Gas separation: processes – Solid sorption – Inorganic gas or liquid particle sorbed
Reexamination Certificate
2000-10-25
2002-07-30
Spitzer, Robert H. (Department: 1724)
Gas separation: processes
Solid sorption
Inorganic gas or liquid particle sorbed
C095S096000, C095S118000, C095S128000, C095S130000, C095S132000, C095S136000, C095S139000, C095S140000, C095S143000, C095S901000
Reexamination Certificate
active
06425939
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of the separation of gaseous mixtures by adsorption on a carbonated adsorbent, such as active carbon, with improved properties, in particular a PSA process to produce hydrogen.
BACKGROUND OF THE INVENTION
A PSA unit for the purification of hydrogen contains an adsorbent or a combination of adsorbents which must be capable of selectively retaining the impurities contained in the gas to be treated.
The most common impurities of the gases containing hydrogen are: N
2
, CO
2
, CH
4
, CO, C
2
H
4
, C
2
H
6
, C
3
H
8
, C
4
+, BTX (benzene-toluene-xylene) compounds, water vapor, mercaptans, H
2
S, SO
2
.
These compounds are eliminated from the hydrogen flow by an assembly of adsorbents disposed in series.
Conventionally, alumina or silica gel essentially retain the water vapor; activated carbon is used to retain the heavy hydrocarbons, the CO
2
and the water vapor; and zeolite is used to eliminate particularly the impurities N
2
, CO and CH
4
.
The proportion of the different adsorbents depends on the composition of the gas to be treated under pressure.
Thus, there are a great number of possible combinations of adsorbents, taking account of the exact nature of the adsorbents and their relative proportions.
The production of high purity hydrogen is of great interest in the industrial field, it being widely used in a number of synthesis processes such as hydrocracking, the production of methanol, the production of oxoalcohols and isomerization processes.
In the prior art, the PSA processes have been very effective for the separation of gaseous mixtures and particularly for the production of pure hydrogen or oxygen from gaseous mixtures contaminated by various impurities.
The PSA processes preferably use the selective adsorption of a given adsorbent for one or several of the contaminating substances in the gaseous mixture to be purified.
Consequently, the production of hydrogen by a PSA process (Pressure Swing Adsorption=Adsorption with Pressure Variation) has been widely studied.
However, most of the papers relating to this subject concern essentially the production cycles and the manner of conducting these cycles, so as to maximize the recovery and/or the purity of the hydrogen product, or else to reduce capital cost.
However, the choice of the adsorbent is delicate: it depends on the one hand on the nature of the mixture to be treated. As a general rule, the adsorbents are selected as a function of their ability to adsorb and desorb a particular compound.
Indeed, the PSA processes involve the use of pressure cycles.
In a first phase, the adsorbent bed ensures the separation of at least one constituent from the mixture by adsorption of this constituent on the bed of adsorbent.
In a second phase, the adsorbent is regenerated by lowering the pressure of the adsorbent beds operating in parallel.
U.S. Pat. No. 4,381,189 and French 2,330,433 illustrate particularly such an operation.
The elimination of the impurities contained in a flow of hydrogen takes place most of the time by means of at least two adsorbent beds disposed in series, namely conven- tionally an activated carbon bed and a zeolite bed.
In this connection can be cited WO-A-97/45363, which relates to a process for the purification of hydrogen base gaseous mixtures, polluted by various impurities, of which carbon monoxide and at least one other impurity selected from carbon dioxide and straight chain hydrocarbons, branched or cyclic, saturated or unsaturated, C
1-8
. The gas flow to be purified is placed in contact, in an adsorption zone, with a first adsorbent selective to carbon dioxide and C
1-8
hydrocarbons, and a second adsorption which is a zeolite of the faujasite type exchanged at least 80% with lithium and whose Si/Al ratio is less than 1.5, to eliminate at least carbon dioxide (CO
2
). According to this document, the improvement afforded by the process is due to the use of a particularly effective zeolite, namely zeolite X exchanged with lithium.
Moreover, U.S. Pat. No. 3,150,942 teaches the use of a zeolite containing sodium or sodium and calcium cations, to purify a hydrogen flow.
Analogously, U.S. Pat. No. 4,477,267 discloses a process for the purification of hydrogen using a zeolite X exchange 70 to 90% with calcium cations and containing moreover an inert binder.
U.S. Pat. No. 4,957,514 discloses a process for the purification of hydrogen using zeolite X exchanged with 60 to 80% barium cations.
Moreover, U.S. Pat. No. 5,489,327 relates to the purification of gaseous hydrogen by contact with a zirconium hydride alloy.
Finally, JP-A-860146024 discloses a PSA process to purify impure gases using a mordenite type zeolite exchanged with lithium, on the production side and a zeolite one on the supply side.
Furthermore, U.S. Pat. Nos. 3,702,525, 3,986,849, 4,077,779, 4,153,428, 4,696,680, 4,813,980, 4,963,339, 3,430,418, 5,096,470, 5,133,785, 5,234,472, 5,354,346, 5,294,247 and 5,505,764 disclose PSA cycles of operation to produce hydrogen.
Conversely, certain documents emphasize that the adsorbent or the adsorbents used in a PSA process to purify hydrogen have little or no importance.
Thus, the paper Pressure Swing Adsorption, 1994, VCH publishers, D. M. Ruthvens, S. Farooq, K. S. Knaebel, page 238, teaches that “as the selectivity for most of the impurities is high in comparison to that of hydrogen, any adsorbent whatever can be used” to purify hydrogen.
Analogously, according to U.S. Pat. No. 4,299,596, all the conventional adsorbents can be used to purify hydrogen, for example, activated carbon, silica gel, molecular sieves, such as zeolites, carbonated sieves.
Furthermore, U.S. Pat. No. 4,482,361 mentions the possibility of using no matter what suitable adsorbents, such as zeolitic molecular sieves, activated carbon, silica gels, activated alumina or the like.
Analogously, U.S. Pat. No. 4,834,780 teaches that adsorption can be carried out in all cases in which an adsorbent has been selected that is suitable for the separation process in question, for example, activated carbon, silica gel, alumina gel or molecular sieves.
It is thus apparent, in view of the prior art, that those skilled in the art conventionally consider that an improvement of the effectiveness of a PSA production for the production or purification of hydrogen can result only in an improvement of the production cycle or of the zeolitic material used, but that the influence of the adsorbent used is seldom of importance, which is to say that the adsorption has but little influence on the efficiency of the PSA process.
Starting with this, the problem which thus arises is to improve the PSA processes for the purification of hydrogen, which is to say to improve the efficiency of elimination of the impurities contained in a hydrogen flow to be purified.
The present invention seeks to solve this problem, which is to say that the process of the invention permits improving the conventional processes of the PSA type for separation of hydrogen or processes by adsorption with pressure variation.
SUMMARY OF THE INVENTION
The invention thus relates to a process for the purification of a gaseous hydrogen flow containing at least one gaseous impurity selected from the group consisting of carbon monoxide, water vapor, nitrogen, H
2
S, SO
2
, carbon dioxide, chlorine, lower C
1-3
alcohols, ammonia and linear hydrocarbons, branched or cyclic, saturated or unsaturated, C
1-8
, in which the gaseous flow of hydrogen to be purified is contacted with at least one carbonated porous adsorbent characterized by a limit volume of adsorption (W
0
) and by an energy parameter (E
0
) according to the Dubinin theory, wherein:
0.18 ml.g
−1
≦W
0
≦1.50 ml.g
−1
and
15 kJ.mole
−1
≦E
0
≦45 kJ.mole
−1
.
As the case may be, the process of the invention can comprise one or several of the following characteristics:
W
0
is comprised between 0.20 ml.g
−1
and 1.20 ml.g
−1
,
W
0
is greater than or equal to 0.25 ml.g
−1
,
W
0
is greater than or equal to 0.30
Moreau Serge
Polster Bernd
L′Air Liquide, Societe Anonyme a Directoire et Conseil de
Spitzer Robert H.
Young & Thompson
LandOfFree
Process for the production of hydrogen using a carbonated... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for the production of hydrogen using a carbonated..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for the production of hydrogen using a carbonated... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2902459