Adsorption & Absorption of Toxic Gases

ADSORPTION AND ABSORPTION OF EXHAUST GASES FROM VEHICLES

Rinkesh.A.Bafna, Kushal.A.Khanderia, Asst.Prof. N.Anandakumar

Abstract— As India is developing in a faster rate the need for vehicles has tremendously increased. In this scenario, we strongly need an efficient way to control the increasing air pollution led by the exhaust gases from the vehicles. These exhaust gases contains carbon monoxide (CO) and hydrocarbons in high proportions which adversely increases the Global Warming and Green House Effect. The goal of this paper is to introduce a method which adsorbs the hydrocarbons and absorbs carbon monoxide led by the vehicles thereby controlling the Global Warming and Green House Effect. The absorption of carbon monoxide is done by using cuprous salt and adsorption of hydrocarbons is done by using a complex nanomaterial. i.e., Carbon Monolithic Aero gels. Using cuprous salt for absorption of carbon monoxide is no more an innovative idea. But in today’s world of Nano Technology usage of Aero gels (Nanomaterial) to adsorb Hydrocarbons needs a major concern. So in this paper we highlight the production, usage and regeneration of Carbon Monolithic Aero gels.

Keyword -. BTX -Benzene, Toluene and Xylene compounds.

INTRODUCTION

|Pollutant |Pollution load (in ton/day) |
|Carbon monoxide |421.84 |
|Hydrocarbons |184.37 |
|Nitrogen oxides |110.45 |
|Particulate Mater |12.77 |
|Total Pollution Load |729.43 |

Composition of exhaust gases produced by the vehicles
The material which adsorbs Hydrocarbons is a Monolithic Carbon Aero gel with the advantage of not only being able to retain Hydrocarbons but it can also be easily regenerated and therefore can be used in several cycles. The study of the elimination of volatile organic compounds from anthropogenic sources – road traffic in cities, solvents, industry, etc. – such as BTX is very important as these substances are highly pollutant. In order to eliminate these pollutants, it is necessary to use materials with a high concentration of micro pores, which is where the absorption of pollutants takes place, but these pores must be the correct size and properly arranged. Thus, we achieve a high level of efficiency when eliminating and retrieving BTX after the saturation of the material.
Furthermore, the design of the adsorbent bed must allow a sufficient contact for the elimination of compounds and at the same time avoid a decrease in pressure. Finally, the material used must withstand the mechanical forces of vibration and movement. The monolithic carbon aero gels, which are the materials we worked with, satisfy all these requirements.

PRODUCTION OF AEROGELS

Production of Aero gels is done by sol-gel process. First a gel is created in the solution and then the liquid is carefully removed to leave the aero gel intact. The first step is the creation of the colloidal solution of solid particles known as “sol”. Carbon Aero gel is made by the creation of colloidal carbon. The process starts with a liquid alcohol like ethanol, which is mixed with a silicon alkoxide precursor, for example tetramethyl orthocarbonte (TMOS) or tetraethyl orthocarbonte (TEOS).A hydrolysis reaction forms particles of silicon dioxide forming a salt solution. The oxide suspension begins to undergo condensation reaction which results in creation of metal oxide bridges linking the dispersed colloidal particles.
When this interlinking has stopped the flow of liquid within the material, this is known as gel. This process is known as gelatins. These reactions generally have moderately slow reacting rates, and as a result either acidic or basic catalyst are used to improve the processing speed. Basic catalysts tend to produce more transparent with less shrinkage.

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The removal of the liquid from a true aero gel involves special processing. Gels where the liquid is allowed to evaporate normally are known as Xerogels. As the liquid evaporates, the forces caused by surface tensions of the liquid-solid interfaces are enough to destroy the fragile gel network. As a result xerogels cannot achieve the high porosities and instead peak at lower porosities and exhibit large amount of shrinkage after drying.
By increasing the temperature and pressure the liquid is forced into a supercritical fluid state where by dropping the pressure it could instantly gasify and remove the liquid inside the Aero gel, avoiding damage to delicate three-dimensional network. While this can be done with ethanol, the high temperatures and pressures lead to dangerous processing conditions. A safer, lower temperature and pressure method involves a solvent exchange. This is typically done by exchanging ethanol for liquid acetone, allowing a better miscibility gradient, and then onto liquid carbon dioxide and then bringing the carbon dioxide above its critical point. A variant on this process involves the direct injection of supercritical carbon dioxide into the pressure vessel containing the aero gel. The end result of either process removes all liquid from the gel and replaces it with gas, without allowing the gel structure to collapse or lose volume.
Aero gel composites have been made using a variety of continuous and discontinuous reinforcements. The high aspect ratio of fibers such as fiber glass has been used to reinforce aero gel composites with significantly improved mechanical properties.
Resorcinol-Formaldehyde aero gel (RF Aero gel) is made in a way similar to production to carbon aero gel.
Carbon aero gel is made from a resorcinol formaldehyde aero gel by its pyrolysis in inert gas atmosphere, leaving a matrix of carbon. It is commercially available as solid shapes, powder or composite paper.

CHARACTERISTICS OF AEROGELS

1 Properties

The below given table shows various properties of aero gels
|Density (g/cm3) |0.6 |
|Dielectric Constant (n/d) |18-40Ghz |
|Surface Area, BET (m2/g) |400- 1,200 |
|Compressive Modulus (MPa) |3,000 |
|CTE (ppm/C°) |20 - 80°C |
|Electrical Resistivity (ohm-cm) |0.05 |
|Thermal Conductivity (W/m/°K) |0.4 |
|Colour |Colourless |
|Condition |Microporous |

2 Advantages

The proposed scheme has the following advantages; 1. Carbon Aero gels resist heat to great extent as they are very good thermal insulators.

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2. They are microcellular foam material which is low in density and have an area-to-mass of 400-1000m2/g. 3. They exist in covalent bond with 3-dimensional network and are Hygroscopic in nature. 4. The Tensile strength is very high.

[pic] A 2.5 kg brick is supported by a Piece of carbon aero gel weighing only 2 grams.

5. These materials have high porosity (>50%) pores that are less than 100nm. 6. This monolithic structure leads to very high surface area (400-1100m2/g). 7. These monolithic structure leads to very high electrical conductivity (25-100S/cm). The aero gel chemical composition, microstructure, and physical properties can be controlled at the nanometer scale, giving rise to unique optical, thermal, acoustic, mechanical and electrical properties diameters.

REGENERATION

Adsorption capacity measurements show that such modified hydrophobic silica aero gels are excellent adsorbents for different toxic organic compounds from water. In comparison to granulated active carbon (GAC) they exhibit capacities which are from 15-400 times higher for all tested compounds. Adsorption properties of hydrophobic silica aero gel remain stable even after 20 adsorption/desorption cycles. Self indicating silica gels when become saturated can be regenerated by heating at 100-120oC until they return to their original colours. The heating literally drives off the adsorbed moisture. Regeneration can be carried out repeatedly, although eventually the crystals will lose their colour. When regenerating self indicating silica gel sachets, only the minimum necessary heat can be used. This will prevent the sachet material from deteriorating. Although non-indicating silica gel can be regenerated in exactly the same way, it is not apparent when the silica gel is regenerated other than by checking its weight-it will return to its original dry weight when completely regenerated.
This regeneration process comprises of 5 main steps, namely, washing with an extract of organic compounds and removing volatile organic materials remaining thereafter,
Oxidation to oxidize organic compounds remaining and, preferably, bleach the material;
Washing with an acid to remove soluble inorganic matter;
Heating to dry the material and combust any remaining organic compounds present: and recovering the regenerated material.

CONCLUSION

The proposed system is simple and easy for implementation, but it is secure to its production in large scale as Nanotechnology is still developing globally. Yet this substance is quite economical Eco-friendly and can easily be regenerated. Aero gels have high tensile strength, high thermal insulating property, high tendency to adsorb Hydrocarbons and can easily be regenerated. All these properties pave a way to its implementation in daily life.

References

1] HTTP://WWW/ASPENAEMAKING CARBON AEROGELS.LAWRENCE BERKELEY NATIONAL LABORATORY 2] Http://www.eetd.lbl.gov./ECS/Aerogels/sa-making.html. 3] Http://www.Rogels.com/products/pdf/Cryogel 4] NASA Photos of aero gel 5] Http://www.Aspenaerogels.com

References: 1] HTTP://WWW/ASPENAEMAKING CARBON AEROGELS.LAWRENCE BERKELEY NATIONAL LABORATORY 2] Http://www.eetd.lbl.gov./ECS/Aerogels/sa-making.html. 3] Http://www.Rogels.com/products/pdf/Cryogel 4] NASA Photos of aero gel 5] Http://www.Aspenaerogels.com