DE3528884C2 - - Google Patents

Description

Technical field

The present invention relates to manufacture of dimethylaminomethyl-substituted polyacrylamide with cationic properties used in wastewater treatment and / or in the drainage of sewage sludge used in sewage plants is used as a flocculant.

The present invention shows one way of manufacturing a dimethylaminomethyl-substituted polyacrylamide, the manufacture does not involve the hydrolysis of polyacrylamide allows.

State of the art

In the treatment of wastewater and / or sewage sludge Flocculants used to

• 1) flocculate colloidal particles and other substances, or
• 2) to achieve that sludge is more easily dewatered to the Increase dry matter content.

Cationic polymers are often used, in particular substituted polyacrylamides, as in formula I.

Where R is methyl or ethyl and -N- (CH₃) ₂ the active group is the

forms.

Another cationic polymer is dimethylaminomethyl substituted Polyacrylamide of formula II

Anyway, these polymers are made during their manufacture slightly hydrolyzing to form:

Whereby their cationic properties are considerably reduced will.

The dimethylaminomethyl substituted polyacrylamide is after the Mannich reaction from polymethylacrylamide, a secondary Amine and formaldehyde prepared, z. B. formaldehyde  and dimethylamine form dimethylaminomethanol. In US PS 42 65 835 (column 8) is the implementation of the hydrochloric acid adduct of the reaction product of formaldehyde and dimethylamine with polyacrylamide in aqueous solution under clearly acidic conditions (pH 3 with HCl) and described at elevated temperatures (65 ° C).

Description of the invention

Surprisingly, the possibility of hydrolysis has now been discovered to prevent if you have an aminomethyl-substituted polyacrylamide of formula II. It is also possible the predicted stability of the aminomethylation of the external amino groups to increase. The invention is characterized in that a low% aqueous polyacrylamide solution by dissolving Polyacrylamide is made in water to have a stable viscosity of Obtain 1200 mPa · s with stirring for <24 h without "shearing", after which secondary amides and formaldehyde in stoichiometric amounts, each according to the intended degree of substitution, are added and allowed with the polyacrylamide at <25 ° C and pH <10 for 72-96 hours to react while stirring without "scissors".

The reaction temperature should preferably not exceed 20 ° C. The response time can also be 120 hours.

Further characterization is given by the "subclaims".

In order to get maximum molecular weight, it is important to manufacture the aqueous polyacrylamide (normally 1.2% by weight polyacrylamide) to be carried out under gentle conditions. That is, destructive Movements such as screw blade stirring should be avoided. Slow running gate stirrers can be used, is also possible gentle pumping with eccentric screw pumps or mammoth pumps. Centrifugal pumps should be avoided. The same gentle stirring  should be maintained during the substitution reaction, to avoid destroying the polymer chains.

example

1000 kg of water were carefully mixed with 12 kg of solid polyacrylamide a molecular weight of 10 × 10⁶ mixed. The solution was pumped around for 30 hours until the viscosity reached a value 1200 mPa · s (Brookfield Viscosimeter, spindle no.3) would have. A "shear" of the polyacrylamide was not found will.

2.8 kg of formaldehyde were added to the solution of the polyacrylamide and 4.2 kg of dimethylamine. It was due to the influence of dimethylamine reached a pH of 11. Formaldehyde and dimethylamine were added to a degree of substitution to get from 100%. The temperature in the reaction vessel was held at 18 ° C for 96 hours at this time, the reaction solution was easily pumped around moved by means of an externally arranged screw eccentric pump. After the reaction was complete, an aqueous solution of polydimethylaminomethylacrylamide with a degree of substitution of 100% received. No hydrolysis was found.

Correspondingly, polydimethylaminomethylacrylamide was used manufactured with a degree of substitution of 30% below Add 84 kg of formaldehyde and 1265 kg of dimethylamine to one 1.2% by weight solution of polyacrylamide in water (12 kg Polyacrylamide in 1000 kg water).

The flocculation and settling properties of the present polymers have been tested with sewage sludge and with a number commercially available flocculants compared can be used in various sewage systems. The tests  were measured in ml / minute in a measuring cylinder carried out. Different types of polymer of the present Invention were used. Invention / 100 means a Polymer with 100% degree of substitution. Invention / 59 means a polymer with 59% degree of substitution, etc.  

Overview

The reaction speed is obviously slow, but it can can be catalyzed by a short-chain polymer of the formula III:

R¹ is O ^- Me⁺, O / NH₂ (CH₃) ₂ / or O / NH₂ (C₂H₅) ₂ / Me⁺ is Na, K or salts of monocarbonisms, R is a mixture of -CHO; -CH (OH) ₂ and CO-O-CH₂CH₂COO ^- Me⁺ when R¹ is O ^- Me⁺ or CO-O-CH₂CH₂COO / NH₂ (CH₃) ₂ / when R¹ is O / NH₂ (CH₃) ₂ / or CO -O-CH₂ CH₂ COO / NH₂- (C₂H₅) ₂ / when R¹ is O / NH₂ (C₂H₅) ₂ / and the ratio n : m varies between 0.7-0.5: 0.3-0.15 . The chain contains p molecules, where p is 20-60. This can significantly reduce the response time. R 1 must not be OH, because this leads to undesired protonization of the cationic polymer.

Claims (3)

1. A process for the preparation of dimethylaminomethyl substituted polyacrylamide by "Mannich" reaction, characterized in that in the first step a low-concentration aqueous polyacrylamide solution is carried out by dissolving polyacrylamide in water, while gently agitating the solution for at least 24 hours, and in second step, the resulting aqueous solution of polyacrylamide reacts with dimethylamine and formaldehyde in stoichiometric amounts, depending on the desired degree of substitution of the end product, the reaction being carried out at a pH greater than 10 and a temperature of 25 ° C. or less over a period of time of at least 72 hours with gentle agitation of the reaction mixture. 2. A method according to claim 1, characterized in that the Reaction temperature is kept below 20 ° C. 3. A method according to claim 1, characterized in that the Response time is 72 to 120 hours.