Heating a Sorbitol Solution to 375F

[oompaloompa]

Hello everyone. I work for a small cooking equipment manufacturer. My background is in Mechanical Engineering so I thought I might ask you guys over here for some help. We have a customer wishing to heat a 70% Sorbitol solution(sugar substitute) to a temperature of 375 degrees F. Our largest cooker is cylindrical in shape, double-walled with exhaust near the top, product open to atmosphere, and has gas burners underneath capable of putting out 520,000 Btu/hr. We recently tested our unit with 110 gallons of Sorbitol in attempt to heat this product to the desired temp. We found the product temperature hovered around 220 degrees F for more than a few hours. We suspect that the water in the solution had to boil off before the product could reach the higher temps. We need to speed up this process, without pressurizing the unit. Our guess is that we need more surface area in the tank. Is this correct? If so, what type of physical features would you suggest we add to the tank i.e., fins, tubes, etc.

Thanks in advance for the help.

Michael

 

[StoneCold]

Oompaloompa
There are a couple of things you should consider before you keep going on this. Do you know the normal boiling point of Sorbitol? Do you know the flash point of Sorbitol?
Do you know the LEL of Sorbitol?
Do you have DSC on this material to make sure it is stable in air at 375F.

You should make sure you are not vaporizing a flammable amount of Sorbitol in the room, especially with a fired heater in there. All that being said you probably need agitation in the vessel to get to the 375F. But you should do this in a beaker before you get carried away and try it on a large scale.

Regards.

StoneCold

 

[Montemayor]

Mike:

Stonecold has raised some strong points regarding your basic data that have to be addressed for the sake of safety and viability of the test(s).

If you have a 70% (weight) water solution of Sorbitol you may not be able to heat it up to the required 375 oF. The properties of pure Sorbitol are:

Boiling point = 565 oF (at atmospheric pressure)
Freezing point = 205 oF (at atmospheric pressure)

But the above properties are of the PURE substance. What you need is the boiling point (at atmospheric pressure) of the 70% (weight) water solution. You will probably find out that this solution will boil at a much lower temperature than 375 oF. The reason I dare to guess that is because, as you state, you have spent more than a few hours at 220 oF. That tells me that all you have been doing at 220 oF is boiling off a lot of water vapor and, as a result, creating a stronger, concentrated solution of Sorbitol – which does not comply with your defined scope of work (bringing a 70% (weight) water solution up to 375 oF at atmospheric pressure). I strongly suspect that you will find that the only way you are going to be able to reach 375 oF with a 70% (weight) water solution is to do it under pressure. What the resultant pressure will be depends on the solubility characteristics of the Sorbitol.

If you persist and keep on heating the Sorbitol until you achieve 375 oF at atmospheric pressure, I am sure that you will find that the Sorbitol concentration at that point will be greater than 70% by weight – which nullifies your attempt. And this will happen no matter how “fast” you speed up the heating process or if you increase the heating area, add fins, tubes, etc.

I suspect that you may not have any of the safety issues and concerns that Stonecold points out, but I certainly would follow Stone’s recommendations and establish or identify these points as either benign or not applicable.

Has your client ever heated a 70% solution to 375 oF at atmospheric pressure?

 

[oompaloompa]

Thank you both for the quick responses.

We do have the MSDS for Sorbitol. I did note the flash point, which for pure Sorbitol is around 1100F, if I recall correctly. The boiling point for the solution, however, is 220F.

I'm trying to get a grasp on the chemistry of what is going on with the water. Is the temperature of the product staying at 220F until all the water is evaporated? If that is the case, I agree that the SOLUTION must be under pressure in order to reach the 375.

Our machine does have an agitator, but we didn't run it during the test. The flame below is shrouded, and the heat circulates inside the jacket of the cylinder, and exhausts out the side, near the top. Fresh air is brought in to the burner near the floor.

My customer claims to be carrying this process out on his own equipment, a simple open-flame stove, but on 1/3 the scale let's say. He is cooking approx 30 gallons in an open container, under open flame. He says it is more efficient (time-wise) for him to do this, than us heat our large batch.

I am of the opinion that he is cooking off the water, and being left with a pure solution. Whether he is aware of this or not is unknown to me at this point. A lot of our customers claim ignorance in dealing with equipment manufacturers like us because they wish to keep their processes secret.

With that said, if it turns out he needs PURE Sorbitol at 375F, is there a faster way to boil off the water assuming we keep the BTU's the same?

Thanks again.

Michael