T 0980/99 (Production of urea/UREA CASALE) 02-10-2002

Reasons for the Decision

1. The appeal is admissible

Main request

2. Article 56 EPC - Inventive step

2.1. The claimed invention relates to a method of retrofitting a pre-existing plant for urea production including technical features as defined in Claim 1 (cf. point VI above). In accordance with the "problem-solution approach" consistently applied by the Boards of Appeal to assess inventive step on an objective basis, it is necessary to establish the closest state of the art being the starting point, to determine in the light thereof the technical problem which the invention addresses and solves, and to examine the obviousness of the claimed solution to this problem in view of the state of the art. The closest prior art is normally a prior art document disclosing subject-matter aiming (a) at the same objective as the claimed invention and (b) having the most relevant technical features in common.

2.2. Document (2) discloses a process in which the total synthesis of urea from ammonia and carbon dioxide is carried out in two separate and simultaneous phases (cf. column 1, lines 10 to 13). An overall result is achieved, in which the advantages of urea synthesis with a large excess of ammonia are combined with the advantages of complete recycle urea synthesis. The two phase or dual cycle synthesis thus results in large overall improvement in operating efficiency and economy (column 1, lines 25 to 30). This process refers to the same principle as the method of preparation of urea of the claimed invention, namely the combination of two reactors in a complete recycling process. Furthermore, the process of document (2) is disclosed in details by reference to the figure:

A feed of ammonia (1) and carbon dioxide (2) in a molar ratio NH3:CO2 between 4 and 10 is passed in an autoclave (3) to achieve high conversion to urea (cf. column 3, lines 10 to 20). The resulting urea-containing stream is passed to an excess ammonia separation vessel (7) for removing excess ammonia which is condensed and recycled or stored (column 3, lines 26 to 30; lines 57 to 60). The residual effluent stream (17) is removed and passed into ammonium carbamate decomposer (18). An additional urea synthesis effluent stream (19), also containing ammonium carbamate, is passed into ammonium decomposer (18) together with stream (17)(cf. column 3, lines 61 to 66). This stream (19) comes from the second urea synthesis autoclave (55) which receives an aqueous ammonium carbamate solution (54) (see below) and additional ammonia (56) and carbon dioxide (57) and which operates with a relatively low proportion of excess ammonia, and achieves a lower percent conversion than the autoclave (3) (cf. column 2, lines 47 to 50; column 4, lines 63 to 75). The mixed gas-liquid stream removed from ammonium carbamate decomposer (18) is passed into decomposer separator vessel (23) to separate via (24) a mixed off-gas (cf. column 4, lines 1 to 2) and via (25) a liquid consisting primarily of an aqueous urea solution with a slight amount of residual ammonium carbamate and free ammonia (cf. column 4, lines 6 to 9). The mixed off-gases from separator (23) are passed into the condenser stripper (43) to be scrubbed to remove bulk of carbon dioxide so that a final ammonia stream free of carbon dioxide is removed via (47) and condensed to liquid ammonia stream (49) suitable for direct recycle (cf. column 4 lines 46 to 62). An aqueous ammonium carbamate solution is also withdrawn from unit (43) and passed into the second urea autoclave (55) (column 4, lines 63 to 67).

2.3. Thus, the resulting plant disclosed in document (2) comprises the same technical features as the resulting plant obtained by the claimed method. Indeed, the reactor (R2) corresponds to the reactor (55), the recovery section (SE-RI) corresponds to the system comprising the decomposer (18), the separator vessel (23) and the condenser stripper (43). The reactor (R1) corresponds to the reactor (3) also connected to the said system (18), (23) and (43) and to fresh ammonia and carbon dioxide. The said system is also connected to reactor (55), i.e. reactor (R2), for recycling carbamate solution (unreacted products). Furthermore, since the pure ammonia removed from the condenser (43) is recycled, one of the alternatives which emerges unambiguously for the skilled reader from the disclosure of document (2) is that the ammonia is recycled to the reactor (3), i.e. reactor (R1).

2.4. Document (2) discloses, furthermore, the utilization of this process for modifying an existing 6 to 1 urea synthesis facilities to provide an economically full recycle operation (cf. column 2, lines 62 to 68). The Appellant conceded that document (2) related to a retrofitting method.

2.5. In conclusion, one of the objectives of document (2) is a method of retrofitting a pre-existing plant. The resulting plant obtained by implementing the said method of retrofitting corresponds to that now claimed (cf. point 2.3 above), the sole difference lying in the starting pre-existing plant to be retrofitted. Document (2) describes a method of modifying existing 6 to 1 urea synthesis facilities to provide an economically full recycle operation (cf. column 2, lines 62 to 68), by adding a reactor coupled with a recycling process, while the claimed method relates to a method of retrofitting a pre-existing plant including a reactor coupled with a recycling process by adding a reactor working as "once-through" (without recycle), the resulting plants being the same.

2.6. Document (6) is the Snamprogetti process as described in the patent in suit (cf. column 1, lines 18 to 52 and Figure 1). This description is not a prior art disclosure since it was part of the application as filed and, moreover, does not refer to any source of information made available to the public which could have confirmed the content of this description. It is, therefore, not admissible from a legal point of view to consider such a description as prior art. This finding has nevertheless no consequence on the issue to be decided since the parties agreed to rely in lieu thereof on the disclosure of document (22) which discloses the said Snamprogetti process with recycling of the carbamate solution to the reactor. However, document (22) cannot be the closest prior art since it does not address the same objective as the claimed invention, namely a method of retrofitting a pre-existing plant.

2.7. Document (16) discloses several methods for revamping urea plants using "conventional" or "stripping" total recycle processes to improve performances. However, those methods do not involve a two-reactor technology and, therefore, document (16) has less relevant technical features in common with the claimed invention than document (2).

2.8. The Appellant argued that the disclosure of document (2) could not be considered as the closest state of the art since the technology disclosed was old, did not help to increase the specific throughput of the reaction volume as taught by document (3) (cf. column 2, line 12 to column 3, line 4) and, in fact, was considered as obsolete at the time the patent in suit was filed. Furthermore, the yield obtained in implementing the process according to document (2) was lower than that obtained with the preexisting plant, contrary to the claimed method.

2.9. However, in accordance with the "problem-solution approach" consistently applied by the Board of Appeal to assess inventive step, the closest prior art is normally a prior art document disclosing subject-matter aiming at the same objective as the claimed invention and having the most relevant technical features in common and that irrespective of its age. Which prior art qualifies as the closest in respect of what is claimed depends indeed on its technical closeness in respect to the latter and not on its age thereto. The Board has no reason therefore to accept an age related approach for establishing the starting point for the assessment of inventive step as advocated by the Appellant.

2.10. Since document (2) aims at the same objective as the claimed invention and has the most technical features in common with the claimed invention, it is the Board's conclusion that it represents the prior art closest to the patent in suit and thus, the starting point in the assessment of inventive step.

2.11. The Appellant argued that the claimed invention provided advantages in terms of yield over the technology disclosed in document (2). However, he submitted nothing relevant in that respect. Indeed, since the resulting plant as defined in Claim 1 is the same as that of document (2), the Board can only conclude that the yields obtained in both processes are comparable. Therefore, the problem to be solved in view of document (2) can only be seen in the provision of a further method for retrofitting a pre-existing plant for urea production.

2.12. In view of the example described in the patent in suit, the technical problem is solved over the whole claimed area, which was not contested.

2.13. It remains to be decided whether or not the claimed solution is obvious over the cited prior art.

The relevant question to be answered is whether the person skilled in the art, starting from document (2), would have envisaged to retrofit a pre-existing plant for urea production involving a recycling process in the way as defined in Claim 1. The Board observes, in that respect, that the disclosure of document (2) is not limited to retrofitting a pre-existing urea plant involving a "once-through reactor" but also encompasses a more general embodiment involving the combination of a one-through reactor to a complete recycle process. Indeed, this document discloses that:

"Two synthesis autoclaves are employed in the process. The first autoclave receives feed streams of ammonia and carbon dioxide, with a high excess of ammonia being employed, and achieves a very high percent conversion to urea. The effluent from the first reactor is combined (emphasis added by the Board) with the effluent from the second reactor, and the resulting stream is processed to yield product urea solution, pure ammonia, and aqueous ammonium carbamate solution. The aqueous ammonium carbamate solution is then recycled to the second reactor, together with additional ammonia and carbon dioxide. This second reactor is operated with a relatively low proportion of excess ammonia, and achieves a lower percent conversion than the first reactor" (cf. column 2, lines 35 to 50).

This general process is also reflected by Claim 1 of this document.

Therefore, one of the alternative methods within the teaching of document (2) for modifying a pre-existing plant is to combine a high yield reactor with a process involving a second reactor to which the aqueous carbamate solution is recycled (it being understood that the recycling of pure ammonia to the high yield reactor emerges unambiguously from the disclosure of document (2) (cf. point 2.3 above). This teaching leads the person skilled in the art, when following the description of the figure to combine the reactor (3) to the complete recycle process involving the reactor (55), the system comprising the decomposer (18), the separator vessel (23), the condenser stripper (43), namely the recycling section, and connecting means to reactor (55) for recycling carbamate solution and, thus, straightforwardly and without inventive ingenuity to the claimed invention.

2.14. The Board concludes that the subject-matter of Claim 1 does not involve an inventive step and, therefore, the present request must fail.

First auxiliary request

3. Article 123(2)(3) and Rule 57(a) EPC - Amendments

3.1. In accordance with the provisions of the decision of the Enlarged Board of appeal G 9/91 (cf. OJ EPO 1993, 408, point 19 of the reasons), the Board must examine whether the amendments to the granted claims comply with the requirements of the EPC (e.g. with regard to the provisions of Article 123(2) EPC). This applies to the subsequent requests too.

The subject-matter of present Claim 1 differs essentially from that of the main request in that the features (c) to (e) relating to the presence of a separator were added (cf. point VI above). Those amendments are designed to overcome the grounds of opposition, namely absence of novelty and/or inventive step. Therefore, those amendments can be admitted under Rule 57(a) EPC.

3.2. Those added features find support in the application as filed on pages 12 and 13, bridging paragraph. It follows that those amendments do not extend beyond the content of the application as filed. Nor do they extend the protection conferred.

4. Article 56 EPC - Inventive step

4.1. Document (2) also discloses that the resulting urea-containing stream is passed to an excess ammonia separation vessel (7) for removing excess ammonia which is condensed and recycled (column 3, lines 26 to 30; lines 57 to 60) and that the residual effluent stream (17) is admitted in the recycling section (18), (23) and (43). The Appellant argued that the pressure of the urea solution leaving the "once-through" reactor (3) was reduced to a value between 14 and 41 bars, while the second reactor operated between 140 and 400 bars as could be deducted from the example. It was clear, therefore, that the ammonia which was separated in the vessel (7) should be condensed and re-compressed with high utilities consumption for recycling. By contrast, the ammonia removed from the flash separator (SEP) as defined in step (c) could be directly recycled to the pre-existing plant reactor without energy consumption. However, this difference does not emerge from the definition of the separator (SEP) in Claim 1. It is true that the description of the patent mentions that the separator (SEP) operates at reactor pressure (R2). However, this feature is not present in the wording of the claim and cannot be considered for distinguishing the vessel (7) of document (2) and the separator (SEP) of the claimed invention. The added features, therefore, cannot distinguish further the claimed invention from document (2) which remains the closest state of the art.

4.2. For the same reasons as those set out above (cf. point 2.13), the claimed subject-matter is obvious over document (2).

4.3. The Board concludes that the subject-matter of Claim 1 does not involve an inventive step and, therefore, the first auxiliary request must fail.

Second auxiliary request

5. Amendments - Article 123(2), 84 and Rule 57(a) EPC

5.1. The subject-matter of present Claim 1 differs essentially from that of the first auxiliary request in that the features related to a stripper (S) and means for recycling, from the stripper, a great part of carbamate and part of the free ammonia to reactor (R2) were added (cf. point VI above). Those amendments are designed to overcome the grounds of opposition, namely absence of novelty and/or inventive step. Therefore, those amendments can be admitted under Rule 57(a) EPC.

5.2. The Appellant argued that those added features found support in the application as filed, namely on page 4, line 18 to page 5, line 18 in relation with Figure 1 which refers to the isobaric stripping process (Snamprogetti); on page 8, line 16 to page 10, line 18 in relation with Figure 2 which is the process according to the claimed invention "in its more significant conceptual features (emphasis added by the Board)" and on page 10, lines 20 to 21 and page 11, line 22 to page 12, line 10 in relation to Figure 3 which is the application to the retrofitting of the selfstripping process NH3 of Snamprogetti.

5.3. The Board does not deny that for deciding whether or not one or several amendments satisfy the requirements of Article 123(2) EPC, the whole content of the application as filed is to be taken into account. This cannot mean, however, that various information belonging to different levels of disclosure (prior art, general disclosure and example) may be combined unless this intermediate generalization be directly and unambiguously derivable from the application as filed.

5.4. In that context, the subject-matter of present Claim 1 is the result of the combination of the subject-matter of Claim 1 of the first auxiliary request which essentially reflects the schematic representation of Figure 2 with part of the embodiment of the isobaric stripping process (Snamprogetti) such as set out in Figures 1 and 3. However, the latter is a complete recycling process involving a "recycling section (SE-RI)" comprising not only a stripper (S) but downstream, a middle pressure phase (SMP) and a rectification column (CR) (cf. page 5, lines 4 to 14 of the application as filed). In the present case, the fact of incorporating in the general concept a particular element makes this concept fall apart since according to the application as filed this particular element cannot operate without the cooperation of the other elements (SMP) and (CR). In other terms, singling out the stripper (S) from the specific embodiment of Figures (1) and/or (3) and incorporating this element in a more conceptual definition such as set out in Figure 2 represents an intermediate disclosure of subject-matter which is not directly and unambiguously derivable from the application as filed contrary to the requirements of Article 123(2) EPC.

5.5. Furthermore, although the feature (f) in the first auxiliary request, i.e. "providing conduit means (7) between said recycling section (SE-RI) and the reactor (R2) of the pre-existing plant for feeding thereto said solution (SC) of unreacted products" is clear because the expression "recycling section" is defined at a certain conceptual level, it becomes unclear once the term "comprising a stripper" is added as is the case in this request. Indeed, that raises the question from which part of the recycling section does the conduit mean (7) start. This information is not present in the claim but in the description (Figure 3) where it is indicated that the solution (SC) is recycled from the rectification column (CR). An essential technical feature was, therefore, omitted in contravention with the requirements of Article 84 EPC.

5.6. In view of the above reasons, the present request must fail.

Third auxiliary request

6. Amendments - Article 123(2), 84 and Rule 57(a) EPC

6.1. The subject-matter of present Claim 1 differs essentially from that of the second auxiliary request in that the stripped carbamate, the free ammonia and the flash vapours (VF) are recycled to the reactor (R2) via a carbamate condenser. Those amendments are designed to overcome the grounds of opposition, namely absence of novelty and/or inventive step. Therefore, those amendments can be admitted under Rule 57(a) EPC.

6.2. However, for the same reasons as explained above concerning the second auxiliary request, mentioning the stripper (S), while omitting the other technical features necessary in the embodiment of Figures 1 and/or 3 for the recycling, amounts to an inadmissible singling out contrary to the requirements of Article 123(2) EPC. Furthermore, for the same reasons as explained above concerning the second auxiliary request, present Claim 1 is in contravention of the requirements of Article 84 EPC.

6.3. In view of the above reasons, the present request must fail.

Fourth auxiliary request

7. Amendments - Article 123(2), 84 and Rule 57(a) EPC

7.1. The subject-matter of present Claim 1 differs essentially from that of the third auxiliary request in that

(a) the stripped carbamate and free ammonia are recycled to the reactor (R2) via a carbamate condenser;

(b) The reactor (R1) is positioned in parallel to the reactor (R2) and upstream of the recycling section (SE-RI);

(c) Pumping devices are present for feeding high purity ammonia and carbon dioxide at operative conditions higher compared with the reactor (R2) of the pre-existing plant;

Those amendments are designed to overcome the grounds of opposition, namely absence of novelty and/or inventive step. Therefore, those amendments can be admitted under Rule 57(a) EPC.

7.2. However, for the same reasons as explained above concerning the second and third auxiliary request, mentioning the stripper (S), while omitting the other technical features necessary in the embodiment of Figures 1 and/or 3 for the recycling, amounts to an inadmissible singling out contrary to the requirements of Article 123(2) EPC. Furthermore, for the same reasons as explained above concerning the second auxiliary request, present Claim 1 is in contravention with the requirements of Article 84 EPC.

7.3. For the above reasons, the fourth auxiliary request must also fail.

Fifth auxiliary request

8. Amendments - Article 123(2), 84 and Rule 57(a) EPC

8.1. The subject-matter of Claim 1 contains some but not all the features derivable from Figure 1 and some but not all the features derivable from Figure 3. Although the now claimed invention may be seen in a method of retrofitting a plant as set out in Figure 1 by incorporating a second reactor (R1) to provide the retrofitted plant according to Figure 3, it is however necessary that the technical features defining the present Claim 1 reflects this method. This is not the case here. Indeed:

In Figure 1, fresh ammonia is provided to reactor (R2), while it is no longer provided to reactor (R2) in Figure 3. Also, a pump (P) is present in Figure 1 for pumping NH3 (NEP) into reactor (R2), while it is no longer present in Figure 3. Those features are nevertheless present in Claim 1. The claimed subject-matter, therefore, cannot find support in the combination of the embodiments of Figures 1 and 3 but goes beyond this combination and extends the content of the application as filed (Article 123(2) EPC).

Furthermore, there is an internal contradiction in this claim since, according to a feature, NH3 at high purity is recycled to reactor (R2), while according to another feature, NH3 is recycled to reactor (R1). This contradiction renders this claim also unclear (Article 84 EPC).

8.2. The present request must also fail.

8.3. Since the subject-matter of the main request does not comply with the requirements of Article 56 EPC and since the subject-matter of the other requests does not comply with the requirements of Article 123(2) or 84 EPC, the appeal must be dismissed.