T 0971/92 (Terephthalic acid/AMOCO) 07-09-1994

1. The appeal is admissible.

2. The Board is satisfied that no objection under Article 123(2) arises against the subject-matter of the present claims and that their subject-matter is novel with respect to the cited state of the art.

3. The only relevant question that remains to be answered in the present appeal is therefore that of inventive step.

3.1. Document (1), which is mentioned in the present patent application, describes the conventional process for obtaining so-called "polymer grade" terephthalic acid by hydrogenation of an impure (technical grade) terephthalic acid feedstock. In this process the technical grade terephthalic acid containing about 2 to 3 weight percent of 4-carboxybenzaldehyde and further coloured contaminants of the benzil, fluorenone or anthraquinone structure (see column 1, lines 62 to 67 and col 2, lines 58 to 63) is dissolved in water under pressure, preferably at a temperature of about 240 to 275 C (column 2, line 64 to column 3, line 37) and this solution is treated either batchwise or continuously with hydrogen at a partial pressure of about 70 to 1000 kPa (10 to 150 p.s.i.a, column 4, lines 16 to 18) in the presence of palladium on charcoal (column 5, lines 19 to 24). The resulting solution is separated from the catalyst, if necessary, and the purified terephthalic acid recovered by crystallisation (column 5, lines 32 to 35). According to column 4, lines 24 to 32 the main impurity to be reduced is 4- carboxybenzaldehyde, but nevertheless the measurement of the optical density, e.g. at 340 or 380 nm (see column 8, lines 39 to 72) of the recovered terephthalic acid may serve as a useful yardstick to measure the reduction or conversion of characteristically yellow-coloured impurities. Although the reduction requires very little hydrogen, it is preferred to use hydrogen in the range of 1 to 5 moles excess over the stoichiometric amount. The process may be performed in the absence of a separate gas phase of hydrogen, i.e. all the hydrogen required for reducing the impurities can be in solution (column 6, lines 19 to 24). According to column 4, lines 10 to 14 even very small amounts of hydrogen, corresponding to a partial pressure as low as 1 to 3 p.s.i.a. are in principle sufficient for the reduction reaction but would not be commercially attractive because the reaction would be too slow or incomplete.

3.2. The technical problem set out in the description of the present patent application is to "optimise control" of the reduction of coloured compounds (see page 2, lines 7 to 15) in the above process of producing "polymer grade" terephthalic acid.

During the oral proceedings the Appellant submitted, with reference to a diagram similar to that reproduced below

(DIAGRAM)

that the expression "control" implies that the process is performed under conditions where the product quality in fact depends on the process parameters, in particular on the hydrogen concentration, i.e. conditions outside the area of the horizontal part of the curve in the above diagram. Thus he submitted that the real problem was to control the process in a manner that a "predetermined level" of the Hunter b*-value (well known for measuring the yellow appearance of a product, see description, page 7, line 29 to page 9, line 9) of the purified product could be maintained. The expression "predetermined level" should in his submission be construed to mean a level different from the minimum level indicated in the above diagram, because the latter is the inevitable level caused by non-reducible impurities and cannot be influenced by modulating the process parameters.

3.3. In other words, the Appellant wishes to have the present independent claims of both sets under consideration construed to be limited to the production of a purified terephthalic acid still containing some reducible yellow- coloured impurities. The Board is not satisfied that such a narrow construction of the expression "predetermined", which excludes the minimum level of the Hunter b*-value corresponding to complete reduction of all reducible impurities, is in accordance with the content of the application documents as filed, since the excess of hydrogen over the stoichiometric amount recommended in the present application (see page 6, lines 16 to 22) is exactly the same as that indicated as the preferred range in document (1), column 4, lines 19 to 24, and the hydrogen partial pressures and reaction temperatures used in the examples of the present application are all within the preferred range recommended in document (1), so that no indication can be found in the application documents as filed that the desired product of the claimed process should be different from "polymer grade" terephthalic acid, i.e. terephthalic acid of the quality described in document (1) (see column 8, line 39 to column 9, line 7). Moreover, the Appellant himself relied on this narrow construction of the scope of the present claims for the first time during the oral proceedings, whereas his earlier submissions were clearly based on the broader construction of the above expression which includes the said minimum level. In any case, however, the question of inventive step could not have been decided in the Appellant's favour even on the basis of the Appellant's narrow construction of the scope of the present application.

3.4. On that basis, the technical problem to be solved by the present patent application would be to provide a process for obtaining a terephthalic acid containing a predetermined amount of reducible yellow-coloured impurities, defined by its Hunter b*-value. Since the main and the auxiliary request have to be considered in relation to the same technical problem, and the Appellant acknowledged that nothing turned on the differences between the technical features recited in the respective main claims of the two requests, there is no need to deal with these requests separately.

3.5. The application proposes to solve this problem essentially by modulating the amount of hydrogen so as to obtain the desired "predetermined" Hunter b*-value (main request) or, more precisely, by calculating the necessary amount of hydrogen from the degree of purity of the crude terephthalic acid, indicated by the optical density at 340 nm (auxiliary request).

3.6. Although document (1) does not directly address the problem of obtaining such a product, it contains some basic information about the required amount of hydrogen and about the possibilities of checking the completeness of the reduction (see e.g. column 4, lines 24 to 32 and lines 10 to 14, referred to in item 3.1. above). From this disclosure the skilled person would infer that the completeness of the reduction reaction would depend on the hydrogen partial pressure in the manner reflected in the above diagram, i. e. in the manner the skilled person would expect on the basis of his common general knowledge, and could be monitored by measuring the optical density of the product. Moreover, document (1) describes the additional determination of the yellow colour of the purified product by dissolving it in DMF and determining the colour of the solution by comparison with APHA colour standards (column 8, lines 7 to 11). In the Board's judgment, nothing inventive can be seen in replacing this measurement of the yellow colour by the measurement of the Hunter b*-value, which is another well-established method for measuring the same property (see the present application, page 9, lines 5 to 9). In addition, as has already been mentioned in item 3.3. above, the excess of hydrogen over the stoichiometric amount recommended in the present application is exactly the same as that indicated as the preferred range in document (1), and the hydrogen partial pressures and reaction temperatures used in the examples of the present application are all within the preferred range recommended in document (1).

Thus the Board holds that the solutions of the above technical problem provided by the main and the auxiliary request did not require inventive skill. This was no longer disputed by the Appellant during the oral proceedings.

3.7. The Board is also not satisfied that an inventive step can be seen in the mere appreciation of the above technical problem, as submitted by the Appellant.

3.7.1. It is the Board's position that the appreciation of conventional technical problems which form the basis of the normal activities of the notional "person skilled in the art", such as the removal of shortcomings, the optimisation of parameters, the saving of energy or time cannot involve an inventive step. The appreciation of a technical problem may thus only contribute to the inventive step in very exceptional circumstances. However, if an applicant nevertheless wishes to rely on an allegation that the inventive activity resides in the recognition of a technical problem to which the solution is admittedly obvious, as in the present case, then the minimum requirement that must be fulfilled is that this technical problem is clearly and unambiguously disclosed in the application as filed. For the reasons set out in item 3.3 above, the Board holds that this requirement is not met in the present case. Thus the Appellant's submission fails already for this reason.

3.7.2. Moreover, it appears from document (1) that the degree of purity of "polymer grade" terephthalic acid was solely determined by commercial demands of the fiber industry, which did not accept a poorer quality. Thus the only reason why the skilled person did not seriously contemplate choosing reaction conditions leading to incomplete purification was a commercial one (see document (1), column 4, lines 10 to 16). The Appellant has asserted during the oral proceedings that in the meantime manufacturers of polyester fibers were prepared to accept a poorer quality of terephthalic acid. However, in the Board's judgment, the observation of the market in order to be able to respond to any of its demands belongs to the normal activities of the notional "person skilled in the art". Therefore the mere recognition that there was now a market for terephthalic acid made to less stringent purity requirements does not mean that any inventive step is involved in adapting a known process so as to make a less pure terephthalic acid.

3.7.3. During the oral proceedings the Appellant has additionally asserted that it has been found that terephthalic acid having a "predetermined" Hunter b*-value has technical advantages over the purer product described in document (1), without, however, providing evidence to this effect. He admitted that the application as filed did not disclose any particular Hunter b*-value or range of such values which could be correlated to such a technical effect. Therefore the Board holds that this submission cannot be taken into account in the assessment of the inventive step of the process of the present application, as this advantage, if it exists, relates only to something which has neither been described nor claimed in the present application, as any invention would here relate to the use of the impure product and not to the process of manufacturing it.