Monthly Archives: January 2013

A visit to the Buxbaum laboratory from Metromedia

It’s a slow news day in Detroit, so the folks from Metromedia came to visit my laboratory at REB Research. You can visit too. We’re doing cool stuff most of the time, we’re working on a hydrogen-fueled plane that stays aloft for weeks (not that cool, actually, the Hindenberg did it in the 30s). On this particular day I’ve got a cool hat on, and a beige suit. I’m putting hydrogen in my car. Hydrogen increases the speed of combustion, and so it adds to milage — or it has when we’ve added it from electrolysis sources.buxbaum-003

The fun thing about science is that there are always surprises.

Adding hydrogen to a Malibu at REB Research

Adding hydrogen to a Malibu at REB Research

Small hydrogen generators for cooling dynamo generators

A majority of the electricity used in the US comes from rotating dynamos. Power is provided to the dynamos by a turbine or IC engine and the dynamo turns this power into electricity by moving a rotating coil (a rotor) through a non-rotating magnetic field provided by magnets or a non-rotating coil (a stator). While it is easy to cool the magnets or stator, cooling the rotor is challenging as there is no possibility to connect it cooling water or heat transfer paste. One of the more common options is hydrogen gas.

It is common to fill the space between the rotor and the stator with hydrogen gas. Heat transfers from the rotor to the stator or to the walls of the dynamo through the circulating hydrogen. Hydrogen has the lowest density of any gas, and the highest thermal conductivity of any gas. The low density is important because it reduces the power drag (wind drag) on the rotor. The high heat transfer coefficient helps cool the rotor so that it does not burn out at high power draw.

Hydrogen is typically provided to the dynamo by a small hydrogen generator or hydrogen bottle. While we have never sold a hydrogen generator to this market, I strongly believe that our membrane reactor hydrogen generators would be competitive; the cost of hydrogen is lower than that of bottled gas; it is far more convenient and safe; and the hydrogen is purer than from electrolysis.

Why isn’t the sky green?

Yesterday I blogged with a simple version of why the sky was blue and not green. Now I’d like to add mathematics to the treatment. The simple version said that the sky was blue because the sun color was a spectrum centered on yellow. I said that molecules of air scattered mostly the short wavelength, high frequency light colors, indigo and blue. This made the sky blue. I said that, the rest of the sunlight was not scattered, so that the sun looked yellow. I then said that the only way for the sky to be green would be if the sun were cooler, orange say, then the sky would be green. The answer is sort-of true, but only in a hand-waving way; so here’s the better treatment.

Light scatters off of dispersed small particles in proportion to wavelength to the inverse 4th power of the wavelength. That is to say, we expect air molecules will scatter more short wavelength, cool colors (purple and indigo) than warm colors (red and orange) but a real analysis must use the actual spectrum of sunlight, the light power (mW/m2.nm) at each wavelength.

intensity of sunlight as a function of wavelength (frequency)

intensity of sunlight as a function of wavelength

The first thing you’ll notice is that the light from our sun isn’t quite yellow, but is mostly green. Clearly plants understand this, otherwise chlorophyl would be yellow. There are fairly large components of blue and red too, but my first correction to the previous treatment is that the yellow color we see as the sun is a trick of the eye called additive color. Our eyes combine the green and red of the sun’s light, and sees it as yellow. There are some nice classroom experiment you can do to show this, the simplest being to make a Maxwell top with green and red sections, spin the top, and notice that you see the color as yellow.

In order to add some math to the analysis of sky color, I show a table below where I divided the solar spectrum into the 7 representative colors with their effective power. There is some subjectivity to this, but I took red as the wavelengths from 620 to 750nm so I claim on the table was 680 nm. The average power of the red was 500 mW/m2nm, so I calculate the power as .5 W/m2nm x 130 nm = 65W/m2. Similarly, I took orange to be the 30W/m2 centered on 640nm, etc. This division is presented in the first 3 columns of the following table. The first line of the table is an approximate of the Rayleigh-scatter factor for our atmosphere, with scatter presented as the percent of the incident light. That is % scattered = 9E11/wavelength^4.skyblue scatter

To use the Rayleigh factor, I calculate the 1/wavelength of each color to the 4th power; this is shown in the 4th column. The scatter % is now calculated and I apply this percent to the light intensities to calculate the amount of each color that I’d expect in the scattered and un-scattered light (the last two columns). Based on this, I find that the predominant wavelength in the color of the sky should be blue-cyan with significant components of green, indigo, and violet. When viewed through a spectroscope, I find that these are the colors I see (I have a pocket spectroscope and used it an hour ago to check). Viewed through the same spectroscope (with eye protection), I expect the sun should look like a combination of green and red, something our eyes see as yellow (I have not done this personally). At any rate, it appears that the sky looks blue because our eyes see the green+ cyan+ indigo + purple in the scattered light as sky blue.220px-RGB_illumination

At sunrise and sunset when the sun is on the horizon the scatter percents will be higher, so that all of the sun’s colors will be scattered except red and orange. The sun looks orange then, as expected, but the sky should look blue-green, as that’s the combination of all the other colors of sunlight when orange and red are removed. I’ve not checked this last yet. I’ll have to take my spectroscope to a fine sunset and see what I see when I look at the sky.

Why isn’t the sky green and the sun orange?

A simple reason the sky isn’t green is that the sun is not orange is that the sun’s color and the sky color relate to the sun’s surface temperature. This is called black body radiation because, if you heat up a black object it will first glow red, then orange, yellow, green etc. Red is a relatively cool color because it’s a low frequency (long wavelength) and low frequencies are the easiest for a black body to produce. As the temperature increases, the amount of short wavelength colors increases faster than the amount of long wavelength colors, and the object glows in a color that represents its temperature.

Our star is called a yellow sun because the center color of the radiation our sun provides is yellow. The sun provides radiation in all colors and wavelengths, but because of its temperature, most of the radiated energy appears in the visible spectrum from violet to red, with yellow as the center. The sun also radiates some energy as invisible light, ultraviolet and infra-red, but not all that much. Thus, the simple answer to why the sun isn’t blue or green, it’s that the sun is too cool to be these colors.

Of the light of the sun, some small amount (about 10%) scatters off of the molecules in the air. This is called Rayleigh scatter, and the fraction radiated is proportional to the 4th power of the frequency. Because the scatter is frequency dependent, the high frequencies (blue, indigo, and violet) scatter a lot, about 20%, while the red hardly scatters at all. As a result the sky looks blue, while the sun looks pretty much the same if viewed from earth or from space.

The sun looks orange at sundown because the sunlight has to go through more air, and a lot more of the yellow, green, and blue scatter away before we see it. I might expect the sky to look somewhat greenish at sundown, but I have not noticed. If the molecules in the air were bigger we’d still see the same color, though its intensity would be greater. That’s the effect that carbon dioxide has — it causes more sunlight to scatter, making the sky a brighter blue (it also holds in the infra-red, but that’s a different story). If the sun were cooler (orange say), the sky might appear as green. That’s because there would be less violet and blue in the sunlight, and the sky color would be shifted to the longer wavelengths. My summary is thus, that on planets where the sun is cooler than ours, the sky is green.

Rayleigh scatter only applies to molecules and other objects that are much smaller than the size of the light wavelength. A typical molecule of air is about 1 nm in size (1E-9 of a meter), while the wavelength of yellow light is about 580 nm long. Clearly, the molecules of air are much smaller than the wavelength of light. With snow, the size of the crystals are 500-2000 nm in size, so the snow looks like all the colors of the sun together, and that’s white. White = the sum of all the colors: red + orange + blue + green + yellow + violet + indigo.

Newfie joke (Newfie’s are Canadians from Newfinland)

Here’s a Newfie joke; it was originally another joke, but I tweaked it because I was in Frankenmuth today watching folks snow sculpt and ice-fish. As for Newfinland, it’s basically the Appalachia of Canada. The folks there aren’t considered to be particularly bright. Anyway.

So this Newfie decides it’s time he took up ice fishing. It’s winter and all his other Newfie friends ice fish. So he gets a setup with an ice drill, a few short fishing poles, a plastic pail to sit on, and a little tent, and he goes to set it up on the ice early one morning.

He finds a nice, empty spot, but as soon as he’s set up the pail and tent but he hears a voice from somewhere around him, “Go home, there are no fish under the ice.” He looks all around but he can’t see anyone. Who said that? Was that comment for him? He goes back to start drilling, and he hears the voice again. “Go home; there are no fish under the ice.” Well, he still can’t see anyone, but figures that maybe he should go to a different spot. He picks up his stuff, moves about 50 feet away and starts to set up again, when he hears the voice again, just as loud. “Go home, there are no fish under the ice.” “Who are you?” yells the Newfie to no-one in particular, “God?” “I’m the rink manager. There are no fish under the ice.”

Helium leak detector repaired and refurbished in Frankenmuth

To those who know Frankenmuth, MI, it is generally as “Little Bavaria,” the German-themed vacation town of quaint houses and shops; of cheese, wurst, beer, Christmas ornaments, and Oom Pa Pa bands. I know it in a slightly different way as the only town to get your helium leak detector repaired. There are at least three shops in Frankenmuth that repair helium leak detectors (or make new specialty versions), and this is the source of the reference leaks that most qualified shops use. So I was here yesterday and today, both for the World-class snow sculpture contest, and to get my helium leak detector looked at. It was acting funny; it turns out there was a leak in the leak detector plus a bad potentiometer on a switchover circuit. The leak is already fixed, and I should have it back in my shop next week (Wednesday).

Snow-sculpting in Frankenmuth 2013; I was there to have my helium leak detector fixed.

Snow-sculpting in Frankenmuth 2013; I was there to have my helium leak detector fixed.

veeco He-leak detector at REB Research.

Purifying the Hydrogen from Browns gas, HHO, etc.

Perhaps the simplest way to make hydrogen is to stick two electrodes into water and to apply electricity. The gas that is produced is mostly hydrogen, and is sometimes suitable for welding or for addition to an automobile engine to increase the mileage. Depending on the electrodes and whether salt is added to the water, the gas that is produced can be Browns gas, HHO,  town gas, or some relative of the three. We are sometimes asked if we can purify the product of this electrolysis, and my answer is typically: “maybe,” or “it depends.”

If the electrode was made of stainless steel and the water contained only KOH or baking soda, the gas that results will be mostly hydrogen and you will be able to purify it somewhat with a polymer membrane if you wish. The gas isn’t very explosive generally, since most of the oxygen that results from the electrolysis will go into rusting out the electrodes. The reaction is thus, H2O + Fe –> H2 + FeO. To see if this is what you’ve got, you can use determine the ratio of gas production with a simple version of the Hoffman apparatus made from (for example) two overturned glass jars, or by separating the electrodes with a paper towel. You can also determine the H2 to O2 ratio (if you know a bit more physics) from a measure of the amperage and the rate of gas production. The hydrogen you form with steel plates will always contain some oxygen though, as well as some nitrogen and water vapor. While a polymer membrane will remove most of the oxygen and nitrogen in this gas, it won’t remove all, and it will not generally remove any of the water. With this gas, I suspect that you would be better off just using it as it is. This is particularly so if the fraction of oxygen is more than a few percent: hydrogen with more oxygen than this becomes quite explosive.

Since this gas will contain water, you probably don’t want to store it, and you probably don’t want to purify it over a metal, either, There are two reasons for this: the water can condense out during storage, and will tend to rust whatever metal it contacts (it’s often alkaline). What’s more, the small amount of oxygen in the hydrogen is likely to react over a hydrogen storage metal to form water and heat. This may give rise to the explosion you were trying to avoid. This is clearly the quick a dirty approach to making hydrogen.

Another version of electrolysis gas, one that’s even quicker and dirtier than the above involves the use of table salt instead of KOH or baking soda. The hydrogen that results will contain chlorine as an impurity, and will be quite toxic, but it will be somewhat less explosive.The hydrogen will smell like bleach and the water you use will turn slightly greenish and quite alkaline. Both the liquid and gas are definitely bad news unless your aim was to make chlorine and alkali; this is called the chlor-alkali process for a reason. On a personal note, as a 12 year old I tried this and was confused about why I got equal volumes of gas on the cathode and anode. The reason was that I was making Cl2, and not O2: the chemistry is 2 H2O + 2 NaCl –> H2 + Cl2 + 2 NaOH. I then I used the bromide version reaction to make a nice sample of bromine liquid. That is, I used KBr instead of table salt. Bromine is brown, oily, and only sparingly soluble in water.

Another version of this electrolysis process involves the use of graphite electrodes. If you are lucky, this will give you a mix of CO and hydrogen and not H2 and O2. This mix is a called “town gas.” It’s a very good welding gas since it is not explosive. It is, however, quite toxic. If you begin to get a headache using this gas stop immediately: you’re experiencing CO poisoning. The reaction here is H2O + C –> H2 + CO. CO headaches just get worse and worse until you die. If you are not lucky here you can get HHO instead of town gas, and this is quite explosive: H2O –> H2 + 1/2 O2. The volume ratio will be a key clue as to which you are making; another clue is to put a small volume in a paper bag and light it. If the bag explodes with a terrific bang, you’ve made the wrong gas. Stop!

With all of these gases I would recommend that you add a polymer of paper membrane in the water between the electrodes. Filter paper will work fine for this as will ceramic paper; the classic membrane for this was asbestos. If you keep the two product gas streams separate as soon as they are formed, you’ll avoid most of your explosion-safety issues. Few people take this advice, I’ve found; they think there must be some simpler way. Trust me: this is the classic, safe way to make electrolysis hydrogen.

A balloon filled with pure hydrogen will not ignite. To show you, here is a 2.5 min long video where I poke a lit cigar into a mylar balloon filled with hydrogen from my membrane reactor generators. Note that this hydrogen does not even burn in the balloon because it is oxygen free. As a safety check try this with your hydrogen, but only on a much-smaller scale. Pure hydrogen will not go boom, impure hydrogen will. My advice: keep safe and healthy. You’ll feel better that way, and your heirs will be less inclined to sue me.

In case you are wondering how electrolysis hydrogen can add to the gas mileage, the simple answer is that it increases the combustion speed and the water vapor decreases the parasitic loss due to vacuum. I’ve got some more information on this here. I hope this advice helps with your car project or any other electrolysis option. In my opinion, one should use a membrane in the water to separate the components at formation in all but the smallest experiments and with the smallest amperage sources. Even these should be done only in a well-ventilated room or on a car that is parked outside of the house. Many of the great chemists of the 1800s died doing experiments like these; learn from their mistakes and stay among the living.

What causes the swirl of tornadoes and hurricanes

Some weeks ago, I presented an explanation of why tornadoes and hurricanes pick up stuff based on an essay by A. Einstein that explained the phenomenon in terms of swirling fluids and Coriolis flows. I put in my own description that I thought was clearer since it avoided the word “Coriolis”, and attached a video so you could see how it all worked — or rather that is was as simple as all that. (Science teachers: I’ve found kids love it when I do this, and similar experiments with centrifugal force in the class-room as part of a weather demonstration).

I’d like to now answer a related question that I sometimes get: where does the swirl come from? hurricanes that answer follows, though I think you’ll find my it is worded differently from that in Wikipedia and kids’ science books since (as before) I don’t use the word Coriolis, nor any other concept beyond conservation of angular momentum plus that air flows from high pressure to low.

In Wikipedia and all the other web-sits I visited, it was claimed that the swirl came from “Coriolis force.” While this isn’t quite wrong, I find this explanation incomprehensible and useless. Virtually no-one has a good feel for Coriolis force as such, and those who do recognize that it doesn’t exist independently like gravity. So here is my explanation based on low and high pressure and on conservation of angular momentum.  I hope it will be clearer.

All hurricanes are associated with low pressure zones. This is not a coincidence as I understand it, but a cause-and-effect relationship. The low pressure center is what causes the hurricane to form and grow. It may also cause tornadoes but the relationship seems less clear. In the northern hemisphere, the lowest low pressure zones are found to form over the mid Atlantic or Pacific in the fall because the water there is warm and that makes the air wet and hot. Static air pressure is merely the weight of the air over a certain space, and as hot air has more volume and less density, it weighs less. Less weight = less pressure, all else being equal. Adding water (humidity) to air also reduces the air pressure as the density of water vapor is less than that of dry air in proportion to their molecular weights. The average molecular weight of dry air is 29 and the molecular weight of water is 18. As a result, every 9% increase in water content decreases the air pressure by 1% (7.6 mm or 0.3″ of mercury).

Air tends to flow from high pressure zones to low pressure zones. In the northern hemisphere, some of the highest high pressure zones form over northern Canada and Russia in the winter. High pressure zones form there by the late fall because these regions are cold and dry. Cold air is less voluminous than hot, and as a result additional hot air flows into these zones at high altitude. At sea level the air flows out from the high pressure zones to the low pressure zones and begins to swirl because of conservation of angular momentum.

All the air in the world is spinning with the earth. At the north pole the spin rate is 360 degrees every 24 hours, or 15 degrees per hour. The spin rate is slower further south, proportionally to the sine of the latitude, and it is zero at the equator. The spin of the earth at your location is observable with a Foucault pendulum (there is likely to be one found in your science museum). We normally don’t notice the spin of the air around us because the earth is spinning at the same rate, normally. However the air has angular momentum, and when air moves into into a central location the angular speed increases because the angular momentum must be conserved. As the gas moves in, the spin rate must increase in proportion; it eventually becomes noticeable relative to the earth’s spin. Thus, if the air starts out moving at 10 degrees per hour (that’s the spin rate in Detroit, MI 41.8° N), and moves from 800 miles away from a low pressure center to only 200 miles from the center, the angular momentum must increase four times, or to 40 degrees per hour. We would only see 30 degrees/hr of this because the earth is spinning, but the velocity this involves is significant: V= 200 miles * 2* pi *30/360 = 104 mph.

To give students a sense of angular momentum conservation, most science centers (and colleges) use an experiment involving bicycle wheels and a swivel chair. In the science centers there is usually no explanation of why, but in college they tend to explain it in terms of vectors and (perhaps) gauge theories of space-time (a gauge is basically a symmetry; angular momentum is conserved because space is symmetric in rotation). In a hurricane, the air at sea level always spins in the same direction of the earth: counter clockwise in the northern hemisphere, clockwise in the southern, but it does not spin this way forever.

The air that’s sucked into the hurricane become heated and saturated with water. As a result, it becomes less dense, expands, and rises, sucking fresh air in behind it. As the hot wet air rises it cools and much of the water rains down as rain. When the, now dry air reaches a high enough altitude its air pressure is higher than that above the cold regions of the north; the air now flows away north. Because this hot wet air travels north we typically get rain in Michigan when the Carolinas are just being hit by hurricanes. As the air flows away from the centers at high altitudes it begins to spin the opposite direction, by the way, so called counter-cyclonally because angular momentum has to be consevered. At high altitudes over high pressure centers I would expect to find cyclones too (spinning cyclonally) I have not found a reference for them, but suspect that airline pilots are aware of the effect. There is some of this spin at low altitudes, but less so most of the time.

Hurricanes tend to move to the US and north through the hurricane season because, as I understand it, the cold air that keeps coming to feed the hurricane comes mostly from the coastal US. As I understand it the hurricane is not moving as such, the air stays relatively stationary and the swirl that we call a hurricane moves to the US in the effective direction of the sea-level air flow.

For tornadoes, I’m sorry to say, this explanation does not work quite as well, and Wikipedia didn’t help clear things up for me either. The force of tornadoes is much stronger than of hurricanes (the swirl is more concentrated) and the spin direction is not always cyclonic. Also tornadoes form in some surprising areas like Kansas and Michigan where hurricanes never form. My suspicion is that most, but not all tornadoes form from the same low pressure as hurricanes, but by dry heat, not wet. Tornadoes form in Michigan, Texas, and Alabama in the early summer when the ground is dry and warmer than the surrounding lakes and seas. It is not difficult to imagine the air rising from the hot ground and that a cool wind would come in from the water and beginning to swirl. The cold, damp sea air would be more dense than the hot, dry land air, and the dry air would rise. I can imagine that some of these tornadoes would occur with rain, but that many the more intense?) would have little or none; perhaps rain-fall tends to dampen the intensity of the swirl (?)

Now we get to things that I don’t have good explanation for at all: why Kansas? Kansas isn’t particularly hot or cold; it isn’t located near lakes or seas, so why do they have so many tornadoes? I don’t know. Another issue that I don’t understand: why is it that some tornadoes rotate counter cyclonicly? Wikipedia says these tornadoes shed from other tornadoes, but this doesn’t quite seem like an explanation. My guess is that these tornadoes are caused by a relative high pressure source at ground level (a region of cold ground for example) coupled with a nearby low pressure zone (a warm lake?). My guess is that this produces an intense counter-cyclonic flow to the low pressure zone. As for why the pressure is very low in tornadoes, even these that I think are caused by high pressure, I suspect the intense low pressure is an epee-phenomenon caused by the concentration of spin — one I show in my video. That is, I suspect that the low pressure in the center of counter-cyclonic tornadoes is not the cause of the tornado but an artifact of the concentrated spin. Perhaps I’m wrong here, but that’s the explanation that seems to fit best with the info I’ve got. If you’ve got better explanations for these two issues, I’d love to hear them.

Hydrogen Cylinders versus Hydrogen Generators for Gas Chromatography

Hydrogen is an excellent cover gas for furnace brazing and electronic manufacture; it’s used as a carrier gas for gas chromatography or as a flame-detector gas, and it’s a generally interesting gas for chemical formation and alternate energy. If you are working in one of these fields you’ve got two maing options for sources of hydrogen: hydrogen cylinders and hydrogen generators with the maid difference being cost. Cylinder hydrogen is the more-commonly used for small demand applications, often aided by palladium membrane hydrogen purifiers if purity is an issue. Hydrogen generators are more generally used for larger -demand applications because they provide added safety, conveinience, and long-term savings. Having nothing better to do this evening, I thought I’d go through the benefits and drawbacks of each as applies to gas chromatography.

Point of use Cylinder Hydrogen Is Simple and Allows Easy Monitoring and Control. The smallest laboratories, those with one or two gas chromatographs, generally use a single hydrogen cylinder for each GC. This is called “point of use.” Each cylinder is typically belted to a wall and often fed into some type of hydrogen purifier (a getter or membrane). From there it supplies carrier and/or fuel gas to its application. When a cylinder is empty, the application is stopped, and the purifier is often stopped too (not necessary with membranes). A new cylinder switched in and, after a short break in period, the process is restarted. The biggest advantage here is simplicity; another advantage is the ease of pressure control and monitoring. Pressure is controlled by a regulator located right at the gas chromatograph. You can always check it and adjust it as needed. A main disadvantage is that the process has to stop whenever a cylinder needs switching.

Multi-cylinder Systems Provide Fewer interruptions in Gas Supply. Larger laboratories with multiple GCs tend to use multiple hydrogen cylinders with complex switchover systems, or hydrogen generators. When multiple cylinders are used, they are typically racked together and connected to a manifold and a purifier. Tanks are emptied in series so that there is no disruption. When each take empties, the hydrogen tank is switched automatically or manually to maintain the flow and pressure. One problem with this is that the pressure does not typically stay constant as the cylinders switch since each has its own regulator and all will be set slightly differently. As the hydrogen cylinders have separate regulators, there can be pressure changes during cylinder switches; and, as the packs are located further from the GC there is a tendency for the pressure to vary as the flow varies.

Another issue with cylinder packs is that purity can suffer as there is more room for leaks and degassing in the line. This can be solved by point-of-use purifiers installed in the hydrogen lines just prior to the GC or other application.

A final issue with cylinder packs is safety: with so many cylinders, there is a lot of potential for really disastrous leaks and fires: one leak can empty many cylinders and there is no likely room that is big enough to disperse that hydrogen quickly enough. The potential is made greater since the cylinder packs are often located at a distance from where the experiments (and people) are. Maintenence becomes an issue too since the manifolds and automatic switches become complicated quickly. The hydrogen is under great pressure, and even if fires are avoided, a pressure release can be deadly. Manifolds are complex enough that they generally require a trained technician to trouble-shoot any problems; it can also take an expert to handle multiple cylinder changes to minimize contamination and pressure variation.

A main advantage of hydrogen generators is that it avoids cylinder changes; it’s also somewhat safer and saves money for larger users. Changing cylinders can be difficult and time consuming as mentioned above; hydrogen bottles must be monitored to check that gas does not run out, and you’ve got to make sure that cylinders don’t fall (especially on you), and that leaks don’t arise, and that explosive hydrogen does not escape. Much of this is alleviated with a hydrogen generator. One can have a very large tank of water or methanol — far larger than any reasonably safe gas tank, so running out is less of a problem. In some systems, the water can come from municipal pipes so there is almost no chance of running out.

Safety is provided by limiting the output of the generator to the amount the room will vent. Thus, a room with 100 ft3 of air circulation can host a hydrogen generator of up to 4.5 scfh output (about 2 slpm) with no fear of reaching explosive limits. Further, unlike cylinders, most hydrogen generators can be fitted with alarm features to alert the user to operating problems, and most have automatic shut down capabilities that trigger if the unit malfunctions. All of these factors contribute greatly to the overall safety of in the lab.

Another advantage is that methanol and water are a lot cheaper than hydrogen and there is no switchover system, cylinder rental, and less manpower need (cylinder rental cost is often greater than the cost of gas). The first cost of the generator is typically on the order of $10,000, similar to the cost of a manifold switchover system and a hydrogen purifier.

The Source Options for High purity hydrogen generators are electrolysis and methanol reformer generators. These are virtually the only continuous use hydrogen generators. They are both available in outputs from 150 ccm to 50 slpm, i.e. enough to supply single or multiple GC’s (also used for modest-sized braze furnaces, IC tool production, and laboratory-scale fuel cell testing). All hydrogen generators provide continuous hydrogen outputs as feed water or methanol is provided upstream of the hydrogen output, and they all offer safety advantages. They all take less space than the cylinders and avoid the leaks and impurity spikes that arise when cylinders are switched.

In Electrolytic Hydrogen generators Purified water, either purchased separately, or purified on-site is mixed with an electrolyte, generally KOH, and converted to hydrogen and oxygen by the electrolytic reaction H2O –> H2 + ½ O2.  As the hydrogen produced is generally “wet”, containing water vapor, the hydrogen is then purified by use of a desiccant, or by passage through a metal membrane purifier. Desiccants are cheaper, but the gas is at best 99.9% pure, good enough to feed FIDs, but not good enough to be used as a carrier gas, or for chemical production. Over time desiccants wear out; they require constant monitoring and changing as they become filled with water vapor. Often electrolytic hydrogen generators also require the addition of a caustic electrolyte solution as caustic can leak out, or leave by corrosion mechanisms.

In Reformer-based hydrogen generators a methanol-water mix is pumped to about 300 psi and heated to about 350 °C. It is then sent over a catalyst where it is converted to a hydrogen-containing gas-mix by the reaction CH3OH + H2O –> 3H2 + CO2. Pure hydrogen is extracted from the gas mix by passing it through a membrane, either within the reactor (a membrane reactor), or by use of a membrane purifier external to the reactor.

Both systems provide continuous gas supply of high purity gas. The need to change and store cylinders is eliminated, saving time and cost. One adds water or methanol-water as needed, and hydrogen is produced as long as there is electricity in the lab. Eliminating cylinder changeouts reduces downtime and minimizes the potential for air contamination.

Consistent gas purity is enhanced further because hydrogen generators often contain metal membranes. Hydrogen is delivered at  99.9999% purity, and remains constant over time. This consistent purity provides reliability for the GC system. Electrolysis systems with only a desiccant to remove water vapor from the hydrogen should be used only where high hydrogen purity less important than high hydrogen pressure. Even with a fresh cartridge, desiccant-purified gas never exceeds 99.9% and this purity decreases with time as the desiccant wears out; if purity is an issue add a membrane purifier, or use a methanol reformer.

Single cylinders are quite compact; where many cylinders would be needed space saving favors use of a generator. The relatively small size of hydrogen generators allows them to be conveniently located on the lab bench; they consume a lot of valuable lab and storage space than multiple cylinders. Related to space savings is zoning. Once you have many cylinders, you begin to run into zoning issues regarding how close your laboratory can be to bus stops, churches, and children. Zoning can limit distances to 500 feet, or 1/10 mile.

Short term cost savings favor cylinders; long term and large outputs favor generators. Hydrogen in cylinders is fairly expensive, the more so when cylinder rental is included. In Detroit, where we are, hydrogen costs about $70 each cylinder low low-purity gas, or $200 for high purity gas. Each cylinder contains 135 scf of gas. If you use 1/10 cylinder per day, you will find you’re spending about $7,300 per year on hydrogen gas, with another $1000 spent on cylinder rental and delivery. This is about the cost of a comparable hydrogen generator plus the water or methanol and electricity run it. If you use significantly less hydrogen you save money with cylinders, if you use more there is significant savings with a generator.

Most hydrogen generators have delivery pressure limitations compared to cylinders. Cylinders have no problem supplying hydrogen at 200 psi or greater pressures. By contrast, generators are limited to only the 60-150 psig range only. This pressure limitation is not likely to be a problem, even for GCs that need higher pressure gas or when the generator must be located far from the  instruments, but you have to be aware of the issue when buying the generator. Electrolysis systems that use caustic provide the highest pressures, but they tend to be the most expensive, and least safe as the operate hot and caustic can drip out. Fuel cell generators and reformers provide lower pressure gas (90 psi maximum, typically), but they are safer. In general generators should be located close to the instruments to minimize supply line pressure drop. If necessary it can pay to use cylinders and generators or several generators to provide a range of delivery pressures and a shorter distance between the hydrogen generator and the application.

Click here for the prices of REB Research hydrogen generators. By comparison, I’ve attached prices for electrolysis-based hydrogen generators here (it’s 2007 data; please check the company yourself for current prices). Finally, the price of membrane purifiers is listed here.

Maintenance required for optimal performance. Often electrolytic hydrogen generators require the addition of a caustic electrolyte solution; desiccant purified gas will require the monitoring and changing of desiccant cartridges to remove residual moisture from the hydrogen. Palladium membrane purifiers systems, and reformer systems need replacement thermocouples and heaters every few years. Understanding the required operating and maintenance procedures is an important part of making an informed decision.

Conclusion:

Cylinder hydrogen supplies are the simplest sources for labs but present a safety, cost, and handling concerns, particularly associated with cylinder change-outs. Generators tend to be more up-front expensive than cylinders but offer safety benefits as well as benefits of continuous supply and consistent purity. They are particularly attractive alternative for larger labs where large hydrogen supply can present larger safety risks, and larger operating costs.