Industrial Adsorbents Presentation
Fred Ghanem provides a comprehensive look at the two new ranges of industrial adsorbents from Purolite Life Sciences.
Fred Ghanem provides a comprehensive look at the two new ranges of industrial adsorbents from Purolite Life Sciences.
Our colleague Fred Ghanem provides a comprehensive presentation outlining our two new ranges of industrial adsorbents, PuroSorb™ and Macronet®. Learn more about the properties of each range and their wide range of applications.
Watch the full presentation below and find the full presentation transcript included.
Hi welcome to the Purolite Life Science webinar on industrial adsorbents, specifically on our PuroSorb™ and Macronet® products.
First, what are adsorbents? Simply they are polymeric spherical beads. They are very stable in many different solvents and they also have a very high pH range of resistance from pH of 0 to 14.
But one of the most important characteristics of adsorbents is that they are very highly porous so that they have a very high surface area as a result.
So they act very similarly to an activated carbon, with a surface area that can range from 400 to 1500 m2/dry gram so it’s quite large of a surface area and that’s very characteristic of every adsorbent in the industry.
How they work is they typically attract molecules by hydrophobic interaction. Hydrophobic means they are water hating and therefore if the molecule is not very soluble in the water, or if it prefers it is hydrophobic in nature, it will actually leave the water phase and goes on to the adsorbents.
During the elution, since the adsorbent most of the time does not have ion exchange capability, most of the time the regeneration is done and the elution is done by increasing the solvent concentration to increase the solubility of the molecules that are stuck onto the resin back into a solvent phase. Or, the other way is to reduce the hydrophobic interaction between the resin and the molecule.
So what do adsorbents compete against? Well I did mention before that it does compete against activated carbon but the adsorbents are usually very easy to elute and reuse many many times so over the ages and the cyclability, synthetic adsorbents become a very inexpensive way of adsorbing molecules of interest.
But it is important to list that there are two other methods of purification that do compete against adsorbents. One is solvent extraction and the other one is crystallization.
The solvent extraction as it mentions, it uses a lot of solvents to do the extraction of the molecule from one solvent to the other. But that also requires quite a bit of organic solvents, a lot of flammable stuff going on everywhere in the system, but typically the capital costs of the system is moderate when compared to the high cost of the synthetic adsorbent system.
Crystallization on the other hand is one of the cheapest capital cost investment. But it does require quite a bit of energy because you are reducing the temperature to try to crystallize one molecule over the other. And sometimes a lot of the molecules you’re dealing with cannot be crystallized so crystallization might not work as that purification step.
Adsorbents like I mentioned, it does attract molecules by hydrophobic or hydrophobic interactions, and as you can see from this table, hydrophobic interaction is one of the strongest bonds that there is. It’s sometimes does act even stronger than ionic interaction.
So it is an important resin to take advantage of in our purification steps.
When you’re looking at a molecule, you’re always trying to figure out what types of resin to use. So some of the characteristics of the molecules usually you’re looking for, is it, are you asking yourself, is it soluble, in the solvent or the water? You know for example is it polar or non-polar required for a solvent? Is the chemical interaction of the molecule, is it hydrophobic? Does it have some ionic properties to it? Does it have carbonyls on it? Also the molecular weight of the molecule is important, as well as what is the concentration of that molecule and what are the competing other molecules in that solution?
Based on those informations, you can decide on what types of resin to use such as, based on the solubility, you’ll decide if the resins need to be ionic or non-ionic. Based on its molecular structure, you can decide if the resin does have to have a hydrophobic surface, if it has to have ionic functionality or has to interact by hydrogen bonding with the carbonyls. And based on the molecular size and the capacity, you could decide on pore size or the pore distribution required for the resin, as well as the appropriate surface area and particle size of the bead.
One of the characteristics as well other than surface area that’s important about adsorbents is the porosity. The pore size is very important because it enables certain molecules to get in, while at the same time it excludes others. So in this case scenario you can see some of the larger molecules have been excluded, and therefore they will bypass the adsorbents and will come out first from the column.
This is usually followed by the smaller hydrophobic molecules that usually can’t be bonded onto the matrix and then eluted later. But in case you have a lot of hydrophilic small molecules such as salts, these usually would go through all of the pore structure of the bead because they are very small. But they do not interact with the resin surface because they are hydrophilic, but it will act more like a size exclusion so the smaller the salts are, the longer pathways it will take through the entire bead structure. And therefore it will take a while before these kind of salts come out.
As the presentation mentioned, there are two different adsorbents that Purolite offers, the Macronet® and the PuroSorb™.
Why is there two? Well, they are actually a little bit different in their chemistries. The Macronet® is, you know, while it has a highly porous structure, it also has some microporous structure which means that the Macronet is a stronger bead because as there is a lot of micropores, it increases the strength of the bead and that strength is actually equivalent to some of the ion exchangers in the market.
But because of the microporous structure, it also creates two different porosities, a micropore structure and a macropore structure that are, you can see them very easily when you are doing pore distribution measurements.
On the other hand, the PuroSorb™ has only a wide pore distribution, so the porosity will be much larger so it enables you to remove molecules that are much larger in size.
It is important to note that the Macronet® is the only adsorbent that we offer currently that has the capability of adding functional groups to it, such as weak base anion or strong acid cation. This is mainly in case you want to add some ion exchange in addition to the hydrophobic interaction.
While the PuroSorb™ does not have any ion exchange offering, but it is offered in different structures or polymeric structures such as polystyrenic and polymethacrylate.
So when do you use a polystyrenic and when do you use a polymethacrylate? Well, polystyrenic are hydrophobic and they do adsorb things by hydrophobic interaction. But the polymethacrylate, they’re not typically as hydrophobic as the polystyrenic so the bond is a little bit weaker. This is usually very good if you’re dealing with molecules that are very hydrophobic, that you would like them to really move later on from the adsorbent. Because if it sticks too strongly, you’ll require a much stronger eluent and sometimes it takes too long to get the stuff back off. That’s why the polymethacrylate is offered in this case scenario.
Some of the physical properties to take into consideration is the specific gravity of also these adsorbents. All polystyrenic resins in the market usually have a specific gravity or range from 1.01 to 1.03 so they’re very close to the water specific gravity so a lot of the times, some of the companies do see that the resin is floating, that means the resins need to be conditioned well prior to use so that way it would sink.
On the other hand the polymethacrylate is a little bit heavier, with 1.09 to 1.11, so we do not have that issue with it floating and it would settle very fast. That is why a lot of the time, you can see some of the polymethacrylate adsorbent could be used in expanded bed application, or the flow is coming from the bottom up, but typically you do not see that at all with the polystyrenic matrix because if you’re going up flow, you could lift up the entire bed due to its low specific gravity.
Looking at the structure of the polystyrenic resins, you can see that it has a lot of benzene rings and that is very important because in addition to the hydrophobic interaction that the polystyrenic bead does, it’s also does bonding by pi/pi interaction. While the benzene rings on the resin can also interact with the benzene rings on the target molecule. So that enables you to have a little bit more selectivity when needed.
On the other hand, the polymethacrylate is more aliphatic. It does not have benzene rings, so it could attract better products that are more aliphatic than products that have benzene rings.
And as I mentioned before, we do have two molecules, ion exchange with ion exchange capabilities and those are the Macronet products. Whether it’s a strong cation exchanger or a weak anion, and that usually gives you the additional characteristic of an ion exchange in addition to having the hydrophobic interaction.
So looking at some molecule examples, so you can see the polyphenol and the naringin and you can see that you have benzene rings but you can also see that a lot of hydroxyl groups everywhere. The hydroxyl groups gives it the ability to dissolve in water because it becomes a little more hydrophilic that way, but the benzene ring gives it the hydrophobic interaction that it requires to bond onto the adsorbents. And because it also has benzene rings, it can have the pi/pi interaction to connect with the styrenic resins much better. On the other hand, when you’re looking at the other hydrophobic molecules such as the aliphatic compounds, Vitamin D and Linalool for example, these things you don’t see any benzene rings. A lot of it is a non-polar type of structure, no oxygens anywhere so these look more like oily substances, so it doesn’t mix at all with water. It can usually float, so you would use a different type of solvent to push these things through the resin bed.
In this case scenario, a polymethacrylate based resin is better, because it will interact better with the aliphatic. Also sometimes you can use the polymethacrylate based resin to interact with the hydrogen groups on a target molecule as well as a carbonyl interaction. That’s called hydrogen bonding.
Purolite does offer a lot of different resins. Many different polystyrenic bead resins, a few polymethacrylate and a few ion exchange. So for the polystyrenic base matrix, you can see we can offer the largest selection, and they differ mainly by pore size and pore volumes. So as I mentioned before, pore size is important when you try to remove certain molecular weight compounds based on size. But the pore volume is also important because it measures the volume behind the pores that are large enough to remove large molecular weight compounds. So in this scenario you can see that the Macronet 202 and the Macronet 270 have a small pore volume but much higher surface area so it tells you that there is a lot of micropore structure that gives you that high surface area, but not as much of the macropore structure to give you the large capacity that is required for large molecular weight adsorption. So when you’re dealing with large molecular weights such as peptides and so on, you typically will deal with the PuroSorb™ or our PAD products.
On the other hand, the polymethacrylate, we do offer two as well, and also they differ by the pore volume and the surface area and the pore diameter.
And the last two are the Macronets® that have ion exchange capabilities. So the Macronet 102 is the weak anion so it gives you that weak base exchanger capability in addition to hydrophobic interaction. And then the Macronet® 502 which is the polystyrenic cross-linked also with a strong acid cation to remove things that have amines on it for example. Target molecules that are hydrophobic but also have amines.
So when we talked about porosity like I mentioned before you can see the type of molecules that are capable of being removed. So we have a resin that are PAD1200 as well as PAD400 and 610. These adsorbents have very large pore structure and therefore are usually ideal to remove peptides and colors but as the porosity goes smaller, then you can start extracting smaller molecules as well with a higher capacity because your surface area now is maximized for those types of molecules so in this case scenario, for flavours PAD900 is usually good. For small antibiotics you have the 950 and the 600s. And when you go as small as a volatile organic such as gas, we do have products for those as well.
If your molecule is small enough to get into the pore structure of many of our adsorbents, an example of this is a Cephalosporin C kind of adsorption, you can see that it is a linear increase in capacity based on the surface area. And that’s only if the Cephalosporin can get in to the pore structure. So higher surface area means higher capacity, but again, as long as it can get in.
How do you elute adsorbents? Usually you can elute them by alcohols or other solvents and the main reason of this is you either are decreasing the hydrophobic interaction between the resin and the hydrophobic molecule by weakening the resin.
Sometimes what you can see when you are adding these type of solvents, the resin is swelling and therefore it is taking on more water, therefore by taking on more water it’s becoming less hydrophobic and giving up its load of molecules.
But also the reason why another solvent would work, it also would increase the solubility, that what you have stuck onto the resin, it will increase the solubility into the solvent so it prefers to go back into the solvent rather than stay onto the resin.
On the other hand in caustic and acid use, and there are some companies that actually use that because they can, they want to stay away from alcohols and solvent because of their flammability, and by using caustic and acid usually what you are doing is you’re ionizing the target molecule, therefore it’s becoming more hydrophilic, and less attracted to the adsorbents. But when you use caustic and acid, you end up you have to neutralize the resin.
Some think they can remove your molecules by using salt, you cannot do that. Salt might be useful in ion exchange regeneration but in dealing with an adsorbent, once you add salt you’re actually increasing the hydrophobic interaction between the molecule and the resin. So you’ll stick much stronger onto the resin.
So incase you want to get the stuff off the resin, you have to avoid salt or reduced salt as much as possible.
This is a molecule that usually has both capabilities that can be taken off from the resin by using a solvent as well as by using an acid or base. An example here is Tryptophan, and you can see it does have a benzene ring so you can attract it to a styrenic based matrix. And therefore if you use a solvent such as ethanol, you can actually elute it back off but if you do need to use acid or bases, you can see that if you reduce the pH quite a bit, both of those amine groups will be protonated and they become more hydrophilic areas of that matrix and therefore at that point the Tryptophan becomes much less hydrophobic and can get off the resin.
Most of the applications in the world are using adsorbents. The eluent that’s being used is typically alcohol or acetone, but, in the case for the citrus juice industry, they want to avoid using alcohol and acetone because of its flammability and therefore they design a way of regenerating these types of adsorbent by using a caustic followed by an acid and sometimes they use some peroxide and the main reason for that is that the breakdown the large molecular weight compound that stick as a foulent onto the adsorbent so it breaks it down to smaller molecules and it also adds carboxylic acids on them, therefore when you use the caustic on the next regeneration, they become hydrophilic and let go of the resin.
And the last one is the volatile organics that can be removed by adsorbents as well. In this case scenario, you are not using a solvent for that, but you’re using heat such as low pressure steam to push it back off. The reason why it works, now usually adsorption increases when heat goes up, but also elution increases when the heat goes up. And at a certain temperature, the elution profile is going to be much stronger than the adsorption profile and that’s how steam can work to remove the volatile organic.
But that only can work on very small molecules where the hydrophobicity is not very strong.
When you’re regenerating with solvents, it’s important to know what type of solvent is the best for what use. In this case scenario you can see the strength of an adsorbent is shown by how much it can swell the resin. So the acetone, it has the most amount of swelling when it’s compared for example to the other alcohol chains, and the longer the alcohol chain, the stronger it is as a solvent.
In this graph you can see like a 20% acetone concentration could have the same swelling as a 60% methanol. That means for 20% acetone you could regenerate something that a 60% methanol could have been doing.
You can see that 50% of the swelling cam around that concentration. At the bottom you can see the strength of the different types of solvents. So the acetone was stronger than the propanol and stronger than the ethanol and then methanol.
Caustic wash that’s using the citrus is actually weaker than the methanol. And the steam is one of the weakest.
All of our resins typically we can offer them in smaller particle size but mainly three that we offer in many different smaller particle sizes and they are the PAD600, 900 and 1200. Now why is it important to offer smaller bead resins? Because smaller bead resin can give you the selectivity of the separation. So if you’re using an adsorbent, let’s say you’re removing three molecules and as you’re loading it, then most hydrophobic molecules takes the longest to come off, with the least hydrophobic will be displaced first so it comes out first.
So as the bead gets smaller, you’re going to get the very good peak separations as you can see here.
Chromatography is typically used when you’re dealing with these types of smaller adsorbents and it is best used when the concentration of your molecules are at 5% or higher so that you can take advantage of that separation because smaller bead resins are typically more expensive than the larger bead ones.
How do you store these adsorbents? Most of these adsorbents do not have functional groups. If they did have functional groups, then ion exchange capabilities for example can act like a salt medium for the resin and usually it can store very well.
But if they have no functional group there’s no way to prevent that resin after long storage from mold growth for example.
To avoid that, several solutions can be added into the resin when you’re storing it for long periods of time such as 10% salt, dilute caustic concentration which enables you to get a pH of 12 or 13 as well as 20% alcohol such as ethanol or IPA.
But it is very important to avoid freezing temperatures because what that does, it freezes the moisture inside of the bead, therefore that moisture will expand and break the bead under stress.
A lot of our resins do follow some regulatory requirements. In the United States we do follow the FDA 21CFR so you can see that some of our adsorbents follow the 173.25 which is mostly dedicated towards the ion exchange part of the adsorbents. The 173.65 is more towards the adsorbent, non-functionalized resins.
But there is also another one which is the 177.2710 that’s towards different structures of these types of adsorbents. One thing to mention is that a PAD950 which is a polymethacrylate, we have an opinion letter for that to be used for also in the food industry. So when it doesn’t follow any of these regulations, we usually as Purolite have to acquire such an opinion letter to get it approved for use for that industry.
But all of our adsorbents do follow all the regulations of RESAP, they are all Halal, Kosher, GMO free and we have a TSE/BSE statement that we can offer as well.
Some of the applications for these adsorbents that I will go through are orange debittering, polyphenol extraction, patulin removal, corn sweetener refining and I’ll finish up the presentation with some of the other applications.
In the citrus juice debittering, they want to use these adsorbents is to remove Limonin out of orange or lemon juice or naringin out of the grapefruit juice.
These bitterness are typically in the skin of these fruits because when you’re doing these kinds of processing, you’re throwing the entire fruit and you’re not peeling the skin off.
Since Limonin it has a lot of non-polar structure, Limonin could be removed very well with a PAD950 while the naringin does not have the non-polar structure and it has more of a benzene ring structure, it could be removed with the PAD900 which is the polystyrenic based bead.
But in the industry today some people do still use PAD900 to styrenics to remove Limonin, but it will require a much stronger regeneration because it’s styrenic it will require much more eluent to get these things off.
This industry as I’ve mentioned before does avoid the use of solvents, so they typically use caustic and acid neutralization.
On the polyphenol extraction, which is usually from berry juices, there is two applications in that industry, sometimes it’s the anthocyanin which is the antioxidants that you’re trying to remove. Or sometimes it’s the flavonoids or you know which are related flavors.
You can see the polystyrenic gives you very high capacities and it can remove both very very well. But on the polymethacrylate, you are sacrificing some of the anthocyanins which is usually the polyphenols, but will have a much lower capacities but what it does give you is selectivity which means it is not removing, you know you can separate one from the other much better.
This is one of the reasons why in the citrus industry that using sometimes the polymethacrylate as well because if you have that selectivity, they want to sometimes leave some of the flavors inside of the juice and just remove the bitterness.
And therefore, by using the polymethacrylate, they can sometimes see that selectivity difference and keep most of the flavor inside of the juice.
For patulin, this is usually when the apple sometimes falls down from the tree and it’s picked up from the ground it starts growing some mold. That mold has some patulin ingredients and the World Health Organization saw that there’s some danger for these things and it could be cancerous.
So it had to be removed in a process and there’s many ways to remove patulin out of the apple juice market. Either by using an adsorbent and using alcohol as a regenerate, or using one of our adsorbents that has an ion exchange capability that can be regenerated just by caustic, and the way this ion exchange capability works is because patulin as you can see on one side of it, it can turn to be a carboxylic acid when it hits the adsorbents and as a carboxylic acid it can be removed by anion so you’re using an anion capability adsorbent as an additional benefit.
The Macronets that have the ion exchange capabilities can also be used in the sweetener industry and typically to remove things like taste and odors as well as colors.
And you can do polishing as well depending on what your final compounds need to be or sweetener needs to be.
The other applications in the industry are the adsorption of gases such as volatile organics like I mentioned before or also the removal of pesticide, insecticide and so on from water.
Right now the industry is looking at removing it also from juices, so that could be another way of using these kinds of adsorbents.
And some of the adsorbents can be used to immobilize enzymes so that the enzyme could be used for dozens of cycles rather than just every single cycle therefore reducing the enzymatic application and cost to something that’s affordable in the food industry.
It also could be used as a size exclusion, for example because of the pore structure of the resin, it enables based on the size of the salt, since salt does not interact with the resin it’ll just flow through all the pore structure so based on the size of the salt it can be removed by size.
Finally, one of our largest applications right now for adsorbents is in the pharmaceutical industry where you try to purify antibiotics, peptides and so on.
There is a lot of applications for adsorbents as you can see from this table, this is more of our recommended resins or where you can start.
The more you know about your application, and the more you know about what the competing molecules that exist in that feed, you know other adsorbents could be better suited for the application but this is a way of where to start first to see if it’s feasible.
Thank you very much, this is my presentation. If you have any questions please don’t hesitate to contact Life Sciences at Purolite.com