Photo Ionization Detector

8/7/2019 Photo Ionization Detector

1/25

THAKKAR AKASH M.

080280117 045

6TH

I .C.

PHOTO IONIZATIONDETECTOR


2/25

CONTENTS:

y What is a detector?

y Types of detectors

y Photo Ionization

y Why to use a PID?y Construction of PID

y Principle & Working

y Features

y Characteristics

y Applications

y Limitations

y Conclusion


3/25

What is a Detector?

yA gas detector is a device which detects thepresence of various gases within an area, usuallyas part of a safety system.

y It is used to detect a gas leak and interface with acontrol system so a process can be automaticallyshut down.

y

A gas detector can also sound an alarm tooperators in the area where the leak is occurring.

y Gas detectors can be used to detect combustible,flammable and toxic gases and oxygen depletion.


4/25

Types of Detectors:

y Thermal Conductivity Detector

y Flame Ionization Detector

y Photo Ionization Detector

y Helium Ionization Detector

y Electron Capture Detector

y Flame Photometric Detector

y

Ultrasonic Detectory Catalytic Detector

y Semiconductor Detector


5/25

What is Photo-Ionization?

y Photo ionization is the physical process in which anincident photon ejects one or more electrons from anatom, ion or molecule.

y The ejected electrons, known as photoelectrons, carry

information about their pre-ionized states.

i.e:

Where mv2

/2 = K.E. of free electron, 13.6 eV is the binding energy of an electron,h

is Planck'sconstant and is the frequency of the photon.

y This formula defines the photoelectric effect.


6/25

PHOTOIONIZATION:


7/25

Why to use a PID?

y PID's are primarily screening devices.

y They will detect any VOC.

y Simply put, a PID tells you that something is there,

never what it is (besides that it is a voc), and onlysometimes how much.

y VOCs are typically not acutely toxic but have chroniceffects.

y Because the concentrations are usually low and thesymptoms slow to develop, analysis of VOCs andtheir effects is a demanding area.


8/25

PID Technology

y Technology uses an ultraviolet (UV) lamp toionize any contaminants in the air.

yWhen contaminant particles become ionized,they carry an electrical charge which can beread.

y Gas that is sampled must have ionization

potential (IP) less than that of the UV bulb.


9/25

Construction

y The PID is comprised of an ultraviolet lamp (which isthe heart of a PID) that emits photons.

y Ions produced during this process are collected by

electrodes.y The current generated provides a measure of the

analyte concentration.

y Because only a small fraction of the analytemolecules are actually ionized, this method isconsidered nondestructive, allowing it to be used inconjunction with another detector to confirmanalytical results.


10/25

Construction Diagram:


11/25

Different models of PIDs:


12/25

Principle & Working: (1/2)

y A PID is an ion detector which uses high-energyphotons, typically in the ultraviolet (UV) range, to

break molecules into positively charged ions.

y As compounds emerge from the GC's column they arebombarded by high-energy photons and are ionizedwhen molecules absorb high energy UV light.

y UV light excites the molecules, resulting in temporary

loss of electrons in the molecules and the formation ofpositively charged ions.


13/25

(2/2)

y The gas becomes electrically charged and the ionsproduce an electric current, which is the signaloutput of the detector.

y The greater the concentration of the component, themore ions are produced, and the greater the current.

y The current is amplified and displayed on anammeter.

y The ions recombine after passing the detector toreform their original molecules.


14/25

Working Diagram:


15/25

What Does a PID Measure? (1 of 2)

8.4

9.24

9.54

9.99

10.1

10.5

10.6611.32

11.41

12.1

14.01

0 10.6

Styrene

Benzene

MEK

Vinyl Chloride

IPA

Ethylene

Acetic acidMethylene Chloride

Carbon tetrachloride

Oxygen

Carbon monoxide


16/25

What Does a PID Measure? (2 of 2)

y Organic: Aromatics

Benzene

Ethyl benzene

Toluene

Xylene Ketones & aldehydes

Acetone

MEK

Acetaldehyde

Amines & amides

Diethyl amine Chlorinated

hydrocarbons Trichloroethylene (TCE)

Sulfurcompounds Mercaptans

Carbon disulfide

Unsaturatedhydrocarbons Butadiene

Isobutylene

Alcohols Ethanol

Saturated hydrocarbons Butane

Octane

y Inorganic Ammonia

Arsine


17/25

What PIDs Do Not Measure

y Radiation

y Air Nitrogen

Oxygen

Carbon monoxide

Water vapor

y Toxics Carbon monoxide

Hydrogen cyanide Sulfur dioxide

y Natural gas

Methane

Ethane

y

Acids Hydrochloric acid

Hydrofluoric acid

Nitric acid

y

Others Freon

Ozone


18/25

Calibration of PIDs:

y PIDs are typically calibrated with isobutylene asthis gas is stable, easy to handle and can be stored athigh pressure, allowing calibration bottles to provide

many calibrations.y Also the responsiveness of isobutylene is about at the

mid-point in the range of sensitivity of PIDs.

y Readings for other gases are obtained by multiplying

the reading by a correction factor.


19/25

Examples of CF:

y Benzene = 0.53

y Toluene = 0.5

y Acetone = 1.1

y Nitrobenzene = 1.9

y Diesel fuel = 0.7


20/25

CF Example: Toluene

y Toluene CF with 10.6eV lamp is 0.5

If PID calibrated to isobutylene reads 100 ppm in aToluene atmosphere, then the actual concentration is

50 ppm Toluene units.0.5 x 100 ppm= 50 ppm


21/25

Typical Specifications:


22/25

Advantages and Applications: (1/2)

y The photoionizaton detector is the most efficient andinexpensive type of gas detector.

y They are capable of giving instantaneous readings and

monitoring continuously.y They are widely used in military, industrial, and

confined working facilities for safety.

y PIDs are non-destructive detectors. They do not

destroy/consume the components they detect.Therefore they can be used before other detectors inmultiple-detector configurations.


23/25

(2/2)

y Nonspecific gas and vapor detection for organics andsome inorganic

y Sensitivity is related to the ionization potential of

compoundy Portable with remote sensing capabilities

y Response time of 90% in less than 3 seconds

y Sensitivity from 0.1 - 2,000 PPM

y Part per billion unit available

y More sensitive to aromatic and unsaturatedcompounds than the FID.


24/25

Disadvantages:

Will not indicate what materials are present

Does not monitor for specific gases or vapors

Cannot detect Hydrogen cyanide or methane

Cannot detect some chlorinated organics

High humidity and precipitate will negatively affectmeter response

Photo ionization detectors are calibrated to a singlechemical

UV lamps are expensive.


25/25

Q & A

Date post:	08-Apr-2018
Category:	Documents
Upload:	akash127
View:	223 times
Download:	0 times

Photo Ionization Detector

Documents