T 0398/09 (Distillation of (meth)acrylic acid (esters)/NIPPON SHOKUBAI) 02-02-2012

1. The appeal is admissible.

All requests

2. Amendments (Article 100(c) EPC)

2.1 The Respondent argued that the claims of all of the requests contained subject-matter extending beyond the content of the application as filed, since the feature "(meth)acrylic esters" was not disclosed without the limitation that these esters should be easily polymerizable, as required by the compounds of claim 7 as originally filed, when combined with claim 1 as originally filed. In view of steric hindrance of the ester group, at least some (meth)acrylic esters would not be easily polymerizable.

2.2 However, a process for inhibiting the polymerization of (meth)acrylic esters is disclosed on page 1, lines 1 to 4 of the application as filed, said passage not limiting these esters to those which are easily polymerizable. Instead, this passage states that the invention relates to the polymerization of "(meth)acrylic esters, and other easily polymerizable compounds", which implies that (meth)acrylic esters are per se easily polymerizable according to the invention. Thus, on restricting original claim 1 from "easily polymerizable compounds" to inter alia "(meth)acrylic esters", the specification that these should be easily polymerizable becomes superfluous.

2.3 For these reasons, the Board concludes that the unqualified feature "(meth)acrylic esters" is disclosed in the application as originally filed, such that the ground for opposition pursuant to Article 100(c) EPC based on said feature is not justified.

3. Inventive step (Article 56 EPC)

Lack of inventive step was the sole reason for refusing the patent in suit. Thus, the Board considers that in the present case, it is appropriate to first examine whether or not the claimed subject-matter of the Appellant's requests involves an inventive step, novelty having been objected to on the basis of a document which is prior art in the sense of Article 54(3) EPC, i.e. not relevant for inventive step of requests entitled to priority.

Main request

3.1 The patent in suit is directed to a process for inhibiting polymerization during the distillation of (meth)acrylic acid and/or (meth)acrylic ester by wetting surfaces of parts of the distillation unit.

3.1.1 A similar process already belongs to the state of the art, namely to the disclosure of document (2). More particularly, this document discloses the distillation of vinyl monomers, such as acrylic acid (see Example 1), whereby the distillation tower comprises perforated trays which ensure that the liquid flowing down through the tower causes a substantial wetting of the back surfaces of said trays and substantially the entire wall surface of the tower (cf. claim 1), said wetting being to prevent the polymerization of the vinyl monomers (see column 1, lines 61 to 67).

3.1.2 Thus, the Board considers, in agreement with the Appellant, the Respondent and the Opposition Division, that in the present case the distillation process of document (2) represents the closest state of the art and, hence, takes it as the starting point when assessing inventive step.

3.2 In view of this state of the art, the Appellant defined the problem underlying the patent in suit as the provision of an alternative process for inhibiting polymerization during the distillation of (meth)acrylic acid and/or (meth)acrylic ester (see paragraph [0010] of the specification of the patent in suit).

3.3 As the solution to this problem, the patent in suit proposes the process according to claim 1, characterised in that the wetting of the surface of a constitutive member of the distillation unit is effected by spraying.

3.3.1 The Appellant argued that the claimed solution was also characterised by the fact that the constitutive member could be one which was not disclosed in document (2), namely a tray supporting member, a packing supporting member, a flange, a nozzle, an end plate, a chimney, a downcomer, a baffle, or a shaft of an agitator.

However, the constitutive member in claim 1 of the patent in suit may also be a column wall, which is also the case in document (2) (see point 3.1.1 above), such that so long as the claim is not restricted to constitutive members different from those of document (2), said members cannot be considered to be characterising features of the invention.

3.3.2 The Appellant additionally contended that the composition of the liquid to be sprayed, namely that it had substantially the same, and not exactly the same, composition as the liquid surrounding the constitutive member to be sprayed, was also a feature not disclosed in document (2) and thus characterising for the claimed solution. By virtue of this definition of said liquid, the claimed process embraced spraying with a wider range of liquid compositions than in document (2), wherein the composition of the wetting liquid could not be controlled and thus had the same composition as that of the liquid surrounding the constitutive member.

However, a feature cannot be considered to be a distinguishing feature vis-à-vis a prior art feature merely by virtue of the fact that it is broader than the prior art feature, but nevertheless fully embraces said prior art feature. Since the composition of the wetting liquid in claim 1 of the patent in suit is defined as "having substantially the same composition with that of a liquid surrounding said constitutive member", it embraces the composition of the liquid flowing down through the tower according to document (2), which the Appellant did not contest. Thus, said feature also cannot be considered to be a feature characterising the solution claimed (cf. point 3.3.1 above).

3.4 The Board has no reasons to doubt, and the Respondent has not contested, that the technical problem defined above has effectively been solved by wetting the surface of a constitutive member of the distillation unit by spraying as defined in claim 1.

3.5 Finally, it remains to be decided whether or not the proposed solution to the problem underlying the patent in suit is obvious in view of the state of the art. In other words, whether in the light of document (2), which already teaches the perpetual wetting of surfaces of parts of a distillation column by percolation of the distillation liquid through specifically designed perforated trays in order to inhibit polymerization, it was obvious to carry out the wetting by spraying as opposed to percolation.

3.5.1 When starting from the process for distilling vinyl monomers with inhibition of polymerization known from document (2), it is a matter of course that the person skilled in the art seeking to provide an alternative distillation process wherein polymerization is inhibited would turn his attention to that prior art addressing distillation of the same monomers which also aims to avoid the problem of polymerization, for example, document (3). Said document (see page 3, lines 1 to 7 and page 7, lines 23 to 25) is concerned with distilling readily polymerizable liquids, such as (meth)acrylic acid and (meth)acrylic esters, without causing the formation of undesirable polymerization products. It prevents polymerization by wetting the entire surface of the condenser upon which the vapour from the distillation condenses (see page 3, lines 21 to 24), said wetting being carried out by "conventional spraying means" (see page 6, lines 1 to 21). Thus, the person skilled in the art would know from document (3) that the wetting of surfaces of a distillation unit on which polymerization may occur may also be carried out by spraying, and would thus incorporate this method into the process of document (2) without exercising any inventive ingenuity. For these reasons, the subject-matter of claim 1 is obvious.

3.6 For the following reasons the Board cannot accept the Appellant's arguments designed for supporting inventive step.

3.6.1 The Appellant argued that the skilled person would not have transferred the teaching of the spraying of the condenser from document (3) to the process of document (2) in isolation, since in document (3), the vapour from the evaporator was maintained in a superheated state and the walls of the evaporator and conduit pipe leading to the condenser were heated so that the vapour would not condense until it reached the condenser, which was physically separated from the evaporator. Thus, the skilled person would not have transferred the teaching concerning the spraying of dry surfaces without also superheating the distillation vapour.

However, the skilled person already knows from document (2) that he should ensure perpetual wetting of surfaces of the distillation column where polymerization is likely to occur, these being according to document (2) mainly at the tower wall, the back surfaces of the trays or the exterior surfaces of downcomers (see column 1, lines 31 to 33), i.e. where the vapour is partially condensed (see column 1, lines 50 to 60). He thus knows that if he achieves this wetting, polymerization is inhibited such that superheating of the vapour, as performed in document (3), would be superfluous. Hence, already being aware from document (2) that polymerization can be prevented by wetting of surfaces susceptible to formation of polymerization products, he would learn from document (3) that said wetting can be carried out by spraying and would therefore transfer this teaching from document (3) to the process of document (2).

3.6.2 The Appellant also argued that in document (3) the condenser was sprayed, which was not one of the constitutive members listed in the patent in suit, such that the skilled person could not arrive at the present invention by simply combining the teachings of document (2) and (3).

However, as already discussed above, the necessity of wetting other constitutive members of the distillation unit, such as the column wall, is already taught by document (2) (see column 1, lines 31 to 33). The only teaching that the skilled person needs to transfer from document (3), when the problem underlying the patent in suit is merely to provide an alternative process for inhibiting polymerization during the distillation of (meth)acrylic acid and/or (meth)acrylic ester, is the manner in which the column wall should be wetted, not that it should be wetted in the first place. Hence, this argument of the Appellant does not convince the Board.

3.6.3 The Appellant further argued that document (3) was concerned with the wetting of a dry surface (see page 6, line 5), whereas the patent in suit was concerned with the prevention of stagnation of liquids on surfaces which were already covered in a liquid film.

However, the starting point for inventive step is document (2), in which acrylic acid is distilled in a distillation column. Since the distillation process of the patent in suit is not defined differently than that of document (2), then the liquid covering of the constitutive members of the distillation unit, such as column walls, before wetting, cannot be a distinguishing feature of the process of the patent in suit. Thus even if the surfaces wetted in document (2) were already covered in a liquid film, document (2) teaches nonetheless that said surfaces should be perpetually wetted, document (3) merely providing the skilled person with another method for carrying out this wetting.

3.7 As a result the Appellant's main request is not allowable for lack of inventive step pursuant to Article 56 EPC.

Auxiliary request 1

4. Inventive step (Article 56 EPC)

4.1 Claim 1 of auxiliary request 1 differs from claim 1 of the main request in that the feature "distillation unit" has been replaced by "distillation column" and "a baffle" and "a shaft of an agitator" have been deleted from the list of constitutive members. However, the constitutive member may still be a column wall.

4.2 Since the closest prior art document (2) already discloses that the distillation unit is a distillation column, this amendment cannot contribute to inventiveness of the subject-matter of claim 1 of auxiliary request 1 vis-à-vis this document.

4.3 The Appellant argued that the skilled person would no longer have combined the teaching of document (3) with that of document (2), since the wetting in document (3) took place in the condenser which, in contrast to the term "distillation unit", did not fall under the term "distillation column".

However, as indicated in point 3.6.2 above, the only teaching that the skilled person needs to transfer from document (3) to arrive at the present invention is the manner in which the column wall should be wetted, namely by spraying.

4.4 Therefore, the considerations having regard to the assessment of inventive step given in points 3.1 to 3.6 above and the conclusion drawn in point 3.7 above with respect to claim 1 of the main request apply also to claim 1 of auxiliary request 1.

Auxiliary request 2

5. Claim 1 of auxiliary request 2 differs from claim 1 of the main request in that "a column wall" has been deleted from the list of constitutive members. The distillation process does therefore now indeed additionally differ from the process of document (2) by the nature of the constitutive member to be wetted, namely a tray supporting member, a packing supporting member, a flange, a nozzle, an end plate, a chimney, a downcomer, a baffle, or a shaft of an agitator (see point 3.3.1 above).

5.1 It thus now needs to be examined whether the wetting by spraying of these specific constitutive members can contribute to the inventiveness of the distillation process.

5.2 The closest prior art document (2) states that the polymerization takes place "mainly" at the tower wall, the back surfaces of the trays and the exterior portions of the downcomers, these surfaces clearly being the largest surfaces in a distillation column and thus offering a greater area on which polymerization can occur. However, document (2), by virtue of the use of the term "mainly", does not exclude the formation of polymers on other constitutive members of a distillation column, and teaches that polymerization is a ready occurrence on the aforementioned surfaces in view of the fact that vapour is partially condensed thereon (see column 1 lines 50 to 60). Furthermore, document (3) teaches that the undesirable polymerization products are mainly formed at the dead spaces (i.e. liquid and vapour retention portions), the vapour-liquid contacting zones, the vapour phase zones in which the effect of the polymerization inhibitors is low and the like. Thus, the teaching of both of these documents is of general applicability to any surfaces in distillation units where vapour (partially) condenses, the problem of polymerization due to the adhesion of condensate on an agitator shaft, for example, being specifically mentioned in document (3) (see page 7, lines 11 to 19 and Fig. 1, 19). It was thus obvious for the skilled person to spray the surface of any constitutive member where vapour condensation may occur, such as an agitator shaft, in order to prevent polymerization.

5.3 The Appellant argued that the gist of the teaching of document (2) was to avoid the use of downcomers. The agitator shaft mentioned in document (3) was heated in order to prevent condensation, and thus also polymerization, thereon. Hence, neither of these documents taught the wetting of these constitutive members in order to prevent polymerization, but rather removal of said member and heating thereof, respectively. Document (3) also taught to keep the distillation apparatus simple, which implied a lack of other constitutive members.

However, both documents teach that polymer formation is particularly likely at parts of a distillation unit upon which condensation occurs, document (3) specifically mentioning the shaft of an agitator in this respect. Both documents teach that polymerization upon condensation can be avoided by wetting, in the case of document (3), by spraying. That polymerization may also be avoided by the removal of downcomers or by heating of constitutive members and superheating of the gaseous phase does not lessen these teachings.

5.4 Thus the considerations having regard to inventive step with respect to the main request apply also to the auxiliary request 2, i.e. the subject-matter claimed does not involve an inventive step.

Auxiliary request 3

6. Claim 1 of auxiliary request 3 differs from claim 1 of auxiliary request 1 in that it is specified that the temperature of the sprayed liquid is 1 to 30ºC lower than the surface of the constitutive member.

6.1 In view of this additional feature, the Appellant now defined the problem underlying the patent in suit as the provision of a process for inhibiting polymerization during the distillation of (meth)acrylic acid and/or (meth)acrylic ester which results in less polymerization (see paragraph [0016] of the specification of the patent in suit).

6.2 To demonstrate that the process achieves the alleged improvement, the Appellant, who by alleging this fact carries the burden of proving it (see T 355/97, point 2.5.1 of the reasons, not published in OJ EPO), relied upon a comparison of Examples 1 and 3 of the patent in suit. Example 1 allegedly showed that by spraying with a liquid having a temperature 10ºC less than the surface of the constitutive member, namely a manhole, less polymerization occurred than when spraying with a liquid having a temperature 45ºC less than said surface, as in Example 3.

6.2.1 The Appellant alleges that the temperature of the liquid sprayed in Example 1 was 10ºC less, and that in Example 3, 45ºC less, than the surface of the manhole.

However, the temperature of the surface of the manhole is not given in either example, the Appellant merely speculating that its temperature was the same as the bottoms temperature of the column, which is given as 100ºC. The manhole is, however, not at the bottom of the column (otherwise it would already be covered in liquid), but rather at some point above the bottom (as, for example, the manhole denoted 4 in Fig. 3 of the patent in suit), the column having a top temperature of 63ºC. The manhole is also not necessarily insulated, such that its surface temperature does not have to be the same as the liquid film or vapour surrounding it. Since the surface temperature of the manhole in Example 1 is unknown, it cannot be determined with certainty whether spraying with a liquid having a temperature of 90ºC in fact falls within the ambit of the newly introduced feature of claim 1 of auxiliary request 3, namely that the temperature of the sprayed liquid is 1 to 30ºC lower than the surface of the constitutive member. As such, Examples 1 and 3 are not suitable for showing any improvement associated with this newly introduced feature.

6.2.2 The Appellant conceded that the surface temperature of the manhole was not explicitly given in either example, but argued that it could be assumed that the process conditions of Example 1 fell under the present claim, as it was usual patent drafting practice that examples fell within the claims, specifically drawing attention to original claim 2 in this respect. In any case, a clear tendency towards more polymerization upon excessive reduction of the temperature of the sprayed liquid could be concluded from Examples 1 and 3.

However, the Board holds that it cannot be assumed that the examples of the patent specification must fall within the scope of present claim 1, for at least the reason that there was no claim requiring the feature that the temperature of the sprayed liquid is 1 to 30ºC lower than the surface of the constitutive member either in the application as filed or in the patent as granted.

With regard to original claim 2, this claim is directed to a process wherein the temperature of the sprayed liquid is equal to or lower than the surrounding of the constitutive member (emphasis added). Thus even if it were to be assumed that the process of Example 1 fell within the scope of this claim, it would still not necessarily fall under claim 1 of auxiliary request 3, wherein the temperature of the sprayed liquid must be 1 to 30ºC lower than the surface of the constitutive member.

6.2.3 Furthermore, Examples 1 and 3 do not clearly show whether or not any improvement is in fact actually achieved in Example 1. More particularly, Example 1 states merely that "the operation could be continued over about one month without trouble" and Example 3 that "a noticeable amount of polymer was found in the withdrawn liquid after 25-day operation, and the operation was stopped to inspect the column. Polymer of about 0.5 kg was seen to be attached on the bottom of the column".

Thus in Example 3 the operation was stopped to "inspect" the column, not because it was clogged (as was the case, for example, in Example 2). One can thus only derive from these two examples that in Example 3, 0.5 kg of polymer was formed, the amount formed in Example 1 not being indicated. It is thus possible that polymer was indeed formed in the process of Example 1, but not of a sufficient amount to compromise the operation of the column. It is thus not possible to unambiguously conclude that less polymer is formed in Example 1.

6.2.4 Hence, the comparative Examples relied upon by the Appellant for supporting the alleged improvement cannot demonstrate that the technical problem has been solved, since it has not been shown that Example 1 falls under, and Example 3 outside, the scope of claim 1 of auxiliary request 3, and in any case, it has not been convincingly shown that less polymerization occurs in Example 1.

6.3 According to the jurisprudence of the Boards of Appeal, alleged but unsupported advantages cannot be taken into consideration in respect of the determination of the problem underlying the invention (see e.g. decision T 20/81, OJ EPO 1982, 217, point 3, last paragraph of the reasons). Since in the present case the alleged improvement, namely less polymerization, lacks the required experimental support, the technical problem as defined in point 6.1 above needs reformulation, namely as the provision of an alternative process as in point 3.2 above.

6.3.1 The temperature of the sprayed liquid of less than 1 to 30ºC than the surface of the constitutive member is neither critical nor a purposive choice for solving the objective problem underlying the patent in suit, since no unexpected effect has been shown to be associated with this particular temperature range. The act of picking out at random a range for the temperature of the sprayed liquid is within the routine activity of the skilled person faced with the mere problem of providing an alternative process for inhibiting polymerization during the distillation of (meth)acrylic acid and/or (meth)acrylic ester. Therefore, the arbitrary choice of a temperature of the sprayed liquid of less than 1 to 30ºC than the surface of the constitutive member cannot provide the claimed process with any inventive ingenuity.

6.4 Thus, the considerations having regard to inventive step with respect to auxiliary request 1 apply also to auxiliary request 3, i.e. the subject-matter claimed does not involve an inventive step.

7. Other issues

The Respondent also submitted that the subject-matter of all requests was neither novel nor inventive over a document being comprised in the state of the art at least according to Article 54(3) EPC, and that the subject-matter of auxiliary request 3 was not clear (Article 84 EPC). It also contested the admissibility of auxiliary requests 1 and 3 into the proceedings.

In view of the negative conclusion in respect of inventive step for the subject-matter of all requests starting from document (2) as closest prior art, as set out in points 3 to 6 above, a decision of the Board on these issues is unnecessary. In addition, the Respondent raised no objections under Article 123(2) EPC to any of the amendments made to the auxiliary requests, nor did the Board see any reason to question their allowability under this article of its own motion.