Research Progress on the Typical Variants of Simulated Moving Bed: From the Established Processes to the Advanced Technologies
Round 1
Reviewer 1 Report
The authors have written a review article on the progress of significant variants of simulated moving bed separation process, where, three significant types of SMB variants were introduced and analyzed. The article can be accepted after addressing following comment:
1. The authors have discussed about the economy also but i dont see any costs comparision to see the difference.
2. The authors should provide a table in summary to show the key differences in the three types.
3. Based on some technical and economic data, the authors may present the pros and cons of each technology.
4. The acknowledgement may be added.
Author Response
Reviewer #1：The authors have written a review article on the progress of significant variants of simulated moving bed separation process, where three significant types of SMB variants were introduced and analyzed. The article can be accepted after addressing following comment:
- The authors have discussed the economy also but I don’t see any costs comparison to see the difference.
Response: Thank you very much for your comment. The discussion and comparison about the economy (with some detailed data of products’ purity, recovery, and material consumption) for each SMB variant are added to each section as below.
“In conclusion, the two-zone SMB has the advantage of low cost and is more economical due to the isolation of two regeneration zones. Moreover, relatively high purity can be achieved on this simplified equipment. For example, in Lee’s work[36], compared to the conventional SMB, the two-zone SMB improved the purity and recovery of the fructose-rich product from 0.78% and 4.11% to 15.67% and 15.87%, respectively. As a result, the separation cost was reduced due to the low material consumption and simple column arrangement.” (added in page 5)
“The results showed that, in the 2-2-2 column operation mode, the purity of both DHA and EPA reached 99% and the recovery was close to or at 100%. The solvent consumption was 1.11 L/g, which was significantly lower compared with 1.46 L/g in the 1-1-2 mode[42].” (added in page 6)
“The results showed that the product purity was generally improved by 1%-4%, the recovery was generally improved by 0.8%-4.8%, and the productivity was increased by up to 13.8 g/L/h using TT-SMB compared to conventional SMB.” (added in page 6)
“With the same feeding method, the 3 zone SMB improved the recovery by up to 8.87% and the purity by up to 7.82% compared to the 4 zone SMB.” (added in page 7)
“Specifically, in this case the productivity of amino acid was increased up to 110%, and meanwhile the desorbent consumption was reduced up to 53%.” (added in page 9)
“The result proved that a temperature gradient with a 20 K difference could significantly improve the productivity of the SMB device by 20%.” (corrected in page 10)
“When a pressure gradient is used, the product purity is increased by up to 2.3% and the productivity is increased by 0.29 g/kg compared to the isobaric mode.” (added in page 11)
“Compared to conventional SMB, the ModiCon could regulate the feed concentration and increase productivity by about 50% and reduce solvent consumption by about 25%[62].” (added in page 11)
“When the VariCol process was used, the product recovery was generally improved by 0.15%-0.56% and the product purity was generally improved by 0.1%-0.52% compared to the conventional SMB[69].” (added in page 12)
“The final product purity of up to 97.8% was obtained with a productivity of 2.10 g/L/h and a solvent consumption of 12 g/L, which proved better than that of conventional SMB process.” (added in page 13)
“The results revealed that the solvent consumption of SSMB was significantly less than that of SMB for the same purity and recovery requirements, which further proved the technical and economic superiority of SSMB process[87].” (added in page 14)
In addition, the economic differences of three main variants are also showed in Table 1.
- The authors should provide a table in summary to show the key differences in the three types.
Response: “Table 1. A summary and comparison of three SMB variants” was added to page 15 and described the key differences of the three types.
Table 1. A summary and comparison of three SMB variants
|
|
Modification mechanism |
Switching mode |
Advantage |
Disadvantage |
Classification |
|
Zone variant |
Non-essential functional zones are reduced by combing or deleting one or several columns. |
Three-zone SMB possesses a unique three-step switching mode, the others’ is similar to the conventional SMB. |
The economical efficiency is improved due to the simplified device and the better separation performance. |
The solid and liquid phases cannot be adequately regenerated and recycled. |
One-column SMB, two-zone SMB, three-zone SMB, bypass SMB and SMBs with more than four zones. |
|
Gradient variant |
The adsorption behavior of each zone is adjusted by introducing a gradient parameter. |
Similar to conventional SMB switching mode basically. |
Higher productivity, purity, and lower desorbent consumption can be achieved. |
Poor stability, high design difficulty, may only be used under limited conditions. |
Concentration gradient, temperature gradient and pressure gradient. |
|
Feed or operation variant |
The feed or operation mode is changed without altering the SMB configuration. |
For VariCol mode, only one inlet or outlet is switched within each stwitching time, and each port is switched independently. SSMB has unique three step switching mode. Others’ is similar to that of conventional SMB. |
High utilization of mobile phase and low water consumption. Complicated and multiple systems can by separated by this variant.
|
The operation and optimization works become more complex due to the internal instability . |
ModiCon, VariCol, PowerFeed, ISMB, SSMB, Pseudo-SMB, OSS, BF-SMB, SMB cascades, SimCon. |
- Based on some technical and economic data, the authors may present the pros and cons of each technology.
Response: Thanks for the comment. Some complementary data was added into the manuscript as described in “response 1”. The discussion about advantages and disadvantages of each technology was also added in each section, for example in table 1 and at the end of each section.
Here are two examples:
“For example, in Lee’s work[36], compared to the conventional SMB, the two-zone SMB improved the purity and recovery of the fructose-rich product from 0.78% and 4.11% to 15.67% and 15.87%, respectively. As a result, the separation cost was reduced due to the low material consumption and simple column arrangement. Besides, there still exist obvious disadvantages: (1) Although the port switch of two-zone SMB is similar to that of conventional four-zone SMB, it cannot achieve the countercurrent movement of the solid and liquid phases, so it is not available for continuous operation. (2) The purity and recovery of the two-zone SMB is lower than that of the four zone SMB owing to the simplification. (3) The final purity cannot be easily increased by increasing the number of columns in each zone.” (page 5)
“SSMB is not only an improvement of the conventional SMB, but also an modification of the ISMB. The main advantages are: (1) High utilization of mobile phase and low water consumption can effectively reduce the cost, so the SSMB is suitable for industrial production. (2) When separating some specific mixtures, the separation performance of SSMB is significantly higher than that of SMB. (3) the back mixing problem existing in the separation process of SMB can be effectively solved by SSMB. (4) Ternary separation can be achieved by adding the inlet and outlet ports. In addition, SSMB also possesses some disadvantages: (1) The operation is more complicated and increases the control difficulty. (2) The utilization rate of stationary phase is lower. (3) The flow rate ratio (m value) is influenced by various factors and is not constant during the switching time, which indicates that the SSMB can not be directly designed by using m value.” (page 14)
- The acknowledgement may be added.
Response: Thank you. The acknowledgement is added as below.
“The authors express their great thanks for the support from the National Natural Science Foundation of China (Grant No. 22268031), the Natural Science Foundation of the Inner Mongolia Autonomous Region (Grant No. 2021BS02003), and the Basic Research Funding for Universities Directly Under Inner Mongolia Autonomous Region (JY20220212).”
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Accept
Author Response
Reviewer #2：Accept.
Response: Thank you for the reviewer’s affirmation and recommendation.
Reviewer 3 Report
Review of: Research progress on the significant variants of simulated moving bed separation process.
Overall analysis of the manuscript
This review manuscript is very, very incomplete even in comparison with other review articles already published in the literature. Moreover, as I explain in the following, recent progresses in the area are not covered. Hence, I recommend its rejection.
SMB is now an established process and numerous review articles in recent years focused exactly on new SMB variations. Here are some examples, which are not even cited in the manuscript, which is not acceptable: DOI: 10.1080/15422119.2013.851087, DOI: 10.1016/j.chroma.2015.08.045, DOI: 10.1002/ceat.201700206.
Techniques such as VariCol, ModiCon, PowerFeed, gradients and different number of SMB zones have all been already thoroughly reviewed. Simple Cascade of SMBs and SMBs with more than four zones were not considered for review and the same applies for techniques such as outlet streams swing-SMB, SimCon, Backfill SMB, just to name a few other recent strategies. The article essentially reviews what was already reviewed and does not provide updates, lacking judgment and cutting-edge outlook on subsequent multi column research trends (DOI: 10.1016/j.chroma.2015.08.045). It does not reflect the word “progress” used in the title.
Accordingly, and agreeing with “Processes” journal instructions for authors (https://www.mdpi.com/journal/processes/instructions) in which reviews should “provide concise and precise updates on the latest progress made in a given area of research”, reviewer suggests the rejection of this manuscript.
Author Response
Reviewer #3：This review manuscript is very, very incomplete even in comparison with other review articles already published in the literature. Moreover, as I explain in the following, recent progress in the area are not covered. Hence, I recommend its rejection. SMB is now an established process and numerous review articles in recent years focused exactly on new SMB variations. Here are some examples, which are not even cited in the manuscript, which is not acceptable: DOI: 10.1080/15422119.2013.851087, DOI: 10.1016/j.chroma.2015.08.045, DOI: 10.1002/ceat.201700206.
Techniques such as VariCol, ModiCon, PowerFeed, gradients and different number of SMB zones have all been already thoroughly reviewed. Simple Cascade of SMBs and SMBs with more than four zones were not considered for review and the same applies for techniques such as outlet streams swing-SMB, SimCon, Backfill SMB, just to name a few other recent strategies. The article essentially reviews what was already reviewed and does not provide updates, lacking judgment and cutting-edge outlook on subsequent multi column research trends (DOI: 10.1016/j.chroma.2015.08.045). It does not reflect the word “progress” used in the title.
Accordingly, and agreeing with “Processes” journal instructions for authors (https://www.mdpi.com/journal/processes/instructions) in which reviews should “provide concise and precise updates on the latest progress made in a given area of research”, reviewer suggests the rejection of this manuscript.
Response：Thank you very much for your comment. We have read all the articles mentioned and consider your suggestions carefully and added some new, advanced SMB technologies of these three variants, meanwhile the modification mechanism, operating modes, advantages, disadvantages, and applications of these SMB processes were thoroughly investigated. Specifically, “SMBs with more than four zones” was added to section 1 “Zone variant”; “Pseudo-SMB”, “Outlet Swing Stream (OSS) SMB”, “SMB cascades”, “Backfill SMB”, “SimCon” were added to section 3 “Feed or operation variant”. The manuscript was modified, the detailed updates are as below.
Following references were added:
[25] Aniceto J P S, and Silva C M. Simulated moving bed strategies and designs: from
established systems to the latest developments [J]. Separation & Purification Reviews, 2015, 44: 41-73.
[26] Faria R P V, Rodrigues A E. Instrumental aspects of simulated moving bed chromatography [J]. Journal of Chromatography A, 2015, 1421: 82-102.
[42] Kim K M, Lee J W, Kim S H, Silva F V S, Seidel-Morgenstern A, Lee C H. Advanced operating strategies to extend the applications of simulated moving bed chromatography [J]. Chemical Engineering & Technology, 2017, 40: 2163-2178.
MUN S. Enhanced Separation Performance of a Five-Zone Simulated Moving Bed Process by Using Partial Collection Strategy Based on Alternate Opening and Closing of a Product Port [J]. Industrial & Engineering Chemistry Research, 2010, 49(19): 9258-9270.
[55] XIE Y, CHIN C Y, PHELPS D S C, et al. A Five-Zone Simulated Moving Bed for the Isolation of Six Sugars from Biomass Hydrolyzate [J]. Industrial & Engineering Chemistry Research, 2005, 44(26): 9904-9920.
[56] WOOLEY R, MA Z, WANG N H L. A Nine-Zone Simulating Moving Bed for the Recovery of Glucose and Xylose from Biomass Hydrolyzate [J]. Industrial & Engineering Chemistry Research, 1998, 37(9): 3699-3709.
[57] JIANG C, HUANG F, WEI F. A pseudo three-zone simulated moving bed with solvent gradient for quaternary separations [J]. J Chromatogr A, 2014, 1334: 87-91.
[90] WEI F, SHEN B, CHEN M, et al. Study on a pseudo-simulated moving bed with solvent gradient for ternary separations [J]. J Chromatogr A, 2012, 1225: 99-106.
[91] KURUP A S, HIDAJAT K, RAY A K. Optimal operation of a Pseudo-SMB process for ternary separation under non-ideal conditions [J]. Separation and Purification Technology, 2006, 51(3): 387-403.
[92] BORGES DA SILVA E A, RODRIGUES A E. Design of chromatographic multicomponent separation by a pseudo-simulated moving bed [J]. AIChE Journal, 2006, 52(11): 3794-812.
[93] Sá GOMES P, RODRIGUES A E. Outlet Streams Swing (OSS) and MultiFeed Operation of Simulated Moving Beds [J]. Separation Science and Technology, 2007, 42(2): 223-52.
[94] KIM K M, LEE C H. Backfill-simulated moving bed operation for improving the separation performance of simulated moving bed chromatography [J]. J Chromatogr A, 2013, 1311: 79-89.
[95] KIM J K, WANKAT P C. Designs of simulated-moving-bed cascades for quaternary separations [J]. Industrial & Engineering Chemistry Research, 2004, 43(4): 1071-80.
[96] WANKAT P C. Simulated moving bed cascades for ternary separations [J]. Industrial & Engineering Chemistry Research, 2001, 40(26): 6185-93.
[97] SONG J Y, KIM K M, LEE C H. High-performance strategy of a simulated moving bed chromatography by simultaneous control of product and feed streams under maximum allowable pressure drop [J]. J Chromatogr A, 2016, 1471: 102-17.
Following discussion was added:
“1.5. SMBs with more than four zones
Generally, conventional four-zone SMBs only can handle binary mixture’s separation task. To separate multi-mixtures, more zones need to be added to break through the limitations in terms of zone variants. The following is a brief description of the five-zone SMB and the nine-zone SMB.
A five-zone SMB is a closed loop with multiple chromatographic columns in series, generally equiped with two inlets (feed and desorbent ports) and three outlets (extractant 1, extractant 2, and extractive residue). The three inlets are assigned to low-affinity substance A, medium-affinity substance B and high-affinity substance C. Usually, the inlet is between zone III and zone IV, and low-affinity substance A is collected from the raffinate port (between zone IV and zone V), while high-affinity substance C and medium-affinity substance B are collected at the extract 1 port (between zone I and zone II) and extract 2 port (between zone II and zone III), respectively. For example, Mun[55], Xie et al.[56] have successfully separated multiple components by designing and using a five-zone SMB with high yields and purity. The nine-zone SMB can be regarded as a five-zone SMB in parallel with the conventional four-zone SMB, and the whole system forms two closed loops with bypass stream. In Wooley et al.’s work[57], a nine-zone SMB was applied to extract two sugars from the biohydrolysis product with a purity close to 100% and a recovery of 88%.”
“3.6. Pseudo-SMB
Pseudo-SMB is a new SMB technology mainly used to separate ternary mixtures. The process can be seen as a combination of true moving bed and simulated moving bed. There are two main steps. The first step is similar to the TMB process, where the ternary mixture (A, B and C) is injected into the inlet and the desorbent (D1) is also injected, with the aim of separating component B, which has intermediate affinity for the desorbent. The second step is similar to the SMB process, and closes the device with only the desorbent (D2) injected from the inlet in order to collect the component A and C, respectively. In the process of separating ternary mixtures, the pseudo-SMB is relatively easy to operate and has advantages for small-scale ternary separation[26, 92-95].”
“3.7. Outlet Swing Stream (OSS) SMB
Gomes et al.[96] proposed an unusual SMB in which the flow rates of zones II and III were kept constant based on the conventional SMB, and the flow rates of each outlet (extract, raffinate and desorbent) were artificially manipulated to dynamically adjust the flow rates of zones I and IV for the separation operation. It can effectively improve the product purity and reduce the desorbent consumption[26].”
“3.8. Backfill-SMB
To improve the separation and chromatography performance of conventional SMB, Kim et al.[97] proposed a strategy called Backfill-simulated moving bed (BF-SMB). A part of the product is refilled into the SMB from the feed node or intermediate node as a feed to simulate a TMB-like effect, enriching the main components near the product extraction node, thereby improving the separation of the SMB performance. This strategy can effectively improve product purity without compromising recovery and desorbent consumption[42, 97].”
“3.9. SMB cascades
Complex separation tasks, such as separation of ternary or more multiple mixtures, can be handled by properly connecting multiple SMBs working in succession. This process is called SMB cascades, also known as tandem SMB. It is generally operated using two (or more) consecutive SMB units. A ternary (or multiple) mixture is fed from the inlet into the first SMB unit, and after separating a single material, the remaining mixture is introduced into the second SMB unit for further separation. If the initial feed has only three mixtures, two SMB cascades will separate them all; if there are more than three, a third SMB unit will need to be passed through, and so on. Since each unit is independent of each other, it is possible to set independent parameters without interfering with each other. After the cascade operation, the separation performance is greatly improved compared to the conventional SMB. However, it is important to note that the more SMBs are cascaded, the more diluted the sample is, and thus the productivity is reduced. Therefore, the idea of bypass SMB as mentioned before can be used for proper priming to ensure sample purity[26, 98, 99].”
“3.10. SimCon
Song et al.[100] proposed a novel SMB strategy called SimCon. Under the constraints of the maximum allowable pressure or flow rate, the feed flow and product flow are simultaneously controlled. This operation can make the flow and pressure fluctuations in the column as small as possible to improve the performance of the SMB. The SimCon operation consists of three steps: In the first step, when the desorbent is injected, only the raffinate port is opened. In the second step, all inlet and outlet ports are opened, which is consistent with the conventional SMB process and is called an intermediate step. In the final step, only the raffinate port is closed, and the other ports are opened[42]. Experimental data have confirmed that compared with conventional SMB, SimCon operation can increase the product purity by 3.2%, the recovery rate by 3.1%, the productivity by 0.9g/Lh, and the desorbent consumption by 0.04L/g[100]. The separation performance and process cost can be effectively optimized by the SimCon strategy.”
Accordingly, the title of this manuscript was modified as “An investigation on the typical variants of simulated moving bed: From the established processes to the advanced technologies”, because the word “research progress” is more specialized and focuses on the cutting-edge technologies. Meanwhile, Figure 2. was corrected as below.
Figure 2. The framework structure of review.
Reviewer 4 Report
Please see uploaded file.
Comments for author File: Comments.pdf
Author Response
Major points:
1) The title should be modified to state that this paper is a review rather than a research paper,
e.g. to “Review of significant variants of simulated moving bed separation processes”
Response: Thank you very much for the reviewer’s comments. The title is modified to “The research progress on the typical variants of simulated moving bed: From the established processes to the advanced technologies”, which could reflect it is a review paper and meanwhile emphasize the key point.
- 2a: Line 26-36: You summarize the principle behind the SMB separation process, with which the expert certainly is familiar. The novice however is not, and I suspect that you need to explain the counter current flow of the solid and the fluid phases a bit more detailed, e.g. by using a figure such that a novice can understand that the port switching is indeed a simulation of the movement of the solid phase.
Response: Yes, it is necessary to explain the “counter-current movement of solid and liquid phase”, because it is an important phenomenon or mechanism of SMB process. As a result, we added Figure 1. into the manuscript as below. In this figure, the novice can clearly understand the difference between counter-current and co-current movement.
Figure 1. Schematic diagram of counter-current movement.
2b: By the way, this suggestion also points to the fact that you do not explicitly write (in lines 72-80) for whom this review is intended. That must be stated.
Response: Thank you for the suggestion. The sentence below is added to Line 82-84.
“Finally, this work can provide practical suggestions and references for SMB research works and industrial applications(both intend for the expert and novice), meanwhile put forward the application prospect and future development direction.”
2c: Line 46-48: “For efficient operation, the solid and liquid phase regeneration zones are typically operated in co-current mode by setting the operating parameters appropriately.” This important point is not illustrated well by Figure 1. Instead one can use a Figure (e.g. as mentioned above) where the ports are constant and the Liquid and solid phase exhibit counter current movement. Since you later refer to the solids flow rate it seems advantageous to introduce it already here!
Response: “Figure 1. Schematic diagram of counter-current movement” is added to the manuscript, in which the ports are constant and the Liquid and solid phase exhibit counter current movement.
3) Line 291: What is meant by “…periodic steady-state fluctuations…”?
In a continuously operated SMB you will have periodicity due to the port switching. If you focus upon one specific time point within a period, e.g. the end point, then at steady state that point will have the same concentrations and flow rates period after period. In fact, the whole time profiles of the period is repeated period after period. Thus, you have a stationary process.
Response: Yes, the expression of “periodic steady-state fluctuations” is not exact, every point in the SMB system should show a steady-state characteristic in each period. So, we corrected it to “...cyclic steady-state characteristics...”, and within this steady-state (within a period time), the mobile phase composition is not constant due to the mechanism of concentration gradient SMB.
The revised part is shown below (in Line 337-341 of the manuscript).
“However, in the concentration gradient mode, the mobile phase composition is not constant, which leads to cyclic steady-state characteristics when the inlet and outlet ports are switched periodically. Similarly, the internal adsorption equilibrium relationship of the solute also shows cyclic steady-state variations, which will reduce the stability of the system and thus make the process design more difficult.”
4) Line 78-80: “Finally, this work can provide practical suggestions and references for SMB research works and industrial applications, meanwhile put forward the application prospect and future development direction.” Since you focus on investigating SMB variants, it is difficult to see how you can propose industrial applications? That would require a more stringent focus on the applications, where of you only have references a few.
Response: At first, SMB is a very practical separation technology, we hope this review work could provide some useful references for its application. In addition, the main purpose of developing the diverse SMB variants is to improve the separation efficiency and extend its industrial application potential. As we described in the paper, the modified SMB variants can improve the productivity, purity, economic cost, etc. And we also listed all the advantages and disadvantages of each variant, which could provide guidance for the specific separation tasks. As a result, we think it is helpful for the SMB’s application.
Minor points:
- 73-74: You write: “This paper mainly focuses on the SMB variants investigation and divides them into three categories: zone variant, gradient variant and feed variant.” This sentence could be more clearly framed as: “This paper mainly focuses on an investigation of SMB variants and divides these into: zone variant, gradient variant and feed variant.”
Response：Thanks a lot. This sentence is corrected in the manuscript, as shown in Line 77-78.
- 313: “The result proved that the…” should be “The result demonstrated that the…”
Response：This sentence is corrected in the manuscript, as shown in Line 358.
3) In subsection titles please specify the full name of the variant followed by its acronym in parenthesis, e.g. line 431: Sequential simulated moving bed (SSMB). .
Response：Thank you for the reviewer’s suggestion. The subsection titles are corrected as below.
Line 462: Intermittent simulated moving bed (ISMB);
Line 487: Sequential simulated moving bed (SSMB);
Line 535: Backfill-SMB (BF-SMB).
Author Response File: Author Response.pdf
Round 2
Reviewer 3 Report
Overall appraisal after revision After revision Authors changed the article title from “Research progress on the significant variants of simulated moving bed separation process” to “An investigation on the typical variants of simulated moving bed: From the established processes to the advanced technologies”. Authors added some missing SMB schemes suggested by me and another one not suggested by me (i.e., Pseudo-SMB,) and included one table comparing some SMB variants and more bibliography. Nonetheless, as I stated in my previous review report, those were only a few recent strategies that were missing. It makes no sense that Authors write their manuscript guided by Reviewers! The revised manuscript does not present a critical discussion about small variants of SMB and recent strategies with more than four zones. Unfortunately, in comparison with literature, this manuscript brings nothing of interest. Authors stated that the “title of this manuscript was modified (…) because the word “research progress” is more specialized and focuses on the cutting-edge technologies”. Reviewer still considers that the manuscript does not provide more recent and crucial updates and, thus, lacks judgment and cutting-edge outlook. By leaving out strategies, readers do not get a full picture of what was done around the SMB. Reviewer still suggests the rejection of this manuscript.Author Response
Response: Thank you for the reviewer’s comments. The purpose of writing this paper is to provide practical suggestions and references for SMB research works and industrial applications (intend for both the expert and novice), meanwhile put forward the application prospect and future development direction. As a result, the main part focuses on the introduction and summary of each SMB variant, which both contains the established and advanced technologies. For each variant, the separation mechanism, switching modes, advantages and disadvantages, and applications were summarized in order to provide a comprehensive understanding and objective description for the reader. Based on this paper, we hope readers could obtain a clear, objective framework for the diverse SMB variants and the useful methods to improve the SMB separation performance, which will be beneficial for the SMB application extension and SMB efficiency enhancement. Therefore, this is why the reviewer thinks we still lack some updates and judgement.
Author Response File: Author Response.pdf
