Protecting the Ozone Layer & Bystanders by Destroying Fumigant Emissions.

 

 

 

 

 

 

 

 

 

 

 

Our proprietary scrubbing system chemically destroys methyl bromide vented from Quarantine & Pre-shipment (Q/PS) fumigation enclosures of up to 300,000 cubic feet (8,500 cubic meters) without delaying the aeration cycle or velocity of fumigated products as they pass from the fumigation chamber into the distribution chain.

 

Process Description

Step 1:  Aeration with Carbon Adsorption

For very large volume fumigations Value Recovery, Inc has developed a two-stage system to destroy methyl bromide present in ventilation air stream.  Air is ventilated from the enclosure using large fans that pull fresh air under suction into the enclosure and "sweep" the air containing methyl bromide into the outlet stream. This methyl bromide laden air stream is then passed over a large carbon bed where the methyl bromide is adsorbed or trapped onto carbon particles. The ventilation rates meet and exceed APHIS standards (minimum of 4 air turnovers per hour) and thus do not influence the time it takes to aerate the fumigated goods. The length of time for the ventilation is fixed by USDA protocols to ensure that all of the methyl bromide is desorbed from the fumigated goods.

Step 2:  Desorption from Carbon Bed into Scrubber

After the aeration step, the methyl bromide is driven off the carbon using a relatively small volume of fresh warm air and introduced into the scrubber where the methyl bromide is chemically destroyed.  The air is warm enough to re-generate the carbon for the next aeration cycle and thus the carbon bed is used over and over again making this a very economical process.  The design allows for the carbon bed to be re-generated and used every 24 hours.  The scrubber efficiency is guaranteed to be greater than 90% for large industrial systems and can be made to go above 99% for smaller ones.

Process Chemistry

The methyl bromide (MB) is destroyed chemically by breaking the air stream containing MB down into fine bubbles to allow the MB to easily contact the liquid scrubber solution.  The liquid solution contains sodium thiosulfate (potassium and ammonium analogs also work) and the MB reacts (and is thus destroyed) quickly with it to make sodium methyl thiosulfate and sodium bromide as shown below. 

 

The scrubber solution is a clear aqueous solution with no particulate. The carbon-halogen (carbon-bromine) bond within methyl bromide is broken in a fast nucleophillic substitution reaction that produces no hazardous byproducts.  Finely dispersed air bubbles provide enought contact area with the surrounding liquid to allow for significant gas-liquid mass transfer of the methyl bromide to the aqueous phase where the reaction takes place.

Non Hazardous Byproducts

The spent scrubber solution has passed the California "fish test" [(Chapter 11, Article 3, Title 22 Section 66261,24(a)(6)].  This test showed a 100% survival of rainbow trout over all three concentrations tested over 4 days.

Summary

In essence, our technology takes advantage of methyl bromide's exceptional reactivity, and uses this reactivity as the strategy for destroying methyl bromide after fumigation and irreversibly converting it into a benign and thus safe chemical species.

 

Note:  Value Recovery does not use the the colloquialism known as 'recapture'.    Unfortunately, this rudimentary term has gained wide acceptance due to the advocacy of a non-scientific standard.  The standards we advocate are based on the chemical industry and thus "emissions controls" is the proper representation for this process since the process is analagous to pollution control strategies and devices found in oil refineries, chemical plants and catalytic converters on automobiles.