Membrane bioreactors for syngas permeation and fermentation

Figures & data

Figure 1. Schematic representation of the simplified Wood–Ljungdahl pathway of acetogens and their (native) metabolic end products [1,2]. Acetogenic microorganisms are able to produce different combinations of the depicted organic products, depending on their metabolism.

Table 1. Expression of local mass transfer coefficients.

Mass transfer coefficient	Expression
Liquid	(7) $$k_l=S{h}_l\frac{D_l}{d}$$(7)
Gas	(8) $$k_g=S{h}_g\frac{D_g}{d}$$(8)
Microporous membrane	(9) $$k_m^m=\frac{D\epsilon }{\delta {\tau }_m}$$(9)
Dense membrane	(10) $$k_m^d=\frac{P}{\delta }=\frac{S_m{D}_m}{\delta }$$(10)

Table 2. Expression of overall mass transfer coefficients (based on the liquid side), for gas–liquid membrane contacting applications [25].

Membrane material	Flat sheet geometry	Hollow fiber geometry^a
Microporous	(11) $$\frac{1}{K_L}=\frac{1}{k_{g}H}+\frac{1}{k_m^{m}H}+\frac{1}{k_l}$$(11)	(12) $$\frac{1}{K_L}=\frac{d_o}{k_{g}H{d}_i}+\frac{d_o}{k_m^{m}H{d}_{lm}^m}+\frac{1}{k_l}$$(12)
Dense	(13) $$\frac{1}{K_L}=\frac{1}{k_{g}H}+\frac{1}{k_m^{d}H}+\frac{1}{k_l}$$(13)	(14) $$\frac{1}{K_L}=\frac{d_o}{k_{g}H{d}_i}+\frac{d_o}{k_m^{d}H{d}_{lm}^d}+\frac{1}{k_l}\mathrm{ }$$(14)
Integral asymmetric/ microporous-dense composite	(15) $$\frac{1}{K_L}=\frac{1}{k_{g}H}+\frac{1}{k_m^{m}H}+\frac{1}{k_m^{d}H}+\frac{1}{k_l}$$(15)	(16) $$\frac{1}{K_L}=\frac{d_o}{k_{g}H{d}_i}+\frac{d_o}{k_m^{m}H{d}_{lm}^m}+\frac{d_o}{k_m^{d}H{d}_{lm}^d}+\frac{1}{k_l}{\hspace{0.17em}}^{\mathrm{b}}$$(16)

In the presence of a biofilm layer on the membrane, an extra mass transfer resistance term is included in the equation.

^agas at shell side and liquid at lumen side; ^bdense layer in contact with liquid.

Figure 2. Concentration profile of compound i when moving from the gas to liquid phase through a: hydrophobic microporous membrane (A), dense membrane (B) and integral asymmetric/composite membrane (C). C_i^G: concentration of i in the gas phase, C_i ^L: concentration of i in the liquid phase, C_i^M: concentration of i in the membrane phase, δ_g: thickness of gas boundary layer; δ_l: thickness of liquid boundary layer; δ_m: thickness of membrane boundary layer, α: gas-membrane interface, β: membrane-liquid interface, γ: microporous-dense layers interface.

Table 3. Design parameters for membrane module selection. [26].

Parameter	Plate and frame	Spiral wound	Tubular	Capillary fibers	Hollow fibers
Manufacturing cost ($/m^2)	50–200	5–50	50–200	5–50	2–10
Concentration polarization/fouling control	Good	Moderate	Very good	Good	Poor
Permeate-side pressure drop	Low	Moderate	Low	Moderate	High
Suitability for pressured operation	Marginal	Yes	Marginal	No	Yes
Limitation to specific types of membrane material	No	No	No	Yes	Yes
Area per volume (m^2/m^3)	200–600	800–1000	–	–	2000–5000

Table 4. Different HFM reactor configurations studied for syngas mass transfer, respective characteristics and the maximum K_La reported.

Membrane fiber properties			Configuration			Am/VL (m^−1)	Operational settings					KLa (h^−1)	Reference
Material	Porous size (µm)	ID/OD (µm)	HFM reactor	Gas feed location	Gas supply		TMP (kPa)	Gas composition	Gas flow rate (mL min^−1)	Liquid recirculation rate (mL min^−1)	Stirring speed reservoir (rpm)
PS	NR	500/660	Stand-alone	Lumen	Open-end	4366	0.7–4.8	Air	1000–2000	80	NA	50^b	[11]
PES	NR	1100/1300	Stand-alone	Lumen	Open-end	2271	0.7–4.8	Air	1000–2000	40	NA	20^b
PP	NR	480/630	Stand-alone	Lumen	Open-end	4361	0.7–4.8	Air	1000–2000	80	NA	240^b
FPS	NR	200/280	Stand-alone	Lumen	Open-end	9198	0.7–4.8	Air	1000–2000	80	NA	50^b
PDMS	Non-porous	200/300	Stand-alone	Lumen	Open-end	10,000	0.7–4.8	Air	1000–2000	400	NA	1062^b
PDMS	Non-porous	200/300	Stand-alone	Lumen	Open-end	10,000	NA	20% O2, 80% Ar	4.6	200	NA	484^b	[42]
								100% CO	5.0	184	NA	420
								100% H2	5.0	181	NA	840
PVDF	0.1	700/1200	Internal	Lumen	Closed-end	63	37.2	99.99% CO	NA	NA	NA	155	[43]
CHF	NA	NR	Internal	Lumen	Closed-end	200	241	99.99% CO	NA	500	NA	1	[10]
PVDF	0.1	700/1200	Internal	Lumen	Closed-end	29	36.5	99.99% CO	NA	NA	NA	69	[44]
PP	0.2	330/630	Coupled to external STR reservoir	Lumen	Open-end	253	0	CO2	128	385	500	24	[45]
PP	0.04	220/300	Coupled to external STR reservoir	Lumen	Open-end^a	175	103.4	99.5% CO	5000	1000	200	1096^c	[24]
PP	0.2	376/426	Coupled to external STR reservoir	Lumen	Open-end	56	114.5	50.0% CO, 30% H2, 20% CO2	140	670	90	385^c,d	[46]
CHF	NR	200/240	Coupled to external reservoir	Shell	Closed-end	200	206.8	99.99% CO	NA	1500	NA	946^c	[13]
PVDF	0.2	800/1400	Coupled to external reservoir	Lumen	Closed-end	2250	203	NR	NA	1500	NA	1^d	[47]

A_m/V_L: Ratio of membrane surface area per total liquid working volume (including external reservoir); ID/OD: Inner diameter/Outer diameter; PDMS: polydimethylsiloxane; PS: polystyrene; PES: polyethersulfone; PP: polypropylene; FPS: Fresenius polysulfone; PE: polyethylene; PU: polyurethane; PVDF: polyvinylidene fluoride; CHF: composite hollow fiber; NA: Not applicable; NR: Not reported.

^aOpen-end fiber configuration with consecutive gas feed to the headspace of external STR; ^bvalue measured for O₂; ^ca = A_m/V_m: membrane surface area per liquid volume in HFM module; ^dvalue measured for CO.

Table 5. HFM bioreactor configurations for syngas fermentation and respective operational conditions.

Entry	HFM bioreactor configuration	Gas feed side/ Gas supply configuration	Syngas feed composition	Liquid working volume (L)	Am/VL (m^−1)	Microorganisms	Temperature (^oC)	pH	Duration of fermentation (d)
1	HFM-BCR	Lumen/closed	80% CO, 20% CO2	0.4	27.5	Eubacterium limosum KIST612	37	7^e	3
2	HFM-BCR^a	Lumen/closed	80% CO, 20% CO2	2	29	C. autoethanogenum DSM10061	37	4–6	≃ 8.3
3	Stand-alone^b	Lumen/open	40% N2, 25% CO, 20% CO2, and 15% H2	1.5	306.7	Clostridium ljungdahlii DSM13258`	37	5.0–6.0	7
4	Stand-alone^b	Lumen/closed	40% CO2, 60% H2	0.24	458.3	Mixed culture from methane production reactor (mesophilic)	35	6.0	80
5	Stand-alone^b	Lumen/closed	40% CO2, 60% H2	0.32	875.0	Mixed culture from methane production reactor (mesophilic)	35	4.5– 4.8	26
6	Stand-alone^b	Lumen/closed	60% CO, 40% H2	0.32	71.9	Mixed culture from digester treating starch wastewater (mesophilic)	35	4.5	108
7	Stand-alone^b	Lumen/closed	40% CO, 60% H2	0.39	256.4	Mixed culture from anaerobic digester (mesophilic)	35	6	165
8	Stand-alone^b	Lumen/closed	40% CO2, 60% H2	0.32	71.9	Anaerobic sludge from a full-scale biogas producing reactor	55	6	120
9	Coupled to external STR^b	Lumen/open	20% CO, 5% H2, 15% CO2, 60% N2	8	175	Clostridium carboxidivorans P7	37	4.5–5.5	NR
10	Coupled to external STR^b	Shell/open	40% CO, 30% H2, 30% CO2	≃3	31	Clostridium ragsdalei ATCC	37	5.9	20
11	Stand-alone^b	Lumen/closed	60% CO, 40% H2	0.32	71.9	Mixed culture from digester treating starch wastewater (mesophilic)	35	4.5	27
12	Stand-alone^b	Lumen/closed	40% CO, 60% H2	0.39	615.4	Mixed culture from anaerobic digester (mesophilic)	55	6.5	60
13	Stand-alone^b	Lumen/closed	40% CO2, 60% H2	0.32	71.9	Anaerobic sludge from a full-scale biogas producing reactor	55	6	40
14	Stand-alone^b	Lumen/closed	40% CO2 60% H2	0.32	875.0	Mixed culture from methane production reactor (mesophilic)	35	4.5–4.8	134
15	Coupled to external reservoir	Lumen/closed	Varying CO:N2 ratio	0.16	5.6	Carboxydothermus hydrogenoformans DSM6008	70	6.9–7.8	126
16	Submerged in STR	Lumen/closed	100% CO	0.4	282.5	Mixed culture from digested sewage sludge	55	7.2	131
Entry	Liquid operation mode	HRT (day)	Liquid recirculation velocity (mL min^−1)	Products	Product titers (g L^−1)	Productivity (g L^−1 day^−1)	Syngas utilization efficiency (%)	Biofilm formation	Reference
1	Batch	NA	NA	Acetate	1.96	0.65^f	NR	No	[43]
2	Batch	NA	NA	Ethanol	2.73	1.18	NR	No	[44]
				Acetate	1.53
`3	Batch	NA	120	Ethanol	1.09	NR	CO – 14%	Yes	[48]
				Acetate	0.71
4	Batch	NA	500	Acetate	7.4	0.19	H2 – 100%	Yes	[49]
				Butyrate	1.8	0.06
				Hexanoate	0.98	0.03
				Octanoate	0.42	0.02
5	Batch	NA	500	Acetate	12.5	0.59	H2 – 100%	Yes	[50]
				Butyrate	0.1	NR
6	Sequential batch	NA	NR	Ethanol	16.9	NR	NR	Yes	[51]
7	Sequential batch	NA	NR	Acetate	4.22	NR	CO > 95%
							H2 >95%	Yes	[52]
				Butyrate	1.35	NR
				Hexanoate	0.88	NR
				Octanoate	0.52	NR
8	Sequential batch	NA	NR	Acetate	42.0	2.0	NR	Yes	[53]
				Butyrate	0.6	NR
9	Continuous	1.04	200	Ethanol	23.93^c	3.44	CO ≃ 81 %
							H2 ≃74%	Yes	[24]
				Acetic acid	≃8^c	≃2.8
10	Continuous	5	500	Ethanol	15.0	NR	NR	Yes	[54]
11	Continuous	9	NR	Ethanol	4.2	0.47	NR	Yes	[51]
				Acetate	1.0	0.11
12	Continuous	1.5	NR	Acetate	24.6	16.4	CO > 95%
							H2 > 95%	Yes	[52]
13	Continuous	1	NR	Acetate	10.5	10.5	NR	Yes	[53]
				Butyrate	NR^d	NR
14	Continuous	9	500	Acetate,	3.6	0.4	H2 – 100%	Yes	[50]
				Butyrate	0.02	NR
15	Continuous	≃16	1500	Hydrogen	NR	6.06^g	CO – 69.3%	Yes	[47]
16	Continuous	10	NA	Methane	NR	1.992^h	NR	Yes	[55]

A_m/V_L – Membrane surface area per reactor working volume.

NA – Not Applicable.

NR – Not Reported.

^aWith gas recirculation; ^bwith liquid recirculation; ^cproduct titers for HRT of 8.33 days; ^donly trace amounts of butyrate produced; ^einitial pH, pH was not controlled; ^faverage productivity, calculated from available data. ^gProductivity calculated from available data (volumetric CO removal rate and CO conversion efficiency); ^hProductivity reported in mL L⁻¹ day⁻¹ (at the operational temperature and pressure).

Table 6. Summary of flow configurations in a hollow fiber membrane reactor and their respective advantages.

Selection item	Option		Advantages
Gas supply configuration	Open-end		High gas velocities in membrane lumen; High average gas fluxes and transfer rates; No water condensation; No gas back diffusion.
	Closed-end		100 % Gas transfer.
Gas feed location	Shell-side feed		None
	Lumen-side feed		Low susceptibility of blockage by biofilm growth.
Flow pattern	Axial Flow	Co-current	Higher feed velocities.
		Counter-current
	Cross Flow	Radial flow distribution	Uniform shell-side flow distribution; Avoids flow channeling, bypassing and dead zones; Higher mass transfer coefficient.
		Helically wound bundle
		Flow diverters and baffles
		“U” shape closed-end bundle

Figure 3. HFM modules with (A) tubesheets at both ends; (B) a single tubesheet in a U shaped bundle; (C) one tubesheet and one sealed end; (D, E) gas feed entering the bundle from the perforations on the central tube and exiting from (D) the port on the housing or (E) the perforations toward the other end; (F) Baffles with alternating clearances at top and bottom to force the flow up and down. Based on [41].

Table

Abbreviation	Meaning
EPS	Extracellular Polymeric Substances
HFM	Hollow Fiber Membrane
HFM-BCR	Hollow Fiber Membrane Bubble Column Reactor
HRT	Hydraulic Retention Time
PDMS	Polydimethylsiloxane
PMP	Polymethylpentene
PP	Polypropylene
PTMSP	Poly(1-trimethylsilyl-1-propyne)
PVDF	Polyvinylidene fluoride
STR	Stirred Tank Reactor

Table

Symbols	Meaning	Unit
a	Interfacial area	m^−1
Am	Membrane surface area	m
C	Dissolved gas concentration	mol.m^−3
D	Diffusion Coefficient	m^2.s^−1
d	Diameter	m
di	Inner Diameter of hollow fiber membrane	m
dlm	Logarithmic mean diameter of hollow fiber membrane	m
do	Outer diameter hollow fiber membrane	m
H	Dimensionless gas-water Henry coefficient	mol.m^−3gas.(mol.m^−3liquid)^−1
k	Volume specific mass transfer coefficient	m.s^−1
KL	Overall Mass Transfer Coefficient, based on liquid side	m.s^−1
KLa	Volumetric mass transfer coefficient, based on liquid side	s^−1
L	Length of hollow fiber membrane	m
M	Molecular weight	kg.mol^−1
P	Permeability	m^2.s^−1
Q	Volumetric flow through the membrane module	m^3.s^−1
R	Ideal Gas Constant	J.mol^−1.K^−1
S	Solubility coefficient or Gas-membrane partition coefficient	mol.m^−3membrane.(mol.m^−3gas)^−1
Sh	Sherwood number	(dimensionless)
T	Temperature	K
t	Sampling time	s
V	Volume	m^3
v	Velocity	m.s^−1
δ	Membrane thickness	m
ΔC	Concentration difference	mol.m^−3
ε	Porosity
τ	Tortuosity
Subscript
*	Saturated
eff	Effective
g	In the gas phase
k	Knudsen (diffusivity)
l	In the liquid phase
lm	Logarithmic mean
L	Liquid
L,out	Liquid outlet of membrane module
m	In the membrane
M	Membrane module
R	Reservoir
p	Pore
0	Initial
Superscript
d	Dense layer
m	Microporous layer

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