Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-09-01
2001-05-29
Nutter, Nathan M. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C527S400000, C530S500000, C530S506000, C530S507000
Reexamination Certificate
active
06239198
ABSTRACT:
The invention relates to a process for treatment of aromatic polymer-containing alkaline solutions which can be precipitated by acidification and which allows separation of these polymers in solid form and drying in air at normal pressure and using temperatures between 40 and 110° C. without becoming black.
Most aromatic polymers are easily soluble under alkaline conditions. In certain cases, as in lignins obtained by alkaline leaching of wood, acidification enables precipitation and separation thereof. The problem which arises in doing so consists in finding out whether the precipitated product can be filtered and dried. It often precipitates specifically in gelatinous form and then cannot be centrifuged and is even less filterable. Even in the cases in which separation is possible by filtering or centrifuging, the resulting product tends to become black during drying. This often applies in lignins which have been subjected to chemical changes, in the course of which groups are introduced which increase the polarity of the molecules, i.e. improve solubility. It is thus difficult to find a process with which the separation of products of good quality is possible and which works for any type of precipitatable aromatic polymers. But there are still problems in conjunction with the low concentration (less than 15% by weight polymers). It is often impossible to separate polymers in these cases, even if the known processes described below are effective for the same polymers at higher concentrations. Based on the increased investment costs and the increased power consumption in industrial plants concentration by evaporation is not a solution to this problem either. It is rather a matter of finding an alternative method which is reliable and economical.
The literature contains a large number of proposals for separation of this type of polymer, especially lignins, and for improving filterability. These processes include use of a mineral or organic acid for reducing the pH at a relatively high optimized temperature and subsequent filtration of the resulting precipitate with reheating (Wienhaus et al., Papier 1990 (11), pp. 563-569; Binglin, Water Treatment 1988 (3), pp. 445-454; Alen at al., Tappi 1979 (11), pp. 108-110).
A process with which it would be possible to make the separated product filterable and dryable and which is effective however for any type of aromatic polymers for which there is a precipitation pH in an aqueous medium has not been known to date.
The object of the invention is to avoid the above described defects of the known processes. To achieve this object it is proposed as claimed in the invention that the solution be acidified and afterwards heated and the resulting precipitate separated as a solid. This process may seen nonsensical because in cold precipitation a mixture is produced which is extremely viscous and which has a very gelatinous appearance. In addition the precipitated polymers contained in this viscous suspension cannot be separated either by centrifuging or by filtration or by other methods. The suspension first becomes more liquid upon reheating and at a certain time exceeds a threshold (depending on the polymer type around 40-80° C.) at which it surprisingly becomes filterable and gives no occasion for undesirable coloration during drying. The exact temperature at which good filtration becomes possible depends largely on the respective polymer and must be optimally selected for each case.
The surprising element consists in that it is not a process which can be reversed in terms of heat engineering. It is absolutely essential to precipitate at a relatively cool temperature and afterwards to heat. If precipitation is done at an optimum temperature without reheating after precipitation, in certain cases a reasonable filtration capacity can be achieved; the result however is far from that effect which is achieved with proposed processes. Filtration takes place less promptly, and in most cases, for example in polymers with a relatively low precipitation pH of less than 5, the polymer becomes completely black during drying.
Especially good and reproducible results were achieved here when the polymers to be precipitated have the criteria that the peak on the viscosity curve is below pH of 8 or a lower inflection point is located on the titration curve below a pH of 6.5.
The main advantage of the invention is that it enables production of products with very low contents of water-soluble minerals, especially sodium salts and hemicelluloses, at very low cost. When using products for example as copolymers in plastic materials (duroplastics or thermoplastics) the purity is an important factor for technical data (mechanical properties, absence of electrolytes, such as sodium, for electrical insulation capacity, etc.) of the end material. Since the product can easily be filtered using for example a Buechner filter or band filter, specifically the salts can be removed by washing. In particular in the case of highly diluted solutions, for example waste water from certain cellulose plants with increased consumption of washing water, the described process allows separation of a quality product at a competitive price, since the energy necessary for evaporation is saved.
Filtration can be further improved when the product is allowed to mature after reheating for a few minutes with moderate to vigorous and very uniform stirring. This maturation time must however be limited. If it is extended over a very long time, for example by allowing the liquid to stand warm for several hours or by allowing it to cool, the filtration time increases again. In addition, cooling of the liquid following the primary stage of reheating or optionally also after an additional maturing time leads to an increase of the filtration rate.
As another optional step the invention allows sedimentation of the polymer before filtration. In this way a reduction of the amount of water to be filtered by a factor over 5 which can extend to more than 20 is possible. In following the entire process as claimed in the invention the decisive factor is the pH value to enable sedimentation. If it is not low enough, the product does not settle even if it is filterable. This pH is typically at least one point below the peak of the viscosity curve. If conversely the pH value is too low, the filtration rate can become slower again.
Other additional treatments can be done before or after precipitation and before or after heating: addition of flocculants (FeCl
3
, Al
2
(SO
4
)
3
) or of polyelectrolytes (for example of the acrylic type) and electrolytic flocculation treatment. These measures can further improve separability and can also increase the amount of solids which can be separated, since they also allow precipitation of additional polymer fractions. The effectiveness of the flocculation aids is especially great in most cases when they are added before acidification and before heating.
On the other hand, this process makes it possible to form a great diversity of new technical approaches to obtaining polymers with special properties adapted to the requirements. Due to the improved separation of polymers it becomes possible specifically to undertake chemical changes in the aqueous alkaline phase without the product thus becoming more difficult to separate and purify. The reactions which can take place in these changes include all those reactions which introduce chemical groups which change the charge distribution and thus the precipitation behavior: etherification (methylation, ethylation, carboxymethylation, alkoxylation with epoxy, etc.) and esterification (sulfonation, nitration, reactions with organic acids or diacids, etc.). The chemical reactions which form new functional groups by decomposition of the polymer are also named: oxidations, for example with oxygen, hydrogen peroxide, ozone, oxidation salts, such as periodates or permanganates, oxoammonolysis, oxidative or reductive electrochemical reactions or enzymatic reactions. These reactions can even influence the distribution of molecular size and e
Abächerli Alfred
Doppenberg Frank
Granit S.A.
Nixon & Vanderhye
Nutter Nathan M.
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