What is a VOC?

• VOC stands for Volatile Organic Compound
• Volatile chemicals produce vapors at room temperature
• Organic is a chemical containing carbon molecules
• Volatile Organic Compounds included industrial chemicals, solvents, alcohols, and even gasoline
• VOCs combine with sunlight to form atmospheric ozone, or smog

What is Zeolite?

Zeolite is a naturally occurring mineral, in crystal form, found in volcanic rocks and sedimentary formations of ancient sea beds.  Natural zeolite is made of  hydrous aluminum silicates of sodium, calcium, potassium or barium. Over 40 types of zeolite are found naturally occurring in nature, each having a unique chemical composition and crystalline structure.

Natural zeolite is hydrophilic (water loving) and readily adsorbs and desorbs water.  Natural zeolites can be used for ion exchange and water softening.  Synthetic zeolites have been developed for commercial applications.  Over 70 types of synthetic zeolites have been created.

Hydrophobic zeolite is an inorganic crystal with properties suited to adsorbing VOCs.  Hydrophobic zeolite is a stable crystal.  The zeolite’s inert properties mean that it does not promote chemical reactions.  It is also non-flammable to extreme temperatures and will not react with strong acids.  
 

How Do Zeolites Work?

The basic structure of a zeolite is a tetrahedra or pyramid formed by silicon dioxides (SiO2) The tetrahedra have one silicon atom in the center and oxygen at each of the corners.

Zeolites are linked by sharing the oxygen atom.  Linked zeolites form pores.  The size of the pores is determined by the number of zeolite molecules that are joined together.  As a crystal the zeolite has a set structure, therefore each type of zeolite has a distinct arrangement of zeolite molecules.  As each type of zeolite is unique each pore size is unique. 

The size of the organic compound determines which zeolite pore size is best suited for adsorption.  Munters Zeol uses a mixture of hydrophobic zeolites with different pore sizes.  This mixture allows a wide range of organic solvents to be adsorbed.  Most commercially available solvents are adsorbed by our hydrophobic zeolites.

A VOC is attracted and held in the zeolite pore by a weak attractive force.  (This is a weak physical attractive force between chemically neutral compounds.)  The VOC will remain in the pore until energy (e.g. heat) is applied.  The heat overcomes the attractive force and the VOC breaks free from the zeolite and is released into the air.

When VOC laden air flows past zeolite molecules, the zeolite acts as a reverse filter or molecular sieve, capturing the compounds which will adsorb and allowing the compounds that are too large to flow past.

Zeolite and the HoneyCombe® Rotor

Munters Zeol combined the hydrophobic zeolite technology with its HoneyCombe® rotor technology.  A system was created that can operate continuously with constant adsorption and desorption, has a low pressure drop, and maximized the surface area.  One square foot of HoneyCombe® media has a surface area of 492,480 ft2 ( 45,753 m2).

HoneyCombe® rotors were developed over 40 years ago by Munters.  Munters is the world’s leading supplier of process systems using HoneyCombe® rotors for dehumidification, heat exchange, and VOC abatement. Munters’ HoneyCombe® rotors have numerous benefits.  Rotors allow for high air flow, truly continuous operation.  With a low pressure drop rotors have stable outlet conditions.  The hydrophobic zeolite is permanently bonded with the HoneyCombe® rotor therefore no attrition of the zeolite occurs. 

Munters HoneyCombe® rotors are manufactured at the ISO 9001 certified facility in Amesbury, Massachusetts.  The rotors are manufactured from a corrugated mineral fiber substrate permanently bonded with a proprietary mixture of hydrophobic zeolite and inorganic materials.  The hydrophobic zeolite rotor is inorganic, completely inert and has rigidity, physical integrity and the ability to withstand thermal stress.  The permanently bonded hydrophobic zeolite is an integral part of the HoneyCombe® matrix and will not be leached out or removed physically or chemically.

How a Munters Zeol Rotor Concentrator Works

As a low concentration VOC laden air stream enters the hydrophobic Zeolite HoneyCombe® rotor the air passes through the HoneyCombe® media.  The rotor turns several revolutions per hour continuously transporting VOC laden zeolite back into the regeneration sector and regenerated zeolite into the process section.  In the process section the VOCs are adsorbed onto the zeolite and the clean air is exhausted to the atmosphere.

In an isolated section, a small, hot stream of clean air is drawn through the rotor.  This stream is normally only 5–10% of the process volume.  The hot air desorbs the VOCs from the zeolite forming a concentrated VOC laden air stream.  The regenerated zeolite is returned to the process.

The concentrated stream is sent to a small oxidizer.  The oxidizer converts the VOCs to carbon dioxide and water vapor which are exhausted to the atmosphere. 

The energy content of the VOCs contributes to the oxidation process further reducing the fuel requirement.

The concentrated VOC stream can also be sent to alternate technologies, such as a condenser which recovers the VOCs for potential reuse, or a biofilter.