# US 11,998,872 B2 · Biogas upgrading apparatus and process

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- Number: US 11,998,872 B2
- Document ID: US11998872B2
- Status: Granted
- Kind: B2
- Application number: 17/498,890
- Filed: 2021-10-12
- Published: 2023-04-13
- Granted: 2024-06-04
- Earliest claimed: 2021-10-12
- Assignees: Air Products and Chemicals, Inc.
- Applicants: Air Products and Chemicals, Inc.
- Inventors: Donald E. Henry
- Web page: https://patentgrep.com/patent/US11998872B2

## CPC

- B01D 53/226: {in serial connexion}
- B01D 53/227: {in parallel connexion}
- B01D 53/228: {characterised by specific membranes}
- B01D 61/58: Multistep processes
- C10L 3/104: {Carbon dioxide}
- C12M 47/18: {Gas cleaning, e.g. scrubbers; Separation of different gases (separating dispersed particles from gases or vapours B01D45/00; separation of gases or vapours B01D53/00; gas washing apparatus for laboratory uses B01L5/04)}
- B01D 2256/245: Methane
- B01D 2257/104: Oxygen
- B01D 2257/504: Carbon dioxide
- B01D 2258/05: Biogas
- B01D 2311/06: Specific process operations in the permeate stream
- B01D 2311/08: Specific process operations in the concentrate stream
- B01D 2311/25: Recirculation, recycling or bypass, e.g. recirculation of concentrate into the feed
- B01D 2311/2512: to feed side
- B01D 2317/022: Reject series
- B01D 2317/025: Permeate series
- B01D 2317/06: Use of membrane modules of the same kind
- B01D 2317/08: Use of membrane modules of different kinds
- Y02C 20/40: of CO2
- Y02E 50/30: Fuel from waste, e.g. synthetic alcohol or diesel
- Y02P 20/59: Biological synthesis; Biological purification
- B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28)
- C10L: FUELS NOT OTHERWISE PROVIDED FOR; NATURAL GAS; SYNTHETIC NATURAL GAS OBTAINED BY PROCESSES NOT COVERED BY SUBCLASSES C10G OR C10K; LIQUIFIED PETROLEUM GAS; USE OF ADDITIVES TO FUELS OR FIRES; FIRE-LIGHTERS
- C12M: APPARATUS FOR ENZYMOLOGY OR MICROBIOLOGY; {APPARATUS FOR CULTURING MICROORGANISMS FOR PRODUCING BIOMASS, FOR GROWING CELLS OR FOR OBTAINING FERMENTATION OR METABOLIC PRODUCTS, i.e. BIOREACTORS OR FERMENTERS}
- Y02C: CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS

## Abstract

A biogas upgrading system can include a multiple stage membrane system that is configured to remove oxygen so that the biogas is upgraded to have a higher concentration of methane, a pre-selected oxygen (O2) concentration (e.g. less than or equal to 0.2 mol %, etc.), and a pre-selected carbon dioxide (CO2) concentration (e.g. less than or equal to 5 mol %, etc.). The membrane system can be configured to reject O2 by utilizing a low CO2/O2 selectivity that is within a pre-determined range (e.g. less than 5 or less than 4.5). In some embodiments, the upgraded biogas that is output from the system can be entirely made up of methane, carbon dioxide, and oxygen. In other embodiments, the biogas can be almost entirely composed of these components along with a small amount of nitrogen and a trace amount (e.g. less than or equal to 0.2%-0.1%, etc.) of other components.

## Claims

### Claim 1

A process for purifying a biogas feed flow via removal of oxygen (O2) and carbon dioxide (CO2), the process comprising:
providing the biogas feed flow to a first stage of a membrane system to produce a first stage nonpermeate flow and a first stage permeate flow, the biogas feed flow comprising between 30 mol % and 80 mol % methane, between 20 mol % and 70 mol % CO2, and between 0.2 mol % and 3 mol % O2, the first stage nonpermeate flow being comprised of methane, O2, and CO2 such that the first stage nonpermeate flow has a lower concentration of CO2 than the first stage permeate flow, the first stage permeate flow being comprised of methane, O2, and CO2 and having a lower methane concentration than the first stage nonpermeate flow; and
supplying the first stage nonpermeate flow to a second stage of the membrane system to produce a second stage nonpermeate flow and a second stage permeate flow, the second stage nonpermeate flow comprising at least 90 mol % methane and less than 1 mol % O2, the second stage permeate flow having a CO2 content that is greater than a CO2 content of the second stage nonpermeate flow;
wherein the oxygen reduction factor of the process is the ratio of the molar concentration of O2 within the biogas feed flow and the molar concentration of O2 within the second stage nonpermeate flow; and
wherein the process is performed so that the oxygen reduction factor is between 0.9 and 2.2.

### Claim 2 (depends on 1)

The process of claim 1, comprising:
supplying the first stage permeate flow to a third stage of the membrane system to produce a third stage nonpermeate flow and a third stage permeate flow; and
providing the third stage nonpermeate flow to form a recycling stream for feeding the third stage nonpermeate flow to the first stage or a compressor system.

### Claim 3 (depends on 2)

The process of claim 2, wherein the recycling comprises:
mixing the third stage nonpermeate flow with the second stage permeate flow to form the recycling stream before feeding the recycling stream to the compressor system for undergoing compression to a pre-selected pressure.

### Claim 4 (depends on 3)

The process of claim 3, comprising:
mixing the recycling stream with the biogas feed flow before the biogas feed flow is fed to the compressor system, the compressor system being upstream of the membrane system.

### Claim 5 (depends on 1)

The process of claim 1, comprising:
supplying the first stage permeate flow to a third stage of the membrane system to produce a third stage nonpermeate flow and a third stage permeate flow;
wherein at least one membrane of the first stage has a CO2/O2 selectivity value between 3.4 and 4.5 when at a temperature of 30° C.; and
wherein at least one membrane of the third stage has a CO2/O2 selectivity value of between 3.4 and 4.5 when at a temperature of 30° C.

### Claim 6 (depends on 1)

The process of claim 1, wherein at least one membrane of the first stage has a CO2/O2 selectivity value of between 3.4 and 4.5 when at a temperature of 30° C.

### Claim 7 (depends on 1)

The process of claim 1, wherein each and every membrane of the first stage, each and every membrane of the second stage, and/or each and every membrane of the third stage has a CO2/O2 selectivity value of between 3.4 and 4.5 when at a temperature of 30° C.

### Claim 8 (depends on 1)

The process of claim 1, wherein the process is performed so that the oxygen reduction factor is between 1.0 and 1.25.

### Claim 9 (depends on 1)

The process of claim 1, wherein the second stage nonpermeate flow is an upgraded biogas output flow having a methane content of at least 95 mol % methane.

### Claim 10 (depends on 1)

The process of claim 1, wherein the second stage nonpermeate flow has less than or equal to 0.2 mol % O2.

### Claim 11

A biogas upgrading system, comprising:
a membrane system configured to receive a biogas feed flow output from a biogas system, the biogas feed flow comprising between 30 mol % and 80 mol % methane, between 20 mol % and 70 mol % CO2, and between 0.2 mol % and 3 mol % O2, the membrane system comprising:
a first stage positioned and configured to receive the biogas feed flow to produce a first stage nonpermeate flow and a first stage permeate flow, the first stage nonpermeate flow being comprised of methane, O2, and CO2 such that the first stage nonpermeate flow has a lower concentration of CO2 than the first stage permeate flow, the first stage permeate flow being comprised of methane, O2, and CO2 and having a lower methane concentration than the first stage nonpermeate flow; and
a second stage connected to the first stage to receive the first stage nonpermeate flow to produce a second stage nonpermeate flow and a second stage permeate flow, the second stage nonpermeate flow comprising at least 90 mol % methane and less than 1 mol % O2, the second stage permeate flow having a CO2 content that is greater than a CO2 content of the second stage nonpermeate flow;
wherein the oxygen reduction factor of the biogas upgrading system is the ratio of the molar concentration of O2 within the biogas feed flow and the molar concentration of O2 within the second stage nonpermeate flow; and
wherein the biogas upgrading system is configured so that the oxygen reduction factor is between 0.9 and 2.2.

### Claim 12 (depends on 11)

The biogas upgrading system of claim 11, comprising:
a third stage connected to the first stage to receive the first stage permeate flow and produce a third stage nonpermeate flow and a third stage permeate flow, the third stage connected to a recycle conduit such that the third stage nonpermeate flow is passable through the recycle conduit to a position upstream of the first stage of the membrane system.

### Claim 13 (depends on 12)

The biogas upgrading system of claim 12, comprising:
a compressor system positioned upstream of the first stage to compress the biogas feed flow before the biogas feed flow is fed to the first stage, the third stage connected to the recycle conduit such that the third stage nonpermeate flow is passable through the recycle conduit to the compressor system without use of another compressor system.

### Claim 14 (depends on 13)

The biogas upgrading system of claim 13, wherein the recycle conduit is configured to mix the third stage nonpermeate flow with the second stage permeate flow to form a recycling stream before feeding the recycling stream to the compressor system for undergoing compression to a pre-selected pressure.

### Claim 15 (depends on 11)

The biogas upgrading system of claim 11, and the second stage nonpermeate flow has less than or equal to 0.2 mol % O2.

### Claim 16 (depends on 11)

The biogas upgrading system of claim 11, wherein at least one membrane of the first stage has a CO2/O2 selectivity value of between 3.4 and 4.5 when at a temperature of 30° C.

### Claim 17 (depends on 11)

The biogas upgrading system of claim 11, wherein:
at least one membrane of the first stage, at least one membrane of the second stage, and/or at least one membrane of the third stage has a CO2/O2 selectivity value of between 3.4 and 4.5 when at a temperature of 30° C.; or
each and every membrane of the first stage, each and every membrane of the second stage, and/or each and every membrane of the third stage has a CO2/O2 selectivity value of between 3.4 and 4.5 when at a temperature of 30° C.

### Claim 18 (depends on 11)

The biogas upgrading system of claim 11, wherein the biogas upgrading system is configured so that the oxygen reduction factor is between 1.0 and 1.25.

### Claim 19 (depends on 11)

The biogas upgrading system of claim 11, wherein the second stage nonpermeate flow is an upgraded biogas output flow having a methane content of at least 95 mol % methane.

### Claim 20 (depends on 11)

The biogas upgrading system of claim 11, comprising:
the biogas system, the biogas system comprising at least one digester that forms the biogas feed flow and at least one biogas cleaning device positioned to treat the biogas feed flow before the biogas feed flow is fed to the first stage of the membrane system.