Notes on DCM;
Any stripper with DCM (Methylene Chloride), will work. The best brand to use is by far the most common brand. Something to do with music,…”Jazz company” or something like that.
The thicker “paste”, types need to be mixed with equal volume of H20. And they are frankly kind of a pain in the ass. There is a new type that is a liquid stripper. It is the most desirable and contains in excess of 50% DCM.
See below for procedures. First we need to know some things;
1.1 1.1 What is Dichloromethane
Dichloromethane (DCM) is a colorless non-flammable liquid. It does not occur naturally and is produced in high amounts by chemical companies. DCM was introduced as a solvent over 60 years ago to replace more flammable alternatives. Due to its high toxicity, recommendations have been issued by the US Environmental Protection Agency (EPA) to reduce its production. Luckily most producers of this chemical have complied and the production of this chemical has been continuously reduced in the past years.
Though it is biodegradable in soil, it is not readily absorbed in soil, and either volatilizes into the air or sinks through the soil, into the ground water table. Exposure to this substance has been shown to result in ill health. As a result it is a dangerous substance to be dealt with and should be slowly moved out of the industry.
DCM is chiefly used an active ingredient in paint removers (30%), both for consumers and the industry, where it can be present in concentrations of up to 80% [US Environmental Protection Agency (EPA)]. Other common uses today are: adhesives (16%), aerosol and coating (11%), foam manufacture (10%), chemical processing (9%) and metal cleaning (8%) [Halogenated Solvent Alliance, Inc.]. It is also used in chemical processing, where, among other uses, it is used to extract unwanted substances from foodstuff. It is very efficient, organic, liquid and inflammable. These qualities and applications have made this substance a favourite among chemical companies. It can be produced in large quantities, and once acquired it can be applied to various needs.
1.2 Facts and Figures
[ The following information is from the EPA ]
CAS No. 75-09-2
Common Synonyms MC, dichloromethane,
DCM, methylene bichloride,
methylene dichloride
Molecular Formula CH2Cl2
Chemical Structure
Physical State colorless liquid
Molecular Weight 84.94g
Melting Point -958C at 101.3 Pa
Boiling Point 39.758C at 101.3 Pa (
that’s 103.5 in FWater Solubility 1.32 x 104 mg/L at 208C
Density 1.3255 g/mL
Vapor Density (air = 1) 2.93
Flash Point Nonflammable
Odor Threshold 214 ppm (in air)
Conversion Factors 1 ppm = 3.48 mg/m3;
1 mg/m3 = 0.288 ppm
2. Industrial Processes
DCM does not occur naturally and is produced in large amounts by two main chemical companies in North America: Dow Chemicals, Occidental Chemicals and Vulcan chemical.
DCM and tri-chloromethane (TCM) are simultaneously produced at the same facilities, since the production of DCM produces TCM in reasonable large amounts. When producing DCM it is important to maintain a high percent of excess methane in proportion to the chlorine to achieve optimal yield and to avoid unwanted temperature fluctuations. The high excess of methane (CH4) also minimizes the concentration of un-reacted chlorine in the finished process. In addition a very high level of purity with respect to CH4 has to be observed. Much CH4 is acquired from secondary processes in other chemical facilities as well distillation of natural gas using the Linde process.
2.1 The Hoechst Process for DCM
The Hoechst’s process, introduced in 1923, is still the most common method used today with the mere addition of new technology but without any modifications of the actual process. CH4 gas and monochlormethane (MCM, recycled from the previous reaction) is brought into contact with chlorine (Cl2) gas and both gases are pushed into a reactor in which constant gas circulation is sustained. The reactor temperature is maintained at 350 – 450 8C (by proper choice of Cl2 – CH4 /MCM ratio) and the reaction is conducted adiabatically. The fully reacted mixture and the resulting hydrogen chloride is then cooled and washed out with dilute hydrochloric acid in the form 31% hydrochloric acid. Finally the last traces of HCl(aq) are washed away by the use sodium hydroxide and the products are largely compressed, dried, cooled, and allowed to condense. Methane and gaseous MCM are recycled. The liquid is distilled by high pressure into its principal components – MCM, DCM, TCM and Tetrachloromethane (TetraCM). This process delivers generally about 70% DCM by weight. Most of the remainder is TCM with some MCM and trace amounts of TetraCM.
3. Biodegradation Pathway
As mentioned above, DCM is very volatile and hence does not stay in surface waters very long. Degradation therefore occurs in the atmosphere. Aerobic and anaerobic methylotrophic bacteria (methylotrophic microorganisms are bacteria and fungi which are growing on carbon compounds which are more reduced than CO2 (i.e. have less oxygen), [Heinrich Klein, Brunel University, Britain]) utilize DCM as an energy and cabon source. This transforms DCM into inorganic chloride and formaldehyde (University of Michigan Biocatalysis/Biodegradation Database). These bacteria use dichloromethane dehalogenase as an enzyme to catalyze DCM. Inorganic chloride is not biodegradable and formaldehyde is a major metabolite in the growth process of methylotrophic bacteria. Below is a graphical depiction of the first process. Methylophilus sp. DM11, Pseudomonas sp. , Hyphomicrobium sp. DM2, and Methylobacterium sp. DM4 are the organisms that initiate the above described process.
4. Envioronmental effects
DCM enters surface water streams from industrial effluents and can reach groundwater through underground injection and through soil. Dichloromethane occurs in soil due to landfills in which dichloromethane containers have been deposited. It occurs in the air through evaporation from surface waters, surface soils and from evaporation during use. Air is inhaled by humans and animals, and surface water is directly used by animals
Environmental studies have shown that dichloromethane is highly toxic to humans and animals. In air it has a half life of approximately 130days [EPA], which is a long time when considering the quickness with which DCM works. When inhaled it has harmful effects on the internal systems of animals and humans. It would do harm to the ozone layer, but it usually undergoes reaction with hydroxyl radicals to form a substance less harmful to the ozone layer and then continuous its breakdown into other chemicals. In soil it could biodegrades slowly, but this sort of biodegradation in soil or subsurface soil only occurs in landfill sides where there are a substantial amount of microbial populations (i.e. methylotrphic). Generally its high volatility forces it to enter the atmosphere. Otherwise it sinks through the soil all the way to the groundwater. It is as volatile in water as it is in soil, but since the groundwater table does not have a layer of air on top, it remains in ground water. In water it hydrolyzes slowly, with a half-life of about 18 months [EPA].
4.1 Effects on humans
DCM is also very harmful before it is treated as a waste material. As mentioned above it volatilizes readily into the atmosphere. Hence, workers who use dichloromethane will inevitably inhale air contaminated with DCM. Since it usually occurs in high concentrations, and has a high vapour pressure, it poses imminent health risks to all users.
.
DCM is readily absorbed by the lungs and gastrointestinal tract. Some skin absorption is also existent. DCM, once absorbed, travels to the liver, kidney, lungs, brains and muscles within one hour after inhalation according to animal studies reported by the Agency for Toxic Substances and Disease Registry [ATSDR]. The ATSDR further reports that within 48hrs dichloromethane expands its spreading to the testes and the epididymal fat.
In all known cases, exposure to DCM has been shown to affect the nervous system and internal organs in a negative way. It has been reported that direct contact has led to burns, and over exposure has led to worker death [EPA]. The Registry of Toxic effect of Chemical Substances [RTECS] reports that the lowest lethal dose for direct exposure is 357mg/kg, which translates roughly to 720ppm.
DCM metabolizes to carbon monoxide in humans, which in turn results in the formation of carboxylhemoglobin (COHb). COHb deprives the body of oxygen. Dichloromethane, while permanently damaging the human body by oxygen deprivation, leaves the subject initially in a state of euphoria, like a drug. Once the concentration of COHb increases, the subject experiences “psychomotor effects” (e.g. time – interval discrimination) and cardiovascular changes.
4.2 Effects on animals
Like most chemicals this substance was tested on animals to verify human reactions. Wild animals are not as exposed to this chemical as much as humans, as there are not many uses outside the urban setting. Nonetheless, groundwater and river water can lead to harmful digestion. Luckily most animals have a keener sense of smell and avoid liquid containing DCM. Animal studies in rats have resulted in liver damage and kidney damage after acute exposure (5-6hrs). After chronic exposure the same organs become the target (2yrs) [RTECS]. It also metabolizes to CO, resulting again COHb.
5. Conclusion
All studies have shown that dichloromethane is a dangerous substance to the environment not only as a waste product, but also during usage. Every worker who handles DCM endangers his health permanently. It is therefore necessary that strict laws be set in place. DCM should be moved out of the industry and replaced by less hazardous materials even at the loss of efficiency and profit. The extreme toxicity of DCM does not allow a truly save maximum contamination limit. Any maximum contamination limit can be broken by careless storage or accidents. DCM works fast. Before anyone knows what exactly had been spilled, workers can be exposed to lethal amounts of DCM. Deaths and illnesses are hardly worth profit and efficiency, especially in a legal system that allows workers’ families to sue anybody that can be held responsible. DCM should therefore be discontinued for both, hidden economical reason and apparent environmental reasons.
Doing a bit more research we will find the BP’S of some other potential chemicals;
DCM 39.75 degrees C (103.5 in F)
Methanol 64.7 degrees C (148.46 degrees F.)
Toulene 111 degrees C (231 degrees F).
Notice the unusually low BP of DCM. The key to a good distillation is keeping a very low temp. It can be distilled out of the can quite easily. A rubber stopper can be used. (DCM attacks polys and synthetics) Rubber stoppers are partly synthetic, but mostly organic. They will soften and degrade but only very slightly. A #6 stopper is what you’re after. Copper tube, works, as well as any other metal. S/D, then goes into his condenser with another rubber stopper. Any ghetto setup will work as well, as long as one doesn't use any poly or synthetic materials. If you can’t locate the correct rubber stopper then, use rubber tape, found in the electrical dept. of your local hardware store.
DCM , is very slightly soluble in H20, upon distillation it will have a cloudy appearance. Let it stand and it will clear in a few hours. To make sure it’s moisture free, pour it through a thick layer of absorbent material, filters or paper towel, works well.
Store in airtight container.
Other notes; make sure that you add a bit of H20 to your receiving flask to keep your evaporation rate, down.
S/D has been using this method for several months and will tell you that it’s tried and true to produce reasonably pure, anhydrous DCM.For handling chemical resitant gloves, or Nitril disposable are needed.
S/D from a Gallon of liquid stripper is yielding a half gal DCM
http://chem200e.tripod.com/dcm.html
http://www.worldwidemetric.com/metcal.htm
