WO2002079125A1

WO2002079125A1 - High-throughput selective hydrogenation process and apparatus

Info

Publication number: WO2002079125A1
Application number: PCT/US2001/048117
Authority: WO
Inventors: Wei Liu
Original assignee: Corning Incorporated
Priority date: 2001-03-30
Filing date: 2001-12-11
Publication date: 2002-10-10

Abstract

Selective hydrogenation processes and apparatus utilizing one-pass, high-throughput monolithic honeycomb reactors (14) are provided for use in a variety of pre- and post-treatment applications involving the selective hydrogenation of fluid hydrocarbon process streams of industrially important materials.

Description

HIGH-THROUGHPUT SELECTIVE HYDROGENATION PROCESS AND APPARATUS

Background of the Invention This invention relates to chemical processes and reactors utilizing honeycomb monolith catalysts to carry out selective hydrogenation reactions for the purification of chemical process streams.

Honeycomb catalysts are widely and successfully used in automotive emission control systems and in some industrial stack gas treatment systems. However, most of the present commercial uses of honeycomb catalysts are for gas phase reactions, examples being the oxidation of hydrocarbons by oxygen and the reduction of nitrogen oxides in selective catalytic reduction (SCR) processes. A comprehensive review of practical uses for honeycomb catalysts is given by P.G. Menon, M.F.M. Zwmkels, E.M. Johansson, and S.G. Jaras in "Monolithic Honeycombs in Industrial Catalysis", Kinetics and Catalysis, 39(5), 615-624 (1998).

The use of honeycomb catalysts in the chemical processing industries has been quite limited even though considerable basic research has been conducted to understand issues related to use of honeycomb catalyst technology for gas/liquid catalytic reactions. Examples of particular reactions of interest are hydrocarbon conversion reactions such hydrogenation, hydrotreating, and other two-phase gas/liquid catalytic reactions. Some fundamental aspects of the potential of monolith catalysts for use in non-automotive applications are reviewed by A. Cybulski and J. A. Moulijn in "Monoliths in Heterogeneous Catalysis", Catal. Rev.-Sci. Em., 36(2), 179-270 (1994). Also, a kinetics study for olefin hydrogenation over a honeycomb catalyst has been reported by Smits et al. in "Selective Three-Phase Hydrogenation Of Unsaturated Hydrocarbons In A Monolithic Reactor", Chemical Engineering Science, 51(11) , 3019- 3025 (1996)). These and other publications discussing potential applications for monolithic honeycomb catalysts have not, however, provided sufficient information to confirm the actual utility, if any, of honeycomb catalysts in most of the candidate industrial applications of interest.

At present, many of the process steams in refinery and other chemical processes contain small amounts of impurities in the form of reactive unsaturated hydrocarbons containing unsaturated carbon-carbon bonds. These impurities are often undesirable and need to be removed in order to provide a high quality product or improve downstream processing efficiency, and so selective hydrogenation of the process streams is required.

In selective hydrogenation processes, the undesirable component must be saturated selectively over the desirable component by the reactive addition of hydrogen. Selective hydrogenation often involves use of fixed beds of solid catalysts such as alumina-supported palladium, platinum or nickel beads or pellets, with the reaction being carried out inside a reactor vessel loaded with catalyst particles under closely controlled reaction conditions.

One example of such a process is disclosed in published European patent application EP 885273. That process involves the selective hydrogenation of dienes in reformate process streams over a supported nickel catalyst. In this case, dienes are undesirable impurities in the process stream mainly comprised of mono-aromatics

(benzene, toluene, and xylene). Another example is selective hydrogenation of pyrolysis gasoline (pygas), discussed for example by V. Regaini and C. Tine in "Upflow Reactor For The Selective Hydrogenation Of Pyrolysis Gasoline - A Comparative Study With Respect To Downflow", Appl. Catal.. (10) 43-51 (1984)). In the pygas hydrogenation process, highly reactive olefin species such as styrene and dienes are selectively hydrogenated over mono-olefins and aromatics by a nickel/alumina catalyst.

In the above two examples, the selective hydrogenation reaction is carried out within the fixed catalyst pellet bed by passing a two-phase gas-liquid process stream through the bed. Alternatively, selective hydrogenations of these types can be carried out in slurry reactors wherein smaller solid catalyst particles are dispersed to form slurries within the liquid phase process stream. Reaction conditions appropriate for these hydrogenation reactions are separately optimized for each reaction and reactor type. However, because of the generally low catalytic conversion efficiencies of these reactors, relatively large reactor vessels are usually required in order to handle the process stream at commercially viable flow rates. The low conversion efficiencies of these reactors are reflected in the low liquid hourly space velocities (LHSV) or weight hourly space velocities (WHS V) at which commercial hydrogenation reactions are conventionally carried out. Liquid hourly space velocities in the range of 2-10 m3/m3-hour (hr^"1) are typical.

Other disadvantages of present commercial practices include the need for complex process flow designs and controls for the integration and efficient operation of these reactors in chemical processing plants. These are due in part to the high pressure drop characteristics of these reactors. The resulting high capital and operational costs make widespread use of this technology cost-prohibitive.

Summary of the Invention

The present invention provides selective hydrogenation processes and apparatus utilizing high-throughput monolithic honeycomb reactors that offer significant enhancements in productivity and process performance over conventional selective hydrogenation reactors. Further, the reactors and processes may be adapted for efficient use in a variety of pre- and post-treatment applications involving the selective hydrogenation of fluid hydrocarbon process streams of industrially important materials.

An important feature and advantage of the invention is that the honeycomb reactors are operated in a high liquid-hour-space- velocity flow mode. In the past, three- phase (gas, liquid, solid) catalyst reactors have generally been run in a low liquid space velocity regime because of poor gas/liquid/catalyst contacting efficiency and/or high pressure drop incurred at high space velocities. The present invention takes fuller advantage of the low pressure drop characteristics of monolithic honeycomb catalysts by operating honeycomb reactors at unconventionally high space velocities, yet achieving surprisingly high conversion efficiencies, activity and selectivity during operation in that regime. Minimum conversion rates are at least 10% of the hydrocarbon species targeted for conversion, but conversions of up to 100% even at high space velocities can be achieved under preferred conditions of reactor operation. In one aspect, then, the invention resides in a process for the selective hydrogenation of at least one unsaturated hydrocarbon species present in a process feed stream comprising at least one and more typically two or more unsaturated or otherwise reducible hydrocarbon species. In accordance with that process, a process feed stream comprising the unsaturated hydrocarbon species and hydrogen gas is passed as a two- phase mixture through a monolithic honeycomb catalyst bed at a liquid hourly space velocity in the range of 10 to 8000 v/v/hr (hr-1). The pressure within the reactor can be as high as 1000 bar, but is more typically in the range of about 1-200 bar. Catalyst bed temperatures are maintained in the range of 20-500°C. Utilizing these process conditions results in a selective and efficient hydrogenation of one of the hydrocarbon species without undesirable side reactions that would cause the loss of other desirable hydrocarbon components in the process stream. Examples of side reactions can be hydrogenation of desirable components, hydro- isomerization, hydrocracking, polymerization, etc. The processing efficiencies of reactors constructed and operated at high hourly space velocities in accordance with the invention are sufficiently high that these reactors can be used in a one-pass rather than differential reactor operating mode. In the one-pass mode, most or all of the product stream produced by the reactor is collected for distribution or further processing on other equipment, rather than being re- processed through the hydrogenation reactor. Differential reactors, on the other hand employ extensive recycling of the reactant stream to achieve useful levels of conversion of the compounds to be treated. An important aspect of the present invention is that it provides one-pass conversions in excess of 50% and more typically 80-100% of the theoretical limit of the hydrocarbons targeted for hydrogenation, with good selectivity for the desired hydrogenations over competing hydrogenation reactions involving other unsaturated or reducible hydrocarbons present in the reactant stream.

Description of the Drawing The invention may be further understood by reference to the drawing, which is a schematic process diagram illustrating the use of a selective hydrogenation reactor according to the invention in an on-line or single pass mode. Detailed Description One suitable arrangement for carrying out the invention is to process the two- phase gas-liquid process stream in a co-current- down-flow mode, as schematically illustrated in Fig. 1 of the drawing. Referring more particularly to Fig. 1, a liquid hydrocarbon feed 10 and a hydrogen gas feed 12 are introduced together into a reactor vessel 14 through a gas/liquid distributor 16 at the top of the reactor. The liquid hydrocarbon feed can be heated by routing all or portions of the feed through heater 18. The reactor vessel is packed with monolith catalyst modules 20. The gas/liquid distributor delivers gas and liquid into individual monolith channels. The processed feed or product stream 22 exits at the bottom of the reactor and directly goes to downstream processing. Alternatively, product stream 22a exits at the bottom of the reactor and then, passes through cooler 24 and into gas/liquid separator 26. Separation of the cooled fraction of the product stream produces an offgas fraction 28 and condensed product portion 22b which is sent out of the unit as a product stream. Suitable monolith catalyst modules for use in the reactors of the invention include monolithic metallic or ceramic honeycomb structures such as employed for the treatment of gas reactant streams in the prior art, these structures comprising a plurality of parallel-oriented open-ended cells or channels bounded by relatively thin channel walls traversing the structure from a first or inlet face to a second or outlet face of the monolith. An active hydrogenation catalyst is disposed upon or within the channel walls of the structure.

Useful honeycomb monoliths for the purpose of constructing selective hydrogenation reactors in accordance with the invention include those having an open frontal or inlet area (OF A) in the range of 10 to 95%, the remainder of the inlet face comprising the wall structure of the monolith. The channels populating the structure are provided at a channel density of 10 to 5000 channels per square inch (cpsi) of transverse honeycomb cross-section, and will have an average channel diameter in the range of about 0.1 to 5.0 mm. Average channel wall thicknesses in these honeycombs will be the range of about 0.001 to 3.0 mm. Preferred honeycomb structures have a more narrowly defined geometry, including cell densities in the range of 10-2500 cpsi,

OFA values of 10-90%, and channel wall thicknesses in the range of 0.025-1.0 mm. Any of the known hydrogenation catalysts adapted for promoting the particular hydrogenation reaction of interest for the reactor being constructed may be selected for inclusion in the honeycomb. Examples of suitable hydrogenation catalysts include metals and compounds containing those metals selected from the group consisting of Ni, Pd, Pt, Co, Mo, as well as combinations and mixtures of these metals and metal compounds.

Li general it will be the most easily hydrogenated unsaturated hydrocarbon in the feed stream that will be reacted with hydrogen in the channels of the monolith reactor. Each honeycomb catalyst channel in these reactors works as a small separate tube reactor with the active catalyst metal supported on the wall. The gas and liquid are confined inside each of these channels in intimate contact with active metal catalysts, most typically nickel or palladium, such that the hydrogenation of at least one of the species present in the process stream can be carried out with high efficiency. Thus the process stream may pass rapidly through the honeycomb catalyst bed at low pressure drops while still maintaining conversion efficiency at a high level.

The reactor effluent consists of a modified process stream wherein the concentration of at least one unsaturated hydrocarbon present in the initial stream has been substantially reduced. The modified stream, comprising increased proportions of the hydrocarbons not hydrogenated in the reactor, may be sent directly to downstream processing as a two-phase fluid or separated into gas and liquid product streams in a gas/liquid separator. As shown in Fig. 1, means may also be provided for heating the process stream prior to its introduction into the monolith reactor, or for cooling the stream prior to processing it through a gas/liquid separator, if desired.

The efficiency and selectivity of the monolith hydrogenation reactor are such that it may be operated at an unconventionally high liquid hourly space velocity

(LHSV). As noted above, space velocities in the range of 10-8000 v/v/hr (hr^"1) can be used; preferred velocities are in the range of about 15-1000 v/v/hr (hr^"1). For purposes of the present description LHSV is defined as:

FV_C

LHSV = -

V.. Wherein FV_F is the liquid feed volume flow rate and Vcat is the catalyst packing volume. Another measure of processing rate is the weight hourly space velocity (WHSN), defined as:

WHSV = - HSV

wherein FW_F and pF are the liquid feed mass flow rate and density, respectively, and Wcat and peat are the catalyst packing weight and packing density in the packed bed, respectively.

With appropriate selection of the channel sizes and channel wall thicknesses in the honeycomb monolith packings, high liquid space velocities can be employed while maintaining pressure drops through the catalyst beds at less than 5 bar. For the selective hydrogenation processes of interest for the present invention, increases in process stream temperature due to the reaction exotherms are typically less than 100°C. With this temperature and pressure drop control, no hydrogen and feed injection in middle of the reactor apparatus is normally required. Thus, the present invention results in a simple, compact, high-productivity monolith reactor that works as an online reactor.

Reactor pressures may be anywhere in the range from about 1-1000 bar, but are more preferably kept in the range of about 1-200 bar. Preferred reactor temperatures are in the range of 20-250°C. A broad range of H2 gas:oil volume ratios, e.g., in the range of 0.001 to 1000 ΝL/L, can be used. ΝL is defined for purposes of the present description as the volume that would be occupied by the hydrogen gas component of the feed stream if measured at 25°C and one atmosphere of pressure.

The selective on-line hydrogenation reactors of the invention have substantial advantages over conventional catalyst-pellet based reactors. The simple reactor configuration offers substantial process flexibility in combination with high productivity. Thus, low capital and operation costs are realized. Accordingly the online reactor can be used as a post-treater for down-stream liquid product purification, or as a feed pre-treater upstream of a main process unit. There are a variety of applications wherein post- or pre-treatment of the process stream will be advantageous. For example, so-called BTX aromatic process streams in the chemical processing industry, mainly composed of benzene (B), toluene (T), and xylene (X), often contain olefin impurities. Reformate generated during catalytic reforming processes in petroleum refining is an example. An effective method for producing a high quality BTX feedstock is to selectively hydrogenate the olefins over the aromatics in the process stream. Selective hydrogenation in accordance with the invention can effectively accomplish the removal, either as an on-line post-treater of product effluent from the reforming reactor or as a pre-treater installed upstream of the aromatics extraction unit.

Another application example for selective hydrogenation is in a guide reactor for hydrotreating reactor in a refinery. Refinery streams such as cat naphtha, coke naphtha, virgin naphtha, distillate, gas oil, etc., often contain small amounts of highly reactive species such as diolefins, or catalyst poisons such as organic silicon compounds. These highly reactive compounds complicate downstream processing by causing problems such as catalyst bed plugging and gum or polymer formation. Online hydrogenation in accordance with the invention can quickly remove these reactive species so that down-stream processing flexibility and efficiency are greatly improved. The reactant feed stream composition as well as the concentrations of targeted hydrocarbons in the liquid component of the reactant feed stream may vary widely depending upon the particular feed stream to be processed. In some feed streams the targeted hydrocarbon can be a mono-aromatic hydrocarbon that is present in only minor proportion, e.g., 0.5% by weight; in others mono-aromatics can be the matrix hydrocarbon and constitute up to 99.9% by weight of the feed. Feed streams comprising up to 99.9% of mono-olefins or di-olefins can be treated; on the other hand, feedstreams comprising di-olefins as the species to be converted might include only up to about 20% of di-olefin constituents.

The invention may be further understood by reference to the following specific examples, which are, however, intended to be illustrative rather than limiting. Example I - Selective Olefin Hydrogenation (prior art)

Benchmark olefin hydrogenations are conducted over nickel-alumina catalysts using catalyst particles of differing sizes. 1/8" nickel/alumina catalyst beads are crushed and sieved into two different sizes, 335μm and 132μm on average. Equivalent weights of the beads and each of the two sizes of crushed catalyst are then blended with

60-mesh SiC powder and loaded into a reactor tube of 1" diameter.

Each catalyst sample is preliminarily reduced by flowing hydrogen through the reactor tube at a pressure of 220 psig and a temperature of 400°C for about 10 hours. After cooling the reactor to the desired reaction temperature, a liquid hydrocarbon feed reactant stream consisting of 5% 1-octene, 5% styrene, and 90% toluene is introduced along with hydrogen into the top of the reactor. The hydrogen gas: oil volume ratio of the feed stream is 50 NL/L.

The liquid-gas reactant stream is then flowed downwardly through the catalyst bed in a co-current flow mode to convert the styrene in the stream to ethylbenzene (EB), and to convert the 1-octene into n-octane. The reactor effluent is then cooled and separated into gas and liquid products, the latter being collected and analyzed to determine the conversion efficiency of the process.

Table 1 below shows conversion results obtained for the different sizes of Ni/alumina catalyst beads/particles for a number of conversion runs. Included in the Table for each of the runs conducted are the liquid hourly space velocity of the process stream, the process stream temperature observed at the bottom of the reactor, and the percent conversion for each of the species undergoing hydrogenation under the conditions described.

Table I - Selective Olefin Hydrogenation (Prior art)

As is evident from a study of the data in Table I, styrene conversion over the 1/8" catalyst is only about 30% at the liquid hourly space velocity of 48 hr^"1 employed for the first run. This conversion rate can increase somewhat as the bottom bed temperature is raised from 30.9°C. to 60.6°C. However, at similar temperatures, styrene conversion reaches 99.8% over the 335μm-crushed catalyst at 48 hr^"1 LHSV feed rates, and 98% over the 132μm-crushed catalyst at LHSV feed rates as high as 220 hr^"1. Not surprisingly, hydrogenation activity over these Ni/alumina catalysts increases substantially with the decrease in catalyst particle size. Thus the effect of particle size on conversion rate is far more significant than that of the reaction temperature. Nevertheless, raising reaction temperatures is the only practical approach to higher conversion efficiencies in industrial hydrogenation processes even though it is known that the catalyst deactivation rate increases with temperature. This is because reduced catalyst particle sizes, while increasing catalyst activity and theoretically permitting higher process feed rates, substantially increase pressure drop in the reactor. In turn, such pressure drop increases tend to limit the reactor throughput.

Example U. - Selective Olefin Hydrogenation over a Honeycomb Catalyst

Nickel-alumina honeycomb catalysts are prepared by impregnating 30 wt.% gamma alumina-washcoated cordierite honeycomb substrates with a nickel salt solution. The honeycomb substrates have a cell density of 400 cpsi, a channel wall thickness of about 0.2 mm, and a square channel design with channel openings about 1.0 mm. square.

Larger substrate honeycombs of these geometries are cut into cylindrical monoliths about 1 cm in diameter and 15 cm in channel length, and the cylindrical monoliths are then immersed in a 2M aqueous nickel nitrate solution with degassing under vacuum for a few minutes. The monoliths are then removed from solution and excess liquid is removed from the honeycomb channels with a compressed air stream. The thus- impregnated monoliths are next air-dried in an oven at 100°C for about 16 hours, and then calcined at 400°C for 2 hours in an electric furnace. They are finally pre-reduced in situ in flowing hydrogen at a pressure of 220 psig and a temperature of

400°C for 10 hours prior to testing for selective hydrogenation efficiency.

To evaluate the unit activity of a honeycomb catalyst prepared as described, a representative channel of the monolith is fitted with a 1/8 inch O.D. steel inlet tube while the other channels are isolated from the process feed by plugging. A sample feed stream consisting of hydrogen gas and liquid reactant is then delivered directly into the catalyzed monolith channel at a reactor pressure of 220 psig. and flowed downwardly through the honeycomb in a co-current down-flow mode. The liquid reactant is made up of 0.5% 1-octene, 0.5 wt.% styrene, and the balance toluene. The gas and liquid feed stream constituents are mixed and preheated to the desired reaction temperature in the delivery tube prior to contact with the nickel-alumina honeycomb catalyst.

Some results of the hydrogenation processing of this feed stream through the honeycomb catalyst are reported in Table 2 below. Included in Table 2 for each of the runs conducted are the liquid flow volume of the feed stream, in cm³/minute, the liquid hourly space velocity of the process stream, in inverse hours, the process stream temperature observed at the bottom of the reactor, the hydrogen gas-to-oil ratio of the process stream in NL/L, and the percent conversion for each of the species undergoing selective hydrogenation under the conditions described. The channel cross-section and channel volume of the honeycomb catalyst exposed to the liquid feed are taken as the catalyst cross-section and channel volume, respectively, from which the liquid hourly space velocity (LHSV) of the feed stream are calculated. Also reported is the level of undesirable accompanying conversion of toluene to methyl cyclohexane (MCYH), which the process will desirably suppress.

Table 2. - Selective Olefin Hydrogenation (Monolithic Catalyst)

Reaction conditions Conversion Efficiency

Catalyst Bed Liquid LHSV H₂/Oil Styrene to 1-octene to Toluene to Temperature .-^"I

Feed (hr ¹) ratio EB (wt.%) n-octane MCYH CO (NL/L) (wt.%) (wt.%) cc/min

63.7 0.5 200 20 82.3 71.2 0.289

63.6 0.5 200 100 87.2 75.8 0.343

66.1 2 800 5 65.1 50.7 0.032

66.4 2 800 50 77.9 66.3 0.046

67.6 10 4000 5 49.5 36.4 0.008

As the data in Table 2 reflect, significant olefin conversions are observed in honeycomb catalyst channels even at very high feed stream flow rates. For example, styrene conversions of about 82% are observed at LHSV values of 200 hr^"1, with 50% conversion still being achieved at LHSV values of 4000 hr^"1. In sharp contrast to the observed high conversion rates for the olefins, the saturation conversions of toluene were minimal, showing the high selectivity of the hydrogenation process under these conditions of feed stream flow. These advantages of the monolithic reactor design for the selective hydrogenation of olefins over aromatics at very high feed stream throughputs were not expected.

Example Ul - Selective Olefin Hydrogenation (Long Monolith Catalyst)

If desired, the degree of selective hydrogenation of olefins present in an aromatic process feed stream can readily be increased without reducing process throughput rates simply by increasing the length of the one-pass reactor. This result is shown using a nickel-alumina honeycomb catalyst similar to that described in Example IJ above, but having a length double (30 cm) that of the Example U monolith. When prepared and tested in a co-current down-flow processing mode in accordance with the same test procedure and under the same test conditions described in Example JJ, a monolith of this design yields conversion results such as reported in Table 3 below.

Table 3. - Selective Olefin Hydrogenation (Long Reactor)

Reaction conditions Conversion, wt.%

Catalyst Bed Liquid LHSV H₂/Oil Styrene to 1-octene to Toluene to Temperatures (°C) Feed (hr^"1) ratio EB (wt.%) n-octane MCYH Top Bottom cc/rnin (NL/L) (wt.%) (wt.%)

64.9 66.1 0.5 98 20 99.2 94.5 2.391

61.0 62.6 1.0 197 50 99.5 96.2 0.794

61.9 63.3 2.0 394 50 98.9 92.3 0.349

60.6 67.3 4.0 787 50 97.7 89.9 0.132

61.1 65.8 10.0 1968 50 90.0 80.4 0.063

61.2 62.9 2 197 5 94.5 74.1 0.573

61.0 62.6 2 197 50 99.5 96.2 0.794

60.7 66.3 10 1968 2.5 78.8 63.5 0.025

60.9 65.4 10 1968 5 85.2 74.4 0.069

61.1 65.8 10 1968 50 90.0 80.4 0.063

As the data presented in Table 3 indicate, higher olefin conversion rates are obtained at the same liquid feed rates in monolithic catalysts of longer length than in the shorter length monoliths reported in Table 2. For example, styrene conversions increase to 99% from 82.3% at a liquid feed rate of 0.5cc/min, and to 90% conversion from 49.5% at liquid feed rate of lOcc/min. Further, undesirable toluene conversions decrease to below 1.0 % if sufficiently high liquid hourly space velocities are used. Other data collected during tests of this catalyst confirm that, at constant temperature, pressure, feed gas/oil ratio, and liquid flow volumes, olefin conversions increase with catalyst/gas/liquid contact time. Yet aromatic conversion rates remain surprisingly low. Example IV - Selective Upflow Olefin Hydrogenation

As previously suggested, selective hydrogenation in accordance with the invention is not limited in its applicability to co-current down-flow feed stream processing. Similarly desirable conversion efficiencies may be achieved in a co-current up-flow mode as well.

To demonstrate these efficiencies, the monolithic nickel-alumina catalyst of Example IJJ is tested utilizing the feed stream of that example in a co-current up-flow processing configuration. The testing procedures and process conditions are otherwise the same as reported in Example U.

The results of this testing are reported in Table 4 below. Again, significant olefin conversions are observed at high LHSV processing rates, with minimal saturation of toluene occurring under these processing conditions.

Table 4. Selective Upflow Olefin Hydrogenation

Reaction conditions [Co-current Upflow] Conversion, wt.%

Liquid

Catalyst Bed LHSV H₂/Oil Styrene to 1-octene to Toluene to Temperature Feed (hr^"1) ratio EB (wt.%) n-octane MCYH

(cc/min) (°C) (NL/L) (wt.%) (wt.%)

60.9 0.5 98 100 91.91 84.46 0.50 61.1 1 197 50 86.63 76.42 0.25 61.6 2 394 50 77.34 64.19 0.13 61.2 4 787 50 76.75 65.07 0.14 61.9 10 1969 50 57.41 37.40 0.04

61.1 1 197 5 72.70 55.77 0.06 62.2 10 1969 5 48.22 31.21 0.02

Example V - Other Selective Olefin Hydrogenations

Other selective hydrogenation reactions that proceed over conventional catalysts such as alumina-supported metals (e.g., nickel, palladium, etc.) can also be carried out with high efficiency at high liquid hourly space velocities in honeycomb monolith reactors in accordance with the invention. Data confirming such efficiency is provided through the testing of the honeycomb catalyst of Example IJJ above utilizing an aromatic process feed stream incorporating several alternative unsaturated hydrocarbons. One feed stream utilized for such testing consists of about 0.3% of 1- hexene (1-C6=), 0.2% of 2-hexene (2-C6=), 0.3% of heptene (1-C7=), 0.3% of 1-octene (1-C8=), 0.3% of 2-octene (2-C8=), and the remainder toluene.

Testing is carried out in a co-current down-flow mode under process flow, temperature and pressure conditions like those of Example IJJ. Some results for these tests are reported in Table 5 below.

Table 5. Other Selective Olefin Hydrogenations

Reaction conditions Conversions, wt %

Catalyst Bed ^^ιq"^ld LHSV H₂/Oil Toluene 1-C₆ ^~ 2-Gf 1-C₇ ⁼ 1-C₈ ⁼ 2-Q

Temperature (°C) (hr^"1) ratio

Top Bottom (NL/L)

62.2 63.2 1 205 5 0.56 92.2 70.1 91.1 90.4 69.9

60.7 61.9 2 411 5 0.14 86.5 60.2 87.0 84.0 62.5

61.1 68 4 822 5 0.09 83.8 70.6 84.8 82.5 69.9

60.7 68.7 4 822 50 0.16 87.5 75.4 87.1 85.2 72.4

61.6 67.8 10 2054 5 0.02 76.7 52.2 78.3 74.7 54.4

The data in Table 5 confirm that significant conversion efficiencies for all of the olefin species are achieved at LHSV feed rates above 200 hr^"1. And, only minimal aromatic saturation of the toluene aromatic fraction of the feed is observed. Thus high throughput processing is effective for a variety of different olefin compounds of differing carbon numbers and differing locations for the unsaturated carbon-carbon bonds utilizing the selective hydrogenation process of the invention.

Example VI - Selective Hydrogenation - Heavy Cat Naphtha Feed

The selective hydrogenation of a heavy cat naphtha process feed stream can also be efficiently carried out at high liquid feed rates in accordance with the invention. For the selective hydrogenation of naphtha feeds of this type, reaction conditions are -1^'6- - typically selected to maximize the hydrogenation of dienes in the feed stream, with only a minimal reduction in the desirable olefin content of the feed.

Data recording the properties of a heavy cat naphtha used as the feedstock for this test, that naptha having a diene number of 10 as determined by the maleic anhydride method, are reported in Table 6a below:

Table 6a - Heavy Cat Naphtha Feedstock

Sulfur content, wt.% 0.033 D86 Distillation, °F

Bromine number 59 5% 183°

Diene number 10 10% 198°

ASTM color <2.0 20% 220°

D86 Distillation, °F 30% 240°

Over 144° 40% 260°

End 476° 50% 280°

Recovery % 98 60% 300°

Residue % 1 70% 320°

Loss % 1 80% 344°

90% 380°

95% 427°

A honeycomb monolith catalyst prepared as described above in Example HI is employed for the processing of this naphtha feed stream, except that the 400-cpsi, gamma alumina- washcoated cordierite substrate is calcined for 4 h at lOOOoC prior to Ni impregnation to convert the gamma alumina into theta alumina. The testing procedure employed substantially follows the procedure used in Example UL except that for selective naphtha hydrogenation in accordance with the present example the collection of representative test data is deferred until after stabilization of the monolithic catalyst and reactor have been achieved. This generally occurs within about one day of reactor startup.

Naphtha feed stream processing according to this example is carried out in a co- current down-flow mode with the reactor pressure being maintained at about 220 psig.

Runs are carried out at various selected temperatures and liquid space velocities, with results as shown in Table 6b below. Diene conversions in Table 6b are reported in terms of the percent reduction in the Diene number for the product, while olefin conversions are reported as percent decreases in the Bromine number. As is known, the Diene number is a measure of the conjugated di-olefin content of the product stream, while the Bromine number measures the content of unsaturated carbon-carbon double bonds (olefins) therein.

Table 6b - Selective Heavy Cat Naphtha Hydrogenation

Catalyst Bed Liquid LHSV H₂/Oil Ratio Conversions, %

Temperature (°C) Feed (hr^"1) (NL/L)

Top Bottom (cc/min) Dienes Olefins

61.8 65.9 2 394 5 15.0 -1.7

61.8 66.1 2 394 50 17.8 6.7

150.0 162.1 2 394 50 74.8 5.0

145.6 167.9 10 1969 50 43.9 0.0

As the data in Table 6b reflect, diene conversions increase with temperature and decrease at higher liquid space velocities, but significant diene conversions can easily be achieved with only minimal loss of olefins. Thus, for example, a reduction in Diene number of approximately 75% is achieved through reactor operation at a reactor inlet temperature of about 150°C and a LHSV of 394 hr-1, with olefin losses under these conditions corresponding to a reduction of only about 5% in the Bromine number. Thus the process of the invention is particularly efficient for achieving the selective hydrogenation of dienes in a complex hydrocarbon matrix containing monoolefins at high space velocities.

Example VII- Selective Hydrogenation - Light Cat Naphtha Feed The testing procedure of Example VI is repeated, but using a light cat naptha feed to replace the heavy cat naphtha feed of that Example. Table 7a below reports the properties of the feedstock used for this testing. Table 7a - Light Cat Naphtha Feedstock

Sulfur content, wt.% 0.007 D86 Distillation, °F

Bromine number 111 5% 110°

Diene number 14.1 10% 114°

ASTM color <0.5 20% 120°

D86 Distillation, °F 30% 126° Over 99° 40% 133° End 284° 50% 141°

Recovery % 97.5% 60% 152°

Residue % 1% 70% 168°

Loss % 1.5% 80% 190°

90% 226°

95% 260°

When the processing of this light naphtha feed stream is carried out in a co- current down-flow mode, with reactor pressures again being maintained at about 220 psig., results such as reported below in Table 7b are observed. As in Example VI above, the conversion efficiency and selectivity of the process for each set of reported operating conditions are reflected in the reported percent reductions for the Diene and Bromine numbers of the products.

Table 7b - Selective Light Cat Naphtha Hydrogenation

Although the data in Table 7b show a decrease in diene conversion with increased space velocity at constant temperature as expected, significant increases in conversion efficiencies are achieved with relatively moderate temperature increases. For example, at a LHSV feed rate of 394 hr^"1 the diene conversion increased from 28.9% to about 63% as the temperature is increased from 61°C to about 100°C. Diene conversions are somewhat lower above this temperature, but in all cases, the olefin conversions are insignificant.

Example VJJI - Saturation of Aromatic Process Feeds

The hydrogenation process of the invention is also useful for carrying out a number of hydrogenation reactions that are kinetically more difficult to complete than the olefin hydrogenations of Examples I-VIJ above, and at higher than expected throughput rates. An example of such a process is the conversion by selective hydrogenation of toluene to mefhyl-cyclohexane. To carry out such a process, a nickel-alumina catalyst monolith similar to the catalyst employed in Example IJJ above is provided. However, in place of the 400 cpsi cordierite substrate, a 100 cpsi gamma alumina honeycomb substrate having channels of 2 mm diameter and generally circular cross-section, rather than square cross-section, is used to support the nickel catalyst. This nickel catalyst is similarly deposited from a nickel nitrate catalyst solution and is pre-reduced in situ in hydrogen at a pressure of 220 psig and a temperature of 400oC for 10 hours prior to the commencement of testing.

The liquid feed stream used for the tests consists of a methyl-cyclohexane matrix comprising a minor toluene fraction as an impurity. The feed stream is mixed with hydrogen in a gas/oil ratio of 50NL/L prior to treatment by the catalyst in a co- current down-flow processing mode.

Table 8 below lists toluene hydrogenation conversion efficiencies for this process under several different reaction conditions. Included in Table 8 for each of the runs conducted are the top and bottom temperatures of the honeycomb catalyst, the liquid flow and liquid hourly space velocities of the feed stream, the toluene content in the methyl-cyclohexane feedstock, and the weight percent conversion of the toluene fraction in the feedstock. Methyl-cyclohexane is observed as the dominant toluene hydrogenation product in these tests; no byproducts resulting from side reactions such as hydrocracking are observed. Table 10. - Toluene Methyl-cyclohexane Conversion

As is evident from a study of the data in Table 8, substantial toluene conversion efficiencies are readily obtained at relatively high throughput rates and relatively moderate reaction temperatures through selective hydrogenation in accordance with the invention. For example, at a catalyst bed top temperature of about 150°C, 99% toluene conversion is achieved at a LHSV feed rate of 31.3 hr^"1, and 93.7% conversion efficiencies are still realized at LHSV feed rates as high as 94.0 hr^"1. Further, due to the relative temperature insensitivity of this process, conversion rates of 92.7 % at this high feed rate are still achieved at catalyst bed top temperatures as low as 104oC at LHSV. of 94 hr^"1.

While the foregoing description and examples set forth particular illustrations of the practice of the invention and its wide applicability to selective hydrogenation processes and other gas/liquid catalytic reactions, it will be apparent that numerous modifications and variations upon those practices and procedures may be resorted to by those skilled in the art within the scope of the appended claims.

Claims

I claim:

1. A process for the selective hydrogenation of at least one unsaturated hydrocarbon species present in a hydrocarbon process feed stream comprising the steps of: delivering a two-phase gas-liquid feed stream comprising a hydrogen-containing gas and a hydrocarbon mixture comprising at least one unsaturated hydrocarbon species in combination with other hydrocarbon species to a monolithic honeycomb catalyst bed; and passing the feed stream through the catalyst bed at a liquid hourly space velocity in the range of 10 to 8000 hr^'1; thus to cause the selective hydrogenation of the unsaturated hydrocarbon species without substantial reduction of the other hydrocarbon species.

2. A process in accordance with claim wherein hydrogenation of 10 to 100% of the unsaturated hydrocarbon species is achieved in a single pass through the catalyst bed.

3. A process in accordance with claim 2 wherein the feed stream is maintained at pressures in the range of about 1-1000 bar within the catalyst bed.

4. A process in accordance with claim 2 wherein the temperature within the catalyst bed is maintained in the range of about 20-500°C.

5. A process for the removal of an unsaturated hydrocarbon species from a liquid hydrocarbon reactant stream comprising the step of passing the reactant stream and a hydrogen-containing gas reactant through a monolithic catalyst bed under reaction conditions comprising: a liquid hourly space velocity in the range of 10 to 8000 hr^"1; a temperature in the range of 20 to 500°C; a pressure in the range of 1.0 to 200 bar; and a volume ratio of hydrogen-containing gas to liquid reactant in the range of 0.001 to 1000 NL L. -2^'2-

6. A process in accordance with claim 5 wherein

(a) the liquid hourly space velocity is in the range of about 15 to 1000 hr^'1 and the temperature is in the range of about 20 to 250°C, and (b) 10 to 100% of the unsaturated hydrocarbon species is removed from the reactant stream during one pass through the monolithic catalyst bed.

7. A process in accordance with claim 5 wherein the reactants pass through the catalyst bed at a pressure drop of less than 5 bar.

8. A process in accordance with claim 5 wherein the reactants undergo a temperature increase of less than 100°C. in the catalyst bed.

9. A process in accordance with claim 5 wherein the liquid reactant comprises a mono-aromatic hydrocarbon species in a proportion ranging 0.5 to 99.9% by weight.

10. A process in accordance with claim 5 wherein the liquid reactant comprises a hydrocarbon species selected from the group consisting of mono-olefin and di-olefin hydrocarbons in a proportion ranging up to 99.9 % by weight.

11. A process in accordance with claim 10 wherein the liquid reactant comprises a di-olefin hydrocarbon species in a proportion ranging up to 20 % by weight.

12. A process in accordance with claim 5 wherein the monolithic catalyst bed comprises at least one honeycomb monolith incorporating an active hydrogenation catalyst, the monolith having an open frontal area of 10 to 95%, a channel density of 10 to 5000 cpsi, an average channel diameter in the range of 0.1 to 5.0 mm, and an average channel wall thickness in the range of 0.001 to 3.0 mm.

13. A process in accordance with claim 12 wherein active hydrogenation catalyst is a metal selected from the group consisting of Ni, Pd, Pt, Co, Mo, and mixtures or compounds thereof.