Chemistry: molecular biology and microbiology – Micro-organism – tissue cell culture or enzyme using process... – Preparing oxygen-containing organic compound
Reexamination Certificate
2000-09-19
2002-03-26
Prats, Francisco (Department: 1651)
Chemistry: molecular biology and microbiology
Micro-organism, tissue cell culture or enzyme using process...
Preparing oxygen-containing organic compound
C435S128000, C435S183000, C435S191000, C435S227000, C526S199000, C526S317100, C526S329300
Reexamination Certificate
active
06361981
ABSTRACT:
This invention relates to processes for making aqueous solutions of ammonium acrylate and other acrylic monomers.
There is a major industrial need to produce aqueous acrylic acid, or a water soluble salt thereof such as ammonium acrylate or sodium acrylate, for instance for use as a polymerisable monomer, It is necessary that the aqueous solution should be as free as possible of impurities which are undesirable either from an environmental point of view or because they might interfere with subsequent polymerisation.
One common way of making acrylic acid industrially comprises hydrolysing acrylonitrile to form acrylamide and then hydrolysing the acrylamide to form ammonium acrylate or acrylic acid. Although most commercial processes of this type rely upon chemical hydrolysis, enzymatic hydrolysis is known for each stage (ie nitrile hydratase for converting nitrile to amide and amidase for converting amide to acid salt). The manufacture of acrylic acid by this technique is economically inconvenient, for instance because it requires an extensive amount of equipment for the two stages. Also extensive purification procedures are generally required. For instance it is essential to remove impurity amounts of acrylonitrile to very low levels and this may necessitate extensive distillation.
Another commonly used process for making acrylic acid is by hydration of propylene oxide. This avoids the need to conduct purification procedures in order to eliminate any acrylonitrile contamination but has the disadvantage that the process has to be conducted in complex, generally pressurised, apparatus.
There have been a few proposals in the literature for use of a nitrilase enzyme for converting aqueous acrylonitrile direct to aqueous ammonium acrylate. It is generally accepted that the direct conversion is more effective on aromatic than aliphatic nitrites, eg Stevenson et al, Biotech and Appl. Biochem. 15, 283-302 (1992).
In one example of EP-A-444640 acrylonitrile at a concentration of below 200 mM was hydrolysed using nitrilase catalyst to achieve almost quantitative conversion to acrylic acid, together with some acrylamide contamination.
In JP-B-632596 a 2% acrylonitrile solution is utilised in one example and in another example a 25% acrylonitrile solution is hydrolysed to a 32.9% ammonium acrylate solution. In a further example a 15% (meth) acrylonitrile solution is utilised to give a 23% ammonium (meth) acrylate solution.
In Biotech and Appl Biochem 11, 581 to 601 (1989) it is stated that the particular enzyme discussed in that article has Km for acrylonitrile of 17 mM. No process conditions are given but this value necessarily indicates that a substantial amount of acrylonitrile will remain in the product. The article indicates that 4-6% acrylamide is formed. The same article also indicates that the enzyme discussed in that article has a much higher activity for benzonitrile than for acrylonitrile.
In J Bacteriol September 1990 page 4807 to 4815 the properties of R rhodochrous K22 are analysed and it is stated that this has Km for acrylonitrile of 1.14 mM. This value also indicates the necessary presence of substantial amounts of acrylonitrile in the end product. There is no information given as to the concentration of ammonium acrylate which can be obtained but the article does note that enzyme activity is rapidly lost at above 55° C.
In Appl Microbiol Biotech 1990, 34, pages 322 to 324 a fed batch process of converting acrylonitrile to acrylic acid is described. The acrylonitrile has to be kept at a concentration below 200 mM (1.06%) and the product is said to contain 38% acrylic acid after 24 hours. The products were extracted by solvent extraction followed by evaporation and distillation.
These enzymic conversion processes provide a useful alternative to the two step enzymatic conversion (ie acrylonitrile to acrylamide and then acrylamide to ammonium acrylate) and the chemical conversion process, but all retain the requirement for extensive purification procedures to reduce acrylonitrile levels.
According to the invention, we make an aqueous solution containing at least 30% by weight (meth) acrylic acid or salt thereof and below 0.2% (meth) acrylonitrile by a process comprising providing water and (meth) acrylonitrile in an amount sufficient to provide, upon hydrolysis, a concentration of (meth) acrylic acid or salt thereof of at least 30% by weight and providing during the process in contact with the (meth) acrylonitrile, an enzyme for converting (meth) acrylonitrile to ammonium (meth) acrylate and which has Km for (meth) acrylonitrile below 500 &mgr;M and Ki for ammonium (meth) acrylate above 100,000 &mgr;M, allowing hydrolysis of (meth) acrylonitrile to occur to provide a reaction solution which has a concentration of (meth) acrylonitrile of below 0.2% and a concentration of ammonium (meth) acrylate of above 30% and recovering a solution having concentrations of ammonium (meth) acrylate of above 30% and acrylonitrile of below 0.2%.
Thus in the invention we use an enzyme which can scavenge (Seth) acrylonitrile to extremely low concentrations to produce ammonium (meth) acrylate even when the amount of ammonium (meth) acrylate or other (meth) acrylic acid salt present in the reaction solution can be very high. As a result we obtain, for the first time, a high concentration of ammonium (meth) acrylate or other (meth) acrylic acid monomer contaminated with only a very low amount of (meth) acrylonitrile. In particular, by using an enzyme which has a very low Km value we are able to achieve a very low (meth) acrylonitrile content in the final product and by using an enzyme which also has a high Ki value we are able to achieve this low concentration of (meth) acrylonitrile in the presence of a high concentration of ammonium (meth) acrylate.
It is very surprising that we can provide a process which can produce high concentration ammonium (meth) acrylate or other (meth) acrylic acid salt and very low concentration (meth) acrylonitrile. In particular it is surprising that we can achieve this using, as is preferred, a dilute concentration of acrylonitrile. By use of the invention it is even possible to achieve the desired product in a single stage in good yield and to excellent purity, with the need for purification to remove (meth) acrylonitrile thus avoided. It is particularly surprising that this can be achieved in a process which is conducted at a ratio of concentrations starting material:end product of <0.2:>30.
In the invention we provide (meth) acrylonitrile and water for reaction to (meth) acrylic acid or salt thereof by hydrolysis. It is possible to carry out the majority of the hydrolysis using chemical means to produce an aqueous solution containing (meth) acrylic acid (or salt thereof) and unreacted (meth) acrylonitrile. The defined enzyme is then provided in contact with the (meth) acrylonitrile and further hydrolysis of the unreacted (meth) acrylonitrile is allowed to occur until the reaction solution has a concentration of (meth) acrylonitrile of below 0.2% and a concentration of ammonium (meth) acrylate of above 30%.
The amount of (meth) acrylonitrile is usually below 0.1% and may be so low as to be non-detectable by convenient analytical techniques.
Processes of the invention may be carried out in two stages in a single reactor. Alternatively the chemical stage may take place in one reactor and the resultant solution containing dissolved (meth) acrylic acid or salt and residual (meth) acrylonitrile can be transferred to a bioreactor where reduction of residual (meth) acrylamide takes place on contact with the defined enzyme.
Preferably however substantially all hydrolysis of (meth) acrylonitrile is catalysed by the defined enzyme. In this case the solution produced contains at least 30% by weight ammonium (meth) acrylate. Thus preferably we charge a reactor with the acrylonitrile, enzyme and water and we recover the final solution.
We find that ammonium acrylate monomer produced by wholly enzymatic processes of the invention (bio-ammonium acrylate) shows excellent pro
Hughes Jonathan
Symes Kenneth Charles
Ciba Specialty Chemicals Water Treatments Limited
Crichton David R.
Prats Francisco
Srivastava Kailash C.
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