The present decision is in no way spectacular but it presents in a very pedagogical manner how inventive step is nowadays assessed by the Boards in the chemical realm:
Novelty of the subject-matter having been acknowledged, the assessment of inventive step begins with the search for the closest prior art.
The closest prior art
[4.1] The closest state of the art is normally a prior art document disclosing subject-matter with the same objectives as the claimed invention and having the most relevant technical features in common.
The objective of the patent in suit was to recover thermally instable N-vinyl-2-pyrrolidone by continuous distillation from its reaction mixture […]. Document D6 discloses the distillation of a ternary mixture. It neither mentions N-vinyl-2-pyrrolidone nor the distillation of any other thermally instable compounds. Document D13 does not relate to continuous distillation. In contrast thereto, document D7 discloses the continuous distillation of N-vinyl-2-pyrrolidone and addresses the thermolability of this compound […]. Therefore, document D7 rather than document D6 or D13 represents the closest prior art.
The next step is to determine the problem solved by the difference(s) of the claimed subject-matter with respect to the closest prior art:
The problem to be solved
[4.2] The [patent proprietor] argued that a comparison between example 3 of document D7 with the examples of the patent in suit showed that a higher percentage of N-vinyl-2-pyrrolidone is recovered by means of the process claimed in the patent in suit […]. In particular, the [patent proprietor] pointed out that - in example 3 of document D7 300 g/h of N-vinyl- 2-pyrrolidone were fed into the distillation column whereas only 185 g/h of pure N-vinyl-2- pyrrolidone were withdrawn from the column under steady state condition, which meant that only 62% of the N-vinyl-2-pyrrolidone was recovered […]. In contrast to this - in examples 1 and 2 of the patent in suit, 96% and 95%, respectively, of the N-vinyl-2-pyrrolidone was recovered at a purity of 99.9% by weight […].
This finding can be used to reformulate the problem to be solved only if - said examples of document D7 and of the patent in suit are comparable to the extent that the alleged effect is convincingly shown to have its origin in the distinguishing feature of the invention (see T 197/86 [6.1.3]), and, in the affirmative, that - it is probable that this effect is achieved over the whole range of the claims of the patent in suit, and - that the effect is related to the problem to be solved as disclosed in the respective application as filed (see T 1188/00 [4.5]).
[4.2.1] Hence, it is first to be assessed whether or not the comparison of the example 3 of document D7 with examples 1 and 2 of the patent in suit shows that this increase in the portion of N-vinyl-2-pyrrolidone recovered in high purity is due to the distinguishing feature.
A feature which distinguishes the subject-matter claimed from the disclosure in document D7 as the closest prior art is that the claims of the patent in suit require that an additional column is present in which water is distilled off […].
However, the process of examples 1 and 2 of the patent in suit does not differ only from that of example 3 of document D7 in that an additional column was used but also in that - the mixtures to be separated in the patent in suit contained water whereas no presence of water is reported in document D7, and in that - the distillation temperatures in the examples of the patent in suit were higher.
Consequently, the increased portion of high purity N-vinyl-2-pyrrolidone recovered in examples 1 and 2 of the patent in suit can only be clearly attributed to the distinguishing feature if the presence of water and the higher distillation temperature do not contribute to this effect.
As both parties pointed out, document D12 discloses that N-vinyl-2-pyrrolidone may - hydrolyse in acidic aqueous solutions into 2-pyrrolidone and acetaldehyde, and may - polymerise at high temperatures so that vacuum distillation at “temperatures above 120°C should be avoided” […]. Hence, the presence of water in the mixture separated in the examples of the patent in suit is rather expected to decrease the portion recovered due to hydrolysis of part of the N-vinyl-2-pyrrolidone.
The increase in temperature from - 95°C in example 3 of D7 […], to - 160°C and 195°C in the distillation columns used in example 1, and 178°C and 205°C in example 2 […], i.e. to temperatures well above those recommended in document D12 in order to inhibit polymerisation of N-vinyl-2-pyrrolidone, is also expected to decrease the portion of N-vinyl-2-pyrrolidone recovered.
Hence, the observed increase in the recovered portion of N-vinyl-2-pyrrolidone can be attributed to the fact that an additional distillation column is used in examples 1 and 2 of the patent in suit, namely to the feature distinguishing the subject-matter of the present claims over the disclosure of document D7.
[4.2.2] Then it is to be determined whether it is probable that this effect is achieved over the whole range of the claims of the patent in suit. The only independent claim requires
- a pressure of 2.66x104 Pa or less and a temperature of 180°C or less in the first column, and
- a pressure of 1.33x104 Pa or less and a temperature of 230°C or less in the second column […].
Document D12 recommends vacuum distillation of Nvinyl 2 pyrrolidone. There is no indication in this document that the application of a reduced pressure might affect the stability of N-vinyl-2-pyrrolidone. High temperatures do, however, accelerate its polymerisation and thus lead to a decrease the recovery of N-vinyl-2-pyrrolidone […].
The increased recovery of N-vinyl-2-pyrrolidone can be considered to be demonstrated over the whole range of the claims if the respective examples work under the most unfavourable conditions, namely close to the maximum temperatures indicated in the claims. This is indeed the case in example 2 where the bottom liquid temperature of the first column is 178°C in the first and 205°C in the second column (which is close to the maximum values of 180°C and 230°C indicated in present claim 1). Hence, it has been shown that the effect is achieved over the whole range of the claims.
[4.2.3] Finally, it is to be assessed whether the effect is related to the problem to be solved as disclosed in the respective application as filed. According to the application as filed, the problem to be solved was to provide “... a process ... which makes it possible to recover chemically unstable N-vinyl-2-pyrrolidone efficiently and steadily and in high purity …” […]. The demonstrated increase in the portion of high purity N-vinyl-2-pyrrolidone recovered thus is related to the problem initially disclosed.
[4.2.4] Therefore, the problem posed and solved in view of document D7 as the closest prior art may be redefined as to provide a continuous distillation of a liquid composition containing N-vinyl-2-pyrrolidone, N-(2-hydroxyethyl)-2-pyrrolidone and water, resulting in an increased recovery of highly pure chemically unstable N-vinyl-2-pyrrolidone.
[4.2.5] The cause of this problem as disclosed in document D7 is the thermolability of N-vinyl-2-pyrrolidone, namely its tendency to decompose at high temperatures […].
It still remains to be shown that the solution to this problem involved an inventive step:
Was the solution obvious?
[4.3] The [opponent] argued that it was obvious for the person skilled in the art to combine the disclosure of document D7 with that of D6 or D13 and thus to end up with the subject-matter of the present claims […].
The fact that the features of a claim of a patent not disclosed in the closest prior art are preferred features of another document of the prior art does not suffice to consider the subject-matter of this claim to be obvious. Obviousness requires additionally that said other document gives an indication that said preferred features contribute to the solution of the problem solved in the patent. Such an indication can be an explicit one if the other document mentions that said preferred features solve the problem, it can be an implicit one if said other document informs how to avoid conditions which are known to be a cause of the problem.
[4.3.1] Document D7 as such gives no indication that the distillation might be performed using two distillation columns.
[4.3.2] Document D6 mentions that the continuous countercurrent distillation of multicomponent mixtures containing N components requires N-1 columns if all the components are to be obtained in pure form. Otherwise, when a single column is used, either the top or the bottom product consist of more than one component […]. Figure 10.71 on page 721
shows a system of two columns for separating a three component mixture ABC, where the bottom product of the first column containing B and C is fed to a second column separating these components by distilling off component B.
However, document D6 does not relate to the problem of increasing the recovery of thermolabile monomers, let alone of N-vinyl-2-pyrrolidone. Thus, it gives no explicit indication to the person skilled in the art in charge of solving this problem to modify the process disclosed in document D7 by splitting up the distillation into two distillation steps in two different columns. Moreover, it does not address the conditions which are known to have an effect on the recovery of N-vinyl-2- pyrrolidone, i.e. to the presence or absence of heat, light, air or water during distillation […]. Therefore, the person skilled in the art would not consult document D6 when solving the problem mentioned above.
[4.3.3] Document D13 claims a process for making N-vinyl compounds by decomposition of the respective alphaalkoxyalkyl compounds (see claim 1). In example 5 the catalytical elimination of methanol from N-2- methoxyethyl-2-pyrrolidone yields N-vinyl-2-pyrrolidone. Most of the methanol is distilled off during the reaction and the product is purified by fractional distillation.
The [opponent] argued that document D13 suggested to distil off the lowest boiling compound first (namely the alcohol) and thus to perform the distillation in two steps which required two columns if performed continuously […]. However, there is no hint in document D13 that a two step distillation process might increase the recovery of thermolabile N-vinyl-2-pyrrolidone. Therefore, also document D13 does not give an indication that a modification of the process disclosed in document D7 by splitting up the distillation into two steps might be helpful for solving the problem mentioned above.
[4.3.4] Consequently, the subject-matter of claim 1 involves an inventive step. The same holds for the subject-matter of dependent claims 2 and 3.
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