CA1199550A - Method of cleaning the jacket of a glass-lined reactor - Google Patents

Abstract

CLEANING PROCESS

Abstract of the Disclosure -Jacket of a glass-lined reactor is cleaned with aqueous mix of chelant, dispersant, and metal passivator.

Description

"` 1~L995Sal This invention is directed to cleaning the interior of the jacket of a glass-lined reactor, using a cleaner especially formulated to remove scale and rust without, however, forming hydrogen, which tends to diffuse through the reactor wall and attack the glass lining inside the reactor.
Substantially any heating or cooling medium circulated through the jacket of a jacketed glass-lined reactor will gradually cause formation of rust and/or result in scale These deposits interfere with heat transfer and require periodic removal. For such purpose, acidic cleaners are probably the worst, for the reason above given. Alkaline cleaners have been used, but fail to remove hardness-type scale. Hydrosulfite cleaners remove iron, but not hardness scale.
We largely avoid the disadvantages of prior art jacket cleaning processes by the use of a special aqueous cleaner comprising a chelant, a dispersant, a metal passivator, and (optionally) an antifoaming agent.
Thus, a method is provided of cleaning the jacket of a glass-lined reactor comprising circulating through the jacket an aqueous cleaning solution comprising a mixture of water and a cleaner concentrate comprising from 6.821 to 37.4775 weight percent of a chelant, from 0.1 to 5.5 weight percent of a dis-persant, and from 0.175 to 1.05 weight percent of a ferrous metal passivator, and water to make lO0 weight percent.
The following example illustrates without limiting the invention.

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Example 1 The jacket of a 1000 gallon glass-lined reactor had become filled with scale which had reduced the water flow and caused a reduction in heat transfer.
Due to the glass lining, acid cleaning of the reactor jacket was impossible, because of the possibility of the glass lining being damaged by gas pressure from the acid reaction. In t-he past, these reactors have been dismantled, sandblasted to remove the scale, and relined.
Such a relining requires from 14 to 16 weeks at a cost of approximately 70~ of the original price of this reactor.
Therefore, a cleaning product that would effectively remove scale and passivate the metal parts while at the same time not damage the glass lining was required.
Our cleaner~concentrate~comprised: -Wt. %
38% aqueous solution of ethylene diamine tetra acetic acid (chelant and cleaner) 98.625 Polyglycol (antifoaming agent) .005 Sodium lignosulfonate (dispeesant) .16 Sodium polymethacrylate, 4500 mol. wt.
(dispersant) .55 Hydrazine, 35~ aqueous solution ~metal passivator) 66 100 . 000 The cleaniny procedure was as follows:
(1) Feed 5.5 gallons of cleaner with 50 gallons of city water (Rochester, N. Y.) to the reactor jacket.
(2) Circulate this solution at 120-150F for 4-8 hours.

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~3) Drain the reactor jacket an~i measure the specific conductance of effluent against a standard of 305 micromhos for the city water in this example. (305 micromhos was the conductivity of the water before the addition of the chemical.) (4) Based on the conductivity reading, determine whether sufficient cleaning has taken place or whether an additional charge of chemical is required. If the conductivi~y of the cleaning solution has increased by at least SO~ after recirculation, then suficient cleaning will have taken place.
The following table shows the results of the chemical cleaning. The first column shows the analysis of the cleaning solution after chemical addition but before recirculation. The second analysis is that of the cleaning solution after 4 hours of recirculation. Note the changes in the total dissolved solids, the hardness of CaC03, the calcium content, and the iron content. The total dissolved solids nearly doubled. The amount of hardness increased by more than six times. The iron was increased eight-fold. All these measurements show that the scale that consisted largely of calcium and iron was being dissolved by the cleanser.

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Water Analysis Cleaner ~lu5 Cil:y ~qater efore Circulation Af~er Circulation Total dissolved solids, ppm18,698 35,61û

p~I 11 . 9 12 Rardness as CaCO3 223 1,406 Specific conductance, micromhos/cm 9,4~0 14,700 Calcium as Ca, ppm 76 546 Magnesium as Mg, ~prn 8 10 Iron a~ Fe, ppm 8.6 80 Silica as SiO2 1 1.1 9ss~

The c eaner used in the above example is available *

commercially as Polymate 661 (a concentrate~ from the Dearborn Chemical Division, Chemed Corporation. In a more general sense, the following is suitableo chelant 17.95 - 98.625 wt%
antifoaming agent O - 0005 dispersant .1 - 5.5 metal passivator .5 - 3.0 water~ to make 100~

The concentrate is suitably diluted with water in a ratio of about 5.5 volumes of concentrate per 50 volumes of waterO This makes the use solution. Within the range given, more chelant is used, depending on the severity of the scale.
Besides ethylene diamine tetra acetic acid, other well known chelants can be used, e.g., trisodium nitrilotri-acetate monohydrate.
Besides polyglycol, other well known antifoaminy agents are s~itable, e.g., antifoams based on organic esters~
Besides sodium lignosulfonate and/or sodium polymetha-crylate, other well known dispersants are suitable, e.g., the nr~anophosphonates, hydroxy-ethylidene diphosphonic acid and the like.
Besides hydrazine, other well-known metal passivators are suitable, e.g., diethylhydroxylamine~

* Trademark ~`~ 6 -

Claims (8)

WHAT IS CLAIMED IS:

1. A method of cleaning the jacket of a glass-lined reactor comprising circulating through the jacket an aqueous cleaning solution comprising a mixture of water and a cleaner concentrate comprising from 6.821 to 37.4775 weight percent of a chelant, from 0.1 to 5.5 weight percent of a dispersant and from 0.175 to 1.05 weight percent of a ferrous metal passivator, and water to make 100 weight percent.

2. The method of claim 1 in which the chelant is ethylene diamine tetra acetic acid t the dispersant is a mix of sodium lignosulfonate and sodium polymethacrylate, and the metal passivator is hydrazine.

3. The method of claim 1 in which the cleaning solution further comprises an antifoaming agent.

4. The method of claim 3 in which the chelant is ethylene diamine tetra acetic acid, the dispersant is a mix of sodium lignosulfonate and sodium polymethacrylate, the metal passivator is hydrazine and the antifoaming agent is a polyglycol.

5. The method of claim 1 in which the solution is circulated at 120-150°F. for 4-8 hours.

6. The method of claim 1 in which the solution is circulated through the jacket until the conductivity of the solution increases by at least about 50%.

7. The method of claim 1 in which the cleaner con-centrate and the water are mixed in the respective volume ratio of about 5.5:50.

8. The method of claim 1 in which the solution further comprises from 0 to 0.005 weight percent of an antifoaming agent.