Title of Invention

A PROCESS FOR THE PRODUCING OF AMMONIA SYNTHEIIS GAS FROM A FEEDSTOCK

Abstract

This invention relates to a process for the production of ammonia synthesis gas from a feedstock containing dimethyl ether by steam reforming dimethyl ether in presence of a reforming catalyst to a product gas, wherein necessary heat for the endothermic steam reforming reactions is supplied through oxidation of part of the hydrogen contained in the steam reformed feedstock process in heat conducting relationship with the steam reforming reactios.

Full Text

A process for The present invention relates to/the production of ammonia synthesis gas from a feedstock containing dimethyl-ether (DME) and/or methanol (MeOH) by adiabatic catalytic steam reforming in presence of an oxygen containing atmosphere. It is known from EP-A-0 761 942 and EP-A-0 754 649 to reform DME to hydrogen and carbon monoxide rich gases in presence of solid acid catalysts. The reactions proceeding during steam reforming of DME are: The above reactions are endothermic and require heat for reasonable reactions rates. By the process described in the above EP-A-0 761 942 heat is supplied by hot exhaust gas from a gas turbine. It is further known from WO 98/18572 to catalytically hydrolyse DME with steam in heat conducting relationship with the exothermic water-gas shift reaction. It has now been found that DME may adiabatically be steam reformed, when carrying out the reaction in heat conducting relationship with partial oxidation reaction of part of hydrogen formed during steam reforming of DME/MeOH. Based on the above finding, the present invention provides a process for the production of hydrogen rich gas from a feedstock containing dimethyl ether and/or methanol by steam reforming dimethyl ether and/or methanol in presence of a reforming catalyst to a product gas being rich in hydrogen, wherein necessary heat for the endothermic steam reforming reactions is supplied through oxidation of part of hydrogen in the steam reformed feedstock in heat con¬ducting relationship with the steam reforming reactions. The above steam reforming reactions and partial oxidation of hydrogen are carried out in one or more catalyst zones arranged operated adiabatically. When employing a single catalyst zone, it is preferred to employ a catalyst with combined activity for the aforementioned DME and MeOH steam reforming reactions and the oxidation of hydrogen. Useful catalysts of the above type may be solid acids including zeolitic materials, alumina silicates, silica alumina, alumina and mixtures thereof, combined with a methanol decomposition catalyst, e.g. Cu, or Cu-Zn-alumina in a weight ratio of preferably between 1:5 and 5:1, coated with silica and shell impregnated with one or more noble metals e.g. platinum and/or palladium according to conventional catalyst manufacturing procedure. Such type of catalyst with combined steam"reforming and oxidation activity will preferably be used in a fluid bed reactor, wherein a pro¬cess stream of DME and/or methanol, steam and oxygen con¬taining atmosphere will be introduced at the bottom of the reactor. Alternatively, the inventive process may be performed in a quench type adiabatic reformer or adiabatic heat exchange reformer with a number of fixed bed catalyst layers of a DME and/or methanol reforming catalyst as described above and intermediate beds of an oxidation catalyst. When employing a quench type reformer, preheated process gas of DME and/or methanol and steam is introduced in a first bed with the reforming catalyst and partially con¬verted to a gas containing hydrogen. A part of the hydrogen is then oxidized with oxygen containing atmosphere being introduced into the partial reformed process gas from the top catalyst bed and oxidized in a bed of oxidation cata¬lyst arranged between the top catalyst bed and a subsequent fixed bed of reforming catalyst. Heat evolving from the exothermic oxidation reaction proceeding in the oxidation catalyst bed is, thereby, transferred to the reacting process gas in an amount sufficient to maintain the endo-thermic reforming reactions in subsequent reforming cata¬lyst bed. The oxygen containing atmosphere may be added to the pro¬cess gas in several steps, whereby each step is performed as described above. The oxygen containing atmosphere for use in the inventive process, may be any atmosphere containing oxygen in an amount sufficient to the oxidation of the required amount of hydrogen in order to provide the necessary heat for the endothermic reforming reactions at a reasonable reaction rate. The oxygen containing atmosphere may be pure oxygen, oxy¬gen-enriched air, or oxygen depleted air. An advantage by using air or oxygen depleted air in the above process will be that valuable ammonia synthesis gas is produced in the process. As further an advantage of the above process, carbon dioxide recovered from the effluent stream of the process may be utilized in the preparation of urea by to the known urea process schemes. Accordingly, the present invention provides a process for the production of ammonia synthesis gas from a feedstock comprising dimethyl ether comprising feeding the feedstock to a reaction zone and subjecting the same to endothermic steam reformation in presence of a reforming catalyst to produce a hydrogen rich gas, feeding at least one stream of oxygen and nitrogen containing atmosphere to the reaction zone for producing ammonia synthesis gas and performing exothermic selective oxidation of part of the hydrogen produced by the steam reforming process to provide heat for the endothermic steam reforming reaction, recovering from the reaction zone the resulting ammonia synthesis gas, said reforming catalyst consisting of a mixture of solid acid such as herein described and a known methanol reforming catalyst coated with siUca and shell impregnated with one or more noble metals. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The above features and advantages of the invention will be further apparent from the following description, disclosing in detail specific embodiments of the invention by reference to the drawings, in which Fig. 1 shows a simplified flow sheet of a process for the preparation of ammonia synthesis gas from DME feedstock steam by reforming in an adiabatic DME reformer according to a specific embodiment of the invention; and Fig. 2 a similar process carried out in an adiabatic heat exchange DME reformer according to a further embodiment of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the reformer shown in Fig. 1, feedgas of DME and steam is introduced into a first bed 5 of DME reforming catalyst. The feedgas is preheated to about 270°C, optionally by heat supplied from the reformed feedgas 5 in heat exchanger 6. By passage through bed 5, the feedgas is partially reformed to a hydrogen containing process gas. The process gas is mixed with a first stream of air 2 in a mixer and a part of the hydrogen content in the process gas oxidized in oxidation catalyst bed 9. Heat evolving during the oxidation reaction is, thereby, transferred to the reacting process gas, which is further reformed in DME reforming catalyst bed 10. Further heat is then supplied to the reacting process gas through oxidation of a part of hydrogen in oxidation cata¬lyst bed 11 and 13 with air supplied through line 3 and 4, respectively. The process gas is then further reformed in catalyst bed 12 and 14 to final product gas 5. In the heat exchange DME reformer shown in Fig. 2 a DME and steam containing feed stream 1 is similar to the above process reformed to hydrogen containing process gas with heat supplied by oxidation of part of the hydrogen content in the process gas. In contrast to the above process, shown in Fig. 1, the feed gas is in the heat exchange reformer of Fig. 2 reformed in one step by passage through catalyst bed 4 being in indirect heat exchange with oxidation reactions of part of the hydrogen contained in the reacted process gas in oxidation catalyst bed 5. Similar to the above process shown in Fig. 1 the feed gas may be preheated with heat contained in product gas 3 by heat exchange in heat exchanger 6. The actual gas composition and process parameters used in the above described processes are summarized in the Table below, in which position numbers correspond to the refer¬ence numbers in the figures. Table 1 Pig.l Position 1 2 3 4 5 Pressure 34 33 33 33 31.5 [ato] Temperature 350 166 166 166 458 [°C] Flow rate 7707 894 669 808 13979 [kmol/h] Composition O2 20.85 20.85 20.85 H2 39.58 H2O 85.71 0.56 0.56 0.56 31.34 N2 77.63 77.63 77.63 13.16 CO 0.52 CO2 0.03 0.03 0.03 15.21 Ar 0.94 0.94 0.94 0.16 MeOH 0.03 DME 14 .29 Fig. 2 Position 1 2 3 Pressure 39 3 9 37.5 [ato] Temperature 269 173 350 [°C] Flow rate 11047 2488 17615 [kmol/h] Composition O2 20.86 H2 32.78 H2O 89.58 0.4 9 43.05 N2 77.69 10.97 CO 0.49 CO2 0.03 12.56 Ar 0.94 0.13 MeOH 0.01 DME 10.42 Although the present invention has been described in rela¬tion to particular embodiments thereof, many other vari¬ations and modifications and other uses will become aparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims. WE CLAIM; 1. A process for the production of ammonia synthesis gas from a feedstock comprising dimethyl ether comprising feeding the feedstock to a reaction zone and subjecting the same to endothermic steam reformation in presence of a reforming catalyst to produce a hydrogen rich gas, feeding at least one stream of oxygen and nitrogen containing atmosphere to the reaction zone for producing ammonia synthesis gas and performing exothermic selective oxidation of part of the hydrogen produced by the steam reforming process to provide heat for the endothermic steam reforming reaction, recovering from the reaction zone the resulting ammonia synthesis gas, said reforming catalyst consisting of a mixture of solid acid such as herein described and a known methanol reforming catalyst coated with silica and shell impregnated with one or more noble metals. 2. The process as claimed in claim 1, wherein the oxygen containing atmosphere consists of air, oxygen depleted or enriched air. 3. A process for synthesizing ammonia wherein the ammonia synthesis gas produced by the process as claimed in claims 1 and 2 are converted into ammonia in a known manner. 4. A process for the production of ammonia synthesis gas from a feedstock substantially as herein described with reference to the accompanying drawings.

Documents:

0071-mas-1999 abstract duplicate.pdf

0071-mas-1999 abstract.pdf

0071-mas-1999 claims duplicate.pdf

0071-mas-1999 claims.pdf

0071-mas-1999 correspondence-others.pdf

0071-mas-1999 correspondence-po.pdf

0071-mas-1999 description (complete) duplicate.pdf

0071-mas-1999 description (complete).pdf

0071-mas-1999 drawings duplicate.pdf

0071-mas-1999 drawings.pdf

0071-mas-1999 form-19.pdf

0071-mas-1999 form-2.pdf

0071-mas-1999 form-26.pdf

0071-mas-1999 form-4.pdf

0071-mas-1999 form-6.pdf

0071-mas-1999 others.pdf

0071-mas-1999 pctsearch report.pdf

0071-mas-1999 petition.pdf