CAPÍTULO I: FUNDAMENTOS TEÓRICOS SOBRE LA FABRICACIÓN DE
1.3 Bloques huecos de hormigón
1.3.1 Historia y origen de los bloques huecos de hormigón
(CHj.CHOH.COOH)
HistoricalLactic acid was identified by Scheele in 1970 in sour milk, hence its name. Its production by fermentation was recognized by Blondeau in 1874, and it was Lister who in 1877 isolated the organism in pure culture. Commercial production o f lactic acid probably started in 1847.
Properties
Lactic acid is a colorless, odorless, syrupy liquid, miscible in all proportions of water, alcohol and ether, but insoluble in chloroform. Lactic acid is very corrosive and except in the fermentation stage, corrosion -resistant material must be used for its production.
Fermentation Process
Industrial lactic acid is prepared by the fermentation of dextrose, maltose, lactose and sucrose. In the USA. com sugar, molasses and whey are the main raw materials, while in Germany potato starch is mainly used.
A number o f microorganisms can produce lactic acid by fermentation: some produce only lactic acid and are called “homofermentative”, while others in addition volatile acids are termed “heterofermentative “ fermentation.
We consider here only the organisms fermenting molasses and sucrose. By far the best known is Lactobacillus delbruckii, which are long, slender, Gram-positive rods, non-mobile , sporulating, and producing very little gas. They are microaerophilic.
The mechanism of fermentation can be considered to take place from glucose via pyruvic acid to lactic acid as follow:
C„H12
0
6 v,a^ COIysis CH3.CO.COOH --- ► CH3CHOH.COOHGlucose pyruvic acid Lactic Acid
There is, however, no completely satisfactory explanation yet for the fermentation yield which varies between 92 -94% o f the glucose. Lower yields are due to incomplete breakdown of the sugar or to side reactions of the lactic acid produced.
The fermentation process can be summarized as follow: Molasses is diluted to a fermentable sugar concentration of 10% and 2% of nitrogen nutrient added. The mash is then sterilized at boiling temperature for 30 minutes, cooled to 50°c and its pH adjusted to 6.0 with calcium carbonate. Calcium phosphate is added 0 % P2O5). The mixture is then inoculated with 5% of bacteria culture and the temperature maintained at 50°c.
4. Purification
The fermentation process is completed and is then treated with an excess o f lime to a pH of 10-11 to precipitate the calcium lactate. The lactic acid is recovered from calcium lactate in the fermented wort by concentration through evaporation under vacuum, liberation with sulfuric acid and subsequent purification by filtration and decolorization. This is the standard process producing a crude acid of 22% strength, but the number of refinements and variations are used according to the grade o f lactic acid to be produced as Total Acidity of: 44% (Technical Grade); 50%; (Edible; Plastic Grade) and 85% .
5. End uses and Economics.
Lactic acid is an important compound in the leather industry for the deliming of hides and for the bating and plumping o f leathers. It is used in the dyeing of silk, and as a mordant in the printing o f woolens.
it has recently acquired growing importance in the plastic industry, and the esters o f lactic acid are proving useful as solvents, plasticizers and modifiers.
In the Food Industry, the use of lactic acid and lactates is of rapidly growing importance in confectionery, fruit juices, essences, lemonades, syrups, pickles. Also in curing meat, in canned vegetables and fish products. Calcium lactate is used in baking powder and has great potential as an additive in poultry feed.
A. Read and Translate into Vietnamese alt New Words Baking /'beikiry Sự nướng (bánh), sự nung (gạch), mẻ (bánh, gạch) Trừ, trừ ra, loại trừ Mứt, kẹo. Công nghệ mứt kẹo Sự ăn mòn, sự mài mòn Án mòn, phá hủy dần, chất ăn mòn Sự điều trị, sự chữa trị, xử lý để được ìâu hơn
Nguyên, sống, thô, chưa luyện Khử canxí, khử tạp chất dính ở da Mức, hạng, phân loại, tăng ỉên Da sống, lột đa, trốn, ẩn nấp Bating Confectionery Corrosion /'beitiry /konTek/snari/ /ka'roud5n/ /ka’rousiv/ /kjuairy Coưosive Curing Crude Deliming /knr.d/ / dilainiin/ Grade Hide /greid/ /haid/
I
Heterofcrmentative fermentation
/hetero foi’mentativ/ Lèn men dị hình Homofermentative /homo iVmentativ/ Lên men đồng hình fermentation
Leather /'leõa/ Da. thuộc da, bọc bằng đa
Mash /maej/ Dịch cháo đặc, bột ngâm nước nóng đe
nấu rượu bia, bóp nát Modifier
Modify
/'mDdifais/ /'mDdifai/
Giảm bớt, giám nhẹ, biến đổi, bo nghĩa, thay đổi, sửa đổi
Mordant /'mD;d3nt/ Chua cay. đay nghiến, giữ màu
(nhuộm), ăn mòn (axit)
Microaerophilic /'maikrou'earoufilic/ Vi hiếu khí, cần rất ít không khí
Plumping /plAmpiry Làm hoàn chỉnh, loại bỏ hết cặn bấn
Refinement /ri’fainmant/ Sự lọc, sự tinh chế, sự tinh tể, sự tế nhị, cái hay, cái đẹp
Rod
/rDd/ Cái que, gậy, thanh, hình que. sào
Slender /'slends/ Mảnh khảnh, eo thon, ít ỏi, que mảnh
Variation /,vesri'ei/n/ Sự biến đổi, sự thay đối, sự khác nhau, sự biến thiên, biến dị, biến tấu
Wort /wa:t/ dịch đường đưa đi lên men
Plasticizer /’plaestisaizs/ Chất làm dẻo, chất làm mềm dẻo, nhựa tổng hợp
B. Grammars
Cách dùng long (for a long time)
long được dùng trong cậu hỏi và câu phủ định.
Have you been waiting long?
it doesn V take long to get to her house.
She seldom stays long.
(For) a long time dùng trong câu khẳng định / waited fo r a long time but she did not arrive.
It take fo r a long time to get to her house.
long cũng được dùng trong câu khẳng định khi đi với too/enough/as/so
The meeting went on much too long.
I have been working here long enough time to get new job.
You can stay as long as you wont.
Sorry / / took so long.
Long before = lâu trư ớ c khỉ Long after = mãi sau khí Long ago = cách đây đã lâu
We used to live in Paris, but that was long before you were born.
Long after the accident, he used to dream that he vras dying.
Long ago in a distance country, there lived a beautiful princess.
long phải đặt sau trợ động từ
This is a problem that has long been recognized.
All day/ all night/ all week/ all year long= suốt cả
She sits dreaming all day long.
Before long : ngay bây giờ, chẳng bao lâu nữa / will be back before long.
Trong câu phủ định for a long time = đã lâu, trong 1 thời gian dài Còn for long = ngắn, không dài, chốc lát
She didn't speakfor long = She only spoke fo r a short time.
She didn't speak fo r a long time= she were silent fo r a long time.
How long have you been here for? (bao gồm hoặc đề cập đến cả tương lai)
How long have you been here for?
ưntỉlỉ the end o f next week.
How long have you been here for?
c.
Exercises.1. Answer the following questions:
a. What are the main properties o f lactic acid?
b. Can you list the main raw materials for Industrial lactic acid fermentation ?
c. Can you distinguish between homofermentative and heterofermentative lactic acid fermentation ?
d. Describe the main principles for purification of lactic acid from fermentation broth?
e. Why does lactic acid as an organic important one for our life? 2. Translate into English.
a. Axit lactic được đưa vào sản xuất công nghiệp từ năm 1881.
b. Axit lactic là một axit rất dễ ăn mòn vì vậy phải dùng các vật liệu chống ăn mòn để chế tạo thiết bị cho sản xuất axit lactic.
c. Chủng vi khuẩn có khả năng lên men rỉ đuờng và đường sacaroza là trực khuẩn Gram (+) có tên là Lactobacillus deỉbruckiỉ, nỏ không chuyên động, không tạo bào tử và
là loại vi hiếu khí.
đ. Axit lactic ngày càng được ứng dụng nhiều trong công nghiệp da, CN chất dẻo và rất nhiều trong công nghiệp Thực phẩm