CS246521B1 - Removing method of impurities from industry gases by adsorption - Google Patents

Abstract

The present invention relates to a method for removing impurities from industrial gases by adsorption on adsorbents type alumogel and / or silica gel and / or molecular sieves and / or getters of the type zinc oxide, cuprous oxide and copper and the like in which the purified industrial gas it passes gradually during cleaning two adsorbents and / or getters differing with physical or chemical properties, placed in layers in a row adsorption space or in succession reactors.

Description

The present invention relates to a process for the removal of impurities from industrial gases by adsorption on adsorbents of the alumogel and / or silica gel and / or molecular sieve and / or zinc oxide, copper (I) oxide and copper and the like type. adsorbents and / or getters, differing in physical or chemical properties, placed in successive layers in a single adsorption space or in downstream reactors.

The present invention relates to a process for removing impurities from industrial gases on zone-packed adsorbers with various adsorbents, which solves the increase in adsorber efficiency or the long-term operational utilization of already passed adsorber cartridges.

Currently, conventional adsorbents of the silica gel type, alumogel type and molecular sieves, mainly type 3 A (K-formaj, 4 A (Na-form), 5 A (CA-form), are used for large-scale purification of gases, especially olefins on petrochemical units. 13 and 13 X (Na-form, Ca-form) These molecular sieves, in addition to their high adsorption properties, also exhibit a filtering molecular sieve effect which allows gradual separation of individual impurities according to the effective cross-section of the molecules.

At present, the adsorber is filled with only one type of adsorbent, which is selected as optimal for removal of the respective impurity, or the entire spectrum of impurities.

For drying of gases with high relative humidity, adsorbents of sllikagel or alumogel type are used, which, when fully utilized in drying gases with relative humidity close to one, operate in the area of capillary condensation. Total sorption capacities are between about 0.35 to 0.65 cm ^{3 of} H ² O / g adsorbent. The advantage of this use of adsorbents of the silica gel and alumogel type is the high sorption capacity due to the capillary condensation of water, the disadvantage is the wide diffusion zone due to slow equilibrium and relatively high evaporation.

For drying gases at low and medium relative pressures, molecular sieves of type 3 A (K-form), 4 A (Na-form), 5 A (Ca-form) and in many cases 13 X (Na-form, Ca) are used. (form), where the 3 A molecular sieve has been widely used for its selective adsorption. Type A molecular sieves have a total sorption capacity of about 0.21 centimeters cubic H2O / g adsorbate. Their advantage lies in a much higher adsorption efficiency at medium and low relative pressures than in alumogel and especially silica gel. A disadvantage of these types of adsorbents is the slow diffusion of water at extremely low humidity, in the area of gas drying below ppm.

Alumogel with a very low sorption capacity, usually a maximum of 3 to 5%, can be used for deep drying of gases. This low sorption capacity is generally considered to be a disadvantage, but its advantage is a higher rate of water adsorption under conditions where the partial water pressure is less than about 10 Pa.

Catalytic units, such as carbon monoxide (CO) and carbon dioxide (CO2) methanation, oxygen removal to form H2O, etc., are used to remove other undesirable, especially trace impurities, which manifest themselves primarily as catalytic poisons on the polymerization units of petrochemical production. the reaction product has to be removed on the downstream type A molecular sieves. Another group includes zinc oxide ZnOs for capturing sulfur traces, copper Cu - CuO2 copper for removal of oxygen traces and oxidation of carbon monoxide to carbon dioxide. H2O water and carbon dioxide

CO2 must be captured on molecular sieves.

The advantage of conventional adsorbents of the silica gel type and in particular of alumogel lies in the relatively high sorption capacity when drying gases with a relative adsorbate pressure close to one; however, this high sorption capacity cannot be used for deep post-treatment and the adsorber packings filled with alumogel must be over-dimensioned.

An advantage of the molecular sieve type, and consists in a strong shortening of the diffusion zone, the disadvantage is the reduced overall sorption capacity of about 50% compared alumogelu sílí- _t or a kieselguhr. Long-term operation of the molecular sieve partially changes the diffusion coefficients due to the deposition of polymeric substances or due to crystallographic changes, which give rise to defects, such as a change in the intensity of the X-ray diffraction lines during diffraction. The adsorption isotherm is almost identical to the fresh sample, but diffusion parameters change. These facts are demonstrated in Figure 1, where A is the equilibrium CO2 adsorption isotherm on fresh and used 5 A molecular sieves for petrochemical units: A - 1 fresh unused 5 A molecular sieve, A - 2 5 A molecular sieve after two years of operation in the petrochemical unit, row

A-3 reactivated 5 A molecular sieve at 773 K for 6 hours.

B is the kinetic adsorption characteristic of CO2 on a fresh, used and reactivated 5 A molecular sieve. Desorption pressure approx. 1 mPa after 3 to 5 minutes: Β — 1 fresh unused 5 A molecular sieve, B — 2 5 A molecular sieve after two years of operation in petrochemical units, B — 3–1 reactivated molecular sieve at 773 K and 2 h,

B-3-2 reactivated 5 A molecular sieve at 773 K and 4 h, B-3-3 reactivated 5 A molecular sieve at 773 K and 6 h.

η is the relative concentration of adsorbate defined as the ratio of the concentration at the point z / 1 (relative length of adsorber) to the concentration of the input adsorbate at the time constant input.

In the current mode of operation, where the adsorber is filled with only one type of adsorbent or getter, after some time, usually guaranteed by the manufacturer based on monitoring the physicochemical properties of the adsorbent, adsorption efficiency decreases and the entire adsorber charge needs to be replaced with a new adsorbent or getter. , which is very expensive.

This drawback removes a new way of removing impurities from industrial gases5

24S52IN, for example ethylene, in particular gas purification from trace impurities in the concentration range below ppm, for example H2S and lower mercaptans, carbon dioxide and the like, by adsorption on adsorbents of alumogel type and / or silica gel and / or molecular sieve and / or getters zinc oxide, copper oxide, copper and the like. according to the invention, characterized in that the purified industrial gas passes through at least two adsorbents and / or getters successively with different adsorption characteristics, equilibrium or kinetic, arranged in layers in a single adsorption space or in downstream reactors. In particular, the process according to the invention is carried out in such a way that 50 to 67% by volume of adsorbent in the inlet part of the adsorption is an alumogel or silica gel capillary type adsorbent and the remaining 50 to 33% by volume of adsorbent in the outlet of the process by molecular sieve A, preferably sieve A 3, wherein the relative inlet adsorbate pressure, defined as the ratio of adsorbate concentration to adsorbate vapor pressure at the adsorption temperature, is in the range of 50 to 100%. For gas drying, an embodiment of the process is suitable such that 50 to 67% by volume of adsorbent in the upstream portion of adsorption is used or regenerated alumogel, the remaining 50 to 33% by volume of adsorbent in the upstream portion of type A 3 molecular sieve. The volume is fresh alumogel. For cleaning gas from trace impurities in the region below ppm, for example H2S and lower mercaptans, carbon dioxide and the like. the adsorbent or getter used with altered diffusion coefficients or elution times is 50 to 67% by volume at the sorption inlet, the remaining 50 to 33% by volume is fresh sorbent of the same type, or more effective for the impurity of interest.

The proposed arrangement according to the invention, i.e. zone loading of adsorber with various adsorbents and molecular sieves, retains all the advantages of the simultaneous arrangement of filling adsorber with one type of adsorbent, but at the same time solves its basic disadvantage manifested mainly after prolonged deployment. it is necessary to compensate by higher frequency of regeneration. The basic approach of the proposed layered adsorber arrangement is to minimize the diffusion zone by using either an adsorbent with a high sorption capacity or an adsorbent already used on the inlet layer, and using an adsorbent with higher adsorption rates or a longer elution time at the outlet zone. of different type, or fresh adsorbent, which in turn shortens the diffusion zone and permits intensification of the device.

This will result in economic and especially technical operations on large-scale purification processes in higher purity of exhaust gases and in prolongation of working cycles between individual regenerations, resulting in secondary energy savings.

For clarity, the process according to the invention is illustrated in the accompanying drawings, in which Fig. 1 shows the static and kinetic data of adsorption on a 5 A (Ca-form) molecular network. Fig. 2 shows the relative course of adsorption defined as adsorbed amount of water vapor adsorber sector divided by maximum water vapor adsorption on alumogel at relative pressure X = 1 (partial pressure fractured by vapor pressure as a function of the relative length of adsorber z, defined as the ratio of the inlet distance to the total fill height). flow adsorber and Fig. 4 shows experimental CO2 adsorption isotherms at 298 K.

This method can be used, for example, for drying gases, especially after wet scrubbing, where the adsorber inlet is filled with 50 to 67% of the used or reactivated alumogel, the other part, i.e. (50 to 67) to (85 to 100%) filled with molecular sieves. 3 A, where pure alumogel can be used at the output of about 15%, which results in a shift of the elution time towards higher values, which is demonstrated in Figure 2, which represents the relative dynamic characteristics of H2O at a relative pressure of X = 1 alumogel A, MS 3 AB and 50% alumogel at the inlet and MS 3 A at the outlet (50%) for different relative times and differential flow rate to 35 ml / min, adsorber cross-section 1.53 cm ² .

In Fig. 2A, this pattern is demonstrated for alumogel, where the relative value of adsorption is 1.0, while for the 3 A molecular sieve (K-formaj - Fig. 2 B, it reaches a maximum value of 0.47 conditioned by the 3 A molecular sieve adsorption capacity ratio). (K-form) 0.21 cm ³ H ² O / g and alumogel 0.45 cm ³ H ² O / g. By comparing the adsorption gradient for alumogel and 3 A (K-form) molecular sieve (Figs. 2A, 2Bj), The adsorption capacity of the alumogel is higher than that of the 3 A (K-form) molecular sieve, the 3 A (K-form) molecular sieve has greater saturation and gas scavenging efficiency than that of the alumogel, which is shown in Figure 2C, where the first half of the adsorber is filled with alumogel and the second half with a 3 A molecular sieve (K-form), which results in a prolonged breakdown time of water vapor at low concentrations of the order of tens to one ppm water vapor. to intensify the adsorber compared to the state where it was only filled with high-capacity adsorbent alumogel or highly efficient for saturation - with a 3 A molecular sieve (K-formaj).

A second possibility of using this method is to remove traces of carbon dioxide and other impurities from olefins. The first part of the ad246521 sorber with a volume of 50 to 67% is filled with the adsorbent used, namely a molecular sieve whose sorption capacity is the same as that of a fresh molecular sieve but shows somewhat shorter elution times than the new adsorbent. a new adsorbent, also a molecular sieve, which guarantees reliable operation of the device for the next operating period. This arrangement permits further utilization of the spent adsorbent provided its physical properties exhibit the desired values for twice the time without the need to reactivate the sieve. This possibility of using the invention is illustrated in Fig. 3, which shows the adsorption characteristics of CO 2 on the MS 5 A (Ca-form) charge, where η denotes the relative concentration defined as the CO2 concentration at the z / 1 point of the adsorption column. enter: A - unused charge, B - charge after two years of operation in petrochemical unit, C - charge composed at MS 5 output (50 ° / o) unused and charge composed of MS at output (50 ° / o) 5 A of the used, for different relative times and differential flow rate to 35 ml / min, adsorber cross-section 1.53 centimeters, adsorbate inlet pressure 3.03 kPa.

Fig. 3 shows the relative course of adsorption in a flow adsorber, where η is defined as the ratio of CO2 adsorption (at a constant inlet CO2 concentration of 10 ppmj at a distance from the beginning (z is defined as the distance from the beginning and height of the adsorber) to equilibrium adsorption at 10 ppm CO2 Despite the fact that the equilibrium adsorption data between the fresh and used 5 A molecular sieves (Ca-form) does not differ significantly, as shown in Fig. 4 (indicating experimental CO2 adsorption isotherms at 298 K on fresh molecular sieves 5). A (Ca-form) and the molecular network after the guarantee deployment of type 5 A (Ca-form), the kinetic data shown in Fig. 1B indicate an increase in desorption rate for the used 5 A (Ca-form j) molecular sieves, resulting in shortening CO2 elution times, as evidenced by the results shown in Figure 3 A for fresh and unused molecular sieves 5 A (Ca-form) and 3 B Fig. 3C shows the filling method according to the invention, wherein the first half of the filling is filled with the used 5 A molecular sieve, where this adsorbent is completely equal to the new sieve as it works at equilibrium In both conditions, the adsorption capacity is practically the same and the other half, ie the outlet part is filled with fresh 5 A molecular sieve, which eliminates the impaired kinetic parameters of adsorption of the used molecular sieves with the guaranteed time period.

A third possibility of using the invention is to purify the gas from trace impurities by getter, for example hydrogen sulphide H2S and lower mercaptans, where the first part of the reactor is filled with 50 to 75% spent getter, the impurity content being minimal and physical and sorption properties (e.g. ) did not decrease significantly by sintering the microcrystals in the process of long-term detoxification, the second part of the reactor is supplemented with a new, not yet used getter. In many cases, the efficiency of the getter can be increased by a small temperature increase of 5 to 10 K.

The process according to the invention is further illustrated by 2 examples.

Example 1

For the production of low-pressure polyethylene for the purification of C2H4 ethylene, the adsorption process of the removal of CO2 on the molecular sieve AW 09350 (5 A - Ca-form) from the C2H4 ethylene gas is carried out.

The operating cycle of the above mentioned process with molecular sieving takes place at approximately 4 to 5 daily intervals, alternating operation - regeneration. After utilizing the declared lifetime of the molecular sieve AW 09350 (5 A - Ca-form j, which is 2 years of such operation), the problem arises whether to replace the molecular sieve with a new or used molecular sieve. Polymerization, which is technologically directly dependent on the quality of carbon dioxide purification from C2H4 ethylene, is a decision to continue to use a molecular sieve only on the basis of the results of chemical-physical analyzes of a particular molecular sieve.

The C2H4 ethylene is purified from a number of undesirable compounds, namely carbon dioxide that enters the system and is secondarily formed by the oxidation of CO by adsorption on a 5 A molecular sieve.

The adsorbent efficiency can be assessed from the adsorption isotherms, where Langmuir isotherm G = G ( _S j _{r +} ^ _p G adsorbate mass,

G (Jj) sorption capacity per unit of adsorbent mass, p partial adsorbate pressure, and constant.

By comparing the fresh and used adsorbent, especially the constants G (?), The degree of molecular sieve deactivation can be ascertained.

If the values of the constants G (£) a and are almost identical, it can be concluded that the molecular sieve samples are not toxic.

Four randomly sampled AW 09350 molecular sieve samples were analyzed (5 A - - Ca form was compared with the new molecular sieve (MS in operational use 246521 for 1 year). It can be stated (see Fig. 1, Table 1) that adsorption is the same, taking into account the experimental errors and homogeneity of the samples and the molecular sieve used is completely equivalent to the fresh molecular sieve, whereby the carbon content of C is equal and lower

Table 1. Langmuir isotherm constants greater than 0.45 wt. (see Table 1). Due to the limited mechanical strength, it is necessary to separate from the molecular sieve used a part which still has sufficient strength. The sorbent used is screened to fill 60% of the volume at the inlet to the adsorption.

H ₂ O

G (2) a

new pattern 169.38 0.5664 used vz. 1 156.94 0.5547 used vz. 2 164.64 0.4620 used vz. 3 171.56 0.5335 used vz. 4 180.96 0.5155

CO2 C

G (2) and .0 / 0

145.05 0.6099 0.45 142.82 0.6274 0.17 140.35 0.7718 0.21 162.44 0.5806 0.37 171.38 0.6223 0.42

In this way, only 40% of the fresh molecular sieve is filled into the adsorber while maintaining the desired process efficiency.

Example 2

Purification of C2H4 ethylene from sulfur compounds

The production of low pressure polyethylene in the purification of C2H4 ethylene is carried out by the removal of sulfur compounds from the C2H4 gas. The reaction is carried out on a zinc oxide getter according to the simplified scheme:

Noc: 2 ° C

ZnO + H2S ----- ► ZnS + H2O

The guaranteed lifetime of the getter is 2 years. The getter cannot be regenerated on the plant, so it is destined for disposal after its useful life.

The perfect function of this process is necessary for the function of the next stage of C2H4 hydrogenation, which loses its reliability when sulfur compounds are present.

The decision to further use the getter is only feasible based on the results of chemical-physical analyzes of the particular getter.

Ethylene is deprived of sulfur compounds (H2S, SO2, etc.) on zinc oxide, where in the first phase S ² is chemisorbed - to form —SH and —OH groups and in the second phase to form ZnS for subsequent diffusion of S ² - ions into of the zinc oxide bulk phase, thereby substantially self-regenerating the system.

The function of the system essentially corresponds to a getter working on the chemisorption principle and in the subsequent phase to diffuse the surface S ² ions into the bulk phase, where the equilibrium between the concentration of surface ions S ² and the ions S ^{2 is established} in the whole volume phase.

Given the typical function of an adsorbent system (with a chemisorption and then diffusion mechanism) based on the knowledge of trace element deposition in catalyst grains, where they concentrate in catalyst surface layers and especially at reactor inlets (chemisorption poisoning theory), deposition of S ² - ie the adsorbent toxic mainly at the inlet to the reactor (tower) and the width of the toxic zone is primarily a function of the concentration of sulfur compounds in the purified medium.

Given the constant situation, it can be assumed that the ZnO getter's toxicity is zone-restricted.

After taking the samples of the used getter, their physico-chemical analysis is carried out, in particular the determination of ZnO, ZnS in mass, and X-ray evaluation. Based on these analyzes, 55% of the inlet volume was filled with the getter used, the remaining 45% of the volume was filled with the new getter while maintaining the desired effect.

Claims (4)

SUBJECT Process for removing impurities from industrial gases by adsorption, for example ethylene, in particular purifying gases from trace impurities in the concentration range below ppm, for example H 2 S and lower mercaptans, carbon dioxide and the like, on alumogel and / or silica gel and / or molecular sieve adsorbents, and / or zinc oxide, cuprous oxide or the like, characterized in that the purified industrial gas passes through at least two adsorbents and / or getters differing in adsorption characteristics, equilibrium or kinetic, arranged in layers one after the other in the adsorption phase space or in downstream reactors. 2. A process according to claim 1, wherein 50 to 67% of the adsorbent volume in the adsorption inlet portion is an alumo246521 gel or silica gel adsorbent operating in the capillary condensation region and the remaining 50 to 33% of adsorbent volume in the outlet of molecular sieve A; preferably A4, wherein the relative inlet adsorbate pressure, defined as the ratio of adsorbate concentration to adsorbate vapor at the adsorption temperature, is in the range of 50 to 100%. 3. A method according to claim 1 for drying gas, wherein 50 to 67% of the adsorbent volume in the adsorption inlet is used or regenerated alumogel, IX 50 to 33% by volume of the adsorbent in the downstream part a molecular sieve type 3A, where appropriate, the output of about 15 ^l0 / volume includes fresh alumogel. 4. The process of claim 1 wherein 50 to 67% by volume at the inlet of the sorption is spent spent adsorbent or getter with reduced diffusion coefficients or elution times, the remaining 50 to 33% by volume is fresh sorbent of the same type or more effective for the impurity being monitored.