diy thermometer sensitivity

[John Larkin]

On Wed, 12 Jun 2013 09:18:19 +1000, "David Eather" <eather@tpg.com.au> wrote:

On Tue, 11 Jun 2013 03:28:29 +1000, <mrdarrett@gmail.com> wrote:

I have a need to measure temperature accurately from 78.0 C to 79.0 C
(eventually I'll need to turn on a solenoid valve for cooling water at
79 C and turn it off at 78 C).

I saw this on the web:
http://playground.arduino.cc/ComponentLib/Thermistor

and I happen to have an Arduino on me. I read about how a 2N3904 can
function as a temperature sensor if you tie the base and collector
together, so I did that instead of placing an order and waiting for a
thermistor to arrive.

A friend said to put the 10k resistor on the +5V line, then have the
transistor below that, then tie the emitter to ground. Did that. A
wire goes from the B-C-resistor junction to the ADC input on the Arduino.

It works. The serial port monitor tells me that for ice water, the
10-bit ADC value is 141. Boiling water from the microwave gives me 105.
Room temperature at 23 C gave me 132.

I made a best-fit line with my OpenOffice spreadsheet and had the
Arduino calculate the temperature. But now the sensitivity seems to
only be 3 degrees. Temperature will jump even on gradual heating by 3
degrees.

I would like to expand the range from 105 to 141 somewhat (10 bits
should get me 0 to 1023, right?)

I tried substituting 500 ohms for the 10k resistor (5V/500 ohms = 10 mA,
should be ok) but still didn't get much improvement in sensitivity.

Any suggestions?

Thanks!

Michael

Use a DS18B20 => digital output and .25 degree C accuracy out of the box
(if you buy genuine from someone like newark, mouser or element 14)

LM71 is nice, too.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

 

On Tuesday, June 11, 2013 9:24:24 PM UTC-7, John Larkin wrote:

....

A follow-up silly question... is the temperature-sensing transistor R2?



Thanks for the circuit John!



Michael



The sensor is the transistor itself, the Vbe junction drop multiplied by

1+R2/R3. All the resistors are ordinary resistors.



If 1+R2/R3 is 5, the collector voltage will be roughly 3 volts at 80C, dropping

about 12 or so millivolts per degree C, 5 times the usual Vbe change with

temperature.



Cute, but a tacky way to measure temperature.

It is cute! Thanks!

If you think that is tacky, you'd laugh at what I'm using the temperature sensor for.

Michael

 

On Tuesday, June 11, 2013 9:24:24 PM UTC-7, John Larkin wrote:

On Tue, 11 Jun 2013 09:10:26 -0700 (PDT), mrdarrett@gmail.com wrote:



On Tuesday, June 11, 2013 6:31:04 AM UTC-7, George Herold wrote:



...



You're only using a fraction of the ADC range.







A Vbe multiplier would help.







+5-----R1-------+------+--- to ADC



                |      |



                |      |



               R2      |



                |      C



                +----B



                |      E



                |      |



               R3      |



                |      |



                |      |



               gnd    gnd







The collector voltage will be about 0.6 * (1 + R2/R3) which can be



scaled up to, say, 3 volts at 80C.







You can Spice this. R1 might be, say, 5K and R3 maybe 10K.







I'd put a capacitor across R3 so the transistor doesn't rectify stray



RF.







As noted, signal average to remove ADC noise.







Umm, a silly question. Is this to 'gain-up' the transistor Vbe



voltage with transistor as temp sensor? Or to 'gain-up' a thermistor



stuck in as R2?







I was first thinking the later... but then changed my mind.







George H.





A follow-up silly question... is the temperature-sensing transistor R2?



Thanks for the circuit John!



Michael



The sensor is the transistor itself, the Vbe junction drop multiplied by

1+R2/R3. All the resistors are ordinary resistors.



If 1+R2/R3 is 5, the collector voltage will be roughly 3 volts at 80C, dropping

about 12 or so millivolts per degree C, 5 times the usual Vbe change with

temperature.



Cute, but a tacky way to measure temperature.

Pretty cool (pun intended.)

Voltage decreases as the temperature increases. I used a 50k resistor for R2. I'm getting around 700 out of 1024 on the ADC at room temperature, and temperature dropped as I put my fingers on it. Calibration time...

Must R3 be 2x R1, or does R1 provide all the current protection I need? Since I choose R2/R3 = 5, would 100 ohms for R3 and 470 ohms for R2 be fine?

Thanks again!

M

 

On Monday, June 10, 2013 5:29:26 PM UTC-7, John Larkin wrote:

On Mon, 10 Jun 2013 10:28:29 -0700 (PDT), mrdarrett@gmail.com wrote:



I have a need to measure temperature accurately from 78.0 C to 79.0 C (eventually I'll need to turn on a solenoid valve for cooling water at 79 C and turn it off at 78 C).



I saw this on the web:

http://playground.arduino.cc/ComponentLib/Thermistor



and I happen to have an Arduino on me. I read about how a 2N3904 can function as a temperature sensor if you tie the base and collector together, so I did that instead of placing an order and waiting for a thermistor to arrive.



A friend said to put the 10k resistor on the +5V line, then have the transistor below that, then tie the emitter to ground. Did that. A wire goes from the B-C-resistor junction to the ADC input on the Arduino.



It works. The serial port monitor tells me that for ice water, the 10-bit ADC value is 141. Boiling water from the microwave gives me 105. Room temperature at 23 C gave me 132.



You're only using a fraction of the ADC range.



A Vbe multiplier would help.



+5-----R1-------+------+--- to ADC

| |

| |

R2 |

| C

+----B

| E

| |

R3 |

| |

| |

gnd gnd



The collector voltage will be about 0.6 * (1 + R2/R3) which can be

scaled up to, say, 3 volts at 80C.



You can Spice this. R1 might be, say, 5K and R3 maybe 10K.



I'd put a capacitor across R3 so the transistor doesn't rectify stray

RF.



As noted, signal average to remove ADC noise.

What kind of capacitor in parallel with R3?

So far after calibration I'm getting:

750 = 1 C
709 = 25.5 C
340 = 91 C

....although I do notice the numbers jump around quite a bit more. Probably need that cap.

Very nice! Thank you!

M

 

[David Eather]

On Wed, 12 Jun 2013 14:25:22 +1000, John Larkin
<jjlarkin@highnotlandthistechnologypart.com> wrote:

On Wed, 12 Jun 2013 09:18:19 +1000, "David Eather" <eather@tpg.com.au
wrote:

On Tue, 11 Jun 2013 03:28:29 +1000, <mrdarrett@gmail.com> wrote:

I have a need to measure temperature accurately from 78.0 C to 79.0 C
(eventually I'll need to turn on a solenoid valve for cooling water at
79 C and turn it off at 78 C).

I saw this on the web:
http://playground.arduino.cc/ComponentLib/Thermistor

and I happen to have an Arduino on me. I read about how a 2N3904 can
function as a temperature sensor if you tie the base and collector
together, so I did that instead of placing an order and waiting for a
thermistor to arrive.

A friend said to put the 10k resistor on the +5V line, then have the
transistor below that, then tie the emitter to ground. Did that. A
wire goes from the B-C-resistor junction to the ADC input on the
Arduino.

It works. The serial port monitor tells me that for ice water, the
10-bit ADC value is 141. Boiling water from the microwave gives me 105.
Room temperature at 23 C gave me 132.

I made a best-fit line with my OpenOffice spreadsheet and had the
Arduino calculate the temperature. But now the sensitivity seems to
only be 3 degrees. Temperature will jump even on gradual heating by 3
degrees.

I would like to expand the range from 105 to 141 somewhat (10 bits
should get me 0 to 1023, right?)

I tried substituting 500 ohms for the 10k resistor (5V/500 ohms = 10
mA,
should be ok) but still didn't get much improvement in sensitivity.

Any suggestions?

Thanks!

Michael

Use a DS18B20 => digital output and .25 degree C accuracy out of the box
(if you buy genuine from someone like newark, mouser or element 14)

LM71 is nice, too.

+/- 1.5 degrees accuracy - he is trying to control to within 1 degree
(it almost sounds like he is trying to separate methanol from ethanol)

 

[John Larkin]

On Tue, 11 Jun 2013 22:55:40 -0700 (PDT), mrdarrett@gmail.com wrote:

On Tuesday, June 11, 2013 9:24:24 PM UTC-7, John Larkin wrote:
On Tue, 11 Jun 2013 09:10:26 -0700 (PDT), mrdarrett@gmail.com wrote:



On Tuesday, June 11, 2013 6:31:04 AM UTC-7, George Herold wrote:



...



You're only using a fraction of the ADC range.







A Vbe multiplier would help.







+5-----R1-------+------+--- to ADC



                |      |



                |      |



               R2      |



                |      C



                +----B



                |      E



                |      |



               R3      |



                |      |



                |      |



               gnd    gnd







The collector voltage will be about 0.6 * (1 + R2/R3) which can be



scaled up to, say, 3 volts at 80C.







You can Spice this. R1 might be, say, 5K and R3 maybe 10K.







I'd put a capacitor across R3 so the transistor doesn't rectify stray



RF.







As noted, signal average to remove ADC noise.







Umm, a silly question. Is this to 'gain-up' the transistor Vbe



voltage with transistor as temp sensor? Or to 'gain-up' a thermistor



stuck in as R2?







I was first thinking the later... but then changed my mind.







George H.





A follow-up silly question... is the temperature-sensing transistor R2?



Thanks for the circuit John!



Michael



The sensor is the transistor itself, the Vbe junction drop multiplied by

1+R2/R3. All the resistors are ordinary resistors.



If 1+R2/R3 is 5, the collector voltage will be roughly 3 volts at 80C, dropping

about 12 or so millivolts per degree C, 5 times the usual Vbe change with

temperature.



Cute, but a tacky way to measure temperature.


Pretty cool (pun intended.)

Voltage decreases as the temperature increases. I used a 50k resistor for R2. I'm getting around 700 out of 1024 on the ADC at room temperature, and temperature dropped as I put my fingers on it. Calibration time...

Must R3 be 2x R1, or does R1 provide all the current protection I need? Since I choose R2/R3 = 5, would 100 ohms for R3 and 470 ohms for R2 be fine?

Thanks again!

M

There are a few constraints.

You need R1 to be low enough to pull the collector voltage up. It's fighting the
collector current and the current in R2. If R1 is too low, you'll get a lot of
current in Q1 and it will self-heat. Something like 1 mA in R1 is reasonable, so
it might be 2K, assuming +5 on one end and +3 on the other.

R2 and R3 should be low enough that transistor beta doesn't matter much, but you
can't steal too much current from R1. Go for 250 uA in R2 maybe. With beta=100,
1 mA in the colletor, base current will be 10 uA, so that doesn't load R2||R3
much. I'm thinking 2K or 3K for R3.

You're gonna calibrate it anyhow, so a little base current error or a little
self-heating don't matter.

This all assumes a fairly narrow operating temp range, which is your case.

I told you it was tacky.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

 

[John Larkin]

On Tue, 11 Jun 2013 23:07:12 -0700 (PDT), mrdarrett@gmail.com wrote:

On Monday, June 10, 2013 5:29:26 PM UTC-7, John Larkin wrote:
On Mon, 10 Jun 2013 10:28:29 -0700 (PDT), mrdarrett@gmail.com wrote:



I have a need to measure temperature accurately from 78.0 C to 79.0 C (eventually I'll need to turn on a solenoid valve for cooling water at 79 C and turn it off at 78 C).



I saw this on the web:

http://playground.arduino.cc/ComponentLib/Thermistor



and I happen to have an Arduino on me. I read about how a 2N3904 can function as a temperature sensor if you tie the base and collector together, so I did that instead of placing an order and waiting for a thermistor to arrive.



A friend said to put the 10k resistor on the +5V line, then have the transistor below that, then tie the emitter to ground. Did that. A wire goes from the B-C-resistor junction to the ADC input on the Arduino.



It works. The serial port monitor tells me that for ice water, the 10-bit ADC value is 141. Boiling water from the microwave gives me 105. Room temperature at 23 C gave me 132.



You're only using a fraction of the ADC range.



A Vbe multiplier would help.



+5-----R1-------+------+--- to ADC

| |

| |

R2 |

| C

+----B

| E

| |

R3 |

| |

| |

gnd gnd



The collector voltage will be about 0.6 * (1 + R2/R3) which can be

scaled up to, say, 3 volts at 80C.



You can Spice this. R1 might be, say, 5K and R3 maybe 10K.



I'd put a capacitor across R3 so the transistor doesn't rectify stray

RF.



As noted, signal average to remove ADC noise.


What kind of capacitor in parallel with R3?

Ceramic, roughly 0.1 uF, doesn't matter much.

So far after calibration I'm getting:

750 = 1 C
709 = 25.5 C
340 = 91 C

...although I do notice the numbers jump around quite a bit more. Probably need that cap.

Very nice! Thank you!

You could software filter to smooth the noise out.

Average blocks of, say, 100 samples. Or make a continuous lowpass filter,

OUT = OUT + (IN - OUT) * K (in floats)

where K is small, like 0.01. In integer math, you can do an arithmetic
right-shift to approximate the multiply. >>7 is like multiplying by 1/128.


--

John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

 

On Wednesday, June 12, 2013 5:49:15 AM UTC-7, David Eather wrote:

On Wed, 12 Jun 2013 14:25:22 +1000, John Larkin

jjlarkin@highnotlandthistechnologypart.com> wrote:



On Wed, 12 Jun 2013 09:18:19 +1000, "David Eather" <eather@tpg.com.au

wrote:



On Tue, 11 Jun 2013 03:28:29 +1000, <mrdarrett@gmail.com> wrote:



I have a need to measure temperature accurately from 78.0 C to 79.0 C

(eventually I'll need to turn on a solenoid valve for cooling water at

79 C and turn it off at 78 C).



I saw this on the web:

http://playground.arduino.cc/ComponentLib/Thermistor



and I happen to have an Arduino on me. I read about how a 2N3904 can

function as a temperature sensor if you tie the base and collector

together, so I did that instead of placing an order and waiting for a

thermistor to arrive.



A friend said to put the 10k resistor on the +5V line, then have the

transistor below that, then tie the emitter to ground. Did that. A

wire goes from the B-C-resistor junction to the ADC input on the

Arduino.



It works. The serial port monitor tells me that for ice water, the

10-bit ADC value is 141. Boiling water from the microwave gives me 105.

Room temperature at 23 C gave me 132.



I made a best-fit line with my OpenOffice spreadsheet and had the

Arduino calculate the temperature. But now the sensitivity seems to

only be 3 degrees. Temperature will jump even on gradual heating by 3

degrees.



I would like to expand the range from 105 to 141 somewhat (10 bits

should get me 0 to 1023, right?)



I tried substituting 500 ohms for the 10k resistor (5V/500 ohms = 10

mA,

should be ok) but still didn't get much improvement in sensitivity.



Any suggestions?



Thanks!



Michael



Use a DS18B20 => digital output and .25 degree C accuracy out of the box

(if you buy genuine from someone like newark, mouser or element 14)



LM71 is nice, too.



+/- 1.5 degrees accuracy - he is trying to control to within 1 degree

(it almost sounds like he is trying to separate methanol from ethanol)

Your guess is pretty darned close

Michael

 

[George Herold]

On Jun 12, 11:15 am, mrdarr...@gmail.com wrote:

On Wednesday, June 12, 2013 5:49:15 AM UTC-7, David Eather wrote:
On Wed, 12 Jun 2013 14:25:22 +1000, John Larkin

jjlar...@highnotlandthistechnologypart.com> wrote:

On Wed, 12 Jun 2013 09:18:19 +1000, "David Eather" <eat...@tpg.com.au

wrote:

On Tue, 11 Jun 2013 03:28:29 +1000, <mrdarr...@gmail.com> wrote:

I have a need to measure temperature accurately from 78.0 C to 79.0 C

(eventually I'll need to turn on a solenoid valve for cooling water at

79 C and turn it off at 78 C).

I saw this on the web:

http://playground.arduino.cc/ComponentLib/Thermistor

and I happen to have an Arduino on me.  I read about how a 2N3904 can

function as a temperature sensor if you tie the base and collector

together, so I did that instead of placing an order and waiting for a

thermistor to arrive.

A friend said to put the 10k resistor on the +5V line, then have the

transistor below that, then tie the emitter to ground.  Did that.  A

wire goes from the B-C-resistor junction to the ADC input on the

Arduino.

It works.  The serial port monitor tells me that for ice water, the

10-bit ADC value is 141. Boiling water from the microwave gives me 105.

Room temperature at 23 C gave me 132.

I made a best-fit line with my OpenOffice spreadsheet and had the

Arduino calculate the temperature.  But now the sensitivity seems to

only be 3 degrees.  Temperature will jump even on gradual heating by 3

degrees.

I would like to expand the range from 105 to 141 somewhat (10 bits

should get me 0 to 1023, right?)

I tried substituting 500 ohms for the 10k resistor (5V/500 ohms = 10

mA,

should be ok) but still didn't get much improvement in sensitivity.

Any suggestions?

Thanks!

Michael

Use a DS18B20 => digital output and .25 degree C accuracy out of the box

(if you buy genuine from someone like newark, mouser or element 14)

LM71 is nice, too.

+/- 1.5 degrees accuracy - he is trying to control to within 1 degree

(it almost sounds like he is trying to separate methanol from ethanol)

Your guess is pretty darned close

Michael- Hide quoted text -

- Show quoted text -

Oh, Are you distilling ethanol from water?

http://en.wikipedia.org/wiki/Ethanol#Charts
http://en.wikipedia.org/wiki/File:Vapor-Liquid_Equilibrium_Mixture_of_Ethanol_and_Water.png
(What the bleep is an Azeotropic point?)

I assume this graph moves around with external pressure.

George H.

 

[Jon Kirwan]

On Wed, 12 Jun 2013 13:25:41 -0700 (PDT), mrdarrett@gmail.com
wrote:

http://homedistiller.org/calcs/calc
snip
At 78.15 degrees you see the azeotrope (liquid and vapor
have the exact same composition, 0.9558, or 95.58% ethanol).
That is my target.

I note that even at 78.24C on your web link that the vapour
fraction has dropped 5% already. I'd almost wonder if there
is a vapour sensor system you could arrange to measure in
situ and use this as feedback in closed loop control.

It seems almost easier that way, because you are talking here
about significant differences with only tens of milliKelvins
accuracy (not precision) differences. And, as already
suggested, even if you have a well calibrated temperature
measurement and the sensor(s) is(are) placed optimally, you
may also need atmospheric pressure and relative humidity
figures in there, as well. And tables to use in controlling
things. Or else you control those factors, too.

Thanks for the posts, by the way. I am not a chemist and I
had only vague notions of how difficult this distillation
process might be. I now have a much better appreciation for
it.

Jon

 

[Jon Kirwan]

On Wed, 12 Jun 2013 14:42:06 -0700, I wrote:

On Wed, 12 Jun 2013 13:25:41 -0700 (PDT), mrdarrett@gmail.com
wrote:
http://homedistiller.org/calcs/calc
snip
At 78.15 degrees you see the azeotrope (liquid and vapor
have the exact same composition, 0.9558, or 95.58% ethanol).
That is my target.

I note that even at 78.24C on your web link that the vapour
fraction has dropped 5% already. I'd almost wonder if there
is a vapour sensor system you could arrange to measure in
situ and use this as feedback in closed loop control.

It seems almost easier that way, because you are talking here
about significant differences with only tens of milliKelvins
accuracy (not precision) differences. And, as already
suggested, even if you have a well calibrated temperature
measurement and the sensor(s) is(are) placed optimally, you
may also need atmospheric pressure and relative humidity
figures in there, as well. And tables to use in controlling
things. Or else you control those factors, too.

Thanks for the posts, by the way. I am not a chemist and I
had only vague notions of how difficult this distillation
process might be. I now have a much better appreciation for
it.

I should have added that I actually have a fiber optic sensor
system (uses phosphors for sensing temperature) that can work
well with fibers down to 10 microns in diameter (low mass)
and has a repeatable precision across instruments and sensors
of about 5 milliKelvins in the temperature range you are
discussing. (single sigma.) The accuracy, of course, is a
matter of calibration points, accuracies, and the software
and theory used to interpolate intermediary table values.

Jon

 

On Wednesday, June 12, 2013 12:36:25 PM UTC-7, George Herold wrote:

....

LM71 is nice, too.



+/- 1.5 degrees accuracy - he is trying to control to within 1 degree



(it almost sounds like he is trying to separate methanol from ethanol)



Your guess is pretty darned close



Michael- Hide quoted text -



- Show quoted text -



Oh, Are you distilling ethanol from water?

Haha, I plead the Fifth. The closer I can get to the 95% EtOH-H2O azeotrope at around 78 degrees (seems like the exact number depends on which source you read 78.2? 78.3? 78.5? I give up), the better. If I completely lose control and allow it to get as high as 95 degrees, my column simplifies to a single-stage (allowing way too much water in the distillate) and that completely defeats the purpose of having a column.

They never told us how important temperature control was when I was taking the Mass Transfer (eh, Diffusion Theory) class in college.

I tried manually controlling temperature with my sprinkler valve... uhoh, my thermometer reads 85 degrees... FULL OPEN! Whoops, too much cold feed, now my heating element has stopped boiling and temperature plunges below 78.... waiting for the boiler to boil again... drives ya nuts after awhile.

Thanks,

Michael

 

On Wednesday, June 12, 2013 12:36:25 PM UTC-7, George Herold wrote:

....

(What the bleep is an Azeotropic point?)

Oh, I didn't notice that question.

Glad you asked!

Consider a mixture of 96% alcohol and 4% water. You try to distill it. You collect the cooled-down distillate vapors. The composition is... 96% alcohol and 4% water. Distillation did nothing to separate the two.

http://en.wikipedia.org/wiki/Azeotrope

"A well-known example of a positive azeotrope is 95.63% ethanol and 4.37% water (by weight).[4] Ethanol boils at 78.4 °C, water boils at 100 °C, but the azeotrope boils at 78.2 °C, which is lower than either of its constituents.[5] Indeed 78.2 °C is the minimum temperature at which any ethanol/water solution can boil at atmospheric pressure."

You can separate the water out by passing it through a dessicating agent, like ANHYDROUS magnesium sulfate.

 

On Wednesday, June 12, 2013 12:36:25 PM UTC-7, George Herold wrote:

....

http://en.wikipedia.org/wiki/Ethanol#Charts

http://en.wikipedia.org/wiki/File:Vapor-Liquid_Equilibrium_Mixture_of_Ethanol_and_Water.png

(What the bleep is an Azeotropic point?)



I assume this graph moves around with external pressure.



George H.

Yeah the charts are pretty. The tables from Perry's Chemical Engineering Handbook are probably more useful in this context, however.

http://homedistiller.org/calcs/calc

Go down to "Equilibrium Data", Mass Fraction (g/g), and Vapour .

At 78.15 degrees you see the azeotrope (liquid and vapor have the exact same composition, 0.9558, or 95.58% ethanol). That is my target.

As temperature rises a bit you see the vapor fraction of ethanol drops. Even just at 79.8 degrees, less than 2 degrees above 78.15, the ethanol composition has dropped to 83%. So the dessicant step later on has to work that much harder to make that ethanol dry. (Trying to make a fuel here, not planning to drink it.) As temperature rises to 95.5 degrees, well, you basically just made a single-stage distiller. A beer mix will distill at around 95 degrees. It's about 5% ethanol. The vapor will be 34% ethanol or so, not quite concentrated enough to catch fire with a match.

 

[Jon Kirwan]

On Wed, 12 Jun 2013 15:27:23 -0700 (PDT), mrdarrett@gmail.com
wrote:

snip
Yup, there are many possibilities. When I was taking the
Thermo classes I noticed all the data were at the
atmospheric boiling points, and wondered what the
compositions of the distillate would be if you simply
allowed the material to evaporate at *room temperature* and
collected the vapors (sitting in an ice bath). Then when I
took the Mass Transfer classes I realized it would take a
*really long time* waiting for it to all evaporate, and
moved on.

Really neat stuff if you mix Electrical Engineering folks
with Chemical Engineering folks!

Here's a pretty good overview of using distillation columns
on ethanol.

http://www.demec.ufmg.br/disciplinas/eng032-BL/distillation.pdf

Note the 14 or so stair-steps on Page 278. Each one of
those steps represents a "stage" in the column. Or, it
would be the equivalent of doing a bench-scale distillation
14 times. (That's why a column is preferred; to save
energy.)

Michael

Thanks for the link. It was EXACTLY what I was looking for.
And I had already figured out, from walking through your
earlier table, that it would take maybe 10 steps to get to
95%, which I can buy as white lightening or everclear at the
store. I was beginning to wonder if mass manufacturing had
figured out something else that was less troublesome. Then
you gave me this. So the answer is 'no, they actually do it
that way and there is no shortcut.' 14 steps makes sense to
me.

I've known since high school that anything more than 95% is
very hard to keep around any length of time. If you so much
as open the bottle much, it "sucks" water out of the air and
dillutes. It also makes me understand the cost differences
between USP and CP.

Thanks, again. Very informative stuff about a common subject
most of us ill-appreciate.

Jon

 

[Jon Kirwan]

On Wed, 12 Jun 2013 16:16:06 -0700 (PDT), mrdarrett@gmail.com
wrote:

On Wednesday, June 12, 2013 3:59:18 PM UTC-7, Jon Kirwan wrote:

snip
Thanks, again. Very informative stuff about a common subject
most of us ill-appreciate.
Jon

You're welcome! I'm glad you have an interest in the subject!

I do. My wife actually wants me to be able to provide
tincture alcohol (95%) for the preparations we make for our
daughter's grand mal seizure control in the case of the
"apocalypse" (break down of general access to common
supplies.) [No, I'm not so worried. But if it comforts her to
know we can do it, then I don't mind demonstrating a
capability.]

The stuff you get at the hardware store... it might be made
from fermentation, or it might be made from petroleum. If
petroleum, it is probably made from hydration of ethylene
gas.

It's from the liquor store. Oregon as a state managed system.
We use it for tinctures (extraction solvent.)

http://www.chemguide.co.uk/physical/catalysis/hydrate.html

Now that you mention it... there was a guy who recently
invented a really cool membrane that would allow water to
"evaporate" from an ethanol-water mixture, but keep the
ethanol trapped in.

http://www.bbc.co.uk/news/science-environment-16747208
http://www.rsc.org/chemistryworld/News/2012/January/graphene-oxide-membrane.asp

Not sure if it broke the 96% azeotrope. Either way, it's
not like I can get my hands on that membrane, so I'm stuck
trying to make ethanol from kitchen scraps. =)

Regards,

Michael

Crap. Even MORE to learn about!! And yes, I'd be in a similar
boat as you.

Thanks again!

Jon

 

On Wednesday, June 12, 2013 2:42:06 PM UTC-7, Jon Kirwan wrote:

On Wed, 12 Jun 2013 13:25:41 -0700 (PDT), mrdarrett@gmail.com

wrote:

http://homedistiller.org/calcs/calc

snip

At 78.15 degrees you see the azeotrope (liquid and vapor

have the exact same composition, 0.9558, or 95.58% ethanol).

That is my target.



I note that even at 78.24C on your web link that the vapour

fraction has dropped 5% already. I'd almost wonder if there

is a vapour sensor system you could arrange to measure in

situ and use this as feedback in closed loop control.



It seems almost easier that way, because you are talking here

about significant differences with only tens of milliKelvins

accuracy (not precision) differences. And, as already

suggested, even if you have a well calibrated temperature

measurement and the sensor(s) is(are) placed optimally, you

may also need atmospheric pressure and relative humidity

figures in there, as well. And tables to use in controlling

things. Or else you control those factors, too.



Thanks for the posts, by the way. I am not a chemist and I

had only vague notions of how difficult this distillation

process might be. I now have a much better appreciation for

it.



Jon

Yup, there are many possibilities. When I was taking the Thermo classes I noticed all the data were at the atmospheric boiling points, and wondered what the compositions of the distillate would be if you simply allowed the material to evaporate at *room temperature* and collected the vapors (sitting in an ice bath). Then when I took the Mass Transfer classes I realized it would take a *really long time* waiting for it to all evaporate, and moved on.

Really neat stuff if you mix Electrical Engineering folks with Chemical Engineering folks!

Here's a pretty good overview of using distillation columns on ethanol.

http://www.demec.ufmg.br/disciplinas/eng032-BL/distillation.pdf

Note the 14 or so stair-steps on Page 278. Each one of those steps represents a "stage" in the column. Or, it would be the equivalent of doing a bench-scale distillation 14 times. (That's why a column is preferred; to save energy.)

Michael

 

On Wednesday, June 12, 2013 3:59:18 PM UTC-7, Jon Kirwan wrote:

....

Thanks for the link. It was EXACTLY what I was looking for.

And I had already figured out, from walking through your

earlier table, that it would take maybe 10 steps to get to

95%, which I can buy as white lightening or everclear at the

store. I was beginning to wonder if mass manufacturing had

figured out something else that was less troublesome. Then

you gave me this. So the answer is 'no, they actually do it

that way and there is no shortcut.' 14 steps makes sense to

me.



I've known since high school that anything more than 95% is

very hard to keep around any length of time. If you so much

as open the bottle much, it "sucks" water out of the air and

dillutes. It also makes me understand the cost differences

between USP and CP.



Thanks, again. Very informative stuff about a common subject

most of us ill-appreciate.



Jon

You're welcome! I'm glad you have an interest in the subject!

The stuff you get at the hardware store... it might be made from fermentation, or it might be made from petroleum. If petroleum, it is probably made from hydration of ethylene gas.

http://www.chemguide.co.uk/physical/catalysis/hydrate.html

Now that you mention it... there was a guy who recently invented a really cool membrane that would allow water to "evaporate" from an ethanol-water mixture, but keep the ethanol trapped in.

http://www.bbc.co.uk/news/science-environment-16747208
http://www.rsc.org/chemistryworld/News/2012/January/graphene-oxide-membrane.asp

Not sure if it broke the 96% azeotrope. Either way, it's not like I can get my hands on that membrane, so I'm stuck trying to make ethanol from kitchen scraps. =)

Regards,

Michael

 

On Wednesday, June 12, 2013 4:23:55 PM UTC-7, Jon Kirwan wrote:

....

You're welcome! I'm glad you have an interest in the subject!



I do. My wife actually wants me to be able to provide

tincture alcohol (95%) for the preparations we make for our

daughter's grand mal seizure control in the case of the

"apocalypse" (break down of general access to common

supplies.) [No, I'm not so worried. But if it comforts her to

know we can do it, then I don't mind demonstrating a

capability.]

Oh... if it for human consumption, be VERY careful. Typical yeast fermentation produces byproducts in small amounts: methanol (causes blindness and death), and "fusel oils" such as butanol (which make excellent vehicle fuels by the way - better than ethanol). If I understand it correctly, the folks who make vodka, etc. know from experience to discard a certain amount of the first distillate liquid, which contain these. And they use batch stills... if you see "triple distilled" then you guessed it, they distilled the liquid three times...

A homemade continuous column would NOT remove the methanol and fusel oils, so be very careful.

How much do you need? Might be more efficient to stock up now before the apocalypse. (Which could be anything... giant earthquake in Seattle... some geologists think that could happen... Yellowstone blowing up... North Korea getting lucky...)

The stuff you get at the hardware store... it might be made

from fermentation, or it might be made from petroleum. If

petroleum, it is probably made from hydration of ethylene

gas.



It's from the liquor store. Oregon as a state managed system.

We use it for tinctures (extraction solvent.)



http://www.chemguide.co.uk/physical/catalysis/hydrate.html



Now that you mention it... there was a guy who recently

invented a really cool membrane that would allow water to

"evaporate" from an ethanol-water mixture, but keep the

ethanol trapped in.



http://www.bbc.co.uk/news/science-environment-16747208

http://www.rsc.org/chemistryworld/News/2012/January/graphene-oxide-membrane.asp



Not sure if it broke the 96% azeotrope. Either way, it's

not like I can get my hands on that membrane, so I'm stuck

trying to make ethanol from kitchen scraps. =)



Regards,



Michael



Crap. Even MORE to learn about!! And yes, I'd be in a similar

boat as you.

Yup, don't you have it when scientific progress advances faster than we can read.

Thanks again!



Jon

=)

Michael

 

[George Herold]

On Jun 12, 4:25 pm, mrdarr...@gmail.com wrote:

On Wednesday, June 12, 2013 12:36:25 PM UTC-7, George Herold wrote:

...

http://en.wikipedia.org/wiki/Ethanol#Charts

http://en.wikipedia.org/wiki/File:Vapor-Liquid_Equilibrium_Mixture_of...

(What the bleep is an Azeotropic point?)

I assume this graph moves around with external pressure.

George H.

Yeah the charts are pretty.  The tables from Perry's Chemical Engineering Handbook are probably more useful in this context, however.

http://homedistiller.org/calcs/calc

Go down to "Equilibrium Data", Mass Fraction (g/g), and Vapour .

At 78.15 degrees you see the azeotrope (liquid and vapor have the exact same composition, 0.9558, or 95.58% ethanol).  That is my target.

As temperature rises a bit you see the vapor fraction of ethanol drops.  Even just at 79.8 degrees, less than 2 degrees above 78.15, the ethanol composition has dropped to 83%.  So the dessicant step later on has to work that much harder to make that ethanol dry.  (Trying to make a fuel here, not planning to drink it.)  As temperature rises to 95.5 degrees, well, you basically just made a single-stage distiller.  A beer mix will distill at around 95 degrees.  It's about 5% ethanol.  The vapor will be 34% ethanol or so, not quite concentrated enough to catch fire with a match.

How do you measure the ethanol fraction? (density?)
Seems to me you need to feed that 'signal' back to the thermal control
loop.

Say, isn't it legal to distill some of your own hooch in the US?
Maybe you need a permit/ license?

George H.