_La, all of which are rate-controlled quantities, and they can all be converted from one to another.
Attempts to derive generalized predictive methods for the mass transfer efficiency of packings using the two-film theory and dimensionless groups, and for the pressure drop and capacity using mechanistic models, have met with varying degrees of success. Published results of these attempts are the works of Bolles and Fair (1979), Bravo et al. (1987), Fair and Bravo (1987), Stichhnair et al. (1989), Fair and Bravo (1990), to name a few. The models used in these predictive methods were checked against many sources of pilot plant data, especially those made by Fractionation Research, Inc. (FRI) and the Separation Research Program (SRP) of the University of Texas at Austin.
On the other hand, reliable semi-empirical or empirical correlations of efficiency, capacity and pressure drop specific to a packing supplier’s products can be found in their product bulletins, (e.g., Norton Chemical Process Products Corporation [NCPPC] 1987, 1992). These correlations are based on thermodynamic and physical properties of the systems, physical properties of the packings and numerous pilot plant tests and often operating data from industrial distillation columns. A very important need for ongoing pilot plant testing of tower packings in various distillation services arises because the existing predictive methods are either based on, or have been checked against only a limited data base i.e., limited number of chemical systems, system pressures (and temperatures) as well as packings. Thus pilot plant testing allows one to extend the database, which may suggest the need to refine the predictive models whether they are empirical, semi-theoretical or theoretical.
Often times, pilot plant distillation tests are necessitated because the customer requests such tests. The customer is anxious to have these tests performed because they want to minimum design and installation risk when building a multimillion-dollar facility. These risks can arise because of the lack of good vapor-liquid equilibrium data, the likelihood of azeotrope formation or interactions between key components not well understood, uncertainties in new design goats like high product purities even for familiar chemical systems, need to evaluate a new operating mode, etc.
The authors will discuss, based upon their experience in mass transfer tower design, operation of Norton’s distillation pilot plants, and field feedback from the operation of commercial units, topics such as:

Packing size to tower diameter ratio
Distributor technology
Bed depth
Chemical system to be distilled
Sampling techniques
Reproducibility of results
Operation pitfalls

Crystallization

noreply@blogger.com (Wdzone) — Wed, 13 Jan 2010 02:07:00 +0000

Crystallization refers to the formation of solid crystals from a homogeneous solution. It is essentially a solid-liquid separation technique and a very important one at that. Crystals are grown in many shapes, which are dependent upon downstream processing or final product requirements. Crystal shapes can include cubic, tetragonal, orthorhombic, hexagonal, monoclinic, triclinic, and trigonal. In order for crystallization to take place a solution must be "supersaturated". Supersaturation refers to a state in which the liquid (solvent) contains more dissolved solids (solute) than can ordinarily be accomodated at that temperature.

As with any separation method, equilibrium plays an important role. Below is a general solubility curve for a solid that forms hydrate (a compound that has one or more water molecules attached) as it cools.

In Figure 1, X may be any solid that can form hydrates such as Na₂S₂O₃. The number of hydrate molecules shown in Figure 1 is strictly arbitrary and will vary for each substance.

So how do you grow crystals? Let's consider an example that is fairly easy to envision. Take a pot of boiling water and add table salt while stirring to make a water-salt solution. Continue adding salt until no more salt will dissolve in the solution (this is a saturated solution). Now add one final teaspoon of salt. The salt that will not dissolve will help the first step in crystallization begin. This first step is called "nucleation" or primary nucleation. The salt resting at the bottom of the pot will provide a site for nucleation to occur.

On an industrial scale, a large supersaturation driving force is necessary to initiate primary nucleation. The initiation of primary nucleation via this driving force is not fully understood which makes it difficult to model (experiments are the best guide). Usually, the instantaneous formation of many nuclei can be observed "crashing out" of the solution. You can think of the supersaturation driving force as being created by a combination of high solute concentration and rapid cooling. In the salt example, cooling will be gradual so we need to provide a "seed" for the crystals to grow on. In continuous crystallization, once primary nucleation has begun, the crystal size distribution begins to take shape. Think about our salty water, as you look at Figure 2 describing the progression of crystallization.

The second chief mechanism in crystallization is called secondary nucleation. In this phase of crystallization, crystal growth is initiated with contact. The contact can be between the solution and other crystals, a mixer blade, a pipe, a vessel wall, etc. This phase of crystallization occurs at lower supersaturation (than primary nucleation) where crystal growth is optimal.

Again, no complete theory is available to model secondary nucleation and it's behavior can only be anticipated by experimentation. Mathematic relationships do exist to correlate experimental data. However, correlating experimental data to model crystallization is time consuming and often considered extreme for batch operations, but can easily be justified for continuous processes where larger capital expenditures are necessary. For batch operations, only preliminary data measurements are truly necessary.
We've discussed how crystallization occurs once supersaturation is reached, but how do we reach supersaturation? We have already covered one such method in our salt crystallization example. Since the solubility of salt in water decreases with decreasing temperature, as the solution cools, its saturation increases until it reaches supersaturation and crystallization begins (Figure 3). Cooling is one of the four most common methods of achieving supersaturation. It should be noted that cooling will only help reach supersaturation in systems where solubility and temperature are directly related. Although this is nearly always the case, there are exceptions. In Figure 3, you'll note that Ce₂(SO₄)₃ actually becomes less soluble in water at higher temperatures.

The four most common methods of reaching supersaturation in industrial processes are:

1. Cooling (with some exceptions)
2. Solvent Evaporation
3. Drowning
4. Chemical Reaction

Drowning describes the addition of a nonsolvent to the solution which decreases the solubility of the solid. A chemical reaction can be used to alter the dissolved solid to decrease its solubility in the solvent, thus working toward supersaturation. Each method of achieving supersaturation has its own benefits. For cooling and evaporative crystallization, supersaturation can be generated near a heat transfer surface and usually at moderate rates. Drowning or reactive crystallization allows for localized, rapid crystallization where the mixing mechanism can exert significant influence on the product characteristics.

Equipment Used in Crystallization

1. Tank Crystallizers
This is probably the oldest and most basic method of crystallization. In fact, the "pot of salt water" is a good example of tank crystallization. Hot, saturated solutions are allowed to cool in open tanks. After crystallization, the mother liquor is drained and the crystals are collected. Controlling nucleation and the size of the crystals is difficult. The crystallization is essentially just "allowed to happen". Heat transfer coils and agitation can be used. Labor costs are high, thus this type of crystallization is typically used only in the fine chemical or pharmaceutical industries where the product value and preservation can justify the high operating costs.

2. Scraped Surface Crystallizers
An example may be the Swenson-Walker crystallizer consisting of a trough about 2 feet wide with a semi-circular bottom. The outside is jacketed with cooling coils and an agitator blade gently passes close to the trough wall removing crystals that grow on the vessel wall.

3. Forced Circulating Liquid Evaporator-Crystallizer
Just as the name implies, these crystallizers combine crystallization and evaporation, thus the driving forces toward supersaturation. The circulating liquid is forced through the tubeside of a steam heater. The heated liquid flows into the vapor space of the crystallization vessel. Here, flash evaporation occurs, reducing the amount of solvent in the solution (increasing solute concentration), thus driving the mother liquor towards supersaturation. The supersaturated liquor flows down through a tube, then up through a fluidized area of crystals and liquor where crystallization takes place via secondary nucleation. Larger product crystals are withdrawn while the liquor is recycled, mixed with the feed, and reheated.

4. Circulating Magma Vacuum Crystallizer

In this type of crystallizer, the crystal/solution mixture (magma) is circulated out of the vessel body. The magma is heated gently and mixed back into the vessel. A vacuum in the vapor space causes boiling at the surface of the liquid. The evaporation causes crystallization and the crystals are drawn off near the bottom of the vessel body.

References:

Price, Chris J., "Take Some Solid Steps to Improve Crystallization", Chemical Engineering Progress, September 1997, p. 34.

Geankoplis, Christie J., Transport Processes and Unit Operations, 3rd Ed., Prentice Hall, New Jersey, 1993, ISBN: 0-13-930439-8

Brown, Theodore L., Chemistry: The Central Science, 5th Ed., Prentice Hall, New Jersey, 1991,
ISBN: 0-13-126202-5

http://www.cheresources.com/cryst.shtml

current health articles

noreply@blogger.com (Wdzone) — Mon, 28 Dec 2009 12:40:00 +0000

healthkut.com is a health blog provides latest buzz on current health events and current health articles. its also a leading platform for informative articles on various diseases and conditions, womans health, infertility etc wide range of health and medical topics.

Enthalpy

noreply@blogger.com (Wdzone) — Sat, 19 Dec 2009 11:12:00 +0000

Four quantities called "thermodynamic potentials" are useful in the chemical thermodynamics of reactions and non-cyclic processes. They are internal energy, the enthalpy, the Helmholtz free energy and the Gibbs free energy. Enthalpy is defined by

H = U + PV

where P and V are the pressure and volume, and U is internal energy. Enthalpy is then a precisely measurable state variable, since it is defined in terms of three other precisely definable state variables. It is somewhat parallel to the first law of thermodynamics for a constant pressure system
Q = ΔU + PΔV since in this case Q=ΔH

It is a useful quantity for tracking chemical reactions. If as a result of an exothermic reaction some energy is released to a system, it has to show up in some measurable form in terms of the state variables. An increase in the enthalpy H = U + PV might be associated with an increase in internal energy which could be measured by calorimetry, or with work done by the system, or a combination of the two.

The internal energy U might be thought of as the energy required to create a system in the absence of changes in temperature or volume. But if the process changes the volume, as in a chemical reaction which produces a gaseous product, then work must be done to produce the change in volume. For a constant pressure process the work you must do to produce a volume change ΔV is PΔV. Then the term PV can be interpreted as the work you must do to "create room" for the system if you presume it started at zero volume.

First Law of Thermodynamics

noreply@blogger.com (Wdzone) — Sat, 19 Dec 2009 11:09:00 +0000

The first law of thermodynamics is the application of the conservation of energy principle to heat and thermodynamic processes:

The first law makes use of the key concepts of internal energy, heat, and system work. It is used extensively in the discussion of heat engines. The standard unit for all these quantities would be the joule, although they are sometimes expressed in calories or BTU.

It is typical for chemistry texts to write the first law as ΔU=Q+W. It is the same law, of course - the thermodynamic expression of the conservation of energy principle. It is just that W is defined as the work done on the system instead of work done by the system. In the context of physics, the common scenario is one of adding heat to a volume of gas and using the expansion of that gas to do work, as in the pushing down of a piston in an internal combustion engine. In the context of chemical reactions and process, it may be more common to deal with situations where work is done on the system rather than by it.

Advances in Chemical Oxidation of Total Reduced Sulfur from Kraft Mills Atmospheric Effluents

noreply@blogger.com (Wdzone) — Sat, 19 Dec 2009 10:59:00 +0000

Catalin Florin Petre, Laval University
Simon Piché, Laval University
André Normandin, Mesar/Environair Inc.
Faical Larachi, Laval University

Abstract

Chemical oxidation techniques in use for the reduction of malodorous total reduced sulfur (TRS) emissions in the kraft mills atmospheric effluents were reviewed with an emphasis on recent industrial improvements in chlorine dioxide (ClO₂) oxidation of TRS as well as on laboratory developments of an iron-based chemistry process. The ClO₂ approach was implemented successfully at the industrial scale in two Québec kraft mills. The approach consisted in mixing the non-condensable gases (NCG) containing the TRS with gaseous chlorine dioxide obtained either as a residue from a bleach plant vent stream or through vaporization of fresh solution. Full-scale tests have shown that the amount of chlorine dioxide injected or mixed in the NCG was sufficient to reduce the TRS load below the 10 ppmv-regulated levels in a cost efficient way as compared with incineration. A prospective approach validated in laboratory conditions and using the iron redox chemistry for alkaline oxidative scrubbing of TRS is being investigated at Laval University to reduce the odor pollution and to convert TRS into valuable sulfur. Two configurations were evaluated, one consisting of homogeneous Fe(III) sequestered in trans-1,2-diaminocyclohexanetetraacetic acid (cdta) chelates and another of heterogeneous Fe(III) as Fe/Ce oxides-hydroxides mixtures. The relative performances, advantages and weaknesses of the various chemical oxidation processes were discussed. In addition, the fundamentals of the alkaline oxidative scrubbing of TRS using the iron-based alkaline approach were summarized in terms of the gas-liquid thermodynamic equilibria and of the homogeneous and heterogeneous iron redox reactions.

Recommended Citation

Petre, Catalin Florin; Piché, Simon; Normandin, André; and Larachi, Faical (2007) "Advances in Chemical Oxidation of Total Reduced Sulfur from Kraft Mills Atmospheric Effluents," International Journal of Chemical Reactor Engineering: Vol. 5: R2.
Available at: http://www.bepress.com/ijcre/vol5/R2

Efek dari Katalis pada Laju Reaksi

noreply@blogger.com (Wdzone) — Sat, 19 Dec 2009 10:50:00 +0000

Halaman ini menjelaskan bahwa penambahan katalis mempengaruhi laju reaksi. Halaman ini mengansumsikan bahwa Anda telah mengerti prinsip dasar dari teori tumbukan dan distribusi energi molekular Maxwell-Boltzmann pada gas.

Fakta-fakta

Apa itu katalis?

Katalis adalah suatu zat yang mempercepat suatu laju reaksi, namun ia sendiri, secara kimiawi, tidak berubah pada akhir reaksi. Ketika reaksi selesai, kita akan mendapatkan massa katalasis yang sama seperti pada awal kita tambahkan.

Beberapa contoh
Beberapa katalis umum yang digunakan :

reaksi	katalis
Dekomposisi hidrogen peroxide	mangan(IV)oksida, MnO₂
Nitrasi benzena	asam sulfur pekat
Produksi amonia dengan proses Haber	besi
Konversi dari SO₂ ke SO₃ melalui proses Kontak untuk memproduksi asam sulfur	vanadium(V)oxida,V₂O₅
Hidrogenasi C=C ikatan rangkap	�@

Penjelasan

Pentingnya aktivasi energi

Tumbukan-tumbukan akan menghasilkan reaksi jika partikel-partikel bertumbukan dengan energi yang cukup untuk memulai suatu reaksi. Energi minimum yang diperlukan disebut dengan reaksi aktivasi energi.

Kita dapat menggambarkan keadaan dari energi aktivasi pada distribusi Maxwell-Boltzmann seperti ini:

Hanya partikel-partikel yang berada pada area di sebelah kanan dari aktivasi energi yang akan bereaksi ketika mereka bertumbukan. Sebagian besar dari partikel tidak memiliki energi yang cukup dan tidak menghasilkan reaksi.

Katalis dan aktivasi energi

Untuk meningkatkan laju reaksi kita perlu untuk meningkatkan jumlah tumbukan-tumbukan yang berhasil. Salah satu cara alternatif untuk mewujudkannya adalah dengan menurunkan energi aktivasi.

Dengan kata lain, menggeser energi aktivasi seperti diagram dibawah ini :

Menambahkan katalis memberikan perubahaan yang berarti pada energi aktivasi. Katalis menyediakan satu rute alternatif bagi reaksi. Rute alternatif ini memiliki energi aktivasi yang rendah. Diagram dibawah ini merupakan gambaran keadaan energi.

Ingat, katalais hanya mempengaruhi laju pencapaian kesetimbangan, bukan posisi keseimbangan (misalnya : membalikkan reaksi). Katalis tidak menggangu gugat hasil suatu reaksi kesetimbangan dan konsentrasi atau massanya setelah reaksi selesai sama dengan konsentrasi atau massa reaksi sebelum reaksi dilangsungkan.

Waste recycling

noreply@blogger.com (Wdzone) — Sat, 19 Dec 2009 10:40:00 +0000

When you anticipate of recycling do you blow and anticipate that you just don't accept the time or activity to do it? Do you see visions of hundreds of bags of abandoned artificial bottles in some far-away branch accepting accessible to be broiled down? Do you anticipate that recycling is something that has to be hard; contrarily if it's not hard, again it doesn't count? I'm ashamed to say that at one time, these were the thoughts that ran through my arch and they justified my affidavit for not recycling. I'm actuality to acquaint you that I was mistaken; recycling isn't something difficult, or something you accept to go out of your way to participate in and if it's easy, well, it's just easy; and it still counts against recycling.

Reforming of Agent Ammunition in a Micro Reactor

noreply@blogger.com (Wdzone) — Mon, 23 Nov 2009 17:43:00 +0000

Reforming of agent ammunition is arduous but actual adorable for hydrogen production. It can facilitate the bazaar access of ammunition beef due to the absolute basement for administration of agent fuel. Reforming in micro reactors enables acceptable calefaction alteration and accordingly baby and bunched ammunition processing systems e.g. for electrical activity bearing in abetting ability units.

Due to the complication of diesel, reforming of altered agent apparatus and about-face intermediates in a micro reactor is advised systematically aural this work. Methane and propane were activated as about-face intermediates and hexadecane as a agent surrogate. All abstracts were conducted over a rhodium agitator on Al2O3 or CeO2.
For dehydration of the college baking hydrocarbons a micro structured bang bill was bogus to actualize a accomplished hydrocarbon aerosol which evaporates in baptize vapour. Furthermore a circuitous gas chromatographic adjustment to analyse hydrocarbons up to C16 and the abiding gases in one assay run was developed.
Experimental after-effects appearance that the about-face abundance of the ammunition molecules in the augment decreases linearly for beeline alternation hydrocarbons with an accretion amount of carbon atoms. Calculations appearance that the empiric conversions and artefact gas compositions are abutting to the thermodynamic equilibrium. The agitator arrangement Rh/CeO2 offers bigger reforming achievement and college attrition to coking allegedly due to beneath acerb sites compared to Al2O3 and the oxygen accumulator accommodation of CeO2.
The advancing plan will appraise the reforming behaviour of added archetypal agent ammunition apparatus e.g. mixtures of hexadecane and methylnaphthalene or constructed agent fuel. Abstracts will be conducted in an optimised micro reformer, which disposes the heating activity by afire e.g. ammunition corpuscle off-gases. This aswell offers the application of alpha up and amount alteration behaviour.