7 Industrial Applications You Didn't Think were Compatible with Microwave Processing

7/27/2019 7 Industrial Applications You Didn't Think were Compatible with Microwave Processing

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7APPLICATIONS YOU DIDNT KNOW WERE COMPATIBLE WITH MICROWAVEBy McKenzie Fritch, Marion Mixers, Inc.

You probably have a microwave at home, and one or two in the break room at work.

Chances are you use it for heating, defrosting, and cooking food. But the same

characteristics we value in microwave for small-scale food preparationrapid,thorough heating and precise controlmake it a competitive technology for any

number of other uses as well. Last year, we invented the Microwave Mixer, an

industrial microwave system with a powerful but gentle agitator built into the

vessel. Since then, weve run a variety of tests, seen all kinds of MSDS sheets, and

found some very interesting applications where efficiency can be substantially

increased with microwave. While you may have guessed a few of the following, or

may even work with them yourself, we hope at least one or two applications off our

list will catch your eye and perhaps start you thinking.

1.ANALYTICAL CHEMISTRY

Microwaves have a growing tradition ofsuccess in the laboratory. Since the

landmark 1975 article by Samra et. al. on

the use of microwave for wet ashing, the

use of microwaves in the laboratory for

sample digestion of elemental analysis

has become accepted and routine, used

on a great variety of sample types to

speed up an otherwise time-consuming

task.

Microwave assisted extraction (MAE) isanother quickly growing use of microwave in the field of analytical chemistry. MAE

provides an incredible savings in time and material compared to conventional

extraction techniques. A traditional, pre-microwave method we may use for

comparison is Soxhlet extraction, reliable but known for its long turn-around and

guzzling of materials. As Srogi (2006) has written, Soxhlet extraction requires 12-

24h for most extractions and its high consumption of organic solvent (hundreds of

millimeters) is another disadvantage. However, In contrast to conventional

methods, microwave-assisted extraction (MAE) can reduce the extraction time to

less than 30 min and solvent consumption volumes to fewer than 50mL (pp. 1264-

1266). Although the first experiments with MAE began 30 years ago with household

microwave ovens, today there are a variety of 2450 MHz and now 915MHz

microwave models on the market specifically designed for extraction (Srogi 2006).

Other chemical processes also receive the timesaving benefits of dielectric

microwave heating. Drying is one of the most important, and may be used to rid the

sample of volatile compounds, including water. Microwave drying, usually combined

with vacuum (Microwave Vacuum Drying: MVD), is significantly faster and causes


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less quality loss to the sample than traditional drying methods such as air or oven

(Srogi 2006). In some segments of research this benefit is simply handya good

time-saver that minimizes down-time in intermediate drying and reaction steps. For

others, however, the dramatically reduced heating times are absolutely critical,

providing results that conventional heating methods could not. For example, there

are some copper complexes that are not possible to synthesize with conventionalheating methodsonly through the superfast, dielectric heating microwave

provides. Radiopharmaceuticals are another niche application to which the ultrafast

heating is not just convenient, but essential. These compounds lose radioactivity

quickly, meaning they require the fastest possible preparation and application. For

now, this means microwave. Microwaves have also been used in analytical

chemistry for moisture measurement, analyte desorption and adsorption,

chromogenic reaction, and sample nebulization and clean-up.

2.TREATMENT OF BIOMASS AND BIOSOLIDS

Waste remediation through theproduction and use of biomass and

biosolids is an important and quickly

growing field. However, both the

environmental and financial payoffs of

this type of recycling are extremely

limited until the waste has been

dewatered. Depending on the type of

biomass and the industry producing it,

waste may be up to 90% water (food

industry waste has a particularly high moisture content percentage). Wastes in this

state are very inefficient to use. While wet feedstock may be (and often is) sentstraight to the boiler to be both dried and processed, this is a recipe for extreme

inefficiency and even increased risk. In the case of wood-based feedstock, more

Volatile Organic Compounds (VOCs) are released the longer the feedstock is in the

boiler. Drying feedstock before processing it through the boiler greatly reduces this

residence time, and also allows for a lower boiler temperature to be used, cutting

down on both product degradation due to high temperatures and the amount of

VOCs being released. Other feedstocks (eggshells, municipal waste, corn cobs, etc.)

also experience the benefits of pre-drying

treatment that show up in reduced

processing times and fuller, more complete

combustions. Boilers are not efficientdryers, and unnecessary energy is expended

when they are used to perform both

functionsdrying and combustion. The

equipment is not used to its fullest spatial

potential, either. When moist product is

both dried and combusted in a boiler, for

example, extra space must be left in the


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boiler for air in order to accommodate smoke formation. This cuts down the amount

of actual product that can be processed at one time. Using a boiler to dry product

can mean sacrificing up to 50% of the machines capacity, depending on the material

being processed. When material is pre-treated through a dryer, however, a boiler

can be filled to its true capacity, increasing output, or may be downsized for a

reduction in equipment costs. The efficiency gains in the boiler help to offset theprice of a dewatering system. Depending on the type of feedstock to be dewatered,

microwave can be a viable solution for this type of pretreatment. Even better, it can

be used as a finish dryer for biomass that is not burned, but processed for other uses

(fertilizer, etc.).

An important indirect benefit of

biomass drying, both as a

pretreatment and as a finish

processing, is dramatically reduced

transportation and storage costs. Wet

biomass is heavy and expensive tomove. Dewatered biomass is cheaper

to haul, and takes up less room

because material size is reduced

during the dewatering process. This

could result in lower landfill and

disposal costs, or if the material is

meant for resale, extra time for producers to find buyers as demand for waste as

fertilizer varies during different times of the year. Dry material is also far less

susceptible to quality threats such as mice and mold, making it better adapted to

longer-term storage.

Microwave is an interesting solution for the pre-drying treatment of biomass.

Though not as efficient as other technologies when removing the bulk of water from

material, microwave is incredibly well suited to the removal of the final 10% of

moisture. Even small amounts of moisture make a big difference in transportation

cost and combustion efficiency, and microwaves ability to eradicate even trace

amounts of liquid makes it an ideal choice for finish drying.

3. POWDER PROCESSING

Microwaves trace dewatering capabilities are also in critical demand in the powder

processing industry. This industry is extremely diverse, and microwave applicationshave been found to fit a variety of different sectors within it. Below are just a couple

of examples.

CARBON BLACK.Carbon black is a critical ingredient in most products made from

rubber: tires, hoses, belts, etc. The 2000 EPA report on carbon black states that 70%

of the carbon black produced in the US three years prior went toward the

production of tires, and another 11% to non-tire automotive products. The addition


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of carbon black to rubber makes the final product stronger, more durable, and more

resistant to wear. Carbon black is also valued for its rich, dark color. A smaller but

important fraction of the carbon black produced annually is used in pigment to color

plastics, inks, coatings, paints, and other materials.

Carbon black is made by two primary processes: thermalblackand the more commonfurnace black. The furnace

black process uses feedstock oil which is introduced to high-

temperature gases to cause a partial combustion. A black

steam results from which the carbon black molecules must

be filtered. After filtration, the producer is left with a

quantity of fluffy black powder. In the powder form, carbon

black is difficult to use, transport, and control. Because of

these issues, many producers choose to pelletize the

powder, combining it with water or binders to form small

units of product. The pellets must then be dried before they

are transported or stored. Their optimum moisture content is incredibly low, lessthan 0.25%.

Whenever desired final moisture content percentages are this low, a good first

thought is always microwave. Microwave offers the benefits of incredibly fast,

incredibly precise heating, particularly when it comes to nabbing the last bit of

moisture. When combined with gentle agitation, as with the innovative Microwave

Mixer from Marion Mixers, Inc., these inherent strengths of microwave are

complemented by the ability to ensure uniform heating and product quality to

minimize scorched or rejected pellets.

ANIMAL BLOOD PLASMA.Anotherpowder application of microwave

drying is the animal blood plasma

industry. Slaughterhouses no longer

see blood as waste, but as a valuable

byproduct. Over the past 40 years,

technology has grown to support the

collection, coagulation, and drying of

animal blood into powder to be used

as an additive in pet foods and

fertilizer. A common setup in use

today is continuous coagulation of collected blood, followed by mechanicaldewatering (up to about 50%) and then drying of the coagulate into powder.

Microwave offers a huge advantage here, not only because of its quick turn-around

time, but also because of the precise control it makes possible. Drying blood is

difficult. Temperatures must be high enough to remove moisture and kill pathogens,

but cross the very thin margin into too-high temperatures, and the very proteins

that make the blood valuable will be killed. Microwave heating is unique in that

temperature can be controlled within one to two degrees, quickly taking the


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temperature up to dry the material rapidly, but stopping just short of the line. When

microwave is combined with in-vessel agitation, another common problem is

solved. Powder is no longer allowed to cling to the walls of the vessel during drying,

increasing yields and facilitating even product heating.

Powdered Eggs. 65 million tons of hen eggs were produced globally in 2012. More thanhalf of those eggs were produced in Asia where the poultry industry is considered as the

fastest growing in the world. Of the total number, approximately 1.3 billion eggs overallwere used in food, medical and other applications. Even the egg shells and membranes

are sold to various companies that include them in pet food as a calcium supplement or

for pharmaceutical products. Frozen liquid pasteurized eggs (egg whites and yolks) are

used worldwide for its important benefits including food safety, lower total cost, andimproved operations.

Powdered eggs are fully dehydrated eggs. They are made using spray drying in the sameway that powdered milk is made. The major advantages of powdered eggs over fresh

eggs include the price and the reduced weight per volume of whole egg equivalent. Also,powdered eggs do not need refrigeration and have a longer shelf life. Egg whites, yolks,

and combined whites and yolks can be processed into separate powders.

For creating powered eggs, microwave is also beneficial when used as a finishing dryer.In some areas of the world prone to high humidity, microwave drying may be necessary

to maintain a lower moisture count beyond spray drying to maintain a longer shelf life.

Microwave drying also will not denature the powder as sometimes occur with excessivetemperatures with spray drying to achieve lower moisture levels. Microwave mixing

allows uniform heat transfer in the batch also improving product quality.

4.PYROLYSIS FOR RECYCLING AND WASTE-

TO-ENERGY

Pyrolysis is an important process in the

creation of fuel from waste and recycled

resources. Microwave has been found to

be an effective agent for pyrolysis, both

for plastics and farm waste. We will

look at each in more depth here.

PLASTICS AND RUBBER.One type of

pyrolysis is the thermal degradation ofa material, usually in an oxygen-free

environment. Microwave pyrolysis for

polymer processing is becoming a more important and better-investigated field due

to the increasing need for recycling measures. Especially for difficult-to-dispose

items like automobile tires, which are bulky, spatially inefficient, and banned from

landfills in many countries, recycling alternatives are in great demand, pushing

research forward. Undri et. al. (2011) investigated this specific application in their


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article Microwave Pyrolysis of Polymeric Materials and commented that todays

disposal strategies for waste polymeric materials lean toward reuse instead of

incineration or landfilling (p. 207). Pyrolysis is one of these new alternative reuses,

by which plastic waste and tires can be turned into synthetic fuel.

Undri and his team set up a system consisting of heatexchanging pipes, collecting flasks, and a microwave

oven into which they fed chopped tires. In the best

conditions, [their system was] able to pyrolyze 0.4Kg

of tires in 14 minutesa figure they extrapolated to

predict that 4 kg might be pyrolyzed in 120 minutes

(p. 212). This showed a significant efficiency gain

when compared to results obtained using

conventional pyrolization methods. This efficiency

was due mostly to the rapid heating offered by

microwave: pyrolization starts almost immediately

within 20 secondswithout lengthy preheating (p.212). The only pretreatment necessary was the

addition of a microwave absorbent to the plastic

materials being processed. (Unlike tires, which

naturally absorb microwaves, plastic polymers must be mixed with an absorbent

such as coal, metal-oxide, or carbon-containing materials for satisfactory pyrolysis

by microwave).

Khaghanikavkani et. al. (2013) conducted a similar study, limited exclusively to

plastics, in their article Microwave Pyrolysis of Plastic and also found,microwave

pyrolysis of plastic can be achieved much faster than thermal pyrolysis (p. 10).

FARM WASTE.Microwave pyrolysis also works on organic compounds. One

particularly exciting application for this is farm and agricultural waste. Manure,

straw, and all kinds of other wastes can be converted into useful oils and char. After

the material has been softened by preheating in a reactor, the material is exposed to

microwave radiation and then decomposes into its component sugars and finally

into oils and char. In an article released by the International Society of Chemical

Industry, Patrick Walter (2011) writes, These microwave processorscould also be

very useful for farmers looking to make more money from agricultural residues. By

joining forces several farms could buy a processor and turn farm waste, such as

straw, into a much higher quality solid fuel. As this quote illustrates, most farm

waste does not get turned into transportation fuel (it will be awhile, in other words,until your car runs on pyrolyzed

sheep manure).

Manure can, however, be a valuable

source of remote biomass power

generation. The pyrolysis process has

a advantages over direct combustion,

anaerobic digestion, gasification, and


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other competitors, which Serio et. al. (2002) discussed in their article Pyrolysis

Processing of Animal Manure to Produce Fuel Gases. Pyrolysis allows for higher

throughput and consumes less water than anaerobic digestion, and is conducive to

the processing of poultry litter, which is less efficiently treated by other processes

(p. 588). The oil and char produced can then be used to fuel other processes,

lessening dependence on coal.

Microwave pyrolysis is a field that is still growing, but will doubtless continue to

increase in importance and relevance as our world population grows and waste-to-

energy measures are continually sought.

5.PETRO CHEMICALS

Frac sand is a high-quality, exceptionally pure and impressively strong silica or

quartz sand that is used in the oil and gas industries as an aid to the hydraulic

fracturing of underground rock. Some rocks contain great supplies of natural gas or

oil, but are not porous enough to allow these resources to pass through them and

reach the wells installed by gas or oil companies. In order to open up the rock toallow natural gas and oil to flow to the well where they can be collected, companies

use a process called hydraulic fracturing (this is where we get the abbreviated term

frac), in which water is blown through the rock at immense pressure levels,

bursting the rock into numerous fractures and filling them with fast-moving water.

But its not just water: guar gum and other similar chemicals are routinely added to

it, transforming the water into a powerful gel that is ideally suited to carry hundreds

of thousands of pounds of frac sand with it into the fractures, driving them deeper

and deeper into the earth.

When the water stops, the sand keeps working. Without the pressure of the water

flowing through them, most of the newly created cracks and byways in the rockwould naturally begin to constrict and close. If enough sand has been used, however,

it fills in these holes and holds them open. This secondary purpose of the frac sand

explains its reputation as a proppantit props open the pathways in the rock for

oil and gas to flow through.

Again, not just any sand can be used. Quartz sandstone or silica (the rock frac sand is

derived from) is specifically selected for their high crush resistance. The golden

standard for quartz, for example, is the American Petroleum Institutes order that it

be able to withstand compressive stresses of 4,000-6,000 psi. Most other sands

could not hold up under the pressure of so much rock. Even within the family of frac

sand, there are important differences. Variation in size, roundness, and sphericityare also important considerations. Rounded grains of sand will be carried more

effectively by the water into the cracks, and the size of the grains should be

determined according to the application.

With so much sand being expended per job (often over one ton per well), users of

frac sand cant afford to transport itin anything other than a completely dry state.

Microwave is a potential solution for drying frac sand, getting rid of those last


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percentages of moisture content that, especially on so large a scale, add up.

Microwave has also been tested with smaller quantities of ceramic sand, and works

well. Another attractive option for drying frac sand is the pulse jet dryer, a

technology recently released by Marion Mixers, which can handle higher

throughputs while still providing the advantages of rapid heating and drying.

6.GREASE INDUSTRY

The grease industry has in very recent years proven itself an ideal application for

microwave, particularly in the subset of biobased greases. Vegetable oils,

specifically, respond remarkably well to microwave, exhibiting quick and uniform

heating that can be attributed to their di-polarity. The polarity of microwaves

stimulates the di-polar molecules in the vegetable oils, causing them to move rapidly

in an attempt to align themselves with the waves. This motion (and the subsequent

collisions between the molecules) causes friction, heating the material.

Most other greases, however, do best

when microwave heating is combinedwith agitation. Especially for thicker

greases that maintain their low viscosity

despite heating, such as aluminum and

calcium-based greases, the addition of

agitation to the microwave vessel is a big

step forward, providing huge gains in

both process efficiency and product

consistency. Marion Mixers, Inc., is the

first company to add an agitator inside the microwave vessel, and has worked

extensively with Dr. Lou Honary to create a microwave mixing product specifically

suited to the grease industry. Dr. Honary is a member of the National LubricatingGrease Institute (NLGI) board of directors, a professor at University of Northern

Iowa, and perhaps one of the biggest microwave advocates in his field. He has used

the National Ag-Based Lubricants Center at the University of Northern Iowa as a

microcosm for implementing the new technology. In a 2013 article written for NLGI,

Honary reported that the National Ag-Based Lubricants Center at UNI had seen

increased grease stability, color, and yields with the use of microwave, as opposed

to conventional equipment (p. 5).

Improved product quality isnt the only gain microwave mixing offers grease

processors, however. Two other, important benefits include reduced equipment

footprint and increased operator safety. Compared to conventional boilers andkettles, microwaves require much less plant space. And unlike conventional grease

processing equipment, which itself heats up in order to heat the material,

microwave sends energy and heat to the material onlynotthe vesselfor

decreased operator risk. The potential gains both in plant space and efficiency help

to offset the cost of investment. The smaller footprint of these microwave systems

and their relative cost effectiveness makes them highly desirable manufacturing

methods, Honary wrote. Smaller manufacturers would potentially be able to


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produce specialized greases in either small or large quantities at significantly

reduced cost (p. 6).

7. Mineral Processing

Mineral processing is another application that could be transformed by the use of

microwave technology. Admittedly, this application is still in the works. Many

studies, beginning with the first in the late 1960s, have been conducted on the use ofmicrowave in the processing of minerals. The broadness of the mineral field,

however, makes for incredibly specific research and results, and generalizable

information is difficult to come by. All minerals and ores have different thresholds

for microwave, and are affected by microwaves in different waysin fact, some

minerals are microwave transparent, meaning they are not affected at all. Lots of

research is left to be done, but well share here some of whatis known.

The larger the particle size of the material, the more effective microwave

treatment tends to be. Also, longer treatment length (increased exposure time)

often means better results. This is particularly true for microwave drying

applications.

Microwave pretreatment can improve grinding and leaching efficiency. When

ore minerals are rapidly heated in a microwave transparent matrix, the material

experiences thermal stress and micro-cracks form along the mineral boundaries.

These small cracks can make a significant improvement in the efficiency of later

processing tasks, especially in comminution (grinding), which goes much faster

when the material has been pretreated. Minerals with higher water content, such as

low-grade coal, may respond especially well, as microwave causes the water inside

the material to react, resulting in additional breakage. In the mineral chapter of

their bookThe Development and Application of Microwave Heating, S.M. Javad

Koleini and Kianoush Barani (2012) explained that an equivalent to pressureleaching can also be accomplished with microwave. At ambient temperature,

microwave energy applied to the leaching of ore or concentrate in slurry or paste

form can have the same effect as pressure leaching, with similar extraction yields (p.

100).

The current challenge, however, is still efficiency. Microwave can take the most

energy-consuming of the mineral processing tasks, comminution, and push its usual

low energy efficiency percentage of 1% up to over 20% (85). This would be great if

the microwave itself wasnt consuming any energy. Although grinding efficiency

goes up, some researchers have found that it was not enough of an increase to

cancel out the energy being used by the microwave. Better microwaves designedspecifically for this application should in time provide yields that compensate for

the energy they use.

Microwave can hold its own in the regeneration of spent carbon. Carbon is often

used by gold ore processors in the adsorption and desorption of gold cyanocomplex.

After each adsorption/desorption cycle, the carbon is said to be spent and must be


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regeneratedtypically by a mineral acid wash followed by heating in a rotary kiln

at a very high temperature (p.96).

Microwaves have been substituted for the rotary kiln in pilot scale tests and found

to produce carbon equally good or better than that regenerated by conventional

methods (p. 96).

CONCLUSION

The list weve made here is nowhere near complete, but its a good introduction to

the breadth and variety of microwave-suitable applications. Although the

applications are vastly different there is a good deal of consistency throughout

themconsistent, predictable reasons why microwave, specifically, could do the job

so well. The strong points for microwave across all applications boil down to the

following:

Rapid heating and drying for extreme time savings

Precise temperature control

Increased operator safety

Even product heating when combined with agitation

If you have an application that could benefit from one of the above, or found your

own application in our top 7 list and would like to know more, please contact

Marion Mixers, Inc. online atwww.marionmixers.comor by phone at 319.377.6371

to talk with an expert or schedule a test.
http://www.marionmixers.com/http://www.marionmixers.com/http://www.marionmixers.com/http://www.marionmixers.com/


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REFERENCE LIST

Honary, L. (June, 2013).An update on the use of microwaves in manufacturing grease.

Unpublished paper presented at NLGI 2013 Annual Meeting, Tuscon, AZ. Khaghanikavkani, E., Farid, M. M., Holdem, J. & Williamson, A. (2013). Microwave

pyrolysis of plastic. Chemical engineering and process technology 4(3).

http://dx.doi.org/10.4172/2157-7048.1000150.

Koleini, S. M. J., & Barani, K. (2012). Microwave heating applications in mineral

processing. In The development and application of microwave heating (4). Retrieved

from http://www.intechopen.com/books/the-development-and-application-of-

microwave-heating.

Serio, M.A., Bassilakis, R., Kroo, E., & Wojtowicz, M.A. (2002). Pyrolysis processing of

animal manure to produce fuel gases.ACSfuel chemistry division preprints, 47.Retrieved from http://web.anl.gov/PCS/ENFL/index.html.

Srogi, K.(2006). A review: Application of microwave technologies for environmental

analytical chemistry.Analytical letters, 39, 1261-1288.

doi:10.1080/00032710600666289.

Undri, A., Rosi, L., Frediani, M., & Frediani P. (2011). Microwave pyrolysis of polymeric

materials. In Microwave heating (10). Retrieved from

http://www.intechopen.com/books/microwave-heating/microwave-pyrolysis-of-

polymeric-materials.

U.S. Environmental Protection Agency. (2000). Economic impact analysis for the proposed

carbon black manufacturing NESHAP(EPA-452/D-00-003). Retrieved from

http://www.epa.gov/ttnecas1/regdata/EIAs/carbonblackeia.pdf

Walter, P. (2011). Microwave turns waste into watts.

C&I Magazine, 5. Retrieved from http://www.soci.org/Chemistry-and-Industry/CnI-Data/2011/5/Microwave-turns-waste-into-watts.

7 Industrial Applications You Didn't Think were Compatible with Microwave Processing

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