Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymerizing in reactor of specified material – or in reactor...
Reexamination Certificate
1999-10-05
2001-01-30
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymerizing in reactor of specified material, or in reactor...
C526S064000, C526S065000, C526S067000, C526S071000, C526S089000, C526S285000, C526S332000, C528S425000
Reexamination Certificate
active
06180728
ABSTRACT:
The present invention relates to apparatus for effecting gas-liquid reactions which occur with a gas-in-liquid and liquid-in-gas dispersion mechanism.
In particular, the present invention relates to apparatus for the semi-continuous polymerisation of monomers with the use of a chain initiator.
In a yet more particular embodiment, the present invention relates to new semi-continuous apparatus for the production of polyadducts of alkylene oxides, by an addition reaction of the alkylene oxide on a chain initiator which has at least one active hydrogen. These products, particularly the polyadducts of ethylene and propylene oxides, are used mainly as non-ionic surfactants and polyether-polybls.
Non-ionic surfactants are very widely used as wetting agents, dispersants, stabilisers, emulsifying agents and anti-emulsifying, anti-foaming and foaming agents and, in general, as auxiliary chemicals and functional fluids in the textile, paper, cellulose, pharmaceutical, food, cosmetic, paint, resin, mineral extraction and processing, advanced recovery and extraction of petroleum industries, in chemical adjuvants and functional fluids. In particular the use should be mentioned of non-ionic surfactants based on natural or synthetic fatty alcohols, as primary components in the formulation of household and industrial detergents and also of polyether-polyols as the main intermediates in the production of polyurethanes (rigid, semi-rigid, flexible foams, elastomers, adhesives, sealants, etc).
Italian Patent No. 1 226 405 describes a method for the production of polymerisation products of alkylene oxides starting from alkylene oxides, ethylene and/or propylene oxides being most commonly used, and compounds having an active or mobile hydrogen atom with suitable catalysts. The method of this patent uses a two-section reactor of which the upper is termed the gas-liquid reactor and the lower is an accumulation reservoir, disposed essentially horizontally. The gas-liquid reaction takes place in the upper section, the chain initiator being supplied from a plurality of spray heads on a central distributor while the lower body acts as a receiver and for recycling through a pump and an external heat exchanger, the reaction product coming from the upper section being resupplied to the latter to continue the polymerisation reaction.
Italian Patent No. 1 226 406 describes a method for obtaining polymerisation products of alkylene oxides which uses a two-section reactor of which the upper is termed the gas-liquid reactor and the lower is an accumulation reservoir, each section having a plurality of spray heads. The first phase of the reaction occurs in the lower section which is arranged vertically and continues until a given quantity of polymerisation product is formed; subsequently the polymerisation reaction is transferred to the upper section, arranged horizontally, where the reaction can continue until the desired product is obtained.
The processes described in the aforesaid patents, however, have several disadvantages. First of all they use two-section reactors which complicates the overall structure of the plant and increases costs; two-section reactors also have a large-diameter communication aperture and, for Italian Patent 1 226 406, a larger number of apertures, thus increasing the possibility of loss of alkylene oxide and formation of dead zones and internal surfaces exposed to the oxide. As two-section internal distributors are provided, the surface-volume ratio of these reactors is very high, increasing the probability of secondary reactions. The double-bodied configuration and presence of internal distributors also creates dead spaces within the reactor which makes it difficult to drain and clean the reactor, thus increasing problems in changing production.
As the processes just described are based on the recycling of reagents and of the reaction mixture by means of pumping through ducts or even simply under gravity, the processes described in the aforesaid patents do not allow the use of solid-state chain initiators or suspensions which cannot be pumped, thus limiting their use solely to chain initiators which are liquid or in solution with relatively low viscosities.
It should also be mentioned that the flow under gravity of the reaction product which collects in the upper horizontal section and is then ducted down into the lower one induces retrodiffusion and hence overexposure to the oxide atmosphere.
In order to carry out alkoxylation reactions with solid chain initiators or, in general, with chain initiators which cannot be pumped, it is necessary to use a different type of apparatus.
For this purpose a reactor is usually used which has an internal stirrer and, for example, an internal coil. The chain initiator and the catalyst are loaded into the reactor and then, while being stirred, are melted until they reach an homogeneous liquid state. At this point the reaction may be started by the introduction of the alkylene oxide which is made to flow from the bottom to the top through the liquid phase of the chain initiator and catalyst.
The problem at the root of the invention is that of providing apparatus for the production of polyadducts of alkylene oxides which can be used with any chain initiator, catalyst and alkylene oxide and which also overcomes the problems mentioned above.
This problem is solved, according to invention, by apparatus as claimed in the main claim.
To advantage, the apparatus has the characteristics claimed in the dependent claims.
By virtue of its structural characteristics, the apparatus according to the invention has numerous advantages. As the apparatus has a stirrer within the reactor and an external recycle system for the reaction mixture, it may be used for reactions with any type of chain initiator and catalyst, whether they are solid or liquid. The apparatus according to the invention may also be used if the reagents are in suspension, in situations in which the catalyst may be harmed if pumped and in situations in which the product obtained has a viscosity such that it cannot be pumped and recycled any further.
Should the reagents be easy to pump, the apparatus according the invention may be used with external recycling. In this case the reaction mixture will be returned externally from the lower part of the reactor to the upper part and reintroduced into the latter by atomisation. The reaction will then be optimised by an exchange of material and heat which are very efficient, the reagent being vaporised in contact with particles of catalysed initiator which are finely dispersed in the atmosphere in the reactor.
Should the reagents be difficult or impossible to pump, however, the recycle duct may be excluded from the reaction process and the reaction will occur in the intermediate and lower parts of the reactor, the vaporised reagent being injected from suitable diffusors positioned at the bottom thereof.
The change over from the first to the second type of operation is possible even during the process should the reaction mixture, in time, acquire the necessary characteristics for it to be pumped so that the external recycling system can be used, which is always preferred since, as stated above, it improves the mass and heat exchange processes during the reaction.
This characteristic of the invention is particularly advantageous in situations in which it is desired to produce a product with a high molecular weight (up to 90 times the volume of the chain initiator). In this case the weight ratio between the chain initiator and the normally solid catalyst in the initial load is very high, rendering the initial reaction mixture extremely viscous. As the reaction proceeds, the catalyst concentration falls with the consequent lowering of the viscosity of the reaction mixture. At this point it is then possible to switch the apparatus over from operating with internal stirring to operating with external recycling.
A further advantage of the apparatus according to the invention lies in the particular shape of the reactor. As its lower part is conical, the reactor
Acquah Samuel A.
Linde Aktiengesellschaft
Millen White Zelano & Branigan, P. C.
LandOfFree
Apparatus for the production of polyadducts of alkylene... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for the production of polyadducts of alkylene..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for the production of polyadducts of alkylene... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2511613