Patent Publication Number: US-2005135978-A1

Title: Method and apparatus for optimizing throughput in a trickle bed reactor

Description:
This application claims the benefit of priority from U.S. Provisional Application Ser. No. 60/510,984 filed Oct. 14, 2003, the entirety of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates to a trickle bed reactors and more particularly to a method for optimizing the throughput of a trickle bed reactor by varying the geometry of the reactor columns in accordance with the temperature profile of the reaction, by increasing the rate of heat transfer to the coolant proximate the initial section of the reactor columns by increasing the velocity of the coolant surrounding those sections and by directing the coolant flow perpendicular to the reactor columns, and to a trickle bed reactor designed to implement such method.  
     BACKGROUND OF THE INVENTION  
      The overall rate of heat transfer of a system having two fluids separated by a barrier is in part a function of the hydrodynamics of the fluids on both sides of the barrier and of the resistance to heat transfer of the separating barrier material. A trickle bed reactor is an instrument in which heat transfer takes place between fluids separated by a barrier and in which the rate of heat transfer across the barrier is a major design consideration.  
      Trickle bed reactors are widely used both in the petrochemical industry, for example in the hydrotreatment of heavy petroleum fractions, and in fine chemical productions, such as hydrogenations, oxidations, halogenations and the like. The conventional trickle bed reactor includes a vertical reactor column or tube of uniform internal diameter. The reactor column is packed with catalytic material or non-reactive packing, depending upon the application. The reactor column is surrounded by an enclosure through which a temperature control fluid flows. The wall of the column forms a barrier separating the reactant fluid and the temperature control fluid.  
      In this document, the trickle bed reactor of the present invention is described as it would be used to perform an exothermic gas-liquid reaction, for example to oxidize a solute in a liquid phase as part of a process to form a pharmaceutical product. However, it should be understood that the disclosed application has been selected for illustrative purposes only. The present invention should not be considered to be limited to the disclosed application as many other uses for the trickle bed reactor of the present invention will be readily apparent to those skilled in the art.  
      In our example, the compound to be oxidized is introduced as a solute in a liquid phase to the reactor column at its inlet end, located at the top of the reactor column. Gravity causes the solute to trickle down the column, through the inert packing present in the column, as an oxygen containing gas moves within the column. The gas phase could be introduced to move counter-currently or co-currently with the solute. The oxidized product exits the outlet end of the column, located at the bottom of the column. When the flow of the oxygen containing gas is counter-current with the solute flow, as it is in the disclosed example, the gas is pumped into the liquid outlet end of the column and removed from the liquid inlet end of the column.  
      Because an exothermic reaction is taking place, heat will build up in the reactor column and must be continuously removed. This is accomplished by circulating a temperature control fluid, in this case a liquid or gas coolant, through an enclosure surrounding the reactor column. The heat must be removed from the reactor column because elevated temperature leads to the formation of impurities in the oxidized product and those impurities are difficult to remove. The amount of impurities produced during oxidation is a function of the temperature in the reactor column and increases as the temperature becomes greater.  
      Further, intermediates formed during oxidation may be thermally unstable and have an explosive nature. Consequently, safety concerns require strict control of the amount of heat generated in the reactor column, particularly when large quantities of product are being produced.  
      Thus, key factors for control of reactor performance and safety are the regulation of the temperature profile and of the amount of impurities produced. The reactor must have a heat transfer capability sufficient to keep the temperature within a given range. Flow control plays a major role in the impurity profile. The reactor must also provide sufficient residence time for the oxidation to take place.  
      We have observed the temperature profile in a conventional laboratory scale trickle bed reactor with an inert packed reactor column of uniform internal diameter, surrounded by a coolant containing enclosure of uniform diameter, as oxidation is taking place. It is clear that in such a reactor, the exotherm of the oxidation causes a steep temperature increase that reaches a maximum in the initial section of the reactor column located near the top of the column and that the temperature then decreases in the remaining section of the column.  
      That temperature profile suggests that the cooling power of the reactor column is initially lower than the rate of heat generated by the oxidation. This situation reverses in the bottom of the column due to a decrease of the rate of oxidation as the concentration of the substance to be oxidized decreases. The oxidation rate also decreases in the bottom of the column because of the decrease in temperature.  
      That situation is amplified as the reactor is scaled-up for manufacturing quantities. In the case of large-scale production, an optimized reactor design would require the temperature to be controlled tightly within a narrow temperature range to keep the creation of impurities to a minimum and to avoid the explosive hazard resulting from overheating. That is achieved in the present invention by tailoring the cooling efficiency of the reactor column as the reaction proceeds along the column.  
      When the flow rate of the stream is scaled proportionally to the diameter it is known that the cooling power of a reactor column is a function of the internal diameter of the column. As the internal diameter of the column increases, the surface to volume ratio decreases, as does the cooling efficiency of the column.  
      Scaling-up the production rate of a reactor is generally achieved by increasing the column diameter. Increasing the column diameter increases the ratio of the volume occupied by the fluid in the reactor column relative to the surface area of the reactor column, thus reducing the rate of heat transfer per unit volume of the reactant. Consequently, if an exothermic reaction is carried out in a column, scaling up the process carried out within the column will lead to an increase in the temperature profile within the column. For some processes, such as the process of interest herein, scaling up the reactor by simply increasing the column diameter is not an option because high temperatures may be reached, adversely impacting the impurity profile, as well as the catalyst structure and efficiency. Further, the overall safety of the process may be compromised.  
      Those skilled in the art of reactor design have tried to solve this problem by splitting the flow of the liquid into separate streams and providing multiple uniform diameter reactor columns within the reactor, one for each liquid stream. Another approach has been to divide the reactor column lengthwise into sections, each of which is maintained at a different temperature, using different chillers to regulate the temperature of the coolant provided to each section. However, when the high throughputs are desired, large numbers of reactor columns are needed, requiring a cumbersome set up. Further, utilizing different zones of temperature was found not to substantially improve reactor performance for the application of interest as our objective is to increase the throughput by at least a factor of two for a given reactor length.  
      A different proposed solution to the temperature control problem has been to operate the reactor in a forced unsteady state by periodically interrupting or “pulsing” the liquid flow rate to the inlet of the reactor column. Varying the liquid flow rate in this matter may provide some improvement in reactor performance as compared to steady-state operation. However, that improvement is not substantial and the mechanism necessary to accurately control the liquid flow rate in this fashion, particularly in a production scale reactor, is complex.  
      We propose dealing with the throughput problem in a production scale trickle bed reactor, in part, by altering the geometry of the reactor columns in accordance with the temperature profile of the reaction. The only reference that we are aware of that suggests altering the geometry of a reactor column is Russian Patent No. 1088781A. That reference discloses a shell and tube catalytic reactor using gas streams only made up of three or more multi-section component tubes of equal overall length, where the diameter of the successive sections of each of the tubes increases in the flow direction of the reaction stock in a geometric progression.  
      However, the reactor described in the Russian patent is not a trickle bed reactor. It does not utilize inert packing in the reactor tubes. It cannot be used to perform a gas-liquid reaction, such as the oxidation of a liquid, because it lacks inlet and exhaust ports necessary to provide a co-current or counter-current gas-liquid flow within the reactor tubes.  
      In the Russian system, the gas reactants are mixed outside the reactor and then pumped under pressure into the reactor inlet. No liquid stream is present. In addition, there is no provision in the reactor for equalizing the flow rates to the individual reactor tubes, an important feature when multiple reactor tubes are utilized to perform a gas-liquid reaction.  
      In addition to altering the geometry of the reactor columns, we propose increasing the throughput of our reactor by increasing the rate of heat transfer to the coolant. We do this by increasing the velocity of the coolant surrounding the sections of the reactor columns where additional heat removal is required.  
      The Russian patent teaches no structure for tuning the velocity of the coolant, and thus increasing the heat removal capacity of the coolant, in accordance with the heat generated by the reaction. In fact, that reference teaches the opposite. In the Russian reactor, the velocity of the coolant is smallest adjacent the tube sections with the greatest rate of heat transfer requirement, resulting in the exact opposite of the desired effect.  
      Further, we propose increasing the cooling efficiency of the reactor columns by utilizing laterally offset baffles to direct the flow of coolant perpendicular to the axis of each reactor column. The Russian patent does not teach the use of baffles or any other coolant flow directing structure.  
     BRIEF SUMMARY OF THE INVENTION  
      In order to optimize the throughput in our production scale trickle bed reactor, we have designed the reactor with multiple reactor columns wherein the geometry of the components is selected in accordance with the temperature profile of the reaction taking place. We have accomplished this by varying the inner diameter of reactor columns to control the temperature in accordance with the heat created by the reaction. We have designed the reactor columns to be of sufficient size to provide adequate residence time to complete the reaction. We have also incorporated a means for equalizing the flow rate of the liquid to each of the reactor columns.  
      In addition, the rate of heat transfer to the coolant from the initial sections of the reactor columns has been increased by increasing the velocity of the coolant surrounding those sections of the reactor columns, where the greatest amount of heat exchange is required. We have also configured the baffle system within the coolant enclosure to cause the coolant to flow in a direction perpendicular to the axis of each of the reactor columns in order to increase the rate of heat transfer along the entire length of the columns.  
      Our approach has resulted in high continuous productivity for the production scale trickle bed reactor while the operating temperature of the reactor is maintained within a very narrow range. This leads to an inherently safer process as the heat transfer is tuned to avoid hot spots that can have catastrophic safety and product quality consequences. The productivity of each column of the reactor is tuned by modifying the length of each of its sections.  
      It is therefore a prime object of the present invention to provide a method of optimizing throughput in a trickle bed reactor by altering the geometry of the reactor columns in accordance with the temperature profile created by a gas-liquid reaction.  
      It is another object of the present invention to provide a method of optimizing throughput in a trickle bed reactor by tailoring the rate of heat transfer to the coolant as the diameter of the reactor columns are varied.  
      It is another object of the present invention to provide a method of optimizing throughput in a trickle bed reactor by causing the coolant to flow in a direction perpendicular to the axis of each of the reactor columns.  
      It is another object of the present invention to provide a trickle bed reactor having multiple reactor columns with different diameter sections that receive solute in a liquid phase at equal flow rates.  
      It is another object of the present invention to provide a trickle bed reactor that provides high continuous productivity with an operating temperature within a narrow temperature range.  
      It is another object of the present invention to provide a trickle bed reactor that produces faster and more stable reactions by controlling the temperature within a narrow optimal range.  
      In accordance with one aspect of the present invention, a trickle bed reactor is provided for oxidizing a solute in a liquid phase. The reactor includes a reactor column containing inert packing. The reactor column has an inlet end into which the solute in a liquid phase is introduced and an outlet end from which the oxidized product is removed. Means are provided for creating a flow of oxygen containing gas through the column. An enclosure substantially surrounds the column. Means are provided for introducing coolant to one end of the enclosure and for removing coolant from the other end of the enclosure. The column includes first and second connected sections. The first column section has a smaller inner diameter than the second column section.  
      The first column section is proximate the inlet end of the column. The second column section is proximate the outlet end of the column.  
      The column further includes an intermediate column section. The intermediate column section connects the first and second column sections. The intermediate column section varies in inner diameter from the inner diameter of the first column section to the inner diameter of the second column section.  
      The enclosure has first and second ends. The coolant is introduced into the end of the enclosure proximate the outlet end of the column. The coolant is removed from the end of the enclosure proximate the inlet end of the column.  
      The reactor further comprises means for increasing the rate of heat transfer to the coolant proximate the first column section by increasing the velocity of the coolant surrounding the first column section.  
      The heat transfer rate increasing means include means for reducing the volume occupied by the coolant proximate the first column section. This can be achieved by providing a jacket surrounding the first column section through which the coolant flows. The jacket is located with the portion of the enclosure proximate the first column section. It can also be accomplished by reducing the volume of the portion of the enclosure surrounding the first column section by decreasing the diameter of that enclosure portion or by introducing a space occupier within that portion of the enclosure.  
      Means are provided for directing the flow of coolant in a direction substantially perpendicular to the axis of the reactor column. Those means include at least two laterally offset baffles spaced along the reactor column.  
      In accordance with another aspect of his present invention, a trickle bed reactor is provided for performing a gas-liquid reaction. The reactor includes at least two packed reactor columns. Each of the reactor columns has an inlet end into which a solute in a liquid phase is introduced and an outlet end from which the product is removed. Means are provided to control the flow rates of the solute into each reactor column. Means are provided for creating a gas flow within each column. An enclosure substantially surrounds the columns. Means are provided for introducing coolant to the enclosure and for removing coolant from the enclosure. Each column includes first and second connected sections. The first column section of each column has a smaller inner diameter than the second column section of that column.  
      Each reactor column further includes an intermediate column section. The intermediate column section connects the first and second column sections. The intermediate column section varies in inner diameter from the inner diameter of the first column section to the inner diameter of the second diameter section.  
      The first column section of each column is proximate the inlet end of the column. The second column section of each column is proximate the outlet end of the column.  
      The solute flow rate control means includes means for measuring the flow rate of solute to each reactor column and means for adjusting the solute flow rate to each column.  
      The coolant enclosure has first and second ends. The coolant is introduced into the enclosure proximate the outlet end of the columns. The coolant is removed from the enclosure proximate the inlet end of the columns.  
      The reactor further comprises means for increasing the rate of heat transfer to the coolant proximate the first column section of each reactor column by increasing the velocity of the coolant surrounding those column sections.  
      The heat transfer rate increasing means includes means for reducing the volume occupied by the coolant proximate the first column section of each of the reactor columns. This can be achieved by surrounding the first column section of each of the reactor columns with a jacket through which the coolant flows. The jackets are located within the portion of the enclosure proximate the first column sections. It can also be accomplished by reducing the size of the enclosure portion proximate the first column sections or by introducing a space occupier within that portion of the enclosure.  
      Means are provided for directing the flow of coolant in a direction substantially perpendicular to the axis of each of the reactor columns. Those means include at least two laterally offset baffles spaced along the reactor columns.  
      In accordance with another aspect of his present invention, a trickle bed reactor is provided for performing a gas-liquid reaction. The reactor includes a packed reactor column. The reactor column has an inlet end into which the solute in a liquid phase is introduced and an outlet end from which the product is removed. Means are provided for creating a gas flow within the column. An enclosure substantially surrounds the column. Means are provided for introducing coolant into the enclosure and for removing coolant from the enclosure. The reactor column includes first and second connected sections. Means are provided for increasing the rate of heat transfer to the coolant proximate the first column section by increasing the velocity of the coolant surrounding the first column section.  
      The enclosure includes a first enclosure portion surrounding the first column section and a second enclosure portion surrounding the second column section. The heat transfer rate increasing means includes means for reducing the volume occupied by the coolant in the first enclosure portion. These means may include a jacket surrounding each of the first column sections. The jacket is situated within the first enclosure portion. These means may alternatively include a first enclosure portion with a smaller coolant containing volume, either because of reduced diameter or because of the presence of a space occupier.  
      The first column section has a smaller inner diameter than the second column section. Each reactor column further includes an intermediate column section. The intermediate column section connects the first and second column sections. The intermediate column section varies in inner diameter from the inner diameter of the first column section to the inner diameter of the second diameter section.  
      The first section of the column is proximate the inlet end of the column. The second column section of the column is proximate the outlet end of the column.  
      The coolant enclosure has first and second ends. The coolant is introduced into the enclosure proximate the outlet end of the column. The coolant is removed from the enclosure proximate the inlet end of the column.  
      Means are provided for directing the flow of coolant in a direction substantially perpendicular to the axis of the reactor column. Those means include at least two laterally offset baffles spaced along the reactor column.  
      In accordance with another aspect of his present invention, a trickle bed reactor is provided for performing a gas-liquid reaction. The reactor includes a packed reactor column. The reactor column has an inlet end into which solute in a liquid phase is introduced and an outlet end from which the product is removed. Means are provided for creating a gas flow within the column. An enclosure substantially surrounds the column. Means are provided for introducing coolant to the enclosure and for removing coolant from the enclosure. The reactor column includes first and second connected sections. The first column section has a smaller inner diameter than the second column section. Means are provided for directing the flow of coolant in a direction substantially perpendicular to the axis of the reactor column.  
      The coolant flow directing means includes at least two laterally offset baffles spaced along the reactor column. Preferably, those means includes a plurality of baffles spaced along the column with each baffle laterally offset relative to the adjacent baffles.  
      Means are provided for increasing the rate of heat transfer to the coolant proximate the first column section by increasing the velocity of the coolant flow proximate the first column section.  
      The enclosure includes a first enclosure portion surrounding the first column section and a second enclosure portion surrounding the second column section. Heat transfer rate increasing means are provided. These means include means for reducing the volume occupied by the coolant in the first enclosure portion. This may be achieved by including a jacket surrounding each of the first column sections. The jackets are situated with the first enclosure portion. It may alternatively include a first enclosure portion with a reduced coolant containing volume, either because of reduced diameter or because of the presence of a space occupier.  
      Each reactor column further includes an intermediate column section. The intermediate column section connects the first and second column sections. The intermediate column section varies in inner diameter from the inner diameter of the first column section to the inner diameter of the second diameter section.  
      The first section of the column is proximate the inlet end of the column. The second column section of the column is proximate the outlet end of the column.  
      The coolant enclosure has first and second ends. The coolant is introduced into the enclosure proximate the outlet end of the column. The coolant is removed from the enclosure proximate the inlet end of the column.  
      In accordance with another aspect of his present invention, a method is provided for optimizing the throughput of a trickle bed reactor adapted to oxidize a solute in a liquid phase in a reactor column containing inert packing. The solute is introduced into the inlet end of the reactor column and the oxidized product is removed from the outlet end of the reactor column. A gas flow is created through the column. Coolant is introduced an enclosure substantially surrounding the reactor column. Coolant is removed from the enclosure. The solute is caused to flow along the reactor column from a first column section having a relatively smaller inner diameter to a second column section having a relatively greater inner diameter.  
      The first column section is situated proximate the inlet end of the column. The second column section is situated proximate the outlet end of the column.  
      The solute is caused to flow through an intermediate column section connecting the first and second column sections. The inner diameter of the intermediate column section varies from the inner diameter of the first column section to the inner diameter of the second diameter section.  
      The coolant is introduced into the enclosure proximate the outlet end of the column. The coolant is removed from the enclosure proximate the inlet end of the column.  
      The rate of heat transfer to the coolant proximate the first column section is increased by increasing the velocity of the coolant proximate the first column section. This is accomplished by reducing the volume occupied by the coolant in the portion of the enclosure surrounding the first column section.  
      This may be achieved by surrounding the first column section with a jacket through which the coolant flows, the jacket being situated within the portion of the enclosure surrounding the first column section. It may alternatively be achieved by reducing the volume of the enclosure portion proximate the first column section by decreasing its diameter or inserting a space occupier within that enclosure portion.  
      The flow of coolant is directed in a direction substantially perpendicular to the axis of the reactor column. This is accomplished by utilizing at least two laterally offset baffles spaced along the reactor column.  
      In accordance with another aspect of his present invention, a method is provided for optimizing the throughput of a trickle bed reactor with at least two packed reactor columns adapted to perform a gas-liquid reaction. Solute in a liquid phase is introduced into the inlet end of each column and the product is removed from the outlet end. The flow rate of the solute into each reactor column is controlled to be substantially equal. A gas flow is created within each column. Coolant is introduced into an enclosure surrounding the reactor columns and is removed from the enclosure. The solute is caused to flow along each reactor column from a first column section having a relatively smaller inner diameter to a second column section having a relatively greater inner diameter.  
      The solute is caused to flow through an intermediate section of each column connecting the first and second column sections. The inner diameter of the intermediate column section varies from the inner diameter of the first column section to the inner diameter of the second diameter section. The first section of each column is proximate the inlet of the column. The second section of each column is proximate the outlet end of the column.  
      The solute flow rate is controlled by measuring the flow rate of liquid to each reactor column and by regulating the liquid flow rate to each reactor column.  
      The rate of heat transfer to the coolant from each of the first column sections is increased by increasing the velocity of the coolant proximate those first column sections. This is accomplished by reducing the volume occupied by the coolant proximate the first column sections.  
      The enclosure includes a first enclosure portion surrounding the first column sections and a second enclosure portion surrounding the second column sections. The heat transfer rate is increased by reducing the volume occupied by the coolant in the first enclosure portion. A jacket surrounding each of the first column sections and located within the first enclosure portion may be used to accomplish this. Alternatively, a first enclosure portion having a reduced coolant containing volume, either because of reduced diameter or the presence of a space occupier therein, may be utilized.  
      The flow of coolant is directed in a direction substantially perpendicular to the axis of each of the reactor columns. This is achieved by having at least two laterally offset baffles spaced along the reactor columns.  
      In accordance with another aspect of the present invention, a method is provided for optimizing the throughput of a trickle bed reactor performing a gas-liquid reaction in a packed reactor column. A solute in a liquid phase is introduced into the inlet end of the reactor column and the product is removed from the outlet end of the reactor column. A gas flow is created through the column. Coolant is introduced into an enclosure substantially surrounding the reactor column. The coolant is removed from the enclosure. The solute flows along the reactor column from a first column section to a second column section. The rate of heat transfer to the coolant from the first column section is increased by increasing the velocity of the coolant flow proximate the first column section.  
      Increasing the coolant velocity proximate the first column section is accomplished by reducing the volume occupied by the coolant proximate the first column section. A jacket surrounding each of the first column sections may be used. The jacket is located within the enclosure portion surrounding the first column sections. Alternatively, the coolant containing volume of enclosure portion surrounding the first column sections can be reduced, either by reducing the diameter of that enclosure portion or by introducing a space occupier within that enclosure portion.  
      The inner diameter of the first column section is relatively smaller than the inner diameter of the second column section.  
      The solute is caused to flow through an intermediate column section connecting the first column section and the second column section. The inner diameter of the intermediate column section varies from the inner diameter of the first column section to the inner diameter of the second diameter section.  
      The first section of the column is situated proximate the inlet end of the column. The second column section of the column is situated proximate the outlet end of the column.  
      The flow of coolant is directed in a direction substantially perpendicular to the axis of the reactor column. This is achieved by utilizing at least two laterally offset baffles spaced along the reactor column.  
      In accordance with another aspect of his present invention, a method is provided for optimizing the throughput of a trickle bed reactor performing a gas-liquid reaction in a packed reactor column. A solute in a liquid phase is introduced into the inlet end of the reactor column and the product is removed from the outlet end of the reactor column. A gas flow is created through the column. Coolant is introduced into an enclosure substantially surrounding the reactor column. The coolant is removed from the enclosure. The solute is caused to flow along the reactor column from a first column section having a relatively smaller inner diameter to a second column section having a relatively greater inner diameter. The flow of coolant is directed in a direction substantially perpendicular to the axis of the reactor column.  
      The coolant flow is directed by utilizing at least two laterally offset baffles spaced along the reactor column. Preferably, a plurality of baffles are spaced along the column. Each baffle is laterally offset relative to the adjacent baffles.  
      The velocity of the coolant through the enclosure portion proximate the first column section is increased by reducing the volume occupied by the coolant in that enclosure portion.  
      The solute is caused to flow through an intermediate column section connecting the first and second column sections. The inner diameter of the intermediate column section varies from the inner diameter of the first column section to the inner diameter of the second diameter section.  
      The first section of the column is situated proximate the inlet end of the column. The second column section of the column is situated proximate the outlet end of the column.  
      In accordance with another object of the present invention, a method is provided for optimizing the throughput of a trickle bed reactor adapted to oxidize a solute in a liquid phase in a reactor column with inert packing by varying the geometry of the reaction column. The method includes the steps of introducing solute to be oxidized to the inlet end of the column. The oxidized product is removed from the outlet end of the column. An oxygen containing gas is introduced into one end of the column. The gas is removed from the other end of the column. The column is cooled. The solute is caused to flow through the reactor column from the inlet end to the outlet end, the inner diameter of the reactor column varying in accordance with the temperature profile generated by the oxidation reaction along the column.  
      The rate of heat transfer to the coolant surrounding the section of the column proximate the inlet end is increased by increasing the velocity of the coolant proximate that section of the column. This is accomplished by reducing the volume occupied by the coolant surrounding the section of the column proximate the inlet end.  
      The flow of coolant is directed in a direction substantially perpendicular to the axis of the reactor column. This is accomplished by utilizing at least two laterally offset baffles spaced along the reactor column. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
      To these and to such other objects that may hereinafter appear, the present invention related to a method and apparatus for optimizing the throughput of a trickle bed reactor, as described in detail in the following specification and recited in the annexed claims, taken together with the accompanying drawings, wherein like numerals refer to like parts, and in which:  
       FIG. 1  is a schematic illustration of the first preferred embodiment of the trickle bed reactor of the present invention;  
       FIG. 2  is a side view of the central portion of the first preferred embodiment of the reactor of the present invention, showing the sections of the reactor columns and the baffle arrangement;  
       FIG. 3  is a cross-sectional view of the lower portion of the reactor taken along line  3 - 3  of  FIG. 2 ;  
       FIG. 4  is a cross-sectional view of the upper portion of the reactor taken along line  4 - 4  of  FIG. 2 ;  
       FIG. 5  is a cross-sectional view of the upper portion of a second preferred embodiment of the present invention; and  
       FIG. 6  is a cross-sectional view of the upper portion of a third preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      As seen in the drawings, the first preferred embodiment of a trickle bed reactor of the present invention includes a hollow closed ended outer tube-like enclosure or shell  10  of uniform diameter made of non-reactive material such as stainless steel. Within enclosure  10  are situated a number of parallel hollow cylindrical reactor columns  12 , four of which are present in the embodiment illustrated in the drawings. The walls of columns  12  are also made of non-reactive material, such as stainless steel.  
      In the lower portion of the reactor, the interior of enclosure  10  defines a space through which a temperature control fluid flows. In this application, the reactor is performing an exothermic oxidation and the temperature control fluid is a liquid coolant for removing heat generated by the oxidation from the reactor columns  12 , as described in detail below. However, the same equipment could be used to perform endothermic reactions.  
      Each of the reactor columns  12  has a liquid inlet end  14  at the top of the column and a liquid outlet end  16  at the bottom of the column. The inlet ends  14  of each of the columns  12  are each connected to a source  18  of a solute in a liquid phase, which is the liquid to be oxidized, by a separate supply line  20 . Each of the supply lines  20  includes a device for measuring the liquid flow rate through the supply line, such as a flow meter  22  and a device for regulating the flow through the supply line, such as a metering valve  24 . This permits the operator to monitor and regulate the liquid flow rate to each reactor column so as to maintain equal liquid flow rates to the inlet  14  of each of the columns.  
      Each of the reactor columns  12  is filled with a non-reactive packing or catalyst packing  26 , as illustrated in  FIG. 2 . The solute to be oxidized is introduced to the inlet end  14  of each column and moves down each column by gravity, through the packing  26  therein, to the outlet end  16  of that column.  
      As the solute moves down each column, an oxygen containing gas is forced through the column in a counter-current or co-current flow in order to oxidize the solute. In the embodiment disclosed herein, the gas flow is counter-current with solute movement and the gas enters the bottom of enclosure  10  from a gas inlet port  28  connected to a source  30  of the gas under pressure. The gas is removed from enclosure  10  at a gas outlet port  29  located near the top of enclosure  10 .  
      The liquid coolant is circulated around the reactor columns  12 , in order to remove the heat generated within the reactor columns as the oxidation is taking place. The coolant enters the lower portion of the enclosure through a coolant inlet port  32  located at the bottom of enclosure  10 . Port  32  is connected to a source  34  of the coolant through a chiller  36  that cools the liquid to the desired temperature. The coolant is removed from the upper portion of the enclosure through a coolant outlet port  38  located at the top of the enclosure. Although in the embodiment disclosed herein the cooling agent flow is counter-current with solute movement, a co-current cooling agent flow is also possible.  
      In the embodiment disclosed herein, enclosure  10  is divided longitudinally into three portions: an upper enclosure portion  10   a , a central enclosure portion  10   b  and a lower enclosure portion  10   c . Upper enclosure portion  10   a  is isolated from central enclosure portion  10   b  and lower enclosure portion  10   c  by a partition  44 .  
      A secondary coolant inlet port  46  is situated near the bottom of upper enclosure portion  10   a . A secondary coolant outlet port  48  is situated near the top of lower enclosure portion  10   c . This permits coolants at different temperatures to be separately supplied to and removed from enclosure portion  10   a , on the one hand, and central and lower enclosure portions  10   b  and  10   c , on the other hand, if desired. However, by connecting secondary ports  46  and  48  together, such as by a connector tube  50  or by simply removing separation  44 , coolant from a single source can be circulated along the entire length of the enclosure, eliminating the need for separate chillers.  
      Each of the reactor columns  12  is divided into three sections: an initial column section  12   a  at the top of the column, a final column section  12   c  at the bottom of the column and an intermediate column section  12   b  connecting initial section  12   a  with final section  12   c.    
      The initial column section  12   a  of each reactor column  12  has an inner diameter that is smaller than the inner diameter of the final column section  12   c  of the reactor column. The inner diameter of the connecting section  12   b  of each column varies from that of the inner diameter of the initial section  12   a  to the inner diameter of the final column section  12   c.    
      Reducing the inner diameter of the initial section  12   a  of each of the reactor columns relative to the inner diameter of the final section  12   c  of each of the columns increases the heat transfer capability along the initial column sections relative to that of the final column sections. Since the heat generated by the oxidation is greatest during the initial portion of the oxidation, increasing the heat transfer capability in initial section  12   a  of each column relative to that of the final column section  12   c  of each column permits greater control over the heat generated. Moreover, the greater inner diameter of each final column section  12   c  provides sufficient residence time for the oxidation to take place. Varying the column geometry in this manner contributes to better temperature control and thus greater throughput.  
      The rate of heat transfer is further enhanced along the initial section  12   a  of each reactor column by increasing the velocity of the coolant around those sections. This is achieved by tuning the geometry of the reactor such that the volume occupied by the coolant proximate the initial column sections  12   a  is reduced.  
      The volume occupied by the coolant proximate the initial column sections can be reduced to increase the velocity of the coolant surrounding those sections in one of three ways. In the first preferred embodiment of the invention, as illustrated in  FIGS. 1, 2  and  4 , jackets  69  of relatively small volume are provided surrounding each of the initial column sections  12   a . The coolant flows through jackets  69 . The jackets, in aggregate, have a coolant containing volume considerably less than the volume of enclosure portion  10   a , if present, as illustrated in  FIG. 4 . Alternatively, the volume occupied by the coolant within the upper portion  10   a  of the enclosure can be decreased by reducing the diameter of that section of the upper enclosure portion  10   a′ , as seen in the second preferred embodiment of the invention illustrated in  FIG. 5 . In that embodiment, the diameter of enclosure portion  10   a′  is less than the diameter of enclosure portion  10   c.    
      The volume occupied by the coolant surrounding the initial column sections  12   a  can also be reduced by placing one or more space occupiers  52  within the upper portion  10   a  of the enclosure to reduce its internal volume, as seen in the third preferred embodiment of the invention illustrated in  FIG. 6 . The space occupiers  52  may be void or may be formed of heat insulating material.  
      In the Russian patent noted above, the volume occupied by the coolant adjacent the initial tube sections is quite large. Consequently, the velocity of the coolant adjacent the initial tube sections, and hence the rate of heat transfer from those column sections, is, quite small. This is the exact opposite from the desired effect because a higher rate of heat transfer is desired in the initial section of the reactor, where heat is generated by the reaction at a greater rate.  
      Another design feature that contributes to the increased heat transfer efficiency of the reactor relates to the use and positioning of baffles  68  within lower enclosure portion  10   c  and baffles  70  within jackets  69  in the upper enclosure portion  10   a . In particular, baffles  68  are situated within lower enclosure portion  10   c  in spaced relation along column sections  12   c . Each baffle  68  is laterally offset with respect to the adjacent baffles so as to force the coolant to move in a zigzag pattern in which the coolant flow is directed in a direction substantially perpendicular to the axis of each column section  12   c  as the coolant repeatedly passes the column. Similarly, baffles  70  are situated within jackets  69  with upper enclosure section  10   a  in spaced relation along column sections  12   a . Each baffle  70  is laterally offset with respect to the adjacent baffles, for the same reason.  
      The reactor disclosed herein for purposes of illustration has two longitudinal coolant stages for simplicity of explanation of the design principles utilized in the invention. However, it should be understood that the reactor of the present invention could include as many longitudinal coolant stages as is required to optimize the configuration.  
      Further, while the preferred embodiments of the reactor disclosed herein for purposes of illustration include initial and final column sections of substantial length having uniform diameters and a relatively short, tapering intermediate column section with a continuously varying diameter, it is also possible to fashion the initial and final uniform diameter column sections of short length and have the continuously varying diameter intermediate section extend virtually the entire length of the reactor. In fact, the reactor could include a reactor column with a continuously varying diameter along its entire length, if desirable.  
      It should now be appreciated that the present invention relates to a method and apparatus for optimizing the throughput of a trickle bed reactor. The reactor geometry is designed so as to increase the heat transfer along the initial sections of the reactor columns where the heat generation is the greatest. This is accomplished by reducing the inner diameter of the initial section of each of the reactor columns relative to the final section of each of the reactor columns and by increasing the rate of heat transfers from the initial column sections by reducing the velocity of the coolant surrounding those sections. Further, the cooling efficiency along the entire length of the reactor columns is increased by utilizing a plurality of spaced laterally offset baffles in order to direct the coolant flow in a direction perpendicular to the axis of each of the reactor columns.  
      While only a limited number of preferred embodiments of the present invention have been disclosed for purposes of illustration, it is obvious that many variations and modifications could be made thereto. It is intended to cover all of those variations and modifications that fall within the scope of the present invention, as defined by the following claims: