Tag Archives: membrane reactor

New REB hydrogen generator for car fueling, etc.

One of my favorite invention ideas, one that I’ve tried to get the DoE to fund, is a membrane hydrogen generator where the waste gas is burnt to heat the reactor. The result should be exceptional efficiency, low-cost, low pollution, and less infrastructure needs. Having failed to interest the government, I’ve gone and built one on my own dime. That’s me on the left, with Shua Spirka, holding the new core module (reactor, boiler, purifier and purifier) sized for personal car fueling.

Me and Shua and our new hydrogen generator core

Me and Shua and our new hydrogen generator core

The core just arrived from the shop last week, now we have to pumps and heat exchangers. As with our current products, the hydrogen is generated from methanol water, and extracted 99.99999% pure by diffusion through a metal membrane. This core fit in a heat transfer pot (see lower right) and the pot sits on a burner for the waste gas. Control is tricky, but I think I’ve got it. If it all works like it’s supposed to, the combination should be 80-90% energy-efficient, delivering about 75 slpm, 9 kg per day. That’s the same output as our largest current electrically heated generators, with a much lower infrastructure cost. The output should be enough to fuel one hydrogen-powered automobile per day, or keep a small fleet of plug-in, hydrogen-hybrids running continuously.

Hydrogen automobiles have a lot of advantages over Tesla-type electric automobiles. I’ll tell you how the thing works as soon as we set it up and test it. Right now, we’ve got other customers and other products to make.

Robert Buxbaum, February 18, 2016. If someone could supply a good hydrogen compressor, and a good fuel cell, that would be most welcome. Someone who can supply that will be able to ride in a really excellent cart of the future at this year’s July 4th parade.

My steam-operated, high pressure pump

Here’s a miniature version of a duplex pump that we made 2-3 years ago at REB Research as a way to pump fuel into hydrogen generators for use with fuel cells. The design is from the 1800s. It was used on tank locomotives and steamboats to pump water into the boiler using only the pressure in the boiler itself. This seems like magic, but isn’t. There is no rotation, but linear motion in a steam piston of larger diameter pushes a liquid pump piston with a smaller diameter. Each piston travels the same distance, but there is more volume in the steam cylinder. The work from the steam piston is greater: W = ∫PdV; energy is conserved, and the liquid is pumped to higher pressure than the driving steam (neat!).

The following is a still photo. Click on the YouTube link to see the steam pump in action. It has over 4000 views!

Mini duplex pump. Provides high pressure water from steam power. Amini version of a classic of the 1800s Coffee cup and pen shown for scale.

Mini duplex pump. Provides high pressure water from steam power. A mini version of a classic of the 1800s Coffee cup and pen shown for scale.

You can get the bronze casting and the plans for this pump from Stanley co (England). Any talented machinist should be able to do the rest. I hired an Amish craftsman in Ohio. Maurice Perlman did the final fit work in our shop.

Our standard line of hydrogen generators still use electricity to pump the methanol-water. Even our latest generators are meant for nom-mobile applications where electricity is awfully convenient and cheap. This pump was intended for a future customer who would need to generate hydrogen to make electricity for remote and mobile applications. Even our non-mobile hydrogen is a better way to power cars than batteries, but making it mobile has advantages. Another advance would be to heat the reactors by burning the waste gas (I’ve been working on that too, and have filed a patent). Sometimes you have to build things ahead of finding a customer — and this pump was awfully cool.

New hydrogen generator from REB Research

Here’s the new, latest version of our Me150 hydrogen generator with our wonder-secretary, Libby, shown for scale. It’s smaller and prettier than the previous version shown at left (previous version of Me150, not of secretary). Hydrogen output is 99.9999% pure, 9.5 kg/day, 75 slpm, 150 scfh H2; it generates hydrogen from methanol reforming in a membrane reactor. Pricing is $150,000. Uses about 7 gal of methanol-water ($6 worth) per kg of H2 (380 ft3). Can be used to fill weather balloons, cool electric dynamos, or provide hydrogen fuel for 2-10 fuel cell cars.

New REB Research hydrogen generator 150 scfh of 99.9999% H2 from methanol reforming

New REB Research hydrogen generator 150 scfh of 99.9999% pure H2 from methanol-water reforming against metal membranes.

Dr. Robert E. Buxbaum

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.

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.

What is the best hydrogen storage medium?

Answering best questions is always tricky since best depends on situation, but I’ll cover some hydrogen storage options here, and I’ll try to explain where our product options (cylinder gas purifiers and methanol-water reformers) fit in.

The most common laboratory option for hydrogen storage is inside a tank; typically this tank is made of steel, but it can be made of aluminum, fiberglass or carbon fiber. Tanks are the most convenient source for small volume users since they are instantly ready for delivery at any pressure up to the storage pressure; typically that’s 2000 psi (135 atm) though 10,000 (1350 atm) is available by special order. The maximum practical density for this storage is about 50 g/liter, but this density ignores the weight of the tank. The tank adds a factor of 20 or to the weight, making tanks a less-favored option for mobile users. Tanks also add significantly to the cost. They also tend to add impurities to the gas, and there’s a safety issue too: tanks sometimes fall over, and compressed gas can explode. For small-volume, non-mobile users, one can address safety by chaining up ones tank and adding a metal membrane hydrogen purifier; This is one of our main products.

Another approach is liquid hydrogen; The density of liquid hydrogen is higher than of gas, about 68 g/liter, and you don’t need as a tank that’s a big or heavy. One problem is that you have to keep the liquid quite cold, about 25 K. There are evaporative losses too, and if the vent should freeze shut you will get a massive explosion. This is the storage method preferred by large users, like NASA.

Moving on to metal hydrides. These are heavy and rather expensive but they are safer than the two previous options. To extract hydrogen from a metal hydride bed the entire hydride bed has to be heated, and this adds complexity. To refill the bed, it generally has to be cooled, and this too adds complexity. Generally, you need a source of moderately high pressure, clean, dry hydrogen to recharge a bed. You can get this from either an electrolysis generator, with a metal membrane hydrogen purifier, or by generating the hydrogen from methanol using one of our membrane reactor hydrogen generators.

Borohydrides are similar to metal hydrides, but they can flow. Sorry to say, they are more expensive than normal metal hydrides and they can not be regenerated.They are ideal for some military use

And now finally, chemical materials: water, methanol, and ammonia. Chemical compounds are a lot cheaper than metal hydrides or metal borohydrides, and tend to be far more readily available and transportable being much lighter in weight. Water and/or methanol contains 110 gm of H2/liter;  ammonia contains 120 gms/liter, and the tanks are far lighter and cheaper too. Polyethylene jugs weighing a few ounces suffices to transport gallon quantities of water or methanol and, while not quite as light, relatively cheap metallic containers suffice to hold and transport ammonia.

The optimum choice of chemical storage varies with application and customer need. Water is the safest option, but it can freeze in the cold, and it does not contain its own chemical energy. The energy to split the water has to come externally, typically from electricity via electrolysis. This makes water impractical for mobile applications. Also, the hydrogen generated from water electrolysis tends to be impure, a problem for hydrogen that is intended for storage or chemical manufacture. Still, there is a big advantage to forming hydrogen from something that is completely non-toxic, non-flammable, and readily available, and water definitely has a place among the production options.

Methanol contains its own chemical energy, so hydrogen can be generated by heating alone (with a catalyst), but it is toxic to drink and it is flammable. I’ve found a  my unique way of making hydrogen from methanol-water using  a membrane reactor. Go to my site for sales and other essays.

Finally, ammonia provides it’s own chemical energy like methanol, and is flammable, like methanol; we can convert it to hydrogen with our membrane reactors like we can methanol, but ammonia is far more toxic than methanol, possessing the power to kill with both its vapors and in liquid form. We’ve made ammonia reformers, but prefer methanol.

How and why membrane reactors work

Here is a link to a 3 year old essay of mine about how membrane reactors work and how you can use them to get past the normal limits of thermodynamics. The words are good, as is the example application, but I think I can write a shorter version now. Also, sorry to say, when I wrote the essay I was just beginning to make membrane reactors; my designs have gotten simpler since.

Above, for example, is a more modern, high pressure membrane reactor design:  72 tube reactor assembly; high pressure. The area at right is used for heat transfer. Normally the reactor would sit with this end up, and the tube area filled or half-filled with catalyst, e.g. for the water gas shift reaction, CO + H2O –> CO2 + H2. According to normal thermodynamics, the extent of reaction for this will not be affected by pressure once it reaches equilibrium, only by temperature. If you want the reaction to go reasonably to completion, you have to operate at low temperatures, 250- 300 °C, and you have to cool externally to remove the heat of reaction. In a membrane reactor, you can operate at much higher temperatures and you don’t have to work so hard to remove heat. The trick is to operate with the reacting gas at high pressures, and to extract hydrogen at lower pressures. With a large enough difference between the reacting pressure and the extract pressure, you can achieve high extents (high conversions) at any temperature.

Here’s where we sell membrane reactors; we also sell catalyst and tubes.

Largest hydrogen purifier to date pressure test

Here is our latest hydrogen purifier to date being pressure tested. Output is 650 slpm; that’s 40 m3/hr, 3.5 kg/hr. The device is tied down for burst-pressure testing behind a blast fort, just in case the thing bursts during tests. So far, no failures, no leaks. I sure hope the customer pays.

here's our largest H2 purifier being burst-pressure tested

here’s our largest H2 purifier being burst-pressure tested

New hydrogen generator for gas chromatographic use

Shown below is our latest product: a lower cost hydrogen generator, designed for use to provide the carrier and flame gas for gas chromatography. It’s our highest pressure, lowest hydrogen output product, outputting hydrogen at up to 90 psi. The output is still higher than any other generator in the GC space, and the purity is greater; 99.99995%, good enough to be used as the carrier gas, not just the detector gas. Fairly low price too.http://www.rebresearch.com/
Photo: Our latest new product: a lower cost, hydrogen generator for use with gas chromatography. It's our highest pressure, lowest hydrogen output product, but the output is still higher than any other in the GC space, and the price is less at that purity. </p><br />
<p>http://www.rebresearch.com/
As always, the hydrogen is made from methanol-water reforming in a membrane reactor, but we did a couple of things differently from previous designs. We closed up the front more so you don’t stick your fingers where they don’t belong. We also have a more-transpartent tank so you have a better idea what the liquid level is. The use of the membrane reactor is why our hydrogen is purer; we go through a metal membrane and our competition, (Porter, etc) uses only a desiccant.