Acid Hood Operations - The University of Texas at Dallas

Acid Hood Operations
Roger Robbins
Arnold Duenes
2/14/2006
The University of Texas at Dallas
ERIK JONSSON SCHOOL OF ENGINEERING
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 1 of 25
Acid Hood Operations
Roger Robbins
Arnold Duenes
2/14/2006
Table of Contents
Acid Hood Operations ....................................................................................................... 4
Introduction ................................................................................................................... 4
Description .................................................................................................................... 4
Feature Details.............................................................................................................. 5
Control Panel ............................................................................................................ 5
DI Water ................................................................................................................ 5
Exhaust ................................................................................................................. 6
Machine Start/Stop................................................................................................ 7
EMO Button........................................................................................................... 7
Audio Enunciator ................................................................................................... 7
Touch Screen ........................................................................................................ 7
Process Features ...................................................................................................... 8
Hotplate ................................................................................................................. 8
Sink ....................................................................................................................... 8
Acid Neutralization Tank ....................................................................................... 9
N2 Gun and DI Water Spray .................................................................................. 9
HF Acid Antidote ................................................................................................... 9
Operating Software ..................................................................................................... 10
Overview ................................................................................................................. 10
Login.................................................................................................................... 10
Timer Operation .................................................................................................. 11
Neutralization System ......................................................................................... 11
Neutralization Chemistry ............................................................................................. 13
Chemical Definitions ............................................................................................... 13
Mole..................................................................................................................... 13
Gram-Equivalent Weight ..................................................................................... 13
Normality ............................................................................................................. 14
Density ................................................................................................................ 14
Concentration ...................................................................................................... 14
Chemical Calculations............................................................................................. 14
Rules of Operation ...................................................................................................... 15
Appendix A...................................................................................................................... 17
Neutralization Chemistry Theory ............................................................................. 17
Appendix B...................................................................................................................... 20
Neutralization: Staff Procedure .............................................................................. 20
Purpose....................................................................................................................... 20
NOTES: ................................................................................................................... 20
Neutralization Introduction .......................................................................................... 20
Neutralization Procedure............................................................................................. 20
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 2 of 25
Neutralization Parameters........................................................................................... 23
Process Monitor/Setup ............................................................................................ 24
Caustic Pump Setup ............................................................................................... 24
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 3 of 25
Acid Hood Operations
Roger Robbins
Arnold Duenes
2/14/2006
C:\Mydocuments\CleanRoomGeneral\Equpment\Hoods\Acid\AcidHoodOperation.doc
Introduction
This document describes the Clean Room’s new 4 foot Acid Hood from
Leatherwood Plastics, Inc., of Lewisville, Texas. This hood is intended to be our general
purpose acid hood for a single user at a time. We fondly call it the Acid Hood, but it
actually has a real name: “HA01.”
Description
The acid hood is constructed of a chemical and fire resistant white plastic,
(PVCC), with a 3 by 2.5 foot perforated work surface. Included at the work deck level is
a De-Ionized water sink with a gooseneck faucet, an explosion proof hotplate, a DI water
spray gun, a Nitrogen blow off gun and a flexible thermocouple thermometer for
measuring the temperature of liquids on the hotplate. The hood is controlled by a solid
state controller with a touch screen control panel. There are two process timers on the
front panel below the work surface – “Sink timer” and “Hotplate timer.” Alarms are
handled by the upper portion of the left hand side control panel. The Big Red
emergency off button is also located prominently on this panel. Exhaust is monitored by
a Photohelic differential pressure gauge on the left side of the front panel below deck
level. Under the hood is a chemical tank used to actively neutralize acids from the sink.
This is an automatic neutralization system that measures the pH of the liquid in the tank
and when the level rises to 90% of the tank capacity, the system will pump Sodium
Hydroxide into the tank to neutralize the acid mix. When the pH is stable above 6.0, the
system will pump the contents of the tank into the acid drain of the building. At the
conclusion of this operation, the tank refills to 35% of its capacity with DI water to act as
a dilution agent for acids poured down the drain – thus reducing the localized heating
from the heat of mixing. Figure 1 illustrates the features discussed in this paragraph.
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 4 of 25
Exhaust Alarm
Control
Panel
Beaker
Thermocouple
Thermometer
HF Antidote
Manual
Hotplate
Touch
Screen
DI Water
Faucet &
Acid Sink
DI Water
Gun
Exhaust
Pressure
Gauge
N2 Gun
Process Timers
Start & Stop Buttons
Figure 1. Illustration of 4 ft Acid Hood features.
Feature Details
Control Panel
The control panel is shown in Figure 2 with labels. This panel is composed of
two segments: 1) a section of actuator buttons and indicator lights, and 2) a touch
screen linked to a microprocessor for controlling the operation of the hood. These will
be described in detail in the following sections.
DI Water
The hood has a recirculating de-ionized water plumbing system to prevent
stagnant water from growing microorganisms and contaminating the purity of the water.
There is a monitor readout of this condition at the top of the control panel that displays
the resistivity of the water in meg ohms. The nominal value of good DI water is 18.1
meg ohms or better. If you notice that the value has slipped below the 17 meg ohm
level, please notify the clean room staff and if this would impact your work, discontinue
processing your work in this hood.
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 5 of 25
DI Water Condition Meter
(Meg Ohms)
Loss of Exhaust Indicator Light
Hood Start Button
Audio Alarm Enunciator
Emergency OFF Button
Alarm Silence Button
Hood Power off Button
Figure 2. Hood Control Panel details.
Figure 3. Photohelic Exhaust pressure
gauge (left), and alarm horn (right)
Exhaust
The photohelic pressure gauge, Figure 3, measures the exhaust pressure in the
exhaust line above the hood and if the pressure falls out of the acceptable range, it will
trigger the alarm horn, (Figure 3), which will then complain very loudly and light up the
red alarm light on the control panel to light up, Figure 2. If this happens, quickly bring
your work to a safe conclusion and discontinue the use of the hood. Also immediately
notify clean room staff. There may be a general loss of exhaust requiring clean room
evacuation. Follow staff direction. By the way, the exhaust alarm cannot be silenced
except by shutting off the main power to the hood. Do not attempt to change the
photohelic pressure gauge set points!
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 6 of 25
Machine Start/Stop
The Green “HOOD START” button on the control panel turns on the electricity to
the hood functions. The Red “MACHINE STOP” button turns off “most” of the electricity
to the hood. The hood is generally left “ON” all the time. This control is used when
service or problem diagnostic is required.
EMO Button
The EMergency Off button is used if the hood is having an electrical problem that
portends of immediate emergency. If there is smoke coming from the insides or the
hotplate is seriously overheating, etc. Please don’t hesitate to use this button. If you
have had to push the EMO button, please notify Clean Room Staff immediately!
Audio Enunciator
The audio enunciator is a piezoelectric beeper that announces either a nonemergency fault or the completion of a timed event. There is a convenient yellow alarm
silencer button which you can use to cause immediate cessation of the annoying beeps.
However, please make sure that the cause of this alarm is corrected before leaving the
hood. Notify Clean Room staff if necessary.
Touch Screen
The Touch Screen is the user
interface for the microprocessor controller
for the hood. This controller has a
password and multiple display screens for
monitoring and controlling the hood. This
is where the acid dump catch tank is
monitored and dilution and neutralization
parameters are set. This will be
discussed in the control section later in
the document.
Figure 4. Touch Screen
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 7 of 25
Process Features
Hotplate
The hotplate, shown in Figure 5, is
a simple manual stirring hotplate with local
controls located under the removable
panel just in front of the hotplate. There is
a protective skirt around the hotplate
heating surface to protect the hotplate
from accidental spills into the sunken
hotplate recess. The local control knobs
set the temperature and control the
stirring magnet speed.
As labeled in Figure 1, the hood
has a flexible Thermocouple Thermometer
to measure the temperature of liquids in a
container sitting on the hot plate. The
Figure 5. Hotplate showing splash skirt and
temperature is indicated on the touch
cover for hotplate control knobs.
screen.
Sink
The DI water is delivered to the sink through a gooseneck faucet that has
recirculating DI water all the way to the valve. This insures that the water will not have a
stagnant line that can grow microorganisms which may contaminate your substrate. As
subtly mentioned above, this sink will accept all waste acid, thus removing the
dangerous liabilities to health associated with saving individual containers of acids and
handling them through a manual waste disposal system. When acids are disposed of in
this sink, a moderate amount of DI water should be used to clear out any puddles of
concentrated acid in the drain lines.
Figure 6. DI water sink accepts waste
acids for neutralization.
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 8 of 25
Acid Neutralization Tank
When fluids drain out of the sink,
they drain directly into a catch tank
under the hood. This tank has an active
neutralization system that measures the
pH and supplies a 50% concentrated
Sodium Hydroxide solution to the tank in
a programmed cycle to neutralize the
acid. When the tank is full, the
neutralized solution is pumped into the
building acid drain. There are two
pumps involved with this system: 1) a
recirculating pump used to stir the fluid
Figure 7. Catch tank (Right) and Caustic
in the tank, and 2) a caustic pump to
Reservoir (Left) under the hood.
deliver the Sodium Hydroxide. Both
of these pumps are diaphragm pumps that make a noticeable clacking sound from
behind the hood – this is normal.
N2 Gun and DI Water Spray
The hood has the standard Nitrogen blow-off gun and DI water spray hose to
facilitate drying and water rinsing of substrates. Note that the DI water hose is made of
coaxial Teflon tubing and is somewhat stiff to stretch, and it will spring back with
considerable force if it slips out of your hands – be careful and get a good grip. Figure 1
shows the recessed location of both these hood tools.
HF Acid Antidote
There should always be a supply of Hydrofluoric Acid (HF) antidote in plastic
tubes in the back of the hood work surface. If you accidentally get HF on your skin,
wash it off with DI water for about 10 minutes and then apply the antidote crème by
rubbing it into the skin for about 5 minutes. This Calcium Gluconate antidote will react
with the HF to create benign Calcium Fluoride salt, thus capturing the F- ions that can do
serious damage to the body. If a large spill gets on you then remove clothing and do a
15 minute shower in the emergency shower at the entrance to the room. Call for help
immediately – contact with this much HF could be life threatening. If you get a lot of HF
acid on your body, your buddy must call 911 to get paramedic help and be checked out
by a doctor quickly. More information on this situation is contained in the Clean Room
Safety Handbook.
(Tube of Calcium Gluconate Gel – HF Antidote)
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 9 of 25
Operating Software
Overview
The active hood functions are controlled by a microprocessor whose interface
with the operator is the aforementioned touch screen on the control panel. The control
processor is concerned with two significant hood functions: 1) Neutralization of the
collected acid in the catch tank under the work surface, and 2) general
security/timer/temperature/alarm data presentation. These functions will be discussed in
detail below.
Login
From the “Main” screen on the touch
screen, there will be a soft button at the very top
center of the screen entitled “Log-in,” as shown in
Figure 7. The login level enables various portions
of the controller capability to the operator. Normally
the hood will be logged in under the operator level.
The password for this level is currently set at
“UTD.” This level enables complete availability of
all features of the hood in normal operation.
Figure 8. Main Screed with initial
.
option buttons
Higher levels of the login tree enable operating parameter changes reserved for staff. If
you need a parameter changed, please see the staff person in charge of the hood. Push
the thin top rectangle button that says “Login,” if you have to login. (Figure 8 shows a
screen with that button reading “Log Out,” since the hood is already logged in). The
resulting screen will look like that in Figure 9. Press the central button entitled “Log In
Please.” This brings up the keypad screen shown in Figure 10.
Figure 9. Log in Screen
Figure 10. Log In Keypad. Note the Return
key in the lower right corner
Since the operator password is “UTD,” simply enter those letters and press the “Return”
key in the lower right corner of the keypad. This will enable the hood software and bring
up the Main screen as shown in Figure 8.
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 10 of 25
Timer Operation
The two buttons on the Main screen important to hood operators are the ones
entitled “Cycle Timers,” and “Neutralization Process.” Pressing the “Cycle Timers”
button produces a new screen as in Figure 11, and shows the timer indicators.
Figure 11. Cycle Timer screen. Enter
time by pressing the appropriate numeral
block until the desired number appears.
The clocks are started from the front
panel on the front surface under the
work area.
When you have the time set, press “Main” and the system will return to the Main screen
for additional action. The timers are started and stopped from the front panel below the
work surface as indicated in Figure 1. This screen also shows the liquid-in-beaker
thermocouple thermometer temperature.
Neutralization System
The screen view most useful for standard operations is the “Neutralization”
screen. This is a somewhat complicated depiction of the hood’s drain plumbing and
neutralization pumping and valving system. Figure 12 shows this screen.
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 11 of 25
Figure 12. Neutralization process screen showing the hood’s drain plumbing and valving
configuration along with the neutralization tank and pumping plumbing.
The reason that this screen is informative is that when the Neutralization Tank is filled to
about 90% of capacity with fluid, the software closes the Sink valve and therefore the
hood operator cannot drain any more fluid into the tank. After the valve closes the
Neutralization process starts. This involves recirculating the fluid in the Neutralization
Tank to stir the mixture and then pulsing the Caustic Reservoir pump to neutralize the
acid in the tank by small spurts of caustic. The pH of the tank fluid is constantly
measured and when the neutralization process brings the pH above the set point of 6.0,
the caustic pump is shut down and the tank pump then pumps the now neutralized fluid
from the tank into the building Acid drain. When the tank is empty, it fills with DI water to
35% of its capacity so that any new concentrated acid poured down the sink will mix with
neutral water and become dilute so that any future reaction will be slow and not so hot.
In any case, the operator needs to know when the neutralization tank fills to or above
90% because the sink drain valve closes at this point. The neutralization process, by the
way takes about 20 minutes in this hood.
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 12 of 25
Neutralization Chemistry
This section will be a short exposition of simple neutralization chemistry. The
purpose is to understand how the acids are neutralized and how much Sodium
Hydroxide (NaOH) is required to neutralize a given quantity of acid. This is somewhat
complicated because in this general purpose hood, we will be neutralizing a number of
different acids with different initial concentrations. The amount of base, (NaOH is our
choice) required to neutralize the acid depends on what type of acid and how
concentrated it is compared to the base concentration. The concept of neutralization
states that the base has to supply OH- ions to the solution in such numbers as to match
the number of H+ ions that the acid has added to the solution. This means that we need
to know what the reaction equation looks like and what the oxidation number is for the
reactants. In fact we need to recall a number of chemical definitions to be able to
calculate the volumes of the constituents involved in the neutralization.
Chemical Definitions
Mole
One Mole of a substance is its collective molecular weight expressed in grams,
(formula weight).
EX: H2SO4 = 2x1 +1x32 + 4x16 Æ 98gm (Red numbers are atomic masses and
multipliers are the number of times the
atom appears in the molecule)
Gram-Equivalent Weight
One gram-equivalent weight, (E), of a substance is its gram-atomic weight
divided by its oxidation number.
EX: H2SO4 = (2x1 + 1x32 + 4x16)/2 Æ E = 49gm-eq
(Red numbers are atomic masses, multipliers are the number of times the
atom appears in the molecule, and the Blue 2 is the oxidation number of
the sulfate ion (SO4-2) in the sulfuric acid molecule reacting with NaOH)
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 13 of 25
Normality
In order to calculate the quantities involved in a chemical solution reaction, we
need some measure of the concentration of the chemical in its solvent (water). The
most convenient expression of this for calculating neutralization reactions is the
Normality value.
Normality, N, is defined as the number of gram-equivalent weights of a
substance per liter of solution.
N = gram-equivalent weights / liters of solution
Æ N=E/V
Note that since this definition involves the oxidation number of a substance, N can vary
depending on the exact chemical reaction it is involved in.
Density
This is defined as the simple physical quantity of weight per volume – (gm/ml)
Concentration
Concentration of a chemical in a water solution is expressed as the percentage
by mass of a substance per mass of the total solution. i.e. 49% HF in water
EX: 49% by wt of HF in 1000gm solution Æ .49x1000gm = 490 gm of HF in 1000 gm
of solution
Chemical Calculations
Calculating how much sodium hydroxide one needs to neutralize some amount
of acid is explained in detail in Appendix A. However to make things a bit easier, I have
included an imbedded EXCEL table with the formulas already included so that you can
find the answer to the above question by inputting the starting parameters in a table and
puff, the answers appear in the last column. Table 1, below, includes the standard
chemicals used in the acid hood and calculates the amount of NaOH required to
neutralize the acids. If you have a mix of acids, then calculate the volume of NaOH
required for one acid and add the NaOH amount from the next (independent) acid
reaction.
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 14 of 25
Table 1*
Acid Neutralization Calculation Chart
Sodium Hydroxide Acid-Neutralization Calculator
11/17/2006
RAR
Calculator instructions: Input numbers in Blue. Read answers in Red
Nominally, this calculator is designed to tell how much sodium hydroxide is required to
neutralize a given volume of acid. Thus, just fill in the volume of the acid and
the chart will fill in the required sodium hydroxide volume in red. Units are Liters.
1 Gal = 3.7854 Liters
1 Liter = 0.264 Gal
NaOH Vol
Wt %
Liq
(L) req for
Oxidation Formula Volume Density Concen
(gm/mL) tration Normality Neutralizing
Reactants
Number Wt (gm)
(L)
NaOH
1
40
1.53
50
19.125
H2SO4
H3PO4
HNO3
HCl
HF
HF
CH3COOH
2
3
1
1
1
1
1
98
98
63
36.5
20
20
60
1
1
1
1
1
1
1
1.84
1.7
1.42
1.18
1.012
1.0012
1.048
96
85
70
38
10
1
98
36.04898
44.234694
15.777778
12.284932
5.06
0.5006
17.117333
1.88491397
2.31292517
0.82498184
0.64234936
0.26457516
0.02617516
0.89502397
*Double click in the chart. Excel will open and allow input and auto calculation.
Rules of Operation
For safety sake, we have generated a set of rules to apply to operators of this
hood. They are listed below:
•
•
•
•
•
When first approaching the hood to start work, please notice the
conditions in the hood and note any situational dangers. Either correct
them or notify Clean Room Staff.
Work with a BUDDY.
Stay in the Clean Room when heating stuff on the Hot Plate.
Wear appropriate Personal Protective Equipment.
o Double gloves – standard CR gloves with acid gloves over them
o Safety glasses
o Acid apron
o Face shield
o Solid top shoes!
Fill out chemical use form.
o Name/Buddy Name
o Date
o Phone number
o Chemicals in use
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 15 of 25
•
•
•
•
•
•
Only one experiment at a time is allowed.
Never place a chemical container on the floor.
Acid Hood glassware is stored on the cart to the left of the hood.
Always remember to turn off the hotplate when you are finished.
Dispose of your acids in the sink while running a moderate amount of DI
water with the acid.
o Rinse your acid containers thoroughly with DI water
o Wet wipe and dry off the work surface so the following person will
not be harmed by liquid acid spills.
When you are finished, clean up your work area and return all the tools
and PPE you have been using to their proper place – especially papers
and rags.
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 16 of 25
Appendix A
Neutralization Chemistry Theory
Acid - Base Neutralization Reactions:
1/11/200
RR
How much 50% Sodium Hydroxide solution is needed to neutralize n liters of 96% Sulfuric Acid?
Solution :
Step 1. Calculate the gram-equivalent weights of the reactants. [The gram - equivalent wt of a
element is the gram atomic weight divided by the oxidation number of the reacting element in
the compound of interest.]
Given:
Solution Densities
from bottle:
ρ NaOH := 1.53
gm
mL
ρ H2SO4 := 1.84
gm
mL
50% NaOH by wt
96 % H2(SO)4 by wt.
Atomic Mases:
Na(OH)
Na := 23gm O := 16gm
H := 1gm
Gm Eq Wt of Na(OH) = Na + O + H = 40 gm
H2(SO)4
H = 1 gm
S' := 32gm
Equiv Wt of Sulfuric Acid
O = 16 gm
2 ⋅H + 4 ⋅S' + 4 ⋅O
= 97 gm
2
GmEqWt of H2(SO)4 =
Equiv Wt of Sulfuric Acid
Step 2. Calculate the Normality of each solution. [The normality is the number of gram
equivalents per liter - a chemical concentration unit.]
Na(OH):
a) Calculate the number of grams of Na(OH) in one liter of solution from the density
and concentration percentage:
3 gm
ρ NaOH = 1.53 × 10
Solution Density
L
Since the concentration is only 50% Na(OH), the number of gms of Na(OH) in one
liter is:
ρ NaOH ⋅0.5 ⋅1L = 765 gm
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
Mass of sodium hydroxide in 1 Liter
6/2/2006
Page 17 of 25
Now to find the number of equiv wts of Na(OH) in one liter, (the Normality of the
solution), we divide the above number of gms in one liter by the equiv wt
ρ NaOH ⋅0.5
Norm1 :=
Na + O + H
. # gm equiv wt in 1 L
1
Norm1 = 19.125
L
Normality of Na(OH) solution
(Units are in mass-equivalents per Liter)
H2(SO)4:
a) Calculate the number of grams of H
2(SO)4 in one liter of solution from the density
and concentration percentage:
ρ H2SO4 = 1.84 × 10
3 gm
Solution Density
L
Since the concentration is only 96% H
2(SO)4, the number of gms of H
2(SO)4 in one
liter is:
3
ρ H2SO4 ⋅0.96 ⋅1L = 1.766 × 10 gm
Mass of Sulfuric Acid in 1 Liter
b) Now to find the number of equiv wts of 2H(SO)4 in one liter, (the Normality of the
solution), we divide the above number of gms in one liter by the equiv wt
2ρ H2SO4 ⋅0.96
Norm2 :=
2 ⋅H + S' + 4 ⋅O
1
Norm2 = 36.049
L
. # gm equiv wt in 1 L
2 ⋅H + S' + 4 ⋅O = 98 gm
Normality of H2(SO)4 solution
(Units are in mass-equivalents per Liter)
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 18 of 25
Step 3 Calculate the amount of Na(OH) required to neutralize a given amount of Sulfuric acid
The law of neutralization claims that the number of gm equivalent weights of base neutralize t
same number of gram equivalents of acid.
Stated in different form, the Neutralization rule claims:
. H2(SO)4 + 2Na(OH) ---> Na2(SO)4 + 2H2O
Norm2 ⋅V2
Norm1 ⋅V1
(Claim)
(Norm2 is the Normality of the acid)
Therefore, to calculate the volume of sodium hydroxide required to neutralize, say 4
liters of sulfuric acid:
V2 := 4L
Norm2
⋅V
V1 :=
Norm1 2
V1 = 7.54 L
(Claim equation rearranged)
ANSWER: The volume of sodium hydroxide
required to neutralize 4 Liters of sulfuric acid is
7.54 Liters, takng into account the solution
concentrations specified.
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 19 of 25
Appendix B
Neutralization: Staff Procedure
Arnold Duenes
Purpose
This appendix is intended to explain to Clean Room Staff how to run a
neutralization operation on Leatherwood Plastic’s General 4 ft Acid Bench #189.
NOTES:
•
•
•
•
Execution of this procedure is limited to trained Clean Room Staff Only
Proper Personal Protective Equipment is requires when operating bench or
during maintenance.
The name of this hood is “HA01.” …means Hood, Acid, #1
The Neutralization Process must be ENABLED on the touch screen.
Neutralization Introduction
This acid hood (HA01), has an onboard acid neutralization system located under
the work deck. Acid waste dumped in the DI Water/Acid sink will drain into a 15 gallon
neutralization tank, and when the tank level reaches 90% full (13.5 gal), the pneumatic
valve below the sink will close. If the neutralization process is ENABLED, and the liquid
in the neutralization tank has a pH lower than 6.0, a 50% solution of NaOH (Sodium
Hydroxide) will be pumped into the tank from a smaller 2 gallon caustic reservoir until the
pH is equal to or greater than 6.0. At this point, the liquid in the neutralization tank will
be recirculated (stirred) for a programmed specific time period and then pumped to the
building acid drain. When the tank level drops to 5% or less, the drain cycle will cease
and new DI water will fill the tank to 35% (5.25 gal), recirculate for 3 minutes and then
the DI Water/Acid sink valve will open. At this point the hood can be used again.
Neutralization Procedure
1. Once logged in, [from the main menu], you can access the neutralization menu
by selecting NEUTRALIZATION PROCESS, (Figure B1).
Login:
Figure B1. Sequence of screens to enable login.
Select Neutralization:
Resulting the screen:
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 20 of 25
Figure B2. Select the Neutralization Process
2. In the top center of the Neutralization Process Screen a rectangular tab should
be highlighted in red and read “STOP NEUTRALIZATION.” This confirms that
the Neutralization is ENABLED.
a. If the tab is highlighted in green and reads “ENABLE NEUTRALIZATION,”
you will need to depress the tab to enable the neutralization process.
i. If this is the case, you will need to determine why neutralization
was disabled in the first place.
1. Under normal conditions, users are not allowed to disable
neutralization.
2. It is possible that neutralization was intentionally disabled
by Clean Room staff as a result of a tool issue/problem.
There should be a sign if this has occurred!
ii. Actuation of the machine EMO/shutdown button will automatically
disable neutralization.
b. When neutralization is first enabled, the recirculation pump will turn on for
5 minutes. This is a default action to stir the solution to obtain a proper
pH reading. The time is programmable.
3. Familiarize yourself with the plumbing diagram as displayed on the screen in
Figure B3.
Figure B3. Neutralization Process Screen
a. The sink drain valve is V1.1
i. Highlighted in green when opened
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 21 of 25
ii. Highlighted in red when closed
b. Actual and set-point pH are displayed next to the neutralization tank
symbol
i. The top pH reading is the actual pH
ii. SP (Set Point) pH reading should be 6.0 (a programmable
parameter)
c. There are 3 other pneumatic operated valves in the diagram:
i. V1.2 = recirculation valve (stirs contents of tank)
ii. V1.3 = waste drain valve (valve opens when pumping to drain)
iii. V1.5 = DI Water fill valve
d. There are two pumps in the diagram:
i. Recirculation pump (next to neutralization tank)
ii. Caustic Supply pump (next to caustic reservoir)
e. The Neutralization tank icon displays a real-time liquid level
i. Note these tank level parameters:
1. The sink valve closes when a 90% tank level is reached
2. At 5% or less, the hood will switch from drain to DI Water
fill.
3. DI Water will fill tank to 35% full (programmable parameter)
f. The caustic reservoir icon will always show green (full) unless it is empty
i. There is only one float sensor at the bottom of the caustic
reservoir
ii. Wear appropriate PPE when refilling the 2 gal caustic reservoir
with 50% concentrated NaOH. (Splash back is common because
of the viscosity of the solution)
1. Wear acid gloves, apron and face shield
4. During normal operation, users are trained to be aware of the tank level,
especially when it is very close to 90%. In such a case, it is best to flow DI Water
from the gooseneck faucet, reach 90% full, then wait for neutralization to
complete (normally it takes about 20 minutes for the tank contents to be
neutralized and pumped to acid drain). This practice is intended to prevent
noxious levels of acid waste to collect in the sink while neutralization is taking
place.
a. Summary
i. If tank level is 87% - 90% full, flow DI Water into the sink from
sprayer or gooseneck to achieve 90% full and start of
Neutralization process. Wait for process to complete ~ 20 min
ii. At 90% full, the sink valve will close and neutralization will take
place if needed; if contents are already neutralized, they will be
pumped to drain when the 3 min stabilization time expires.
iii. Inform potential users that the hood is unavailable when the sink
valves close – they will know not to use hood
iv. Visually check the level of caustic in the under deck reservoir (Add
NaOH if necessary) Figure B4.
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 22 of 25
Figure B4. Under Deck caustic tank (left) and neutralization tank (Right). The caustic
tank will slide out enough to fill through the lift-off lid at the front top.
Neutralization Parameters
1. Normally, the hood is set to level 1 access: OPERATOR LOGGED IN
2. To access the menus where all programmable parameters are found, you must
log in to level 5 access: LEATHERWOOD LOGGED IN
a. To accomplish this, you must first log out
b. Log in using the tool’s manufacturer serial number
i. For security this number is intentionally not included in this
document.
ii. Your training will include this number. If only you could remember
it… /
3. Looking at the main Menu, the tab menus labeled Process Monitor/Setup and
Tool Setup Parameters are where all neutralization parameter are found.
Figure B5. Highest level Login Screen: LEATHERWOOD LOGGED IN
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 23 of 25
Process Monitor/Setup
The process monitor option contains three set up parameters: 1) pH Minimum
target, 2) Neutralize @ nn% Tank Level, and 3) Water Fill to kk %. Figure B6 shows this
screen.
Figure B6. Neutralization Process Setup screen showing full screen (Left) and Pop-Up
window for entering data (Right).
1. Process Setup
a. pH Minimum Target
i. Select the numeric box by touching it. This will bring up a pop-up
window enabling you to enter the minimum pH value that must be
achieved at the conclusion of the neutralization process. This
number is currently set at 6.0
b. Close sink valve @ nn% Tank Level
i. Selecting this box will bring up the same keypad pop-up window
where you can enter the level at which the sink valve will close.
This number is currently set at 90%
c. Water Fill to kk% Tank Level
i. Selecting this box will also bring up that familiar pop-up numeric
keypad allowing you to enter the fill level of the tank after the drain
cycle. This number is currently set at 35%. This level insures that
the pH sensor is continuously wetted.
Caustic Pump Setup
This setup procedure is hidden behind the TOOL SETUP PARAMETERS button
on the main screen of Figure B5. After pressing this button, a screen will popup showing
the thermocouple calibration setup. Pressing the NEXT button will then bring up the
CAUSTIC PUMP SETUP screen. There are several sections of this screen, called
Stages that describe parameters in sequence in the neutralization process.
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 24 of 25
Figure B7. Caustic Pump Setup Screen displays by touching the NEXT button from the
Left screen that popped up when you hit the TOOL SETUP PARAMETERS button on
the MAIN screen (Figure B5).
1. Stage 1
a. Caustic Pump RUN Constantly Below n.n pH. This means that the
caustic pump will supply Sodium Hydroxide continuously if the actual pH
of the tank contents is less than n.n. Currently this number is set at 1.0.
2. Stage 2.
a. The button labeled “pH Stabilize Time After Reaching Stage 1 Prior to pH
Set-point” allows a time input that sets the amount of time that the system
will wait after reaching a pH of n.n (1.0) before it moves on to stage 3. If,
in this wait time the pH falls below n.n (1.0), it will again pump Sodium
Hydroxide continuously until n.n (1.0) or higher is achieved.
b. “Caustic Pump Cycle after Reaching Stage 1 Set-point” is currently set at
2 sec ON, and 15 sec OFF. After the 2 min stabilization time expires, the
caustic pump will use these ON/OFF times to cycle (pump Sodium
Hydroxide) until the desired pH value is achieved, i.e. a pH of 6.0.
3. Stage 3
a. “pH Stabilize Time After Reaching pH Set-point Prior To Waste Dump” is
currently set at 3 min 0 sec. This means that once a pH of 6.0 or above is
achieved, the system will wait for this amount of time and then pump to
drain the tank.
b. Other parameters in this menu
i. Recirculation Pump – the caustic pump uses these parameters
when neutralization is enabled. The current parameters are 5 min
ON, 25 min OFF.
ii. pH values (actual and set-point) are displayed in this menu.
DOCUMENT TITLE: Acid Hood Operations
AUTHOR: Roger Robbins, Arnold Duenes
6/2/2006
Page 25 of 25