Solutions of carboxylic peracids are generally obtained by the action of hydrogen peroxide on the corresponding carboxylic acid. French Pat. No. 2,462,425, discloses a process especially applicable to the preparation of stable dilute solutions of peracetic acid in which, in a first stage, a concentrated solution of aliphatic carboxylic peracid is prepared from the acid or the corresponding anhydride and concentrated hydrogen peroxide, in the presence of the minimum amount of a strong acid catalyst necessary to obtain balance of the system in a maximum period of 48 hours; and, in a second stage the concentrated solution of aliphatic peracid is diluted with a solution that contains at least a reactive constituent to bring the concentration of aliphatic peracid to the nominal concentration of the mixture.
This process makes it possible to prepare rapidly, on an industrial scale, solutions of aliphatic carboxylic peracids in aqueous form that contain several percents by weight of a peracid and that remain stable over time. Thus, dilute solutions containing between 1 and 20% by weight of carboxylic peracid, particularly monoperacetic acid, are easily obtained in very good industrial conditions. Preferably, the concentration of the prepared solutions is from 2 to 5% by weight of carboxylic peracid.
These dilute solutions of peracids are more appreciated because they are easier to transport and handle than concentrated solutions, because of the combustive nature of the peracid, and sometimes because of its odor and its irritating properties with respect to the skin, eyes and respiratory tract.
Solutions of peracetic acid, for example, are particularly suited for the sterilization of asceptic enclosures, such as incubators for premature animals or the growing of axenic animals, and the disinfection of hospital rooms and equipment. These solutions are also used to disinfect surfaces of work areas, rooms and equipment of the food industry. There are also applications such as disinfection and sterilization in operations for cleaning the inner walls of apparatus and circuits of manufacturing units of the food industry.
As far as food technology is concerned, stainless steel tends to be necessary more and more to the detriment of aluminum and other traditional materials (galvanized iron, wood, etc.). The composition of the most widely used stainless steel contains 18% chromium and 10% nickel. Although this stainless steel is virtually inert with respect to food products, most of the disinfecting and sterilizing agents authorized in the food industry cause corroding of the stainless steel; that is the case, for example, with chlorinated products.
Generally, commercial solutions of peracetic acid are diluted before use with water to bring the concentration of peracetic acid to between 30 and 300 mg/liter. No matter what its concentration, a solution of peracetic acid, diluted with deionized water, does not corrode the stainless steels currently used in the food industry, but taking into account the volumes of water called into play, particularly in disinfection in the food industry, the disinfecting of equipment by this process using deionized water is economically prohibitive.
When the water for dilution is ordinary water which contains traces of dissolved chlorides, a cavernous or pitted corrosion of certain grades of stainless steel is found. This corrosion is connected to the presence of chlorides in ordinary water which are oxidized by the peracids. This corrosion is particularly insidious because it occurs in places where the liquids are preferably not stirred; it is located, for example, in the dead zone of joints, connections valves and pipes. These dead zones are difficult to clean during rinsing operations with clear water, followed by cleaning with soda and nitric acid, which usually precede the disinfection phase.
This problem is particularly critical for the milk industry. Actually, milk has a marked tendency to leave on the inner walls of the pipes and apparatus, especially when they are heated, a film of organic matter consisting of fatty matter, nitrogenous matter and inorganic salts; this contamination promotes the growth of microbial flora. This problem is obviously increased further when there is a phenomena of cavernous corrosion which makes bacterial sites almost inaccessible to the cleaning and disinfecting agents.
On the other hand, because milk is an environment favorable to the growth of germs, the officials of the milk industry are particularly concerned with keeping their equipment in a satisfactory state of asepsis; consequently, they must look for the best compromise between the effectiveness of the cleaning and disinfecting agents and the risk of damage to their equipment. Under these conditions, the use of an effective disinfecting agent on the microbiological level which is moreover noncorrosive with respect to the equipment, is particularly valued.