Lube-Tech PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
strongly reduces the duration of the preservation period of the fluids.
BIT (1,2-benzisothiazolin-2-one): BIT based biocides are also used in many MWFs. They are considered because of better stability at high pH and temperature and ease of formulation. They constitutes a sustainable formaldehyde-free option. There are some challenges with BIT chemistry too. They are less effective against Pseudomonas species which are common in the Indian environment. Also, BIT are reported to display an efficacy gap against Mycobacterium species. BIT gets rapidly deactivated if the contaminated sump has SRB actively growing in it.
Oxazolidine and OIT
The combination of oxazolidines (4,4 dimethyl oxazolidine, Ethyldihydro-1H,3H,5H-oxazolo[3,4-c]oxazole) along with OIT (2-n-octyl-4-isothiazolin-2-one) has been found to be performing well in India and is increasing in popularity. Oxazolidines are highly active against bacteria. it is effective against SRBs and Pseudomonas species and having some efficacy against Mycobacterium species as well. Oxazolidines also have pH buffering capacity and are high pH and temperature stable. Oxazolidines also remain unaffected in the presence of low levels of sulphides. OIT is a very effective antifungal molecule. It is stable in alkaline MWF systems. When used in combination, OIT and oxazolidine, it provides a strongly extended sump life in typical Indian conditions.
Morpholines:
Morpholines (4-(2-nitrobutyl)morpholine, 4,4’-(2-ethyl-2- nitrotrimethylene)dimorpholine) are commonly used in MWF concentrates because they are very stable in MWF formulations. Morpholine constitutes a formaldehyde free option for the protection against wide range of bacteria, fungi and against Mycobacterium species under typical MWF use conditions. There are few problems associated with morpholine based biocides which includes odour, lachrymation, and possible skin sensitization. It may also react with nitrites of secondary amines to form nitrosamines which are known carcinogens.
Problems With Tankside Addition:
In India, one of the common practices that have developed over the years is the tankside addition of biocides for resolving untimely microbial spoilage issues. Although this practice provides immediate help, it has its own side effects. The biocides used in tankside such as isothiazolinones quickly inhibit the growth of microbes and then kill. During its action it also gets consumed. These biocides solve the problem for a short period of time, but as time passes, the dead bacteria become a nutrient source for other bacteria and fungi. Also, dead bacteria can contribute to increased biofilms mass. As non-oxidizing biocides don’t help reduce biofilms EPS, biofilms can become even stronger. So, controlling the bacteria in the early stage of sump management is more important than a brute force method. It is very critical to do tankside addition as a supplement to concentrate-based microbial control on need basis.
Figure 2. General biofilm in pipeline CASE STUDIES:
A very famous multinational MWF manufacturer operating in India was facing the problem of a foul smell, microbial corrosion and instability in their semi-synthetic MWF fluids despite using Triazine based biocides at 3-4% concentration in the MWF concentrate. A recent microbial audit in one of their customer’s plants showed the presence of biofilms and SRBs in their fluids (Fig 4 and 5). The samples also contained fungi and majority of microbes found in different samples were Gram negative bacteria capable of producing slime as well as some Gram positive bacteria.
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Figure 3. SRB growth, blackening of SRB media due to H2
S formation LUBE MAGAZINE NO.138 APRIL 2017 39
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