Gas separation: processes – Solid sorption – Inorganic gas or liquid particle sorbed
Reexamination Certificate
2000-08-10
2003-06-17
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Solid sorption
Inorganic gas or liquid particle sorbed
C095S141000, C095S148000, C095S902000
Reexamination Certificate
active
06579347
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method for removing dimethyl sulfide (DMS) and tertiary butyl mercaptan (TBM) as the sulfur compounds present in city gas.
2. Related Art of the Invention
The sulfur compounds must be removed from the city gas before it is purged into the air, while a city gas system is under construction or repair. The city gas as the fuel for fuel cells must be desulfurized, to prevent the deactivation of steam reforming catalysts, such as those on Ru and Ni.
Activated carbon, either as it is or modified by some reagent, has been mainly used for removal of the sulfur compounds from the fuel gas.
Desulfurization under consideration for the city gas as the fuel for fuel cells involves hydrodesulfurization of the sulfur compounds into hydrogen sulfide, which is then removed by zinc oxide.
Removal of the sulfur compounds in air for deodorization is generally effected by oxidative decomposition of mercaptan compounds at room temperature in the presence of an oxide of transition metal, e.g., copper or manganese, or by adsorption of these compounds on activated carbon, either as it is or supported.
Each of the above conventional techniques has its own disadvantages.
Activated carbon is difficult to regenerate, because of its combustibility, and must be replaced when sufficiently deactivated. When modified by some reagent, it removes sulfur compounds by chemical reaction, which makes it difficult to regenerate, although showing excellent adsorption-related characteristics (the first problem).
A combination of hydrodesulfurization pretreatment and removal of H
2
S in the presence of zinc oxide for fuel cell fuels needs high temperature of 300 to 400° C. for the hydrodesulfurization process, which lowers overall efficiency of the power output by the cell. It is also necessary to replace deactivated zinc oxide (the second problem).
The deodorization in an oxidative atmosphere in the presence of an oxide of transition metal, e.g., copper or manganese, mercaptan compounds may be partially oxidized at room temperature into a disulfide, which will cause offensive odor, and is difficult to remove the sulfur compounds, e.g., sulfides, other than mercaptan compounds (the third problem).
SUMMARY OF THE INVENTION
In consideration of the above first and second problems involved in the conventional techniques for removing the sulfur compounds, it is an object of the present invention to provide a method for removing dimethyl sulfide (DMS) and/or tertiary butyl mercaptan (TBM) as the sulfur compounds present in city gas. It is another object of the present invention to provide a method for removing the sulfur compounds by the aid of the above adsorbent.
The present invention provides a method for removing dimethyl sulfide (DMS) and/or tertiary butyl mercaptan (TBM) as the sulfur compounds present in city gas by using the sulfur compounds adsorbent containing one of faujasite, &bgr;, L and MFI type zeolite, and also provides a method for removing the sulfur compounds, in which the above adsorbent is intermittently regenerated.
One aspect of the present invention is a method for removing dimethyl sulfide (DMS) and/or tertiary butyl mercaptan (TBM) as sulfur compounds present in city gas by using a sulfur compound adsorbent containing one of faujasite, &bgr;, L and MFI type zeolite.
Another aspect of the present invention is a method for removing sulfur compounds, wherein said zeolite comprises Si and another type of metal M in the framework, Si/M atomic ratio being 250 or less and M being selected from the group consisting of Al, Fe and Ga.
Still another aspect of the present invention is a method for removing sulfur compounds, wherein the cation in said zeolite is H
+
.
Yet another aspect of the present invention is a method for removing sulfur compounds, wherein said zeolite is treated for dealuminization.
Still yet another aspect of the present invention is a method for removing sulfur compounds, wherein said sulfur compound adsorbent contains an inorganic binder.
A further aspect of the present invention is a method for removing sulfur compounds, wherein said inorganic binder is silica.
A still another aspect of the present invention is a method for regenerating an adsorbent for sulfur compounds, containing one of faujasite, &bgr;, L and MFI type zeolite and an inorganic binder, wherein at least heating step is included for regenerating said adsorbent after said adsorbent is used for a process which removes dimethyl sulfide (DMS) and/or tertiary butyl mercaptan (TBM) as the sulfur compounds present in city gas.
Yet another aspect of the present invention is the method for regenerating an adsorbent for sulfur compounds, wherein a gas released from said adsorbent during said regeneration process is oxidized in the presence of an oxidation catalyst.
Yet another aspect of the present invention is a method for removing sulfur compounds, comprising a first step which passes city gas which contains dimethyl sulfide (DMS) and/or tertiary butyl mercaptan (TBM) as the sulfur compounds over a first adsorbent containing ultrastable Y type zeolite, and second step which passes the gas from the first step over a second adsorbent containing MFI or faujasite type zeolite having an alkaline or alkaline-earth metal in the cation site.
Yet another aspect of the present invention is a method for removing sulfur compounds, comprising:
a first step of passing a mercaptan-containing city gas over a first adsorbent containing zeolite with H
+
as the cation or dealuminized zeolite; and
a second step of passing the gas from the first adsorbent over a second adsorbent containing zeolite having an alkaline or alkaline-earth metal in the ion-exchanged site.
THE PREFERRED EMBODIMENTS OF THE INVENTION
City gas is intentionally incorporated with trace quantities of a sulfur compound as the odorant in order to give a warning of gas leak. The odorant type differs by city gas supplier. In Japan, tertiary butyl mercapatan (TBM), dimethyl sulfide (DMS) or tetrahydrothiophene is added to city gas to several ppm. Unlike natural gas or coke oven gas which contains various types of sulfur compounds, the city gas is intentionally incorporated with the sulfur compound of known structure at a known concentration. Therefore, the sulfur compound in the city gas can be removed by adsorption, when an adequate adsorbent is selected to efficiently adsorb the compound.
The present invention removes the sulfur compounds by the aid of an adsorbent which contains one of faujasite (X or Y type), &bgr;, L and MFI type zeolite. It is composed of inorganic materials, and can be regenerated under heating.
Tertiary butyl mercaptan and dimethyl sulfide are the typical odorants used for the city gas, the latter being more difficult to remove by adsorption and showing an earlier break-through. It is therefore important to increase amount of dimethyl sulfide adsorbed. Use of faujasite, &bgr;, L or MFI type zeolite can increase the adsorbed quantity from that adsorbed by other types of zeolite, such as A type.
The present invention needs no heating for adsorption, because adsorbed amount increases as temperature decreases, and is more advantageous over the method involving hydrodesulfurization, because of simplified equipment designs and saved energy.
The adsorbent of the present invention comprises Si and another type of metal M in the skeleton structure. Zeolite having an Si/M molar ratio of 250 or less shows excellent adsorption characteristics, which tend to improve as Si/M ratio decreases. It is known that zeolite of low Si/M molar ratio is generally high in acidity. The inventors of the present invention have investigated zeolite acidity by the temperature-programmed desorption method of ammonia (ammonia TPD), to find that zeolite of low Si/M molar ratio shows a larger quantity of ammonia desorbed, or higher in acidity, indicating that acidity of zeolite contributes to removal of a sulfur compound present in fuel gas. It is preferable that an element M that comprises, together
Hosaka Masato
Ono Yukiyoshi
Tachibana Yuko
Wakita Hidenobu
RatnerPrestia
Spitzer Robert H.
LandOfFree
Method for removing sulfur compound present in city gas does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for removing sulfur compound present in city gas, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for removing sulfur compound present in city gas will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3109312