Claims
- 1. A method of dispersing pitch contained in the aqueous medium of a pulp or papermaking process which comprises adding to said medium an effective amount for the purpose of a water soluble, chlorine-resistant phosphonate of high calcium tolerance having the structural formula ##STR15## where R.sub.1 and R.sub.2 represent a mixture of --CH.sub.3 and --C.sub.2 H.sub.5 or where R.sub.1 and R.sub.2 each represent a group having the formula C.sub.x H.sub.2x+1 ; where x is from 2 to and including 13; Y is hydrogen, a mixture of ##STR16## wherein x is as earlier defined; M is a water soluble cation; and n is 1 or greater.
- 2. A method according to claim 1, wherein the phosphonate is added in an amount of from about 0.5 to about 100 parts per million parts of said aqueous medium.
- 3. A method according to claim 2 wherein x is from 2-9.
Technical Field
This application is a division of application Ser. No. 941,536 filed Sept. 11, 1978, now U.S. Pat. No. 4,201,669.
The present invention is directed to aqueous systems such as, but not limited to, cooling water systems, pulp and paper mill systems, boiler water systems and gas scrubber systems where the formation and/or deposition of materials contained therein can and would most likely cause problems because of decreased flow rates, lost energy efficiency, poor quality products or pollution considerations. The problems associated with scale formation and deposition, the deposition of iron compounds, etc. in industrial water systems such as once-through and recirculating cooling water systems are well known in the art and are documented comprehensively in chapters 25 through 27 (pages 178-197) of the Betz Handbook of Industrial Water Conditioning, seventh edition, 1976, Betz Laboratories, Inc., Trevose, PA 19047. Similarly, the situation with respect to scale and deposition formation in gas scrubbing operations in the various industries is described in that publication on pages 314 to 327 and the problems associated with pitch in the production of quality paper are described on pages 284 and 285.
For the above-defined applications, certain organophosphonates have been used reasonably effectively to control the scale and deposit problems occurring in cooling water systems, pulp and paper mill systems, boiler systems and scrubber systems. The phosphonates which have been used extensively are amino tri(methylene phosphonic acid), i.e., N(CH.sub.2 PO.sub.3 H.sub.2).sub.3 or its water soluble salts, commonly referred to in the art as ATMP; diethyltriamine pentamethylene phosphonic acid, whose formula is [(H.sub.2 O.sub.3 PCH.sub.2).sub.2 NCH.sub.2 CH.sub.2 ].sub.2 NCH.sub.2 PO.sub.3 H.sub.2, commonly known as DPPA; and 1-hydroxyethane-1,1-diphosphonic acid, i.e., ##STR1## or its water soluble salts, commonly referred to as HEDP.
Applicants noticed during the study of these compounds and compounds closely related thereto that the nitrogen containing phosphonates were quickly degraded when used in systems where the chlorine content was high either naturally or as a consequence of other additives which provide chlorine. It was determined that the chlorine attacked the nitrogen of the compounds with a resultant decrease in their activity. Chlorine is found in many cooling water systems by virtue of the fact that it is commonly used as a microbial control agent. Chlorine is found in many pulp systems because of the hypochlorite pulp bleaching aids utilized. Again, chlorine drastically curtails the advantages of employing any amino containing phosphonates. Because of this, certain arrangements had to be provided for where scale formation or deposit control became a problem in a chlorine-containing environment. One special formulary arrangement led to the use of the earlier described 1-hydroxyethane 1,1-diphosphonic acid or its water soluble salts (HEDP), notably the potassium and sodium or ammonium forms. Since the HEDP compounds do not contain nitrogen, they possessed a greater degree of resistance to chlorine attack and accordingly are utilized quite satisfactorily in a chlorine environment. The HEDP compounds, however, although possessing the desirable chlorine resistance, were found to have their own peculiar problem. It was discovered that when the HEDP was formulated, or when products containing such were diluted, prior to usage, with water containing a relatively high calcium ion concentration, the HEDP compounds, whether in acid form or salt forms, had the tendency to react with the available calcium ion present to form a salt which precipitated and which hindered the efficacy of the HEDP compounds for scale and deposit control purposes. A similar result occurred when HEDP formulations were added to high calcium ion containing waters within a system, e.g., cooling water operating at elevated cycles of concentration, scrubbers using lime and magnesium oxide as additives, pulp and paper systems, boiler systems and evaporator systems, etc. The HEDP reacted with the calcium ions present to form a precipitate which not only reduced the efficacy of the HEDP formulations but increased the cost of treatment. In addition, and equally important, is the fact that with the reaction there existed another potential deposit in the form of the HEDP precipitating calcium salt.
Applicants, once realizing the foregoing problems associated with the use of the two primary phosphonic acid derivatives, embarked on a program to develop a compound which would possess the attendant advantages of those compounds possessing the phosphonic acid or salt group but which did not also have the calcium and chlorine disabilities. Applicants hoped to discover a compound or compounds which had general utility as deposit and scale control agents either as crystallization inhibitors or dispersants and which could be used in every environment regardless of whether it contained chlorine and/or high calcium ion concentration.
Applicants discovered during their research and developmental effort that compounds of the general formula ##STR2## where R.sub.1 and R.sub.2 each represent a group but not necessarily the same group having the formula C.sub.x H.sub.2x+1 where x is from 1 up to and including 13; where Y is hydrogen, ##STR3## or mixtures thereof; M is a water soluble cation such as Na, K or NH.sub.4 ; and n is 1 or greater so long as the oligomer is water soluble (n from 1 to 16 is preferred); possessed not only the desired chlorine resistance and in most instances calcium tolerance, but also were effective as crystallization inhibitors and dispersants. What was particularly impressive with the compounds was their ability at substoichiometric amounts to inhibit or control the crystallization of such potential scale salts as calcium and/or magnesium phosphates, sulfates and carbonates. Certain of the compounds were also found to be quite suitable at lower dosage levels as dispersants for iron oxides and calcium oleate, the most common ingredient in pulp and paper mill pitch.
The appropriately substituted alkane-1, 1-diphosphonic acids needed for this work were prepared by well-documented literature procedures and were dehydrated to the respective ester condensate oligomers by acetic anhydride. The free hydroxyl groups from the oligomerization process are predominately acetylated by the acetic anhydride but can also contain lesser amounts of the elements of the reactant carboxylic acids or acid chlorides as a result of mixed anhydride exchange reactions.
As explained comprehensively in U.S. Pat. No. 3,336,221 which is hereby incorporated by reference, the "threshold" effect, i.e., the ability of a compound at less than stoichiometric amounts to prevent precipitation of scale salts in a scale-forming environment, is significant to the water treatment industry because of economies and the desire to keep the amount of added materials in an aqueous medium to a minimum.
As with the ATMP described by the cited patent, the threshold active compounds of the present invention will control precipitation of the scale-forming salts when added in threshold amounts of up to about 100 parts by weight per million parts of water containing the scale-imparting ions. Preferably they are used at a rate of from about 0.5 to 25 parts per million. In the alternative, the amount of threshold compound may be based upon the scale-forming cation contained in the aqueous medium. If this latter alternative is utilized, threshold inhibition takes place at a weight ratio of the threshold active compound to scale-forming cation component of 1 to 100 up to 1 to 34,000, but preferably from 1 to 200 up to 1 to 4,000. This of course is substantially less than the sequestration requirements which range in weight ratio of the sequestration agent to the scale-forming cation of greater than 10 to 1.
Molecular weight of the oligomers of the present invention does not appear to be critical; accordingly "n" of the formula is expressed as being 1 or greater. The oligomer of the invention where R.sub.1 and R.sub.2 are methyl is disclosed in Prentice U.S. Pat. No. 3,621,081, with its use as a detergent builder being disclosed and claimed in U.S. Pat. No. 3,562,169.
Detergent builders, according to D. J. Shaw, "Introduction to Colloid and Surface Chemistry", Buttersworth, London, 1966, "fulfill a number of functions, the most important being to sequester (form soluble non-adsorbed complexes) Ca.sup.+2 and Mg.sup.+2 ions and act as deflocculating agents, thus helping to avoid scum formation and dirt redeposition." A. W. Adamson, "Physical Chemistry of Surfaces", Intersciences Publishers, New York, 1967, page 497, gives a similar definition for detergent builders. It is important to recognize that these definitions require that, at a minimum, sufficient quantities of builder must be added on a stoichiometric mole basis to sequester the hardness ions. This significantly contrasts with the sub-stoichiometric amounts used in threshold treatment of industrial systems.
A significant number of oligomers were prepared for testing for efficacy, chlorine resistance, and calcium tolerance. However, the Prentice method was only effective in producing the oligomeric derivative where R.sub.1 or R.sub.2 represented --CH.sub.3 and/or --C.sub.2 H.sub.5. Above --C.sub.2 H.sub.5 a different method had to be utilized in order to secure isolatable and testable products. When the various homologs were produced and tested, certain peculiarities within the series were observed. For example, the oligomers most easily produced and which were the most effective, the most chlorine-resistant and the most calcium-tolerant were those having "R.sub.1 " and "R.sub.2 " groups where x was 1 through and including 3. Above 3 and up to about 5, the oligomers, although generally effective, resistant to chlorine and tolerant of calcium, were not as effective. These comparisons will be more evident from the results which are hereunder recorded in the Tables.
US Referenced Citations (4)
Divisions (1)
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941536 |
Sep 1978 |
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Patent Grant
4253912
