Olefin hydroformylation process in an internal loop reactor

FIELD OF THE INVENTION

0001The invention relates to improvements in reactors, particularly internal loop reactors. In embodiments, there are also improvements in heterogeneous (gas/liquid phase) exothermic reactions, particularly hydroformylation reactions, using the improved reactor.

BACKGROUND OF THE INVENTION

0002The hydroformylation reaction, also known as the Oxo Reaction or Oxo Process, consists in reacting a synthesis gas made up of a mixture of carbon monoxide and hydrogen and at least one C_nH_2n olefin so as to obtain a mixture of aldehydes and primary alcohols containing n+1 carbon atoms. The reaction is generally catalyzed with carbonyls of transition metals such as cobalt. This type of reaction is described in detail in patents too numerous to recite. It is commercially highly important, producing products that find uses in plastics, soaps, lubricants, and other products

0003The reactors in which the Oxo Process is carried out can be identical or different in all process stages. Examples of types of reactor which can be used are bubble columns, loop reactors, jet nozzle reactors, stirred reactors and tube reactors, some of which can be cascaded and/or provided with internals. <patcit id="pcit0001" dnum="WO2005058782A"><text>WO 2005058782</text></patcit> discloses the hydrogenation stage of the Oxo Process which uses at least two reactors.

0004As part of the reactor of the "loop" type the liquid phase is recycled and the gas phase is allowed to exit the reactor at the top of the loop. External loop reactors are illustrated, for instance, in <patcit id="pcit0002" dnum="US4312837A"><text>U.S. 4,312,837 (Papp et al.</text></patcit>). The typical reactor used in Oxo is an external loop reactor, but internal loop reactors are also used.

0005An example of an conventional internal loop reactor is illustrated in <figref idref="f0001">Fig. 1</figref> of the present disclosure. Such a reactor is made up of at least two concentric vertical tubes <b><u>1</u></b> and <b><u>2</u></b> connected to each other at their upper and lower ends. As shown in <figref idref="f0001">Fig. 1</figref>, the vertical column <b><u>1</u></b> of loop reactor <b><u>4</u></b> acts as the ascending branch ("riser") while vertical column <b><u>2</u></b> act as the descending branch ("downcomer"). The vertical columns are supplied with jacketed cooling means <b><u>3</u>.</b> Ascending vertical column <b><u>1</u></b> is continuously supplied at its base with the synthesis gas and liquid phase through inlet <b><u>5</u>.</b> Essentially all the synthesis gas and the excess liquid phase is evacuated at the upper connection <b><u>6</u></b>, while essentially only the liquid phase circulates between ascending column <b><u>1</u></b> and descending column <b><u>2</u></b> said circulation illustrated by arrows <b><u>7.</u></b> The difference between the specific gravities of the gas/liquid phase mixture on the one hand and the liquid phase alone on the other hand results in a difference in hydrostatic pressure between the ascending branch and the descending branch, thus leading to circulation of the liquid phase in the reactor.

0006Loop reactors of both the internal and external type are used in reactions other than the Oxo Process. They are useful particularly in exothermic and/or heterogeneous (gas/liquid) reactions and have been used for such diverse reactions as the oxidation of p-xylene (<patcit id="pcit0003" dnum="US4342876A"><text>U.S. 4,342,876</text></patcit>), biotechnological reactions (<patcit id="pcit0004" dnum="WO8804317A"><text>WO 8804317</text></patcit>), and the purification of water (<patcit id="pcit0005" dnum="US6544421B"><text>U.S. 6,544,421</text></patcit>). <patcit id="pcit0006" dnum="US3431188A"><text>US 3431188</text></patcit> discloses an apparatus for a photochemical reaction. It is known that by varying the geometries of the reactor, it is possible to eliminate certain problems encountered in specific reactions. See, for instance, <patcit id="pcit0007" dnum="US4312837A"><text>U.S. 4,312,837</text></patcit> (<patcit id="pcit0008" dnum="FR2430794A1"><text>FR 2430794 A1</text></patcit>); <patcit id="pcit0009" dnum="US4342876A"><text>4,342,876</text></patcit>; <patcit id="pcit0010" dnum="US5277878A"><text>5,277,878</text></patcit>; <patcit id="pcit0011" dnum="US5503810A"><text>5,503,810</text></patcit>; and <patcit id="pcit0012" dnum="US6106789A"><text>6,106,789</text></patcit>. There is, however, no shortage of problems to be solved in these systems and typically solving one problem by simply varying geometries introduces at least one new problem.

0007One of the main problems with conventional loop reactors, is that they are limited in size. At least in part this is simply a matter of the practical difficulty in bending large tubes. In addition, construction of large reactors is also made difficult because the vessels must be erected in the field by sliding internals, which must be standing vertically; otherwise, with reactor on its side, the internals will bend and warp. Furthermore, in the case of the Oxo Process, the reaction typically occurs at very high pressures, such as 4,000 1bs/in (or about 28 MPa), which further limits the size of the vessels as they are known to be constructed in the prior art. As far as the present inventors are aware, the largest known loop reactors have a volume of about 8-12 cubic meters.

0008The present inventors have discovered that by building an internal loop reactor so that the separation between the riser and downcomer portions comprises a heat exchanger, preferably one or more cooling tubes, allows for all the necessary parts to be attached to a reactor head. This allows more convenient construction of the reactor in the field and furthermore reactor volume can be increased considerably over prior art Oxo Reactors.

SUMMARY OF THE INVENTION

0009The present invention provides a process for the catalytic hydroformylation of an olefin feedstock with syn gas, comprising feeding a stream comprising olefin and/or the product of a hydroformylation reaction having the olefin as a starting material, the stream comprising syn gas, to the inlet of an internal loop reactor and obtaining as a product of the internal loop reactor a stream comprising syn gas and the product of a hydroformylation reaction, wherein the internal loop reactor comprises: <ul id="ul0001" list-style="dash" compact="compact"><li>a vertically disposed vessel having a vertical axis, a sidewall, an upper portion and a lower portion;</li><li>a draft tube comprising at least one heat exchange means, the draft tube providing a riser conduit within the draft tube and a downcomer conduit between the draft tube and the sidewall, the draft tube extending into the upper portion of the vessel and comprising at least one opening in the upper portion so as to provide fluid flow communication between the riser conduit and the downcomer conduit and extending into the lower portion of the vessel and comprising at least one opening in the lower portion so as to provide fluid flow communication between the riser conduit and the downcomer conduit;</li><li>an inlet means for introducing the reactants;</li><li>gas outlet in the reactor head through which the gas and excess liquid are allowed to exit out the reactor; wherein the heat exchange means comprises a plurality of cooling tubes attached to each other by webs or metal strips attached between the tubes over a predetermined length.</li></ul>

0010The invention is directed to an internal loop reactor having a heat exchanger defining barrier between riser and downcomer sections, said barrier referred to herein as the draft tube. The draft tube comprises a plurality of cooling tubes, preferably in an elongated annular or cylindrical shape, but may take some pattern other than circular pattern, e.g., a polygon pattern, or a multipointed star pattern, or an irregular pattern

0011In an embodiment, plurality of cooling tubes forming the draft tube are attached to the top of the reactor so as to allow circulation of the liquid phase to the outside downcomer part of the internal loop reactor. In addition, the connection of virtually all necessary internal parts to the top of the reactor allows for ease of construction, as will become apparent in the following disclosure.

0012The plurality of cooling tubes are attached to each other by "webs" or metal strips attached, such as by welding, between the tubes over a predetermined length, such as determined to be the optimum for the height and position of the riser.

0013In a preferred embodiment the bottom portion of the reaction vessel has a hemispherical bottom.

0014In yet another embodiment, lateral support for the plurality of cooling tubes is provided by at least one lateral support rod so as to connect one or more cooling tubes or webs to the outer vessel wall. In preferred embodiment the one or more lateral support rods are hinged at the vessel wall and/or at the connecting point of the cooling tubes or webs. In another preferred embodiment the one or more lateral support rods are constructed of a material that allows flexibility, such as bending.

0015In still another embodiment, a cooling jacket is attached to the reactors shell to provide heat transfer from the reactor.

0016In yet still another embodiment, there is a method of constructing a large scale internal loop reactor wherein all necessary internal parts are connected to a reactor head which can be lowered into a fixed, vertical shell reactor vessel to facilitate construction and maintenance in the field.

0017The invention is also directed to a chemical reaction, more preferably an exothermic and/or heterogeneous (gas/liquid phases) reaction, and still more preferably the Oxo Process, carried out in the reactor according to the invention.

0018It is an object of the invention to facilitate ease of construction and maintenance in the field and allow process scale-up for reactions in reactors of the loop-type.

0019These and other objects, features, and advantages will become apparent as reference is made to the following drawings, detailed description, preferred embodiments, examples, and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

0020In the accompanying drawings, like reference numerals are used to denote like parts throughout the several views.

0021<figref idref="f0001">Figure 1</figref> shows the side view of a prior art internal loop reactor.

0022<figref idref="f0001">Figure 2A</figref> illustrates a side views of a reactor according to an embodiment of the present invention and <figref idref="f0002">Figure 2B</figref> illustrates certain detailed features of such a reactor.

0023<figref idref="f0003">Figure 3</figref> provide a side view showing certain details of embodiments of the present invention as it relates to the top portion of the reactor.

0024<figref idref="f0004">Figures 4A and 4B</figref> shows a top view and bottom view, respectively, of the arrangement of cooling tubes according to an embodiment of the invention.

0025<figref idref="f0005">Figure 5</figref> illustrates the lateral support bars for the cooling tubes according to an embodiment of the invention.

0026<figref idref="f0005">Figure 6</figref> shows a bottom view of the arrangement of cooling tubes according to an embodiment of the invention.

DETAILED DESCRIPTION

0027According to the invention, an internal loop reactor is characterized by a heat exchanger, preferably comprising at least one cooling tube, and more preferably a plurality of cooling tubes, forming the barrier between the riser and the downcomer path of said internal loop reactor, said barrier forming what it referred to herein as the draft tube.

0028As shown in a side view of an embodiment of the reactor according to the invention provided by <figref idref="f0001">Fig. 2A</figref>, the internal loop reactor <u><b>8</b></u> comprises a pressure vessel <b><u>20</u></b> containing a cylinder or draft tube <b><u>16</u></b> suspended from vessel head <b><u>10</u></b> along the vessel centerline. The draft tube <b><u>16</u></b> is formed by the cooling tubes with optional connecting web or sheets and provides, inside of draft tube <b><u>16</u> ,</b> the riser column (which is equivalent in function to riser column <b><u>1</u></b> in <figref idref="f0001">Fig. 1</figref>). In a preferred embodiment, a two-phase mixture comprising syngas and Oxo product and/or reactants from the upstream reactors is fed to the bottom of the reactor through inlet <b><u>24</u></b> and directed, such as by optional sparger <b><u>28</u></b> into the internal riser column provided by draft tube <b><u>16.</u></b> At the top of the riser, gas partially or wholly disengages from the riser outlet and exits the reactor at the top through outlet <b><u>30.</u></b> Liquid, which is at least now partially, virtually, or completely free of gas, flows through gaps or windows <b><u>12</u></b> and <b><u>14</u></b> in the upper portion of draft tube <b><u>16</u></b>, and falls drown the annular space <b><u>18</u></b> (downcomer column) between draft tube <b><u>16</u></b> outer wall and the inner wall of vessel <b><u>20,</u></b> enters the riser column inside of draft tube <b><u>16</u></b> at the bottom of draft tube <b><u>16</u></b> (see also arrow <b><u>700</u></b> in <figref idref="f0002">Fig. 2B</figref> indicating flow direction) to mix with the fresh feed provided through inlet <b><u>24</u></b> setting up an internal circulation loop. (In the preferred embodiment wherein the reaction is the Oxo Reaction, it is preferred that at least some gas goes over into the downcomer so that the reaction continues to some extent in downcomer column <b><u>18.</u></b> By way of non-limiting example, if the riser column contains 10 % by volume gas, it may be convenient to have the downcomer column contain 3 % by volume gas in the upper portion of the downcomer. This may be achieved by proper dimensions of the reactor and/or reaction variables such as concentration of ingredients, temperature, etc.). The pressure vessel <b><u>20</u></b> is preferably fitted with a hemispherical bottom <b><u>11</u></b>. Conveniently, the hemispherical bottom may be removeably affixed or hinged to facilitate inspection and maintenance of the reactor. Features <b><u>34</u></b> and <b><u>36</u></b> in <figref idref="f0001 f0002">Fig. 2</figref> relate to the cooling medium provided to the plurality of cooling tubes and are explained in detail with reference to <figref idref="f0003">Fig. 3</figref>, below. Features <b><u>22A</u>, <u>22B, 22C,</u></b> and <b><u>22D</u></b> are optional thermocouples or other devices which may be used to monitor and/or control, such as by an operator and/or with the aid of a computer, the temperature of the reaction/reactor.

0029One of the advantages of the present invention is that the scale of the Oxo Reaction can be greatly increased from conventional loop reactors used in said Reaction. In preferred embodiments, the reactor <b><u>8</u></b> may have, by way of example and not to be construed as limiting, an internal volume on the order of 20-40 cubic meters operating with a recirculation rate of 700-900 cubic meters per hour and velocities in the riser and downcomer of about 0.4-0.6 meters/second. In embodiments, the internal diameter of vessel <b><u>20</u></b> can be on the order of 1. to 2 meters, and the height of the vessel <b><u>20</u></b> (extending up to the head <b>34</b>) on the order of 20-30 meters. The ratio of the area of the downcomer portion to riser portion is preferably close to unity and can conveniently range from 0.5 to 1.5. However, these numbers may be varied depending on the reaction and desired results and should not be taken at critical limitations. Without wishing to be bound by theory, in embodiments, such a reactor is essentially a nearly isothermal, continuous stirred tank reactor (CSTR).

0030The materials with which to construct the apparatus of the invention do not form a part of the present invention and the various parts may be constructed of conventional materials, e.g., the vessel sidewall <b><u>20</u></b> in <figref idref="f0001">Fig. 2A</figref> may be solid alloy, carbon steel with a bonded liner, and the like.

0031An essential feature of the present invention is that temperature control of the reactor is provided by the heat exchanger (e.g., cooling tube(s)) which also form an essential geometric feature of the internal loop, i.e., the riser and downcomer columns separated by the draft tube comprising said heat exchanger. Typically the riser and downcomer columns will be concentric tubes, which implies that, viewed from the top, the columns comprise essentially two concentric circles, but the shapes do not have to be circular, as will become apparent in this detailed description. Additional temperature control may be provided by optional cooling jacket provided against the vessel wall (not shown in <figref idref="f0001">Fig. 2A</figref>) as in conventional reactors, e.g., analogous to element <b><u>3</u></b> in <figref idref="f0001">Fig. 1</figref>.

0032In preferred embodiments the surface area of the heat exchanger (e.g., one or more cooling tubes) forming the draft tube is made large enough such that the reactor temperature is open loop stable such that no feedback control is needed on the reactor temperature itself. The recirculating cooling water (or heating water, as the case may be) temperature is the only required control system. It will be appreciated by ordinary artisan that the heat exchange medium may be some other fluid besides water, e.g., a hydrocarbon fluid.

0033<figref idref="f0002">Fig. 2B</figref> illustrates some details not shown in <figref idref="f0001">Fig. 2A</figref>. In <figref idref="f0002">Fig. 2B</figref>, there are plural cooling tubes <b><u>19A,</u><u>19B,</u><u>19C</u></b> etc., which together with plate or webs <b><u>41A,</u><u>41B,</u></b> etc., form draft tube <b>16.</b> Plates or webs <b><u>41A,</u><u>41B,</u></b> etc., does not extend all the way to plate or tubesheet <b><u>32</u></b> (discussed in more detail with respect to <figref idref="f0003">Fig. 3</figref>) but rather at least a portion of the plate or <b>web 41</b> is omitted so as to provides at least one window or gap(s) <b><u>12,</u><u>14,</u></b> etc., whereby the liquid, at least partially free of gas, flows into the downcomer <b><u>18,</u></b> as illustrated by arrow <b><u>70.</u></b> As shown in <figref idref="f0002">Fig. 2B</figref>, the gap(s) <b><u>12, 14,</u></b> etc., are spaced a distance <b><u>25A</u></b> from element <b><u>32.</u></b> with distance <b><u>25A</u></b> being readily determined by one of ordinary skill in the art in possession of the present disclosure. When there are plural gaps, as shown in this embodiment <b>(<u>12</u> and <u>14</u>)</b> the gap distance <b><u>25A</u></b> does not need to be the same for each gap. In the embodiment illustrated in <figref idref="f0002">Fig. 2B</figref>, the plates or webs <b><u>41A, 41B,</u></b> etc., may be extended below the bottom of the cooling tubes <b><u>19A,</u><u>19B,</u><u>19C,</u></b> etc., shown by element <b><u>410,</u></b> to at least partially enclose the top of the inlet provided by element <b><u>24,</u></b> discussed above with respect to <figref idref="f0001">Fig. 2A</figref>. However, this extension of the connective web or sheet is merely optional, and in a preferred embodiment the cooling tubes <b><u>19A,</u><u>19B,</u><u>19C,</u></b> etc., as well as the connect webs or sheets <b><u>41A,</u><u>41B,</u></b> etc., extend below the top of inlet <b><u>24,</u></b> so that the feed entering through inlet <b><u>24</u></b> enters the loop reactor inside the draft tube <b>16).</b> Thus draft tube <b><u>16,</u></b> which in the center portion comprises heat exhanger(s) such as <b><u>19A,</u><u>19B,19C,</u></b> etc., and optional plates or webs <b><u>41A,</u><u>41B,</u></b> etc., may comprise only the plate or web <b><u>410</u></b> in the lower portion. The distance by which the cooling tube(s) <b><u>19A, 19B,</u><u>19C,</u></b> extend beyond the plates or webs <b><u>41A,</u><u>41B,</u></b> etc., (if at all), or in the embodiment illustrated, the distance by which the plate or web <u><b>410</b>,</u> extends beyond the cooling tube(s), (if at all), and likewise the distance <b><u>25B</u></b> by which the inlet tube (with optional sparger) extends up into the draft tube (if at all) may be predetermined by one of ordinary skill in the art. Thus, in an embodiment the plates or webs <b>41A</b>, <u><b>41B</b>,</u> etc., may stop some distance prior to the bottom or the cooling tube(s) <u><b>19A</b>,</u><b><u>19B,</u></b> etc. Arrow <b><u>700</u></b> illustrates the movement of the liquid from the downcomer around the base of the draft tube <b><u>16</u></b> formed b<u>y</u> plate or web <b><u>410</u></b> where the liquid is mixed with the material added through inlet <b><u>24</u></b> in the riser portion formed by draft tube <b><u>16.</u></b>

0034In a preferred embodiment (not visible in <figref idref="f0002">Fig. 2B</figref>), in the upper portion of draft tube 16, in order to increase flow from the inside riser column <b><u>15</u></b> over to downcomer column <b><u>18,</u></b> the draft tubes may be "dog-legged" in or out in an alternating fashion. For instance, in <figref idref="f0002">Fig. 2B</figref>, cooling tube <b><u>19B</u></b> may be dog-legged inwardly (with respect to the centerline of the draft tube <b><u>16</u></b>) while cooling tubes <b><u>19A</u></b> and <b><u>19C</u></b> may be dog-legged outwardly. More details of this preferred embodiment will become evident when <figref idref="f0004">Fig. 4A</figref> is discussed below.

0035<figref idref="f0003">Fig. 3</figref> illustrates some of the details of an embodiment of the cooling system for the reactor of the invention. The head of the reactor, <b><u>10,</u></b> contains part of the circulation system (or recirculation system) for the cooling medium, which may be provided by various liquids or gases as would be recognized by one of ordinary skill in the art but for convenience is typically water. In an embodiment, the top head will have two juxtaposed and interconnected compartments <b><u>35</u></b> and <b><u>37,</u></b> respectively, the former from which the inlet <b><u>34</u></b> cooling water is distributed to the cooling tube or plurality of cooling tubes, and the latter to collect the return water which exits through outlet <b><u>36.</u></b> The plural cooling tubes (shown by reference to two cooling tubes <b><u>19A</u>, <u>19B,</u></b> for the sake of clarity) may be arrayed as concentric bayonets-type tubes with the inlet water going down the center tubes <b><u>13A</u>, <u>13B,</u></b> and the outlet water coming up the outer concentric tube <b><u>17A,</u><u>17B,</u></b> or <i>vice versa.</i> Although only two cooling tubes are shown in <figref idref="f0003">Fig. 3</figref> for convenience of view, plural cooling tubes may be arranged concentrically (or in some other geometric pattern or irregular pattern) inside vessel wall <b><u>21</u></b> of vessel <b><u>20</u></b> so as to form downcomer space <b><u>18</u></b> and riser column <b><u>15.</u></b> Riser space <b><u>15</u></b> allows the gas and excess liquid to exit out the reactor through conduit <b><u>31</u></b> in reactor head <b><u>10</u></b> to outlet <b><u>30.</u></b> A single opening (i.e., here the top of the riser column <b>15</b>) near the top of the plurality of cooling tubes (e.g., corresponding to window <b><u>12</u></b> in <figref idref="f0001">Fig. 2A</figref> and <figref idref="f0002">Fig. 2B</figref>) which allows circulation of the essentially gas-free or gas-depleted liquid down the downcomer; connective webs or sheets <b><u>41A,</u><u>41B,</u></b> are not shown in <figref idref="f0003">Fig. 3</figref>. The various parts of reactor head <b><u>10</u></b> may be welded, adhesively connected, bolted, and the like (or combination thereof). Various alternative or auxiliary means of connections would be known to one of ordinary skill and may include the use of gaskets and the like.

0036The inner tube <b>1<u>3A</u></b> passes through the outlet water compartment <b><u>36</u></b> and is open to the top water compartment <b><u>35.</u></b> The outer tube <b><u>17A</u></b> may be welded to the top head and is open to the outlet water compartment <b><u>36.</u></b>

0037One of the unique advantages of the reactor system according to the present invention is that entire top head <b><u>10</u></b> comprising element <b><u>32</u></b> and internal assembly comprising a plurality of cooling tubes illustrated by tubes <b><u>19A</u>, <u>19B,</u></b> etc., can be lowered into the vertical shell during construction as well as lifted out of the shell for any serious maintenance.

0038<figref idref="f0004">Fig. 4</figref> illustrates an embodiment of the draft tube (<b><u>16</u></b> in <figref idref="f0001">Figs. 2A</figref> and <figref idref="f0002">2B</figref>) wherein the draft tube comprises plural cooling tubes formed by cooling tubes <b><u>19A,</u><u>19B,</u></b> etc. <figref idref="f0004">Fig. 4A</figref> is a view taken of a preferred embodiment from the top portion of vessel <b><u>20</u></b> showing only the position of the "dog-legged" tubes (above the connecting sheet or web <b><u>41A, 41B, etc.</u></b> in <figref idref="f0002">Fig. 2B</figref>). In contrast, <figref idref="f0004">Fig. 4B</figref> is a view taken from the middle portion of the vessel <b><u>20</u></b> with the hemispherical end cap (<b><u>11</u></b> in <figref idref="f0001 f0002">Fig. 2</figref>) removed, and shows the connective sheet or webs <b><u>41A,</u><u>41B,</u></b> etc. between each cooling tube.

0039In the arrangement shown in <figref idref="f0004">Fig. 4</figref>, the schematic view is best understood first by reference to <figref idref="f0004">Fig. 4B</figref>. It will be understood that the array of plural cooling tubes <b><u>19A,</u><u>19B,</u></b> etc., can be in some other geometric arrangement than that shown, such as in a square configuration, and the like. Cooling tubes <b><u>19A,</u><u>19B,</u></b> etc. may be welded together or connected such as by sheet metal as shown by elements <b><u>41A,</u><u>41B,</u></b> etc., so that the combination of plural cooling tubes and connective webs or sheets form the draft tube <b><u>16.</u></b> The connective sheets or webs <b><u>41A, 41B,</u></b> etc., connect the plural cooling tubes from near the bottom portion of the draft tube to near the upper portion of the draft tube, the exact distance from the top and bottom being predetermined. The selection of distance between top and bottom is preferably independently determined. The determination may be made by experiment or with the aid of computational fluid dynamic models using commercially available software, or a combination thereof. Using the reactor dimensions provided elsewhere in the present disclosure (i.e.., with respect to vessel volume, height, diameter; etc.), it is sufficient but not required that the distance of the top of the draft tube from the top of the vessel and the distance of the bottom of the draft tube from the bottom of the vessel be on the order of 1 to 3 meters, with about 2 meters being preferred. Thus connected by the sheets or webs between each cooling tube, plural cooling tubes <b>19A,19B,</b> etc. form the draft tube that separates riser column <b><u>15</u></b> downcomer column <b><u>18.</u></b>

0040As mentioned the plural connecting elements, illustrated by sheets or webs <b><u>41A</u></b> and <b><u>41B</u></b> in <figref idref="f0004">Fig. 4B</figref>, connect the plural cooling tubes <b><u>19A,</u><u>19B,</u></b> etc., to a predetermined distance from the head of the reactor (<b>32</b> in <figref idref="f0002">Figs. 2B</figref> and <figref idref="f0003">3</figref>) where the connecting web or sheet stops at said predetermined distance to provide at least one gap for recirculation. These gaps (<b><u>12</u></b> and <b><u>14</u></b> in <figref idref="f0001">Figs. 2A</figref> and <figref idref="f0002">Fig. 2B</figref>) may be accentuated by altering the geometry of the cooling tubes near the top, such as illustrated in <figref idref="f0004">Fig. 4A</figref>, where the cooling tubes each take an alternating inward/outward "dog leg" to provide plural gaps, as discussed briefly above, thus providing or accentuating the gap between the individual cooling tubes <b><u>19A,</u><u>19B,</u></b> etc., and fluid communication between riser column <b><u>15</u></b> and downcomer column <b><u>18.</u></b> Thus, cooling tube <b><u>19A</u></b> is dog-legged outwardly with respect to the center line of the cooling tube (not labeled in <figref idref="f0004">Fig. 4A</figref>) separating riser column <b><u>15</u></b> and downcomer column <b>18,</b> while cooling tube <b><u>19B</u></b> is dog-legged inwardly, and so on. The location of the bends for the dog legs is a convenience place to discontinue the connective plates or webs <b><u>41A</u>, <u>41B</u>,</b> etc.

0041. In consideration of the increased volume allowed in the reactor according to the invention, the exposure of bottom of the plural array of cooling tubes to the process pressures a significant buckling stress not encountered in the design of the existing internal loop reactors. This may be addressed in various ways such as by the embodiment illustrated in <figref idref="f0005">Fig. 5</figref>.

0042In <figref idref="f0005">Fig. 5</figref>, the plural cooling tubes <b><u>19A,</u></b><u><b>19B,</b></u> etc., are connected by plural webs or sheets, as discussed previously. In an embodiment, near the bottom of the draft tube, one or more of the tubes are cut short to allow the rod to pass through the draft tube. The other space on the other side has a wider sheet web to connect the rod to, as shown by connective sheet or web <b><u>41A.</u></b> Element <b><u>42A</u></b> is intended to provide support for the draft tube <b><u>16</u></b> (<figref idref="f0001 f0002">Fig. 2</figref>) comprising plural cooling tubes <b><u>19A,</u><u>19B,</u></b> etc. against the stresses referred to above. Support element <b><u>42A</u></b> is advantageously a flexible metal bar or rod. In an alternative, instead of being connected to the web or sheet <b><u>41A</u></b> it may be directly mated with the cooling tube(s). The connection may be by welding, adhesive, or, as shown in the figure, by a hinge <b><u>40A.</u></b> While support element <b><u>42A</u></b> is advantageously connected to the wall of vessel <b><u>20</u></b> at the point furthest laterally from its connecting point to the draft tube <b><u>16</u></b> (<figref idref="f0001 f0002">Fig. 2</figref>), it may be connected, instead or additionally) to another point on vessel <b><u>20.</u></b> As shown in <figref idref="f0005">Fig. 5</figref>, three support elements (one shown by the combination of features <b><u>40A</u>, <u>41A</u>, <u>42A</u>,</b> the other equivalent elements not numbered for ease of view) are used, but more or less (or no) support elements may be used. Gaps in the circular array of plural cooling tubes <b><u>19A,</u><u>19B,</u></b> etc. are shown in the figure to allow for support element shown individually by <b><u>42A.</u></b> The riser column <b><u>15</u></b> and downcomer column <b><u>18</u></b> in the figure are the same as shown in the other figures. Such gaps in the array of cooling tubes <b><u>19A,</u><u>19B,</u></b> etc. may be provided advantageously at the very bottom of the array simply by having the appropriate one or more cooling tubes shortened slightly.

0043Numerous modifications in the reactor according to the invention may be envisioned by one of ordinary skill in the art in possession of the present disclosure. For instance, as described above, the downcomer <b><u>18</u></b> is fitted with a hemispherical cap, <b><u>11</u></b> in <figref idref="f0001 f0002">Fig. 2</figref>, in order to eliminate a dead zone observed in a cold flow unit which had a flat head. However, a different geometry may be optimal under other conditions.

0044In another embodiment, a circular baffle just above the top of the riser may help spread the plume of gas outward and avoid any possible mass transfer limitations in the top of the reactor.

0045In yet another embodiment, there is a conical slope for the underside of the top head <b><u>10</u></b> in <figref idref="f0001 f0002">Figure 2</figref> (or <figref idref="f0003">Fig. 3</figref>) to facilitate the flow of the gas rich layer and/or avoid stagnant bubbles under the head to the central outlet hole <b><u>30.</u></b>

0046In still another embodiment, reactor <b><u>8</u></b> (by reference to <figref idref="f0001 f0002">Fig. 2</figref>) may have a second cooling means provided around vessel <b><u>20</u></b> such as shown by element <u><b>3</b></u> in prior art <figref idref="f0001">Fig. 1</figref>.

0047It will be appreciated that in the case of plural cooling tubes the pattern formed by the cooling tubes may be other than as illustrated in <figref idref="f0004">Figures <b><u>4A</u>, <u>4B</u></b></figref><b>,</b> and <figref idref="f0005">5</figref>, i.e.., other than in a circular pattern. It may be in an irregular, pattern, or some other regular pattern, such as a square, rectangle, triangle, star pattern, and so on. <figref idref="f0005">Figure 6</figref> illustrates yet another alternative view of a cross-section of. <figref idref="f0002">Fig. 2B</figref> across perspective line 4B, wherein plural cooling tubes <b><u>19A</u>,1<u>9B</u>.</b> etc., form a "zig-zag" pattern, connected by plural plates or webs illustrated by the single plate <b><u>41,</u></b> to form the draft tube <b><u>16</u></b> separating riser column <b><u>15</u></b> and downcomer column <b><u>18.</u></b><figref idref="f0005">Fig. 6</figref> can be seen to be one of many alternatives to the pattern shown by <figref idref="f0004">Fig. 4B</figref>.

0048In a preferred embodiment concerning construction and fabrication of the reactor according to the present invention, each individual cooling tube may be extruded with one or more fins along the outer wall, which may be used to weld the individual cooling tubes into the draft tube so as to provide the connective web or sheets represented by numerals <b><u>41A,</u><u>41B,</u></b> etc.

0049It will be recognized by one of ordinary skill in the art in possession of the present invention that in a preferred embodiment wherein the draft tube comprises plural cooling tubes, a key mechanical feature of the present invention is that the conventional draft tube can be formed as an integral heat exchanger by welding individual heat exchanger tubes together into a shape, such as a circle, which divides the riser and downcomer columns. Without wishing to be bound by theory, among the benefits provided by this approach are that by welding the integral fins from each cooling tube together, the welded assembly assumes a significant stiffness much greater than, any individual cooling tube. This stiffness allows the structure to withstand significant buckling stresses which may arise in certain reactions, such as found in the Oxo Reaction, as discussed elsewhere herein. It is preferred that lateral supports such as provided by the bar or rod indicated by <u>42A</u> in <figref idref="f0005">Fig. 5</figref> be kept to a minimum, as such supports may detrimentally affect process pressure drop and provide locations for the deposition of material (such as cobalt catalyst in the case of the conventional Oxo Reaction).

0050The reactor according to the present invention is particularly suitable for carrying out an exothermic gas-liquid chemical reaction. The reactor may be provided in series or in parallel with other reactors of the same type (e.g., internal loop reactors according to the invention or according to the prior art) or different types, such as one or more external loop reactors in series with one or more reactors according to the present invention. In the case where the reaction is endothermic the heat exchange medium is selected to be suitable for providing heat to the reaction medium, which is within the skill of the ordinary artisan.

0051In a preferred embodiment, the reactor according to the present invention will be downstream of the main Oxo Reactors. In still more preferred embodiments, up to about 10 to 15% of the overall Oxo reaction may occur in the reactor according to the present invention when arrayed in series with plural additional external and/or internal loop reactors. Other configurations are possible, such as providing a reactor according to the present invention in a reactor array such as described in <patcit id="pcit0013" dnum="US5763678A"><text>U.S. Patent No. 5,763,678</text></patcit>. However, it is to be understood that the reactor according to the present invention may function as a stand-alone reactor providing 100% of the reaction product in a continuous or batch reaction.

0052Thus, in embodiments, the invention also relates to a process for catalytic hydroformylation of an olefin feedstock by syn gas comprising feeding a. stream comprising olefin and/or the product of a hydroformylation reaction having said olefin as a starting material, said stream comprising syn gas, to the inlet of a reactor and obtaining as a product of said reactor a stream comprising syn gas and said product of a hydroformylation reaction, the improvement comprising an internal loop reactor characterized by a plurality of cooling tubes forming the annulus between the riser and the downcomer path of said internal loop reactor. The reaction is also characterized by its very large volume, such as at least 15 cubic meters, or at least 20 cubic meters, or at least 25 cubic meters, or more preferable at least 30 cubic meters.

0053In a preferred embodiment, in place of or in addition to thermocouples placed at various points in the reactor, such as at elements <b><u>22A</u>, <u>22B</u>, <u>22C</u>, <u>22D</u></b>, in <figref idref="f0001">Fig. 2A</figref>, it may be advantageous to use an analog continuous signal from a standard flow switch (for example as supplied by numerous vendors such as Fluid Components International) to give a continuous trend readout of the circulation velocity. In a preferred embodiment, such a switch would be adapted to be inserted into one of the aforementioned thermocouple nozzles.

0054In another preferred embodiment, flush mounting of the outlet nozzle to the inside of the head to avoid gas pockets which could allow the onset of Fischer Tropsch reactions.

0055Trade names used herein are indicated by a ™ symbol or ® symbol, indicating that the names may be protected by certain trademark rights, e.g., they may be registered trademarks in various jurisdictions.

0056The invention has been described above with reference to numerous embodiments and specific examples. Many variations will suggest themselves to those skilled in this art in light of the above detailed description.