T 0149/14 (Process for the production of the toluene diisocyanate/Covestro) 31-01-2018

Reasons for the Decision

1. The appeal is admissible.

Main request

2. Amendments (Article 123(3) EPC)

In claim 1 of the main request, the Appellant has deleted the requirement present in claim 1 of the patent as granted according to which the purified toluenediamine contains a total of less than 0.1% by weight of cyclic ketones, based on 100% by weight of toluene diamine. Instead of that, claim 1 of the main request now requires that the threshold of 0,1% by weight is based only upon the cyclic ketones listed in dependent claim 3, thereby extending the scope of the granted claims, contrary to the requirement of Article 123(3) EPC).

The Respondent has not contested that the scope of amended claim 1 was broader than that of granted claim 1, but submitted that the scope of amended claim 1 was that of dependent claim 3 as granted. According the Respondent, there was no provision in the EPC forbidding that a dependent claim had broader scope than that of the independent claim upon which it depends.

However, a dependent claim must satisfy all requirements of the independent claim on which it depends, with the consequence that a dependent claim cannot have a broader scope than that of the independent claim on which it depends.

The process of claim 3 of the patent as granted is a process of claim 1, in which the cyclic ketones are methyl-substituted, ethyl-substituted or unsubstituted cycloalkanones, cycloalkenones, aminocycloalkanones, aminocycloalkenones and cycloalkadiones. Since the process of dependent claim 3 is a process according to independent claim 1, both the requirements of claims 1 and 3 have to be fulfilled. This means that claim 3 requires that the total amount of all cyclic ketones which remains in the purified toluene diamine is less than 0.1% by weight, based on 100% by weight of toluene diamine.

Accordingly, the scope of claim 1 of the main request is also broader to that of dependent claim 3 as granted.

Hence, the Respondent's argument fails.

Auxiliary request

3. Admissibility

This request has been filed with the reply to the statement of the grounds of appeal. Hence, contrary to the Appellant's view, it is not late-filed (Article 12(1), (2) and (4) RPBA).

According to Article 12 (4) RPBA), the Board has nevertheless discretion to hold inadmissible requests which could have been presented in the first instance proceedings. The opposition division maintained the patent in an amended form according to the Respondent's then pending 7**(th) auxiliary request. Filing further requests before the opposition division was thus not necessary. Hence, under the present circumstances, the Board does not see why an auxiliary request filed in response to the Appellant's appeal should be excluded from the appeal proceedings.

Therefore the auxiliary request is admitted into the appeal proceedings.

4. Remittal

The Appellant requested that the case be remitted to the Opposition Division if the auxiliary request were admitted into the proceedings

The justification put forward by the Appellant for its request to remit the case to the first instance was the right to have two instances for the issue of sufficiency of disclosure arising from the amendment. However, Article 111(1) EPC establishes no absolute right for Parties to have matters raised in appeal proceedings examined by two successive instances; on the contrary, it leaves the Board of Appeal to decide upon a remittal in the light of the circumstances. In the present case, the Board and the Parties were in a position to address all issues raised in the appeal proceedings, said issues being in essence the same as those brought forward in front of the Opposition Division. Therefore, under the present circumstances, the Appellant's request to remit the case to the first instance is refused.

5. Inventive step

5.1 Closest prior art

The Board considers, in agreement with the Parties, that document (10) represents the closest state of the art to the invention. This document is a chapter of an encyclopaedia relating to toluene-2,4-diamine (TDA) and thus reflects the general knowledge of the skilled person.

This document discloses that TDA is mainly used for the preparation of toluenediisocyanate (TDI) by phosgenation (see abstract on page 321 and page 322). Document (10) furthermore indicates that TDA is obtained by hydrogenation of dinitrotoluene (DNT) in methanol at a temperature of from 120 to 140°C and at a pressure of from 24 to 35 bars (see page 325, first paragraph). The crude TDA is purified by first removing reaction water and ortho-toluenediamine by distillation under reduced pressure. TDA is then taken from the bottom of this distillation column and is redistilled to remove the heavy products. Typically the second distillation is carried out at a temperature of from 160°C to 180°C under a pressure of from 13 to 26 mbars (see page 326, first paragraphs and figure 3). The process yields more than 99% m-TDA. Document (10) further reports that merchant specifications indicates that TDA may contain impurities such as the ortho isomers (1.3 wt%), toluidines (0.05 wt%) and nitrobodies (0.03 wt%) (see table 3 on page 327). There is no information on the presence of cyclic ketones in the purified TDA.

5.2 Technical problem

According to the Respondent, the technical problem to be solved is to reduce the coloration of the TDI produced by the phosgenation of TDA.

5.3 Solution

According to the Respondent, the solution was the process of claim 1 including purifying TDA according to step b, characterized in that the separation of the high boilers and cyclic ketones from m-TDA is carried out with a distillation column having a stripping section with at least 3 theoretical plates and that the purified toluenediamine contains a total of less than 0.1% by weight of cyclic ketones.

Document (10) is silent about the presence of cyclic ketones in the purified TDA. The Opposition Division and the Appellant were of the view that the purified toluenediamine obtained by the process of document (10) also contained less than 0.1% by weight; the Respondent, argued, on the contrary, that there was no evidence that it was the case.

The Board notes that there is no disclosure or evidence to conclude whether or not cyclic ketones are present in the purified DTA obtained by the process according to document (10) in content above the claimed threshold of 0.1% by weight.

The Respondent argues that the improvement in lack of coloration of the TDI obtained by the claimed process compared to that obtained by process of document (10) is due to the fact that the cyclic ketones content in the TDA obtained by the claimed process is lower than that of the TDA obtained by the prior art process, i.e. below the threshold of 0.1% by weight.

According to the jurisprudence of the Boards of Appeal, each of the parties to the proceedings carries the burden of proof for the facts it alleges (see e.g. decision T 270/90, OJ EPO 1993, 725, point 2.1). In the present case, the Respondent alleges that the content of the cyclic ketones present in the TDA obtained by the process of document (10) is above the threshold of 0.1% by weight. Therefore, the burden of proof for that allegation rests upon him.

In the absence of any substantiating facts and corroborating evidence, the Board therefore considers the Respondent's allegation that cyclic ketones are present in the toluenediamine purified by the process of document (10) above 0.1% by weight as an unsubstantiated allegation, which thus is not to be taken into account by the Board.

The process of claim 1 also differs from the process of document (10) with regard to the indication of the dwell time in step (a) and the specification of the head temperature/pressure and bottom temperature to carry out the distillation in step (b).

However, the Respondent did not rely on these features to characterise the proposed solution to the problem of coloration. Accordingly since these distinguishing features are not intended to contribute to the solution of lowering the colour of TDI, they should not be taken into account when assessing obviousness (see T 22/81, OJ EPO 1983, 226, points 5.1 and 7 of the reasons).

The Board therefore concludes that the solution proposed by the patent-in-suit is the process of claim 1 which is only characterised in that the separation of high boilers and cyclic ketones from mTDA is carried out with a distillation column having a stripping section with at least 3 theoretical plates.

5.4 Success

The Respondent relied on the knowledge of the skilled man in order to demonstrate that the claimed process was a solution to the technical problem defined above and submitted that it was credible that the problem was solved because the TDA obtained by an improved distillation contained fewer impurities which are responsible for the coloration of the TDI.

The Board shares this view and is therefore satisfied that the problem is solved by the subject-matter of claim 1.

5.5 Obviousness

It is general knowledge that obtaining a coloured reaction product, which must be normally colourless, is due to impurities present in the reaction product. These may be formed from the reaction of by-products already present in the starting product. Hence, an obvious way to remedy a coloration problem is to purify the starting materials. Accordingly, the skilled person faced with undesirable coloration of the TDI would regard the purification of the starting TDA product as an obvious solution to reduce TDI coloration.

According to the Respondent there was nothing in document (10) which suggested improving the purity of TDA in order to obtain less coloured TDI.

However, the skilled man knows that impurities in starting materials may result in undesirable by-products in the end-product. The specification of commercial product generally indicates the presence of impurities (also see document (10); table 3 on page 327). In addition, document (10) points out that coloured by-product are formed by the presence of ortho-substituted TDA, which are other by-products formed in the production of the TDA. The Respondent's argument therefore cannot convince the Board.

One obvious way to improve the purification of the TDA is to improve its distillation. As the quality of the distillation column is expressed as a number of theoretical plates, improving distillation can be achieved for example by increasing the number of theoretical plates in the stripping section of the second distillation.

The Respondent argued that there were a lot of possibilities for the skilled man to increase purity of the TDA. There was nothing advising the skilled man to specifically increase the number of theoretical plates in the stripping section of the second distillation.

However, it has not been shown that improving specifically this section of the distillation of the TDA is associated with an unexpected effect. Thus, the arbitrary choice to improve the purification of the TDA by using a distillation column having a stripping section with at least 3 theoretical plates lies within the routine activity of the skilled person faced with the problem of reducing the colour of the TDI.

The Respondent submitted that the invention was based on the discovery of a critical threshold for the content of cyclic ketones in the purified TDA, which provided the skilled person with tools which he can use to check the success of the distillation.

However, this argument fails, first because the claimed process does not include any step comprising measuring the content of cyclic ketone; and also because it has not been shown that the threshold of 0.1 wt% cyclic ketones is critical.

The Respondent furthermore argued that the invention was based on the recognition that cyclic ketones present in the TDA were responsible for the coloration of the TDI. As document (10) did not disclose the presence of cyclic ketones in the TDA, the skilled person would have had no incentive to specifically remove these compounds from the TDA.

However, this argument is irrelevant, since the skilled person does not need to recognise that cyclic ketones are responsible for the coloration of TDI to arrive at the subject-matter of claim 1 without inventive skill. The skilled person faced with the problem of coloration of TDI aims to remove any impurities from TDA. By improving the distillation of TDA, the content of impurities, including the cyclic ketones, will be lowered, if they have not been already be removed by the process of document (10) -see point 5.3 above.

All argument of the Respondent being rejected, the Board concludes from the above that the subject-matter of claim 1 of auxiliary request 1 lacks an inventive step.

6. Other issues

The Appellant also submitted that the invention was not sufficiently disclosed. In view of the negative conclusion with regard to inventive step, a decision of the Board on this issue is unnecessary.