METHOD OF MAINTAINING THE ACTIVITY OF PRE-REFORM CATALYSTS

Abstract

The present invention addresses to a method of maintaining the activity of pre-reform catalysts in hydrogen production units, in order to avoid deactivation by oxidation or coke deposition of pre-reform catalysts in the absence of hydrogen in the feed consisting of hydrocarbon and water vapor.

Claims

1. A METHOD OF MAINTAINING THE ACTIVITY OF PRE-REFORM CATALYSTS, containing nickel as the active phase, in the absence of recycle hydrogen in the feed of the pre-reform reactor, characterized in that the following steps are carried out: a) introducing in the feed of the pre-reform reactor a catalyst activity maintenance fluid, in which the steam/fluid ratio is between 200 and 40 mol/mol and the reactor inlet temperature is between 430and 550° C.; b) stopping the feed of the catalyst activity maintenance fluid in the pre-reform reactor, when the hydrogen returns in the reactor feed and it has reached a H.sub.2/hydrocarbon ratio between 0.1 and 0.2 Nm.sup.3/kg.

2. THE METHOD according to claim 1, characterized in that the catalyst activity maintenance fluid is selected from methanol, formaldehyde, formic acid or mixtures thereof.

3. THE METHOD according to claim 1, characterized in that the steam/fluid ratio is between 150 and 80 mol/mol.

4. THE METHOD according to claim 1, characterized in that the reactor inlet temperature is between 450° C. and 500 ° C.

5. THE METHOD according to claim 1, characterized in that the hydrocarbon (load) is selected from natural gas, liquefied petroleum gas, refinery gas or naphtha.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0034] The present invention will be described in more detail below, with reference to the attached figures, which, in a schematic way and not limiting the inventive scope, represent examples of embodiment thereof. In the drawings, there are:

[0035] FIG. 1 illustrating a graph of H.sub.2/natural gas and steam/methanol ratios in the pre-reform reactor during an event of absence of hydrogen in the feed of this reactor in an industrial unit with a production capacity of 3,000,000 Nm.sup.3/d of hydrogen;

[0036] FIG. 2 illustrating a graph of temperatures at the inlet and the upper, middle and lower regions of the pre-reform reactor bed of an industrial unit with a production capacity of 3,000,000 Nm.sup.3/day of hydrogen during an event in which there was no hydrogen in the reactor feed and, according to the present invention, it was then fed methanol in a steam/methanol ratio between 150 to 100 mol/mol.

DETAILED DESCRIPTION OF THE INVENTION

[0037] The method of maintaining the activity of pre-reform catalysts containing nickel as an active phase, including the continuity in operation of hydrogen or synthesis gas production units, when there is no hydrogen in the feed of the pre-reform reactor, according to the present invention, comprises the following steps: [0038] a) introducing into the feed of the pre-reform reactor a catalyst activity maintenance fluid, in which the fluid is selected from methanol, formaldehyde, formic acid or mixtures thereof, in which the steam/fluid ratio is between 200 and 40 mol/mol, preferably between 150 and 80 mol/mol and reactor inlet temperature between 430 and 550° C., preferably between 450 and 500° C.; [0039] b) stopping the feed of the catalyst activity maintenance fluid in the pre-reform reactor, when the hydrogen returns in the reactor feed and it has reached a H.sub.2/hydrocarbon ratio between 0.1 and 0.2 Nm.sup.3/kg, where the hydrocarbon is selected from natural gas, liquefied petroleum gas, refinery gas or naphtha.

EXAMPLES

[0040] The following examples are presented in order to more fully illustrate the nature of the present invention and the manner of practicing the same, without, however, being considered as limiting its content.

Example 1

[0041] A nickel-based pre-reform catalyst was previously ground and sieved in the range of 25 to 35 mesh. Two grams of the catalyst were loaded into a stainless-steel reactor. The catalyst was activated (reduced) in N.sub.2 flow from room temperature to 350° C. at the pressure of 20 atm (2,027 MPa), which was maintained for 1 hour and then in flow of 10% H.sub.2 in nitrogen until 450° C. After 2 hours at 450° C., the hydrogen was removed and steam or steam/methanol fed for a period of 24 hours. After this period, the steam reforming activity of methane was measured at temperatures of 450° C., 500° C. and 550° C. with a steam/carbon ratio of 2.0 mol/mol and with 5% of hydrogen in the load.

[0042] The results are presented in Table 1 and allow to note that: a) The passage of steam in the absence of hydrogen over the pre-reform catalyst, under typical conditions of industrial operation, makes the material inactive; b) The addition of methanol in steam, at values as low as a steam/methanol molar ratio of 592 mol/mol, allows maintaining a significant fraction of the catalyst activity.

[0043] The use of a low flow rate of methanol is of industrial interest to reduce its consumption, especially due to the absence of hydrogen in the hydrocarbon and steam load at the pre-reformer inlet, typically due to the need for maintenance in the compressors of hydrogen recycling, an activity that tends to last a period of several hours or even days. On the other hand, it is not in the industrial interest to maintain a significant volume of methanol stored, due to infrastructure costs or safety, environmental and health issues.

TABLE-US-00001 TABLE 1 Conversion of methane in a commercial nickel-based pre- reform catalyst after different catalyst treatments. Treatment 450° C. 500° C. 550° C. Steam/methanol in the ratio 12 20 27 of 592 mol/mol Steam/methanol in the ratio 13 24 33 of 103 mol/mol Steam only <1 <1 <1

Example 2

[0044] A nickel-based pre-reform catalyst was previously ground and sieved in the range of 100 to 150 mesh and loaded into a fixed bed in a quartz reactor. Methanol and water vapor were fed by passing nitrogen through saturators maintained at 15° C. The conversion of methanol was studied at atmospheric pressure, a steam/carbon ratio of 2.2 mol/mol and GHSV of 39,000 h.sup.−1. The experiments were repeated, in the same experimental condition but in the absence of catalyst, to determine the conversion from thermal decomposition.

[0045] The results are presented in Table 2. The results show that pre-reform catalyst bed temperatures between 450° C. and 500° C. are preferable to have a high rate of catalytic decomposition of methanol and, at the same time, limit the potential oxidation of the catalyst by steam, allowing the use of lower steam/methanol ratios.

TABLE-US-00002 TABLE 2 Conversion of methanol in the pre-reforming reaction in the presence or absence of a nickel-based catalyst. Thermal Catalytic Temperature (° C.) Decomposition (%) Decomposition (%) 450 ~0 98.6 500 <5 >98.9 650 <5 ~100 700 <5 ~100

Example 3

[0046] This example illustrates the use of methanol or other classes of molecules to maintain pre-reform catalyst activity in the absence of recycle hydrogen. One of the most important requirements for a molecule to be used in the maintenance of pre-reform catalyst activity is to have a high rate of H.sub.2 generation and, at the same time, to present a low risk of olefin formation or other compounds with high potential of coke deposition. This criterion eliminates the use of other alcohols such as ethanol or glycerin, as these molecules, under pre-reform conditions and in the presence of nickel-based catalysts, tend to generate olefins or other compounds that can rapidly increase the deposition rate of coke on the catalyst and, consequently, increase the loss of load in the reactor and reduce the campaign time.

[0047] Table 3 summarizes properties and characteristics of different classes of molecules that could be used in the present invention to replace methanol.

TABLE-US-00003 TABLE 3 Class of compounds and their use to maintain the performance of nickel-based pre-reform catalysts. Compound Note Alcohols Methanol (CH.sub.3OH) can be used, according to the present invention, as it presents a high decomposition rate for H.sub.2 and a low risk of coke formation. Higher molecular weight alcohols, such as ethanol (C.sub.2H.sub.5OH) or glycerin (C.sub.3H.sub.8O.sub.3), should not be used due, to the high rate of formation of olefins or other compounds having a high potential for deposition of coke on the pre-reform catalyst. NH.sub.3 or amines NH.sub.3 generates a temporary loss of pre- that can reform catalyst activity, which can lead generate NH.sub.3. to larger hydrocarbons escaping into the reformer. In addition, if NH.sub.3 escapes and it reaches the “Medium Temperature Shift (MTS)” catalyst, it will cause permanent deactivation. NH.sub.3 or amines that decompose to NH.sub.3 can be used when it is decomposed before being fed to the pre- reform reactor, but this entails the need for additional equipment and consequently additional costs to the process. Organic acids Formic acid (CH.sub.2OH) can be used because it has a high decomposition rate for H.sub.2 and a low risk of coke formation. Higher molecular weight acids, such as acetic acid (CH.sub.3COOH), should not be used due to the tendency to form compounds having a high potential for coke deposition on the pre-reform catalyst. Ketones Ketones, such as acetone (CH.sub.3—CO—CH.sub.3), should not be used due to the tendency to form compounds having a high potential for coke deposition on the pre-reform catalyst. Aldehydes Formaldehyde (COH.sub.2) can be used. Higher molecular weight aldehydes should not be used due to the high rate of formation of olefins or other compounds having a high potential for deposition of coke on the pre-reform catalyst.

Example 4

[0048] This example illustrates the effects on the outlet temperature and the effluent composition of the pre-reform reactor, in the presence of hydrogen or in the absence of hydrogen with methanol injection, for a typical operating condition of an industrial unit. The simulations were performed using the PRO-II (AVEVA) program, modeling the pre-reform reactor as an adiabatic “Gibbs” reactor.

[0049] The results are presented in Table 4 and show that: a) The lack of recycle H.sub.2, in addition to causing the deactivation of the catalyst, due to the oxidation mechanisms of the metallic nickel active phase and the increase in the coke deposition rate, causes the temperature to drop along the pre-reform reactor (comparison between conditions 1 and 2). The drop in temperature, in turn, brings the additional risks of leakage of hydrocarbons with molecular weight above methane, which can lead to coking of the primary reform catalyst that follows the pre-reform one.

TABLE-US-00004 TABLE 4 Effect on the composition and outlet temperature of the pre-reform reactor effluent when there is no recycle H.sub.2 or methanol feed. Condition 1 2 3 4 5 6 Inlet 490 490 490 490 490 490 temperature (° C.) H.sub.2/natural gas 0.09 0 0 0 0 0 (Nm.sup.3/kg) Steam/carbon 2.3 2.3 2.3 2.3 2.3 2.3 (mol/mol) Steam/methanol — — 103 80 40 23.4 (mol/mol) Outlet 444.2 433.7 440.7 442.7 451.3 462.44 temperature (° C.) Effluent composition (% molar) H.sub.2 20.16 17.73 18.43 18.65 19.53 20.51 N.sub.2 0.54 0.55 0.54 0.54 0.53 0.51 CO 0.00 0.00 0.00 0.00 0.26 0.26 CO.sub.2 6.81 7.48 8.13 8.11 8.71 9.49 Methane 72.48 74.24 72.90 72.70 71.24 69.23 Note: Reactor inlet pressure 27 bar (2.7 MPa); pressure drop of 1.4 kgf/cm.sup.2 .Math. m (137.29 kPa .Math. m) composition (mol %) of: N.sub.2 = 0.69; CO.sub.2 = 1.33; methane = 89.91; ethane = 5.53; propane = 1.67; n-butane = 0.65 and n-pentane = 0.30.

[0050] Another risk stems from the fact that some commercial pre-reform catalysts contain magnesium oxide in their formulation, a phase that can hydrate to magnesium hydroxide with a reduction in temperature, leading to events of increase of load loss in the reactor; b) In the absence of recycle hydrogen, the methanol flow rate can be selected in order to avoid sudden changes in the reactor outlet temperature. A very high flow rate of methanol is not desirable, due to issues of cost, safety and storage logistics, but also because it causes more accentuated changes in the composition and temperature of the pre-reform reactor, which causes disturbances in the process (comparison between conditions 1 to 6).

[0051] Alternatively, a higher flow rate of methanol can be used immediately after the drop in the flow rate of recycle H.sub.2 so that there is no discontinuity of the presence of a reducing agent in the feed of the pre-reform reactor and, next, a reduction in methanol flow rate in order to alter the temperatures as little as possible throughout the reactor.

Example 5

[0052] This example, according to the present invention, uses the injection of methanol when the recycle hydrogen fails in an industrial hydrogen production unit by steam reforming. The unit has a nominal capacity of 3,000,000 Nm.sup.3/d and is configured with a pre-treatment section containing CoMo/alumina-type catalysts and zinc oxide-type absorbents. The purified natural gas load is mixed with process steam and recycle hydrogen and fed to the pre-reform reactor. The effluent from the pre-reform reactor feeds the primary reform section and then the “Medium Temperature Shift (MTS)” section. The recycle hydrogen is provided by compressors and, due to maintenance issues, these devices shut down and the consequent failure in the hydrogen supply occurred.

[0053] FIG. 1 illustrates the H.sub.2/natural gas ratio and the injection of methanol into the reactor, in a steam/methanol ratio between 150 to 100 mol/mol, during the failure of the recycle H.sub.2 feed, according to the present invention. The injection of methanol made it possible to maintain the unit in operation, producing hydrogen during the entire period, estimated at around 12 hours, of compressor maintenance.

[0054] FIG. 2 shows the impact on reactor temperatures. After the return of hydrogen in the reactor feed, the temperatures and the effluent composition of the reactor returned to the previous values, indicating that there was no significant deactivation of the inventory.

[0055] It should be noted that, although the present invention has been described in relation to the attached drawings, it may undergo modifications and adaptations by technicians skilled on the subject, depending on the specific situation, but provided that it is within the inventive scope as defined herein.