Adsorption isotherm--GOLD APP INSTRUMENTS

Adsorption isotherm

Adsorption isotherm is the relationship between the pressure and adsorption amount at a constant temperature. The horizontal axis is the relative pressure (P/P₀) which is the equilibrium pressure divided by the saturation pressure. The relative pressure can be 0 to 1 and P/P₀ =1.0 means that the condensation of adsorptive occurs in the sample cell. So an adsorption isotherm is the measurement of adsorptive density which becomes higher than the than the bulk (gas) phase density due to the interaction between the adsorptive and solid surface atoms below its condensation pressure. Adsorption amount in the vertical axis is commonly expressed as V/ml(STP)g^-1 which is expressed by the standard gas volume (at 0^oC and 1 atm).

The figure indicates the classification of adsorption isotherms defined by IUPAC. The type of adsorption isotherm is determined by the pore size and surface character of the material.

I : Microporous materials (e.g. Zeolite and Activated carbon)

II : Non porous materials (e.g. Nonporous Alumina and Silica)

III : Non porous materials and materials which have the weak interaction between the adsorbate and adsorbent (e.g. Graphite/water)

IV : Mesoporous materials (e.g. Mesoporous Alumina and Silica)

V : Porous materials and materials that have the weak interaction between the adsorbate and adsorbent (e.g. Activated carbon/water)

VI : Homogeneous surface materials (e.g. Graphite/Kr and NaCl/Kr)

 

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Adsorption and Absorption--Gold APP Instruments

Adsorption and Absorption

 

Absorption is the process in which a fluid is dissolved by a liquid or a solid (absorbent).

Adsorption is the process in which atoms, ions or molecules from a substance (it could be gas, liquid or dissolved solid) adhere to a surface of the adsorbent. Adsorption is a surface-based process where a film of adsorbate is created on the surface while absorption involves the entire volume of the absorbing substance.

 

Comparison Chart

Items	Absorption	Adsorption
Definition	Assimilation of molecular species throughout the bulk of the solid or liquid is termed as absorption.	Accumulation of the molecular species at the surface rather than in the bulk of the solid or liquid is termed as adsorption.
Phenomenon	It is a bulk phenomena	It is a surface phenomena.
Heat Exchange	Endothermic process	Exothermic process
Temperature	It is not affected by temperature	It is favored by low temperature
Rate of Reaction	It occurs at a uniform rate.	It steadily increases and reach to equilibrium
Concentration	It is same throughout the material.	Concentration on the surface of adsorbent is different from that in the bulk

 

Process

Gas-liquid absorption (a) and liquid-solid adsorption (b) mechanis.

Blue spheres are solute molecules

 

Adsorption and absorption are both sorption processes.

Absorption occurs when atoms pass through or enter a bulky material. During absorption, the molecules are entirely dissolved or diffused in the absorbent to form a solution. Once dissolved, the molecules cannot be separated easily from the absorbent.

Adsorption is generally classified into physisorption (weak van der Waal’s forces) and chemisorption. It may also occur due to electrostatic attraction. The molecules are held loosely on the surface of the adsorbent and can be easily removed.

 

 

Uses

 

Adsorption: Some of the industrial applications for adsorption are air-conditioning, adsorption chillers, synthetic resin and water purification. An adsorption chiller does not require moving parts and hence is quiet. In pharmaceutical industry applications, adsorption is used as a means to prolong neurological exposure to specific drugs or parts thereof. Adsorption of molecules onto polymer surfaces is used in various applications such as in the development of non-stick coatings and in various biomedical devices.

 

Absorption: The common commercial uses of absorption cycle are absorption chillers for space cooling applications, ice production, cold storage, turbine inlet cooling. High efficiency operation, environmentally friendly refrigerants, clean-burning fuels and few moving parts that require maintenance make absorption a very good choice for consumers. 

The process of gas absorption by a liquid is used in hydrogenation of oils and carbonation of beverages.

 

Video Link for comparison of adsorption and absorption http://v.youku.com/v_show/id_XNjIxNzAxOTc2.html

 

 

 

 

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Activated Carbon Can be Used for CH4 Storage and Transportation

 

Activated Carbon Can be Used for CH4 Storage and Transportation

 

Stored natural gas plays a vital role in ensuring that any excess supply delivered during the summer months is available to meet the increased demand of the winter months. However, with the recent trend towards natural gas fired electric generation, demand for natural gas during the summer months is now increasing (due to the demand for electricity to power air conditioners and the like). At the time, the natural gas industry noted that seasonal demand increases could not feasibly be met by pipeline delivery alone. Natural gas in storage also serves as insurance against any unforeseen accidents, political conflicts, natural disasters, or other occurrences that may affect the production or delivery of natural gas. In order to be able to meet seasonal demand increases, underground storage fields were the only option. Before the storage process, transportation takes places an important role. Scientists developed an option for gas storage and economical method for transportation of natural gas by the help of active carbon’s adsorption property. Via the high adsorption rate and capacity of activated carbon, the higher mole of methane, can be possible to store at low pressures by comparison with conventional methods.

 

Adsorption is the process by which molecules of a substance, such as a gas or a liquid, collect on the surface of another substance, such as a solid. The molecules are attracted to the surface but do not enter the solid's minute spaces as in absorption.

 

Activated carbon is a form of carbon processed to be riddled with small, low-volume pores that increase the surface area available for adsorption or chemical reactions. Activated carbon is a carbonaceous adsorbent with a high internal porosity, and hence a large internal surface area. Commercial activated carbon grades have an internal surface area of 500 up to 1500 m2/g. People studied the feasibility of storing CH4 in an abandoned coal mine and transportation of CH4 by tankers in adsorbed state using activated carbon as medium. It can be concluded that active carbon can be used for safe storage and transportation of methane as an alternative to conventional methods.

 

Now, we need to use good performance active carbons that help people to transport as much CH4 as possible in one time. Problem is how to know that very active carbon is suitable for us. Under this situation, we need one instrument to help us, to analysis that active carbon adsorption performance, and that instrument is HIGH PRESSURE GAS SORPTION ANALYZER.

 

We, Gold APP Instruments, had researched and produced high pressure gas sorption analyzer H-Sorb 2600 series by static volumetric principle. Capable of testing nanomaterials adsorption and desorption performance, PCT (pressure composition temperature) or PCI (pressure composition isotherm) curves. H-Sorb 2600 series with 2 analysis ports and 2 degassing ports, fully automated operation, supports night operation without operators watch, longest supporting test time can be last as long as half month (can be upgrade), all-featured data reports can help researchers to get all analysis details they want.

 

Gold APP Instruments China is a professional manufacturer for analytical and research instruments, such as BET surface area analyzers, surface area and porosity analyzers, helium true density analyzers, high pressure gas sorption analyzers and so on, to determine nanomaterials specific surface area, pore size, pore volume, pore size distribution, true density, open and closed spaces, adsorption/desorption isotherms, pressure-composition-isotherm, pressure-composition-temperature curve and so on.

 

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