Sonali Chem Hhw

8/6/2019 Sonali Chem Hhw

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Scientific name: Solanaceae

y Potato or Nightshade family includes tomatoes, cayenne, red and green peppers, tomatillos,

nightshade

potatoes, eggplant and tobacco, also ornamentals such as jessamine. Many plants in this family

have alkaloids that are poisonous or narcotic.

Most useful and economically important plant families

Scientific name: Poaceae or Graminae

y Grass family includes wheat, rice, corn, barley, oats, sugar, sorghum and millet most important

family in terms of world nutrition 50% of humanities calories come from this family.

Scientific name: Fabaceae or Leguminosae

y Legume family includes all beans (green beans, black beans, l ima beans etc.), lentils, peas,

tamarind, peanuts, and chickpeas.

Scientific name: Rosaceae

y Rose family includes not only roses, but also apples, pears, blackberries, raspberries,

strawberries,

crab apples and many ornamentals like roses, meadowsweet, hawthorn and pearlbush.

Scientific name: Rubiaceae

y Coffee is one of the most important cash crops of the tropics. The drugs quinine and ipecac

come

from plants of this family.


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Scientific name: Rutaceae

y Citrus family includes all citrus fruits orange, tangerine, lime, lemon, grapefruit, etc.

Scientific name: Cucurbitaceae

y Squash family includes all those fruits with a rind or tough skin squash, watermelon,

cucumber,

pumpkin, gourds, cantaloupe, honeydew melon, etc.

Scientific name: Sapindaceae

Soapberry

y Soapberry family includes the temperate species maple and chestnut, and tropical fruits such as

guarana, lychee, and akee. This family also contains saponins, which can be used to make soap.

Bromeliad Scientific name: Bromeliaceae

y Bromeliad family includes pineapples and many ornamentals.

Scientific name: Arecaceae or Palmae

y Various palm species have multiple uses including foods like coconuts, dates, palm cabbage,

peach palm fruits and oil palms. Other uses include furniture like the rattan palm, carnuba wax

(found in car polish), vegetable ivory (used for carving), and many species are used for thatch.

Scientific name: Brassicaceae or Cruciferae

y Mustard family includes mustard, horseradish, wasabi, capers, radish, turnip, canola, rapeseed

oil,

cabbage, kale, broccoli, cauliflower, Brussels sprouts (the last 5 come from the same species).

Scientific name: Apiaceae or Umbilleferae

y Carrot family includes carrots, celery, dill, caraway, fennel, parsley, parsnip, anise, ginseng and

cumin.


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Scientific name: Sapotaceae

y Sapodilla family includes some important tropical fruits such as sapodilla, mamey sapote,

eggfruit

and star apples. The latex of the sapodilla tree is called chicle and it is a base for chewing gum.

Scientific name: Malvaceae

y Birthday parties would not be the same without the Mallow family: chocolate, cola and

marshmallow come from this family; as well as okra, cotton and hibiscus.

Scientific name: Orchidaceae

y Orchids are important ornamentals worldwide. Vanilla also comes from this family.

Chemistry

Distillation, Fractional distllation, filteration, chromatography, sedimentation, evaporation

Distillation:

Distillation


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Laboratory display of distillation: 1: A heating device 2: Still pot 3: Still

head 4:Thermometer/Boiling point temperature 5:Condenser6: Cooling water in 7: Cooling

water out 8: Distillate/receiving flask 9:Vacuum/gas inlet 10: Still receiver11: Heat

control 12: Stirrer speed control 13:Stirrer/heat plate 14: Heating (Oil/sand) bath15: Stirring

means e.g.(shown), boiling chipsor mechanical stirrer16: Cooling bath.[1]

Distillation is a method ofseparatingmixtures based on differences in theirvolatilities in a boiling liquid

mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction.

Commercially, distillation has a number of applications. It is used to separate crude oil into more fractions for

specific uses such as transport,power generation and heating. Water is distilled to remove impurities, such as

salt from seawater. Air is distilled to separate its componentsnotably oxygen, nitrogen, and argonfor

industrial use. Distillation offermentedsolutions has been used since ancient times to producedistilled

beverages with a higher alcohol content. The premises where distillation is carried out, especially distillation of

alcohol, are known as a distillery.

Applications of distillation

The application of distillation can roughly be divided in four groups: laboratory scale, industrial distillation,

distillation of herbs for perfumery and medicinals (herbal distillate), and food processing. The latter two are

distinctively different from the former two in that in the processing of beverages, the distillation is not used as a

true purification method but more to transfer all volatiles from the source materials to the distillate.


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The main difference between laboratory scale distillation and industrial distillation is that laboratory scale

distillation is often performed batch-wise, whereas industrial distillation often occurs continuously. In batch

distillation, the composition of the source material, the vapors of the distilling compounds and the distillate

change during the distillation. In batch distillation, a still is charged (supplied) with a batch of feed mixture,

which is then separated into its component fractions which are collected sequentially from most volatile to less

volatile, with the bottoms (remaining least or non-volatile fraction) removed at the end. The still can then be

recharged and the process repeated.

In continuous distillation, the source materials, vapors, and distillate are kept at a constant composition by

carefully replenishing the source material and removing fractions from both vapor and liquid in the system. This

results in a better control of the separation process.

Batch distillation

Main article: Batch distillation

.A batch still showing the separation of A and B

Heating an ideal mixture of two volatile substances A and B (with A having the higher volatility, or lower boiling

point) in a batch distillation setup (such as in an apparatus depicted in the opening figure) until the mixture is

boiling results in a vapor above the liquid which contains a mixture of A and B. The ratio between A and B in

the vapor will be different from the ratio in the liquid: the ratio in the liquid will be determined by how the original

mixture was prepared, while the ratio in the vapor will be enriched in the more volatile compound, A (due to

Raoult's Law, see above). The vapor goes through the condenser and is removed from the system. This in turn

means that the ratio of compounds in the remaining liquid is now different from the initial ratio (i.e. more

enriched in B than the starting liquid).


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The result is that the ratio in the liquid mixture is changing, becoming richer in component B. This causes the

boiling point of the mixture to rise, which in turn results in a rise in the temperature in the vapor, which results in

a changing ratio of A : B in the gas phase (as distillation continues, there is an increasing proportion of B in the

gas phase). This results in a slowly changing ratio A : B in the distillate.

If the difference in vapor pressure between the two components A and B is large (generally expressed as the

difference in boiling points), the mixture in the beginning of the distillation is highly enriched in component A,

and when component A has distilled off, the boiling liquid is enriched in component B.

Continuous distillation

Main article: Continuous distillation

Continuous distillation is an ongoing distillation in which a liquid mixture is continuously (without interruption)

fed into the process and separated fractions are removed continuously as output streams as time passes

during the operation. Continuous distillation produces at least two output fractions, including at least

one volatile distillate fraction, which has boiled and been separately captured as a vapor condensed to a liquid.

There is always a bottoms (or residue) fraction, which is the least volatile residue that has not been separately

captured as a condensed vapor.

Continuous distillation differs from batch distillation in the respect that concentrations should not change over

time. Continuous distillation can be run at a steady state for an arbitrary amount of time. For any source

material of specific composition, the main variables that affect the purity of products in continuous distillation

are the reflux ratio and the number of theoretical equilibrium stages (practically, the number of trays or the

height of packing). Reflux is a flow from the condenser back to the column, which generates a recycle thatallows a better separation with a given number of trays. Equilibrium stages are ideal steps where compositions

achieve vapor-liquid equilibrium, repeating the separation process and allowing better separation given a reflux

ratio. A column with a high reflux ratio may have fewer stages, but it refluxes a large amount of liquid, giving a

wide column with a large holdup. Conversely, a column with a low reflux ratio must have a large number of

stages, thus requiring a taller column.

General improvements

Both batch and continuous distillations can be improved by making use of a fractionating column on top of the

distillation flask. The column improves separation by providing a larger surface area for the vapor and

condensate to come into contact. This helps it remain at equilibrium for as long as possible. The column can

even consist of small subsystems ('trays' or 'dishes') which all contain an enriched, boiling liquid mixture, all

with their own vapor-liquid equilibrium.

There are differences between laboratory-scale and industrial-scale fractionating columns, but the principles

are the same. Examples of laboratory-scale fractionating columns (in increasing efficiency) include:


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Air condenser

Vigreux column (usually laboratory scale only)

Packed column (packed with glass beads, metal pieces, or other chemically inert material)

Spinning band distillation system.

Laboratory scale distillation

Laboratory scale distillations are almost exclusively run as batch distillations. The device used in distillation,

sometimes referred to as a still, consists at a minimum of a reboilerorpotin which the source material is

heated, a condenserin which the heated vapouris cooled back to the liquid state, and a receiverin which the

concentrated or purified liquid, called thedistillate, is collected. Several laboratory scale techniques for

distillation exist (see also distillation types).

Simple distillation

In simple distillation, all the hot vapors produced are immediately channeled into a condenser that cools and

condenses the vapors. Therefore, the distillate will not be pure - its composition will be identical to the

composition of the vapors at the given temperature and pressure, and can be computed from Raoult's law.

As a result, simple distillation is usually used only to separate liquids whose boiling points differ greatly (rule of

thumb is 25 C),[14]

or to separate liquids from involatile solids or oils. For these cases, the vapor pressures of

the components are usually sufficiently different that Raoult's law may be neglected due to the insignificant

contribution of the less volatile component. In this case, the distillate may be sufficiently pure for its intended

purpose.

Fractional distillation

Main article: Fractional distillation

For many cases, the boiling points of the components in the mixture will be sufficiently close that Raoult's law

must be taken into consideration. Therefore, fractional distillation must be used in order to separate the

components well by repeated vaporization-condensation cycles within a packed fractionating column. This

separation, by successive distillations, is also referred to as rectification.[15]

As the solution to be purified is heated, its vapors rise to the fractionating column. As it rises, it cools,

condensing on the condenser walls and the surfaces of the packing material. Here, the condensate continues

to be heated by the rising hot vapors; it vaporizes once more. However, the composition of the fresh vapors are

determined once again by Raoult's law. Each vaporization-condensation cycle (called a theoreticalplate) will

yield a purer solution of the more volatile component. [16] In reality, each cycle at a given temperature does not

occur at exactly the same position in the fractionating column; theoreticalplate is thus a concept rather than an

accurate description.


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More theoretical plates lead to better separations. A spinning band distillation system uses a spinning band

ofTeflon or metal to force the rising vapors into close contact with the descending condensate, increasing the

number of theoretical plates.[17]

Steam distillation

Main article: Steam distillation

Like vacuum distillation, steam distillation is a method for distilling compounds which are heat-

sensitive.[18] This process involves bubbling steam through a heated mixture of the raw material. By Raoult's

law, some of the target compound will vaporize (in accordance with its partial pressure). The vapor mixture is

cooled and condensed, usually yielding a layer of oil and a layer of water.

Steam distillation of various aromatic herbs and flowers can result in two products; an essential oil as well as a

watery herbal distillate. The essential oils are often used in perfumery andaromatherapy while the watery

distillates have many applications in aromatherapy, food processing and skin care.

Dimethyl sulfoxide usually boils at 189 C. Under a vacuum, it distills off into the receiver at only

70 C.


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Perkin triangle distillation setup

1: Stirrer bar/anti-bumping granules 2: Still pot3: Fractionating column 4:Thermometer/Boiling

point temperature 5:Teflon tap 1 6: Cold finger7: Cooling water out 8: Cooling water in 9: Teflon tap

2 10:Vacuum/gas inlet 11: Teflon tap 3 12: Still receiver

Vacuum distillation

Main article: Vacuum distillation

Some compounds have very high boiling points. To boil such compounds, it is often better to lower the

pressure at which such compounds are boiled instead of increasing the temperature. Once the pressure is

lowered to the vapor pressure of the compound (at the given temperature), boiling and the rest of the distillation

process can commence. This technique is referred to as vacuum distillationand it is commonly found in the

laboratory in the form of the rotary evaporator.

This technique is also very useful for compounds which boil beyond theirdecomposition temperature atatmospheric pressure and which would therefore be decomposed by any attempt to boil them under

atmospheric pressure.

Molecular distillation is vacuum distillation below the pressure of 0.01 torr.[19]

0.01 torr is one order of

magnitude above high vacuum, where fluids are in the free molecular flow regime, i.e. the mean free path of

molecules is comparable to the size of the equipment. The gaseous phase no longer exerts significant pressure


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on the substance to be evaporated, and consequently, rate of evaporation no longer depends on pressure.

That is, because the continuum assumptions of fluid dynamics no longer apply, mass transport is governed by

molecular dynamics rather than fluid dynamics. Thus, a short path between the hot surface and the cold

surface is necessary, typically by suspending a hot plate covered with a film of feed next to a cold plate with a

line of sight in between. Molecular distillation is used industrially for purification of oils.

Air-sensitive vacuum distillation

Some compounds have high boiling points as well as being air sensitive. A simple vacuum distillation system

as exemplified above can be used, whereby the vacuum is replaced with an inert gas after the distillation is

complete. However, this is a less satisfactory system if one desires to collect fractions under a reduced

pressure. To do this a "cow" or "pig" adaptor can be added to the end of the condenser, or for better results or

for very air sensitive compounds a Perkin triangle apparatus can be used.

The Perkin triangle, has means via a series of glass orTeflon taps to allows fractions to be isolated from the

rest of the still, without the main body of the distillation being removed from either the vacuum or heat source,

and thus can remain in a state ofreflux. To do this, the sample is first isolated from the vacuum by means of

the taps, the vacuum over the sample is then replaced with an inert gas (such as nitrogen orargon) and can

then be stoppered and removed. A fresh collection vessel can then be added to the system, evacuated and

linked back into the distillation system via the taps to collect a second fraction, and so on, until all fractions

have been collected.

Short path distillation

Short path vacuum distillation apparatus with vertical condenser (cold finger), to minimize the

distillation path; 1: Still pot with stirrer bar/anti-bumping granules 2: Cold finger - bent to direct

condensate 3: Cooling water out 4: cooling water in 5: Vacuum/gas inlet 6: Distillate

flask/distillate.


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Short path distillation is a distillation technique that involves the distillate travelling a short distance, often

only a few centimeters, and is normally done at reduced pressure. [20] A classic example would be a distillation

involving the distillate travelling from one glass bulb to another, without the need for a condenser separating the

two chambers. This technique is often used for compounds which are unstable at high temperatures or to purify

small amounts of compound. The advantage is that the heating temperature can be considerably lower (at

reduced pressure) than the boiling point of the liquid at standard pressure, and the distillate only has to travel a

short distance before condensing. A short path ensures that little compound is lost on the sides of the

apparatus. The Kugelrohris a kind of a short path distillation apparatus which often contain multiple chambers

to collect distillate fractions.

Other types

The process ofreactive distillation involves using the reaction vessel as the still. In this process, the

product is usually significantly lower-boiling than its reactants. As the product is formed from the reactants,it is vaporized and removed from the reaction mixture. This technique is an example of a continuous vs. a

batch process; advantages include less downtime to charge the reaction vessel with starting material, and

less workup.

Pervaporation is a method for the separation of mixtures of liquids by partial vaporization through a non-

porous membrane.

Extractive distillation is defined as distillation in the presence of a miscible, high boiling, relatively non-

volatile component, the solvent, that forms no azeotrope with the other components in the mixture.

Flash evaporation (or partial evaporation) is the partial vaporization that occurs when a saturated liquid

stream undergoes a reduction in pressure by passing through a throttling valve or other throttling device.

This process is one of the simplest unit operations, being equivalent to a distillation with only one

equilibrium stage.

Codistillation is distillation which is performed on mixtures in which the two compounds are not miscible.

The unit process ofevaporation may also be called "distillation":

In rotary evaporation a vacuum distillation apparatus is used to remove bulk solvents from a sample.

Typically the vacuum is generated by a wateraspiratoror a membrane pump.

In a kugelrohra short path distillation apparatus is typically used (generally in combination with a (high)

vacuum) to distill high boiling (> 300 C) compounds. The apparatus consists of an oven in which the

compound to be distilled is placed, a receiving portion which is outside of the oven, and a means of rotating

the sample. The vacuum is normally generated by using a high vacuum pump.

Other uses:


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Dry distillation ordestructive distillation, despite the name, is not truly distillation, but rather a chemical

reaction known as pyrolysis in which solid substances are heated in an inert orreducing atmosphere and

any volatile fractions, containing high-boiling liquids and products of pyrolysis, are collected. The

destructive distillation ofwood to give methanol is the root of its common name - wood alcohol.

Freeze distillation is an analogous method of purification using freezing instead of evaporation. It is not

truly distillation, but a recrystallization where the product is the mother liquor, and does not produce

products equivalent to distillation. This process is used in the production ofice beerand ice wine to

increase ethanol and sugarcontent, respectively. It is also used to produce applejack. Unlike distillation,

freeze distillation concentrates poisonous congeners rather than removing them.

Fractional distillation

From Wikipedia, the free encyclopedia

Fractional distillation is the separation of a mixture into its component parts, orfractions, such as in

separating chemical compounds by theirboiling point by heating them to atemperature at which several

fractions of the compound will evaporate. It is a special type ofdistillation. Generally the component parts boil

at less than 25 C from each other under a pressure of one atmosphere (atm). If the difference in boiling

points is greater than 25 C, a simple distillation is used.

Laboratory setup

Fractional distillation in a laboratory makes use of common laboratory glassware and apparatuses, typically

including a Bunsen burner, a round-bottomed flask and a condenser, as well as the single-

purpose fractionating column.

Apparatus

, Graham condenserorAllihn condenser

vacuum adapter (not used in image to the right)

boiling chips, also known as anti-bumping granules

Standard laboratory glassware with ground glass joints, e.g. quickfit apparatus.

heat source, such as a hot plate with a bath, and ideally with a magnetic stirrer.

distilling flask, typically a round-bottom flask

receiving flask, often also a round-bottom flask

fractionating column

distillation head


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thermometerand adapter if needed

condenser, such as a Liebig condenser

.

Fractional distillation apparatus using a Liebig condenser. A conical flask is used as a

receiving flask. Here the distillation head and fractionating column are combined in one piece.[1]

Sedimentation is the tendency forparticles in suspension to settle out of the fluid in

which they are entrained, and come to rest against a barrier. This is due to their motion

through the fluid in response to the forces acting on them: these forces can be due

to gravity, centrifugal acceleration orelectromagnetism. In geology sedimentation is

often used as the polar opposite of erosion, i.e., the terminal end ofsediment transport.

In that sense it includes the termination of transport by saltation or true bedload

transport. Settling is the falling of suspended particles through the liquid, whereas

sedimentation is the termination of the settling process.

Sedimentation may pertain to objects of various sizes, ranging from large rocks in

flowing water to suspensions of dust and pollen particles to cellularsuspensions

to solutions of singlemolecules such as proteins and peptides. Even small molecules

such as aspirin can be sedimented, although it can be difficult to apply a sufficiently

strong force to produce significant sedimentation.


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The term is typically used in geology, to describe the deposition ofsediment which

results in the formation ofsedimentary rock, and in various chemical and environmental

fields to describe the motions of often-smaller particles and molecules. Process is also

used in biotech industry to separate out cells from the culture media.

Experiments

In a sedimentation experiment called tripothsis, the applied force accelerates the

particles to a terminal velocityvterm at which the applied force is exactly canceled by an

opposing drag force. For small enough particles (low Reynolds number), the drag force

varies linearly with the terminal velocity, i.e., Fdrag=fvterm (Stokes flow) where fdepends

only on the properties of the particle and the surrounding fluid. Similarly, the applied

force generally varies linearly with some coupling constant (denoted here as q) that

depends only on the properties of the particle, Fapp = qEapp. Hence, it is generally

possible to define a sedimentation coefficient that depends only on the

properties of the particle and the surrounding fluid. Thus, measuring s can reveal

underlying properties of the particle.

In many cases, the motion of the particles is blocked by a hard boundary; the resulting

accumulation of particles at the boundary is called a sediment. The concentration of

particles at the boundary is opposed by the diffusion of the particles.

The sedimentation of particles under gravity is described by the MasonWeaver

equation, which has a simple exact solution. The sedimentation coefficient s in this caseequals mb / f, where mb is the buoyant mass.

The sedimentation of particles under the centrifugal force is described by the Lamm

equation, which likewise has an exact solution. The sedimentation coefficient s also

equals mb / f, where mb is the buoyant mass. However, the Lamm equation differs from

the MasonWeaver equation because the centrifugal force depends on radius from the

origin of rotation, whereas gravity is presumed constant. The Lamm equation also has

extra terms, since it pertains to sector-shaped cells, whereas the MasonWeaver

equation pertains to box-shaped cells (i.e., cells whose walls are aligned with thethree Cartesian axes).

Particles with a charge or dipole moment can be sedimented by an electric

field orelectric field gradient, respectively. These processes divided by

its drag (the electrophoretic mobility). Similarly, fordielectrophoresis, the sedimentation

coefficient equals the particle's electric dipole moment divided by its drag.


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Classification of sedimentation:[citation are called electrophoresis and dielectrophoresis,

respectively. For electrophoresis, the sedimentation coefficient corresponds to the

particle charge needed]

Type 1 sedimentation is characterized by particles that settle discretely at a constantsettling velocity. They settle as individual particles and do not flocculate or stick to

other during settling. Example: sand and grit material

Type 2 sedimentation is characterized by particles that flocculate during

sedimentation and because of this their size is constantly changing and therefore

their settling velocity is changing. Example: alum or iron coagulation

Type 3 sedimentation is also known as zone sedimentation. In this process the

particles are at a high concentration (greater than 1000 mg/L) such that the particles

tend to settle as a mass and a distinct clear zone and sludge zone are present. Zone

settling occurs in lime-softening, sedimentation, active sludge sedimentation and

sludge thickeners.

filteration:

Filtration

From Wikipedia, the free encyclopedia

This article is about operation ofsolid-fluid separation. For the mathematical concept, see filtration

(mathematics). For the equipment used, see Filter (disambiguation). Forfiltration used in winemaking,

see Filtration (wine).


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Diagram of simple filtration: oversize particles in the feedcannot pass through the lattice

structure of the filter, while fluid and small particles pass through, becoming filtrate.

Filtration is commonly the 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). Filtration is also used to describe

some biological processes, especially in water treatment andsewage treatment in which undesirable

constituents are removed by adsorption into a biological film grown on or in the filter medium.

[edit]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 ofchemical 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.[1] 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. [2]

Filtration differs from adsorption, where it is not the physical size of particles that causes separation but the

effects ofsurface charge. Some adsorption devices containing activated charcoal and ion exchange

resin are commercially called filters, although filtration is not their principal function.[3]


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Filtration differs from removal ofmagnetic 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. [4]

The remainder of this article focuses primarily on liquid filtration.

[edit]Methods

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 orgas. 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.

[edit]Filter media

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 offilter paper(e.g. Bchner funnel, Belt filter, Rotary vacuum-

drum filter, Cross-flow 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 bybackwashing. Self-cleaning screen

filters utilize point-of-suction backwashing to clean the screen without interrupting system flow.

ChromatographyFrom Wikipedia, the free encyclopedia


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Pictured is a sophisticated gas chromatography system. This instrument records concentrations of acrylonitrile in the air at

various points throughout the chemical laboratory.

Chromatography (from Greek chroma "color" and graphein "to write") is the collective term for

a set oflaboratory techniquesfor the separation of mixtures. It involves passing a mixture dissolved in a "mobile

phase" through a stationaryphase, which separates theanalyte to be measured from other molecules in the

mixture based on differential partitioning between the mobile and stationary phases. Subtle differences in a

compound's partition coefficient result in differential retention on the stationary phase and thus changing the

separation.

Chromatography may be preparative or analytical. The purpose of preparative chromatography is to separate

the components of a mixture for further use (and is thus a form of purification). Analytical chromatography is

done normally with smaller amounts of material and is for measuring the relative proportions of analytes in a

mixture. The two are not mutually exclusive.

Chromatography terms

The analyte is the substance to be separated during chromatography.

Analytical chromatography is used to determine the existence and possibly also the concentration of

analyte(s) in a sample.

A bonded phase is a stationary phase that is covalently bonded to the support particles or to the inside

wall of the column tubing.

A chromatogram is the visual output of the chromatograph. In the case of an optimal separation, different

peaks or patterns on the chromatogram correspond to different components of the separated mixture.

Plotted on the x-axis is the retention time and plotted on the y-axis a signal (for example obtained by

a spectrophotometer, mass spectrometeror a variety of other detectors) corresponding to the

response created by the analytes exiting the system. In the case of an optimal system the signal is

proportional to the concentration of the specific analyte separated.

A chromatograph is equipment that enables a sophisticated separation e.g. gas

chromatographic or liquid chromatographic separation.

Chromatography is a physical method of separation in which the components to be separated

are distributed between two phases, one of which is stationary (stationary phase) while the

other (the mobile phase) moves in a definite direction.

The eluate is the mobile phase leaving the column.

The eluent is the solvent that will carry the analyte.


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An eluotropic series is a list of solvents ranked according to their eluting power.

An immobilized phase is a stationary phase which is immobilized on the support particles, or

on the inner wall of the column tubing.

The mobile phase is the phase which moves in a definite direction. It may be a liquid (LC and

CEC), a gas (GC), or a supercritical fluid (supercritical-fluid chromatography, SFC). The mobile

phase consists of the sample being separated/analyzed and the solvent that moves the sample

through the column. In the case ofHPLC the mobile phase consists of a non-polar solvent(s)

such as hexane in normal phase or polar solvents in reverse phase chromotagraphy and the

sample being separated. The mobile phase moves through the chromatography column (the

stationary phase) where the sample interacts with the stationary phase and is separated.

Preparative chromatography is used to purify sufficient quantities of a substance for further

use, rather than analysis.

The retention time is the characteristic time it takes for a particular analyte to pass through the

system (from the column inlet to the detector) under set conditions. See also:Kovats' retention

index

The sample is the matter analyzed in chromatography. It may consist of a single component or

it may be a mixture of components. When the sample is treated in the course of an analysis,

the phase or the phases containing the analytes of interest is/are referred to as the sample

whereas everything out of interest separated from the sample before or in the course of the

analysis is referred to as waste.

The solute refers to the sample components in partition chromatography.

The solvent refers to any substance capable of solubilizing other substance, and especially the

liquid mobile phase in LC.

The stationary phase is the substance which is fixed in place for the chromatography

procedure. Examples include the silica layer in thin layer chromatography

evaporation

Evaporation is a type ofvaporization of a liquid that occurs only on the surface of a liquid. The other type

of vaporization is boiling, which, instead, occurs on the entire mass of the liquid. Evaporation is also part

of the water cycle.

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.


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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 is 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 plantstomata) are collectively

termedevapotranspiration. Evaporation is caused when water is exposed to air and the liquid molecules

turn into water vapor, which rises up and forms clouds.

[edit]Theory

See also: Kinetic theory

Formolecules 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

highervapor pressure. For example, laundry on a clothes line will dry (by evaporation) more rapidly on awindy 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.


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Aerosol of microscopic water droplets suspended in the air above a hot tea cup after that water

vapor has sufficiently cooled and condensed. Water vaporbehaves like a gas and is, thus,

invisible, but the clouds of condensed water droplets refract and diffuse the sun light and so are

visible.

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